Eldorado Community:
http://hdl.handle.net/2003/35
2024-03-29T12:01:50Z
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Spectroscopic analysis of structural and chemical properties of solid thin film lubricants
http://hdl.handle.net/2003/42409
Title: Spectroscopic analysis of structural and chemical properties of solid thin film lubricants
Authors: Thomann, Carl Arne
Abstract: Upon tribological loading, especially at elevated temperatures or in humidity, chemical transitions and structural processes are known to take place in solid thin film lubricants like amorphous carbons (a-C) and molybdenum disulphide (MoS2) and to critically limit their performance. To accommodate those restrictions, a selection of element-modifications is applied on a regular basis. General aim is to analyse structural and chemical properties in a-C and MoS2 thin films. The understanding of those is a prerequisite for the scientific conception around tribo-film formation, which is identified as critical part of the tribological system.
For this, Raman microscopy is augmented by a setup for optical temperature tuning via a pulsed laser. This work summarises the Raman-accessible film properties and the changes after element-modification and thermal impact. In a-C studies of optical temperature tuning, two ordering mechanisms are found, which are affected by element-modification. As initial reaction upon heating, graphitic clusters within an amorphous matrix increase in number and, subsequently, in size upon further heating. A Five Stage-model of structural relaxation in a-C is proposed. For MoS2, it is found that the formation of tribo-films is strongly dependent on the working environment, the tribo-film gains temperature resistance over untouched thin film material, and tribo-film formation is affected by element-modification. In studies of optical temperature tuning, an initial ordering process of amorphous MoS2 and subsequent chemical reaction to distinct oxides were found.
The results are useful for identification of defect mechanisms and possibly for gauging the status of wear in a-C and MoS2 thin films. Element-modification in a-C with previously unknown effects may now be interpreted within a found Five Stage-model; similarly, the behaviour of MoS2 spectra upon heating can now be evaluated.
2023-01-01T00:00:00Z
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Precision measurements of đŹđąđ§ (đđ·) with the LHCb experiment
http://hdl.handle.net/2003/42408
Title: Precision measurements of đŹđąđ§ (đđ·) with the LHCb experiment
Authors: Meier, Gerwin
Abstract: High-precision measurements of observables of the Standard Model of particle physics, like the CKM matrix parameters, are key to answering the open questions of particle physics. The most precise CKM angle sin(2ÎČ) can be optimally determined by a decay-time dependent measurement of CP violation in BâÏKS0 decays. In this thesis data from BâJ/Ï(âΌΌ)KS0, BâÏ(2S)(âΌΌ)KS0 and BâJ/Ï(âee)KS0 decays is analysed with KS0âÏ+Ï- collected at a centre-of-mass energy of âs = 13TeV with pp collisions by the LHCb experiment between 2015 and 2018. The data corresponds to an integrated luminosity of 6/fb and results in the combination of all three decays for the CP violation parameters in
S(ÏKS0) = 0.717 +/- 0.013 (stat.) +/- 0.008 (syst.),
C(ÏKS0) = 0.008 +/- 0.012 (stat.) +/- 0.003 (syst.),
where S corresponds to sin(2ÎČ). This is consistent with the Standard Model predictions and with previous measurements. Furthermore, this is the most precise single measurement and more precise than the current world average.; HochprĂ€zessionsmessungen von Observablen des Standardmodells der Teilchenphysik, wie die Parameter der CKM-Matrix, sind entscheidend, um offene Fragen der Teilchenphysik zu beantworten. Der am genauesten gemessene CKM Winkel sin(2ÎČ) kann optimal gemessen werden mit Zerfallszeit-abhĂ€ngigen CP-verletzenden Messungen in BâÏKS0 ZerfĂ€llen. In dieser Arbeit wurden Daten von BâJ/Ï(âΌΌ)KS0, BâÏ(2S)(âΌΌ)KS0 und BâJ/Ï(âee)KS0 ZerfĂ€llen mit KS0âÏ+Ï- analysiert. Diese wurden aufgenommen bei einer Schwerpunktsenergie von âs = 13TeV mit pp Kollisionen am LHCb-Experiment zwischen 2015 und 2018. Die Daten entsprechen einer integrierten LuminositĂ€t von 6/fb und resultieren in der Kombination von allen drei ZerfĂ€llen fĂŒr die CP-verletzenden Parameter in
S(ÏKS0) = 0.717 +/- 0.013 (stat.) +/- 0.008 (syst.),
C(ÏKS0) = 0.008 +/- 0.012 (stat.) +/- 0.003 (syst.),
wobei S sin(2ÎČ) entspricht. Das ist konsistent mit den Vorhersagen des Standardmodells und vorherigen Messungen. Die Messung erreicht die gröĂte Genauigkeit einer Einzelmessung und ist genauer als der Weltmittelwert.
2023-01-01T00:00:00Z
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The squeezed dark nuclear spin state in lead halide perovskites
http://hdl.handle.net/2003/42405
Title: The squeezed dark nuclear spin state in lead halide perovskites
Authors: Kirstein, E.; Smirnov, D. S.; Zhukov, E. A.; Yakovlev, D. R.; Kopteva, N. E.; Dirin, D. N.; Hordiichuk, O.; Kovalenko, M. V.; Bayer, M.
Abstract: Coherent many-body states are highly promising for robust quantum information processing. While far-reaching theoretical predictions have been made for various implementations, direct experimental evidence of their appealing properties can be challenging. Here, we demonstrate optical manipulation of the nuclear spin ensemble in the lead halide perovskite semiconductor FAPbBr3 (FAâ=âformamidinium), targeting a long-postulated collective dark state that is insensitive to optical pumping after its build-up. Via optical orientation of localized hole spins we drive the nuclear many-body system into this entangled state, requiring a weak magnetic field of only a few milli-Tesla strength at cryogenic temperatures. During its fast establishment, the nuclear polarization along the optical axis remains small, while the transverse nuclear spin fluctuations are strongly reduced, corresponding to spin squeezing as evidenced by a strong violation of the generalized nuclear squeezing-inequality with Οsâ<â0.5. The dark state corresponds to an ~35-body entanglement between the nuclei. Dark nuclear spin states can be exploited to store quantum information benefiting from their long-lived many-body coherence and to perform quantum measurements with a precision beyond the standard limit.
2023-10-21T00:00:00Z
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Ultrafast coherent lattice dynamics coupled to spins in the van der Waals antiferromagnet FePS3
http://hdl.handle.net/2003/42400
Title: Ultrafast coherent lattice dynamics coupled to spins in the van der Waals antiferromagnet FePS3
Authors: Mertens, Fabian
Abstract: 2D materials, like the antiferromagnetic van der Waals semiconductors FePS3 studied
in this work, open up new possibilities for technological applications due to the
unique interaction of their magnetization with electronic, optical, and mechanical
properties. Furthermore, they provide the potential to study magnetism and
magnetization dynamics in reduced dimensions. Up do date, the coherent control of
the magnetization of these materials has barely been studied. Our research addresses
this gap by using ultrashort light pulses. In this context, time-resolved studies can
give an insight into the evolution of the light-induced dynamics, which essentially
require a dedicated experimental setup.
In this thesis, we present a comprehensive study on the development and application
of a table-top laser setup designed for magneto-optical pump-probe experiments and
adaptable for the investigation of microscopic samples. The system employs two
optical parametric amplifiers, with a tunable photon-energy range of 0.5 eV - 3.5 eV
for both the pump and the probe beam. Remarkable is the high pump amplitude
modulation rate at 50 % of the laser repetition rate, realized via the integration of
an electro-optical modulator, blocking every second pump pulse. Combined with a
high-frequency digitizer, performing single pulse detection, our system can achieve a
high sensitivity, down to 50 ”deg of the probe polarization rotation. The setup can
apply magnetic fields of up to ±9 T, and voltages in the kV regime while providing
a temperature control between 4 K-420 K.
The functionality of the setupâs systems is demonstrated by performing static Kerrrotation
and ultrafast demagnetization measurements in a cobalt single crystal as a
function of the most important experimental parameters.
The major part of this thesis is dedicated to our studies on a coherent optical
lattice mode of terahertz frequency triggered by femtosecond laser pulses in the
antiferromagnetic van der Waals semiconductor FePS3 . This specific 3.2 THz phonon
mode shows a close relation to the antiferromagnetic order, as it vanishes above the
NĂ©el temperature and hybridizes with a magnon mode in the presence of a magnetic
field. We investigate it as a function of sample temperature, probe polarization,
excitation photon energy and externally applied magnetic fields. The resonant
excitation of a crystal-field split electronic ..-.. transition efĂciently pumps the
displacive excitation process of the mode, while the magnetic linear dichroism is
identified as the magneto-optical effect, which reflects the phonon mode in the probe
rotation. By applying magnetic fields of up to 9 T we can generate and observe
the coherent hybridized phonon-magnon mode, thus exploiting the hybridization to
excite coherent spin-dynamics. Furthermore, we investigate the coherent phonons
in the bulk form of FePS3 and in an exfoliated flake with a thickness of 380 nm.
2023-01-01T00:00:00Z
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Characterisation of silicon detectors using the two photon absorption â transient current technique
http://hdl.handle.net/2003/42390
Title: Characterisation of silicon detectors using the two photon absorption â transient current technique
Authors: Pape, Sebastian
Abstract: Modern high energy physics experiments have increasing demands on particle detectors in
terms of their spatial and temporal resolution, as well as their ability to withstand higher
radiation levels. To meet these demands, increasingly complex detectors with ever smaller
device segmentations are being developed that require precise device characterisation.
This work is dedicated to a newly developed characterisation technique: the two photon
absorption - transient current technique (TPA-TCT); a method to characterise particle
detectors with micrometer-scale three-dimensional spatial resolution. Femtosecond laser
light with a wavelength in the quadratic absorption regime is focused to generate excess
charge by two photon absorption in a volume of about 75 ”m3 around the focal point. The
drift of the excess charge carriers is studied to obtain information about the device under
test. In this work, silicon detectors are used to explore and further develop the TPA-TCT.
The technique is applied to pad detectors in order to study the technique and to strip and
monolithic detectors to demonstrate the potential of TPA-TCT for the characterisation
of state-of-the-art detector technologies. The applicability of the TPA-TCT in neutron,
proton, and gamma irradiated devices is shown and radiation damage related effects on
the technique are systematically studied. The reduction of charge multiplication in a low
gain avalanche detector for increasing excess charge densities is observed and the role
of diffusion to partially recover the gain is investigated. New techniques to investigate
the electric field in complex segmented devices are developed and applied to strip and
monolithic detectors. This work paves the way for the TPA-TCT as a tool to characterise
detectors with three-dimensional micrometer-scale spatial resolution.; Heutige und zukĂŒnftige Experimente der Hochenergiephysik stellen immer höhere Anforde-
rungen an Teilchendetektoren in Bezug auf ihre rÀumliche und zeitliche Auflösung sowie
ihre FĂ€higkeit, steigenden Strahlungswerten standzuhalten. Um diese Anforderungen zu
erfĂŒllen, werden immer komplexere Detektoren mit immer kleineren Segmentierungen ent-
wickelt, die eine prÀzise Charakterisierung erfordern. Diese Arbeit widmet sich einer neuen
Charakterisierungstechnik: der Two Photon Absorption - Transient Current Technique
(TPA-TCT); einer Methode zur Charakterisierung von Teilchendetektoren mit dreidimensio-
naler Auflösung im Mikrometerbereich. Femtosekunden-Laserlicht mit einer WellenlÀnge im
quadratischen Absorptionsbereich wird fokussiert, um durch Zwei-Photonen-Absorption in
einem Volumen von etwa 75 ”m3 um den Brennpunkt herum Ăberschussladung zu erzeugen.
Die Bewegung der LadungstrĂ€ger wird untersucht, um Informationen ĂŒber den Detektor
zu erhalten. Im Rahmen dieser Arbeit werden Detektoren aus Silizium verwendet, um die
TPA-TCT zu untersuchen und weiterzuentwickeln. Pad-Detektoren werden untersucht, um
grundlegende Studien bezĂŒglich der TPA-TCT durchzufĂŒhren. Das Potenzial der TPA-TCT
fĂŒr die Charakterisierung moderner Detektortechnologien wird anhand von Streifen- und
monolithische Detektoren demonstriert. Die Anwendbarkeit der TPA-TCT in Neutronen,
Protonen und Gamma bestrahlten Detektoren wird gezeigt, und die Auswirkungen von
StrahlenschÀden auf die Technik werden systematisch untersucht. Die Verringerung der
Ladungsvervielfachung in einem Low Gain Avalanche Detector bei zunehmender Ladungs-
trÀgerdichte wird beobachtet und die Rolle der LadungstrÀgerdiffusion zur teilweisen
Wiederherstellung der VerstÀrkung wird untersucht. Neue Techniken zur Untersuchung
des elektrischen Feldes in komplexen, segmentierten Detektoren werden entwickelt und auf
Streifen- und monolithische Detektoren angewandt. Diese Arbeit ebnet den Weg fĂŒr die
TPA-TCT als Methode fĂŒr die Charakterisierung von Detektoren mit dreidimensionaler
rÀumlicher Auflösung im Mikrometerbereich.
2023-01-01T00:00:00Z
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Development of a tool for Bayesian data analysis and its application in Monte Carlo tuning
http://hdl.handle.net/2003/42386
Title: Development of a tool for Bayesian data analysis and its application in Monte Carlo tuning
Authors: La Cagnina, Salvatore
Abstract: In this thesis, a novel approach to Monte Carlo event generator tuning, grounded in Bayesian reasoning, is presented. The Bayesian Analysis Toolkit (BAT.jl) is introduced as a modern tool for performing Bayesian inference. A numerical test suite that verifies the validity and performance of the BAT.jl package is developed. The test suite is used to evaluate the performance of the Markov chain Monte Carlo (MCMC) sampling algorithms implemented in BAT.jl, utilizing a selection of test functions and different metrics to quantify the quality of the samples. The results show that the MCMC algorithms are able to sample the posterior distributions of the test functions accurately. Utilizing the BAT.jl toolkit, two hadronization models within the Herwig Monte Carlo event generator (MCEG) are successfully tuned to data from the LEP experiments. Several aspects of the tuning procedure are investigated, such as parameter and observable selection and parametrization quality. Samples generated using the tuned parameters, obtained from the global mode of the posterior, are compared to data through a Ï2 test. The resulting p-values for the tuned simulations significantly outperform those from the nominal MCEG samples, indicating a successful tune and an improved description of the data. The posterior is also used to present a method for propagating the parameter uncertainties to the realm of the observables, providing a measure for the tuning uncertainty. Studies on the impact of assigning weights to the observables and the impact of correlations between measurements on the tuning are also presented. These show that weights can alter the tuning results, especially in cases with multiple modes in the posterior. However, their influence on the quality of the tune is minimal in this case. The correlation of measurements has less of an impact on the position of the global mode but substantially affects the associated parameter uncertainties estimates. Finally, a comparison of the two tuned hadronization models is presented, which indicates that the Lund string model describes the data slightly better than the cluster hadronization model for this set of observables.
2023-01-01T00:00:00Z
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Fast and accurate dose predictions for novel radiotherapy treatments in heterogeneous phantoms using conditional 3DâUNet generative adversarial networks
http://hdl.handle.net/2003/42373
Title: Fast and accurate dose predictions for novel radiotherapy treatments in heterogeneous phantoms using conditional 3DâUNet generative adversarial networks
Authors: Mentzel, Florian; Kröninger, Kevin; Lerch, Michael; Nackenhorst, Olaf; Paino, Jason; Rosenfeld, Anatoly; Saraswati, Ayu; Tsoi, Ah Chung; Weingarten, Jens; Hagenbuchner, Markus; Guatelli, Susanna
Abstract: Purpose:
Novel radiotherapy techniques like synchrotron X-ray microbeam radiation therapy (MRT) require fast dose distribution predictions that are accurate at the sub-mm level, especially close to tissue/bone/air interfaces. Monte Carlo (MC) physics simulations are recognized to be one of the most accurate tools to predict the dose delivered in a target tissue but can be very time consuming and therefore prohibitive for treatment planning. Faster dose prediction algorithms are usually developed for clinically deployed treatments only. In this work, we explore a new approach for fast and accurate dose estimations suitable for novel treatments using digital phantoms used in preclinical development and modern machine learning techniques. We develop a generative adversarial network (GAN) model, which is able to emulate the equivalent Geant4 MC simulation with adequate accuracy and use it to predict the radiation dose delivered by a broad synchrotron beam to various phantoms.
Methods:
The energy depositions used for the training of the GAN are obtained using full Geant4 MC simulations of a synchrotron radiation broad beam passing through the phantoms. The energy deposition is scored and predicted in voxel matrices of size 140 Ă 18 Ă 18 with a voxel edge length of 1 mm. The GAN model consists of two competing 3D convolutional neural networks, which are conditioned on the photon beam and phantom properties. The generator network has a U-Net structure and is designed to predict the energy depositions of the photon beam inside three phantoms of variable geometry with increasing complexity. The critic network is a relatively simple convolutional network, which is trained to distinguish energy depositions predicted by the generator from the ones obtained with the full MC simulation.
Results:
The energy deposition predictions inside all phantom geometries under investigation show deviations of less than 3% of the maximum deposited energy from the simulation for roughly 99% of the voxels in the field of the beam. Inside the most realistic phantom, a simple pediatric head, the model predictions deviate by less than 1% of the maximal energy deposition from the simulations in more than 96% of the in-field voxels. For all three phantoms, the model generalizes the energy deposition predictions well to phantom geometries, which have not been used for training the model but are interpolations of the training data in multiple dimensions. The computing time for a single prediction is reduced from several hundred hours using Geant4 simulation to less than a second using the GAN model.
Conclusions:
The proposed GAN model predicts dose distributions inside unknown phantoms with only small deviations from the full MC simulation with computations times of less than a second. It demonstrates good interpolation ability to unseen but similar phantom geometries and is flexible enough to be trained on data with different radiation scenarios without the need for optimization of the model parameter. This proof-of-concept encourages to apply and further develop the model for the use in MRT treatment planning, which requires fast and accurate predictions with sub-mm resolutions.
2022-02-19T00:00:00Z
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Hybrid coherent control of magnons in a ferromagnetic phononic resonator excited by laser pulses
http://hdl.handle.net/2003/42346
Title: Hybrid coherent control of magnons in a ferromagnetic phononic resonator excited by laser pulses
Authors: Scherbakov, Alexey V.; Carr, Alex D.; Linnik, Tetiana L.; Kukhtaruk, Serhii M.; Armour, Andrew D.; Nadzeyka, Achim; Rushforth, Andrew W.; Akimov, Andrey V.; Bayer, Manfred
Abstract: We propose and demonstrate the concept of hybrid coherent control (CC) whereby a quantum or classical harmonic oscillator is excited by two excitations: one is quasiharmonic (i.e., harmonic with a finite lifetime) and the other is a pulsed broadband excitation. Depending on the phase relation between the two excitations, controlled by the detuning of the oscillator eigenfrequencies and the wave forms of the quasiharmonic and broadband excitations, it is possible to observe Fano-like spectra of the harmonic oscillator due to the interference of the two responses to the simultaneously acting excitations. Experimentally, as an example, the hybrid CC is implemented for magnons in a ferromagnetic grating where GHz coherent phonons act as the quasiharmonic excitation and the broadband impact arises from pulsed optical excitation followed by spin dynamics in the ferromagnetic nanostructure.
2024-01-23T00:00:00Z
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From spectroscopy to coherent control: photon echoes of excitons in organic-inorganic perovskites and (In, Ga)As quantum dots
http://hdl.handle.net/2003/42311
Title: From spectroscopy to coherent control: photon echoes of excitons in organic-inorganic perovskites and (In, Ga)As quantum dots
Authors: Grisard, Stefan
Abstract: Photon echoes emerge from the delayed optical response of inhomogeneous ensembles of emitters upon resonant laser excitation. In semiconductors, they allow to uncover internal scattering and interaction dynamics on the picosecond timescale, while also holding promise as the realization of quantum optical memories in future quantum networks. Based on these two fields of application, this work uses photon echoes to investigate two material systems: Organic-inorganic perovskites and (In,Ga)As quantum dots. Organic-inorganic perovskites have attracted significant attention for their exceptional performance in photovoltaics and light-emitting applications. However, a comprehensive understanding of coherent light-matter interactions in this material class and in particular the role of excitons close to the band gap remained elusive. This work reveals that excitons dominate the nonlinear optical response of MAPbI3 and FAPbI3 single crystals and are subject to strong inhomogeneous broadening even at cryogenic temperatures. Compositional substitution is found to induce spatial band gap fluctuations on the nanometer scale that localize excitons accompanied by an extension of their coherence time by two orders of magnitude. Furthermore, exciton interactions are studied through polarization-dependent photon echoes, uncovering the formation of a biexciton state and the contribution of spin-dependent many-body interactions to nonlinear optical spectra. Subsequently, the focus shifts to confined excitons in (In,Ga)As semiconductor quantum dot ensembles, that represent an ideal platform to explore new approaches on how to coherently transfer, manipulate, and retrieve optical information to a solid state on picosecond timescales. First, it is demonstrated that collective Rabi rotations of the photon echoes from a quantum dot ensemble can be observed when a spatially uniform excitation profile is used. In this way, internal mechanisms of decoherence under strong laser excitation are identified. Thereafter, the photon echo sequence is expanded by two control pulses, providing all-optical control over the emission time, spectral response, and polarization state of photon echoes from quantum dots. Here, the interplay of temporally sorted multi-wave-mixing signals is exploited.
2023-01-01T00:00:00Z
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Unfolding the muon neutrino flux
http://hdl.handle.net/2003/42308
Title: Unfolding the muon neutrino flux
Authors: Kardum, Leonora
Abstract: The IceCube Neutrino Observatory, situated at the South Pole within a cubic kilometer of underground ice, is a state-of-the-art experiment for detecting particles of high energies, with a special focus on investigating neutrino physics. The neutrino flux can be divided into three distinct components: astrophysical, originating from extraterrestrial sources; conventional, arising from the decay of pions and kaons in atmospheric cosmic ray cascades; and the prompt component, which has yet to be detected and stems from the decay of charmed hadrons. This study aims to reconstruct the total flux of neutrinos at Earth and places a particular emphasis on examining the predicted angular dependence. Unfolding encompasses a collection of techniques that aim to determine a quantity in a manner independent of specific assumptions, thereby removing the influence of various assumptions made during the process. In this analysis, the energy spectrum of muon neutrinos is unfolded with the employment of an innovative technique for reshaping the observable space to ensure an adequate number of events in the low statistic region at the highest energies. This work presents the unfolded energy and zenith angle spectrum reconstructed from eleven
years of IceCube data in the range from 500 GeV to 4 PeV energies, and compares the findings
with both model predictions and previous measurements.; Das IceCube Neutrino Observatory, das sich am SĂŒdpol in einem Kubikkilometer unterirdischen Eises befindet, ist ein hochmodernes Experiment zum Nachweis von Teilchen mit hoher Energie, wobei der Schwerpunkt auf der Untersuchung der Neutrinophysik liegt. Der Neutrinofluss kann in drei verschiedene Komponenten unterteilt werden: astrophysikalische Neutrinos aus extraterrestrischen Quellen; konventionelle Neutrinos, aus dem Zerfall von Pionen und Kaonen in atmosphĂ€rischen Luftschauern; und prompte Neutrinos, die noch nicht gemessen wurden, aber aus dem Zerfall von Hadronen aus Charm-Quarks erwartet werden. Diese Studie zielt darauf ab, den Gesamtfluss der Neutrinos auf der Erde zu rekonstruieren, und legt einen besonderen Schwerpunkt auf die Untersuchung der vorhergesagten WinkelabhĂ€ngigkeit. Die Entfaltung umfasst eine Reihe von Techniken, die darauf abzielen, eine physikalische GröĂe modellunabhĂ€ngig zu bestimmen. In dieser Analyse wird das Energiespektrum von Myon-Neutrinos mit Hilfe einer innovativen Technik zur Umformung des beobachtbaren Raums entfaltet, um eine angemessene Anzahl von Ereignissen im Bereich der niedrigen Statistik bei den höchsten Energien sicherzustellen. Diese Arbeit prĂ€sentiert das ungefaltete Energie- und Zenitwinkelspektrum, das aus elf
Jahren IceCube-Daten im Energiebereich von 500 GeV bis 4 PeV rekonstruiert wurde, und
vergleicht die Ergebnisse sowohl mit Modellvorhersagen als auch mit frĂŒheren Messungen.
2023-01-01T00:00:00Z
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Enhancing electron correlation at a 3d ferromagnetic surface
http://hdl.handle.net/2003/42262
Title: Enhancing electron correlation at a 3d ferromagnetic surface
Authors: Janas, David Maximilian; Droghetti, Andrea; Ponzoni, Stefano; Cojocariu, Iulia; Jugovac, Matteo; Feyer, Vitaliy; RadonjiÄ, MiloĆĄ M.; Rungger, Ivan; Chioncel, Liviu; Zamborlini, Giovanni; Cinchetti, Mirko
Abstract: Spin-resolved momentum microscopy and theoretical calculations are combined beyond the one-electron approximation to unveil the spin-dependent electronic structure of the interface formed between iron (Fe) and an ordered oxygen (O) atomic layer, and an adsorbate-induced enhancement of electronic correlations is found. It is demonstrated that this enhancement is responsible for a drastic narrowing of the Fe d-bands close to the Fermi energy (EF) and a reduction of the exchange splitting, which is not accounted for in the Stoner picture of ferromagnetism. In addition, correlation leads to a significant spin-dependent broadening of the electronic bands at higher binding energies and their merging with satellite features, which are manifestations of a pure many-electron behavior. Overall, adatom adsorption can be used to vary the material parameters of transition metal surfaces to access different intermediate electronic correlated regimes, which will otherwise not be accessible. The results show that the concepts developed to understand the physics and chemistry of adsorbateâmetal interfaces, relevant for a variety of research areas, from spintronics to catalysis, need to be reconsidered with many-particle effects being of utmost importance. These may affect chemisorption energy, spin transport, magnetic order, and even play a key role in the emergence of ferromagnetism at interfaces between non-magnetic systems.
2022-10-27T00:00:00Z
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Understanding the dynamics of randomly positioned dipolar spin ensembles
http://hdl.handle.net/2003/42249
Title: Understanding the dynamics of randomly positioned dipolar spin ensembles
Authors: GrĂ€Ăer, Timo; Rezai, Kristine; Sushkov, Alexander O.; Uhrig, Götz S.
Abstract: Dipolar spin ensembles with random spin positions are attracting much attention because they help us to understand decoherence as it occurs in solid-state quantum bits in contact with spin baths. Also, these ensembles are systems which may show many-body localization, at least in the sense of very slow spin dynamics. We present measurements of the autocorrelations of spins on diamond surfaces at infinite temperature in a doubly rotating frame which eliminates local disorder. Strikingly, the timescales in the longitudinal and the transversal channel differ by more than one order of magnitude, which is a factor much greater than one would have expected from simulations of spins on lattices. A previously developed dynamic mean-field theory for spins (spinDMFT) fails to explain this phenomenon. Thus, we improve it by extending it to clusters (CspinDMFT). This theory does capture the striking mismatch up to two orders of magnitude for random ensembles. Without positional disorder, however, the mismatch is only moderate with a factor below 4. The pivotal role of positional disorder suggests that the strong mismatch is linked to precursors of many-body localization.
2023-12-01T00:00:00Z
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Modulation of the transient magnetization of an EuO/Co bilayer by controlled optical excitation
http://hdl.handle.net/2003/42246
Title: Modulation of the transient magnetization of an EuO/Co bilayer by controlled optical excitation
Authors: MönkebĂŒscher, David
Abstract: Der ferromagnetische Halbleiter Europiummonoxid (EuO) gilt als vielversprechender Kandidat fĂŒr neuartige spintronische Anwendungen, da er ein groĂes magnetisches Moment und starke magneto-optische Effekte mit isolierenden Eigenschaften vereint. Obwohl EuO mit T_C = 69 K die höchste Curie-Temperatur unter den Europiumchalkogeniden aufweist, ist sie fĂŒr kommerzielle Anwendungen zu niedrig. Viele AnsĂ€tze zur Erhöhung von T_C, wie zum Beispiel die Dotierung mit Gd-Ionen oder epitaktische Verformung, wurden bereits erfolgreich untersucht. Jedoch basieren sie alle auf einer VerĂ€nderung der Stöchiometrie und LeitfĂ€higkeit des Seltenerdoxids. Das Ausnutzen des Proximity-Effektes könnte eine alternative Herangehensweise fĂŒr das starke Erhöhen der magnetischen Ordnungstemperatur von EuO darstellen, die gleichzeitig dessen intrinsischen Eigenschaften bewahrt. Dieser Effekt beruht auf der Kopplung an einen Ferromagneten mit hoher Curie-Temperatur und ist in der Literatur fĂŒr Ă€hnliche System bereits demonstriert worden.
In dieser Arbeit wird ein EuO/Co-Zweischichtsystem dĂŒnner Filme mittels des statischen und zeitaufgelösten magneto-optischen Kerr-Effekts (MOKE) untersucht, um einen Nachweis fĂŒr eine erhöhte Curie-Temperatur von EuO aufgrund der NĂ€he zum Ăbergangsmetall Co zu finden. Des Weiteren wird der Einfluss von Co auf die Spindynamik von EuO untersucht. Statische Messungen der Hysterese der EuO/Co-Probe zeigen eine antiferromagnetische Kopplung zwischen den beiden ferromagnetischen Schichten. Aufgrund der Ăberlagerung des Signals beider Schichten ĂŒbersteigt die Co-Hysterese einen möglichen Restbeitrag von EuO bei erhöhten Temperaturen. Zeitaufgelöste MOKE-Messungen zeigen eine transiente VerstĂ€rkung der EuO-Magnetisierung, die auch dann auftritt, wenn selektiv nur das Ăbergangsmetall angeregt wird. Dieses Verhalten wird auf die Erzeugung eines superdiffusven Spinstroms von MajoritĂ€tselektronen bei der Entmagnetisierung der Co-Schicht zurĂŒckgefĂŒhrt. Der Spinstrom breitet sich in Richtung der EuO-Schicht aus, um deren 5d-ZustĂ€nde zu besetzen, was zu einer Ă€hnlichen MagnetisierungsverstĂ€rkung wie bei einer direkten Photoanregung des Seltenerdoxids fĂŒhrt. Die BeitrĂ€ge beider Schichten zur transienten Spindynamik zeigen entgegengesetze Vorzeichen. Daher bietet die EuO/Co-Probe ein System, in dem die transiente Kerr-Rotation durch Variation externer Parameter wie der Probentemperatur, des angelegten Magnetfelds und der Pumpstrahlfluenz beeinflusst werden kann. Durch eine starke Anregung der Co-Schicht wird ihre Magnetisierung signifikant verringert, wodurch die Hysterese der EuO-Schicht bei transienten Hysteresemessungen zugĂ€nglich wird. Sie ist auch noch bei einer Temperatur von 300 K zu beobachten, was auf eine starke Erhöhung der magnetischen Ordnungstemperatur von EuO, bedingt durch die NĂ€he zu Co, hindeutet.; The ferromagnetic semiconductor europium monoxide (EuO) is a promising candidate for new spintronic applications due to its large magnetic moment and strong magneto-optical effects combined with its insulating properties. Although EuO has the highest Curie temperature among the europium chalcogenides with T_C = 69 K, it still requires excessive cooling in real applications. Many approaches to increase its T_C have been successfully studied, such as doping with Gd ions or epitaxial straining, which inevitably change the stoichiometry and conductivity of the rare earth oxide. An alternative pathway to greatly increase the Curie temperature of EuO while preserving its conductivity and stoichiometry could be based on the magnetic proximity effect. This effect relies on the coupling to a high T_C ferromagnet, and has been demonstrated in the literature for similar systems.
In this thesis, a EuO/Co bilayer of thin films is studied using the static and time-resolved magneto-optical Kerr effect (MOKE) to find an evidence for an elevated EuO T_C due to the proximity to the transition metal Co. Furthermore, the influence of Co on the spin dynamics of EuO is investigated.
Static measurements of the EuO/Co bilayer hysteresis reveal an antiferromagnetic coupling between the two ferromagnetic layers. Due to the superposition of the measured signal of both layers, the Co hysteresis exceeds any possible residual EuO contribution to the magneto-optical signal above its bulk T_C. Time-resolved MOKE measurements show a transient enhancement of the EuO magnetization.
It is still present when the Co layer is selectively photoexcited by tuning the photon energy of the pump beam below the EuO band gap energy. This behavior is attributed to the generation of a superdiffusive spin current of majority electrons upon demagnetizing the Co layer. It propagates towards the EuO layer to populate its 5d states, inducing a similar magnetization enhancement compared to direct photoexcitation of the rare earth oxide. The two layers of the investigated sample system exhibit a contribution to the transient spin dynamics with opposite signs. Therefore, the EuO/Co bilayer provides a system in which the transient magneto-optical Kerr rotation can be tuned by varying external parameters such as the sample temperature, the applied magnetic field and the pump beam fluence. By strongly exciting the Co layer and thus quenching its magnetization, the EuO hysteresis becomes accessible in transient hysteresis measurements. It persists up to a temperature of 300 K, pointing to an experimental evidence for room temperature magnetic order in EuO induced by proximity to Co.
2023-01-01T00:00:00Z
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Spectral and spatial analysis of MAGIC telescope data in a standardized format
http://hdl.handle.net/2003/42245
Title: Spectral and spatial analysis of MAGIC telescope data in a standardized format
Authors: Mender, Simone
Abstract: The precise understanding of the emission and acceleration processes of very-high-energy radiation
in the Universe is still an unsolved mystery today. To study the nature of very-high-energy
gamma rays, Imaging Air Cherenkov Telescopes such as the MAGIC telescopes detect Cherenkov
light produced by particle showers in the atmosphere. State-of-the-art spectral and spatial
analyses of gamma-ray data rely on the open-source Python package Gammapy. Due to this new
approach from the gamma-ray community, the input data needs to be provided in a standardized
format which requires a combination of event lists with instrument response functions. In this
thesis, a spectral analysis of the two TeV radio galaxy candidates TXS 0149+710 and 4C +39.12
observed by MAGIC is conducted. For this, standardized data is produced in an automated and
reproducible way using the new database-driven tool AutoMAGIC, partly developed in the course
of this thesis. Li&Ma significances of 0.32 đ and 0.98 đ are calculated for TXS 0149+710 and 4C
+39.12, respectively. Therefore, only upper limits on the differential flux are given.
For spatial analyses, background models have to be included in the standardized data, which
is not covered by AutoMAGIC yet. To address this challenge, 1441 observations of off data are
processed with AutoMAGIC and the background shape is characterized depending on the azimuth,
zenith distance, and the reconstructed energy. Also, dependencies of the background rate on
the zenith distance, the transmission of the atmosphere, the NSB and the galactic latitude are
investigated. A new method is developed, which creates background models according to the new-
found relations with the azimuth and zenith distance. These background models are compared
with background models created from non-simultaneous off data with more conventional methods.
Spectral and spatial analyses of Crab Nebula data are performed to validate the background methods.; Emissions- und Beschleunigungsprozesse von hochenergetischen Teilchen im Universum sind wei-
testgehend noch nicht verstanden. Um hochenergetische Gammateilchen zu untersuchen, detektie-
ren Tscherenkow-Teleskope, wie beispielsweise die MAGIC-Teleskope, Tscherenkow-Licht, welches
durch Teilchenschauer in der AtmosphÀre erzeugt wird. Um mit dem open-source Python Paket
Gammapy reproduzierbare spektrale und rÀumliche Analysen von MAGIC-Beobachtungen durch-
zufĂŒhren, werden die Daten in einem standardisierten Datenformat benötigt. Dieses Datenformat
erfordert Listen mit Ereignissen, die als Gammaschauer klassifiziert wurden, sowie die zugehörigen
Funktionen der Detektorantwort. FĂŒr die spektrale Analyse von MAGIC-Beobachtungen der
beiden TeV Radiogalaxiekandidaten TXS 0149+710 und 4C +39.12 werden die standardisierten
Daten auf automatisierte und reproduzierbare Weise mit der neuen, datenbankgestĂŒtzten Software
AutoMAGIC erzeugt, welche im Rahmen dieser Arbeit mitentwickelt wurde. FĂŒr TXS 0149+710
und 4C +39.12 werden Li&Ma-Signifikanzen von 0,32 đ und 0,98 đ berechnet, weshalb nur obere
Grenzen des differentiellen Flusses angegeben werden.
FĂŒr rĂ€umliche Analysen mit Gammapy mĂŒssen Hintergrundmodelle in den standardisierten
Daten enthalten sein, was AutoMAGIC momentan noch nicht inkludiert. Um diese Herausfor-
derung zu bewÀltigen, werden 1441 Beobachtungen mit AutoMAGIC prozessiert und die Form
des Hintergrunds in AbhÀngigkeit von Azimut, Zenitdistanz und der rekonstruierten Energie
charakterisiert. AuĂerdem werden die AbhĂ€ngigkeiten der Hintergrundrate von der Zenitdistanz,
der AtmosphÀrentransmission, dem Nachthimmelhintergrund und der galaktischen Breite unter-
sucht. Eine neue Methode wird vorgestellt, welche aufgrund der neu gewonnenen Erkenntnisse
Hintergrundmodelle in AbhÀngigkeit von Azimut und Zenitdistanz erstellt. Zum Vergleich werden
zudem Hintergrundmodelle mit herkömmlichen Methoden erstellt. Zur Validierung der Methoden
werden spektrale und rĂ€umliche Analysen von Krebsnebeldaten durchgefĂŒhrt.
2023-01-01T00:00:00Z
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Decay-time-dependent studies of strange beauty mesons
http://hdl.handle.net/2003/42244
Title: Decay-time-dependent studies of strange beauty mesons
Authors: FĂŒhring, Marc Quentin
Abstract: In this thesis, two decay-time-dependent analyses of Bs0-meson decays are presented. Precise measurements are performed using proton-proton collision data recorded by the LHCb experiment between 2015 and 2018. Based on the reconstruction and selection of 378 700 +/- 700 Bs0 to Ds- pi+ decays, the most precise measurement of the Bs0-Bsbar0 oscillation frequency DeltaMs = (17.7683 +/- 0.0051 +/- 0.0032) psâ1 in the world to date is achieved. This measurement alone is an essential test of the Standard Model of particle physics. In addition, it is a crucial ingredient to increase the precision of decay-time-dependent measurements of other Bs0-decay modes. The presented analysis of Bs0 to Ds K decays benefits from this updated measurement of DeltaMs and from further improvements of algorithms and methods. The CKM angle gamma = (74 +/- 11)°, an important Standard Model parameter, is measured based on 20 950 +/- 180 selected decays. Compared to the analysis using data from 2011 and 2012, the precision is improved beyond what would be expected from the increase in data sample sizes.; In dieser Dissertation werden zwei zerfallszeitabhaÌngige Messungen von Bs0-Meson ZerfaÌllen vorgestellt. Beide Messungen basieren auf der Analyse eines Datensatzes von Proton-Proton Kollisionen aufgezeichnet zwischen 2015 und 2018 am LHCb-Experiment. Die Rekonstruktion und Selektion von 378 700 +/- 700 Bs0 zu Ds- pi+ ZerfaÌllen ermoÌglicht die zur Zeit weltweit praÌziseste Messung der Bs0-Bsbar0 Oszillationsfrequenz DeltaMs = (17.7683 +/- 0.0051 +/- 0.0032) psâ1 . Die Messung von DeltaMs selbst ist ein wichtiger Test des Standardmodells der Teilchenphysik. DaruÌber hinaus liefert sie einen wesentlichen Beitrag um die PraÌzision weiterer zerfallszeitabhaÌngiger Messungen von Bs0-Meson ZerfaÌllen zu steigern. Die vorgestellte Analyse von Bs0 zu Ds K ZerfaÌllen profitiert von der praÌziseren Kenntnis von DeltaMs, sowie von verbesserten Verfahren und Algorithmen. Der CKM Winkel gamma =(74 +/- 11)°, ein wichtiger Standardmodell Parameter, wird anhand von 20 950 +/- 180 selektierten ZerfaÌllen bestimmt. Im Vergleich zu der vorherigen Analyse der in 2011 und 2012 aufgezeichneten Daten faÌllt die Verbesserung damit hoÌher aus, als die erhoÌhte Statistik alleine erwarten laÌsst.
2023-01-01T00:00:00Z
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Small beams, fast predictions: a comparison of machine learning dose prediction models for proton minibeam therapy
http://hdl.handle.net/2003/42239
Title: Small beams, fast predictions: a comparison of machine learning dose prediction models for proton minibeam therapy
Authors: Mentzel, Florian; Kröninger, Kevin; Lerch, M.; Nackenhorst, Olaf; Rosenfeld, A.; Tsoi, A. C.; Weingarten, Jens; Hagenbuchner, M.; Guatelli, S.
Abstract: Background:
Dose calculations for novel radiotherapy cancer treatments such as proton minibeam radiation therapy is often done using full Monte Carlo (MC) simulations. As MC simulations can be very time consuming for this kind of application, deep learning models have been considered to accelerate dose estimation in cancer patients.
Purpose:
This work systematically evaluates the dose prediction accuracy, speed and generalization performance of three selected state-of-the-art deep learning models for dose prediction applied to the proton minibeam therapy. The strengths and weaknesses of those models are thoroughly investigated, helping other researchers to decide on a viable algorithm for their own application.
Methods:
The following recently published models are compared: first, a 3D U-Net model trained as a regression network, second, a 3D U-Net trained as a generator of a generative adversarial network (GAN) and third, a dose transformer model which interprets the dose prediction as a sequence translation task. These models are trained to emulate the result of MC simulations. The dose depositions of a proton minibeam with a diameter of 800ÎŒm and an energy of 20â100 MeV inside a simple head phantom calculated by full Geant4 MC simulations are used as a case study for this comparison. The spatial resolution is 0.5 mm. Special attention is put on the evaluation of the generalization performance of the investigated models.
Results:
Dose predictions with all models are produced in the order of a second on a GPU, the 3D U-Net models being fastest with an average of 130 ms. An investigated 3D U-Net regression model is found to show the strongest performance with overall 61.0%±0.5% of all voxels exhibiting a deviation in energy deposition prediction of less than 3% compared to full MC simulations with no spatial deviation allowed. The 3D U-Net models are observed to show better generalization performance for target geometry variations, while the transformer-based model shows better generalization with regard to the proton energy.
Conclusions:
This paper reveals that (1) all studied deep learning models are significantly faster than non-machine learning approaches predicting the dose in the order of seconds compared to hours for MC, (2) all models provide reasonable accuracy, and (3) the regression-trained 3D U-Net provides the most accurate predictions.
2022-10-30T00:00:00Z
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Brachytherapy meets X-rays
http://hdl.handle.net/2003/42236
Title: Brachytherapy meets X-rays
Authors: Manke, Henning
Abstract: Intraocular tumours are a life-threatening risk. Smaller tumours can be treated with
106Ru applicators. Meanwhile, more prominent tumours get treated with 125I applicators,
which results in a higher risk of side effects, or proton therapy, which is only available
at a limited number of specialised centres and may lead to toxic tumour syndrome.
Therefore, a novel combined therapy concept is presented and analysed in this thesis.
The idea combines the use of 106Ru applicators and external beam radiotherapy performed
with soft X-rays. With the confocal irradiation technique and the utilisation of the 106Ru
applicator as a beam-stop for the X-ray beams, healthy tissue is spared from high dosages
to reduce the risk of side effects. The combined therapy concept can be implemented
in hospitals with relatively low costs and resembles a novel bulb-preserving modality for
large intraocular tumours.
As the first steps to this therapy concept, measurements are performed with a novel solid
phantom with three different detector types to assess the absorption of the X-rays in the
106Ru applicator. Additionally, the clinical benefit is investigated with a novel software
workflow, in which 3D models are created using patient data from the University Hospital
Essen in Germany. The modalities are simulated with these 3D models. Dose-volume
histograms are presented to evaluate the combined therapy concept and to compare it
to stand-alone brachytherapy.; Intraokulare Tumoren stellen ein lebensbedrohliches Risiko dar. Kleinere Tumoren kön-
nen mit 106Ru-Applikatoren behandelt werden. GröĂere Tumoren werden dagegen ent-
weder mit 125I-Applikatoren behandelt, was ein höheres Risiko von Nebenwirkungen mit
sich bringt, oder mit Protonen bestrahlt, was nur an wenigen spezialisierten Zentren
möglich ist. DarĂŒber hinaus birgt die Protonentherapie das Risiko, dass das Tumorgew-
be ischÀmisch wird. In dieser Arbeit wird ein neuartiges kombiniertes Therapiekonzept
vorgestellt und analysiert. Das Konzept kombiniert den Einsatz von 106Ru-Applikatoren
und externer Strahlentherapie in Form von niederenergetischen Röntgenstrahlen. Mit
der konfokalen Bestrahlungstechnik und der Verwendung des 106Ru-Applikators als Ab-
sorber fĂŒr die Röntgenstrahlen kann gesundes Gewebe geschont werden, um das Risiko
von Nebenwirkungen zu minimieren. Es kann relativ kostengĂŒnstig in Kliniken imple-
mentiert werden und stellt eine neue bulbuserhaltende ModalitĂ€t fĂŒr groĂe intraokulare
Tumoren dar.
Als erste Schritte zu diesem Therapiekonzept werden Messungen und deren Ergebnisse
vorgestellt, die mit einem neuen Festkörperphantom und drei verschiedenen Detektor-
typen durchgefĂŒhrt wurden, um die Absorption der Röntgenstrahlen in einem 106Ru-
Applikator zu bewerten. ZusÀtzlich wird der medizinisch-physikalische Nutzen unter-
sucht. Mit einem neuartigen Software-Workflow werden 3D-Modelle mit anonymen Pa-
tientendaten aus dem UniversitÀtsklinikum Essen erstellt und die Strahlentherapie si-
muliert. Dosis-Volumen-Histogramme werden ausgewertet, um das kombinierte Thera-
piekonzept zu bewerten und mit der alleinigen Brachytherapie zu vergleichen.
2023-01-01T00:00:00Z
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Druck- und temperaturabhÀngige Adsorption von Fluiden an hydrophoben GrenzflÀchen
http://hdl.handle.net/2003/42231
Title: Druck- und temperaturabhÀngige Adsorption von Fluiden an hydrophoben GrenzflÀchen
Authors: Moron, Mike
Abstract: Adsorption ist ein an GrenzflĂ€chen auftretendes PhĂ€nomen, bei dem sich MolekĂŒle ĂŒber schwache Wechselwirkungen an einer GrenzflĂ€che anlagern. Adsorption spielt unter anderem bei biologischen und industriellen Prozessen eine wichtige Rolle, wie zum Beispiel bei der Adsorption von Proteinen wĂ€hrend der Blutgerinnung, der heterogenen Katalyse oder der Oxidation von IndustrieschlĂ€mmen in ĂŒberkritischem Wasser. Ein ĂŒberkritisches Fluid (SCF) ist ein Fluid, dass sich oberhalb seines kritischen Drucks p_crit und seiner kritischen Temperatur T_crit befindet. Am kritischen Punkt gibt es im Volumen der Phase keine Unterschiede mehr in der Dichte oder der ViskositĂ€t zwischen der gasförmigen und flĂŒssigen Phase. Das fĂŒhrt dazu, dass SCFs zu FlĂŒssigkeiten Ă€hnliche Dichten und Lösungsmitteleigenschaften aufweisen und dabei gleichzeitig die ViskositĂ€t eines Gases besitzen. Das VerstĂ€ndnis der Adsorptionseigenschaften von Fluiden unter- und oberhalb des kritischen Punkts an festen GrenzflĂ€chen ist von zentraler Bedeutung, um Prozesse in zahlreichen Anwendungen zu optimieren. Die Untersuchung der Adsorption von SCFs stellt jedoch technische Herausforderungen an eine geeignete Probenumgebung, da die kritischen Punkte vieler Fluide, zum Beispiel Wasser (T_crit=374â°C, p_crit=221âbar) oder Ethanol (T_crit=241â°C,
p_crit=63âbar), bei hohen DrĂŒcken und Temperaturen liegen. Im Rahmen dieser Arbeit wurde daher in Zusammenarbeit mit der Firma Dieckers GmbH & Co. KG und der SITEC-Sieber Engineering AG eine Sichtzelle konzipiert und von der SITEC-Sieber Engineering AG gefertigt, die DrĂŒcken von 1000 bar bei Temperaturen bis zu 500 âŠC standhĂ€lt und somit die grenzflĂ€chensensitive Analyse einer Vielzahl ĂŒberkritischer Fluide ermöglicht. Die Sichtzelle wurde erfolgreich an der Strahllinie ID 31 an der ESRF (Grenoble, Frankreich) in Betrieb genommen und erste Messungen zeigten, dass der ĂŒberkritische Bereich von Wasser zugĂ€nglich ist. In dieser Arbeit wurde die Adsorption der Fluide C2F6, C3F8 und C4F10 an mit Octadecyltrichlorsilan (OTS) beschichteten Siliziumwafern in AbhĂ€ngigkeit des Abstands einer vorgegebenen Temperatur oder eines vorgegebenen Drucks zum kritischen Punkt untersucht, wobei der Abstand zum kritischen Punkt durch die Wahl der Fluide variiert wurde. Dabei wurde insbesondere die Entwicklung der Rauigkeit in AbhĂ€ngigkeit der Schichtdicke der adsorbierten Schichten analysiert. Durch die Aufnahme von RöntgenreflektivitĂ€ten (XRR) konnte gezeigt werden, dass die Zunahme der Rauigkeit der adsorbierten Schichten mit steigendem Druck stĂ€rker ist, je nĂ€her sich das Fluid an seiner kritischen Temperatur befindet. Auch oberhalb des kritischen Punkts blieb eine adsorbierte Schicht auf dem OTS-Wafer bestehen, die die gröĂte Rauigkeit aufwies. Im Gegensatz dazu divergieren die Schichtdicken unterhalb des kritischen Punkts bei Erreichen des SĂ€ttigungsdampfdrucks, da das Umgebungsmediums kondensiert und sich eine makroskopisch dicke, flĂŒssige Schicht auf dem OTS-Wafer ausbildet. Um die adsorbierten Schichten angemessen zu bewerten, wurden die OTS-Wafer auf ihre Empfindlichkeit gegenĂŒber Röntgenstrahlen und hohen Temperaturen analysiert. Die XRR-Messungen haben nahegelegt, dass fĂŒr die untersuchten Fluide bei niedrigen Temperaturen keine starke SchĂ€digung der OTS-Schicht zu erwarten ist. Ferner konnte festgestellt werden, dass die SchĂ€digung der OTS-Schicht bei höheren Photonenenergien bei höheren Temperaturen auftritt, so dass höhere Photonenenergien im Allgemeinen besser fĂŒr die Untersuchung der Adsorption mittels XRR geeignet sind. AuĂerdem zeigte sich, dass eine ober- halb des OTS-Wafers befindliche Gasschicht die StabilitĂ€t der OTS-schicht deutlich verringert. Die im Rahmen dieser Arbeit durchgefĂŒhrten XRR-Messungen an der GrenzflĂ€che zwischen den untersuchten Fluiden und OTS tragen nicht nur zum besseren VerstĂ€ndnis der Adsorption von Fluorkohlenwasserstoffen an hydrophoben OberflĂ€chen bei, sondern bieten auch wichtige Einblicke in das Adsorptionsverhalten von SCFs. Dies hat potenzielle Anwendungen in verschiedenen Bereichen, von der OberflĂ€chenbeschichtung bis zur Entwicklung umweltfreundlicher Technologien.
2023-01-01T00:00:00Z
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The electronic structure of iron-bearing compounds in the deep Earth
http://hdl.handle.net/2003/42230
Title: The electronic structure of iron-bearing compounds in the deep Earth
Authors: Albers, Christian
Abstract: Eisen ist das am hĂ€ufigsten vorkommende Ăbergangsmetall in der tiefen Erde. Aufgrund seiner komplexen elektronischen Struktur kann es in zwei verschiedenen OxidationszustĂ€nden (Fe2+ und Fe3+) auftreten und auĂerdem seinen Spinzustand Ă€ndern. Daher spielt es eine wichtige Rolle fĂŒr die physikalischen und chemischen Eigenschaften der tiefen Erdschichten. Im Rahmen dieser Arbeit wurden drei geologisch relevante Probensysteme auf ihre elektronische Struktur bei Druck- und Temperaturbedingungen untersucht, die fĂŒr den unteren Erdmantel relevanten sind. Dazu wurden die (nicht-resonante) KÎČ1,3- und Valenz-zu-Kern-Röntgenemissionsspektroskopie sowie die resonante 1s2p-Röntgenemissionsspektroskopie eingesetzt. ZunĂ€chst fĂŒhrte die Untersuchung von lasergeheitztem FeCO3 bei etwa 80 GPa zur Synthese von Fe4C3O12 und Fe4C4O13. Es konnte nachgewiesen werden, dass sich das Eisen in diesen beiden Phasen in einem Hoch-Spin-Zustand befindet. AuĂerdem konnte das Auftreten von Raman-Banden mit niedriger Wellenzahl in einem Wellenzahlbereich zwischen 100 cmâ1 und 350 cmâ1 Fe4C4O13 zugeordnet werden. Zweitens belegt die Studie an kalt komprimiertem Fe2O3 einen zweistufigen SpinĂŒbergang von α- ĂŒber ζ- zu Î-Fe2O3. DarĂŒber hinaus unterstĂŒtzen resonante 1s2p- Röntgenemissionsspektroskopiemessungen eine mögliche Delokalisierung der elektronischen ZustĂ€nde in den Hochdruckphasen. Drittens zeigt der Einfluss des Drucks auf die elektronische Struktur von FeO einen signifikanten Einfluss auf die Linienform der KÎČ1,3-Emission, obwohl kein SpinĂŒbergang stattfindet. Die Ănderungen der Linienform können mit einer Verzerrung der Kristallstruktur in Zusammenhang gesetzt werden. Dies wird in Zukunft einen wesentlichen Einfluss auf die Interpretation von KÎČ1,3-Spektren haben. ZusĂ€tzlich dazu wurde der Aufbau fĂŒr spektroskopische Messungen erheblich verbessert, indem die Datenerfassungszeiten fĂŒr die KÎČ1,3-Röntgenemissionsspektroskopie innerhalb von Sekunden, fĂŒr hochwertige Valenz-Kern-Emissionsspektroskopie innerhalb von Minuten und fĂŒr resonante Röntgenemissionsspektroskopie-Messungen in weniger als einer Stunde verkĂŒrzt wurden, was einzigartige spektroskopische Möglichkeiten unter extremen Bedingungen bietet.; Iron is the most abundant transition metal in the deep Earth. Due to its complex electronic structure, it can appear in two different oxidation states (Fe2+ and Fe3+) and can also undergo a spin transition. Hence, it plays an important role in the physical and chemical properties of the deep Earth assemblage. Within this thesis, three geologically relevant sample systems were investigated regarding their electronic structure at pressure and temperature conditions that are relevant to the Earthâs lower mantle. Therefore, (non-resonant) KÎČ1,3 and valence-to-core X-ray emission spectroscopy as well as resonant 1s2p X-ray emission spectroscopy were utilized. First, the study of laser-heated FeCO3 at about 80 GPa results in the synthesis of Fe4C3O12 and Fe4C4O13. The iron in both of these phases was verified to be in high-spin state. Furthermore, the emergence of low-wavenumber Raman bands in a wavenumber range between 100 cmâ1 and 350 cmâ1 could be assigned to Fe4C4O13. Second, the study on cold compressed Fe2O3 verifies a two-step spin transition from α- via ζ- to Î-Fe2O3. Moreover, resonant X-ray emission spectroscopy measurements support a possible delocalization of the electronic states in the high pressure phases. Third, the influence of pressure on the electronic structure of FeO shows significant influence on the line shape of the KÎČ1,3 emission, although no spin transition occurred. The line-shape changes could be connected to a distortion of the crystal structure. This will have a substantial influence on the interpretation of KÎČ1,3-spectra in the future. Additionally, the setup for spectroscopic measurements was significantly improved with reduced data acquisition times of KÎČ1,3 X-ray emission spectroscopy within seconds, high-quality valence-to-core emission spectroscopy within minutes and resonant X-ray emission spectroscopy measurements in less than one hour, offering unique spectroscopic opportunities at extreme conditions.
2023-01-01T00:00:00Z
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Observation of high-energy neutrinos from the Milky Way
http://hdl.handle.net/2003/42209
Title: Observation of high-energy neutrinos from the Milky Way
Authors: HĂŒnnefeld, Mirco
Abstract: With the discovery of the astrophysical neutrino flux by IceCube in 2013, the foundation for neutrino astronomy was established. In subsequent years, the first point-like neutrino source candidates, a flaring blazar known as TXS 0506+056 and the active galaxy NGC 1068, emerged. Now, in this work, a new milestone in the rising field of neutrino astronomy is presented: the first observation of high-energy neutrinos from our own Galaxy â the Milky Way. A search for Galactic neutrino emission is performed on 10 years of IceCube data, rejecting the background-only hypothesis at the 4.5Ï significance level.
The observed Galactic neutrino flux, believed to originate from diffuse interactions of cosmic rays, possibly in addition to contributions from unresolved point-like sources, may explain up to 10% of the astrophysical neutrino flux previously measured by IceCube. This observation is enabled by novel tools based on deep learning, developed in this dissertation. In comparison to prior IceCube analyses, the sensitivity is improved by a factor up to four, due to improved event reconstructions and an increased effective area by over an order of magnitude. These tools not only lead to the most sensitive neutrino dataset to date in the Southern Sky, but they also enable a wide variety of future applications and analyses that were previously unattainable.
2023-01-01T00:00:00Z
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Unfolding the spectrum of the blazar Markarian 421 using data from the first Large-Sized Telescope of the Cherenkov Telescope Array
http://hdl.handle.net/2003/42205
Title: Unfolding the spectrum of the blazar Markarian 421 using data from the first Large-Sized Telescope of the Cherenkov Telescope Array
Authors: Biederbeck, Noah
Abstract: The nature of acceleration processes of very-high-energy radiation in the universe is largely unsolved. To study these, Imaging Atmospheric Cherenkov Telescopes measure Cherenkov radiation produced by secondary particles in Extensive Air Showers. The Cherenkov Telescope Array (CTA) is the next generation of ground-based Cherenkov astronomy to be built in the coming years parts on La Palma, Spain and parts at Paranal Observatory, Chile. The first prototype telescope of CTA, the LST-1, was inaugurated in 2018 on La Palma, and has been in the commissioning phase since. In this thesis, I develop a new automated analysis pipeline for analyses of point-like gamma-ray sources for LST-1 observations, using the workflow manager snakemake. I implement regularized unfolding in the open-source high-level gamma-ray analysis software Gammapy. I use the analysis pipeline and the unfolding implementation to analyze data of the blazar Markarian 421, creating an unfolded energy spectrum. The unfolded energy spectrum calculated in this thesis is compared to earlier analyses. It extends the measured range of the multi-wavelength energy spectrum of Markarian 421 to the highest energies.; Die Natur der Beschleunigungsmechanismen fĂŒr sehr hochenergetische Strahlung im Universum ist weitestgehend ungeklĂ€rt. Um diese zu untersuchen, werden bildgebende, atmosphĂ€rische Tscherenkow Teleskope eingesetzt, die Tscherenkowstrahlung messen, die von SekundĂ€rteilchen in ausgedehnten Luftschauern erzeugt wird. Das Cherenkov Telescope Array (CTA) ist die nĂ€chste Generation der bodengebundenen Tscherenkow-Astronomie und wird in den kommenden Jahren teils auf La Palma, Spanien, teils im Paranal Observatory, Chile, gebaut. Das erste Prototyp-Teleskop des CTA, das LST-1, wurde 2018 auf La Palma eingeweiht und befindet sich seitdem in der Phase der Inbetriebnahme. In dieser Arbeit entwickle ich eine neue automatisierte Analysepipeline fĂŒr Analysen von punktartigen kosmischen Gammastrahlungsquellen fĂŒr LST-1-Beobachtungen unter Verwendung des Workflow-Managers snakemake. Ich implementiere regularisiertes Entfalten in der quelloffenen Gammastrahlenanalysesoftware Gammapy. Ich verwende die Analysepipeline und die Entfalungsimplementierung, um Daten des Blazars Markarian 421 zu analysieren und ein entfaltetes Energiespektrum zu erstellen. Das in dieser Arbeit entfaltete Energiespektrum wird mit frĂŒheren Analysen verglichen und erweitert den gemessenen Bereich des multiwellenlĂ€ngen Energiespektrums von Markarian 421 bis zu den höchsten Energien.
2023-01-01T00:00:00Z
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Hadronic accelerators in the universe
http://hdl.handle.net/2003/42193
Title: Hadronic accelerators in the universe
Authors: Fattorini, Alicia
Abstract: The search for the origin of charged cosmic rays remains one of the greatest challenges in
astrophysics. Extremely accelerated particles propagate through the universe carrying
the secrets of the most energetic cosmic phenomena. While neutral particles are not
deflected by magnetic fields and point back to their sources, charged cosmic rays arrive
on Earth as a diffuse flux, making it nearly impossible to identify their origin. The
MAGIC telescopes, primarily designed to detect high-energetic gamma rays, also have
the potential to study charged cosmic rays.
This work presents the analysis chain to produce a proton spectrum from data measured
with the MAGIC telescopes. The analysis chain includes data preparation, machine
learning algorithms for particle reconstruction, and unfolding techniques which consider
remaining background contributions. New simulations of air showers induced by
charged cosmic rays are used in this analysis and tested accordingly.
This work illustrates the potential of IACTs for the research of charged cosmic rays and
provides the first proton spectrum of MAGIC, which constitutes a valuable addition to
previous measurements by other cosmic-ray experiments.; Die Suche nach dem Ursprung der geladenen kosmischen Strahlung ist nach wie vor
eine der gröĂten Herausforderungen der Astrophysik. Extrem beschleunigte Teilchen
propagieren durch das Universum und tragen die Geheimnisse der höchstenergetischen
kosmischen PhÀnomene in sich. WÀhrend neutrale Teilchen nicht von Magnetfeldern
abgelenkt werden und zu ihren Quellen zurĂŒckweisen, erreicht geladene kosmische
Strahlung die Erde als diffuser Teilchenstrom, was es nahezu unmöglich macht, ihren
Ursprung zu bestimmen. Die MAGIC-Teleskope, die in erster Linie fĂŒr die Untersuchung
von hochenergetischer Gammastrahlung konzipiert sind, haben auch das Potenzial,
geladene kosmische Strahlung zu untersuchen.
In dieser Arbeit wird die Analysekette zur Erstellung eines Protonenspektrums aus den
mit den MAGIC-Teleskopen gemessenen Daten entwickelt. Die Analysekette umfasst
die Datenaufbereitung, Algorithmen fĂŒr maschinelles Lernen zur Teilchenrekonstruk-
tion, und Entfaltungstechniken unter BerĂŒcksichtigung von verbliebenen Untergrund-
beitrÀgen. Neue Simulationen der durch geladene kosmische Strahlung induzierten
Luftschauer werden in dieser Analyse verwendet und entsprechend getestet.
Diese Arbeit veranschaulicht das Potenzial von IACTs fĂŒr die Forschung im Bereich der
geladenen kosmischen Strahlung und liefert das erste Protonenspektrum von MAGIC,
welches eine wertvolle ErgÀnzung zu den bisherigen Messungen anderer Experimente
fĂŒr kosmische Strahlung bildet.
2023-01-01T00:00:00Z
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Magneto-optical effects in hybrid plasmonic nanostructures
http://hdl.handle.net/2003/42192
Title: Magneto-optical effects in hybrid plasmonic nanostructures
Authors: Klompmaker, Lars
Abstract: This thesis focuses on magneto-optical effects and their enhancement at optical resonances in hybrid plasmonic nanostructures. One of the main goals is to gain a better understanding of the transverse magnetic routing of light emission (TMRLE) regarding both components of the hybrid plasmonic-semiconductor model system used to investigate this novel effect. Here, the TMRLE describes the routing of light emitted from excitons in a diluted magnetic semiconductor (DMS) quantum well (QW), where the selection rules of the exciton optical transitions are modified by an external magnetic field to have a non-zero transverse spin along the magnetic field direction. By placing the light source near a surface, it can couple to subwavelength evanescent optical fields, such as surface plasmon polaritons (SPPs), which possess a strong transverse spin and spin-momentum locking. This translates the spin of the emitter into a routed wave along the surface and directional emission into the far-field.
Firstly, the temperature dependence of the routing from the DMS QW, used as strongly polarizable light source, is investigated. The findings reveal a significant decline in the achievable emission routing for increasing temperatures, but also the emergence of the light-hole emission, which is routed in the opposite direction to the main heavy-hole emission. Additionally, alternative non-DMS-based QW structures are explored as potential candidates for achieving temperature-independent emission routing.
Secondly, the influence of the plasmonic nanograting, the other constituent of the hybrid structure, on the enhanced routing is demonstrated. The emission directionality is investigated for various grating periods and slit widths, which also reveals the usually hard-to-detect weak coupling between the QW excitons and the SPPs as a large contributor to the emission directionality spectrum.
Lastly, the thesis explores the transverse magneto-optical Kerr effect (TMOKE) for light reflected from or transmitted through a magnetite-based plasmonic waveguide structure. Here, the hybridization of the plasmonic and magnetic waveguide modes leads to a wide-band enhancement of the TMOKE signal in transmission.; Der Fokus dieser Arbeit liegt auf magneto-optischen Effekten und deren VerstĂ€rkung an optischen Resonanzen in hybriden plasmonischen Nanostrukturen. Eines der Hauptziele ist das bessere VerstĂ€ndnis der transversalen magnetischen Lenkung der Lichtemission (TMRLE) bezĂŒglich beider Komponenten des hybriden plasmonischen Halbleiter-Modellsystems, an dem dieser neuartige Effekt untersucht wird. Hier beschreibt der TMRLE die direktionale Lenkung der Lichtemission von Exzitonen aus einem semimagnetischen Halbleiter (DMS) Quantentopf (QW), wobei die Auswahlregeln der optischen Exzitonen-ĂbergĂ€nge von einem externen Magnetfeld so modifiziert werden, dass sie einen transversalen Spin entlang des Magnetfeldes haben. Wird diese Lichtquelle nahe einer OberflĂ€che platziert, so kann sie an evaneszente optische Felder mit starkem transversalem Spin und einer Kopplung von Spin und Ausbreitungsrichtung, wie OberflĂ€chenplasmonpolaritonen (SPPs), koppeln. Dadurch wird der Emitterspin in eine direktionale Welle entlang der OberflĂ€che ĂŒbersetzt, die dann direktional in das Fernfeld emittieren kann.
ZunĂ€chst wird die TemperaturabhĂ€ngigkeit der Emissionslenkung aus dem DMS QW untersucht, welcher als stark polarisierbare Lichtquelle fungiert. Dabei zeigt sich eine starke Abnahme der erreichbaren Emissionslenkung bei steigenden Temperaturen, aber auch der aufkommende Beitrag der Leichtloch-Emission, welche in die entgegengesetzte Richtung der primĂ€ren Schwerloch-Emission gelenkt wird. AuĂerdem werden alternative nicht-DMS-basierte QW Strukturen als Kandidaten fĂŒr eine temperaturunabhĂ€ngige Emissionslenkung untersucht.
Zweitens wird der Einfluss des plasmonischen Nanogitters als weiterer Bestandteil der Hybridstruktur auf die verstĂ€rkte Emissionslenkung gezeigt. DafĂŒr wird die EmissionsdirektionalitĂ€t fĂŒr verschiedene Gitterperioden und -spaltbreiten untersucht, wobei auch die sonst schwer zu detektierende schwache Kopplung der QW-Exzitonen und SPPs als groĂer Beitrag zum DirektionalitĂ€tsspektrum aufgedeckt wird.
Zuletzt wird noch der transversale magneto-optische Kerr-Effekt (TMOKE) fĂŒr reflektiertes und transmittiertes Licht von einer Magnetit-basierten plasmonischen Nanostruktur untersucht. Hier fĂŒhrt die Hybridisierung der plasmonischen und der magnetischen Wellenleitermoden zu einer breitbandigen VerstĂ€rkung des TMOKE Signals in Transmission.
2023-01-01T00:00:00Z
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Measurement of rare leptonic and semi-baryonic B meson decays with the LHCb experiment
http://hdl.handle.net/2003/42177
Title: Measurement of rare leptonic and semi-baryonic B meson decays with the LHCb experiment
Authors: Becker, Maik
Abstract: This thesis presents two measurements probing the Standard Model of particle physics with data recorded by the LHCb experiment in Run 1 and Run 2 of the Large Hadron Collider.
The first measurement is a precise branching fraction determination of the purely leptonic BsâÎŒâșΌ⻠and BdâÎŒâșΌ⻠decays. The BsâÎŒâșΌ⻠branching fraction is determined with a relative uncertainty of 15%, making it the most precise single-experiment result available at publication time. The BdâÎŒâșΌ⻠decay is not observed. An upper limit on its branching fraction is calculated to be of O(1e-10) at a confidence level of 95%. These published results strongly constrain theoretical models of new physics effects in the flavour sector.
The second analysis is the first search for the semi-baryonic BsâppÎŒâșΌ⻠and BdâppÎŒâșΌ⻠decays. It is the first time that decays of Bs mesons via flavour-changing neutral bâsl+l- transitions into a final state with baryons are studied. The current state of the measurement and preliminary results are presented. Expected upper limits on the branching fractions are determined to be of O(1e-9) at a confidence level of 95%.; In dieser Arbeit werden zwei Messungen vorgestellt, die das Standardmodell der Teilchenphysik prĂŒfen. Dazu werden Daten verwendet, die vom LHCb Experiment in Run 1 und Run 2 des Large Hadron Collider aufgezeichnet wurden.
Die erste Messung ist eine prĂ€zise Bestimmung der VerzweigungsverhĂ€ltnisse der rein leptonischen BsâÎŒâșΌ⻠und BdâÎŒâșΌ⻠ZerfĂ€lle. Das BsâÎŒâșΌ⻠VerzweigungsverhĂ€ltnis wird mit einer relativen Unsicherheit von 15% bestimmt und ist zum Zeitpunkt der Veröffentlichung das prĂ€ziseste Ergebnis eines einzelnen Experiments. Der BdâÎŒâșΌ⻠Zerfall wird nicht beobachtet. Die obere Ausschlussgrenze fĂŒr das VerzweigungsverhĂ€ltnis des Zerfalls liegt in der GröĂenordnung von O(1e-10) bei einem Konfidenzlevel von 95%. Diese veröffentlichten Ergebnisse schrĂ€nken die theoretischen Modelle der Effekte neuer Physik im Flavour-Sektor stark ein.
Die zweite Analyse ist eine Suche nach den semi-baryonischen BsâppÎŒâșΌ⻠und BdâppÎŒâșΌ⻠ZerfĂ€llen. Es ist das erste Mal, dass ZerfĂ€lle von Bs Mesonen ĂŒber flavour-verĂ€ndernde neutrale bâsl+l- ĂbergĂ€nge in einen Endzustand mit Baryonen untersucht werden. Der aktuelle Stand der Messung und vorlĂ€ufige Ergebnisse werden vorgestellt. Die erwarteten oberen Ausschlussgrenzen fĂŒr die VerzweigungsverhĂ€ltnisse liegen in der GröĂenordnung von O(1e-9) bei einem Konfidenzlevel von 95%.
2023-01-01T00:00:00Z
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Photon echo from trions in semiconductor quantum wells and quantum dots
http://hdl.handle.net/2003/42175
Title: Photon echo from trions in semiconductor quantum wells and quantum dots
Authors: Kosarev, Alexander
Abstract: The present work is dedicated to the study of the ultrafast coherent dynamics of the excitonic complexes localized in semiconductor nanostructures. We consider the optical control of the optical and spin coherence of the negatively charged excitons using the photon echo technique. In the first two chapters, we overview the basic knowledge of the research area and the experimental techniques. In the third chapter, we considered the freezing of the dephasing in the inhomogeneously broadened ensembles of InGaAs quantum dots driven by the application of a resonant control pulse with an area of multiple of 2p. The freezing of dephasing allows us to vary the timing of the photon echo by up to 5 ps, which even slightly exceeds the echo duration. In the fourth chapter, we consider the resident electron dynamics in the CdTe quantum well. Long-lived three-pulse photon echoes in combination with the pump-probe Kerr rotation allowed us to analyze comprehensively the resident electron dynamics since they are differently impacted by the hopping of the resident electrons between the different localization sites. From the data, we evaluate the hopping rate all-optically. In the fifth chapter, we demonstrate the long-lived three-pulse photon echoes from the ensembles of the InGaAs quantum dots. It allowed us to extend the coherent optical response by at least an order of magnitude. We show that the transverse g-factor of the heavy hole in the trion state strongly impacts the temporal evolution of the system, and therefore modifies the long-lived three-pulse photon echo signal.; Die vorliegende Arbeit widmet sich der Untersuchung der ultraschnellen Dynamik exzitonischer Komplexe, die in Halbleiter-Nanostrukturen lokalisiert sind. Wir betrachten die optische Kontrolle der optischen und SpinkohĂ€renz der negativ geladenen Exzitonen unter Verwendung der Photonenechotechnik. In den ersten beiden Kapiteln geben wir einen Ăberblick ĂŒber das Grundwissen zum Forschungsgebiet und den Versuchstechniken. Im dritten Kapitel betrachteten wir das Einfrieren der Dephasierung in den inhomogen verbreiterten Ensembles von InGaAs-Quantenpunkten, angetrieben durch das Anlegen eines resonanten Steuerpulses mit einer FlĂ€che von einem Vielfachen von 2p. Durch das Einfrieren können wir das zeitliche Maximum des Photonenechos um bis zu 5 ps variieren, was die Echodauer sogar geringfĂŒgig ĂŒberschreitet. Im vierten Kapitel betrachten wir die Dynamik von residenten Elektronen im CdTe-Quantentopf. Langlebige Dreipuls-Photonenechos in Kombination mit der Pump-Probe-Kerr-Rotation ermöglichten uns eine umfassende Analyse der Dynamik von residenten Elektronen, da sie durch das Springen der residenten Elektronen zwischen den verschiedenen Lokalisationsorten unterschiedlich beeinflusst wird. Aus den Daten werten wir optisch die Hopping-Rate aus. Im fĂŒnften Kapitel demonstrieren wir die langlebigen Dreipuls-Photonenechos von InGaAs-Quantenpunkt Ensemblen. Es erlaubte uns, die kohĂ€rente optische Antwort um mindestens eine Grössenordnung zeitlich zu erweitern. Wir zeigen, dass der transversale g-Faktor des schweren Lochs im Trion-Zustand die zeitliche Entwicklung des Systems stark beeinflusst und daher das langlebige Dreipuls-Photonenechosignal modifiziert.
2023-01-01T00:00:00Z
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Switching the magnetization in quantum antiferromagnets
http://hdl.handle.net/2003/42166
Title: Switching the magnetization in quantum antiferromagnets
Authors: Uhrig, Götz S.; Bolsmann, Katrin; Khudoyberdiev, Asliddin
Abstract: The orientation of the order parameter of quantum magnets can be used to store information in a dense and efficient way. Switching this order parameter corresponds to writing data. To understand how this can be done, we study a precessional reorientation of the sublattice magnetization in an (an)isotropic quantum antiferromagnet induced by an applied magnetic field. For this intriguing nonequilibrium issue, we introduce a description including the leading quantum and thermal fluctuations, namely time-dependent Schwinger boson mean-field theory, because this theory allows us to describe both ordered phases and the phases in between them, as is crucial for switching. An activation energy has to be overcome, requiring a minimum applied field ht that is given essentially by the spin gap. It can be reduced significantly for temperatures approaching the NĂ©el temperature, facilitating switching. The time required for switching diverges when the field approaches ht, which is the signature of an inertia in the magnetization dynamics. The temporal evolution of the magnetization and of the energy reveals signs of dephasing. The switched state has lost a part of its coherence because the magnetic modes do not evolve in phase.
2023-09-05T00:00:00Z
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Ultrafast coherent THz lattice dynamics coupled to spins in the van der Waals antiferromagnet FePS3
http://hdl.handle.net/2003/42165
Title: Ultrafast coherent THz lattice dynamics coupled to spins in the van der Waals antiferromagnet FePS3
Authors: Mertens, Fabian; MönkebĂŒscher, David; Parlak, Umut; Boix-Constant, Carla; Mañas-Valero, Samuel; Matzer, Margherita; Adhikari, Rajdeep; Bonanni, Alberta; Coronado, Eugenio; Kalashnikova, Alexandra M.; Bossini, Davide; Cinchetti, Mirko
Abstract: Coherent THz optical lattice and hybridized phononâmagnon modes are triggered by femtosecond laser pulses in the antiferromagnetic van der Waals semiconductor FePS3. The laser-driven lattice and spin dynamics are investigated in a bulk crystal as well as in a 380 nm-thick exfoliated flake as a function of the excitation photon energy, sample temperature and applied magnetic field. The pump-probe magneto-optical measurements reveal that the amplitude of a coherent phonon mode oscillating at 3.2 THz decreases as the sample is heated up to the NĂ©el temperature. This signal eventually vanishes as the phase transition to the paramagnetic phase occurs, thus revealing its connection to the long-range magnetic order. In the presence of an external magnetic field, the optically triggered 3.2 THz phonon hybridizes with a magnon mode, which is utilized to excite the hybridized phononâmagnon mode optically. These findings open a pathway toward the optical control of coherent THz photoâmagnonic dynamics in a van der Waals antiferromagnet, which can be scaled down to the 2D limit.
2022-12-21T00:00:00Z
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High-field/high-frequency EPR spectroscopy in protein research: principles and examples
http://hdl.handle.net/2003/42128
Title: High-field/high-frequency EPR spectroscopy in protein research: principles and examples
Authors: Möbius, Klaus; Savitsky, Anton
Abstract: During the last decades, the combined efforts of biologists, chemists, and physicists in developing high-field/high-frequency EPR techniques and applying them to functional proteins have demonstrated that this type of magnetic resonance spectroscopy is particularly powerful for characterizing the structure and dynamics of stable and transient states of proteins in action on biologically relevant time scales ranging from nanoseconds to hours. The review article describes how high-field EPR methodology, in conjunction with site-specific isotope and spin-labeling strategies, is capable of providing new insights into fundamental biological processes. Specifically, we discuss the theoretical and instrumental background of continuous-wave and pulse high-field EPR and the multiple-resonance extensions EDNMR, ENDOR, TRIPLE, ESEEM, PELDOR, and RIDME. Some emphasis is placed on a balanced description of both the historical spadework and the achieved performance of advanced EPR at 95 GHz and 360 GHz. This culminates in a coherent treatment of state-of-the-art research of high-field EPR in terms of both instrumentation development and application to representative protein complexes such as cofactor binding sites in photosynthesis.
2022-12-13T00:00:00Z
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Tuning the nuclei-induced spin relaxation of localized electrons by the quantum Zeno and anti-Zeno effects
http://hdl.handle.net/2003/42124
Title: Tuning the nuclei-induced spin relaxation of localized electrons by the quantum Zeno and anti-Zeno effects
Authors: Nedelea, Vitalie; Leppenen, Nikita V.; Evers, Eiko; Smirnov, Dmitry S.; Bayer, Manfred; Greilich, Alex
Abstract: Quantum measurement back action is fundamentally unavoidable when manipulating electron spins. Here we demonstrate that this back action can be efficiently exploited to tune the spin relaxation of localized electrons induced by the hyperfine interaction. In optical pump-probe experiments, powerful probe pulses suppress the spin relaxation of electrons on Si donors in an InGaAs epilayer due to the quantum Zeno effect. By contrast, an increase of the probe power leads to a speed-up of the spin relaxation for electrons in InGaAs quantum dots due to the quantum anti-Zeno effect. The microscopic description shows that the transition between the two regimes occurs when the spin dephasing time is comparable to the probe pulse repetition period.
2023-09-07T00:00:00Z
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Polarization- and time-resolved nonlinear optical spectroscopy of excitons in Cu2O
http://hdl.handle.net/2003/42109
Title: Polarization- and time-resolved nonlinear optical spectroscopy of excitons in Cu2O
Authors: Farenbruch, Andreas
Abstract: Excitons are Coulomb-bound states of a negatively charged electron in the conduction band and a positively charged hole in the valence band of a semiconductor or an insulator. Their hydrogen-like absorption spectrum was first detected in 1951 in cuprous oxide Cu2O. In 2014, a spectral scan using an ultra-narrow bandwidth laser extended the P exciton series in a natural Cu2O crystal to a principal quantum number of n = 25. This breakthrough opened up the field of Rydberg physics in semiconductors leading to numerous experimental and theoretical studies investigating their behavior in external fields as well as exciton-plasma and exciton-exciton interactions.
The present study reports on second harmonic generation (SHG) spectroscopy of dark- and bright excitons in Cu2O. SHG is forbidden for laser light propagating along the high-symmetry [110] and [001] crystal axis. By applying a magnetic field up to 10 T perpendicular to the light direction, SHG becomes allowed due to the Zeeman- (ZE) and magneto-Stark effect (MSE). The polarization selection rules for both mechanisms are derived from point group theory considerations. The linear polarization angles of the incoming and outgoing light can be controlled in order to differentiate between both SHG mechanisms.
The spin-forbidden dark paraexcitons are activated by admixture of the M = 0 component of the bright orthoexcitons in a magnetic field. The Rydberg series of dark paraexcitons up to a quantum number of n = 6 is detected using this method. Due to the electron-hole exchange interaction, the paraexcitons are generally located energetically below the orthoexcitons. This order is found to be reversed for the n = 2 state due to mixing of the yellow 2S orthoexciton with the green 1S orthoexciton.
The blue series of excitons involves the same valence band as the yellow series but the second-lowest conduction band. Accessing these states using linear optical spectroscopy is challenging due to the high absorption in this spectral range. MSE and ZE-induced SHG has been shown to be a suitable investigation method enabling the detection of blue 1S, 2S, and 2P excitons and magneto-excitons up to n=8. By analyzing their magnetic-field shift and polariton effect, key properties of blue excitons, such as the resonance energies, the exciton radius, the band gap, the reduced exciton mass, and the anisotropic conduction band mass, are obtained.
Difference frequency generation with two-photon excitation (2P-DFG) allows experimental investigations of excitons in the time domain. The pulses of the first laser induce a coherent exciton population by a two-photon excitation process. The pulses of the second laser stimulate the emission of photons with the energy difference between the excitons and the stimulating photons. By delaying the pulses of the second laser, the 2P-DFG signal is measured as a function of time. This technique is used to measure the coherence times of 1S and higher n excitons and magnetic-field-induced quantum beats of the three 1S orthoexciton states.
2023-01-01T00:00:00Z
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Electronic spin state studies of iron-bearing minerals contained in an X-ray heated diamond anvil cell
http://hdl.handle.net/2003/42097
Title: Electronic spin state studies of iron-bearing minerals contained in an X-ray heated diamond anvil cell
Authors: Kaa, Johannes Martin
Abstract: Ein bedeutender Teil der Erforschung des Inneren von Planeten wird durch die Nachstellung der erwarteten DrĂŒcke und Temperaturen in groĂen Tiefen im Labor durchgefĂŒhrt. WĂ€hrend DrĂŒcke routinemĂ€Ăig statisch mit einer Diamantstempelzelle erzeugt werden, um den Druckbereich in den meisten Planeten des Sonnensystems abzudecken (bis ca. 10 Mbar), sind gleichzeitige Temperaturerhöhungen ein heikles Thema, insbesondere in Verbindung mit in-situ-Röntgenanalyse mit hohen Belichtungszeiten. In dieser Arbeit stellen wir einen neuen Ansatz zur Bestimmung elektronischer ZustĂ€nde von Materie bei hohen DrĂŒcken und Temperaturen vor, bei dem Proben in Diamantstempelzellen (DACs) durch ultrakurze und intensive Röntgenimpulse erhitzt werden, die auch zur Erzeugung fĂŒr das spinzustandsensitive Röntgenemissionssignal (XES) und das struktur-empfindliche Röntgenbeugungssignal (XRD) dienen. In dem Proof-of-Concept-Experiment in der Vakuumkammer 1 (IC1) am HED-Instrument haben wir mit dieser Kombination an Messtechniken FeCO3 bis zu der Schmelztemperatur bei 51 GPa erhitzt und dadurch einen durch einen Temperaturanstieg angetriebenen elektronischen SpinĂŒbergang von niedrigem Spin zu hohem Spin im Fe induziert. Nach der Konzeption, dem Bau und der Inbetriebnahme eines dedizierten von HĂĄmos-Spektrometers in IC1 haben wir (Fe0.5Mg0.5)O bei 100 GPa und FeS zwischen 5-25 GPa bei hohen Temperaturen gemessen. Letzteres diente als vereinfachtes Modell fĂŒr den Marsmantel und -kern und lieferte uns neue Informationen zur Erweiterung der erst kĂŒrzlich veröffentlichten seismischen Messungen. DarĂŒber hinaus wurde das Setup fĂŒr zukĂŒnftige zeitaufgelöste XES von Proben in einer DAC und inelastische Röntgenstreuungstechniken von freistehenden Proben getestet und steht fĂŒr Benutzerexperimente am European X-ray Free Electron Laser zur VerfĂŒgung.
2023-01-01T00:00:00Z
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Enhancing precision radiotherapy: image registration with deep learning and image fusion for treatment planning
http://hdl.handle.net/2003/42096
Title: Enhancing precision radiotherapy: image registration with deep learning and image fusion for treatment planning
Authors: Ratke, Alexander
Abstract: Artificial intelligence is advancing in everyday life and supports its user by generating fast results in areas like communication or image recognition. This thesis aims at exploiting the abilities of deep-learning techniques for deformable image registration (DIR) to improve image alignment in medicine. An unsupervised registration and fusion workflow is developed and evaluated for 39 head scans, produced with computed tomography (CT) and magnetic resonance imaging (MRI). The three-part workflow starts by preprocessing the scans to unify the image formats and to perform affine transformation and rigid registration. Then, a deep-learning model trained for DIR is applied to these images. To obtain an appropriate configuration of the model, parameter tuning is required. The evaluation with the mutual-information metric indicates an improvement in image alignment of up to 14 % when using deep-learning-based DIR. Lastly, image fusion combines the registered CT and MRI scans with a wavelet-based method to merge the information of decomposed images. The workflow is designed for unimodal, e.g. T1- and T2-weighted MRI scans, and multimodal, e.g. CT and MRI scans, image pairs. Since medical imaging is an important basis of treatment-planning processes, the registered and fused images obtained from this workflow are expected to enhance precision radiotherapy.
2023-01-01T00:00:00Z
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Application of machine learning in glow curve deconvolution
http://hdl.handle.net/2003/42094
Title: Application of machine learning in glow curve deconvolution
Authors: Lienau, Evelin
Abstract: Routine dosimetry aims to estimate the radiation dose of occupationally exposed persons for a monitoring interval of one month. The Material PruÌfungsamt NRW (MPA NRW) provides a thermoluminescence (TL) dosimeter based on LiF:Mg,Ti (TL-DOS). Thermal fading causes a time-dependent signal loss when using a TL dosimeter. This signal change is used to gain information about the irradiation event beyond the dose estimate, which can help to improve the radiation protection concept of occupationally exposed persons.
In this work, multivariate analysis techniques for glow curve analysis using deep learning approaches are developed to estimate the irradiation day within a monitoring interval of 40 days with single-dose irradiation using a Cs-137 source with a prediction uncertainty of two days.
To create a data basis for training the application of deep learning, over 10 000 measurements were performed in cooperation with the MPA NRW and the TL-DOS project. Furthermore, a technique to generate realistic glow curves based on generative adversarial networks (GANs) is presented, which makes it possible to expand the measured data set artificially and thus create a larger database for the deep learning approaches.
2023-01-01T00:00:00Z
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Untersuchung von Unsicherheiten von Dosisverteilungen auf Grundlage von Monte-Carlo-Simulationen der Brachytherapie bei Augentumoren
http://hdl.handle.net/2003/42090
Title: Untersuchung von Unsicherheiten von Dosisverteilungen auf Grundlage von Monte-Carlo-Simulationen der Brachytherapie bei Augentumoren
Authors: Ngo, Phuong Quynh
Abstract: Eine hĂ€ufig angewandte Methode zur Behandlung kleiner bis mittelgroĂer intraokularer
Tumoren ist die Brachytherapie mit radioaktiven Ruthenium-106-Applikatoren. FĂŒr die
Therapie von Tumoren in der NĂ€he des Sehnervs werden asymmetrische COB-Applikatoren
verwendet. Diese Applikatoren besitzen einen Ausschnitt, der eine Positionierung der
Applikatoren möglichst nah am Sehnerv ermöglicht. Das Ziel dieser Arbeit ist es, zu
untersuchen, inwieweit die Rotation dieses Applikatortyps die Dosisdeposition beeinflusst,
wobei der Sehnerv die Bewegung begrenzt. Da die Rotation des COB-Applikators um
ihren Mittelpunkt möglicherweise einen signifikanten Einfluss auf die Dosisverteilungen
hat, könnte dies zu Nebenwirkungen beim Einsatz dieses Applikators bei Augentumoren
fĂŒhren. Die möglichen EinflĂŒsse werden mithilfe von Geant4-basierten Monte-Carlo Simulationen
untersucht. Dabei wird ein Falldatensatz in ein generisches CAD-Augenmodell
unter BerĂŒcksichtigung der Positionierung des COB-Applikators mit unterschiedlichen
Rotationswinkeln implementiert. Es werden die Dosisverteilungen im Tumor sowie in den
Risikostrukturen ermittelt und verglichen. Als Resultat ergibt sich, dass die Rotation des
COB-Applikators innerhalb des untersuchten Winkelintervalls keinen signifikanten Einfluss
auf die Dosisverteilungen hat.; A commonly used method for treating small to medium-sized intraocular tumors is brachytherapy
with the radioactive ruthenium-106 eye plaque. For the therapy of tumors near the
optic nerve, asymmetric COB applicators are used. These applicators have a cutout that
allows the applicators to be positioned as close to the optic nerve as possible. The aim of the
present work is to investigate to what extent the rotation of this type of applicator, which
is limited by the optic nerve, affects the dose deposition. Since the rotation of the COB
applicator around its center possibly has a significant influence on the dose distributions,
this could lead to side effects when using this applicator in ocular tumors. The possible
influences will be investigated using Geant4-based Monte Carlo simulations. In this process,
a case dataset is implemented into a generic CAD-eye model considering the positioning of
the COB-type plaque with different rotation angles. The dose distributions in the tumor as
well as in ocular structures at risk are determined and compared. As a result, the rotation of
the COB-type applicator within the investigated angle interval has no significant influence
on the dose distributions.
2022-08-23T00:00:00Z
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Untersuchungen zur Kombination von Brachy- und Röntgentherapie zur Behandlung von Augentumoren
http://hdl.handle.net/2003/42076
Title: Untersuchungen zur Kombination von Brachy- und Röntgentherapie zur Behandlung von Augentumoren
Authors: Stroth, Michelle
Abstract: Die Brachytherapie mit Ruthenium-106 Applikatoren stellt fĂŒr intraokulare Tu- moren mit einer Apexhöhe ĂŒber 6 mm aufgrund der unzureichenden Bestrahlung der Tumorspitze eine Kontraindikation dar. Im Rahmen dieser Arbeit wird ein integriertes Konzept, das die Kombination der Brachytherapie mit externer Röntgen- bestrahlung beinhaltet, zur Behandlung intraokularer Tumoren untersucht. HierfĂŒr wird die kombinierte TherapiemodalitĂ€t anhand von PatientenfĂ€llen, die bereits mit einem Ruthenium-Applikator bestrahlt wurden, simuliert und die Gewichtung der Strahlungsquellen mittels einer Optimierung durch die differentielle Evolution angepasst, sodass die Dosis in den Risikostrukturen minimiert wird. Der Vergleich der Dosis-Volumen-Histogramme der kombinierten Therapieform mit den Dosis- Volumen-Histogrammen der Brachytherapie bestĂ€tigt die Vorteile der Integration der externen Röntgenbestrahlung in die Brachytherapie mit dem Ruthenium-106 Applikator in Bezug auf den Schutz der Risikostrukturen und die HomogenitĂ€t des Dosisprofils im Tumor. Des Weiteren werden als Grundlage fĂŒr experimentelle Untersuchungen der kombinierten TherapiemodalitĂ€t die Unsicherheiten der Ab- solutkalibrierung eines Szintillationsdetektors untersucht. Die Messungen liefern erste Hinweise auf die Ursachen der Unsicherheiten, es werden jedoch detaillierte Analysen mit höherer statistischer Aussagekraft benötigt, um die Ergebnisse zu bestĂ€tigen.; Brachytherapy with Ru-106 eye applicators is contraindicated for intraocular tumors with an apex height above 6 mm due to insufficient irradiation of the tumor apex. In this work, an integrated concept, consisting of brachytherapy with external X-ray irradiation, is investigated for the treatment of intraocular tumors. For this purpose, the combined therapy modality is simulated using patient cases, which were already irradiated with a ruthenium applicator, and the weights of the radiation sources are adjusted by using optimization through differential evolution so that the dose to the structures at risk is minimized. Comparison of the dose-volume histograms of the combined form of therapy with the dose-volume histograms of brachytherapy only, confirms the advantages of integrating external X-ray irradiation using the ruthenium-106 applicator in terms of protection of the structures at risk and homogeneity of the dose profile in the tumor. Furthermore, as a basis for experimental studies of the combined therapy modality, the uncertainties of the absolute calibration of a scintillation detector are investigated. The measurements provide initial indications of the causes of the uncertainties, but detailed analyses with higher statistical power are needed to confirm the results.
2022-09-13T00:00:00Z
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Die Implementierung eines anatomisch approximierten Augenmodells und dessen Einfluss auf die simulierten Dosisverteilungen eines 106Ru-Applikators
http://hdl.handle.net/2003/42075
Title: Die Implementierung eines anatomisch approximierten Augenmodells und dessen Einfluss auf die simulierten Dosisverteilungen eines 106Ru-Applikators
Authors: Stroth, Michelle
Abstract: Die Brachytherapie mit Ruthenium-Applikatoren gilt als effektive Methode zur
Behandlung von intraokularen Tumoren. In dieser Arbeit wird untersucht, inwiefern
die chemische Zusammensetzung der Bestandteile des Auges einen Einfluss auf die
Dosisdeposition bei der Bestrahlung mit einem Ruthenium-106 Augenapplikator
hat. DafĂŒr wird ein generisches Augenmodell konstruiert, das anatomisch an das
menschliche Auge approximiert ist. Des Weiteren werden den jeweiligen Strukturen
ihre chemischen Zusammensetzungen zugeordnet und Simulationen mit einem
Augenmodell aus Wasser und einem Modell, welches aus den organischen Materialien
besteht, durchgefĂŒhrt. Der Vergleich der Tiefendosiskurven bestĂ€tigt den
Einfluss der chemischen Zusammensetzung auf die Dosisdeposition. Simulationen,
in denen die jeweiligen Strukturen der Dosisaufnahme dienen, zeigen, in welchen
Augenbestandteilen dieser Einfluss fĂŒr die Brachytherapie innerhalb eines klinischen
Annahmebereiches liegt.; Brachytherapy with ruthenium plaques is considered as an effective method of
treatment of intraocular tumors. This thesis examines the influence of the chemical
composition of the eye tissues on the dose deposition by irradiation with a Ruthenium-
106 eye plaque. Therefore a generic eye model is constructed, which is anatomically
approximated to the human eye. Furthermore, the chemical compositions of the eye
tissues are assigned to the respective structures and simulations are executed with an
eye model made of water and a model made of the organic materials. The comparison
of the depth dose curves confirms the influence of the chemical composition on the
dose deposition. Simulations in which the respective structures are used for dose
detection show in which eye components this influence for brachytherapy lies within
a clinical acceptance range.
2020-06-26T00:00:00Z
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Microbeams - quick and dirty
http://hdl.handle.net/2003/42003
Title: Microbeams - quick and dirty
Authors: Mentzel, Florian
Abstract: Microbeam radiation therapy (MRT) is a promising yet preclinical radiotherapy treatment for several tumour diagnosis such as gliosarcoma and radioresistant melanoma for which even modern clinical treatments such as intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) yield poor outcome perspectives. The dose prediction during MRT treatment planning, as for most other novel radiotherapies, is mostly performed with very time-consuming Monte Carlo (MC) simulations. This slows down preclinical research processes and renders treatment plan optimization infeasible.
In this thesis, several milestones for the introduction of a fast machine learning (ML) dose calculation method for MRT are presented. First, a 3D U-Net-based ML dose engine is developed using MC training data obtained with Geant4 simulations of a synchrotron broadbeam incident on different bone slab models and a simplified human head phantom as a proof of concept. The developed model is shown to produce dose predictions within less than 100ms which is substantially faster than the used MC simulations with up to 20hours and also the currently fastest approximative MRT dose prediction approach, called HybridDC, with approximately 30minutes. The model is also shown to be superior to a dose prediction approach using generative adversarial networks (GANs) and also a novel transformer-based ML model called Dose Transformer (DoTA), with which it is compared for application in proton minibeam radiation therapy (pMBRT) in a subsequent study. Secondly, the developed ML model and the MC simulations for data generation are extended to account for the spatially fractionated nature of MRT. For this, a novel MC scoring method is developed which is able produce separate dose estimations for the high-dose peak regions where the microbeams traverse the phantoms and the low-dose valley regions in-between those beams. Finally, the developed ML model and the MC scoring method are deployed in a first application of an ML dose prediction method in a preclinical MRT study in collaboration with the University of Wollongong, Australia, conducted at the Imaging and Medical Beamline (IMBL) at the Australian Synchrotron which aimed at treating rats after implanting gliosarcoma cells. It is shown that the ML model can be trained to provide unbiased dose estimations in complex target phantoms even when trained on high-noise MC data, in important finding for the acceleration of future developments of ML models as such datasets can be produced significantly faster. The ML predictions in the rat phantoms deviate at most 10% from the MC simulations, rendering the proposed model a suitable candidate for fast dose predictions during treatment plan optimization in the future.; C (MRT) ist eine vielversprechende vorklinische Strahlentherapie fĂŒr einige Tumordiagnosen, wie beispielsweise Gliosarcome und radioresistente Melanome, fĂŒr die auch moderne Therapiemethoden wie intensity-modulated radiation therapy (IMRT) und volumetric modulated arc therapy (VMAT) schlechte Therapieaussichten haben. Die Dosisvorhersage wĂ€hrend der Behandlungsplanung fĂŒr MRT, ebenso wie fĂŒr viele andere neue Strahlentherapien, wird meistens mit sehr zeitaufwĂ€ndigen Monte Carlo (MC) Simulationen durchgefĂŒhrt. Dies zieht die Forschungsschritte in vorklinischen Studien in die LĂ€nge und verhindert vor allem die Optimierung von BehandlungsplĂ€nen. In dieser Arbeit werden mehrere Meilensteine fĂŒr die EinfĂŒhrung einer schnellen MRT-Dosisberechnungsmethode auf der Basis von ML prĂ€sentiert. Zuerst wird ein machine learning (ML)-Dosisberechnungsmodell auf der Grundlage eines 3D U-Nets entwickelt. Dazu werden zunĂ€chst MC Trainingsdaten mithilfe von Geant4 Simulationen erzeugt, die die Dosisverteilung in verschiedenen Knochenscheibenphantomen und einem vereinfachten Kopfphantom nach Bestrahlung mit einem sogenannten Synchrotron broadbeam vorhersagen. Das entwickelte Modell erzeugt Dosisvorhersagen innerhalb von weniger als 100ms, was signifikant schneller als die Laufzeit der verwendeten MC Simulationen (bis zu 20Stunden) und ebenfalls die zur Zeit schnellsten MRT Dosisberechnungsmethode mithilfe von Approximationen, der sogenannten HybridDC Methode (ca. 30Minuten). DarĂŒber hinaus wird gezeigt, dass das vorgestellte Modell sowohl bessere Vorhersageergebnisse als ein alternativer ML-Ansatz auf Basis von generative adversarial networks (GANs), als auch ein neues Transformer-basiertes ML-Modell namens Dose Transformer (DoTA) erreicht. Der Vergleich mit dem DoTA-Modell erfolgt in einer Studie zur Dosisvorhersage einer anderen neuen Strahlentherapiemethode, der proton minibeam radiation therapy (pMBRT). AnschlieĂend wird das entwickelte ML-Modell und die MC Simulationen weiterentwickelt, um der rĂ€umlich fraktionierten Natur von MRT gerechnet zu werden. Dazu wird eine neue MC Scoringmethode entwickelt, welche separate Dosisverteilungen fĂŒr den Peakbereich, in dem die Microbeams die Phantome durchqueren und eine hohe Dosis deponieren, und fĂŒr den Valleybereich mit deutlich geringeren Dosisdepositionen dazwischen erstellt. AbschlieĂend werden das entwickelte ML-Modell und die neue MC Scoringmethode in einer ersten Anwendung von ML-Dosisvorhersagemethoden in einer vorklinischen MRT-Studie einer Forschungsgruppe der University of Wollongong angewendet, in der mit Gliosarcomen implantierte Ratten an der Imaging and Medical Beamline (IMBL) am Australian Synchrotron bestrahlt wurden. Es wird gezeigt, dass das ML-Modell nach dem Training Dosisvorhersagen ohne Bias erzeugen kann, obwohl es mithilfe von MC Simulationen mit einer hohen statistischen Unsicherheit trainiert wird. Dies ist eine wichtige Erkenntnis fĂŒr die beschleunigte Entwicklung zukĂŒnftiger ML-Modelle, da solche Daten deutlich schneller erzeugt werden können. Die produzierten Dosisvorhersagen weichen zumeist höchstens 10% von den MC Simulationen ab, daher wird das entwickelte Modell als geeigneter Kandidat fĂŒr zukĂŒnftige schnelle Dosisvorhersagen fĂŒr die Planungsoptimierung von MRT-Bestrahlungen eingeordnet
2023-01-01T00:00:00Z
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The Muon Puzzle in cosmic-ray induced air showers and its connection to the Large Hadron Collider
http://hdl.handle.net/2003/41986
Title: The Muon Puzzle in cosmic-ray induced air showers and its connection to the Large Hadron Collider
Authors: Albrecht, Johannes; Cazon, Lorenzo; Dembinski, Hans; Fedynitch, Anatoli; Kampert, Karl-Heinz; Pierog, Tanguy; Rhode, Wolfgang; Soldin, Dennis; Spaan, Bernhard; Ulrich, Ralf; Unger, Michael
Abstract: High-energy cosmic rays are observed indirectly by detecting the extensive air showers initiated in Earthâs atmosphere. The interpretation of these observations relies on accurate models of air shower physics, which is a challenge and an opportunity to test QCD under extreme conditions. Air showers are hadronic cascades, which give rise to a muon component through hadron decays. The muon number is a key observable to infer the mass composition of cosmic rays. Air shower simulations with state-of-the-art QCD models show a significant muon deficit with respect to measurements; this is called the Muon Puzzle. By eliminating other possibilities, we conclude that the most plausible cause for the muon discrepancy is a deviation in the composition of secondary particles produced in high-energy hadronic interactions from current model predictions. The muon discrepancy starts at the TeV scale, which suggests that this deviation is observable at the Large Hadron Collider. An enhancement of strangeness production has been observed at the LHC in high-density events, which can potentially explain the puzzle, but the impact of the effect on forward produced hadrons needs further study, in particular with future data from oxygen beam collisions.
2022-03-09T00:00:00Z
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From high energy physics to hospital
http://hdl.handle.net/2003/41982
Title: From high energy physics to hospital
Authors: Schilling, Isabelle
Abstract: The effort to obtain continual progress in treatment quality in proton therapy facilities implies new technical requirements, mainly for the irradiation machines and the detector systems. For example, the collimation of proton spots generates stepper dose gradients and, thereby, the need for detectors with a high spatial resolution. Besides this, beam currents around 2 nA (â 1.2 â
1010 "protons" /"s" ) during patient treatment set challenging requirements on the detectorsâ readout electronics for single particle tracking or counting.
The knowledge gained in detector development in High Energy Physics (HEP) during the past decades is transferred to proton therapy applications in this work to address the upcoming detector requirements. It provides studies investigating the usage of a pixel detector designed for individual particle tracking in the high-radiation environment of the ATLAS experiment at LHC, namely the ATLAS IBL Pixel Detector, for proton beam measurements at proton therapy facilities. Due to the small pixel size of the detector under study, the shape of single pencil beam proton spots is determined with precision in the smaller pixel direction of 28 ÎŒm. The timing information of the particle hits on the detector allows the distinction between the single spots of scanned proton fields. Dose linearity checks reveal that the detector meets the requirement of an output dose consistency of ± 3 % for the daily quality assurance (QA) in the chosen dose range. Additionally, further studies lead to the conservative assumption that hit rates up to (73.85 ± 0.95) "clusters" /"25 ns" sampled with a frequency of 1 kHz feature a linear dependency on the beam current. Furthermore, the provided information on the deposited energy in the detector is utilized for range verification. Range differences of 1 mm required for the daily QA can be detected for proton energies impinging the sensor in the range of (30 â 44) MeV. Finally, an example of using the detector under study in the field of proton therapy is given by supporting a study investigating the energy deposition of platinum nanoparticles on a macroscopic scale. This work offers a characterization of the ATLAS IBL Pixel detector for proton therapy application and points out improvement opportunities for further detector development.
2023-01-01T00:00:00Z
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Single NV centers as sensors for radio-frequency fields
http://hdl.handle.net/2003/41934
Title: Single NV centers as sensors for radio-frequency fields
Authors: Zhang, Jingfu; Suter, Dieter
Abstract: We show that a single electron spin can serve as a sensor for radio-frequency (rf) magnetic fields. The longitudinal and transverse components of the rf field can be extracted from the phase acquired during free evolution of the spin coherence. In our experimental demonstration, a single electron spin of an NV center in diamond serves as an atomic size of two components of an rf field.
2023-05-09T00:00:00Z
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Revealing the nano-structures of low-dimensional germanium on Ag(1 1 0) using XPS and XPD
http://hdl.handle.net/2003/41840
Title: Revealing the nano-structures of low-dimensional germanium on Ag(1 1 0) using XPS and XPD
Authors: Kesper, Lukas; Schmitz, Marie; Schulte, Malte G. H.; Berges, Ulf; Westphal, Carsten
Abstract: In this work, we present a structural investigation of sub-monolayer films of germanium on Ag(1 1 0) by means of photoelectron spectroscopy (XPS) and diffraction (XPD), as well as low-energy electron diffraction (LEED). Since the rising progress in the synthesis of various kinds of nanoribbons, also germanium nanoribbons (Ge-NR) have been synthesized on Ag(1 1 0), recently. Here, we focus on their structural evolution and found the formation of two different phases of germanium at coverages of 0.5ML and 0.7ML, differing fundamentally from predicted nanoribbon structures. By means of LEED measurements, we obtained evidence for germanium superstructures which are not aligned along the [1ÂŻÂŻÂŻ10]-direction, as expected for nanoribbon growth. Using synchrotron-based high-resolution XPS and XPD experiments of the Ge 3d and Ag 3d core-levels, we resolved the local chemical and atomic order of the germanium films. Thus, the strong internal bonding of the buckled germanium film and a weak Van-der-Waals interaction between silver and germanium were discovered. Moreover, XPD-simulations delivered a detailed model of the structural arrangement of the preliminary nanoribbon phase, which also provided an approach to identify the origin of the two chemically shifted components in the Ge 3d signal by applying a component-wise decomposition of the XPD data.
2022-04-18T00:00:00Z
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Physics-based generative model of curvature sensing peptides; distinguishing sensors from binders
http://hdl.handle.net/2003/41365
Title: Physics-based generative model of curvature sensing peptides; distinguishing sensors from binders
Authors: Hilten, Niek van; Methorst, Jeroen; Verwei, Nino; Risselada, Herre Jelger
Abstract: Proteins can specifically bind to curved membranes through curvature-induced hydrophobic lipid packing defects. The chemical diversity among such curvature âsensorsâ challenges our understanding of how they differ from general membrane âbindersâ that bind without curvature selectivity. Here, we combine an evolutionary algorithm with coarse-grained molecular dynamics simulations (Evo-MD) to resolve the peptide sequences that optimally recognize the curvature of lipid membranes. We subsequently demonstrate how a synergy between Evo-MD and a neural network (NN) can enhance the identification and discovery of curvature sensing peptides and proteins. To this aim, we benchmark a physics-trained NN model against experimental data and show that we can correctly identify known sensors and binders. We illustrate that sensing and binding are phenomena that lie on the same thermodynamic continuum, with only subtle but explainable differences in membrane binding free energy, consistent with the serendipitous discovery of sensors.
2023-03-17T00:00:00Z
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Milli, micro, nano: Venturing to small scales in proton beam therapy physics for radiobiological research
http://hdl.handle.net/2003/41342
Title: Milli, micro, nano: Venturing to small scales in proton beam therapy physics for radiobiological research
Authors: Behrends, Carina
Abstract: In der Strahlentherapie ist es fundamental den Strahlenschaden im Hinblick auf die Tumorkontrolle
und auf Normalgewebskomplikationen zu steuern. Somit mĂŒssen TherapieansĂ€tze einen Kompromiss zwischen der applizierbaren Dosis fĂŒr den klonogenen Zelltod der Tumorzellen und möglichen Nebenwirkungen finden. Mithilfe von strahlenbiologischen Experimenten können weitere Erkenntnisse ĂŒber die schĂ€digende Strahlenwirkung gewonnen werden.
Diese Arbeit stellt drei unterschiedliche und unabhĂ€ngige ForschungsansĂ€tze in der Physik der Protonentherapie von der GröĂenordnung Millimeter bis zu Nanometer vor, um strahlenbiologische Experimente und damit den langfristigen Therapieerfolg zu verbessern.
Im ersten Projekt wird eine Methode zur Optimierung der Feldformung bei der BehandlungsmodalitÀt von gescannten Protonennadelstrahlen in Kombination mit kollimierenden Aperturen prÀsentiert. Eine optimierte Positionierung des Spots relativ zur Aperturkante erzeugt dabei eine kleinere laterale Penumbra.
In einem zweiten Projekt wird ein Versuchsaufbau entwickelt und optimiert, um Protonen, die ursprĂŒnglich auf klinische Energien beschleunigt wurden, so effizient wie möglich mit einer beliebigen Energie bis hinunter zu wenigen MeV bereitzustellen. Mit einem optimalen Setup können niederenergetische Protonen mit maximaler Effizienz fĂŒr strahlenbiologische Experimente bereitgestellt werden.
Das dritte Projekt untersucht den strahlensensitiven Effekt von Platinnanopartikeln (PtNPs) in der Protonentherapie, der potentiell eine erhöhte Tumorkontrolle bei der Behandlung bewirken kann. Es wird experimentell nachgewiesen, dass der strahlensensitive Effekt von PtNPs in der Protonentherapie nicht in einer erhöhten Energiedeposition der Protonen auf makroskopischer Skala begrĂŒndet liegt.
Insgesamt liefern die in dieser Arbeit untersuchten Projekte individuelle BeitrÀge zur Physik in der strahlenbiologischen Forschung und damit zur Verbesserung der Strahlenwirkung in der Protonentherapie.; In radiotherapy, it is fundamental to manage the radiation damage in terms of tumor control and normal tissue complications. Thus, therapeutic strategies aim to find a compromise between the applicable dose for clonogenic cell death of the tumor cells and possible side effects. Radiobiological experiments may provide further insight into the damaging effects of radiation.
Here, three different and independent research approaches in proton therapy physics from the millimeter to nanometer scale are introduced to improve radiobiological experiments and thus long-term therapeutic outcome.
The first project presents a method to optimize field shaping in the treatment modality of proton pencil beam scanning in combination with collimating apertures. An optimized positioning of the spot relative to the aperture edge results in a smaller lateral penumbra.
In a second project, an experimental setup is developed and optimized to deliver protons originally accelerated to clinical energies as efficiently as possible with an arbitrary energy down to only a few MeV. With an optimal absorber thickness, low-energetic protons can be provided with maximum efficiency for radiobiology experiments.
The third project investigates the radiosensitizing effect of platinum nanoparticles (PtNPs) in proton therapy, which can potentially induce increased tumor control during treatment. It is experimentally demonstrated that the radiosensitizing effect of PtNPs in proton therapy is not due to an increased proton energy deposition at the macroscopic scale.
Overall, the projects investigated in this work provide individual contributions to physics in the radiobiological research and thus to the improvement of the radiation effect in proton beam therapy.
2023-01-01T00:00:00Z
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Proteindynamik unter hohem hydrostatischen Druck
http://hdl.handle.net/2003/41329
Title: Proteindynamik unter hohem hydrostatischen Druck
Authors: Moron, Marc
Abstract: Der Einfluss diverser thermodynamischer Parameter auf die Protein-Protein Wechselwirkung, sowie das Phasenverhalten von konzentrierten Proteinlösungen ist von fundamentaler Bedeutung fĂŒr viele physiologische Prozesse. Diese Arbeit befasst sich insbesondere mit dem Einfluss des hydrostatischen Drucks und der Temperatur auf die Kinetik und Dynamik der flĂŒssig-flĂŒssig Phasenseparation (LLPS) in Lysozymlösungen. Die LLPS ĂŒbernimmt einerseits funktionelle Aufgaben, wie beispielsweise die Bildung membranloser Organellen oder die Ăbertragung von Nervensignalen. Andererseits ist eine fehlregulierte LLPS an pathogenen Prozessen, wie der Entstehung von Alzheimer oder Katarakt beteiligt. Aus diesem Grund ist es von groĂer Bedeutung die zugrundeliegenden Mechanismen der LLPS vollstĂ€ndig zu verstehen. In der Vergangenheit befassten sich viele Studien mit der Untersuchung der Protein-Protein Wechselwirkung und des Phasenverhaltens in konzentrierten Proteinlösungen mittels Röntgenkleinwinkelstreuung. Allerdings wurde in diesen Studien das System charakterisiert, nachdem die LLPS vollstĂ€ndig abgeschlossen war, wodurch Informationen ĂŒber die Kinetik und Dynamik wĂ€hrend der Ausbildung der kondensierten Phase verloren gingen. Deshalb wurden in dieser Arbeit Röntgenphotonenkorrelationsspektroskopie-Messungen (XPCS) an konzentrierten Proteinlösungen wĂ€hrend der LLPS durchgefĂŒhrt. XPCS ist das Röntgenanalogon zur dynamischen Lichtstreuung (DLS), mit dem Unterschied das kohĂ€rente Röntgenstrahlung anstelle von Laserlicht verwendet wird. Durch die kleinere WellenlĂ€nge der Strahlung kann somit die Dynamik auf kĂŒrzeren LĂ€ngenskalen auch in trĂŒben Proben untersucht werden. Der Fokus dieser Arbeit lag auf der Untersuchung der Kinetik und Dynamik in AbhĂ€ngigkeit der Quenchtiefe. Im Fall des hydrostatischen Drucks konnte gezeigt werden, dass sich mit steigender Quenchtiefe das Wachstum der konzentrierten Phase verlangsamt und das System fĂŒr die gröĂten Quenchtiefen ein nanostrukturiertes Gelnetzwerk bildet. Die Autokorrelationsfunktionen zeigten zwei ZerfĂ€lle, wobei der schnelle Zerfall der OberflĂ€chenbildung und der langsame Zerfall dem Wachstumsprozess zugeordnet werden konnte. FĂŒr die temperaturinduzierte LLPS wurde eine deutlich langsamere Dynamik und die Ausbildung gröĂerer Strukturen beobachtet. Der zweite Teil dieser Arbeit befasste sich mit der Untersuchung der Dynamik in homogenen Proteinlösungen. Durch Kombination von DLS- und XPCS-Messungen konnte die Existenz von Clustern in Lysozymlösungen nachgewiesen und gezeigt werden, dass die charakteristischen Zeiten einzelner Proteine in homogenen Lösungen schneller sind, als die Wiederholrate der verwendeten Detektoren.; The influence of various thermodynamic parameters on protein-protein interaction, as well as the phase behavior of concentrated protein solutions, is of fundamental importance for many physiological processes. This work focuses in particular on the influence of hydrostatic pressure and temperature on the kinetics and dynamics of liquid-liquid phase separation (LLPS) in lysozyme solutions. On the one hand, LLPS performs functional tasks, such as the formation of membrane-less organelles or the transmission of cellular signals. On the other hand, a misregulated LLPS is involved in pathogenic processes, such as the development of Alzheimer's disease or cataract. Therefore, it is of great importance to fully understand the underlying mechanisms of LLPS. In the past, many studies dealt with the investigation of protein-protein interaction and phase behavior in concentrated protein solutions by small-angle X-ray scattering. However, in these studies, the system was characterized after the LLPS was complete, resulting in the loss of information about the kinetics and dynamics during the formation of the condensed phase. Therefore, in this work, X-ray photon correlation spectroscopy (XPCS) measurements were performed on concentrated protein solutions during LLPS. XPCS is the X-ray analogue of dynamic light scattering (DLS), with the difference that coherent X-ray radiation is used instead of laser light. Due to the smaller wavelength of the radiation, the dynamics can be studied on shorter length scales, even in turbid samples. The focus of this work was to study the kinetics and dynamics as a function of quench depth. In the case of hydrostatic pressure, it was shown that as the quench depth increases, the growth of the concentrated phase slows down and the system forms a nanostructured gel network for the largest quench depths. The autocorrelation functions showed two decays, where the fast decay could be attributed to surface formation and the slow decay to the growth process. For the temperature-induced LLPS, much slower dynamics and the formation of larger structures were observed. The second part of this work addressed the study of dynamics in homogeneous protein solutions. By combining DLS and XPCS measurements, the existence of clusters in lysozyme solutions was demonstrated and it was shown that the characteristic times of individual proteins in homogeneous solutions are faster than the repetition rate of the detectors used.
2023-01-01T00:00:00Z
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Another one cleans the dust
http://hdl.handle.net/2003/41308
Title: Another one cleans the dust
Authors: Schmidt, Kevin
Abstract: Radio interferometers achieve the highest resolutions at the cost of sparse data coverage.
Incompletely sampled sky distributions in Fourier space result in noise artifacts in the source reconstructions.
Established cleaning software is often time-consuming and lacks reproducibility.
In this work, I propose a novel cleaning strategy for radio interferometer data based on convolutional neural networks to adjust current analysis strategies to the new telescope standards.
This deep learning-based approach will allow a straightforward application that generates reproducible results with short reconstruction times.
The newly developed simulation chain enables the simulation of Gaussian radio galaxies and mimics observations by radio interferometers.
By iterative adjustments, complexity is increased, ending up with a simulated data set comparable to MOJAVE archive data.
In parallel, the deep learning framework radionets, capable of uncertainty estimates, is built to analyze large data samples with comparable characteristics.
The improved reconstruction technique will allow scientists to focus more on their scientific analysis and omit a vast workload on data cleaning tasks.
Various evaluation techniques are created to quantify the trained deep learning models' reconstruction quality.
Furthermore, the reconstruction performance is assessed on input data with different noise levels by comparing the resulting predictions with the simulated source distributions.
Source orientations and sizes are well reproduced, while the recovered intensities show substantial scatter, albeit not worse than existing methods without fine-tuning.
Finally, all improvements are combined to train a deep learning model suitable to evaluate MOJAVE observations.
2022-01-01T00:00:00Z
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Standalone track reconstruction on GPUs in the first stage of the upgraded LHCb trigger system & Preparations for measurements with strange hadrons in Run 3
http://hdl.handle.net/2003/41306
Title: Standalone track reconstruction on GPUs in the first stage of the upgraded LHCb trigger system & Preparations for measurements with strange hadrons in Run 3
Authors: Calefice, Lukas
Abstract: The LHCb experiment is undergoing its first major detector upgrade to operate at a five times higher instantaneous luminosity during the Run 3 data taking period. It is equipped with a new set of tracking detectors (VELO, UT, SciFi) to match the conditions of an increased track multiplicity and radiation damage. The hardware trigger stage is removed. The first stage of the software trigger system is implemented to run on about 200 GPU cards with a throughput of 30MHz. An alternative tracking algorithm called Seeding & Matching for the first trigger stage is developed and presented in this thesis. Other than the formerly used forward tracking, the presented algorithm performs the tracking without making use of the UT which allows to run in the early data taking of Run 3 before the UT will be installed. The Seeding is a standalone reconstruction of track segments in the SciFi, which is followed by a Matching step where the SciFi seeds are matched to VELO track segments reconstructed beforehand. The physics and computing performance of the Seeding & Matching is evaluated and found to be compatible with the forward tracking. The Seeding & Matching is now used as the new baseline algorithm and currently being commissioned on the first Run 3 data. Furthermore, preparations for an early Run 3 measurement of the ratios of the production cross-section of Î and KS hadrons are presented in this thesis.; L'expĂ©rience LHCb au CERN est en train d'effectuer son premier majeur upgrade (LHCb) afin de pouvoir prendre des donnĂ©es avec une luminositĂ© cinq fois plus grande pendant le Run 3. Il sera Ă©quipĂ© d'un nouvel ensemble de trajectographes (VELO, UT, SciFi) pour s'adapter aux conditions d'une multiplicitĂ© de traces et d'un rayonnement plus Ă©levĂ©e. La premiĂšre Ă©tape du systĂšme de trigger est mise en Ćuvre pour fonctionner sur 200 cartes GPU Ă un dĂ©bit de donnĂ©es de 30MHz. Une reconstruction de trace alternative, appelĂ©e Seeding & Matching, pour le premier niveau du trigger est dĂ©veloppĂ©e et prĂ©sentĂ©e dans cette thĂšse. Contrairement au forward tracking utilisĂ© prĂ©cĂ©demment, l'algorithme prĂ©sentĂ© ici se passe de l'UT, de sorte qu'il peut ĂȘtre utilisĂ© avant que l'UT ne soit complĂštement installĂ©. Le Seeding est une reconstruction autonome de segments de trace dans le SciFi, suivie d'un Matching oĂč les segments du SciFi sont associĂ©s aux segments de trace VELO reconstruits prĂ©cĂ©demment.
Le Seeding & Matching montre une performance physique et informatique compatible avec le forward tracking.
Il est maintenant utilisĂ© comme nouvel algorithme principal et mis en service avec les premiĂšres donnĂ©es du Run 3. De plus, des Ă©tudes prĂ©paratoires pour une mesure avec les premiĂšres donnĂ©es du Run 3 LHCb des rapports des sections efficaces de production des hadrons Î et KS sont prĂ©sentĂ©es dans cette thĂšse.; Das LHCb-Experiment durchlĂ€uft sein erstes groĂes Detektor-Upgrade, um wĂ€hrend Run 3 Daten mit einer verfĂŒnffachten instantanen LuminositĂ€t nehmen zu können. Es wird dafĂŒr mit einem neuen Satz an Spurfindungsdetektoren (VELO, UT, SciFi) ausgestattet, um sich an die Bedingungen der erhöhten SpurmultiplizitĂ€t und StrahlungsschĂ€den anzupassen. Der Hardware-Trigger wird entfernt. Die erste Stufe des Software-Triggers ist implementiert um auf 200 GPU-Karten bei einem Datendurchsatz von 30 MHz zu laufen. Eine alternative Spurrekonstruktion, genannt Seeding & Matching, fĂŒr die erste Triggerstufe wird entwickelt und ist prĂ€sentiert in dieser Arbeit. Im Gegensatz zu dem vorher verwendeten forward tracking kommt der hier prĂ€sentierte Algorithmus ohne den UT aus, sodass er am Anfang von Run 3 verwendet werden kann bevor der UT vollstĂ€ndig installiert ist. Das Seeding ist eine eigenstĂ€ndige Rekonstruktion von Spursegmenten im SciFi, auf die ein Matching folgt, wo die SciFi-Segmente den vorher rekonstruierten VELO-Spursegmenten zugeordnet werden. Das Seeding & Matching zeigt ein physikalische und Computing- Performance kompatibel mit dem forward tracking. Es wird momentan als neuer Hauptalgorithmus verwendet und mit den ersten Run 3 Daten in Betrieb genommen. ZusĂ€tzlich werden vorbereitende Studien fĂŒr eine Messung mit ersten Run 3 LHCb- Daten von Verh Ìaltnissen der Produktionswirkungsquerschnitte von Î0 und KS0 Hadronen in dieser Arbeit vorgestellt.
2022-01-01T00:00:00Z
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Isotope effects on the dynamics of amorphous ices and aqueous phosphoric acid solutions
http://hdl.handle.net/2003/41297
Title: Isotope effects on the dynamics of amorphous ices and aqueous phosphoric acid solutions
Authors: Ahlmann, S.; Hoffmann, L.; Keppler, M.; MĂŒnzner, P.; Tonauer, C. M.; Loerting, T.; Gainaru, C.; Böhmer, R.
Abstract: The glass transitions of amorphous ices as well as of aqueous phosphoric acid solutions were reported to display very large 1H/2H isotope effects. Using dielectric spectroscopy, in both types of glassformers for equimolar protonated/deuterated mixtures an almost ideal isotope-mixing behavior rather than a bimodal relaxation is found. For the amorphous ices this finding is interpreted in terms of a glass-to-liquid rather than an orientational glass transition scenario. Based on calorimetric results revealing that major 16O/18O isotope effects are missing, the latter scenario was previously favored for the amorphous ices. Considering the dielectric results on 18O substituted amorphous ices and by comparison with corresponding results for the aqueous phosphoric acid solutions, it is argued that the present findings are compatible with the glass-to-liquid scenario. To provide additional information regarding the deeply supercooled state of 1H/2H isotopically mixed and 18O substituted glassformers, the aqueous phosphoric acid solutions are studied using shear mechanical spectroscopy as well, a technique which so far could not successfully be applied to characterize the glass transitions of the amorphous ices.
2022-06-14T00:00:00Z
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Small and Very Small Armed Aircraft and Missiles: Trends in Technology and Preventive Arms Control
http://hdl.handle.net/2003/41273
Title: Small and Very Small Armed Aircraft and Missiles: Trends in Technology and Preventive Arms Control
Authors: Altmann, JĂŒrgen; Suter, Dieter
Abstract: The project âPreventive Arms Control for Small and Very Small Armed Aircraft and Missilesâ investigates the properties of ever smaller aircraft and missiles and explores possibilities for preventive arms control.
The first part of this project report no. 3 covers the technological trends in both categories. (Further) miniaturisation is supported by civilian developments in mobile devices. Cheap production can allow swarms of very many uninhabited aerial vehicle (UAVs). Armed UAVs down to centimetre sizes and missiles down to 20 or 10 mm diameter are possible, with correspondingly very small destructive payloads.
The second part assesses small and very small armed aircraft and missiles under criteria of preventive arms control. Both categories raise problems, mainly for international humanitarian law and military stability. Arms races have to be feared, increasing the threat of proliferation to non-state actors. Options for preventive limitations, confidence building and export control are presented. Recommended are prohibitions of autonomous attack and of swarms of autonomous armed systems, independent of size. If these are unattainable, limits should be established for quality and quantity of swarms; lower limits should be set for the size of armed UAVs and missiles; at a minimum numerical thresholds on the holdings of small and very small UAVs and missiles should be agreed on.
2023-03-01T00:00:00Z
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A pressure-jump study on the interaction of osmolytes and crowders with cubic monoolein structures
http://hdl.handle.net/2003/41261
Title: A pressure-jump study on the interaction of osmolytes and crowders with cubic monoolein structures
Authors: Surmeier, Göran; Paulus, Michael; Schneider, Eric; Dogan, Susanne; Tolan, Metin; Nase, Julia
Abstract: Many vital processes that take place in biological cells involve remodeling of lipid membranes. These processes take place in a milieu that is packed with various solutes, ranging from ions and small organic osmolytes to proteins and other macromolecules, occupying about 30% of the available volume. In this work, we investigated how molecular crowding, simulated with the polymer polyethylene glycol (PEG), and the osmolytes urea and trimethylamine-N-oxide (TMAO) affect the equilibration of cubic monoolein structures after a phase transition from a lamellar state induced by an abrupt pressure reduction. In absence of additives, swollen cubic crystallites form after the transition, releasing excess water over several hours. This process is reflected in a decreasing lattice constant and was monitored with small angle X-ray scattering. We found that the osmotic pressure exerted by PEG and TMAO, which are displaced from narrow inter-bilayer spaces, accelerates the equilibration. When the radius of gyration of the added PEG was smaller than the radius of the water channels of the cubic phase, the effect became more pronounced with increasing molecular weight of the polymers. As the release of hydration water from the cubic structures is accompanied by an increasing membrane curvature and a reduction of the interface between lipids and aqueous phase, urea, which has a slight affinity to reside near membrane surfaces, stabilized the swollen crystallites and slowed down the equilibration dynamics. Our results support the view that cellular solutes are important contributors to dynamic membrane processes, as they can accelerate dehydration of inter-bilayer spaces and promote or counteract membrane curvature.
2022-01-11T00:00:00Z
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Steady-state solutions of split beams in electron storage rings
http://hdl.handle.net/2003/41259
Title: Steady-state solutions of split beams in electron storage rings
Authors: Jebramcik, Marc Andre; Khan, Shaukat; Helml, Wolfram
Abstract: Recently, a novel operation method for synchrotron light sources with transversely split beams has been explored to fulfill the rising demand for flexible and high-throughput X-ray sources required in such diverse fields as time-resolved X-ray spectroscopy, molecular chemistry in organic cells, high-resolution medical imaging, quantum materials science or sustainable energy research. Within that novel operation mode, additional stable regions are produced in the horizontal phase space by operating an electron storage ring on a resonance that is driven by the nonlinear sextupole or octupole magnets. In the longitudinal phase space, a similar split can be produced by introducing an oscillation of the synchrotron phase via a modulation of the phase of the radiofrequency resonator. Strong radiation damping in electron storage rings, however, has to be overcome before additional regions in phase space can become populated by particles and form stable islands. This damping mechanism changes the dynamics of the system and causes diffusion between the different islands in phase space, raising the question what kind of equilibrium state exists in the asymptotic temporal limit. In this paper, a finite-differences approximation in rotating action-angle coordinates is used to solve the VlasovâFokkerâPlanck equation and to study the obtained equilibrium states for the longitudinal as well as the transverse case. The number of solution vectors and the magnitude of the corresponding singular values of the matrix of the underlying finite-differences equation are used as abstract indicators to define the required parameter set that provides stable additional beamlets. As a consequence, the beamlets have a stability that is close to that of the main beam in terms of diffusion caused by the radiation damping and quantum excitation.
2022-11-01T00:00:00Z
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Quantum spin dynamics of quasi-one-dimensional Heisenberg-Ising magnets in a transverse field: confined spinons, E8 spectrum, and quantum phase transitions
http://hdl.handle.net/2003/41252
Title: Quantum spin dynamics of quasi-one-dimensional Heisenberg-Ising magnets in a transverse field: confined spinons, E8 spectrum, and quantum phase transitions
Authors: Amelin, Kirill; Viirok, Johan; Nagel, Urmas; RÔÔm, Toomas; Engelmayer, Johannes; Dey, Tusharkanti; Agung Nugroho, Agustinus; Lorenz, Thomas; Wang, Zhe
Abstract: We report on high-resolution terahertz spectroscopic studies of quantum spin dynamics in the quasi-one-dimensional Ising-like ferromagnet CoNb2O6 and antiferromagnet BaCo2V2O8 as a function of an applied transverse magnetic field. In the ordered phases stabilized by inter-chain couplings, we reveal characteristics for confined spinon excitations, E8 dynamical spectrum, and field-induced quantum phase transitions. The connections between these characteristic dynamical features are found in the field-dependent evolution of the excitation spectra.
2022-12-07T00:00:00Z
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Hydrogen-bonded complexes of neutral nitroxide radicals with 2-propanol studied by multifrequency EPR/ENDOR
http://hdl.handle.net/2003/41249
Title: Hydrogen-bonded complexes of neutral nitroxide radicals with 2-propanol studied by multifrequency EPR/ENDOR
Authors: Savitsky, Anton; Nalepa, Anna; Petrenko, Taras; Plat, Martin; Möbius, Klaus; Lubitz, Wolfgang
Abstract: The hydrogen bond plays a key role in weak directional intermolecular interactions. It is operative in determining molecular conformation and aggregation, and controls the function of many chemical systems, ranging from inorganic, organic to biological molecules. Although an enormous amount of spectroscopic information has been collected about hydrogen-bond formation between molecules with closed-shell electronic configuration, the details of such interactions between open-shell radicals and closed-shell molecules are still rare. Here we report on an investigation of hydrogen-bonded complexes between pyrroline-type as well as piperidine-type neutral nitroxide radicals and an alcohol, i.e., 2-propanol. These nitroxide radicals are commonly used as EPR spin labels and probes. To obtain information on the geometry of the complexes and their electronic structure, multi-resonance EPR techniques at various microwave frequencies (X-, Q-, W-band, 244 GHz) have been employed in conjunction with DFT calculations. The planar five-membered ring system of the pyrroline-type nitroxide radical was found to form exclusively well-defined in-plane Ï-type hydrogen-bonded complexes with one 2-propanol molecule in the first solvation shell in frozen solution. The measured hyperfine parameters of the hydrogen-bridge proton and the internal magnetic parameters describing the electron Zeeman and the electron-nuclear hyperfine and nuclear quadrupole interactions are in good agreement with values predicted by state-of-the-art DFT calculations. In contrast, multi-resonance EPR on the non-planar six-membered ring system of the piperidine-type nitroxide radical (TEMPOL) reveals a more complex situation, i.e., a mixture of a Ï-type with, presumably, an out-of-plane Ï-type complex, both present in comparable fraction in frozen solution. For TEMPOL, the DFT calculations failed to predict magnetic interaction parameters that are in good agreement with experiment, apparently due to the considerable flexibility of the nitroxide and hydrogen-bonded complex. The detailed information about nitroxide/solvent complexes is of particular importance for Dynamic Nuclear Polarization (DNP) and site-directed spin-labeling EPR studies that employ nitroxides as polarizing agents or spin labels, respectively.
2021-12-10T00:00:00Z
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Dielectric coupler for general purpose Q-band EPR cavity
http://hdl.handle.net/2003/41248
Title: Dielectric coupler for general purpose Q-band EPR cavity
Authors: Suter, Dieter; Savitsky, Anton; Judd, Martyna; Jolley, Greg; Cox, Nicholas
Abstract: Here, we report on a robust and efficient mechanism for tuning the microwave coupling of a Q-band (34 GHz), general purpose, cylindrical EPR cavity operating in the TE011 mode. This novel mechanism allows for both the adjustment of the cavityâs coupling over a wide frequency range, as well as its bandwidth from that of a high-Q cavity (about 10 MHz), to a broadband cavity (above 1 GHz). The coupling element consists of a dielectric plate fixed onto a movable waveguide short that allows for two modes of operation. In the first mode, the dielectric plate does not influence the resonance properties of the coupling iris and allows for precise, critical coupling of the high-Q cavity. In the second mode, the dielectric plate is positioned in front of the coupling iris, varying the irisâ resonance properties and allowing very strong overcoupling to be achieved. This mechanism can be generalized for other types of EPR cavities, in particular at high microwave frequencies.
2021-08-19T00:00:00Z
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Comparing biological effectiveness guided plan optimization strategies for cranial proton therapy: potential and challenges
http://hdl.handle.net/2003/41246
Title: Comparing biological effectiveness guided plan optimization strategies for cranial proton therapy: potential and challenges
Authors: Hahn, Christian; Heuchel, Lena; ĂdĂ©n, Jakob; Traneus, Erik; Wulff, Jörg; Plaude, Sandija; Timmermann, Beate; BĂ€umer, Christian; LĂŒhr, Armin
Abstract: Background:
To introduce and compare multiple biological effectiveness guided (BG) proton plan optimization strategies minimizing variable relative biological effectiveness (RBE) induced dose burden in organs at risk (OAR) while maintaining plan quality with a constant RBE.
Methods:
Dose-optimized (DOSEopt) proton pencil beam scanning reference treatment plans were generated for ten cranial patients with prescription dosesââ„â54 Gy(RBE) andââ„â1 OAR close to the clinical target volume (CTV). For each patient, four additional BG plans were created. BG objectives minimized either proton track-ends, dose-averaged linear energy transfer (LETd), energy depositions from high-LET protons or variable RBE-weighted dose (DRBE) in adjacent serially structured OARs. Plan quality (RBEâ=â1.1) was assessed by CTV dose coverage and robustness (2 mm setup, 3.5% density), dose homogeneity and conformity in the planning target volumes and adherence to OAR tolerance doses. LETd, DRBE (Wedenberg model, α/ÎČCTVâ=â10 Gy, α/ÎČOARâ=â2 Gy) and resulting normal tissue complication probabilities (NTCPs) for blindness and brainstem necrosis were derived. Differences between DOSEopt and BG optimized plans were assessed and statistically tested (Wilcoxon signed rank, αâ=â0.05).
Results:
All plans were clinically acceptable. DOSEopt and BG optimized plans were comparable in target volume coverage, homogeneity and conformity. For recalculated DRBE in all patients, all BG plans significantly reduced near-maximum DRBE to critical OARs with differences up to 8.2 Gy(RBE) (pâ<â0.05). Direct DRBE optimization primarily reduced absorbed dose in OARs (average ÎDmeanâ=â2.0 Gy; average ÎLETd,meanâ=â0.1 keV/”m), while the other strategies reduced LETd (average ÎDmeanâ<â0.3 Gy; average ÎLETd,meanâ=â0.5 keV/”m). LET-optimizing strategies were more robust against range and setup uncertaintes for high-dose CTVs than DRBE optimization. All BG strategies reduced NTCP for brainstem necrosis and blindness on average by 47% with average and maximum reductions of 5.4 and 18.4 percentage points, respectively.
Conclusions:
All BG strategies reduced variable RBE-induced NTCPs to OARs. Reducing LETd in high-dose voxels may be favourable due to its adherence to current dose reporting and maintenance of clinical plan quality and the availability of reported LETd and dose levels from clinical toxicity reports after cranial proton therapy. These optimization strategies beyond dose may be a first step towards safely translating variable RBE optimization in the clinics.
2022-10-22T00:00:00Z
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The radiosensitizing effect of platinum nanoparticles in proton irradiations is not caused by an enhanced proton energy deposition at the macroscopic scale
http://hdl.handle.net/2003/41245
Title: The radiosensitizing effect of platinum nanoparticles in proton irradiations is not caused by an enhanced proton energy deposition at the macroscopic scale
Authors: Behrends, Carina; BÀcker, Claus Maximilian; Schilling, Isabelle; Zwiehoff, Sandra; Weingarten, Jens; Kröninger, Kevin; Rehbock, C.; Barcikowski, Stephan; Wulff, Jörg; BÀumer, Christian; Timmermann, B.
Abstract: Objective. Due to the radiosensitizing effect of biocompatible noble metal nanoparticles (NPs), their administration is considered to potentially increase tumor control in radiotherapy. The underlying physical, chemical and biological mechanisms of the NPs' radiosensitivity especially when interacting with proton radiation is not conclusive. In the following work, the energy deposition of protons in matter containing platinum nanoparticles (PtNPs) is experimentally investigated. Approach. Surfactant-free monomodal PtNPs with a mean diameter of (40 ± 10) nm and a concentration of 300 ÎŒg mlâ1, demonstrably leading to a substantial production of reactive oxygen species (ROS), were homogeneously dispersed into cubic gelatin samples serving as tissue-like phantoms. Gelatin samples without PtNPs were used as control. The samples' dimensions and contrast of the PtNPs were verified in a clinical computed tomography scanner. Fields from a clinical proton machine were used for depth dose and stopping power measurements downstream of both samples types. These experiments were performed with a variety of detectors at a pencil beam scanning beam line as well as a passive beam line with proton energies from about 56â200 MeV. Main results. The samples' water equivalent ratios in terms of proton stopping as well as the mean proton energy deposition downstream of the samples with ROS-producing PtNPs compared to the samples without PtNPs showed no differences within the experimental uncertainties of about 2%. Significance. This study serves as experimental proof that the radiosensitizing effect of biocompatible PtNPs is not due to a macroscopically increased proton energy deposition, but is more likely caused by a catalytic effect of the PtNPs. Thus, these experiments provide a contribution to the highly discussed radiobiological question of the proton therapy efficiency with noble metal NPs and facilitate initial evidence that the dose calculation in treatment planning is straightforward and not affected by the presence of sensitizing PtNPs.
2022-07-29T00:00:00Z
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Characterisation of irradiated and non-irradiated silicon sensors with a table-top two photon absorption TCT system
http://hdl.handle.net/2003/41243
Title: Characterisation of irradiated and non-irradiated silicon sensors with a table-top two photon absorption TCT system
Authors: Pape, Sebastian; FernĂĄndez GarcĂa, M.; Moll, M.; Montero, R.; Palomo, F.R.; Vila, I.; Wiehe, M.
Abstract: A tabletop Two Photon Absorption-Transient Current Technique (TPA-TCT) set-up built at CERN was used to investigate a non-irradiated PIN diode, an irradiated PIN diode, and a non-irradiated 5 Ă 5-multipad HPK LGAD. The intrinsic three dimensional spatial resolution of this method is demonstrated under normal incidence of the laser probe. A charge collection versus depth profile of the non-irradiated PIN diode is presented, where reflection on the rear silicon-air interface was observed. It is found that the time-over-threshold versus depth profile is particularly suitable to determine the boundaries of the DUT's active volume. A depth scan of the irradiated PIN diode is discussed and a method to omit the single photon absorption background is presented. Finally, a charge collection measurement in the inter-pad region of the 5 Ă 5-multipad HPK LGAD is presented and it is demonstrated that TPA-TCT can be used to image the implantation and the electric field of segmented silicon devices in a three dimensional manner.
2022-08-16T00:00:00Z
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Mechanische und elektrische Eigenschaften von Ionenleitern
http://hdl.handle.net/2003/41237
Title: Mechanische und elektrische Eigenschaften von Ionenleitern
Authors: Ahlmann, Simon
Abstract: The current global interest in energy storage has triggered the development of new composite
materials and, consequently, new methodologies for manufacturing and testing these products.
In the energy storage research field their mechanical behavior is less investigated, despite of
their high both fundamental and technological relevance. To assess the interplay between charge
and mass transport, this thesis focusses on a large variety of electrolytes using shear rheology
and dielectric spectroscopy as examination methods. Tailoring the mechanical behavior of these
materials, this work investigates the impact of their local and macroscopic viscoelasticity on
their conductivity, with the ultimate goal of finding new recipes for improving the latter.
Our investigations from a series of mixtures with an ionic liquid and a dipolar one shows an
unusual shifting in the coupling between the mechanical and conductvity processes.
A survey of ionogels demonstrate that the interaction of charge carriers with their gel-like
matrix can affect conductivity even in the presence of a strong dynamical disparity between its
macroscopic mechanical and electrical parameters.
Finally, comparing ionic and proton conductors, it is shown that this decoupling significantly
enhances the conductivity in acid hydrates. Our results and their analysis show that enhancing the
degree of decoupling between the mechanical and electrical degrees of freedom, combined with a
reduction of charge correlations in highly concentrated electrolytes are essential for the development
of the next generation of energy storage materials.; Das derzeitige weltweite Interesse an der Energiespeicherung hat zur Entwicklung neuer Verbundwerkstoffe
und folglich zu neuen Methoden fĂŒr die Herstellung und PrĂŒfung dieser Produkte gefĂŒhrt. In der
Energiespeicherforschung wird das mechanische Verhalten jedoch weniger untersucht, obwohl es sowohl von
grundlegender als auch technologischer Bedeutung ist. Um das Zusammenspiel von Ladungs- und Massentransport zu bewerten, konzentriert sich diese Arbeit auf eine Vielzahl von Elektrolyten, wobei Scherrheologie und dielektrische Spektroskopie als Untersuchungsmethoden eingesetzt werden. Indem wir das mechanische Verhalten dieser Materialien anpassen, untersuchen wir den Einfluss ihrer lokalen und makroskopischen ViskoelastizitĂ€t auf ihre LeitfĂ€higkeit, mit dem Ziel, neue AnsĂ€tze zur Verbesserung der LeitfĂ€higkeit zu finden. Unsere Untersuchungen an einer Reihe von Mischungen mit einer ionischen und einer dipolaren FlĂŒssigkeit zeigen eine ungewöhnliche Verschiebung in der Kopplung zwischen mechanischem und LeitfĂ€higkeits-Prozess. Eine Untersuchung von Ionengelen zeigt, dass die Wechselwirkung von LadungstrĂ€gern mit ihrer gelartigen Matrix die LeitfĂ€higkeit auch dann beeinflussen kann, wenn eine starke dynamische Diskrepanz zwischen den makroskopischen mechanischen und elektrischen Parametern besteht.
SchlieĂlich wird durch den Vergleich von Ionen- und Protonenleitern gezeigt, dass diese Entkopplung die
LeitfÀhigkeit in SÀurehydraten signifikant erhöht. Unsere Ergebnisse und deren Analysen zeigen, dass die
Verbesserung des Entkopplungsgrades zwischen den mechanischen und elektrischen Freiheitsgraden in Verbindung mit einer Reduzierung der Ladungskorrelationen in hochkonzentrierten Elektrolyten fĂŒr die Entwicklung der nĂ€chsten Generation von Energiespeichermaterialien von essentieller Bedeutung ist.
2022-01-01T00:00:00Z
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Resonant and non-resonant X-ray emission studies on cobalt bis(o-dioxolene) valence tautomers
http://hdl.handle.net/2003/41223
Title: Resonant and non-resonant X-ray emission studies on cobalt bis(o-dioxolene) valence tautomers
Authors: Otte, Florian
Abstract: The study and design of novel molecular materials, miniaturized molecular switches and sensors, is propelled by the investigation of electronically-labile systems.
This property enables molecules to interconvert between distinct (meta-)stable electronic states.
A prominent group of bistable molecular systems is represented by cobalt-based valence tautomer transition-metal complexes, which can be switched between tautomeric forms by external stimuli such as temperature, pressure, or irradiation by light.
This transition is characterized by a combined metal-ligand charge-transfer and spin-crossover.
The driving force behind valence tautomerism (VT) is the presence of redox-active benzoquinone-ligands, which enable the oxidation and reduction of the central cobalt ion between Co2+ to Co3+.
These systems present scientific value not only due to their electronically-labile behavior and their potential application for the development of molecular storage or sensor units but also as model systems for larger, more complicated complexes.
Valence tautomers have been investigated since the late 1970s. Despite this, the amount of available element-specific and spin-sensitive X-ray spectroscopic data is very limited.
In this thesis, systematic studies on three cobalt valence tautomers were conducted to explore resonant- and non-resonant X-ray emission spectra for the presence of signatures of the VT process.
Based on these spectra, time-resolved ultra-fast investigation on a cobalt valence tautomer has been conducted using ultra-short highly-brilliant X-ray pulses, as they are produced by the European X-ray free-electron laser in Hamburg at the Femtoseconds X-ray Experiments (FXE) instrument.
The obtained X-ray emission results indicate subtle differences between the spectral signatures of the individual valence tautomers, which are enhanced by the application of resonant X-ray emission methods. Time-resolved experiments on a valence tautomer indicate the presence of two ultra-short (sub one picosecond) dynamic processes. The interpretation and correlation with a photocycle for complexes exhibiting VT requires further investigation.; Die Untersuchung und Entwicklung neuartiger molekularer Materialien, miniaturisierte molekulare Einheiten, welche schalten oder messen können, wird vorangetrieben von Studien an elektronisch-labilen Systemen. Diese Eigenschaft verleiht MolekĂŒlen die FĂ€higkeit, in mehreren (meta-)stabilen ZustĂ€nden zu existieren. Eine prominente Gruppe von bistabilen molekularen Systemen stellen die Ăbergangsmetallkomplexe der Kobalt-Valenztautomere dar, welche sich durch Ă€uĂere Reize wie Temperatur, Druck oder bei Einstrahlung von Licht zwischen zwei Tautomeren schalten lassen.
Dieser Ăbergang ist durch einen kombinierten Metal-Liganden Ladungstransfer und einen Spin-Ăbergang charakterisiert. Die treibende Kraft hinter dem Valenz-Tautomerismus (VT) ist die Anwesenheit von redox-aktiven Benzoquinone-Liganden, welche die Oxidation und Reduktion des zentralen Kobaltatoms von Co2+ nach Co3+ ermöglichen.
Derartige Systeme bieten nicht nur aufgrund ihres elektronisch-labilen Verhaltens als Kandidaten fĂŒr die Entwicklung von molekularen Speicher- oder Sensoreinheiten einen wissenschaftlichen Mehrwert; ein tiefergreifendes VerstĂ€ndnis der involvierten elektronischen Prozesse ist auch als Modellsystem fĂŒr andere, gröĂere Komplexverbindungen von Nutzen.
Valenztautomere stehen seit den spĂ€ten 1970er Jahren im Fokus der Forschung. Trotz dieses Umstandes ist die VerfĂŒgbarkeit von elementspezifischen und Spin-sensitiven Röntgenspektroskopie-Ergebnissen stark begrenzt.
Im Rahmen dieser Thesis wurden systematische Studien an drei Kobalt-Valenztautomeren durchgefĂŒhrt, um resonante und nicht-resonante Röntgenemissionsspektren auf Signaturen des VT Ăbergangs zu ĂŒberprĂŒfen.
Die erhaltenen experimentellen Spektren bilden die Basis fĂŒr die zeitaufgelöste Untersuchung an Kobalt-Valenztautomeren mithilfe ultra-kurzer Femtosekunden-Röntgenlichtblitze, wie sie an der GroĂforschungseinrichtung des EuropĂ€ischen Röntgen-Freie-Elektronen-Lasers in Hamburg am Femtoseconds X-ray Experiments (FXE) Instrument verfĂŒgbar gemacht werden.
Die erhaltenen Röntgenergebnisse belegen subtile Unterschiede in den spektralen Signaturen der einzelnen Valenztautomere, welche sich durch die Anwendung von resonanter Röntgenemission in vereinfachter Weise zeigen lassen. Die zeitaufgelösten Messungen an einem Tautomersystem weisen Signaturen von zwei ultra-kurzen (Sub-1-Pikosekunden-) dynamischen Prozessen auf, deren Interpretation und Einordnung in einen Photozyklus weiteren Untersuchungen bedarf.
2022-01-01T00:00:00Z
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Orbit correction and response analysis at DELTA
http://hdl.handle.net/2003/41210
Title: Orbit correction and response analysis at DELTA
Authors: Kötter, Stephan-Robert
Abstract: The DELTA facility is a synchrotron light source located in Dortmund, Germany. Here, the
TU Dortmund University operates a 1.5 GeV storage ring supplying radiation ranging from the
THz to the hard X-ray regime for experiments in chemistry, biochemistry, solid-state physics
and materials science. The ring is equipped with a slow orbit feedback (SOFB) that corrects the
transverse orbit position using a set of steerer magnets. The orbit correction software acts as
the feedback's controller. Until 2021, the ring used a program based on a customized singular
value decomposition (SVD) approach for calculating corrections. Its replacement, which is
better integrated into the experimental physics and industrial control system (EPICS) and also
capable of two methods of energy correction, was implemented and commissioned to routine
operation within the scope of this work. Additionally, the closed-orbit bilinear-exponential
analysis (COBEA) algorithm was generalized to accept combinations of orbit response matrix
columns, so-called response sets, as input. This enables the new response set t algorithm
(RSFA) to extract the coupled beta functions and betatron phase advances as well as the
scaled dispersion from orbit corrections. If it is integrated with the SOFB in an online tting
approach, the RSFA will supply non-invasive measurements of these optical functions. The
new orbit correction software and algorithm are described and evaluated in simulations as well
as experimental studies.; DELTA ist eine Synchrotronstrahlungsquelle in Dortmund, Deutschland. Hier betreibt die
Technische UniversitÀt Dortmund einen 1.5 GeV-Elektronenspeicherring, der Strahlung vom
THz- bis zum harten Röntgenbereich fĂŒr Experimente in der Chemie, der Biochemie, der
Festkörperphysik sowie den Materialwissenschaften zur VerfĂŒgung stellt. Der Ring ist mit einer
langsamen Orbitkorrektur ausgestattet, um die transversale Orbitposition mit Hilfe von Steuermagneten
zu korrigieren. Die Regelung wird durch das Orbitkorrekturprogramm gesteuert. Bis
ins Jahr 2021 wurde ein auf der Methode der SingulÀrwertzerlegung (SVD) beruhender und
auf DELTA angepasster Ansatz verwendet, um diese Korrekturen zu berechnen. Im Rahmen
dieser Arbeit wurde ein neues Programm implementiert und in den Routinebetrieb ĂŒbernommen,
das besser in das Experimental Physics and Industrial Control System (EPICS) integriert
ist und zwei Methoden zur Energiekorrektur bereitstellt. ZusÀtzlich wurde der Closed-Orbit
Bilinear-Exponential Analysis-Algorithmus (COBEA-Algorithmus) verallgemeinert, um Linearkombinationen
von Orbitkorrekturmatrizen, genannt Response Sets, als Eingangsdaten zu
akzeptieren. Das ermöglicht dem neuen Reponse Set Fit Algorithm (RSFA) die gekoppelten
Betafunktionen und BetatronphasenvorschĂŒbe sowie die skalierte Dispersion aus einem Satz
Orbitkorrekturdaten zu extrahieren. WĂŒrde der Algorithmus mit der langsamen Orbitkorrektur
in einem Online-Fitansatz integriert, könnten nicht-invasive Messungen der genannten
optischen Funktionen durchgefĂŒhrt werden. Das neue Orbitkorrekturprogramm und der RSFA
werden beschrieben und aufgrund von Simulationen sowie experimenteller Studien evaluiert.
2022-01-01T00:00:00Z
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Phononkopplung an Spins und Ladungen auf der ultraschnellen Zeitskala im antiferromagnetischen Halbleiter MnTe
http://hdl.handle.net/2003/41199
Title: Phononkopplung an Spins und Ladungen auf der ultraschnellen Zeitskala im antiferromagnetischen Halbleiter MnTe
Authors: Terschanski, Marc
Abstract: Im ersten Teil dieser Arbeit wird ein neu installierter Aufbau beschrieben, der die gleichzeitige DurchfĂŒhrung optischer und magneto-optischer Pump-Probe Experimente als Funktion der Temperatur, eines Magnetfeldes oder eines angelegten elektrischen Feldes ermöglicht. Im zweiten Teil dieser Arbeit wird mit optischen Anregungen untersucht, ob eine Kopplung zwischen dem Spinsystem und dem elektronischen System in dem magnetischen Halbleiter α-MnTe existiert. Dazu wird eine 200 nm dicke Schicht α-MnTe mit verschiedenen experimentellen Methoden vermessen. Die BandlĂŒcke von α-MnTe ist um einen zusĂ€tzlichen Beitrag in der antiferromagnetischen Phase blauverschoben, welcher proportional mit der Untergittermagnetisierung skaliert. Diese statische Kopplung zwischen der BandlĂŒcke und dem Spinsystem wird erfolgreich in unserer Probe reproduziert. Darauf aufbauend wird die Dynamik der BandlĂŒcke unter Verwendung des Pump-Probe Verfahrens untersucht. Die transiente ReflektivitĂ€t zeigt, dass die BandlĂŒcke durch das optisch aktive α-Phonon kohĂ€rent moduliert wird. Im finalen Schritt wird die BandlĂŒcke kohĂ€rent angeregt und die Antwort des Spinsystems, die Rotation der Polarisation, detektiert. Diese ist ebenfalls durch das α-Phonon kohĂ€rent moduliert und zeigt einen zusĂ€tzlichen inkohĂ€renten Beitrag in der antiferromagnetischen Phase, welcher eindeutig auf die magnetische Ordnung zurĂŒckzufĂŒhren ist. Die Zerfallszeit dieses Beitrags entspricht der der Zeitskala der Untergitterdemagnetisierung. Somit konnte in dieser Arbeit eine phonongestĂŒtzte Kopplung zwischen dem elektronischen System und dem Spinsystem in α-MnTe gezeigt werden.; In the first part of this thesis, a newly constructed set-up is described that allows simultaneous optical and magneto-optical pump-probe experiments to be performed as a function of temperature, magnetic field or an applied electric field. In the second part of this work, optical methods are used to investigate whether a coupling exists between the spin system and the electronic system in the magnetic semiconductor α-MnTe. For this purpose, a 200 nm thick layer of α-MnTe is measured with different experimental methods. The band gap of α-MnTe experiences an additional blue shift in the antiferromagnetic phase, which scales proportionally with the sublattice magnetisation. This static coupling between the band gap and the spin system is successfully reproduced in our sample. Based on this, the dynamics of the band gap is investigated using the pump-probe method. The transient reflectivity shows that the band gap is coherently modulated by optical active α-phonons. In the final step, the band gap is coherently excited and the response of the spin system, the rotation of the polarisation, is detected. Again the rotation of polarisation is coherently modulated by the α-phonon and shows an additional incoherent contribution in the antiferromagnetic phase, which is ascribed to the magnetic order. The decay time of this contribution corresponds to the time scale of the sublattice demagnetisation. Thus, a phonon-assisted coupling between the electronic system and the spin system on the femtosecond timescale in α-MnTe has been demonstrated in this work.
2022-01-01T00:00:00Z
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Spin dynamics in interacting semiconductor quantum dots
http://hdl.handle.net/2003/41179
Title: Spin dynamics in interacting semiconductor quantum dots
Authors: Fischer, Andreas
Abstract: We study the spin dynamics in an ensemble of singly charged semiconductor quantum dots. The spin of the confined charge carriers can be polarized by coherent laser pulses. Due to the strong localization of the charge carrier, the hyperfine interaction with the local nuclear spin bath is the main contribution to the electron spin decoherence. Two-color pump-probe experiments indicate a coherent long-ranged interaction between the electron spins in different quantum dots. In this thesis, we develop a semiclassical approach based on spin-coherent states that allows for the efficient simulation of large spin systems and in addition preserves quantum mechanical properties on the level of single spins. We extend the semiclassical approach to open quantum systems using a quantum jump approach. We perform an in-depth analysis of the coherent optical manipulation of an interacting quantum dot ensemble employing pulse sequences with tailored spectra. Moreover, we study the cross-correlation spectra of second and fourth order to obtain complementary information about the spin system. Finally, we examine the intertwined dynamics of the electron spin and the nuclear spins at low temperatures to study the formation of a highly correlated nuclear-spin polaron state.
2022-01-01T00:00:00Z
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Nonequilibrium nuclear spin states in singly charged semiconductor quantum dots
http://hdl.handle.net/2003/41178
Title: Nonequilibrium nuclear spin states in singly charged semiconductor quantum dots
Authors: Kleinjohann, Iris
Abstract: The spin of a localized charge carrier in a semiconductor nanostructure can be coherently controlled by external electromagnetic fields. At cryogenic temperatures, the spin coherence time is limited by the hyperfine interaction with surrounding nuclear spins. The generation of tailored nuclear spin states, however, may drastically increase the electron spin coherence in comparison to the disordered nuclear spin system. By means of a fully quantum mechanical description, we investigate two particular nonequilibrium situations in which a highly ordered nuclear spin state is achieved. First, we focus on the formation of the nuclear-spin polaron state under optical cooling of the nuclear spins. Kinetic rate equations are developed that account for different effective spin temperatures of the charge carrier and the nuclei and provide analytical access to the crossover temperature of the polaron formation. The rate equations are generalized to a Lindblad formalism enabling the numerical investigation of a cooled system with arbitrary anisotropic hyperfine interaction. The second nonequilibrium situation addressed in this thesis is the periodic optical excitation of singly charged quantum dots subject to a transversal magnetic field. Nuclei-induced frequency focusing of the electron spin precession leads to mode-locked spin dynamics. A revival of the electron spin polarization directly before each pump pulse reflects this synchronization of the spin dynamics to the pumping periodicity. In experiments, a magnetic field dependence of the emerging revival amplitude is observed. Our quantum mechanical approach allows for attributing this dependence to the nuclear Zeeman term. Moreover, we discuss various additional influences on the mode-locking effect. We examine the effect of static nuclear-electric quadrupolar interactions, the characteristics of the laser pulses, and the choice of the pulse train.
2022-01-01T00:00:00Z
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Optical excitation and detection of high-frequency coherent phonons and magnons
http://hdl.handle.net/2003/41177
Title: Optical excitation and detection of high-frequency coherent phonons and magnons
Authors: Kobecki, Michal
Abstract: The goal of this work is to obtain better control over all-optical excitation and detection of high-frequency collective excitations, in particular - phonons and magnons. Phonons- a collective movement of atoms in the lattice, and magnons- excitations of a spin system in magnetically ordered materials, recently became the prospective alternative to electrons in quantum computing or in general, information technology. In the scope of this thesis, we present a novel approach to the resonant excitation of fundamental magnon mode in a thin ferromagnetic film of Iron-Gallium alloy, as well as enhanced detection sensitivity of propagating coherent phonon wave packet exploiting giant photo-elasticity of exciton-polaritons in GaAs/AlAs superlattice. Additionally, a possible way to miniaturize the all-optical set-ups for manipulation of collective excitations is proposed by implementing a passively mode-locked semiconductor laser diode.
2022-01-01T00:00:00Z
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Elektronenholographie mittels ElektronenrĂŒckstreubeugung
http://hdl.handle.net/2003/41173
Title: Elektronenholographie mittels ElektronenrĂŒckstreubeugung
Authors: Gianfelice, Matthias
Abstract: Die von Dennis Gåbor 1948 vorgestellte Holographie sollte zur besseren Auflösung
des Elektronenmikroskops beitragen. Die Verwendung mit Elektronenwellen lieĂ
aber noch auf sich warten: Erste experimentelle Umsetzung fand die
Lichtholographie, in deren Rahmen die holographische Idee substantiell
weiterentwickelt werden konnte. Durch Erzeugung eines Phasenkontrasts wird in
einer zweidimensionalen Aufnahme neben der Amplituden- auch eine
Phaseninformation gespeichert. Damit ist die Rekonstruktion der ursprĂŒnglichen
Objektwelle und von jedem Betrachtungsort aus eine dreidimensionale
Bildwiedergabe unter anderer Perspektive möglich.
Im Sinne der ersten Idee GĂĄbors verfolgt die Elektronenholographie das Ziel,
atomare Strukturen aufzulösen. Mittels der Computerholographie kann die
Rekonstruktion der Kristalle sichtbar gemacht werden. In dieser Arbeit sollen
Simulationen der Elektronenholographie mittels EBSD auf planem Schirm zeigen,
dass die erfolgreiche Rekonstruktion eines Wolframeinkristalls mit bereits heute
vorhandenen Apparaturen möglich ist. Dazu wird zunÀchst ein theoretisches
Fundament vorgestellt. Anhand der SchirmgröĂe und -auflösung wird ermittelt,
unter welchen Voraussetzungen eine holographische Rekonstruktion möglich ist.
Ermittelte Grenzwerte werden quantitativ erlÀutert. Durch Definition eines
Bewertungskriteriums ist es möglich, die Rekonstruktionen automatisiert
auszuwerten. Mit der EinfĂŒhrung der Additionsmethode werden die ursprĂŒnglichen
Limitierungen in Teilen aufgehoben und die Rekonstruktion deutlich stabilisiert.
AbschlieĂend wird die experimentelle Umsetzbarkeit diskutiert.; Holography, introduced by Dennis GĂĄbor in 1948, was intended to contribute to a
better resolution of the electron microscope. However, its use with electron
waves still required further research at the time. The first experimental
implementation was light holography, in the context of which the holographic
idea could be substantially further developed. By generating a phase contrast,
the phase information is stored in a two-dimensional image in addition to the
amplitude information. This allows for the reconstruction of the original object
wave and a three-dimensional image reproduction under a different perspective
from any viewing point.
In accordance with GĂĄbor's first idea, electron holography pursues the goal of
resolving atomic structures. By using of computer holography the reconstruction
of crystals can be made visible. In this work, simulations of electron
holography using EBSD on a planar screen will demonstrate that successful
reconstruction of a tungsten single crystal is achievable with equipment
currently available. For this purpose, a theoretical foundation is firstly
prepared. Based on the screen size and resolution, it is determined under which
conditions a holographic reconstruction is possible. The computed limit values
are explained quantitatively. By defining a fitting criterion it is possible to
evaluate the reconstructions automatically. With the introduction of the
addition method the original limitations are improved and the reconstruction is
significantly stabilized. Finally, the experimental feasibility is discussed.
2022-01-01T00:00:00Z
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Measuring coherence properties of exciton-polaritons with homodyne detection
http://hdl.handle.net/2003/41172
Title: Measuring coherence properties of exciton-polaritons with homodyne detection
Authors: LĂŒders, Carolin
Abstract: FĂŒr die Quantentechnologie sind hybride Systeme gefragt, die verschiedene physikalische Systeme verbinden, z.B. ein Materiesystem zur Informationsverarbeitung und Licht zur Kommunikation. FĂŒr die Verbindung zwischen Halbleitern und Licht erforscht die Halbleiter-Quantenoptik, wie Licht den Quantenzustand des Halbleiters beeinflusst und wie der Zustand des Halbleiters ĂŒber das emittierte Licht gemessen werden kann.
Zur Messung des Quantenzustands von Licht wird in der Quantenoptik die vielseitige Methode der optischen Homodyn-Tomographie (OHT) verwendet. Ihre Anwendung auf die Emission von Halbleitern wird jedoch hĂ€ufig durch das Fehlen einer festen Phasenreferenz fĂŒr nicht-resonante Lumineszenz und durch die schnellen Zeitskalen des Systems verhindert.
Diese Herausforderungen werden in dieser Arbeit angegangen. Wir stellen die Anwendung von OHT auf Halbleiterlumineszenz ohne feste Phasenreferenz vor, um die KohĂ€renz-Eigenschaften und den Quantenzustand zu untersuchen. Dabei ermöglichen ein gepulster Lokaloszillator und schnelle Detektoren eine hohe Zeitauflösung. Als Testumgebung fĂŒr die Methode untersuchen wir die Emission eines Exziton-Polariton-Kondensats in einer GaAs-MikrokavitĂ€t.
Konkret zeigt diese Arbeit, welche Informationen durch die Verwendung von einem, zwei und drei Homodyn-DetektionskanÀlen gewonnen werden können. Mit einem Kanal wird die Photonenkorrelationsfunktion zweiter Ordnung g(2)(0) gemessen, mit zwei KanÀlen messen wir
die phasengemittelte Husimi-Funktion und quantifizieren den Grad der QuantenkohÀrenz im Polaritonensystem, und mit drei KanÀlen rekonstruieren wir die regularisierte P-Funktion abhÀngig von postselektierten Anfangsbedingungen und verfolgen den zeitlichen Zerfall der QuantenkohÀrenz.; For quantum technology, hybrid systems are needed to connect different physical systems, e.g. a matter system for information processing and light for communication. For connecting semiconductors and light, semiconductor quantum optics investigates how light influences the quantum state of the semiconductor and how the state of the semiconductor can be measured via the emitted light.
To measure the quantum state of light, optical homodyne tomography (OHT) is a versatile technique that is widely applied in quantum optics. But its application to semiconductor emission is often prevented by the lack of a fixed phase reference for nonresonant luminescence and by the fast time scales of the system.
These challenges are tackled in this work. We present the application of OHT to semiconductor luminescence without a fixed phase reference in order to investigate coherence properties and the quantum state. Thereby, a pulsed local oscillator and fast detectors enable a high time resolution. As a testbed for the method, we investigate the emission from an exciton-polariton condensate in a GaAs microcavity.
Specifically, this work shows which information can be gained by using one, two and three homodyne detection channels. With one channel, the second-order photon correlation function g(2)(0) is measured. Via two channels, we measure the phase-averaged Husimi function and quantify the amount of quantum coherence in the polariton system. With three channels, we reconstruct the regularized P function, depending on postselected initial conditions, and track the temporal decay of quantum coherence.
2022-01-01T00:00:00Z
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Fully automated processing and optimization of single particle and filamentous transmission electron cryomicroscopy samples
http://hdl.handle.net/2003/41171
Title: Fully automated processing and optimization of single particle and filamentous transmission electron cryomicroscopy samples
Authors: Stabrin, Markus
Abstract: Single particle cryo-EM is getting increasingly accessible to researchers from diverse research
areas. Furthermore, recent innovations in cryo-EM hardware development and data acquisition
strategies have led to an increase in data quality as well as quantity. However, the overall quality
of a data set does not directly correlate with the quality of a single image or the number of images
collected, but also strongly depends on the sample itself. Nevertheless, with great data comes great
responsibility and just having a large data set is not necessarily advantageous. To get the most out
of a data collection, the researcher needs to carefully monitor and curate all data, ideally while its
still being collected.
Therefore, automated data processing and the analysis of the collected data live during acqui-
sition becomes increasingly important. To get the most information in the shortest amount of
time, ideally, all major pre-processing steps would be executed while the data are still collected. In
this way, the researcher gets direct feedback about the sample quality and has the chance to make
necessary adjustments to the data collection. While there are several tools available to execute the
processing pipeline, they all use a static set of input settings for each individual task, limiting their
applicability.
In this thesis, I present TranSPHIRE, a tool for fully automated on-the-fly data processing.
It executes all the important pre-processing steps required for the processing of single particle
projects, as well as filamentous samples, in a parallel manner. I demonstrate the capabilities of the TranSPHIRE pipeline based on three different scenarios:
A previously unknown data set; a data set consisting of two sub-populations, where only one is
targeted for particle picking; and a filamentous sample. All three scenarios lead to a high-resolution
3D reconstruction of the target protein in a fully automated manner. Therefore, fully automated
data processing and optimization could pave the way for high-throughput screenings of unknown
samples without user intervention. Additionally, I present sp_meridien_alpha.py, a modification of the single particle 3D refinement program sp_meridien.py, to allow filamentous processing in the SPHIRE package.
In summary, the software tool TranSPHIRE and the filamentous 3D refinement program sp_meri-
dien_alpha.py combined simplify the cryo-EM data collection and processing and thereby present
a valuable contribution to the field.
2022-01-01T00:00:00Z
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The Landé factors of electrons and holes in lead halide perovskites: universal dependence on the band gap
http://hdl.handle.net/2003/41170
Title: The Landé factors of electrons and holes in lead halide perovskites: universal dependence on the band gap
Authors: Kirstein, E.; Yakovlev, D. R.; Glazov, M. M.; Zhukov, E. A.; Kudlacik, D.; Kalitukha, I. V.; Sapega, V. F.; Dimitriev, G. S.; Semina, M. A.; Nestoklon, M. O.; Ivchenko, E. L.; Kopteva, N. E.; Dirin, D. N.; Nazarenko, O.; Kovalenko, M. V.; Baumann, A.; Höcker, J.; Dyakonov, V.; Bayer, M.
Abstract: The LandĂ© or g-factors of charge carriers are decisive for the spin-dependent phenomena in solids and provide also information about the underlying electronic band structure. We present a comprehensive set of experimental data for values and anisotropies of the electron and hole LandĂ© factors in hybrid organic-inorganic (MAPbI3, MAPb(Br0.5Cl0.5)3, MAPb(Br0.05Cl0.95)3, FAPbBr3, FA0.9Cs0.1PbI2.8Br0.2, MA=methylammonium and FA=formamidinium) and all-inorganic (CsPbBr3) lead halide perovskites, determined by pump-probe Kerr rotation and spin-flip Raman scattering in magnetic fields up to 10 T at cryogenic temperatures. Further, we use first-principles density functional theory (DFT) calculations in combination with tight-binding and kââ
âp approaches to calculate microscopically the LandĂ© factors. The results demonstrate their universal dependence on the band gap energy across the different perovskite material classes, which can be summarized in a universal semi-phenomenological expression, in good agreement with experiment.
2022-06-02T00:00:00Z
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Tracing the structural evolution of quasi-freestanding germanene on Ag(111)
http://hdl.handle.net/2003/41159
Title: Tracing the structural evolution of quasi-freestanding germanene on Ag(111)
Authors: Kesper, Lukas; Hochhaus, Julian A.; Schmitz, Marie; Schulte, Malte; Berges, Ulf; Westphal, Carsten
Abstract: In the last decade, research on 2D materials has expanded massively due to the popularity of graphene. Although the chemical engineering of two-dimensional elemental materials as well as heterostructures has been extensively pursued, the fundamental understanding of the synthesis of 2D materials is not yet complete. Structural parameters, such as buckling or the interface structure of a 2D material to the substrate directly affect its electronic characteristics. In order to proceed the understanding of the element-specific growth and the associated ability of tuning material properties of two-dimensional materials, we performed a study on the structural evolution of the promising 2D material germanene on Ag(111). This study provides a survey of germanium formations at different layer thicknesses right up to the arising of quasi-freestanding germanene. Using powerful surface analysis tools like low-energy electron diffraction, x-ray photoelectron spectroscopy, and x-ray photoelectron diffraction with synchrotron radiation, we will reveal the internal and interfacial structure of all discovered germanium phases. Moreover, we will present models of the atomic and chemical structure of a Ag2Ge surface alloy and the quasi-freestanding germanene with special focus on the structural parameters and electronic interaction at the interface.
2022-05-09T00:00:00Z
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Extending the time of coherent optical response in ensemble of singly-charged InGaAs quantum dots
http://hdl.handle.net/2003/41158
Title: Extending the time of coherent optical response in ensemble of singly-charged InGaAs quantum dots
Authors: Kosarev, Alexander; Trifonov, Artur V.; Yugova, Irina A.; Yanibekov, Iskander I.; Poltavtsev, Sergey; Kamenskii, Aleksandr; Scholz, Sven; Sgroi, Carlo Alberto; Ludwig, Arne; Wieck, Andreas; Yakovlev, Dmitri; Bayer, Manfred; Akimov, Ilya
Abstract: The ability to extend the time scale of the coherent optical response from large ensembles of quantum emitters is highly appealing for applications in quantum information devices. In semiconductor nanostructures, spin degrees of freedom can be used as auxiliary, powerful tools to modify the coherent optical dynamics. Here, we apply this approach to negatively charged (In,Ga)As/GaAs self-assembled quantum dots which are considered as excellent quantum emitters with robust optical coherence and high bandwidth. We study three-pulse spin-dependent photon echoes subject to moderate transverse magnetic fields up to 1 T. We demonstrate that the timescale of coherent optical response can be extended by at least an order of magnitude by the field. Without magnetic field, the photon echo decays with T2 = 0.45 ns which is determined by the radiative lifetime of trions T1 = 0.26 ns. In the presence of the transverse magnetic field, the decay of the photon echo signal is given by spin dephasing time of the ensemble of resident electrons T2,eââŒâ4 ns. We demonstrate that the non-zero transverse g-factor of the heavy holes in the trion state plays a crucial role in the temporal evolution and magnetic field dependence of the long-lived photon echo signal.
2022-06-10T00:00:00Z
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On the structural evolution towards germanene
http://hdl.handle.net/2003/41150
Title: On the structural evolution towards germanene
Authors: Kesper, Lukas
Abstract: In den letzten Jahren hat sich die Forschung zu 2D-Materialien aufgrund der PopularitĂ€t von Graphen massiv ausgeweitet. Die erstaunlichen elektronischen und mechanischen Eigenschaften von Graphen haben Aufmerksamkeit erweckt und einen neuen Bereich der Festkörperphysik eröffnet. Es zeigte sich, dass verschiedene Elemente der Gruppe IVA und darĂŒber hinaus in nur einer Monolage (ML) als Honigwabenstruktur stabil sind. Obwohl das chemical engineering zweidimensionaler Elementmaterialien sowie das von Heterostrukturen intensiv vorangetrieben wurde, ist das grundlegende VerstĂ€ndnis der Synthese von 2D-Materialien noch nicht vollstĂ€ndig. Strukturelle Parameter, wie die Welligkeit des Wabengitters, das sogenannte buckling, oder die GrenzflĂ€chenstruktur eines 2D-Materials zum Substrat, wirken sich direkt auf seine elektronischen Eigenschaften aus.
Um das VerstĂ€ndnis des elementspezifischen Wachstums voranzutreiben, wird in dieser Arbeit eine Studie ĂŒber die strukturelle Entwicklung des vielversprechenden 2D-Materials Germanen auf Ag(111) prĂ€sentiert. Sie bietet einen Ăberblick ĂŒber Germaniumformationen, die bei verschiedenen Schichtdicken entstehen, wie die Ag2Ge-OberflĂ€chenlegierung (SAP), die striped Phase (SP) und die gemischte Phase (MP), bis hin zu quasi-freistehendem Germanen (QFG). Mit Hilfe bewĂ€hrter OberflĂ€chenanalysemethoden, wie der niederenergetischen Elektronenbeugung (LEED), wird die langreichweitige und hohe Ordnung der epitaktisch gewachsenen Ge-Strukturen nachgewiesen. Mittels hochauflösender Photoelektronenspektroskopie (XPS) mit Synchrotronstrahlung wird die interne Struktur und GrenzflĂ€chenstruktur aller Germanen-Phasen aufgelöst. Zudem kann die klare Unterscheidung zwischen allen Phasen anhand ihrer elektronischen Struktur gezeigt und der Nachweis von chemisch freistehendem Germanen auf Ag(111) erbracht werden. Die zusĂ€tzlich durchgefĂŒhrte Photoelektronenbeugung (XPD) ermöglicht die Darstellung spezifischer Strukturmodelle ausgewĂ€hlter Germanenphasen mit besonderem Augenmerk auf die strukturellen Parameter und elektronischen Wechselwirkungen an der GrenzflĂ€che. AuĂerdem wird die SAP mit einer Deckschicht aus Al2O3 bedeckt, um seine strukturelle Entwicklung als verborgene Zwischenschicht zu untersuchen.
Diese Arbeit bietet einen Ausblick auf die Synthese vielversprechender Germanenphasen auf Ag(111) und zeigt die Möglichkeit, diese Strukturen vor Umgebungsbedingungen zu schĂŒtzen.; In the past decade, research on 2D materials has expanded massively due to the
popularity of graphene. Its superb electronic and mechanical properties have attracted attention,
which opened a new field in solid-state physics. Various elements of the carbon group IVA and
beyond have been proven to be stable in a single monolayer (ML) formed in a honeycomb structure.
Although the chemical engineering of two- dimensional elemental materials and heterostructures has
been extensively pursued, the fundamental understanding of the synthesis of 2D materials is not yet
complete. Structural parameters, such as the corrugation of the honeycomb lattice, called buckling,
or the interface structure of a 2D material to the substrate, directly influence its electronic
characteristics.
In order to proceed with understanding the element-specific growth, this work presents a study on
the structural evolution of the promising 2D material germanene on Ag(111). It provides a survey of
germanium formations discovered at different layer thicknesses, like the AgâGe surface alloy (SAP),
the striped phase (SP), and the mixed phase (MP), right up to the arising of quasi-freestanding
germanene (QFG). Using robust surface analysis tools like low-energy electron diffraction (LEED),
the long-range and high order of the epitaxially grown Ge structures are demonstrated. The internal
and interfacial structure of all germanene phases is revealed by utilizing high-resolution x-ray
photoelectron spectroscopy (XPS) with synchrotron radiation. Furthermore, a clear distinction
between all phases can be drawn by their electronic structure, the same as collecting evidence for
chemically freestanding germanene synthesized on Ag(111). The additionally performed x-ray
photoelectron diffraction (XPD) allows to present specific models of the atomic and chemical
structure of selected germanene phases, focusing on the structural parameters and electronic
interaction at the interfaces. Moreover, the SAP is encapsulated with a capping layer of AlâOâ in
order to examine its structural development as a buried interlayer upon the encapsulation.
This work offers a perspective on synthesizing promising germanene phases on Ag(111) and provides a
prospect to protect the structures from ambient conditions.
2022-01-01T00:00:00Z
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Establishing a new model system for phase state measurments: The "swimming neuron" Paramecium
http://hdl.handle.net/2003/41146
Title: Establishing a new model system for phase state measurments: The "swimming neuron" Paramecium
Authors: Paeger, Anne
Abstract: The origin of cellular excitability has not yet been clearly elucidated. It has been proposed that the nonlinear stimulus-response curve of excitable cells, manifesting in all-or-none pulses (action potentials), is based on a phase transition in the cell membrane and is not a purely molecule-based phenomenon. Indeed, typical traces of transitions have already been found in a small number of studies with excitable cells. Further investigations are needed to show whether these findings are of a general nature. In this work, state diagrams of the cell membrane of intact, motile specimens of the âswimming neuronâ Paramecium are measured. Therefore, individual cells were trapped in a microfluidic channel and investigated by fluorescence spectroscopy. The thermo-optical state diagrams exhibited reversible sigmoidal
and break-like regimes, which are clear indications for a transition in the cell cortical membranes. This transition had a width of ⌠10 â 15°C and a midpoint that was located ⌠4°C below the growth temperature. It can be shifted due to changes in growth temperature or by the addition of an anesthetic (hexanol). These results suggested that the cortical membrane(s) of Paramecia reside in a phase transition regime under physiological growth
conditions.; Der Ursprung zellulĂ€rer Erregbarkeit ist bis heute noch nicht eindeutig geklĂ€rt. Es wird vermutet, dass die nichtlineare Reiz-Antwort-Kurve erregbarer Zellen, die sich in Alles-oder-Nichts-Pulsen (Aktionspotentialen) manifestiert, auf einen PhasenĂŒbergang in der Zellmembran und nicht auf ein rein molekulares PhĂ€nomen zurĂŒckzufĂŒhren ist. TatsĂ€chlich wurden bereits in wenigen Studien mit erregbaren Zellen typische Spuren von ĂbergĂ€ngen gefunden. Ob diese Befunde allgemeiner Natur sind, mĂŒssen weitere Ergebnisse zeigen. In dieser Arbeit werden Zustandsdiagramme der Zellmembran intakter, beweglicher Exemplare des âschwimmenden Neuronsâ Paramecium gemessen. Dazu wurden einzelne Zellen in einem mikrofluidischen Kanal eingefangen und fluoreszenzspektroskopisch untersucht. Die
thermooptischen Zustandsdiagramme zeigten sigmoidale und bruchartige Regime, die klare Hinweise auf einen reversiblen Ăbergang in den kortikalen Zellmembranen sind. Dieser Ăbergang hatte eine Breite von ⌠10 â 15°C und einen Mittelpunkt, der ⌠4°C unterhalb der Wachstumstemperatur lag. Er kann aufgrund von Ănderungen der Wachstumstemperatur oder durch Zugabe eines AnĂ€sthetikums (Hexanol) verschoben werden. Diese Ergebnisse legen nahe, dass sich die kortikale(n) Membran(en) von Paramecien unter physiologischen Wachstumsbedingungen im Bereich eines PhasenĂŒbergangs befinden.
2022-01-01T00:00:00Z
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On the optical detection of the physical state of excitable membranes
http://hdl.handle.net/2003/41131
Title: On the optical detection of the physical state of excitable membranes
Authors: Fedosejevs, Sara Carina
Abstract: Phase transitions in biological systems are controversially discussed. As the origin of nonlinearities, they have been suggested responsible for cellular functions including nerve pulse propagation.
In pure lipid interfaces characteristic functions, such as permeability, are modulated during a transition. These relations could have drastic implications for cells because their membranes are lipid-based. However, evidence for these transitions in cellular membranes of excitable cells - which are involved in the transmission of nerve pulses - has not been provided so far.
Within this thesis thermodynamic phase states in lipid-based interfaces are characterized based on the use of a fluorescent dye (Atto488-DPPE) as local state reporter. Optical state diagrams of artificial, lipid interfaces are recorded, and state dependent kinetics investigated.
Upon the straightforward application of this method to single, neuronal cells, a nonlinearity in the optical response is detected within the cellular membrane and identified as phase transition.
The transition is extraordinary sharp (1°C) and sensitive to pH variations in the extracellular buffer.
The existence of distinct physical phase states in cellular membranes and their highly nonlinear characteristic provides strong evidence that the membrane state is indeed crucial for excitability and conduction of nerve pulses. The results further underline that the membrane state has the potential to modify cell functionality in general as it is subject to modulation by physiologically important parameters such as pH.; PhasenĂŒbergĂ€nge in biologischen Systemen sind Gegenstand zahlreicher Diskussion. Als Ursprung von NichtlinearitĂ€ten werden sie fĂŒr zellulĂ€re Funktionen einschlieĂlich der Ausbreitung von Nervenimpulsen verantwortlich gemacht. In reinen Lipidmembranen werden charakteristische Funktionen, wie PermeabilitĂ€t, wĂ€hrend eines PhasenĂŒbergangs moduliert.
Diese ZusammenhĂ€nge könnten drastische Auswirkungen auf Zellen haben, da ihre Membranen lipidbasiert sind. Ein Nachweis fĂŒr PhasenĂŒbergĂ€nge in Zellmembranen erregbarer Zellen - die an der Weiterleitung von Nervenimpulsen beteiligt sind - wurde bisher jedoch nicht erbracht.
In dieser Arbeit wird ein optischer Ansatz zur Charakterisierung thermodynamischer PhasenzustĂ€nde in lipidbasierten GrenzflĂ€chen angewandt. Er basiert auf der Verwendung von Fluoreszenzfarbstoffen als lokale Reporter fĂŒr PhasenzustĂ€nde. Optische Zustandsdiagramme von LipidgrenzflĂ€chen werden aufgenommen und zustandsabhĂ€ngige Kinetiken innerhalb der Lipidmembranen untersucht.
Die Anwendung dieser Methodik auf einzelne neuronale Zellen zeigt eine charakteristische NichtlinearitĂ€t in der optischen Antwort des Farbstoffs (Atto488-DPPE), der auf Grundlage der Charakterisierung von Lipidmembranen als Phasenumwandlung identifiziert wird. Diese ĂbergĂ€nge sind auĂergewöhnlich scharf (1°C) und sind sensitiv auf Ănderungen im pH. Der hier erbrachte Nachweis der hochgradigen NichtlinearitĂ€t liefert die Grundlage dafĂŒr, dass der Membranzustand fĂŒr die Erregbarkeit und Weiterleitung von Nervenimpulsen entscheidend sein kann.
2022-01-01T00:00:00Z
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Rare radiative charm decays in and beyond the standard model
http://hdl.handle.net/2003/41130
Title: Rare radiative charm decays in and beyond the standard model
Authors: Adolph, Nico
Abstract: This thesis comprises a study of rare radiative |Îc| = |Îu| = 1 transitions within
and beyond the standard model of particle physics. For the 18 three-body decays
D â P1 P2 ÉŁ with đ = Ï, K decay amplitudes are derived using Lowâs theorem, QCD
factorization and heavy hadron chiral perturbation theory. Standard model predictions for
branching ratios, CP asymmetries as well as forward-backward asymmetries are determined.
Moreover, the effects of new physics in the coefficients of the electromagnetic dipole
operators are investigated respecting the current constraints. The photon polarization in
Dsâ K1(â KÏ Ï) ÉŁ decays is studied with respect to new physics effects in the dipole
coefficients. Within the standard model, the polarization parameter agrees with the SM-
like partner decay đ·+ â đŸ1 (â đŸÏ Ï)) ÉŁ up to U-spin breaking corrections. The existence
of partner decays allows to construct a null test which does not require precise knowledge
of the hadronic K1 â KÏ Ï decay. Finally, different ways to test the standard model with
rare radiative decays of charm baryons are discussed. Based on the approximate SU(3)đč
symmetry of QCD as well as its subgroups, relations between partner decays are worked
out. Branching ratios, CP asymmetries as well as the photon polarizations are considered
as observables and the potential of new physics effects is estimated. Methods for the
extraction of the photon polarization from two-body decays Bc â B ÉŁ of polarized charm
baryons as well as from decay chains Bc â B(â BâČ đ ) ÉŁ with self-analyzing hyperons đ”
are presented.
2022-01-01T00:00:00Z
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Zentrallinien-NMR an stark quadrupolar gestörten Kernen in molekularen und ionischen Kristallen
http://hdl.handle.net/2003/41129
Title: Zentrallinien-NMR an stark quadrupolar gestörten Kernen in molekularen und ionischen Kristallen
Authors: Beerwerth, Joachim
Abstract: Dynamische Prozesse in molekularen und ionischen Kristallen werden mithilfe der Zentrallinien-NMR an den stark quadrupolar gestörten Kernen 11B und 17O untersucht. Dazu werden 11B-Relaxationszeiten in Orthocarboran gemessen und diese bezĂŒglich der MolekĂŒldynamik interpretiert. In Natriumnitrat wird der Dreiplatzsprung des planaren Nitrations mittels 17O-NMR untersucht. Diese Dynamik wird mit NMR-Spektren, stimulierte Echos und Relaxationszeiten untersucht. Mithilfe von Simulationen können aus gemessenen Spektren Sprungraten bestimmt werden. Ein 17O Hochtemperaturspektrum von Natriumnitrat wird mithilfe gemittelter Tensoren beschrieben. Die Reorientierungsdynamik in Natriumnitrat weist eine Aktivierungsenergie von EA = 0,38 eV auf. Als Beispiel fĂŒr einen Tetraedersprung wird Kaliumpermanganat mithilfe der 17O-NMR untersucht. Hier wird mithilfe von stimulierten Echos eine Aktivierungsenergie von EA = 0,35 eV fĂŒr die SprĂŒnge der Sauerstoffatome bestimmt. Auch fĂŒr Kaliumpermanganat werden die Relaxationszeiten gemessen und bezĂŒglich der Reorientierungsdynamik interpretiert.; Dynamic processes in molecular and ionic crystals are investigated using central line NMR on the strongly quadrupolar perturebed nuclei 11B and 17O. For this purpose, 11B relaxation times are measured in orthocarborane and interpreted in terms of molecular dynamics. In sodium nitrate, the three side jump of the planar nitrate group is studied by 17O NMR. The dynamics of the ion are investigated by NMR spectra, stimulated echoes and relaxation times. Combining the results from simulations with measured spectra, jump rates are determined. A 17O high temperature spectrum of sodium nitrate is described using averaged tensors. The reorientational dynamics in sodium nitrate has an activation energy of EA = 0.38 eV. As an example for a tetrahedral jump, potassium permanganate is studied using 17O NMR. Here, with the aid of stimulated echoes, an activation energy of EA = 0.35 eV is determined for the jumps of oxygen atoms. The relaxation times are also measured for potassium permanganate and interpreted with respect to the reorientational dynamics.
2022-01-01T00:00:00Z
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Microwave induced plasma sources at atmospheric pressure and atomic spectroscopy
http://hdl.handle.net/2003/41122
Title: Microwave induced plasma sources at atmospheric pressure and atomic spectroscopy
Authors: Bilgic, Attila Michael
2000-01-01T00:00:00Z
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Exploiting the phenomenology of flavourful ZâČ models
http://hdl.handle.net/2003/41120
Title: Exploiting the phenomenology of flavourful ZâČ models
Authors: Bause, Rigo
Abstract: This thesis comprises recent studies on extensions of the standard model (SM) involving a heavy
Zâ boson. In the SM, flavour-changing neutral current (FCNC) quark transitions only appear at loop level and are highly suppressed. This puts forward flavourful Zâ models, where the new gauge boson couples non-universally to the known quarks and leptons at tree level. The models are able address the persistent deviations of the SM seen in observables of rare B-meson decays referred to as the
B-anomalies. By supplementing the particle content of the SM with new scalars and vector-like fermions, the occurrence of putative Landau poles present in general Zâ scenarios can be averted. We discuss dedicated models in the context of the B-anomalies that allow for a stable and predictive theory up to the Planck scale. Moreover, flavour rotations also enable FCNC transitions in the charm sector, where the resonance pollution in branching ratios of semileptonic decays demands null test observables sensitive to physics beyond the SM. We investigate effects in such decays and present unique correlations to CP-violating observables in hadronic decays, accessible with future measurements by the LHCb and Belle II experiments. Recent studies involving dineutrino modes are discussed as well. We exploit an interplay between neutrino and charged lepton couplings within the SM effective field theory approach that connects decays of opposite flavour sectors. In doing so, we derive limits on diverse sets of dineutrino branching ratios and find novel tests of lepton universality using data from global fits of the B-anomalies.; Die vorliegende Dissertation umfasst Studien zur Erweiterung des Standardmodells durch ein schweres Zâ-Boson. Flavour-verĂ€ndernde neutrale Ströme (FCNCs) von QuarkĂŒbergĂ€ngen treten im Standardmodell in höheren Ordnungen auf und sind stark unterdrĂŒckt. Die Implementation von
Zâ-Modellen ermöglicht solche ĂbergĂ€nge auf Baumgraphen-Niveau, induziert durch nicht-universelle Kopplungen an die bekannten Quarks und Leptonen. Dies liefert eine mögliche ErklĂ€rung der Diskrepanzen zwischen theoretischer Vorhersage und Messung in Observablen von seltenen B-Meson-ZerfĂ€llen, den sogenannten B-Anomalien. Das Auftreten von Landau-Polen in eben solchen Theorien kann durch das HinzufĂŒgen von neuen Teilchen zum Standardmodell-Spektrum abgewendet
werden. In dieser Arbeit untersuchen wir ausgewÀhlte Modelle, die eine direkte ErklÀrung der
B-Anomalien liefern und zusĂ€tzlich eine stabile Vorhersagekraft durch Abwesenheit von Polen und InstabilitĂ€ten bis zur Planck-Skala innehaben. Auch in seltenen charm ZerfĂ€llen können erhebliche BetrĂ€ge zu FCNCs durch das Zâ-Boson generiert werden. In diesem Sektor spielt das Aufstellen von null tests des Standardmodells, sensitiv zu Effekten neuer Physik, eine besondere Rolle, da unter anderem semi-leptonische VerzweigungsverhĂ€ltnisse durch die Verunreinigung von auftretenden Resonanzen schwer zugĂ€nglich sind. Wir befassen uns deshalb auĂerdem mit der Erforschung von Effekten neuer Physik in diesen ZerfĂ€llen und erarbeiten eindeutige Korrelationen zwischen CP-verletzenden Observablen, welche mit zukĂŒnftigen Messungen von den Experimenten LHCb und Belle II ĂŒberprĂŒft werden können. Wir prĂ€sentieren auĂerdem neue Studien zu TeilchenzerfĂ€llen in zwei Neutrinos. Durch das Zusammenspiel zwischen Kopplungen von geladenen Leptonen und Neutrinos unter Zuhilfenahme der effektiven Feldtheorie des Standardmodells bestimmen wir obere Grenzen an eine Vielzahl von Neutrino-VerzweigungsverhĂ€ltnissen, und entwickeln neue Tests der Lepton-UniversalitĂ€t.
2022-01-01T00:00:00Z
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Applications and extensions of flow equations to closed and open quantum systems
http://hdl.handle.net/2003/41108
Title: Applications and extensions of flow equations to closed and open quantum systems
Authors: Schmiedinghoff, Gary
Abstract: Flow equations, also known as continuous unitary transformations, provide a powerful renormalization tool to transform a Hamiltonian and observables to an effective basis, where they take a more amenable form. However, unitary transformations often fail for non-Hermitian Hamiltonians, which appear, for instance, in dissipative systems. Furthermore, flow equation approaches often struggle in the vicinity of critical points.
This thesis aims to cover three separate problems regarding flow equations:
Spin ladders are crucial models for the description of strongly correlated quantum systems. An advanced method of probing such systems in various excitation channels is resonant inelastic X-ray scattering, but the theoretical prediction of the corresponding spectral densities is intricate. In this thesis, we compute the spectral densities of a spin-1/2 Heisenberg ladder with the flow equation method and predict novel three-triplon bound states. We demonstrate that these bound states only arise in the presence of irreducible three-triplon interactions by exploiting the strengths of our method.
Flow equations often fail in the vicinity of a critical point due to the divergent correlation length. The method could be improved by performing it in momentum space, where strongly delocalized physics can be described more easily. To this end, we investigate the transverse-field Ising model and show that the flows of various coefficients have a common convergence behavior, which offers a prospect for considerable improvements in future works. Additionally, we propose and test truncation schemes in momentum space, which could prove useful to describe low-energy physics.
Another current problem is the description of open quantum systems, i.e. quantum systems which are affected by dissipation because they couple to an external bath. Dissipative flow equations provide a framework to treat the non-Hermitian Hamiltonians and Lindbladians appearing in such systems. We propose a novel generator scheme based on the particle-conserving generator and benchmark the convergence speed and accuracy in spite of truncation compared to previously considered generators. We demonstrate that our proposed generator scheme provides high convergence speed and excellent accuracy. Furthermore, we encapsulate all currently known dissipative generator schemes in a universal framework, which can be used to propose various novel generator schemes favoring either convergence speed or accuracy.
2022-01-01T00:00:00Z
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SPP2402-Projektantrag "Greybox-Modellierungen zum Einlaufverhalten beschichteter Werkzeuge im FrÀsprozess als dynamisches Lastkollektiv auf Basis von Operando-, IN- und Ex-situ-Analysen"
http://hdl.handle.net/2003/41101
Title: SPP2402-Projektantrag "Greybox-Modellierungen zum Einlaufverhalten beschichteter Werkzeuge im FrÀsprozess als dynamisches Lastkollektiv auf Basis von Operando-, IN- und Ex-situ-Analysen"
Authors: Debus, Jörg
Abstract: Die Datenpunkte fĂŒr die drei Kurven der Abb. 3a liegen in der txt-Datei "Abb3a" vor. Sie enthĂ€lt vier Spalten mit der Struktur (x y y y), wobei die erste Spalte die gemeinsamen Daten der x-Achse enthĂ€lt. Die anderen drei Spalten umfassen die jeweiligen y-Werte der drei Kurven (input, denoised, target).
FĂŒr die Abb. 3b mit ihren 3 Panels liegen drei txt-Dateien vor, gemÀà dem VerschleiĂzustand (initial, 9800 mm^3, 54800 mm^3). Jede Datei enthĂ€lt sechs Spalten mit xy-Daten fĂŒr jeden der drei verwendeten Cluster. Die ersten beiden Spalten enthalten die xy-Datenpunkte fĂŒr den 1. Cluster, die dritte und vierte Spalte die xy-Daten fĂŒr den 2. Cluster und die letzten beiden Spalten enthalten die xy-Daten des 3. Clusters.
Die txt-Dateien fĂŒr die Abb. 3c besitzen die gleiche Struktur wie die der Abb. 3b. ZusĂ€tzlich sind die xy-Datenpunkte fĂŒr die Regressionskurve, h(Delta E), des Panels fĂŒr 54800 mm^3 in der txt-Datei "Abb3c_54800_fitkurve" enthalten.
Die txt-Datei zur Abbildung 3d enthĂ€lt vier Spalten (x y x y). Die ersten beiden Spalten enthalten die Datenpunkte fĂŒr den initialen Zustand und die beiden letzten Spalten beschreiben den Zustand mit dem Materialabtragsvolumen 54800 mm^3.
Die txt-Datei zum Histogramm der Abb. 3e enthĂ€lt drei Spalten, welche die PrĂ€diktor-Wichtigkeit fĂŒr die Amplitude (1. Spalte), KristallitgröĂe h (2. Spalte) und HintergrundintensitĂ€t (3. Spalte) enthalten.
Die Datei zur Abbildung 3f enthĂ€lt vier Spalten (x y x y). Die ersten beiden Spalten gehören zu der grĂŒnen Kurve und die dritte und vierte Spalte zu der schwarzen Kurve der Abbildung 3f.
2022-10-17T00:00:00Z
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Dynamics and forces in the mitotic spindle
http://hdl.handle.net/2003/41095
Title: Dynamics and forces in the mitotic spindle
Authors: Schwietert, Felix
Abstract: Mikrotubuli sind zylinderförmige Filamente und Teil des Zytoskeletts. Ihre Polymerisationsdynamik zeichnet sich durch eine dynamische InstabilitĂ€t von Wachstums- und Schrumpfphasen aus. Die zufĂ€lligen Wechsel vom schrumpfenden in den wachsenden Zustand und umgekehrt werden als Rettungen bzw. Katastrophen bezeichnet. Letztere können experimentellen Beobachtungen zufolge als Mehrschrittprozesse beschrieben werden. Im ersten Teil dieser Arbeit wird das empirische Dogterom-Leibler-Modell der dynamischen InstabilitĂ€t erweitert, um auszuarbeiten, welche Auswirkungen eine Mehrschrittkatastrophe auf die LĂ€ngenverteilung eines Mikrotubulus in den Regimen gebundenen und ungebundenen Wachstums hat. Es zeigt sich, dass die MikrotubuluslĂ€ngen im gebundenen Regime nicht mehr exponentiell und weniger endlastig verteilt sind, wenn eine Katastrophe aus mehreren Schritten besteht. Wenn Rettungen möglich sind, hat die Verteilung ein Maximum und der Mikrotubulus somit eine wahrscheinlichste LĂ€nge, die gröĂer ist als 0. Im Regime ungebundenen Wachstums nĂ€hert sich die LĂ€ngenverteilung einer Normalverteilung an, die mit steigender Anzahl der Katastrophenschritte schmaler wird.
In der Mitosespindel sind Mikrotubuli durch Kinetochore mit den Chromosomen verbunden und ĂŒben so KrĂ€fte aus, die in der Metaphase zu stochastischen Oszillationen der Chromosomen fĂŒhren. Im zweiten Teil dieser Arbeit untersuchen wir in Modellen der Mitosespindel die kollektive Dynamik von Mikrotubuli, die durch elastische Federn an Kinetochore gebunden sind. Die Modelle beinhalten die dynamische InstabilitĂ€t der Mikrotubuli und die KrĂ€fte, die durch die elastischen Verbindungen wirken. FĂŒr ein einseitiges Modell mit nur einem Kinetochor, das einer externen Kraft ausgesetzt ist, können mithilfe einer MolekularfeldnĂ€herung Fokker-Planck-Gleichungen aufgestellt und gelöst werden. Aus der Lösung folgt eine bistabile AbhĂ€ngigkeit der Kinetochorgeschwindigkeit von der externen Kraft. Im zweiseitigen Modell mit zwei elastisch gekoppelten Kinetochoren fĂŒhrt die BistabilitĂ€t zu Oszillationen, die denen der Chromosomen in der Metaphase gleichen. Das Modell kann erklĂ€ren, warum in Zellen mit einem schnellen polwĂ€rtigen Mikrotubulusfluss keine Oszillationen beobachtet wurden. Polare AuswurfkrĂ€fte gewĂ€hrleisten im Modell eine Anordnung der Kinetochore am SpindelĂ€quator und fĂŒhren zu geregelteren Oszillationen mit verringerter Amplitude. Wenn das Modell so geĂ€ndert wird, dass die Mikrotubuli nur ZugkrĂ€fte auf das Kinetochor ausĂŒben können, treten Oszillationen nur unter der Voraussetzung auf, dass in der NĂ€he der Kinetochore Katastrophen induziert werden. Die Modellparameter können so angepasst werden, dass die modellierten Oszillationen auch in quantitativer Hinsicht mit Messungen in PtK1-Zellen ĂŒbereinstimmen.
Ein wichtiger Bestandteil des Kinetochors sind stĂ€bchenförmige Ndc80-Komplexe, die den Mikrotubulus binden und deren elastischen Eigenschaften als wichtig fĂŒr die KraftĂŒbertragung vom Mikrotubulus auf das Chromosom erachtet werden. Im letzten Teil dieser Arbeit wird eine Methode prĂ€sentiert, die es erlaubt, den zeitlichen Verlauf der effektiven Steifigkeit von Ndc80-Komplexen zu ermitteln, die in einer optischen Falle entgegen einer Kraft dem schrumpfenden Ende eines Mikrotubulus folgen. Die Anwendung der Methode auf mehrere Experimente zeigt, dass sowohl der Wildtyp als auch drei weitere Ndc80-Varianten steifer werden, wenn der schrumpfende Mikrotubulus sie unter Spannung setzt. Die gemessene Steifigkeit hat eine annĂ€hernd lineare AbhĂ€ngigkeit von der angelegten Kraft und ist unabhĂ€ngig vom dynamischen Zustand des Mikrotubulus. Mithilfe eines elastischen Modells kann die Versteifung auf die spezielle Architektur des Ndc80-Komplexes sowie auf das Biegen gekrĂŒmmter Protofilamente zurĂŒckgefĂŒhrt werden. Ein Modell mit einer kraftabhĂ€ngigen BindungsaffinitĂ€t reproduziert die lineare Beziehung zwischen Steifigkeit und Kraft.; Microtubules are cylindrical cytoskeletal filaments. Their polymerization dynamics is characterized by a dynamic instability between phases of growth and shrinkage. The stochastic switches from shrinkage to growth and vice versa are called rescues and catastrophes, respectively. Experimental observations characterized the latter ones as multistep processes. In the first part of this thesis, we extend the empirical DogteromâLeibler model of dynamic instability to discuss the effect that a multistep catastrophe mechanism has on the distribution of microtubule lengths in the two regimes of bounded and unbounded growth. We show that, in the former case, the steady state length distribution is non-exponential and has a lighter tail if multiple steps are required to undergo a catastrophe. If rescue events are possible, we detect a maximum in the distribution, i.e., the microtubule has a most probable length greater than zero. In the regime of unbounded growth, the length distribution converges to a Gaussian distribution whose variance decreases with the number of catastrophe steps.
In the mitotic spindle, microtubules attach to chromosomes via kinetochores, and their depolymerization forces give rise to stochastic chromosome oscillations during metaphase. In the second part of this thesis, we investigate the cooperative stochastic microtubule dynamics in spindle models consisting of ensembles of parallel microtubules, which are attached to kinetochores via elastic linkers. We include the dynamic instability of microtubules and forces on microtubules and kinetochores from elastic linkers. A one-sided model with a single kinetochore exposed to an external force is solved analytically employing a mean-field approach based on FokkerâPlanck equations. The solution establishes a bistable forceâvelocity relation of the kinetochore. Coupling the kinetochores of two such bistable systems elastically in the full two-sided model gives rise to oscillations, which can explain stochastic chromosome oscillations in metaphase. We derive constraints on linker stiffness and microtubule number for these oscillations. Including poleward microtubule flux into the model, we can provide an explanation for the experimentally observed suppression of chromosome oscillations in cells with high flux velocities. Chromosome oscillations persist in the presence of polar ejection forces, however, with a reduced amplitude and a phase shift between sister kinetochores. Moreover, polar ejection forces are necessary to align the chromosomes at the spindle equator and stabilize an alternating oscillation pattern of the two kinetochores. Finally, we modify the model such that microtubules can only exert tensile forces on the kinetochore. Then, induced microtubule catastrophes after reaching the kinetochore are necessary to stimulate oscillations. The model parameters can be adapted to reproduce experimental results for kinetochore oscillations in PtK1 cells quantitatively.
The microtubule-binding Ndc80 complex is an integral part of kinetochores and is essential to transmit forces from dynamic microtubule ends to the chromosomes. The Ndc80 complex has a rod-like appearance and its mechanical properties are considered important for the dynamic interaction between kinetochores and microtubules. In the final part of this thesis, we present a novel method that allows us to time-trace the effective stiffness of Ndc80 complexes following shortening microtubule ends against an applied force in optical trap experiments. Applying this method to wild type Ndc80 and three further variants, we reveal that each variant exhibits strain stiffening, i.e., the effective stiffness increases under tension that is built up by a depolymerizing microtubule. The strain stiffening relation is roughly linear and independent of the dynamic state of the microtubule. We introduce an elastic model, which shows that the strain stiffening can be traced back to the specific architecture of the Ndc80 complex and the bending elasticity of flaring protofilaments. The model reproduces the roughly linear strain stiffening behavior if a force-dependent binding affinity is taken into account.
2022-01-01T00:00:00Z
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Search for new physics in rare decays of đ© mesons at the LHCb experiment
http://hdl.handle.net/2003/41069
Title: Search for new physics in rare decays of đ© mesons at the LHCb experiment
Authors: Battig, Alexander
Abstract: Diese Arbeit prĂ€sentiert Suchen nach den rein leptonischen ZerfĂ€llen Bs0 â e+e- und B0 â e+e-, ebenso wie den leptonfamilienzahlverletzenden ZerfĂ€llen B+ â K+ e+ ÎŒ-. Da diese ZerfĂ€lle im Standardmodell selten oder verboten sind ermöglichen sie Nulltests des Standardmodells. AuĂerdem ermöglichen Messungen dieser KanĂ€le es Modellen von Physik jenseits des Standardmodells EinschrĂ€nkungen aufzuerlegen.
Die Suche nach den ZerfĂ€llen Bs0 â e+e- und B0 â e+e- nutzt Daten, welche vom LHCb Experiment in den Jahren 2011, 2012, 2015 und 2016 aufgezeichnet wurden und stellt die erste Suche am LHC nach diesen ZerfĂ€llen dar. Die bestimmten oberen Ausschlussgrenzen auf die VerzweigungsverhĂ€ltnisse von Bs0 â e+e- und B0 â e+e- liegen in der GröĂenordnung O(10-8), was die vorhergegangenen Ausschlussgrenzen um einen Faktor 30 verbessert.
Die Suche nach den leptonfamilienzahlverletzenden ZerfĂ€llen B+ â K+ e+ ÎŒ- nutzt den kompletten LHCb Datensatz, was obigen DatensĂ€tzen die Daten aus den Jahren 2017 und 2018 hinzufĂŒgt und so die Menge der B Mesonen im analysierten Datensatz effektiv verdoppelt. Da diese Analyse noch nicht veröffentlicht wurde, wird der Status der Analyse zum Zeitpunkt der Abfassung dieses Textes prĂ€sentiert.; In this thesis searches for the purely leptonic decays Bs0 â e+e- and B0 â e+e- as well as the lepton-flavour violating decays B+ â K+ e+ ÎŒ- are presented. As these decays are rare or forbidden in the Standard Model, these searches allow for null tests of the Standard Model. Measurements of these decays also allow to place constraints on scenarios of physics beyond the Standard Model.
The search for the decays Bs0 â e+e- and B0 â e+e- uses data collected by the LHCb experiment in the years 2011, 2012,2015 and 2016, it is the first search for these decays at the LHC. Upper limits on the brnaching fractions of Bs0 â e+e- and B0 â e+e- are set at the order of O(10-8), improving the previous limits by a factor of 30.
The search for the lepton-flavour violating decays B+ â K+ e+ ÎŒ- uses the full LHCb dataset, adding to the above the data collected in 2017 and 2018, effectively doubling the amount of B mesons in
2022-01-01T00:00:00Z
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With bottom-up to the top and beyond
http://hdl.handle.net/2003/41065
Title: With bottom-up to the top and beyond
Authors: Sedlaczek, Kevin
Abstract: In this thesis, the measurement of the inclusive and differential production cross-sections of a top quark in association with an anti-top quark at large transverse momenta in proton-proton collisions, as well as one of the first direct interpretations of such a measurement in the framework of effective field theories (EFT) are presented. The measurement is based on data collected with the ATLAS detector at the Large Hadron Collider at CERN and corresponds to an integrated luminosity of 139 fb-1. Events of the process tt â WbWbâlvbqqb in the region of large transverse momenta are analyzed. After unfolding the data to particle level, the cross-section is presented as function of several kinematic variables relevant to this process. In order to validate the predictions based on the Standard Model of particle physics, the data is compared to several predictions and effects of higher order contributions in quantum chromodynamics are investigated. In this measurement, the impact of systematic uncertainties on the energy reconstruction of jets is reduced by employing a novel method. It introduces a scaling of the energies of the jets in order to decrease discrepancies in the reconstruction of jet energies in data and the different predictions. Using this precision measurement, an indirect and model-independent search for physics beyond the Standard Model (BSM) in the framework of EFT is performed.
In particular, the effects of two EFT operators on the coupling of the top quark to gluons and other quarks are investigated. A model based on the two operators OtG and O(8)tq in the top-quark sector of the EFT framework is employed to interpret the measurement in the context of BSM physics.
Bayesian statistics is used in order to set limits on the effects of these operators via their respective Wilson coefficients CtG and C(8)tq. This analysis is among the very first direct EFT interpretations of a differential cross-section measurement in the top-quark sector. The determined limits on C(8)tq are competitive with recent global combinations, while soundly treating all parameters of the interpretation and without employing any of the assumptions, typical in global combinations. Both Wilson coefficients are found to be compatible with the SM.; In dieser Arbeit wird die Messung der inklusiven und differentiellen Produktionswirkungsquerschnitte eines Top-Quarks in Verbindung mit einem Anti-Top-Quark bei groĂen Transversalimpulsen in Proton-Proton-Kollisionen vorgestellt. Des Weiteren wird eine der ersten direkten Interpretationen einer solchen Messung im Rahmen der effektiven Feldtheorien (EFT) vorgestellt. Die Messung basiert auf Daten, die mit dem ATLAS-Detektor am Large Hadron Collider am CERN aufgenommen wurden und einer integrierten LuminositĂ€t von 139 fb-1 entsprechen.
Es werden Ereignisse des Prozesses tt â WbWbâlvbqqb im Bereich groĂer Transversalimpulse analysiert. Nach der Entfaltung der Daten auf Teilchenebene wird der Wirkungsquerschnitt als Funktion mehrerer, fĂŒr diesen Prozess relevanter, kinematischer Variablen untersucht. Um die Vorhersagen auf der Grundlage des Standardmodells der Teilchenphysik zu ĂŒberprĂŒfen, werden die Messungen mit verschiedenen Vorhersagen verglichen und die Auswirkungen von Korrekturen höherer Ordnung in der Quantenchromodynamik untersucht. Bei dieser Messung werden die Auswirkungen systematischer Unsicherheiten auf die Energierekonstruktion von Jets durch den Einsatz einer neuartigen Methode verringert. Dazu wird eine Skalierung der Energien der Jets eingefĂŒhrt, um die Diskrepanzen bei der Rekonstruktion der Jet-Energien in den Daten und den verschiedenen Vorhersagen zu verringern. Mit dieser PrĂ€zisionsmessung wird eine indirekte und modellunabhĂ€ngige Suche nach Physik jenseits des Standardmodells (BSM) im Rahmen der EFT durchgefĂŒhrt. Insbesondere werden die Auswirkungen von zwei EFT-Operatoren auf die Kopplung des Top-Quarks an Gluonen und andere Quarks untersucht. Ein Modell, das auf den beiden Operatoren OtG und O(8)tq im Top-Quark-Sektor der EFT basiert, wird zur Interpretation der Messung im Kontext von Suchen nach BSM-Physik konstruiert und verwendet. Mit Hilfe der Bayes'schen Statistik werden die Auswirkungen dieser Operatoren ĂŒber ihre jeweiligen Wilson-Koeffizienten CtG und C(8)tq begrenzt.
Diese Analyse ist eine der ersten direkten EFT-Interpretationen einer differentiellen Wirkungsquerschnittsmessung im Top-Quark-Sektor. Die ermittelten erlaubten Parameterbereiche fĂŒr C(8)tq sind konkurrenzfĂ€hig mit den jĂŒngsten globalen Kombinationen, wobei alle Parameter der Interpretation konsistent behandelt werden und keine der fĂŒr globale Kombinationen typischen Annahmen getroffen werden. Beide Wilson-Koeffizienten erweisen sich als kompatibel mit dem SM.
2022-01-01T00:00:00Z
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Measurements of decays in the B->DD family at the LHCb experiment
http://hdl.handle.net/2003/41060
Title: Measurements of decays in the B->DD family at the LHCb experiment
Authors: Mödden, Antje
Abstract: Precision measurements of CKM-matrix elements are used to test the Standard Model of particle physics. Decays of Bs0 mesons that proceed via bâ ccs transitions are used to measure the CP -violating weak mixing phase Ïs that is directly related to the CKM angle ÎČs and has a precise theoretical prediction. The mixing phase Ïs can be measured using Bs0 â Ds+Dsâ decays, where higher-order Standard Model effects can be assessed by exploiting results from analyses in additional decays of the B â DD family. These analyses comprise CP -violation and branching-ratio measurements. Two different analyses of B â DD decays are presented, which utilise data collected by the LHCb experiment.
A search for the Bs0 â Dâ±Dâ decay is presented using data corresponding to an integrated luminosity of 9 fbâ1 collected at centre-of-mass energies of 7, 8 and 13 TeV. The Bs0 â Dâ±Dâ decay is observed and its branching fraction is measured for the first time.
The ongoing measurement of CP violation in Bs0 â Ds+Dsâ decays uses data corresponding to 6 fbâ1 collected at 13 TeV. The measurement of the CP parameters is still kept blind, but the sensitivities to the CP parameters are evaluated and indicate that this will be the most precise measurement in this decay channel.; PrĂ€zisionsmessungen von Parametern der CKM Matrix werden durchgefĂŒhrt, um das Standardmodell der Teilchenphysik zu untersuchen. ZerfĂ€lle von Bs0-Mesonen mit b â ccs ĂbergĂ€ngen werden verwendet, um die CP -verletzende schwache Mischungsphase Ïs zu bestimmen, welche direkt mit dem CKM Winkel ÎČs zusammenhĂ€ngt und eine prĂ€zise theoretische Vorhersage hat. Die schwache Mischungsphase Ïs kann in Bs0 â Ds+Dsâ ZerfĂ€llen gemessen werden, wobei Effekte höherer Ordnung durch Ergebnisse von Analysen zusĂ€tzlicher ZerfĂ€lle der B â DD Familie abgeschĂ€tzt werden können. Diese Analysen umfassen Messungen von CP -Verletzung und VerzweigungsverhĂ€ltnissen. Es werden zwei unterschiedliche Analysen solcher ZerfĂ€lle vorgestellt, welche Daten des LHCb-Experiments nutzen.
Die Analyse von Bs0 â Dâ±Dâ ZerfĂ€llen verwendet Daten, die einer integrierten LuminositĂ€t von 9fbâ1 entsprechen und bei Schwerpunktsenergien von 7, 8 und 13TeV aufgenommen wurden. Der Bs0 â Dâ±Dâ Zerfall wird erstmals beobachtet und das VerzweigungsverhĂ€ltnis gemessen.
Die Messung von CP Verletzung in Bs0 â Ds+Dsâ ZerfĂ€llen ist noch nicht abgeschlossen. Es werden Daten verwendet, die 6 fbâ1 entsprechen und bei einer Schwerpunktsenergie von 13TeV aufgenommen wurden. Die Messung der CP-Parameter ist noch blind, aber die SensitivitĂ€ten können evaluiert werden. Es wird die prĂ€ziseste Messung von CP -Verletzung in diesem Zerfallskanal erwartet.
2022-01-01T00:00:00Z
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Coherent spin dynamics and carrier-nuclear interaction in lead halide perovskite crystals
http://hdl.handle.net/2003/41040
Title: Coherent spin dynamics and carrier-nuclear interaction in lead halide perovskite crystals
Authors: Kirstein, Johan Erik
Abstract: In the present work, the charge carrier spin dynamics in lead halide perovskites APbX3,
with X = {I,Br,Cl} are studied. The lead halide perovskites are distinguished with respect
to the groups of purely inorganic perovskites with A = Cs and hybrid organic inorganic
ones with A = {MA,FA} (methylammonium and formamidinium), as well as their size, i.
e. macroscopic single crystals or nano crystals. The spin dynamics of the charge carriers,
electrons and holes, are mainly investigated using picosecond resolution Kerr and Faraday
spectroscopy. In addition, the observation of the spin dynamics is complemented by exciton
spectroscopy (polarization-resolved photoluminescence, reflection, and transmission) and
time-resolved differential reflectometry. Nanosecond spin dynamics are observed and the
underlying interaction mechanisms are revealed by the experimental techniques, with a focus
on interaction of charge carrier and nuclear spins.; In der vorliegenden Arbeit wird die LadungstrÀger-Spindynamik in Blei-Halogen-Perowskiten
APbX3, mit X = {I,Br,Cl} untersucht. Die Blei-Halogen-Perowskite werden in rein inorganische
Perowskite mit A =Cs und hybride organisch-inorganische mit A = {MA,FA}
(Methylammonium and Formamidinium) sowie in ihrer GröĂe als makroskopische Einkristalle
und Nanokristalle unterschieden. Die Spindynamik der LadungstrÀger, Elektronen und Löcher,
wird hauptsÀchlich anhand von Kerr- und Faraday-Spektroskopie mit einer Pikosekunden
Auflösung untersucht. ZusÀtzlich wird die Spindynamik durch Exzitonen-spektroskopie (polarisationsaufgelöste
Photolumineszenz, Reflektion und Transmission) sowie durch zeitaufgelöste
differentielle Reflektrometrie untersucht. Es werden nanosekundenlange Spindynamiken
beobachtet, deren zugrundeliegende Wechselwirkungsmechanismen durch die experimentellen
Techniken aufgedeckt werden. Ein Schwerpunkt liegt hierbei auf der Untersuchung der
LadungstrÀger-Kern-Spinwechselwirkung.
2022-01-01T00:00:00Z
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|Îc| = |Îu| = 1 transitions in and beyond the standard model
http://hdl.handle.net/2003/41012
Title: |Îc| = |Îu| = 1 transitions in and beyond the standard model
Authors: Golz, Marcel
Abstract: This thesis comprises a study of rare semileptonic |Îc|=|Îu|=1 transitions in the Standard Model and beyond. The Standard Model phenomenology of three-body meson decays Dâ Pll, as well as three- and four-body charmed baryon decays B0 â B1 (â B2 Ï) ll, is analyzed and branching ratios are found to be dominated by resonances. Physics effects beyond the Standard Model are studied model-independently as well as in the framework of leptoquark- and flavorful, anomaly-free Zâ-models. Resonance dominance is shown to be overcome or even used as a catalyst in analyses of clean null-test observables, where any signal indicates new physics. Null tests are based on angular observables, CP-conservation, lepton flavor universality and charged lepton flavor conservation. Already a subset of four angular observables in three- and four-body rare charm baryon decays are sufficient to disentangle beyond Standard Model effects in dipole and (axial) vector Wilson coefficients, whereas (semi-)leptonic rare meson decays Dâ (P)ll are shown to control (pseudo-)scalar and (pseudo-)tensor effects. A global view on connections between different flavor sectors is put forward in the context of flavor summed dineutrino branching ratios. Indirect tests of lepton flavor universality and charged lepton flavor conservation are presented for the charm sector, where dineutrino modes already pose null tests of the Standard Model. In |Îb|=|Îs|=1 transitions, the first evidence for the violation of lepton flavor universality is found in muon over electron ratios of B-meson branching fractions. Complementing the direct probes, dineutrino modes are shown to test charged lepton flavor indirectly in the correlation of B â PΜΜ and B â VΜΜ. Similarly, indirect flavor probes in other quark sectors are also commented on.
2022-01-01T00:00:00Z
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Measurements of CP violation in B0â DD decays at the LHCb experiment
http://hdl.handle.net/2003/41005
Title: Measurements of CP violation in B0â DD decays at the LHCb experiment
Authors: Ibis, Philipp
Abstract: Precise measurements of CKM matrix parameters to probe the Standard Model of particle physics are a main focus of current flavour-physics experiments. Analyses of B â DD decays allow to assess higher-order Standard Model corrections in these measurements. Two decay-time-dependent measurements of CP violation in different B0 â DD decay modes are presented using data collected by the LHCb experiment.
The analysis of B0 â Dâ±Dâ decays utilises data corresponding to an integrated luminosity of 9 fbâ1 collected at centre-of-mass energies of 7, 8 and 13 TeV. The results of the CP parameters correspond to the most precise measurement in this channel. They are consistent with the previous world average.
The analysis of B0 â D+Dâ decays uses data corresponding to 6 fbâ1 collected at 13 TeV. The analysis is ongoing and currently still blind. The evaluated sensitivities show that this will be the most precise measurement of CP violation in this channel.; Ein Schwerpunk von aktuellen Flavourphysik-Experimenten sind PrĂ€zisionsmessungen von Parametern der CKM-Matrix zur Untersuchung des Standardmodells der Teilchenphysik. Auswertungen von B â DD ZerfĂ€llen erlauben es Standardmodell-Korrekturen höherer Ordnung in diesen Messungen zu untersuchen. Es werden zwei Messungen von CP Verletzung in unterschiedlichen B0 â DD ZerfallskanĂ€len prĂ€sentiert, die Daten des LHCb Experimentes benutzen.
Die Analyse von B0 â Dâ±Dâ ZerfĂ€llen wird mit einem Datensatz durchgefĂŒhrt, der einer integierten LuminositĂ€t von 9 fbâ1 entspricht und bei Schwerpunktsenergien von 7, 8 and 13 TeV aufgenommen wurde. Die Ergebnisse der CP -Parameter entsprechen der prĂ€zisesten Messung in diesem Kanal. Sie sind konsistent mit den vorherigen Weltmittelwerten.
Die Analyse des B0 â D+Dâ Zerfalls benutzt Daten, die 6 fbâ1 entsprechen und bei 13TeV aufgenommen wurden. Die Analyse ist noch nicht abgeschlossen und noch blind. Die Unsicherheiten werden bewertet und die prĂ€ziseste Messung von CP-Verletzung in diesem Kanal erwartet.
2022-01-01T00:00:00Z
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Nonlinear optical functionalities of VO2- and GaN-based nanocomposites
http://hdl.handle.net/2003/41002
Title: Nonlinear optical functionalities of VO2- and GaN-based nanocomposites
Authors: Mundry, Jan
Abstract: This thesis presents fundamental research and concepts for active photonic elements operating in the telecom wavelength regime. The aim of the study is to determine the characteristics of the investigated nanostructures and to evaluate the implementation of the proposed materials in potential optical devices.
In the first part of this thesis the optical properties as well as the photonic application of vanadium dioxide (VO2) nanocrystals (NCs) are studied. VO2 exhibits an easily accessible insulator-to-metal phase transition (IMT) near ambient temperatures. Upon excitation it undergoes an atomic rearrangement that is accompanied by a substantial modification of the complex dielectric function. When VO2 undergoes the IMT, the near-infrared transmission peaks of a moderate-finesse etalon containing a sub-wavelength layer of VO2 NCs are found to markedly shift in their spectral position and peak transmissivity. Both heat deposition and optical excitation permit to actively control the etalonâs functionality.
Much less is known about the nonlinear optical properties of VO2 beyond the established IMT. To this end the nonlinear optical response of a thin film of VO2 NCs is investigated with open aperture z-scans involving femtosecond near-infrared pulses. A pronounced saturable absorption on the short-wave side of the resonance as well as a marked reverse saturable absorption in the telecom window are observed. The results hold promise for the use of VO2 nanocrystals as a saturable absorber, e.g., to mode-locked near-infrared lasers.
In the second part a semiconductor heterostructure based on hexagonal ultranarrow GaN/AlN multi-quantum wells (MQWs) is investigated. The tailored inter-miniband (IMB) transition is characterized in terms of its linear as well as ultrafast nonlinear optical properties using the established pump-probe scheme. In line with theoretical predictions for LO-phonon scattering, a fast relaxation is found for resonant IMB excitation. In stark contrast, significantly larger relaxation times are observed for photon energies addressing the above barrier continuum.
The last section reports on a new type of nonlinear metasurface taking advantage of these telecom-range IMB transitions. The heterostructure is functionalized with an array of plasmonic antennas featuring cross-polarized resonances at these near-infrared wavelengths and their second harmonic. This kind of nonlinear metasurface allows for substantial second harmonic generation at normal incidence which is completely absent for an antenna array without the heterostructure underneath.
2022-01-01T00:00:00Z
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Test of lepton flavour universality with rare beauty-quark decays at the LHCb experiment
http://hdl.handle.net/2003/40985
Title: Test of lepton flavour universality with rare beauty-quark decays at the LHCb experiment
Authors: Seuthe, Alex
Abstract: Recent measurements of the lepton flavour universality show evidence of a violation of the Standard
Model of particle physics. However, further investigation with higher sensitivity is needed to either
falsify or confirm the anomalies. This thesis describes the first simultaneous measurement of the lepton
flavour universality ratios đ
đŸ with đ”+ â đŸ +â+ââ decays and đ
đŸâ0 with đ”0 â đŸâ0â+ââ decays using the
entire current available data set of the LHCb experiment recorded during the years 2011 to 2018. Both
ratios are evaluated in two regions of đ2, which is the squared invariant mass of the dilepton system.
Even though the central values of the results are kept blind and will only be published once the analysis
has passed the collaboration-internal review process, the presented sensitivities on đ
đŸ and đ
đŸâ0 already
show that this will be the most precise test of lepton flavour universality with these decays to date. The
analysis work described in this thesis comprises the first measurement of đ
đŸ at low đ2 at LHCb and an
updated measurement of đ
đŸâ0 with an enlarged data set. Statistical and systematic uncertainties as well
as correlations between the four measurements are thus determined coherently for the first time and
allow for improved interpretations. The calibration of the simulation used to determine the selection
efficiency is a crucial component of the analysis to ensure that deviations of the measurements from
the Standard Model expectation are not an effect due to remaining imperfections of the simulation.
Therefore, a complex multi-stage calibration procedure has been developed together with an optimised
selection strategy. Simulation of the signal decays is calibrated with the help of high-yield control
samples chosen to minimise correlations between calibration and signal data sets. The experimental
procedure of the analysis is validated by multiple stringent cross-checks.; JĂŒngste Messungen der Lepton-Flavour-UniversalitĂ€t zeigen deutliche Hinweise auf eine Verletzung
des Standardmodells der Teilchenphysik. Es sind jedoch weitere Untersuchungen erforderlich, um die
Anomalien mit erhöhter SensitivitÀt zu bestÀtigen oder zu falsifizieren. Diese Dissertation beschreibt die
erste simultane Messung der Lepton-Flavour-UniversalitĂ€ts-VerhĂ€ltnisse đ
đŸ mit đ”+ â đŸ +â+ââ-ZerfĂ€llen
und đ
đŸâ0 mit đ”0 â đŸâ0â+ââ-ZerfĂ€llen unter Verwendung des gesamten derzeit verfĂŒgbaren Datensatzes
des LHCb-Experiments, der in den Jahren 2011 bis 2018 aufgezeichnet wurde. Beide VerhÀltnisse werden
in jeweils zwei Bereichen von đ2, der quadrierten invarianten Masse des Dilepton-Systems, bestimmt.
Auch wenn die Zentralwerte der Ergebnisse blind sind und erst veröffentlicht werden, wenn die Analyse
den kollaborationsinternen ĂberprĂŒfungsprozess durchlaufen hat, zeigen die vorgestellten SensitivitĂ€ten
fĂŒr đ
đŸ und đ
đŸâ0 bereits, dass dies der bisher genaueste Test der Lepton-Flavour-UniversalitĂ€t mit diesen
ZerfÀllen sein wird. Die in dieser Dissertation beschriebene Analysearbeit umfasst die erste Messung
von đ
đŸ im unteren đ2-Bereich mit dem LHCb-Experiment und eine aktualisierte Messung von đ
đŸâ0
mit einem vergröĂerten Datensatz. Statistische und systematische Unsicherheiten sowie Korrelationen
zwischen den vier Messungen werden dadurch erstmals kohÀrent bestimmt und ermöglichen verbesserte
Interpretationen. Die Kalibrierung der Simulation, welche zur Bestimmung der Selektionseffizienz
verwendet wird, ist ein entscheidender Bestandteil der Analyse, um sicherzustellen, dass eine mögliche
Abweichung der Messung von der Erwartung des Standardmodells nicht ein Effekt durch verbliebene
Imperfektionen der Simulation ist. Daher wurde ein komplexes mehrstufiges Kalibrierungsverfahren
zusammen mit einer optimierten Selektionsstrategie entwickelt. Die Kalibrierung wird mit Hilfe von
KontrollkanĂ€len durchgefĂŒhrt, die so ausgewĂ€hlt werden, dass die Korrelationen zwischen Kalibrierungsund
SignaldatensÀtzen minimiert werden. Das experimentelle Verfahren der Analyse wird durch mehrere
stringente Cross-Checks validiert.
2022-01-01T00:00:00Z
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Non-degenerate two-photon absorption in bulk ZnSe, GaAs and Si
http://hdl.handle.net/2003/40984
Title: Non-degenerate two-photon absorption in bulk ZnSe, GaAs and Si
Authors: KrauĂ-Kodytek, Laura
Abstract: The two-photon absorption is a nonlinear optical process with various properties which makes it an excellent basis for a wide range of different applications. In this thesis the non-degenerate two-photon absorption coefficient ÎČ(Ï1, Ï2) as a function of the frequency ratio Ï1/Ï2 of the two driving fields is experimentally investigated whereby the sum energy ħÏ1 + ħÏ2 is kept constant. The studied materials are the prototypical semiconductors ZnSe, GaAs and Si. Regardless of the direct or indirect character of the bandgap, the two-photon absorption strength increases with increasing ratio Ï1/Ï2 â„ 1.The experimental data of ZnSe and GaAs agrees well with corresponding theoretical predictions for direct semiconductors. Si shows overall smaller absorption strengths. These results also agree with theoretical predictions for indirect semiconductors. In addition, different crystallographic orientations of the samples and polarization configurations of the two driving fields are analyzed. These results make an important contribution to the so far rarely investigated orientation and polarization anisotropy of the non-degenerate two-photon absorption.; Die Zwei-Photonen-Absorption ist ein nichtlinearer optischer Prozess mit diversen Eigenschaften, welche sie zu einer ausgezeichneten Grundlage fĂŒr ein breites Spektrum verschiedener Anwendungen macht. In dieser Arbeit wird der nicht-entartete Zwei-Photonen-Absorptionskoeffizient ÎČ(Ï1, Ï2) als Funktion des FrequenzverhĂ€ltnisses Ï1/Ï2 bei einer konstanten Ăbergangsenergie ħÏ1 + ħÏ2 experimentell untersucht. Die verwendeten Materialien sind die Halbleiter ZnSe, GaAs und Si. UnabhĂ€ngig von dem direkten oder indirekten Charakter der BandlĂŒcke steigt die Zwei-Photonen-AbsorptionsstĂ€rke mit zunehmendem VerhĂ€ltnis Ï1/Ï2 â„ 1. Die experimentellen Daten von ZnSe und GaAs stimmen sehr gut mit den entsprechenden theoretischen Vorhersagen fĂŒr direkte Halbleiter ĂŒberein. Bei Si zeigen sich im Vergleich insgesamt geringere AbsorptionsstĂ€rken. Auch hier stimmen die Ergebnisse mit den theoretischen Vorhersagen fĂŒr indirekte Halbleiter ĂŒberein. DarĂŒber hinaus werden verschiedene kristallographische Orientierungen der Proben und unterschiedliche Polarisationseinstellungen der beiden anregenden optischen Felder analysiert. Diese Ergebnisse leisten einen wichtigen Beitrag zu der bisher wenig untersuchten Orientierungs- und Polarisationsanisotropie der nicht-entarteten Zwei-Photonen-Absorption.
2022-01-01T00:00:00Z
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Optical action potential
http://hdl.handle.net/2003/40931
Title: Optical action potential
Authors: Fabiunke, Simon
Abstract: Voltage sensitive dyes have been used as an alternative route to detect membrane potentials. This replaces electrophysiological equipment and allows to study action potentials with optical tools. Changes in fluorescence emission are most commonly translated into changes in transmembrane potentials. In this thesis, it is demonstrated that the emission energy of the fluorescent dye Di-4-ANEPPDHQ is a state variable. Incorporation of the dye in artificial lipid membranes, where ion transport is obsolete, changes of the emission spectrum as a function of lateral pressure and temperature were detected, as well as in the presence of lateral propagating pulses. It is found that despite the complete absence of transmembrane ion movement, the spectrum shifted about 20 nm at the main transition, which falsifies the Nernst-potential as the origin of the changes in emission.
To underline the relevance for action potentials in living systems, the same dye is incorporated into an excitable plant cell to investigate action potentials. There, a very similar blue shift of the emission spectrum is found as in the monolayer pulse experiments. In summary, these experiments show that Di-4-ANEPPDHQ (presumably all dyes), should be seen as a phase state reporter. This is entirely consistent with the interpretation of the nervous impulse as a propagating state change as has been proposed by others. This interpretation allows to map the state and state changes optically not only of nerves, but even of the entire brain.; Spannungssensitive Fluoreszenzfarbstoffe werden in der Zellforschung als Alternative zur Vermessung von Membranpotentialen verwendet. Dadurch werden elektrophysiologische GerĂ€te ersetzt und Nervenpulse werden durch optische Techniken vermessen. Die Ănderung des Emissionsspektrums werden ĂŒblicherweise in Ănderungen des Membranpotentials ĂŒbersetzt. In den Experimenten dieser Arbeit wird gezeigt, dass die Emissionseigenschaften des Farbstoffes Di-4-ANEPPDQH eine Variable des thermodynamischen Zustandes ist. Einbettung in kĂŒnstliche Lipid-Systeme (Monolayer, Vesikel), in denen kein Ionentransport stattfindet, zeigen Ănderungen der Emission sowohl als Funktion des lateralen Drucks, der Temperatur als auch in Anwesenheit von akustischen Pulsen. Es kommt zu einer Verschiebung des Emissionsspektrums um ca. 20 nm wĂ€hrend der Hauptphasenumwandlung der untersuchten kĂŒnstliche Systeme. Um die Relevanz fĂŒr biologische Prozesse zu unterstreichen, wurden gleiche Untersuchungen in einer erregbaren Pflanzenzelle vorgenommen. Es konnte eine signifikante Ăhnlichkeit der Aktionspotentiale zu den akustischen Pulsen in Lipidmonolagen im optischen Signal gezeigt werden. Zusammenfassend zeigen die Experimente der Arbeit, dass Di-4-ANEPPDHQ (vermutlich alle Farbstoffe) als Zustandsreporter gesehen werden können. Dies ist konsistent zu der Annahme, dass es sich bei Nervenpulsen um eine propagierende Phasenumwandlung handelt. Diese Interpretation der Fluoreszenz lĂ€sst nicht nur die Vermessung des Zustandes von Nerven zu, sondern auch des gesamten Gehirns.
2021-01-01T00:00:00Z
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Nuclear physics in proton therapy: new approaches for proton beam range verification using delayed gamma-rays
http://hdl.handle.net/2003/40922
Title: Nuclear physics in proton therapy: new approaches for proton beam range verification using delayed gamma-rays
Authors: BĂ€cker, Claus Maximilian
Abstract: In-vivo monitoring of the delivered dose is desirable in radiation therapy. Radionuclides generated during the proton irradiation can be used for imaging methods from nuclear medicine after the treatment session. In order to improve these techniques, this work focuses on three different aspects of nuclear physics from basic nuclear physics measurements to a clinical validation. The most relevant nuclear interaction is the production of C-11 from carbon as this nuclear interaction is used as a monitor reaction for the measurement of several other radionuclides. Furthermore, this is one of the relevant residuals produced from the tissue nuclei. As the data from the literature scatter by about 15%, a new reference cross section value of (68 ± 3) mb at 97 MeV is determined from the cross sections measured in different settings. In a second part, the activation of iodine during proton irradiation is investigated. Several radionuclides are produced from iodine which decay by the emission of positrons and can potentially be used for PET imaging subsequent to the fractional treatment. In the last step, the activation of titanium implants is investigated. A benchmarking test including MC simulations is performed which study reveals the limited applicability of PET imaging with implants for field verification in proton therapy.; Die Ăberwachung der applizierten Dosisverteilung in der Strahlentherapie kann zur Optimierung der Therapie genutzt werden. WĂ€hrend der Protonenbestrahlung erzeugte Radionuklide können nach der Behandlungssitzung zur Bildgebung mit Methoden aus der Nuklearmedizin verwendet werden. Die vorliegende Arbeit untersucht drei verschiedene kernphysikalische Aspekte von der Untersuchung von Kernreaktionen hin zu einer klinischen Validierung, um diese Techniken zu verbessern. ZunĂ€chst wird die Produktion von C-11 aus Kohlenstoff untersucht, da diese Reaktion in der Kernphysik als Monitorreaktion verwendet wird. Die Literaturwerte der Wirkungsquerschnitte variieren um bis zu 15%. AuĂerdem stellt diese Reaktion eine wichtige Produktion von Radionukliden in menschlichem Gewebe dar. Als neuer Referenzwert kann (68 ± 3) mb bei einer Energie von 97 MeV bestimmt werden. In einem weiteren Schritt wird die Aktivierung von Iod untersucht. Da viele Positronenemitter bei der Bestrahlung von Iod produziert werden, kann die Aktivierung von Iod zur PET Bildgebung verwendet werden. Als letztes wird die Aktivierung von Titanimplantaten betrachtet. Dazu wird dazu ein SensitivitĂ€tstest inklusive der AktivitĂ€tsvorhersage durchgefĂŒhrt, der die beschrĂ€nkten Einsatzmöglichkeiten der PET Bildgebung zur Feldverifikation in der Protonentherapie aufzeigt.
2022-01-01T00:00:00Z
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The silicon strip detector of the ATLAS Inner Tracker: from individual sensing units to multi-module petal structures
http://hdl.handle.net/2003/40906
Title: The silicon strip detector of the ATLAS Inner Tracker: from individual sensing units to multi-module petal structures
Authors: Renardi, Alessia
Abstract: Nowadays particle detector technology is taking big steps forwards and new devices
dedicated to particle physics show very high performance. Particularly the semiconductor
detectors have advanced significantly and are used for tracking purposes
in the A Toroidal LHC ApparatuS (ATLAS) experiment at CERN thanks to their
excellent spacial resolution: the compact size of the silicon and its high granularity
allow to reach a precision measurement of few tens of microns.
This thesis is focused on the upgrade of the ATLAS tracking detector required for the
High Luminosity Large Hadron Collider (HL-LHC), starting in 2027. The HL-LHC
foresees an integrated luminosity of L = 3000 fbâ1, which comes with an unprecedented
rate of proton collisions, with a pile-up of h i = 200, and very high radiation
doses. As the current inner detector has not been designed for the HL-LHC environmental
conditions, an all-silicon Inner Tracker (ITk) will take its place during
Phase-II upgrade of the ATLAS experiment.
The ITk strip endcap sub-detector is the main topic of this PhD project. The investigation
covers the assembly of silicon strip endcap modules and their loading on
a local support structure. The building and loading procedures are presented as well
as results of quality control (QC) tests carried out on prototyping components to
establish their working performance and the fulfillment of the specifications. This
work provides the procedure optimization in order to achieve the requirements imposed
by the collaboration.
Results on prototyping components, such as a fully electrical module and a semielectrical
petal, both built and tested at DESY, are presented. They are followed by
tests on an electrical petal performed at low temperature with the evaporative CO2
cooling technique. The QC tests carried out on all prototypes have demonstrated
that they have been properly assembled and are fully functional. Moreover they
fulfil the respective requirements validating therefore the components design and the
building methods.; In der heutigen Zeit macht die Detektortechnologie groĂe Fortschritte, und neue
GerĂ€te fĂŒr die Teilchenphysik sind sehr leistungsstark. Insbesondere die Halbleiterdetektoren
haben sich erheblich weiterentwickelt und werden dank ihrer exzellenten
rÀumlichen Auflösung im A Toroidal LHC ApparatuS (ATLAS) Experiment am
CERN fĂŒr die Spurrekonstruktion eingesetzt. Die dĂŒnnen Siliziumsensoren sowie die
hohe GranularitÀt ermöglichen PrÀzisionsmessungen mit einer Auflösung von einigen
zehn Mikrometern.
Die vorliegende Arbeit befasst sich mit dem Upgrade des ATLAS-Spurdetektors,
das fĂŒr den im Jahr 2027 in Betrieb gehenden High Luminosity Large Hadron Collider
(HL-LHC) erforderlich ist. Der HL-LHC sieht eine integrierte LuminositÀt von
L = 3000 fbâ1 vor, was mit einer bisher unerreichten Rate von Protonkollisionen mit
einem Pile-up von h i = 200 und sehr hohen Strahlungsdosen einhergeht. Da der
derzeitige innere Spurdetektor nicht fĂŒr die Umgebungsbedingungen des HL-LHC
ausgelegt ist, wird er wÀhrend des Phase-II-Upgrades durch den neuen, vollstÀndig
aus Siliziumsensoren bestehenden Inner Tracker (ITk) ersetzen werden.
Der ITk-Streifen-Endkappen-Subdetektor ist das Hauptthema dieses PhD-Projekts.
Es umfasst den Zusammenbau von Siliziumstreifen-Endkappenmodulen und deren
Montage auf einer lokalen TrÀgerstruktur. Es werden die Konstruktions- und Montageverfahren
sowie die Ergebnisse von QualitÀtskontrolltests vorgestellt, die an Prototypkomponenten
durchgefĂŒhrt wurden, um deren FunktionalitĂ€t sowie die ErfĂŒllung
der Spezifikationen sicherzustellen. Im Rahmen dieser Arbeit wurden die Verfahren
optimiert, um die von der Kollaboration gestellten Anforderungen zu erfĂŒllen.
Es werden Ergebnisse zu Prototypkomponenten, wie beispielsweise einem vollstÀndig
elektrischen Modul und einem halbelektrischen Petals vorgestellt, die beide bei DESY
gebaut und getestet wurden. Des Weiteren werden Tests an einem elektrischen Petal
vorgestellt, die bei niedrigen Temperaturen mit der CO2-VerdunstungskĂŒhltechnik
durchgefĂŒhrt wurden. Die an allen Prototypen durchgefĂŒhrten QualitĂ€tskontrolltests
haben gezeigt, dass sie ordnungsgemÀà zusammengebaut wurden und voll funktionsfÀhig
sind. DarĂŒber hinaus erfĂŒllen sie die entsprechenden Anforderungen, so
dass das Design der Komponenten und die Bauverfahren validiert wurden.
2022-01-01T00:00:00Z
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Explanation, Reduction, Progress
http://hdl.handle.net/2003/40887
Title: Explanation, Reduction, Progress
Authors: Scheibe, Erhard
1987-01-01T00:00:00Z
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Experimental consolidation and absolute measurement of the nat C(p,x)11 C nuclear activation cross section at 100 MeV for particle therapy physics
http://hdl.handle.net/2003/40825
Title: Experimental consolidation and absolute measurement of the nat C(p,x)11 C nuclear activation cross section at 100 MeV for particle therapy physics
Authors: BÀcker, Claus Maximilian; Horst, Felix; Adi, Wihan; BÀumer, Christian; Gerhardt, Marcel; Jentzen, Walter; Kazek, Sandra Laura; Kröninger, Kevin; Schuy, Christoph; Verbeek, Nico; Weingarten, Jens; Wulff, Jörg; Timmermann, Beate
Abstract: The natC(p,x)11C reaction has been discussed in detail in the past [EXFOR database, Otuka et al. (Nuclear Data Sheets 120:272â276, 2014)]. However, measured activation cross sections by independent experiments are up to 15% apart. The aim of this study is to investigate underlying reasons for these observed discrepancies between different experiments and to determine a new consensus reference cross section at 100 MeV. Therefore, the experimental methods described in the two recent publications [Horst et al. (Phys Med Biol https://doi.org/10.1088/1361-6560/ab4511 [Titel anhand dieser DOI in Citavi-Projekt ĂŒbernehmen] , 2019) and BĂ€cker et al. (Nuclear Instrum Methods Phys Res B 454:50â55, 2019)] are compared in detail and all experimental parameters are investigated for their impact on the results. For this purpose, a series of new experiments is performed. With the results of the experiments a new reference cross section of (68±3) mb is derived at (97±3) MeV proton energy. This value combined with the reliably measured excitation function could provide accurate cross section values for the energy region of proton therapy. Because of the well-known gamma-ray spectrometer used and the well-defined beam characteristics of the treatment machine at the proton therapy center, the experimental uncertainties on the absolute cross section could be reduced to 3%. Additionally, this setup is compared to the in-beam measurement setup from the second study presented in the literature (Horst et al. 2019). Another independent validation of the measurements is performed with a PET scanner.
2021-08-02T00:00:00Z
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Analysis of the fine structure of the D-exciton shell in cuprous oxide
http://hdl.handle.net/2003/40801
Title: Analysis of the fine structure of the D-exciton shell in cuprous oxide
Authors: Heckötter, Julian; Rommel, Patric; Main, Jörg; AĂmann, Marc; Bayer, Manfred
Abstract: The exciton states in cuprous oxide show a pronounced fine structure splitting associated with the crystal environment and the resulting electronic band structure. High-resolution spectroscopy reveals an especially pronounced splitting of the yellow D excitons with one state pushed above any other state with the same principal quantum number. This large splitting offset is related to a strong mixing of these D states with the 1S exciton of the green series, as suggested by previously published calculations. Here, a detailed comparison of this theory with experimental data is given, which leads to a complete reassignment of the experimentally observed D exciton lines. The origin of different amounts of green admixture to D-envelope states is deduced by analyzing the different terms of the Hamiltonian. The yellowâgreen mixing leads to level repulsion and induces an exchange interaction splitting to D-envelope states, from which one of them becomes the highest state within each multiplet. Furthermore, the assignment of D exciton states according to their total angular momentum F is given and corrects an earlier description given in a former study.
2021-09-03T00:00:00Z
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Room-temperature on-spin-switching and tuning in a porphyrin-based multifunctional interface
http://hdl.handle.net/2003/40800
Title: Room-temperature on-spin-switching and tuning in a porphyrin-based multifunctional interface
Authors: Sturmeit, Henning Maximilian; Cojocariu, Iulia; Windischbacher, Andreas; Puschnig, Peter; Piamonteze, Cinthia; Jugovac, Matteo; Sala, Alessandro; Africh, Cristina; Comelli, Giovanni; Cossaro, Albano; Verdini, Alberto; Floreano, Luca; Stredansky, Matus; Vesseli, Erik; Hohner, Chantal; Kettner, Miroslav; Libuda, Jörg; Schneider, Claus Michael; Zamborlini, Giovanni; Cinchetti, Mirko; Feyer, Vitaliy
Abstract: Molecular interfaces formed between metals and molecular compounds offer a great potential as building blocks for future opto-electronics and spintronics devices. Here, a combined theoretical and experimental spectro-microscopy approach is used to show that the charge transfer occurring at the interface between nickel tetraphenyl porphyrins and copper changes both spin and oxidation states of the Ni ion from [Ni(II), S = 0] to [Ni(I), S = 1/2]. The chemically active Ni(I), even in a buried multilayer system, can be functionalized with nitrogen dioxide, allowing a selective tuning of the electronic properties of the Ni center that is switched to a [Ni(II), S = 1] state. While Ni acts as a reversible spin switch, it is found that the electronic structure of the macrocycle backbone, where the frontier orbitals are mainly localized, remains unaffected. These findings pave the way for using the present porphyrin-based system as a platform for the realization of multifunctional devices where the magnetism and the optical/transport properties can be controlled simultaneously by independent stimuli.
2021-10-12T00:00:00Z
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Lead-dominated hyperfine interaction impacting the carrier spin dynamics in halide perovskites
http://hdl.handle.net/2003/40797
Title: Lead-dominated hyperfine interaction impacting the carrier spin dynamics in halide perovskites
Authors: Kirstein, Erik; Yakovlev, Dmitri R.; Glazov, Mikhail M.; Evers, Eiko; Zhukov, Evgeny A.; Belykh, Vasilii V.; Kopteva, Nataliia E.; Kudlacik, Dennis; Nazarenko, Olga; Dirin, Dmitry N.; Kovalenko, Maksym V.; Bayer, Manfred
Abstract: The outstanding optical quality of lead halide perovskites inspires studies of their potential for the optical control of carrier spins as pursued in other materials. Entering largely uncharted territory, time-resolved pumpâprobe Kerr rotation is used to explore the coherent spin dynamics of electrons and holes in bulk formamidinium caesium lead iodine bromide (FA0.9Cs0.1PbI2.8Br0.2) and to determine key parameters characterizing interactions of their spins, such as the g-factors and relaxation times. The demonstrated long spin dynamics and narrow g-factor distribution prove the perovskites as promising competitors for conventional semiconductors in spintronics. The dynamic nuclear polarization via spin-oriented holes is realized and the identification of the lead (207Pb) isotope in optically detected nuclear magnetic resonance proves that the holeânuclei interaction is dominated by the lead ions. A detailed theoretical analysis accounting for the specifics of the lead halide perovskite materials allows the evaluation of the underlying hyperfine interaction constants, both for electrons and holes. Recombination and spin dynamics evidence that at low temperatures, photogenerated electrons and holes are localized at different regions of the perovskite crystal, resulting in their long lifetimes up to 44 ÎŒs. The findings form the base for the tailored development of spin-optoelectronic applications for the large family of lead halide perovskites and their nanostructures.
2021-10-04T00:00:00Z
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Non-equilibrium dynamics of a driven-dissipative dimerized spin-1/2 chain
http://hdl.handle.net/2003/40786
Title: Non-equilibrium dynamics of a driven-dissipative dimerized spin-1/2 chain
Authors: Yarmohammadi, Mohsen
Abstract: Due to the rise in experimental progress in several photonic facilities, theoretical addressing the non-equilibrium behavior in driven-dissipative quantum systems has triggered considerable interest in recent times. This thesis is devoted to the analysis of dynamics of a dimerized spin chain model which is driven out-of-equilibrium by the presence of a classical steady laser field. A particular study is given on the spin-phonon coupling effect treated as weak-to-strong perturbations, that the infrared-active phonon is driven by the laser. All systems in nature are interacting with their surroundings and the effects of the environment have to be approximated. To begin with, we employ the quantum Markovian master equation, which follows the construction of the dissipation path to a phononic bath for both phonon and spin sectors in the driven coupled spin-lattice system. We approach this thesis by exploring how the non-equilibrium steady states are created, con-trolled, and preserved by the internal and external interactions. This includes a detailed study of non-equilibrium dynamics of driven-dissipative quantum magnetic materials. First, we prepare the tools, protocols, and approximations needed to model a dimerized spin-1/2 chain as a chain of non-interacting triplons. The spin-phonon coupling is treated by the theoretical framework of the mean-field formalism. Second, we approximate the phononic bath with constant damping for each sector to easily derive the master equations of motion for the physical observables in the entire system. Third, we discuss the validity of such approximative master equations by considering many physical degrees of freedom. These settings produce a large variety of interesting phenomena and physical insights.
2022-01-01T00:00:00Z
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XPS and XPD investigations of low-dimensional silicon-based surface-structures
http://hdl.handle.net/2003/40757
Title: XPS and XPD investigations of low-dimensional silicon-based surface-structures
Authors: Schmitz, Marie
Abstract: This work deals with the analysis of the structural arrangement and the chemical properties of two silicon-based surface systems. The investigation is performed using x-ray photoelectron spectroscopy (XPS), x-ray photoelectron diffraction (XPD), and low-energy electron diffraction (LEED) techniques. Before the investigation of the systems, the clean and reconstructed surfaces are investigated using XPS, XPD, and LEED. Initially, a system with sub-monolayer platinum on a p(2 Ă 1) reconstructed Si(100) substrate is prepared via electron beam evaporation. At 1/6 ML Pt a low-dimensional Si-Pt silicide forms after high temperature annealing at approximately T â 1000 °C. High-resolution core-level XPS spectra of the Si 2p and Pt 4f signals indicate a bond between the Si and the Pt atoms. There is no significant component that could show a Pt-Pt interaction. XPD measurements are taken of the Si 2p and Pt 4f signals and subsequently simulated using different starting structures. The best structure model reveals R-factors below 0.1 for both, Si 2p and Pt 4f signals. The unit cell of the structural arrangement contains 4 platinum atoms with a periodicity of ([3, â6]; [4, 0]). The topmost silicon layer rearranged in a cross-like structure between the Pt atoms.
As second system, silicon is deposited onto a (2 Ă 1) reconstructed Au(110) surface, forming a low-dimensional surface alloy. While the sample is held on a temperature of T = 400 °C, 0.2 ML silicon are deposited via physical vapor deposition. The investigation with LEED reveals a combination of two overlapping domains described by the matrices ([10, â2]; [â1, 4]) and ([10, 2]; [1, 4]). High-resolution core-level XPS measurements of the Au 4f and Si 2p signals showed two distinct components that could be assigned to Au-Si bonds. XPD pattern, recorded for Au 4f and Si 2p are simulated with different structural arrangements. R-factors below 0.1 indicate an excellent agreement with the measured data. The resulting structure model is consistent with the size of the unit cell obtained in the LEED measurement. Additionally, it agrees with the missing-row reconstruction of the substrate. In the structure model, the topmost Au atoms are arranged between the Si atoms.; Diese Arbeit befasst sich mit der Analyse der strukturellen Anordnung und den chemischen Eigenschaften von zwei siliziumbasierten OberflĂ€chensystemen. Die Untersuchung wird mit Hilfe der Röntgenphotoelektronenspektroskopie (XPS), der Röntgenphotoelektronenbeugung (XPD) und der Niederenergie-Elektronenbeugung (LEED) durchgefĂŒhrt. Vor der Untersuchung der Systeme werden die sauberen und rekonstruierten OberflĂ€chen mit XPS, XPD und LEED untersucht. ZunĂ€chst wird ein System mit einer dĂŒnnen Schicht Platin auf einem p(2 Ă 1) rekonstruierten Si(100)-Substrat durch Elektronenstrahlverdampfung hergestellt. Bei 1/6 ML Platin bildet sich nach dem Ausheilen bei etwa T â 1000 °C ein niedrigdimensionales Si-Pt Silizid. Hochauflösende XPS-Spektren der Si 2p- und Pt 4f-Signale weisen auf eine Bindung zwischen den Silizium- und Platinatomen hin. Es gibt eine signifikante Komponente, die eine Pt-Pt-Wechselwirkung anzeigen könnte. Es werden XPD-Messungen der Si 2p- und Pt 4f-Signale durchgefĂŒhrt und anschlieĂend mit verschiedenen Ausgangsstrukturen simuliert. Das beste Strukturmodell ergibt R-Faktoren unter 0,1 sowohl fĂŒr Si 2p- als auch fĂŒr Pt 4f-Signale. Die Einheitszelle der Strukturanordnung enthĂ€lt 4 Platinatome mit einer PeriodizitĂ€t von ([3, â6]; [4, 0]). Die oberste Siliziumschicht ordnet sich in einer kreuzförmigen Struktur zwischen den Platinatomen um.
Als zweites System wird Silizium auf eine (2 Ă 1) rekonstruierte Au(110)-OberflĂ€che abgeschieden, wodurch eine niedrigdimensionale OberflĂ€chenlegierung gebildet wird. WĂ€hrend die Probe auf einer Temperatur von T = 400 °C gehalten wird, werden 0,2 ML Si durch physikalische Gasphasenabscheidung aufgebracht. Die Untersuchung mit LEED ergibt eine Kombination aus zwei sich ĂŒberlappenden Bereichen, die durch die Matrizen ([10, â2]; [â1, 4]) und ([10, 2]; [1, 4]) beschrieben wird. Hochauflösende XPS-Messungen der Au 4f- und Si 2p-Signale zeigen zwei unterschiedliche Komponenten, die Au-Si-Bindungen zugeordnet werden können. XPD-Muster, die fĂŒr Au 4f und Si 2p aufgezeichnet werden, werden mit unterschiedlichen strukturellen Anordnungen simuliert. R-Faktoren unter 0,1 zeigen eine ausgezeichnete Ăbereinstimmung mit den gemessenen Daten. Das resultierende Strukturmodell stimmt mit der GröĂe der Einheitszelle ĂŒberein, die bei der LEED-Messung ermittelt wurde. AuĂerdem stimmt es mit der Rekonstruktion der fehlenden Reihen des Substrats ĂŒberein. In dem Strukturmodell sind die obersten Goldatome zwischen den Siliziumatomen angeordnet.
2021-01-01T00:00:00Z
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Tuning spin and charge at a metal-organic hybrid interface
http://hdl.handle.net/2003/40741
Title: Tuning spin and charge at a metal-organic hybrid interface
Authors: Sturmeit, Henning
Abstract: Metal-organic interfaces are key constituents of the various functional building blocks that can be found in molecular electronics and spintronics. Long electron and spin relaxation times of organic molecules make them superior to inorganic materials for many technological devices. When put into contact with a metal electrode, the hybridization of molecular orbitals and metallic states can lead to several intriguing effects, which strongly affect the electronic and magnetic properties of the system. In this regard, the interface obtained by depositing nickel tetraphenyl porphyrin onto the copper (100) surface (NiTPP/Cu(100)) can be seen as an interesting model system. Previous experiments reported an unexpected high charge transfer leading to a partial filling of the molecular orbitals up to the LUMO+3 and a reduction of the central nickel atom. Considering this observation as the point of departure, this thesis aims to develop different approaches to alter the hybridization at this interface. The results of this thesis can be divided into three main topics. First, it is shown that a pre-oxidation of the copper substrate leads to a substantial quenching of the charge transfer from the metal to the molecule and, thereby, weakens the interaction. In a second step, the spin configuration of the chelated nickel ion is changed by an on-top adsorbed NO2 molecule. The third part addresses the temperature-induced changes at the NiTPP/Cu(100) interface upon annealing. Up to the limit of thermal decomposition, the NiTPP molecules do not undergo chemical changes but only conformational modifications.
2021-01-01T00:00:00Z
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A novel hybrid numerical renormalization group approach to non-equilibrium dynamics and spectral functions
http://hdl.handle.net/2003/40734
Title: A novel hybrid numerical renormalization group approach to non-equilibrium dynamics and spectral functions
Authors: Böker, Jan Oliver
Abstract: Wir prĂ€sentieren einen Ansatz zur Behandlung von Quantenstörstellensystemen, der die numerische Renormierungsgruppe (NRG) zu einem offenen-Quantensystem-Formalismus erweitert. Das kontinuierliche Leitungsband wird in eine beliebige Wilsonkette und einen Satz von Reservoirs aufgeteilt, ohne die lokale Badhybridisierungsfunktion zu beeinflussen. An jedes Kettenglied wird jeweils ein Reservoir ĂŒber den Bloch-Redfield Formalismus (BRF) angekoppelt, der eine Born-Markov-NĂ€herung (BMN) impliziert.
Dieser offene-Wilsonketten-Formalismus (OWF) garantiert eine echte Thermalisierung fĂŒr lokale nicht-Gleichgewichtsdynamik, sowie eine endliche Lebenszeit fĂŒr lokale Gleichgewichtsspektralfunktionen. Der Ansatz reproduziert die von der NRG vorhergesagten Gleichgewichtswerte fĂŒr t â â und die korrekten Relaxationsraten fĂŒr das Resonanzlevel-Modell. Durch VerlĂ€ngerung der Wilsonkette wird die Genauigkeit der BMN, speziell fĂŒr die Kurzzeitdynamik, erhöht. Die Formierung der HubbardhĂŒgel und der Kondoresonanz können fĂŒr das Einzelstörstellen-Anderson-Modell reproduziert werden.
Die BMN in zweiter Ordnung ist nicht in der Lage, die Oszillationen, die durch die Banddiskretisierung im Kontext der NRG entstehen, vollstĂ€ndig zu dĂ€mpfen, kann jedoch durch die wohlbekannte z-Mittelung konstruktiv ergĂ€nzt werden. Es stellt sich heraus, dass der BRF ineffizient ist fĂŒr wechselwirkende Systeme, in denen die lokale Wechselwirkung die Bandbreite ĂŒbersteigt. Hierzu diskutieren wir mehrere alternative Optionen.
Die Motivation dieser Arbeit ist rein methodologischer Natur, weshalb wir uns auf die einfachsten Quantenstörstellenmodelle beschrÀnken. Der OWF ist allerdings ebenso vielfÀltig einsetzbar wie die NRG selbst, und damit anwendbar auf z.B. Multi-Störstellenmodelle oder lokalen Gleichgewichts- und Nicht-Gleichgewichts-Transport.; We present an approach for quantum impurity systems that extends the numerical renormalization group (NRG) to an open quantum system formulation. The continuous conduction band is divided into an arbitrary Wilson chain and a set of reservoirs without affecting the local bath hybridization function. One reservoir is coupled to each chain site and is treated by the Bloch-Redfield formalism (BRF), which includes the Born-Markov approximation (BMA).
This open chain formalism (OCF) yields true thermalization in local real-time non-equilibrium dynamics, as well as finite lifetime in local equilibrium spectral functions. It reproduces the t â â steady-state predicted by the NRG and the correct relaxation rates in the resonant level model. By enlarging the Wilson chain, the accuracy of the BMA, especially with respect to short-time dynamics, is increased. The formation of Hubbard-peaks and the Kondo-resonance are reproduced for the single-impurity Anderson model.
The BMA in second order results in the persistence of finite-size oscillations to some degree, which can be damped by the well-established procedure of z-averaging. We find the BRF to be inadequate for interacting models, if the local Coulomb repulsion exceeds the conduction bandwidth, and discuss several options to improve the OCF for this parameter regime.
Since the motivation for this thesis is of pure methodological nature, we restrict to the most simple quantum impurity models to benchmark our algorithm. However, the OCF is as versatilely applicable to more complex models as the pure NRG. Consequently, our approach can be adapted to e.g. multi-impurity models, as well as simulate local transport properties in and out of equilibrium.
2021-01-01T00:00:00Z