Resources for and from Research, Teaching and Studying
Recent Submissions
Synchrotron radiation sources have become an essential part of modern science. The ongoing development to reach higher performance levels with improved quality of synchrotron light demands upgrades of current synchrotron radiation facilities or even construction of new accelerators. During this process, new challenges, both technological and in the accelerator physics, need to be addressed to achieve a higher light quality in terms of brightness, coherence, pulse duration, etc. This includes ...
Initializing quantum registers with high fidelity is a fundamental precondition for many applications like quantum information processing and sensing. The electronic and nuclear spins of a Nitrogen-Vacancy (NV) center in diamond form an interesting hybrid quantum register that can be initialized by a combination of laser, microwave, and radio-frequency pulses. However, the laser illumination, which is necessary for achieving electron spin polarization, also has the unwanted side-effect of dep...
This thesis investigates the variation of signal transmission in topological phases as well as their robustness in one- and two-dimensional systems. For this purpose, multiple approaches in different systems are pursued. First, the possibility of designed modifications at the boundaries is explored in order to change the Fermi velocity at edge states of topological phases. The Fermi velocity as a quantity of the transport behavior describes the speed of signal transmission. The main ide...
This thesis aims to further the understanding of the two-photon interaction dynamic in bulk direct semiconductors in an electronically excited state. The central goal is to assess the practicability of controlling the two-photon transition strength using an ultrafast all-optical scheme and ultimately identify the key parameters and requirements necessary to observe degenerate two-photon gain in these media. Here, a transfer of stimulated two-photon emission to the semiconductor medium is very...
This work will focus on the characterization of different dielectric barrier discharges (DBD) that are used in analytical applications. These discharges are primarily used as ion sources that provide charged species for the subsequent detection with atmospheric mass spectrometers (MS) or ion mobility spectrometers (IMS). The main method of investigation for the DBDs will be based on optical methods such as temporally-, spatially-, and spectrally-resolved optical emission spectroscopy (TSSROES...
Mit dem Ausbau zum High Luminosity LHC (HL-LHC) wird der Spurdetekor des ATLAS-Experiments durch den Inner Tracker (ITk) ersetzt, der Pixel- und Streifensensoren aus Silizium nutzen wird. In Dortmund werden Module für die Endkappe des ITK Streifendetektors gebaut werden. In einem Teil der Arbeit wird der Ablauf derProduktion dieser Module entwickelt. Während des Betriebs werden Strahlenschäden den Leckstrom der Siliziumsensoren erhöhen. Mit Hilfe des Parameters Eeff kann dieser mit der Temper...
Die Messung flüchtiger toxischer Elemente in kleinen Konzentrationen ist von großer Bedeutung im Bereich der analytischen Chemie. Eine Methode dabei ist die optische Emissionsspektrometrie an dielektrisch behinderten Plasmen. Dabei wird der gasförmige Analyt in das Plasma eingeleitet, dissoziiert und anschließend angeregt. Die Intensität des ausgesendeten Lichts ist dann proportional zur Konzentration des Analyten im Plasma. Die Mechanismen bei der Interaktion zwischen dem Plasma und dem Anal...
Analyzing and characterizing mechanical properties of polymers is a vast field of research. In this thesis, linear and nonlinear rheological investigations have been used to study the relaxation behavior of various glass-forming liquids. In simple (non-associating and non-polymeric) liquids, the microscopic flow behavior is associated to the mass transport which is defined by the dynamics of the molecules and therefore the structural relaxation. This is usually discussed in the literatur...
In this thesis, a search for flavour-changing neutral currents in processes involving a singly produced top quark and a photon is presented. In this search, proton-proton collision data are used which were collected by the ATLAS experiment at the LHC and correspond to an integrated luminosity of 81 fb⁻¹. The top quark is assumed to decay into a b quark and a W boson, which is supposed to decay leptonically. Events are selected whose final state contains exactly one photon, one charged lepton,...
Imaging atmospheric Cherenkov telescopes (IACT) observe the sky in the highest energy ranges. From the remnants of cataclysmic supernovae to jets powered by supermassive blackholes in the center of distant galaxies, IACTs can capture the light emerging from the most extreme sources in the universe. With the recent advent of multi-messenger astronomy it has become critical for IACTs to publicly share their data and software. For the first time since the inception of IACT technology, in a...
Der neutrinolose doppelte Beta-Zerfall ist ein hypothetischer Kernzerfall dessen Nachweis grundlegende Fragen über bislang unbekannte Eigenschaften von Neutrinos liefern und auf Physik jenseits des Standard Modells der Teilchenphysik hindeuten würde. Das COBRA Experiment sucht nach diesem Zerfall mit Hilfe von CdZnTe Halbleiter-Detektoren. In dieser Arbeit wird ein wesentlich verbesserter Aufbau des Experiments, genannt Extended Demonstrator (XDEM), präsentiert. Um diesen zur verwirklich...
In this review on advanced biomolecular EPR spectroscopy, which addresses both the EPR and NMR communities, considerable emphasis is put on delineating the complementarity of NMR and EPR regarding the measurement of interactions and dynamics of large molecules embedded in fluid-solution or solid-state environments. Our focus is on the characterization of protein structure, dynamics and interactions, using sophisticated EPR spectroscopy methods. New developments in pulsed microwave and sweepab...
The World Health Organization has been listing cardiovascular disease and its sequelae as one of the leading causes of death worldwide for several years in its annual report. In general this includes all disease that originates from the vascular system and / or from the heart. Due to the high patient rate, there is great interest in researching the exact processes and effects of the diseases on the tissue as well as on the flow behavior. These can be used to develop therapeutic options, but a...
Using the existing simplified model framework, we build several dark matter models which have suppressed spin-independent scattering cross section. We show that the scattering cross section can vanish due to interference effects with models obtained by simple combinations of simplified models. For weakly interacting massive particle (WIMP) masses ≳10 GeV, collider limits are usually much weaker than the direct detection limits coming from LUX or XENON100. However, for our model combinations, ...
Starting in 2021, the LHCb experiment will switch to a fully software-based trigger system. It is an ongoing challenge to ensure that this system will be able to process events at the required rate of 30 MHz. Two alternative approaches to improve and speed up the particle track reconstruction performed in the first stage of LHCb’s software trigger are presented. An alternative method to the Kalman filter track fit inside the VELO reconstruction is presented. This method uses neural networks t...
This thesis presents the first LHCb measurement of 𝐶𝑃 violation in 𝐵0 → 𝐷∗±𝐷∓ decays. Due to the 𝑏 → 𝑐𝑐𝑑 transition, 𝐵0 → 𝐷∗±𝐷∓ decays give access to higher-order Standard Model contributions. The decay-time-dependent measurement is performed on a dataset corresponding to an integrated luminosity of 9 fb−1 recorded by the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The 𝐶𝑃 observables are measured with an unbinned maximum likelihood fi...
A large fraction of the gamma-ray sources presented in the Third Fermi-LAT source catalog (3FGL) is affiliated with counterparts and source types, but 1010 sources remain unassociated and 573 sources are associated with active galaxies of uncertain type. The purpose of this study is to assign blazar classes to these unassociated and uncertain sources, and to link counterparts to the unassociated. A machine learning algorithm is used for the classification, based on properties extracted from t...
Astrophysical tau neutrinos are the last unidentified standard model messenger in astroparticle physics. Their identification can open new windows to neutrino physics, improve knowledge about cosmic neutrino sources and even test physics beyond the standard model. This work aims to constrain the tau neutrino component in the astrophysical neutrino flux observed by the IceCube Neutrino Observatory. Due to neutrino oscillations over cosmic baselines, a significant fraction of tau neutrinos...
Das Ziel dieser Arbeit besteht darin, an Hand von nichtlinearer optischer Spektroskopie, Informationen über fundamentale Zustände in Halbleiter-Materialien zu erhalten. Bei diesen Zuständen handelt es sich um Anregungen von Elektron-Loch Quasiteilchen, den sogenannten Exzitonen. Diese treten im Energiebereich unterhalb der Bandlücke des Materials auf und dominieren dort die optischen Eigenschaften. Im Unterschied zur linearen Optik geschieht die Anregung in der nichtlinearen Optik durch zwei...
S5 0716+714 is a well known BL Lac object, and one of the brightest and most active blazars. The discovery in the Very High Energy band (VHE, E > 100 GeV) by MAGIC happened in 2008. In January 2015, the source went through the brightest optical state ever observed, triggering MAGIC follow-up and a VHE detection with ∼ 13σ significance (ATel ♯6999 ). Rich multiwavelength coverage of the flare allowed us to construct the broad-band spectral energy distribution of S5 0716+714 during its brightes...