Eldorado - Repositorium der TU Dortmund

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Fach- und Universitätsübergreifendes 1319
Fakultäten 13790
Graduate School und Graduiertenkollegs 12
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Sonderforschungsbereiche 1592

Aktuellste Veröffentlichungen

Amtliche Mitteilungen der Technischen Universität Dortmund Nr. 12/2026
(Technische Universität Dortmund, 2026-05-18)
Orientation-dependent stress evolution in diamond abrasive grains under directional loading
(2026-04-29) Brune, Gabriel; Tsagkir Dereli, Tountzer; Olschewski, Lars; Lopes Dias, Nelson Filipe; Kipp, Monika; Biermann, Dirk; Debus, Jörg
Understanding the response of diamond abrasive grains to mechanical loading remains crucial for optimizing their performance in precision manufacturing. In that context, the role of the initial residual stress and crystallographic orientation of the grains is poorly understood. We investigate synthetic diamond grains in two different grit sizes (D126, D252) subjected to directional loading up to 100 N using x-ray diffraction and spatially resolved Raman spectroscopy. Small grains with preferential (111) orientation show an unexpected stress evolution under contact pressures up to 16 GPa, with Raman shifts increasing from 1331.3 to 1333.0cm−1, indicating an enhanced local compressive stress state at the probed surface regions. Conversely, large (311)-oriented grains exhibit a heterogeneous stress development with Raman shifts varying from 1331.5 to 1332.6cm−1, including regions that become more tensile (or less compressive) relative to their initial state. The relationship between the relative Raman shift and a spatially weighted contact pressure follows an empirical power law 𝛿⁢𝐸∝𝑝′𝛼c with opposite, orientation-dependent exponents: 𝛼≈+0.25 for (111) grains showing progressive compression enhancement and 𝛼≈−0.35 for (311) grains exhibiting a trend toward tensile stress components with increasing load. Molecular dynamics simulations reveal that the Schmid factor governs this orientation-dependent response: The low Schmid factor (0.27) for [111] loading restricts dislocation glide, leading to stress retention with high elastic recovery, while the high Schmid factor (0.45) for [311] loading facilitates plastic flow and stress relaxation despite lower peak stress. These findings demonstrate that stress evolution in diamond under directional loading is controlled by the geometric relationship between loading direction and slip systems, providing mechanistic insights for diamond tool design.
From light pulses to selective enhancement: performance analysis of event-based object detection under pulsed automotive headlight illumination
(2026-04-22) Haensel, Leonard; Bertram, Torsten
Pulse-width-modulated (PWM) automotive headlights enhance nighttime event-based camera detection, yet systematic parameter optimization for vulnerable road user detection remains unexplored. This study evaluates PWM frequency, duty cycle, light distribution, ego-vehicle speed, and ambient lighting under European New Car Assessment Programme-inspired crossing scenarios for cyclist and pedestrian detection. Results establish performance ranging from substantial improvements to severe degradation relative to continuous illumination. Cyclist detection achieves robust performance with high-frequency modulation across light distributions, while low-frequency operation with low beam produces severe degradation through background noise accumulation. Pedestrian detection requires high beam with street lighting enabled; low beam universally fails regardless of modulation parameters. Limited parameter combinations achieve simultaneous improvements for both targets. Detection performs optimally on retroreflective surfaces, while low-reflectivity clothing limits capability, requiring target-specific optimization.
From open containers to confined supramolecular architectures
(2026) Ocklenburg, David; Craen, David van; Henke, Sebastian
The work will investigate the preparation and characterization of charge-neutral Zn(II) metal organic cages based on bis(bidentate) hydroxyquinolate ligands, with focus on how ligand topology and functionality modulate anion recognition and guest-directed assembly. Building on a charge-neutral [Zn2L2] host-complex presented by our group in 2022, various rational designed ligands were synthesized and self-assembled with Zn(OAc)2 to yield discrete [Zn2L2] architectures and others. The first chapter will introduce three new bis(bidentate) ligands LmN3-H2, LN3-H2 and Lcrown3-H2 which are designed and synthesized to increase the functionality of the parent [Zn2L2] cage. Spectroscopic and computational analysis indicate that expanded π-surfaces preserve the metal organic cages integrity while enabling additional host-guest π-interactions, and a crown-ether functionalized derivative demonstrates heteroditopic ion-pair binding. Second, to address the challenge that strongly chelating oxalate can disrupt metal-ligand assemblies, a more flexible ligand LDB3-H2 was designed and synthesized to afford a robust charge-neutral [Zn2LDB32] host-complex. This container forms a well-defined 1:1 oxalate host-guest complex in solution. UV/Vis titrations quantify binding and competition experiments demonstrate selective oxalate recognition over longer dicarboxylates and monocarboxylates. Dicarboxylates form host-guest complexes in a slow-guest exchange behavior, whereas mono-carboxylates demonstrate fast-exchange. Finally, a tripodal bis(bidentate) ligand, LTP3-H3, enables guest-induced control over nuclearity and topology. Tricarboxylates template direct formation of trinuclear and hexanuclear onion-type host-guest complexes with architecturally appealing supramolecular features. 1H NMR competition experiments reveal observable interconversion of a trinuclear species into a hexanuclear species and give insight into the respective binding affinities. Kinetic studies suggest an associative-dissociative exchange-transformation mechanism with a substantial activation barrier.
Single-shot characterization of ultrafast electron dynamics using photoelectron spectroscopy
(2026) Savio, Sara; Helml, Wolfram; Ilchen, Markus
Core-level photoionization is a fundamental process in light–matter interaction consisting of absorbing a photon by an atom or molecule, ejecting an electron from one of its inner shells, and creating a core-shell vacancy. This vacancy is then filled through various relaxation pro-cesses, which can result in the emission of secondary electrons or energy redistribution within the system. The results presented in this thesis contain technical and methodological advances in characterizing the decay dynamics of double-core holes (DCH) in gaseous neon atoms, which have a very short lifetime, using intense and ultrashort X-ray pulses on the attosecond (10−18 s) scale at the European XFEL (Eu-XFEL). Ultrafast electron dynamics are mapped on a single-shot basis using an angle-resolving electron time-of-flight (e-TOF) spectrometer. A spectrometer was built and commissioned as part of this work and is presented in detail, including technical information and experimentally retrieved performance data. Non-invasive systematic pulse characterization using the angu-lar streaking technique provides spectral and temporal information about the ionizing XFEL pulses with attosecond resolution. This approach enables single-shot DCH probing based on the knowledge of spectro-temporal details about the ionizing pulses. A comprehensive study was conducted to investigate how the contribution of DCH chan-nels varies with X-ray pulse parameters, including pulse duration, pulse energy, and the pho-ton energy centres of the reconstructed spectra. The results show that the yield of the DCH signal increases in such a way that is compatible with the reconstruction of X-ray pulse dura-tions well below the life time of the single-core hole (SCH) Auger decay in neon, which is on the order of 2.4 femtosecond (10−15 s), thus enabling the characterization of such short-lived ionic states in a single shot. Examining the electronic structure of the core-ionized system before relaxation, combined with detailed information about the ionizing pulse, provides the experimental stage for valuable insights into nonlinear X-ray–matter interaction. Thus the ensuing photoabsorption and relaxation channel intensities achievable at high-repetition-rate, attosecond duration XFEL allow to reveal these ultrafast processes on the natural timescale of electron dynamics.