@inproceedings{58761, author = {{Dechert, Christopher and Riese, Julia and Franke, Patrick}}, location = {{Bochum}}, title = {{{Untersuchung zur Vergleichbarkeit von verschiedenen Methoden zur Bestimmung der effektiven Phasengrenzflächen}}}, year = {{2025}}, } @article{53805, abstract = {{The article introduces a method to learn dynamical systems that are governed by Euler–Lagrange equations from data. The method is based on Gaussian process regression and identifies continuous or discrete Lagrangians and is, therefore, structure preserving by design. A rigorous proof of convergence as the distance between observation data points converges to zero and lower bounds for convergence rates are provided. Next to convergence guarantees, the method allows for quantification of model uncertainty, which can provide a basis of adaptive sampling techniques. We provide efficient uncertainty quantification of any observable that is linear in the Lagrangian, including of Hamiltonian functions (energy) and symplectic structures, which is of interest in the context of system identification. The article overcomes major practical and theoretical difficulties related to the ill-posedness of the identification task of (discrete) Lagrangians through a careful design of geometric regularisation strategies and through an exploit of a relation to convex minimisation problems in reproducing kernel Hilbert spaces.}}, author = {{Offen, Christian}}, journal = {{Mathematics of Computation}}, publisher = {{American Mathematical Society}}, title = {{{Machine learning of continuous and discrete variational ODEs with convergence guarantee and uncertainty quantification}}}, doi = {{10.1090/mcom/4120}}, year = {{2025}}, } @article{60298, abstract = {{In this work, we introduce PHOENIX, a highly optimized explicit open-source solver for two-dimensional nonlinear Schrödinger equations with extensions. The nonlinear Schrödinger equation and its extensions (Gross-Pitaevskii equation) are widely studied to model and analyze complex phenomena in fields such as optics, condensed matter physics, fluid dynamics, and plasma physics. It serves as a powerful tool for understanding nonlinear wave dynamics, soliton formation, and the interplay between nonlinearity, dispersion, and diffraction. By extending the nonlinear Schrödinger equation, various physical effects such as non-Hermiticity, spin-orbit interaction, and quantum optical aspects can be incorporated. PHOENIX is designed to accommodate a wide range of applications by a straightforward extendability without the need for user knowledge of computing architectures or performance optimization. The high performance and power efficiency of PHOENIX are demonstrated on a wide range of entry-class to high-end consumer and high-performance computing GPUs and CPUs. Compared to a more conventional MATLAB implementation, a speedup of up to three orders of magnitude and energy savings of up to 99.8% are achieved. The performance is compared to a performance model showing that PHOENIX performs close to the relevant performance bounds in many situations. The possibilities of PHOENIX are demonstrated with a range of practical examples from the realm of nonlinear (quantum) photonics in planar microresonators with active media including exciton-polariton condensates. Examples range from solutions on very large grids, the use of local optimization algorithms, to Monte Carlo ensemble evolutions with quantum noise enabling the tomography of the system's quantum state.}}, author = {{Wingenbach, Jan and Bauch, David and Ma, Xuekai and Schade, Robert and Plessl, Christian and Schumacher, Stefan}}, issn = {{0010-4655}}, journal = {{Computer Physics Communications}}, publisher = {{Elsevier BV}}, title = {{{PHOENIX – Paderborn highly optimized and energy efficient solver for two-dimensional nonlinear Schrödinger equations with integrated extensions}}}, doi = {{10.1016/j.cpc.2025.109689}}, volume = {{315}}, year = {{2025}}, } @inproceedings{60494, abstract = {{Pillow-plate heat exchangers (PPHEs) represent a viable alternative to conventional shell-and-tube and plate heat exchangers. The waviness of their channels intensifies fluid mixing in the boundary layers and facilitates heat transfer. Applying secondary surface structuring can further enhance the overall thermo-hydraulic performance of PPHEs, thus increasing their competitiveness against conventional heat exchangers. In this work, streamlined secondary structures applied on the PPHE surface were studied numerically to explore their potential in enhancing near-wall fluid mixing. Computational fluid dynamics (CFD) simulations of single-phase turbulent flow in the inner PPHE channel were performed and pressure drop, heat transfer coefficients, and overall thermo-hydraulic efficiency were determined. The simulation results clearly demonstrate a favourable influence of secondary structuring on the heat transfer performance of PPHEs.}}, author = {{Afsahnoudeh, Reza and Riese, Julia and Kenig, Eugeny Y.}}, booktitle = {{Systems and Control Transactions}}, issn = {{2818-4734}}, publisher = {{PSE Press}}, title = {{{Thermo-Hydraulic Performance of Pillow-Plate Heat Exchangers with Streamlined Secondary Structures: A Numerical Analysis}}}, doi = {{10.69997/sct.178665}}, volume = {{4}}, year = {{2025}}, } @article{60565, author = {{Bocchini, Adriana and Gerstmann, Uwe and Schmidt, Wolf Gero}}, issn = {{2469-9950}}, journal = {{Physical Review B}}, number = {{10}}, publisher = {{American Physical Society (APS)}}, title = {{{Microscopic origin of gray tracks in KTiOPO4}}}, doi = {{10.1103/physrevb.111.104103}}, volume = {{111}}, year = {{2025}}, } @article{58642, abstract = {{We present a cost-effective self-assembly method to fabricate low-density dimer NPs in an NPoM architecture, using the M13 phage as a spacer layer. This will enable the development of dynamic plasmonic devices and advanced sensing applications.}}, author = {{Devaraj, Vasanthan and Ruiz Alvarado, Isaac Azahel and Lee, Jong-Min and Oh, Jin-Woo and Gerstmann, Uwe and Schmidt, Wolf Gero and Zentgraf, Thomas}}, issn = {{2055-6756}}, journal = {{Nanoscale Horizons}}, pages = {{537--548}}, publisher = {{Royal Society of Chemistry (RSC)}}, title = {{{Self-assembly of isolated plasmonic dimers with sub-5 nm gaps on a metallic mirror}}}, doi = {{10.1039/d4nh00546e}}, volume = {{10}}, 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}}, } @inproceedings{58861, author = {{Luchterhandt, Lars and Govindasamy, Vivek and Wang, Yutong and Dömer, Rainer and Müller, Wolfgang and Scheytt, J. Christoph}}, booktitle = {{OSSMPIC - Open Source Solutions for Massively Parallel Integrated Circuits}}, title = {{{Case Study on Combining Open-Source Tool Flows for Grids of Processing Cells}}}, 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}}, }