Eldorado - Repositorium der TU Dortmund

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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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    Hole spin coherence in InAs/InAlGaAs self‐assembled quantum dots emitting at telecom wavelengths
    (arXiv, 2024-09-02) Evers, Eiko; Kopteva, Nataliia E.; Nedelea, Vitalie; Kors, Andrei; Kaur, Ranbir; Reithmaier, Johann Peter; Benyoucef, Mohamed; Bayer, Manfred; Greilich, Alex
    Measurements of the longitudinal and transverse spin relaxation times of holes in an ensemble of vertically tunnel-coupled self-assembled InAs/In0.53 Al0.24 Ga0.23 As quantum dots (QDs), emitting in the telecom spectral range, are reported. The spin coherence is determined using the spin mode-locking method in the inhomogeneous ensemble of QDs. Modeling the signal allows us to extract the hole spin coherence time to be in the range of 𝑇2 =0.02 −0.4  μs. The longitudinal spin relaxation time 𝑇1 =0.5  μs is measured using the spin inertia method. The parameters investigated allow us to suggest that the main relaxation mechanism at low magnetic fields is related to the electron–hole spin exchange.
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    Modeling of residence time distributions of twin-screw extrusion processes considering various screw types
    (MDPI AG, 2026-07-18) Kimmel, Vincent; Zöllig, Dario; Hoheisel, Werner; Winck, Judith; Thommes, Markus
    Residence time in pharmaceutical hot-melt extrusion is a crucial process parameter affecting the quality attributes of a dosage form such as content uniformity, bioavailability and toxicity. There is a lack of knowledge about the influence of screw element types on the residence time distribution, which will be addressed in this study. Methods: Different conveying and kneading elements will be characterized concerning their effect on the residence time using a co-rotating twin-screw extruder with a 28 mm screw diameter. Tracer experiments will be performed while concentration time profiles are measured via inline UV-Vis spectroscopy. Results: The residence time distribution of all screw types is primarily related to the volume flow but independent of pressure. The two-compartment model of Reitz was utilized to describe the experimental data mathematically. Screw-type-specific dimensionless parameters were derived to quantify the axial mixing performance, as well as the effect on residence time. Conclusions: The influence of different screw elements on the residence time in hot-melt extrusion processes was quantified using a dimensionless mixing volume and a dimensionless axial dispersion coefficient. The results meet the quantitative descriptions from the literature.
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    Exploring variational entanglement hamiltonians
    (arXiv, 2026-06-12) Kind, Yanick S.; Fauseweh, Benedikt
    Recent advances in analog and digital quantum-simulation platforms have enabled exploration of the spectrum of entanglement Hamiltonians via variational algorithms. In this work we analyze the convergence properties of the variationally obtained solutions and compare them to numerically exact calculations in quantum critical systems. We demonstrate that interpreting the cost functional as an integral permits the deployment of iterative quadrature schemes, thereby reducing the required number of measurements by more than an order of magnitude even in the presence of noise. We further show that a modified ansatz captures deviations from the Bisognano-Wichmann form in lattice models, improves convergence, improves trainability and provides a cost-function-level diagnostic for quantum phase transitions. Finally, we establish that a low cost value does not by itself guarantee convergence in trace distance. Nevertheless, it faithfully reproduces degeneracies and spectral gaps, which are essential for applications to topological phases.
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    From coordination problems to complexity processing – second-order observation of inter-administrative relations
    (Frontiers Media SA, 2026-06-19) Schreiber, Paul R.; El-Mafaalani, Aladin
    This paper offers a conceptual analysis of inter-administrative relations by reconstructing them as an object constituted through analytical observation. Drawing explicitly on Niklas Luhmann’s Social Systems Theory, it employs second-order observation as a methodological framework to examine how inter-administrative relations are made observable within different analytical traditions. It first analyzes how inter-administrative relations are constituted within Actor-Centered Institutionalism, showing that they emerge through the distinction between coordination success and coordination failure and appear predominantly as problems or solutions of policy implementation. In a second step, systems theory is employed as a reflexive observational methodology. Using the system/environment distinction, public administration is observed as a decision system. Inter-administrative relations can then be described as forms that stabilize connectivity between differentiated decision contexts under conditions of environmental complexity. By systematically varying the observational distinctions through which inter-administrative relations are constituted, the paper demonstrates that they are not given empirical objects but take on different analytical forms depending on how they are observed: either as a normative category for evaluating coordination or as conditions of organizational decision-making. In this way, the contribution advances both systems-theoretical and administrative research. It demonstrates how second-order observation can be used as a transdisciplinary methodological tool to reconstruct and compare established analytical frameworks. It further shows that empirical diagnoses and reform proposals are effects of specific observational distinctions.
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    Geometric physically-based simulation of microfinishing: tool design impact on workpiece shape
    (Springer Science and Business Media LLC, 2024-09-12) Siebrecht, Tobias; Bergmann, Jim A.; Heining, Ines; Tilger, Meik; Biermann, Dirk; Wiederkehr, Petra
    Due to complex interrelations between process configurations, tool characteristics and process results, the design of microfinishing operations is challenging. Microfinishing is often conducted to generate high surface qualities and shape accuracies of highly loaded components. For some applications, e.g. bearing seats, the contact surface is desired to provide a convex shape in order to optimise the contact condition of the bearing ring and the shaft shoulder. In this paper, new models for a geometric physically-based simulation system are presented and applied to predict workpiece topographies and shapes resulting from the use of different tool designs in microfinishing operations. These models include a process-specific force control based on modelling the engagement of single grains, the consideration of the initial tool condition as well as the modelling of wear-related breakouts of individual grains. The developed simulation system was validated by a comparison of the results to experimental investigations.