Eldorado - Repositorium der TU Dortmund

Ressourcen aus und für Forschung, Lehre und Studium

Bei diesem Service handelt es sich um das Institutionelle Repositorium der Technischen Universität Dortmund. Hier werden Ressourcen aus und für Lehre, Studium und Forschung gespeichert, erschlossen und der Öffentlichkeit zugänglich gemacht.

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Aktuellste Veröffentlichungen

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    MRI raw data reimagined
    (2025) Rempe, Moritz; Kleesiek, Jens; Kröninger, Kevin; Quick, Harald
    Magnetic Resonance Imaging (MRI) workflows typically discards raw k-Space data, wasting valuable phase information. This thesis challenges the "reconstruct-then-analyze" paradigm, demonstrating that processing complex-valued k-Space data directly significantly enhances diagnostic efficiency and accuracy. This thesis validates this approach through k-Strip, a neural network for direct k-Space segmentation and anonymization, and a prostate cancer classification model that improves predictive performance, particularly in accelerated scans. To address the scarcity of raw MRI data, the thesis introduces PhaseGen, a generative diffusion model. PhaseGen synthesizes realistic raw data, enabling robust training of algorithms even with minimal real-world datasets. These architectures are integrated into an open-source de-identification tool. By establishing the superiority of complex-valued neural networks for MRI signal analysis, this work lays the foundation for a new, data-efficient framework in medical imaging.
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    A tin story on gold
    (2025) Hochhaus, Julian Andreas; Westphal, Carsten; Cinchetti, Mirko
    The rise of two-dimensional materials, triggered by the discovery of graphene, has sparked intense interest in Xenes, monoelemental 2D lattices composed of heavier group-IV elements. Among these, stanene (2D tin) is a particularly promising candidate for next-generation nanoelectronics and spintronics due to its strong spin-orbit coupling and predicted topological properties, such as the quantum spin Hall effect. However, the synthesis of high-quality stanene remains challenging, as the structural evolution of tin (Sn) is highly sensitive to the substrate and growth conditions. The Sn/Au(111) system, while promising, has been the subject of conflicting reports in the literature, with disputed structural models for the observed submonolayer Sn arrangements. This thesis presents a comprehensive structural and chemical analysis of submonolayer Sn growth on Au(111), combining Scanning Tunneling Microscopy (STM), Low-Energy Electron Diffraction (LEED), X-ray Photoelectron Spectroscopy (XPS), and X-ray Photoelectron Diffraction (XPD). By correlating chemical state analysis with detailed structural characterization, the complex interplay between surface ordering and interface alloying is resolved. The structural evolution is categorized into two distinct regimes. At coverages below 0.33 ML, Sn adsorption is characterized by weak substrate interactions. A previously unreported, chemically freestanding (2x2) phase is identified at a coverage of 0.28 ML, representing a precursor state for buckled alpha-stanene. Increasing the coverage leads to the formation of a long-range-ordered Au2Sn surface alloy. Using XPD combined with genetic algorithm optimization, this phase is definitively identified as a substitutional alloy with a Rec(26xsqrt(3)) unit cell, resolving long-standing discrepancies in its atomic structure. At higher coverages (up to 0.66 ML), the growth is driven by the interplay between the interface alloy and the Sn adlayer. This work clarifies the nature of the X-phase, previously interpreted as honeycomb stanene or AuSn alloy. Atomically resolved STM reveals that the X-phase is, in fact, a substrate-symmetry-breaking, square-like Sn arrangement growing atop the Au2Sn alloy, interpreted as the onset of beta-Sn (001)-like growth. Furthermore, a novel striped phase was discovered, featuring alternating stripes of ultraflat honeycomb stanene and the square-like Sn arrangement. These nanoribbon-like structures represent the first experimental realization of ultraflat stanene on Au(111) and the first experimental evidence of nanoribbon-like stanene structures. Collectively, these findings provide a comprehensive framework for the submonolayer Sn/Au(111) system, demonstrating its versatility as a platform for realizing diverse low-dimensional structures and laying the groundwork for future topological investigations.
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    Power-dependent efficiency model of EV chargers for distribution grid simulations
    (2025) Masuch, Marius; Esser, Marcel; Spina, Alfio
    The growing adoption of Electric Vehicles (EVs) and their integration into electrical distribution grids present various challenges. Among others, the efficiency of bidirectional chargers is critical for accurate energy demand forecasting and charging schedule optimisation. This study adapts a mathematical efficiency model, originally developed for photovoltaic inverters, for application to bidirectional EV chargers and incorporates the charging operation into a distribution grid simulation. To account for the power-dependent efficiency of chargers under diverse charging conditions, an approximation based on a step-function is employed. Simulation results indicate that incorporating variable charger efficiency leads to a moderate increase in total EV energy demand (9.4 %) and a minor increase in transformer loading during charging events (0.4 %), while the impact on line loading remains negligible in the considered scenario. The developed variable efficiency model provides a foundation for future research in larger networks with higher EV penetration levels also incorporating functionalities such as Vehicle-to-Grid.
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    Highly efficient lithium extraction from magnesium-rich brines with ionic liquid-based collaborative extractants
    (2023-12-25) Yu, Gangqiang; Zhang, Xinhe; Hubach, Tobias; Chen, Biaohua; Held, Christoph
    Selective extraction of Li+ from high Mg2+/Li+ ratio brines with ionic liquid (IL) based collaborative extractants was investigated by experiments, thermodynamic analyses, and quantum chemical (QC) calculations. Effects of different IL cationic structures and organophosphorus ligands on extraction performances were studied. The results demonstrated that the system 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide + trioctyl phosphate ([HOEMIM][Tf2N] + TOP) was considered as the best extractant, with the very high extraction efficiency of Li+ (83.16 %) and separation selectivity of Li+/Mg2+ (742.11), which is higher than values reported in literature. The thermodynamic model ePC-SAFT was first extended to quantitatively predict the phase equilibria of the so-called “organic–inorganic complex strong electrolyte system” presented in this work. The molecular-level extraction mechanism was explored by QC calculation, indicating that the strong multi-site intermolecular interactions between Li+ and [HOEMIM][Tf2N] + TOP break the Li+ hydration. This work provides guidance to rationally design novel IL-based extractants for efficient extraction of Li+.
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    H2 production under stress: [FeFe]‑hydrogenases reveal strong stability in high pressure environments
    (2024-03-11) Edenharter, Kristina; Jaworek, Michel W.; Engelbrecht, Vera; Winter, Roland; Happe, Thomas
    Hydrogenases are a diverse group of metalloenzymes that catalyze the conversion of H2 into protons and electrons and the reverse reaction. A subgroup is formed by the [FeFe]‑hydrogenases, which are the most efficient enzymes of microbes for catalytic H2 conversion. We have determined the stability and activity of two [FeFe]‑hydrogenases under high temperature and pressure conditions employing FTIR spectroscopy and the high-pressure stopped-flow methodology in combination with fast UV/Vis detection. Our data show high temperature stability and an increase in activity up to the unfolding temperatures of the enzymes. Remarkably, both enzymes reveal a very high pressure stability of their structure, even up to pressures of several kbars. Their high pressure-stability enables high enzymatic activity up to 2 kbar, which largely exceeds the pressure limit encountered by organisms in the deep sea and sub-seafloor on Earth.