@article{63160, author = {{Rose, Hendrik and Schumacher, Stefan and Meier, Torsten}}, issn = {{2469-9950}}, journal = {{Physical Review B}}, number = {{24}}, publisher = {{American Physical Society (APS)}}, title = {{{Microscopic approach to the quantized light-matter interaction in semiconductor nanostructures: Complex coupled dynamics of excitons, biexcitons, and photons}}}, doi = {{10.1103/528f-7smh}}, volume = {{112}}, year = {{2025}}, } @article{62000, author = {{Claes, Leander and Koch, Kevin and Friesen, Olga and Meihost, Lars}}, issn = {{2681-4617}}, journal = {{Acta Acustica}}, number = {{65}}, publisher = {{EDP Sciences}}, title = {{{Machine Learning-Supported Inverse Measurement Procedure for Broadband, Temperature Dependent Piezoelectric Material Parameters}}}, doi = {{10.1051/aacus/2025044}}, volume = {{9}}, year = {{2025}}, } @inproceedings{59689, author = {{Friesen, Olga and Meihost, Lars and Koch, Kevin and Claes, Leander and Henning, Bernd}}, location = {{Copenhagen}}, title = {{{Estimation of piezoelectric material parameters under varying electric field conditions}}}, doi = {{10.71568/DASDAGA2025.078}}, year = {{2025}}, } @article{60566, author = {{Bocchini, Adriana and Rüsing, Michael and Bollmers, Laura and Lengeling, Sebastian and Mues, Philipp and Padberg, Laura and Gerstmann, Uwe and Silberhorn, Christine and Eigner, Christof and Schmidt, Wolf Gero}}, issn = {{2475-9953}}, journal = {{Physical Review Materials}}, number = {{7}}, publisher = {{American Physical Society (APS)}}, title = {{{Mg dopants in lithium niobate: Defect models and impact on domain inversion}}}, doi = {{10.1103/5wz1-bjyr}}, volume = {{9}}, year = {{2025}}, } @inproceedings{59897, abstract = {{This paper discusses the influence of joint orientation with non-rotationally symmetric geometry, on load distribution and structural behavior. The focus is on understanding how changes in the alignment of individual joints affect the distribution of load, neighboring joints, and the overall performance of the component. Lap shear specimens with multiple joints arranged in a line are analyzed to explore these effects. Simplified models are used to model the joints in finite element simulations, allowing for efficient yet accurate analysis of the load distribution and structural response under varying joint orientations. Variations in joint orientation result in measurable changes in the distribution of forces on adjacent joints, influencing their behavior and that of the overall assembly. Experimental validation confirms the numerical results, providing deeper insights into the interaction between individual joints and their surroundings. This work contributes to the development of systematic approaches for optimizing the design of components with non-rotationally symmetric joints. The study highlights the importance of considering directional properties of joints in designing structural components.}}, author = {{Devulapally, Deekshith Reddy and Steinfelder, Christian and Tröster, Thomas and Brosius, Alexander}}, booktitle = {{MATEC Web of Conferences}}, issn = {{2261-236X}}, location = {{Lisabon,Portugal}}, publisher = {{EDP Sciences}}, title = {{{Impact of non-rotationally symmetric joint orientation on neighbouring joints and component performance in lap shear specimens}}}, doi = {{10.1051/matecconf/202540801035}}, volume = {{408}}, year = {{2025}}, } @book{65062, author = {{Tröster, Thomas and Marten, Thorsten and Luig, Simon}}, isbn = {{978-3-96780-214-6}}, publisher = {{Forschungsvereinigung Stahlanwendung e.V. (FOSTA)}}, title = {{{Methodische Auswahl hochfester Mehrphasenstähle bezüglich ihrer lokalen und globalen Duktilität}}}, volume = {{P 1447}}, year = {{2025}}, } @inproceedings{65102, abstract = {{Efficient graph processing is essential for a wide range of applications. Scalability and memory access patterns are still a challenge, especially with the Breadth-First Search algorithm. This work focuses on leveraging HPC systems with multiple GPUs available in a single node with peer-to-peer functionality of the Intel oneAPI implementation of SYCL. We propose three GPU-based load-balancing methods: work-group localisation for efficient data access, even workload distribution for higher GPU occupancy, and a hybrid strided-access approach for heuristic balancing. These methods ensure performance, portability, and productivity with a unified codebase. Our proposed methodologies outperform state-of-the-art single-GPU implementations based on CUDA on synthetic RMAT graphs. We analysed BFS performance across NVIDIA A100, Intel Max 1550, and AMD MI300X GPUs, achieving a peak performance of 153.27 GTEPS on an RMAT25-64 graph using 8 GPUs on the NVIDIA A100. Furthermore, our work demonstrates the capability to handle RMAT graphs up to scale 29, achieving superior performance on synthetic graphs and competitive results on real-world datasets.}}, author = {{Olgu, Kaan and Kenter, Tobias and Nunez-Yanez, Jose and McIntosh-Smith, Simon and Deakin, Tom}}, booktitle = {{Proceedings of the SC '25 Workshops of the International Conference for High Performance Computing, Networking, Storage and Analysis}}, publisher = {{ACM}}, title = {{{Towards Efficient Load Balancing BFS on GPUs: One Code for AMD, Intel & Nvidia}}}, doi = {{10.1145/3731599.3767570}}, year = {{2025}}, } @article{50829, author = {{Heinisch, Nils and Köcher, Nikolas and Bauch, David and Schumacher, Stefan}}, issn = {{2643-1564}}, journal = {{Physical Review Research}}, number = {{1}}, publisher = {{American Physical Society (APS)}}, title = {{{Swing-up dynamics in quantum emitter cavity systems: Near ideal single photons and entangled photon pairs}}}, doi = {{10.1103/PhysRevResearch.6.L012017}}, volume = {{6}}, year = {{2024}}, } @inproceedings{52573, author = {{Dechert, Christopher and Kenig, Eugeny}}, location = {{Bochum}}, title = {{{Der Einfluss von Mikrostrukturen auf die Flüssigkeitsausbreitung in strukturierten Packungen}}}, year = {{2024}}, } @article{33461, abstract = {{Data-driven models for nonlinear dynamical systems based on approximating the underlying Koopman operator or generator have proven to be successful tools for forecasting, feature learning, state estimation, and control. It has become well known that the Koopman generators for control-affine systems also have affine dependence on the input, leading to convenient finite-dimensional bilinear approximations of the dynamics. Yet there are still two main obstacles that limit the scope of current approaches for approximating the Koopman generators of systems with actuation. First, the performance of existing methods depends heavily on the choice of basis functions over which the Koopman generator is to be approximated; and there is currently no universal way to choose them for systems that are not measure preserving. Secondly, if we do not observe the full state, we may not gain access to a sufficiently rich collection of such functions to describe the dynamics. This is because the commonly used method of forming time-delayed observables fails when there is actuation. To remedy these issues, we write the dynamics of observables governed by the Koopman generator as a bilinear hidden Markov model, and determine the model parameters using the expectation-maximization (EM) algorithm. The E-step involves a standard Kalman filter and smoother, while the M-step resembles control-affine dynamic mode decomposition for the generator. We demonstrate the performance of this method on three examples, including recovery of a finite-dimensional Koopman-invariant subspace for an actuated system with a slow manifold; estimation of Koopman eigenfunctions for the unforced Duffing equation; and model-predictive control of a fluidic pinball system based only on noisy observations of lift and drag.}}, author = {{Otto, Samuel E. and Peitz, Sebastian and Rowley, Clarence W.}}, journal = {{SIAM Journal on Applied Dynamical Systems}}, number = {{1}}, pages = {{885--923}}, publisher = {{SIAM}}, title = {{{Learning Bilinear Models of Actuated Koopman Generators from Partially-Observed Trajectories}}}, doi = {{10.1137/22M1523601}}, volume = {{23}}, year = {{2024}}, } @article{53474, abstract = {{We present a novel approach to characterize and quantify microheterogeneity and microphase separation in computer simulations of complex liquid mixtures. Our post-processing method is based on local density fluctuations of the different constituents in sampling spheres of varying size. It can be easily applied to both molecular dynamics (MD) and Monte Carlo (MC) simulations, including periodic boundary conditions. Multidimensional correlation of the density distributions yields a clear picture of the domain formation due to the subtle balance of different interactions. We apply our approach to the example of force field molecular dynamics simulations of imidazolium-based ionic liquids with different side chain lengths at different temperatures, namely 1-ethyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium chloride, and 1-decyl-3-methylimidazolium chloride, which are known to form distinct liquid domains. We put the results into the context of existing microheterogeneity analyses and demonstrate the advantages and sensitivity of our novel method. Furthermore, we show how to estimate the configuration entropy from our analysis, and we investigate voids in the system. The analysis has been implemented into our program package TRAVIS and is thus available as free software.}}, author = {{Lass, Michael and Kenter, Tobias and Plessl, Christian and Brehm, Martin}}, issn = {{1099-4300}}, journal = {{Entropy}}, number = {{4}}, publisher = {{MDPI AG}}, title = {{{Characterizing Microheterogeneity in Liquid Mixtures via Local Density Fluctuations}}}, doi = {{10.3390/e26040322}}, volume = {{26}}, year = {{2024}}, } @article{53663, abstract = {{Noctua 2 is a supercomputer operated at the Paderborn Center for Parallel Computing (PC2) at Paderborn University in Germany. Noctua 2 was inaugurated in 2022 and is an Atos BullSequana XH2000 system. It consists mainly of three node types: 1) CPU Compute nodes with AMD EPYC processors in different main memory configurations, 2) GPU nodes with NVIDIA A100 GPUs, and 3) FPGA nodes with Xilinx Alveo U280 and Intel Stratix 10 FPGA cards. While CPUs and GPUs are known off-the-shelf components in HPC systems, the operation of a large number of FPGA cards from different vendors and a dedicated FPGA-to-FPGA network are unique characteristics of Noctua 2. This paper describes in detail the overall setup of Noctua 2 and gives insights into the operation of the cluster from a hardware, software and facility perspective.}}, author = {{Bauer, Carsten and Kenter, Tobias and Lass, Michael and Mazur, Lukas and Meyer, Marius and Nitsche, Holger and Riebler, Heinrich and Schade, Robert and Schwarz, Michael and Winnwa, Nils and Wiens, Alex and Wu, Xin and Plessl, Christian and Simon, Jens}}, journal = {{Journal of large-scale research facilities}}, keywords = {{Noctua 2, Supercomputer, FPGA, PC2, Paderborn Center for Parallel Computing}}, title = {{{Noctua 2 Supercomputer}}}, doi = {{10.17815/jlsrf-8-187 }}, volume = {{9}}, year = {{2024}}, } @inproceedings{52231, author = {{Blübaum, Lukas and Heindorf, Stefan}}, booktitle = {{The World Wide Web Conference (WWW)}}, location = {{Singapore}}, pages = {{2204–2215}}, publisher = {{ACM}}, title = {{{Causal Question Answering with Reinforcement Learning}}}, doi = {{10.1145/3589334.3645610}}, year = {{2024}}, } @inproceedings{53069, author = {{Banh, Ngoc Chi and Scharlau, Ingrid}}, location = {{Regensburg}}, title = {{{Effects of task difficulty on visual processing speed}}}, year = {{2024}}, } @article{55267, author = {{Schäfer, F. and Trautmann, A. and Ngo, C. and Steiner, J. T. and Fuchs, C. and Volz, K. and Dobener, F. and Stein, M. and Meier, Torsten and Chatterjee, S.}}, issn = {{2469-9950}}, journal = {{Physical Review B}}, number = {{7}}, publisher = {{American Physical Society (APS)}}, title = {{{Optical Stark effect in type-II semiconductor heterostructures}}}, doi = {{10.1103/physrevb.109.075301}}, volume = {{109}}, year = {{2024}}, } @article{52700, abstract = {{We explore the polarization hysteretic behaviour and field-dependent permittivity of ferroelectric-dielectric 2D materials formed by random dispersions of low permittivity inclusions in a ferroelectric matrix, using finite element simulations. We show how the degree of impenetrability of dielectric inclusions plays a substantial role in controlling the coercive field, remnant and saturation polarizations of the homogenized materials. The results highlight the significance of the degree of impenetrability of inclusion in tuning the effective polarization properties of such ferroelectric composites: coercive field drops significantly as percolation threshold is attained and remnant polarization decreases faster than a linear decay.}}, author = {{Myroshnychenko, Viktor and Mulavarickal Jose, Pious Mathews and Farheen, Henna and Ejaz, Shafaq and Brosseau, Christian and Förstner, Jens}}, issn = {{0031-8949}}, journal = {{Physica Scripta}}, keywords = {{tet_topic_ferro}}, number = {{4}}, pages = {{045952}}, publisher = {{IOP Publishing}}, title = {{{From Swiss-cheese to discrete ferroelectric composites: assessing the ferroelectric butterfly shape in polarization loops}}}, doi = {{10.1088/1402-4896/ad3172}}, volume = {{99}}, year = {{2024}}, } @article{46469, abstract = {{We show how to learn discrete field theories from observational data of fields on a space-time lattice. For this, we train a neural network model of a discrete Lagrangian density such that the discrete Euler--Lagrange equations are consistent with the given training data. We, thus, obtain a structure-preserving machine learning architecture. Lagrangian densities are not uniquely defined by the solutions of a field theory. We introduce a technique to derive regularisers for the training process which optimise numerical regularity of the discrete field theory. Minimisation of the regularisers guarantees that close to the training data the discrete field theory behaves robust and efficient when used in numerical simulations. Further, we show how to identify structurally simple solutions of the underlying continuous field theory such as travelling waves. This is possible even when travelling waves are not present in the training data. This is compared to data-driven model order reduction based approaches, which struggle to identify suitable latent spaces containing structurally simple solutions when these are not present in the training data. Ideas are demonstrated on examples based on the wave equation and the Schrödinger equation. }}, author = {{Offen, Christian and Ober-Blöbaum, Sina}}, issn = {{1054-1500}}, journal = {{Chaos}}, number = {{1}}, publisher = {{AIP Publishing}}, title = {{{Learning of discrete models of variational PDEs from data}}}, doi = {{10.1063/5.0172287}}, volume = {{34}}, year = {{2024}}, } @unpublished{55159, abstract = {{We introduce a method based on Gaussian process regression to identify discrete variational principles from observed solutions of a field theory. The method is based on the data-based identification of a discrete Lagrangian density. It is a geometric machine learning technique in the sense that the variational structure of the true field theory is reflected in the data-driven model by design. We provide a rigorous convergence statement of the method. The proof circumvents challenges posed by the ambiguity of discrete Lagrangian densities in the inverse problem of variational calculus. Moreover, our method can be used to quantify model uncertainty in the equations of motions and any linear observable of the discrete field theory. This is illustrated on the example of the discrete wave equation and Schrödinger equation. The article constitutes an extension of our previous article arXiv:2404.19626 for the data-driven identification of (discrete) Lagrangians for variational dynamics from an ode setting to the setting of discrete pdes.}}, author = {{Offen, Christian}}, keywords = {{System identification, inverse problem of variational calculus, Gaussian process, Lagrangian learning, physics informed machine learning, geometry aware learning}}, pages = {{28}}, title = {{{Machine learning of discrete field theories with guaranteed convergence and uncertainty quantification}}}, year = {{2024}}, } @article{55989, abstract = {{Phased arrays are vital in communication systems and have received significant interest in the field of optoelectronics and photonics, enabling a wide range of applications such as LiDAR, holography, wireless communication, etc. In this work, we present a blazed grating antenna that is optimized to have upward radiation efficiency as high as 80% with a compact footprint of 3.5 μm × 2 μm at an operational wavelength of 1.55 μm. Our numerical investigations demonstrate that this antenna in a 64 × 64 phased array configuration is capable of producing desired far-field radiation patterns. Additionally, our antenna possesses a low side lobe level of -9.7 dB and a negligible reflection efficiency of under 1%, making it an attractive candidate for integrated optical phased arrays.}}, author = {{Farheen, Henna and Joshi, Suraj and Scheytt, J. Christoph and Myroshnychenko, Viktor and Förstner, Jens}}, issn = {{2515-7647}}, journal = {{Journal of Physics: Photonics}}, keywords = {{tet_topic_opticalantenna}}, pages = {{045010}}, publisher = {{IOP Publishing}}, title = {{{An efficient compact blazed grating antenna for optical phased arrays}}}, doi = {{10.1088/2515-7647/ad6ed4}}, volume = {{6}}, year = {{2024}}, } @inproceedings{56194, author = {{Afsahnoudeh, Reza and Riese, Julia and Kenig, Eugeny Y.}}, booktitle = {{World Congress on Mechanical, Chemical, and Material Engineering}}, issn = {{2369-8136}}, location = {{Barcelona}}, publisher = {{Avestia Publishing}}, title = {{{A Numerical Analysis of Thermo-Hydraulic Performance of Pillow-Plate Heat Exchangers with Ellipsoidal Secondary Structures}}}, doi = {{10.11159/htff24.145}}, year = {{2024}}, }