@inbook{30288, abstract = {{Lithium niobate (LiNbO3), a material frequently used in optical applications, hosts different kinds of polarons that significantly affect many of its physical properties. In this study, a variety of electron polarons, namely free, bound, and bipolarons, are analyzed using first-principles calculations. We perform a full structural optimization based on density-functional theory for selected intrinsic defects with special attention to the role of symmetry-breaking distortions that lower the total energy. The cations hosting the various polarons relax to a different degree, with a larger relaxation corresponding to a larger gap between the defect level and the conduction-band edge. The projected density of states reveals that the polaron states are formerly empty Nb 4d states lowered into the band gap. Optical absorption spectra are derived within the independent-particle approximation, corrected by the GW approximation that yields a wider band gap and by including excitonic effects within the Bethe-Salpeter equation. Comparing the calculated spectra with the density of states, we find that the defect peak observed in the optical absorption stems from transitions between the defect level and a continuum of empty Nb 4d states. Signatures of polarons are further analyzed in the reflectivity and other experimentally measurable optical coefficients.}}, author = {{Schmidt, Falko and Kozub, Agnieszka L. and Gerstmann, Uwe and Schmidt, Wolf Gero and Schindlmayr, Arno}}, booktitle = {{New Trends in Lithium Niobate: From Bulk to Nanocrystals}}, editor = {{Corradi, Gábor and Kovács, László}}, isbn = {{978-3-0365-3340-7}}, pages = {{231--248}}, publisher = {{MDPI}}, title = {{{Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response}}}, doi = {{10.3390/books978-3-0365-3339-1}}, year = {{2022}}, } @inproceedings{41800, author = {{Sartison, M and Camacho Ibarra, O and Jöns, Klaus D. and Caltzidis, I and Reuter, Dirk}}, title = {{{Scalable integration of quantum emitters into photonic integrated circuits}}}, doi = {{https://doi.org/10.1088/2633-4356/ac6f3e}}, volume = {{2}}, year = {{2022}}, } @article{40371, abstract = {{Multimode integrated interferometers have great potential for both spectral engineering and metrological applications. However, the material dispersion of integrated platforms constitutes an obstacle that limits the performance and precision of such interferometers. At the same time, two-colour nonlinear interferometers present an important tool for metrological applications, when measurements in a certain frequency range are difficult. In this manuscript, we theoretically developed and investigated an integrated multimode two-colour SU(1,1) interferometer operating in a supersensitive mode. By ensuring the proper design of the integrated platform, we suppressed the dispersion, thereby significantly increasing the visibility of the interference pattern. The use of a continuous wave pump laser provided the symmetry between the spectral shapes of the signal and idler photons concerning half the pump frequency, despite different photon colours. We demonstrate that such an interferometer overcomes the classical phase sensitivity limit for wide parametric gain ranges, when up to 3×104 photons are generated.}}, author = {{Ferreri, Alessandro and Sharapova, Polina R.}}, issn = {{2073-8994}}, journal = {{Symmetry}}, keywords = {{Physics and Astronomy (miscellaneous), General Mathematics, Chemistry (miscellaneous), Computer Science (miscellaneous)}}, number = {{3}}, publisher = {{MDPI AG}}, title = {{{Two-Colour Spectrally Multimode Integrated SU(1,1) Interferometer}}}, doi = {{10.3390/sym14030552}}, volume = {{14}}, year = {{2022}}, } @article{30210, abstract = {{Lithium niobate on insulator (LNOI) has a great potential for photonic integrated circuits, providing substantial versatility in design of various integrated components. To properly use these components in the implementation of different quantum protocols, photons with different properties are required. In this paper, we theoretically demonstrate a flexible source of correlated photons built on the LNOI waveguide of a special geometry. This source is based on the parametric down-conversion (PDC) process, in which the signal and idler photons are generated at the telecom wavelength and have different spatial profiles and polarizations, but the same group velocities. Distinguishability in polarizations and spatial profiles facilitates the routing and manipulating individual photons, while the equality of their group velocities leads to the absence of temporal walk-off between photons. We show how the spectral properties of the generated photons and the number of their frequency modes can be controlled depending on the pump characteristics and the waveguide length. Finally, we discuss special regimes, in which narrowband light with strong frequency correlations and polarization-entangled Bell states are generated at the telecom wavelength.}}, author = {{Ebers, Lena and Ferreri, Alessandro and Hammer, Manfred and Albert, Maximilian and Meier, Cedrik and Förstner, Jens and Sharapova, Polina R.}}, issn = {{2515-7647}}, journal = {{Journal of Physics: Photonics}}, keywords = {{tet_topic_waveguide}}, pages = {{025001}}, publisher = {{IOP Publishing}}, title = {{{Flexible source of correlated photons based on LNOI rib waveguides}}}, doi = {{10.1088/2515-7647/ac5a5b}}, volume = {{4}}, year = {{2022}}, } @article{30921, abstract = {{Quantum walks function as essential means to implement quantum simulators, allowing one to study complex and often directly inaccessible quantum processes in controllable systems. In this contribution, the notion of a driven Gaussian quantum walk is introduced. In contrast to typically considered quantum walks in optical settings, we describe the operation of the walk in terms of a nonlinear map rather than a unitary operation, e.g., by replacing a beam-splitter-type coin with a two-mode squeezer, being a process that is controlled and driven by a pump field. This opens previously unattainable possibilities for quantum walks that include nonlinear elements as core components of their operation, vastly extending their range of applications. A full framework for driven Gaussian quantum walks is developed, including methods to dynamically characterize nonlinear, quantum, and quantum-nonlinear effects. Moreover, driven Gaussian quantum walks are compared with their classically interfering and linear counterparts, which are based on classical coherence of light rather than quantum superpositions. In particular, the generation and boost of highly multimode entanglement, squeezing, and other quantum effects are studied over the duration of the nonlinear walk. Importantly, we prove the quantumness of the evolution itself, regardless of the input state. A scheme for an experimental realization is proposed. Furthermore, nonlinear properties of driven Gaussian quantum walks are explored, such as amplification that leads to an ever increasing number of correlated quantum particles, constituting a source of new walkers during the walk. Therefore, a concept for quantum walks is proposed that leads to—and even produces—directly accessible quantum phenomena, and that renders the quantum simulation of nonlinear processes possible.}}, author = {{Held, Philip and Engelkemeier, Melanie and De, Syamsundar and Barkhofen, Sonja and Sperling, Jan and Silberhorn, Christine}}, issn = {{2469-9926}}, journal = {{Physical Review A}}, number = {{4}}, publisher = {{American Physical Society (APS)}}, title = {{{Driven Gaussian quantum walks}}}, doi = {{10.1103/physreva.105.042210}}, volume = {{105}}, year = {{2022}}, } @phdthesis{24760, abstract = {{Anwendungen von Laser-Sinter Bauteilen als Sichtteile sind aufgrund der vergleichsweise schlechten Oberflächenqualität sehr begrenzt. In dieser Arbeit werden dreidimensionale Kennwerte benutzt, um die Oberflächenqualität von Laser-Sinter Bauteiloberflächen und die Einflüsse aus unterschiedlichen Bereichen der gesamten Prozesskette zu evaluieren. Beispielsweise wurden objektive Kennwerte, mit deren Hilfe Orangenhaut zu identifizieren ist, und Prozessparameter, die diese deutlich vermindern, gefunden. Mittels Durchführung von haptischen Versuchen wurde das subjektive Empfinden ermittelt und konnten zu objektiven Kennwerten korreliert werden. Eine mikroskopische Betrachtung des flachen Oberflächenwinkels mit verschieden farbigen Pulvern zeigt neue Erkenntnisse zum Anschmelzvorgang von Partikeln an die Schmelze. Zur nachträglichen Glättung von Oberflächen wurden mechanische, chemische und optische Nachbehandlungsmethoden verwendet und deren Potential aufgezeigt. Eine abschließende neuartige Simulation der dreidimensionalen Topografie bildet die Grundlage für ein Programm zur automatischen und funktionsgerechten Orientierung von Bauteilen, welche am Beispiel eines realen Bauteils erfolgreich validiert wurde. Zusammengenommen zeigen die Ergebnisse, dass die richtige Wahl von Bauorientierung und Prozessparametern entscheidend für die Bauteilqualität ist und selbst eine aufwendige Nachbearbeitung eine ungeschickte Wahl derer nur schwerlich ausgleichen kann. }}, author = {{Delfs, Patrick}}, isbn = {{978-3-8440-7825-1}}, keywords = {{Additive Fertigung, Oberflächenqualität, 3D, Topografie, Simulation, PA12, Laser-Sintern, Rauheit}}, pages = {{126}}, publisher = {{Shaker Verlag GmbH}}, title = {{{Dreidimensionale Oberflächenanalyse und Topografie-Simulation additiv hergestellter Laser-Sinter Bauteile}}}, volume = {{22}}, year = {{2021}}, } @phdthesis{24770, abstract = {{Das Fused Deposition Modeling (FDM) ist ein Verfahren zur additiven Fertigung (AF), welches von der Firma Stratasys Ltd. (früher Stratasys Inc.) kommerzialisiert wurde. Heute existieren auch FDM Maschinen anderer Hersteller. Im Gegensatz zu den Maschinen von Stratasys können bei diesen die Prozessparameter frei gewählt werden. Dadurch ist die Verarbeitung herstellerfremder Materialien möglich. Wie in allen AF-Verfahren, werden im FDM bestimmte Anforderungen an die zu verarbeitenden Materialien gestellt. Die Materialien sollten daher speziell für das FDM ausgewählt bzw. entwickelt werden. Die für eine gute Verarbeitbarkeit notwendigen Materialeigenschaften sind aktuell jedoch nicht hinreichend bekannt. Vielmehr sind auch keine Vorgehensweisen bekannt, um die Verarbeitungseignung verschiedener Materialien im FDM zu bewerten. Im Rahmen dieser Arbeit werden daher Vorgehensweisen vorgestellt, um die Verarbeitungseignung thermoplastischer Kunststoffe im FDM anhand bestimmter Merkmale zu bewerten. Die Schweißnahtqualität, der Bauteilverzug und die Gestaltungsfreiheit werden als wichtige Merkmale identifiziert. Unter Beachtung relevanter Einflussgrößen werden je Merkmal Probekörper und Prüfmethoden entwickelt, um merkmalspezifische Kennwerte zu definieren. Dadurch ist der Vergleich unterschiedlicher Materialien, unabhängig von der verwendeten Maschine und der Datenaufbereitung, möglich. Letztendlich werden verschiedene Materialmodifikationen auf Basis von PA 6 erstellt und mit Hilfe der vorgestellten Vorgehensweisen untersucht und bewertet.}}, author = {{Schumacher, Christian}}, isbn = {{978-3-8440-7925-8}}, pages = {{262}}, publisher = {{Shaker Verlag}}, title = {{{Erarbeitung eines methodischen Vorgehens zur merkmalspezifischen Charakterisierung der Verarbeitungseignung von nicht verstärkten und faserverstärkten Kunststoffen im Fused Deposition Modeling am Beispiel von Polyamid 6}}}, volume = {{24}}, year = {{2021}}, } @article{25272, author = {{Engelkemeier, Katja and Sun, Aijia and Voswinkel, Dietrich and Grydin, Olexandr and Schaper, Mirko and Bremser, Wolfgang}}, issn = {{2196-0216}}, journal = {{ChemElectroChem}}, pages = {{2155--2168}}, title = {{{Zinc Anodizing: Structural Diversity of Anodic Zinc Oxide Controlled by the Type of Electrolyte}}}, doi = {{10.1002/celc.202100216}}, year = {{2021}}, } @inproceedings{25576, author = {{Moritzer, Elmar and Krassmann, Dimitri and Brikmann, Johannes}}, title = {{{Joining of Sheet Metal and Thermoplastic Composites Using Injection Riveting}}}, year = {{2021}}, } @article{25577, author = {{Moritzer, Elmar and Krassmann, Dimitri and Brikmann, Johannes}}, journal = {{Joining Plastics}}, number = {{3-4}}, title = {{{Fügen von thermoplastischen Composites mit Metallteilen durch Spritznieten}}}, volume = {{15}}, year = {{2021}}, } @article{25605, abstract = {{The nonlinear process of second harmonic generation (SHG) in monolayer (1L) transition metal dichalcogenides (TMD), like WS2, strongly depends on the polarization state of the excitation light. By combination of plasmonic nanostructures with 1L-WS2 by transferring it onto a plasmonic nanoantenna array, a hybrid metasurface is realized impacting the polarization dependency of its SHG. Here, we investigate how plasmonic dipole resonances affect the process of SHG in plasmonic–TMD hybrid metasurfaces by nonlinear spectroscopy. We show that the polarization dependency is affected by the lattice structure of plasmonic nanoantenna arrays as well as by the relative orientation between the 1L-WS2 and the individual plasmonic nanoantennas. In addition, such hybrid metasurfaces show SHG in polarization states, where SHG is usually forbidden for either 1L-WS2 or plasmonic nanoantennas. By comparing the SHG in these channels with the SHG generated by the hybrid metasurface components, we detect an enhancement of the SHG signal by a factor of more than 40. Meanwhile, an attenuation of the SHG signal in usually allowed polarization states is observed. Our study provides valuable insight into hybrid systems where symmetries strongly affect the SHG and enable tailored SHG in 1L-WS2 for future applications.}}, author = {{Spreyer, Florian and Ruppert, Claudia and Georgi, Philip and Zentgraf, Thomas}}, issn = {{1936-0851}}, journal = {{ACS Nano}}, number = {{10}}, pages = {{16719--16728}}, title = {{{Influence of Plasmon Resonances and Symmetry Effects on Second Harmonic Generation in WS2–Plasmonic Hybrid Metasurfaces}}}, doi = {{10.1021/acsnano.1c06693}}, volume = {{15}}, year = {{2021}}, } @inproceedings{20244, author = {{Gottschalk, Sebastian and Kirchhoff, Jonas and Engels, Gregor}}, booktitle = {{Business Modeling and Software Design}}, editor = {{Shishkov, Boris}}, location = {{Sofia}}, title = {{{Extending Business Model Development Tools with Consolidated Expert Knowledge }}}, doi = {{10.1007/978-3-030-79976-2_1}}, year = {{2021}}, } @article{28017, abstract = {{Processing aluminum alloys employing powder bed fusion of metals (PBF-LB/M) is becoming more attractive for the industry, especially if lightweight applications are needed. Unfortunately, high-strength aluminum alloys such as AA7075 are prone to hot cracking during PBF-LB/M, as well as welding. Both a large solidification range promoted by the alloying elements zinc and copper and a high thermal gradient accompanied with the manufacturing process conditions lead to or favor hot cracking. In the present study, a simple method for modifying the powder surface with titanium carbide nanoparticles (NPs) as a nucleating agent is aimed. The effect on the microstructure with different amounts of the nucleating agent is shown. For the aluminum alloy 7075 with 2.5 ma% titanium carbide nanoparticles, manufactured via PBF-LB/M, crack-free samples with a refined microstructure having no discernible melt pool boundaries and columnar grains are observed. After using a two-step ageing heat treatment, ultimate tensile strengths up to 465 MPa and an 8.9% elongation at break are achieved. Furthermore, it is demonstrated that not all nanoparticles used remain in the melt pool during PBF-LB/M.}}, author = {{Heiland, Steffen and Milkereit, Benjamin and Hoyer, Kay-Peter and Zhuravlev, Evgeny and Keßler, Olaf and Schaper, Mirko}}, journal = {{Materials}}, keywords = {{grain refinement, crack reduction, laser beam melting, aluminum alloy, titanium carbide, nanoparticle, PBF-LB/M}}, title = {{{Requirements for Processing High-Strength AlZnMgCu Alloys with PBF-LB/M to Achieve Crack-Free and Dense Parts}}}, doi = {{https://doi.org/10.3390/ma14237190}}, year = {{2021}}, } @article{28099, abstract = {{N-body methods are one of the essential algorithmic building blocks of high-performance and parallel computing. Previous research has shown promising performance for implementing n-body simulations with pairwise force calculations on FPGAs. However, to avoid challenges with accumulation and memory access patterns, the presented designs calculate each pair of forces twice, along with both force sums of the involved particles. Also, they require large problem instances with hundreds of thousands of particles to reach their respective peak performance, limiting the applicability for strong scaling scenarios. This work addresses both issues by presenting a novel FPGA design that uses each calculated force twice and overlaps data transfers and computations in a way that allows to reach peak performance even for small problem instances, outperforming previous single precision results even in double precision, and scaling linearly over multiple interconnected FPGAs. For a comparison across architectures, we provide an equally optimized CPU reference, which for large problems actually achieves higher peak performance per device, however, given the strong scaling advantages of the FPGA design, in parallel setups with few thousand particles per device, the FPGA platform achieves highest performance and power efficiency.}}, author = {{Menzel, Johannes and Plessl, Christian and Kenter, Tobias}}, issn = {{1936-7406}}, journal = {{ACM Transactions on Reconfigurable Technology and Systems}}, number = {{1}}, pages = {{1--30}}, title = {{{The Strong Scaling Advantage of FPGAs in HPC for N-body Simulations}}}, doi = {{10.1145/3491235}}, volume = {{15}}, year = {{2021}}, } @phdthesis{28371, author = {{Drewel, Marvin}}, isbn = {{978-3-947647-16-3}}, publisher = {{Verlagsschriftenreihe des Heinz Nixdorf Instituts, Paderborn}}, title = {{{Systematik zum Einstieg in die Plattformökonomie}}}, volume = {{397}}, year = {{2021}}, } @phdthesis{28372, author = {{Frank, Maximilian}}, isbn = {{978-3-947647-17-0}}, publisher = {{Verlagsschriftenreihe des Heinz Nixdorf Instituts, Paderborn}}, title = {{{Systematik zur Planung des organisationalen Wandels zum Smart Service-Anbieter}}}, volume = {{398}}, year = {{2021}}, } @phdthesis{28374, author = {{Bretz, Lukas}}, isbn = {{978-3-947647-20-0}}, publisher = {{Verlagsschriftenreihe des Heinz Nixdorf Instituts, Paderborn}}, title = {{{Rahmenwerk zur Planung und Einführung von Systems Engineering und Model-Based Systems Engineering}}}, volume = {{401}}, year = {{2021}}, } @inproceedings{28440, author = {{Triebus, Marcel and Reitz, Alexander and Grydin, Olexandr and Grenz, Julian and Schneidt, Andreas and Erhardt, Rüdiger and Tröster, Thomas and Schaper, Mirko}}, booktitle = {{13th European LS-DYNA Conference 2021}}, location = {{Ulm}}, title = {{{Forming Simulation of Tailored Press Hardened Parts}}}, year = {{2021}}, } @book{28461, author = {{Tröster, Thomas and Pfeifer, Florian and Nacke, Bernard and Dietrich, André}}, isbn = {{978-3-96780-002-9 }}, publisher = {{Forschungsvereinigung Stahlanwendung e.V.}}, title = {{{Großserientaugliche induktive Platinenerwärmung für den Warmformprozess}}}, volume = {{P1038}}, year = {{2021}}, } @misc{24095, author = {{Moritzer, Elmar and Hecker, Felix and Hirsch, André}}, booktitle = {{Kunststoffland NRW report}}, number = {{2}}, pages = {{42--43}}, title = {{{Aus der Forschung in die Anwendung - Materialqualifizierung im Kunststoff Freiformen}}}, volume = {{2021}}, year = {{2021}}, }