@article{KranzWagnerPointneretal., author = {Kranz, Michael and Wagner, Maria Stella and Pointner, Daniel and Haus, Moritz and Lubnow, Matthias and Lehle, Karla and Krenkel, Lars}, title = {Polymer embedding of membrane lungs for histological investigations of intra-device clot formation}, series = {Cardiovascular Medicine}, volume = {13}, journal = {Cardiovascular Medicine}, publisher = {Frontiers}, address = {Lausanne}, doi = {10.3389/fcvm.2026.1650978}, pages = {21}, abstract = {Extracorporeal membrane oxygenation (ECMO) is an invasive but potentially lifesaving treatment option for severe cardiac or respiratory failure. Despite its beneficial effect, coagulation-related complications, mainly due to clot formation, excessive bleeding and the accumulation of deposits in the membrane lung (ML) remain common, causing higher mortality. In this context, the formation of clots and other deposits in the ML is of particular interest. Previous histological examinations of the polymethylpentene fiber mats inside the ML could only be performed in a top view, prohibiting valid quantification and examination of the multi-layered deposits or fiber mat spanning structures. Our objective was the establishment of a polymer embedding to increase the mechanical stability of the deposits and thus enable cross-sectional microtome cutting through the ML hollow-fibers. Clinically used MLs (PLS, Getinge, Rastatt, Germany) were stabilized with a polymer resin (HistoCURE 8100). Specimens were cut out of the embedded MLs and microtome sections with a thickness of 10 µm were performed. In addition to standard histological staining with hematoxylin-eosin (HE) and Pappenheim (May-Grunwald-Giemsa), fluorescence DNA staining for nucleated cells with 4′,6-diamidino-2-phenylindole (DAPI) and SYTOX™ Green as well as immunohistochemical and immunofluorescence staining for the lysosomal enzyme myeloperoxidase (MPO) and von Willebrand factor (vWF) were established. The protocol provides a method for large volume embedding (400 mL). The cellular and extracellular deposits were securely fixed by the polymer scaffold allowing the examination of clots in MLs in native position which was not possible with conventional paraffin embedding. Multi-layered deposits and fiber mat spanning structures are no longer disrupted during specimen extraction and can now be quantified. Staining with HE, Pappenheim, DAPI, SYTOX™ Green, MPO, and vWF was successfully tested with this protocol. This method may be the foundation for new insights into the complex clotting phenomena observed in MLs}, language = {en} } @techreport{SchuheggerGalka, author = {Schuhegger, Lukas and Galka, Stefan}, title = {Herausforderungen von produzierenden Startups}, doi = {10.35096/othr/pub-8852}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-88520}, pages = {30}, abstract = {Startups bringen mit ihrer Dynamik und neuen innovativen Gesch{\"a}ftsmodellen frischen Wind in die deutsche Unternehmenslandschaft. Die disruptiven Ans{\"a}tze gestalten die Zukunft und damit geraten sie immer weiter in den Fokus, unter anderem auch f{\"u}r Investoren. Das Ziel der Studie ist es, Zusammenh{\"a}nge zwischen Herausforderungen und Eigenschaften von produzierenden Startups darzulegen. Dieses Wissen soll an andere Startups weitergegeben werden, um die Erfolgschancen in der Gr{\"u}nderszene zu erh{\"o}hen. Im Juli 2021 wurde hierzu eine Umfrage entworfen, um die Erfahrungen von Gr{\"u}ndern und Startup-Mitarbeitern zu sammeln und die spezifischen Herausforderungen besser zu verstehen.}, subject = {Unternehmensgr{\"u}ndung}, language = {de} } @unpublished{LehrerStockerDuddecketal., author = {Lehrer, Tobias and Stocker, Philipp and Duddeck, Fabian and Wagner, Marcus}, title = {UCSM: Dataset of U-Shaped Parametric CAD Geometries and Real-World Sheet Metal Meshes for Deep Drawing}, publisher = {SSRN}, doi = {10.2139/ssrn.5268323}, pages = {19}, abstract = {The development of machine learning (ML) applications in deep drawing is hindered by limited data availability and the absence of open-access benchmarks for validating novel approaches, including domain generalization over distinct geometries. This paper addresses these challenges by introducing a comprehensive U-shaped dataset tailored to this manufacturing process. Our U-Channel sheet metal (UCSM) dataset combines 90 real-world meshes with an infinite number of synthetic geometry samples generated from four parametric Computer-Aided Design (CAD) models, ensuring extensive geometry variety and data quantity. Additionally, a ready-to-use dataset for drawability assessment and segmentation is provided. Leveraging CAD and mesh data sources bridges the gap between sparse data availability and ML requirements. Our analysis demonstrates that the proposed parametric models are geometrically valid, and real-world and synthetic data complement each other effectively, providing robust support for ML model development. While the dataset is confined to U-shaped, thin-walled, deep drawing scenarios, it considerably aids in overcoming data scarcity. Thereby, it facilitates the validation and comparison of new geometry-generalizing ML methodologies in this domain. By providing this benchmark dataset, we enhance the comparability and validation of emerging methods for ML advancements in sheet metal forming.}, language = {en} } @misc{StockerLehrer, author = {Stocker, Philipp and Lehrer, Tobias}, title = {Machine Learning Dataset of U-Channel Sheet Metal Geometry Representations with Supervision Information for Drawability Assessment and Part Segmentation [Data set]}, doi = {10.5281/zenodo.15327950}, abstract = {The dataset contains 2533 geometries from four different parametric CAD models sampled from the U-Channel python package. The representations include the original CAD geometries (.step), graph binaries (.bin), meshes (.off), and point clouds (.xyz). Additionally, we provide labels for supervised learning use cases of local and global drawability assessment and part segmentation (.json) for all representations. Custom label computation for drawability assessment is enabled by the provided strains.zip file, which contains minor and major true strains for the given meshes. For more details, refer to the associated publication.}, language = {en} } @article{KuettnerFischerLaumer, author = {Kuettner, Andreas and Fischer, Samuel and Laumer, Tobias}, title = {Mechanical and structural characterization of heat-staked parts realized by selective laser sintering of polyamide 12}, series = {The International Journal of Advanced Manufacturing Technology}, journal = {The International Journal of Advanced Manufacturing Technology}, publisher = {Springer}, doi = {10.1007/s00170-025-17319-4}, pages = {20}, abstract = {Heat staking is a joining process in which thermoplastic pins are formed by heat and pressure in a form-fitting and insoluble way. This study evaluates the mechanical performance and microstructure of selective laser sintered (SLS) polyamide 12 (PA 12) components before and after heat staking, compared with conventionally turned reference specimens. The components were characterized using tensile tests, micrographs, microscopy, and micro-CT measurements. For the tests, the forces and temperatures during heat staking were varied to determine the best process parameters. Tensile tests revealed that SLS joints achieved strengths of up to 33.6 MPa, approaching the 39.9 MPa of the turned references. Microstructural analysis showed a marked reduction in porosity due to heat staking. Porosity decreased from 3.9\% to 1.56\% at a staking force of 300 N and from 4.29\% to 0.81\% at 1000 N, highlighting the beneficial effect of increased force. These results demonstrate that heat staking parameters significantly influence local densification and mechanical performance, and that, under suitable conditions, SLS components can achieve joint strengths comparable to conventionally manufactured parts. The study shows that the heat staking process parameters have a significant influence on the local microstructure and thus on the mechanical performance and provides a basis for optimizing SLS components for new heat staking applications.}, language = {en} } @inproceedings{GalkaStrassburgerLangetal., author = {Galka, Stefan and Strassburger, Steffen and Lang, Sebastian and Reggelin, Tobias}, title = {Introduction to the Minitrack on Simulation Modeling and Digital Twins for Decision Making in the Age of Industry 4.0}, series = {Proceedings of the 57th Hawaii International Conference on System Sciences (HICSS), January3-6, 2024, Honolulu, Hawaii}, booktitle = {Proceedings of the 57th Hawaii International Conference on System Sciences (HICSS), January3-6, 2024, Honolulu, Hawaii}, editor = {Bui, Tung}, publisher = {ScholarSpace}, isbn = {978-0-9981331-7-1}, doi = {10.24251/HICSS.2024.206}, pages = {1647 -- 1648}, abstract = {The minitrack contains contributions with a focus on simulation modeling and digital twins and decision making in the context of Industry 4.0. The use of simulation models and digital twins is manifold, from planning to virtual commission and real-time operational decision support. Cyber-physical systems integrate the real world and the virtual world to enable decision making in the age of Industry 4.0. For example, customer decisions and supply disruptions which directly influence manufacturing and logistics systems require immediate decisions. Thus, models must have the capability to support decision making in manufacturing as well as in internal and external logistics in real-time. Methods include discrete-event simulation, discrete-rate simulation, hybrid simulation, system dynamics simulation, the combination of simulation modeling with machine learning or optimization heuristics, prescriptive analytics, and adaptive systems. Furthermore, this minitrack addresses simulation education and simulation models used for education and training in manufacturing and logistics.}, language = {en} } @phdthesis{Eigenberger, author = {Eigenberger, Andreas}, title = {Die Auswirkungen der mechanischen Kr{\"a}fte eines innovativen Operationsverfahrens f{\"u}r die intraoperative Gewebezubereitung bei autologem Fetttransfer auf das Fettgewebe und dessen Stammzellen}, address = {Regensburg}, pages = {235 Bl{\"a}tter}, language = {de} } @article{WeindlerLehnerEcksteinetal., author = {Weindler, Jeremy and Lehner, Hannes and Eckstein, J. and Dawoud, Belal}, title = {Performance assessment of a green hydrogen-based household energy system supported by a battery storage at different resolutions of the electrical load profile}, series = {International Journal of Hydrogen Energy}, volume = {144}, journal = {International Journal of Hydrogen Energy}, publisher = {Elsevier}, issn = {0360-3199}, doi = {10.1016/j.ijhydene.2025.04.431}, pages = {30 -- 41}, abstract = {Hydrogen deems quite suitable for medium- and long-term energy storage of surplus renewable electricity. Nowadays, all-in-one solutions consisting of an electrolyzer, a compressor, pressurized hydrogen storage tanks, a fuel cell (FC) and the necessary peripheral components are available for single family houses. This work presents a comparative assessment of the system's key performance indicators in a household system with three market available FCs with the nominal powers of 0.8, 1.4 and 7.8 kW. The design tool developed for the assessment of the hybrid energy system along with two energy management system configurations are introduced. An electrochemical and thermal model widely applied in the literature is used to model the FCs, which is validated against the available experimental data in the literature for all three FCs. The influence of the FCs' nominal power, their power dynamic operation range, the use of a battery storage with different capacities and the load profile's resolution have been technically assessed regarding the system's self-sufficiency (SS), the FC's efficiency, full-load operating hours, and number of on/off cycles. It turned out that, the system performance is strongly dependent on the nominal power of the FC and its power dynamic operation range. If no battery-storage is applied, the complete grid independence is not possible, and a high resolution of the load profile is indispensable in the assessment of the system design. A hybrid energy system comprising the 1.4 kW FC, a PV system of 10 kW peak power and a battery of 15 kW storage capacity showed a degree of SS of 98\%. The number of the full-load operating hours and on/off cycles of that FC amount to 768 and 116 cycles, respectively. Such promising results are referred to the high dynamic operation range of the battery, and its high discharge power capacity, which makes it more suitable to cover a remarkably higher fraction of the load deficit, if compared to a system without a battery.}, language = {en} } @article{WeindlerDawoud, author = {Weindler, Jeremy and Dawoud, Belal}, title = {Experimental investigation of a small-scale continuous flow ohmic heating reactor for a highly effective conversion of renewable electricity surpluses into heat}, series = {Applied Thermal Engineering}, volume = {242}, journal = {Applied Thermal Engineering}, publisher = {Elsevier}, issn = {1359-4311}, doi = {10.1016/j.applthermaleng.2024.122401}, pages = {15}, abstract = {Sector coupling is expected to play a decisive role as a key technology to realize the energy transition towards green energy supply. This work introduces, therefore, a comprehensive experimental study on a new power-to-heat system based on the continuous-flow, ohmic heating principle, which aims at utilizing renewable electricity in green processes. The ohmic heating technology, which is widely applied in the food industry, has been adapted and evaluated for delivering heat and domestic hot water to a single-family house. The introduced prototype is designed to convert renewable electricity into heat in the power range between 1000 and 3000 W with a typical electrical household installation (230 V, 50 Hz and 16 A fuse). A dedicated test rig has been developed and a comprehensive experimental campaign has been carried out to investigate the performance of the introduced system under typical operating conditions of a single-family house. Both the conversion efficiency and the dynamics of the thermal response of the introduced system have been assessed. It turned out that, the temperature lift between the return and supply of the reactor, and consequently, the conversion efficiency of electrical into thermal energy, are independent on the return temperature, for a fixed value of the volume flow rate of the electrolyte solution. A remarkable steady-state conversion efficiency of 97.5\% has been measured. In addition, the dynamic response of the ohmic heating system has been found to be strongly dependent on the desired temperature lift. By an implemented controller, 95\% of the steady state temperature lift of 44.5 K can be realized in 50 s, which marks an exceptionally rapid thermal response. The obtained results pave the way towards a field test study of the developed technology in a real household installation as well as to extend the focus on new fields such as green chemical processes.}, language = {en} } @article{SittlMarburgDeckersetal., author = {Sittl, Christopher and Marburg, Steffen and Deckers, Elke and Wagner, Marcus}, title = {Model order reduction for unbounded second-order vibroacoustic systems using infinite elements and Dirichlet-to-Neumann map}, series = {Computer Methods in Applied Mechanics and Engineering}, volume = {453}, journal = {Computer Methods in Applied Mechanics and Engineering}, publisher = {Elsevier}, doi = {10.1016/j.cma.2026.118846}, pages = {22}, abstract = {This work addresses the efficient numerical simulation of time-harmonic vibroacoustic problems in unbounded domains, with a focus on fluid-structure interaction. The underlying mathematical model is a second-order dynamical system arising from the coupling of structural and acoustic domains, incorporating material damping effects, relevant in structural acoustics and noise control applications. A central novelty of the proposed method is its unified computational framework that supports two distinct strategies for treating unbounded fluid domains: (1) non-local absorbing boundary conditions based on Dirichlet-to-Neumann map, and (2) infinite elements, which extend the computational domain rather than truncate it. Both approaches are integrated into a consistent formulation that enables flexible and accurate modeling of exterior wave propagation. To efficiently evaluate frequency-domain transfer functions, the method employs model order reduction using the Pad{\´e}-via-Lanczos technique. While this algorithm typically targets first-order systems, the present approach uses a Schur complement strategy to reduce the second-order system in a way that maintains computational efficiency and storage requirements comparable to first-order formulations. Importantly, the framework seamlessly embeds both interior structural damping and the additional dissipation introduced by the acoustic-domain truncation into the model-order reduction process. The exterior acoustic field is represented via spherical harmonic expansions, with expansion coefficients computed from the reduced system. Numerical results demonstrate the method's accuracy, efficiency, and scalability, making it well-suited for high-fidelity vibroacoustic analysis in unbounded domains.}, language = {en} } @misc{LehrerStockerDuddecketal., author = {Lehrer, Tobias and Stocker, Philipp and Duddeck, Fabian and Wagner, Marcus}, title = {Parametric CAD Models to Create an Infinite Number of Structural U-Shaped Sheet Metal Geometries [Data set]}, doi = {10.5281/ZENODO.14191374}, abstract = {The U-Channel Software is a python package containing four parametric models of U-shaped Sheet metals. The parameters refer to geometric dimensions, angles, fillet radii. Using the models, one can generate an infinite number of U-shaped sheet metal geometries, e.g. as STEP files. The parametric models are inspired by real-world shapes. A feasibility check is provided to ensure plausiblity of the shapes. Further features of the code are creating images of the geometries and generating geometries and images in parallel. For more details, refer to the repository and associated publications.}, language = {en} } @phdthesis{Muehlbauer, author = {M{\"u}hlbauer, Christian}, title = {Entwicklung einer Methodik zur Bewertung und Optimierung des vibroakustischen Verhaltens von Kraftstoffeinspritzsystemen}, doi = {10.25673/109576}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:ma9:1-1981185920-1115312}, pages = {IX, 119}, abstract = {Die vorliegende Dissertation befasst sich mit der akustischen Analyse von Kraftstoffein-spritzsystemen und deren NVH-Optimierung mithilfe ansteuerungstechnischer Maßnahmen. Da sich der K{\"o}rper- und Luftschall beim Betrieb des Verbrennungsmotors mit anderen, nicht untersuchungsrelevanten Ger{\"a}uschkomponenten {\"u}berlagert, ist im Vollmotorbetrieb eine diffe-renzierte komponentenbasierte Ger{\"a}uschmessung nicht m{\"o}glich. Deshalb wurde ein NVH-Sys-tempr{\"u}fstand entwickelt, der eine isolierte akustische Vermessung von Einspritzsystemen im seriennahen Systemverbund erm{\"o}glicht. Die Betriebsparameter des Einspritzsystems wurden an einem Vollmotor in einem leerlaufna-hen Motorbetriebspunkt erfasst und mithilfe eines speziellen Entwicklungssteuerger{\"a}ts auf den NVH-Systempr{\"u}fstand transferiert. Ausgehend von dem definierten Referenzbetriebspunkt wurden sowohl die Randbedingungen als auch die Ansteuerstrategie variiert und deren Einfluss auf das akustische Verhalten analysiert. Dabei zeigten prim{\"a}r der Raildruck und die Anzahl der Einspritzungen einen ausgepr{\"a}gten Einfluss auf die betrachteten (psycho-)akustischen Parame-ter Schalldruckpegel, Lautheit, Sch{\"a}rfe und Impulshaltigkeit. Zur akustischen Optimierung der mechatronischen Komponenten wurden zum einen der An-steuerstrom reduziert und zum anderen ein Bremsimpuls am Ende der Ansteuerung implemen-tiert. Dadurch konnten die mechanischen Prellereignisse deutlich reduziert werden. Mithilfe eines Einspritzratenmessger{\"a}ts wurde allerdings nachgewiesen, dass sich die Optimierungs-maßnahmen insbesondere auf die Streuung der eingespritzten Kraftstoffmasse negativ auswir-ken und damit ein Zielkonflikt aus Ger{\"a}uschqualit{\"a}t und Prim{\"a}rfunktionen entsteht. Als signi-fikanter Kipppunkt wurde bei den Injektoren der {\"U}bergang vom linearen Vollhub-Betrieb zum ballistischen Teilhub-Betrieb identifiziert. Aus diesem Grund wurde die elektrische Ansteue-rung unter der Voraussetzung des Injektor-Vollhub-Betriebs optimiert. Bei der Beurteilung des Einflusses der NVH-optimierten Ansteuerprofile auf die Robustheit der mechatronischen Komponenten wirkten sich eine niedrige Versorgungsspannung sowie eine kurze Ansteuerdauer der Injektoren besonders negativ auf die Streuung der eingespritzten Kraftstoffmasse aus. Vor allem in Verbindung mit der stromreduzierten Ansteuerung wurden die Injektoren nicht mehr zuverl{\"a}ssig und reproduzierbar im Voll-Hub ge{\"o}ffnet. Weiterhin wur-den durch die Bremspuls-Applikation injektorspezifische Abweichungen im Schließverhalten weiter verst{\"a}rkt und erh{\"o}hten damit auch die Abweichungen der mittleren eingespritzten Kraft-stoffmasse zwischen den untersuchten Injektor-Exemplaren. Abschließend wurde die {\"U}bertragbarkeit des Systemverhaltens ermittelt, indem die Optimie-rungsmaßnahmen auf einen weiteren Versuchstr{\"a}ger ausgeweitet wurden. Dabei zeigte sich, dass die Maßnahmen zwar grunds{\"a}tzlich {\"u}bertragbar waren, aber die Parametrierung bez{\"u}glich Ansteuerstromreduzierung und Bremspuls-Applikation zum Teil stark angepasst werden mussten.}, language = {de} } @phdthesis{Schwanzer, author = {Schwanzer, Peter}, title = {Experimentelle Untersuchungen zur On-Board {\"U}berwachung von Partikelfiltern f{\"u}r den Einsatz an direkteinspritzenden Benzinmotoren}, publisher = {Verlag Dr. Hut}, address = {M{\"u}nchen}, isbn = {978-3-8439-5101-2}, pages = {194}, abstract = {This thesis deals with the development of a methodology for an improved on-board diagnosis of particulate filters in vehicles with gasoline direct injection (GDI) technology with regard to future emission legislations. In order to comply with statutory particle number limits, particulate filters are used in the exhaust gas aftertreatment for GDI-engines. The currently applied method for diagnostic purposes, a differential pressure sensor, will not be suitable for future legislations. Therefore, an on-board strategy with real-time ability shall be developed. To achieve this, the application of novel sensor concepts has been investigated, namely electrostatic soot sensors (ePM sensor) and radio frequency antennas (RF sensor). Due to the results of the ePM-sensors, no methodology for an on-board diagnosis based on an ePM sensor concept was made. The RF sensor showed varying sensitivities for different soot and different quantities of volatile components in the filter element. The analysis of the oxidation processes showed that the regeneration of the filter element is detected by the RF sensor. Furthermore, the stored amount of ash could be captured. Due to these findings, a concept for an improved on-board diagnosis strategy by means of an RF sensor concept was developed. In the course of the work it turned out that a combined sensor concept consisting of a differential pressure sensor and a RF sensor is most suitable. In a validation process, this sensor concept showed sufficient results concerning the detection capability of soot and ash loads as well as of the degree of damage of particulate filters. Especially for small amounts of ash, this sensor concept showed specific advantage. Also, the determination of the current amount of soot in the filter element proved to be suitable. Regarding the detection of damages, the sensor concept convinces through a higher sensitivity.}, language = {de} } @phdthesis{Wiesent, author = {Wiesent, Lisa}, title = {Numerical analysis of laser powder bed fused stents made of 316L stainless steel considering process-related geometric irregularities}, address = {Regensburg}, doi = {10.5283/epub.53139}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:355-epub-531392}, pages = {XIV, 115, CXV-CXXXI}, abstract = {Re-narrowing of a coronary vessel after stent implantation, known as in-stent restenosis (ISR), is a predominant problem in the treatment of atherosclerosis. ISR is caused, e.g., by vessel wall injury during stent implantation, malpositioning, over- or undersizing of the stent, and associated adverse alteration of natural blood flow. Advances in metal additive manufacturing, particularly in laser powder bed fusion (L-PBF), are enabling the generation of micro-scale L-PBF lattice structures and thus potentially coronary stents. By enabling new or even patient-specific stent designs, L-PBF stents could improve the conformity of the implanted stent and the vessel wall, thus potentially reducing ISR rates in the future. Research in the field of L-PBF stents is still in its early stages. Previous studies have mainly focused on the analysis of stent design requirements and basic functionality of L-BF stents. Studies regarding the determination of the specific mechanical behavior of L-PBF stents but also regarding their numerical analysis are currently not available. Due to their similar topology, L-PBF stents resemble L-PBF lattice structures with a low structural density. Therefore, it is reasonable to transfer the findings in the field of L-PBF lattice structures to L-PBF stents. L-PBF lattice structures exhibit process-related geometric irregularities that (negatively) affect their morphology and their mechanical behavior. Therefore, for an accurate (numerical) evaluation of L-PBF lattice structures and thus of L-PBF stents, their mechanical behavior must be determined first, and the influence of the process-related geometric irregularities must be analyzed or considered within the numerical models. Furthermore, the mechanical and morphological behavior of filigree L-PBF stents can be altered by post-processing steps (surface, heat treatment). However, studies on L-PBF lattice structures are mainly limited to as-built structures. Therefore, the aim of this doctoral thesis is to determine the effects of L-PBF process-related geometric irregularities and different post-processing conditions on the mechanical behavior of L-PBF 316L stents, as well as to develop a numerical methodology for their numerical evaluation. In a first step, a finite element analysis (FEA) for the prediction of stent deformation during crimping and expansion was developed and validated using extensive experimental data from conventionally manufactured stents. These models accurately predicted the expansion behavior of two different stent designs with different expansion behavior, as well as different positioning of the stent on the balloon catheter. In the second step, the mechanical behavior of L-PBF 316L was determined using uniaxial tensile tests on standard flat tensile specimens with variable specimen thickness and orientation angle. For each specimen configuration, as-built and heat treated specimens were considered. In the as-built condition, besides the anisotropic mechanical properties of L-PBF 316L already known from the literature, a significant increase in strength with increasing specimen thickness was observed, which stagnated at a specimen thickness of t > 1.5 mm, thus reaching a saturation value. Heat treatment resulted in homogenization but no recrystallization of the microstructure. Thus, the melt pool boundaries and substructures were dissolved, and residual stresses were reduced, whereas the elongated and oriented grains and thus the anisotropic microstructure were preserved. Accordingly, the specimen thickness- and direction-dependent mechanical properties of L-PBF 316L were still observed after heat treatment. Thus, for a reliable structural mechanical evaluation of L-PBF parts, their mechanical properties must be determined using test specimens that are comparable in size, orientation angle, and post-treatment condition to the later L-PBF part. In a final step, the mechanical behavior of L-PBF stents was determined and the expansion behavior of L-PBF stents under different post-processing conditions was evaluated by FEAs. The generation of L-PBF miniature tensile specimens of comparable cross section to stent struts and their experimental evaluation is challenging and highly error-prone. Therefore, a combined experimental-numerical approach was developed for the inverse determination of the mechanical behavior of L-PBF 316L stents based on experimental testing and FEA of uniaxial compression of L-PBF stents. The stent models were reconstructed from computed tomography (CT) scans of real L-PBF stents. In this way, process-related geometric irregularities were depicted enabling an accurate prediction of the stent structure-property relationship. Thus, the macroscopic mechanical behavior of L-PBF 316L stents could be determined for the first time and subsequently described numerically by a material model. Morphological analysis of the L-PBF stents further revealed significant discrepancies between the actual L-PBF stents and its computed aided design (CAD) model due to process-related geometric irregularities (surface roughness, strut waviness, enlarged and inhomogeneous strut diameters, internal defects). Numerical expansion analysis of the L-PBF stent models showed that L-PBF stents can exhibit comparable expansion behavior to conventional stents only after surface and heat treatment. However, subsequent analysis of deformation and stress states showed that L-PBF stents, both in the as-built condition and after surface and heat treatment, may exhibit critical local stress/strain concentrations, especially in the areas of pronounced geometric irregularities. Improvements in the L-PBF process, post-processing steps, and stent design are therefore essential to minimize process-related geometric irregularities and thus their strength-reducing effects, ultimately ensuring the structural safety of L-PBF stents. One possible improvement approach is to manufacture the stents on special µ-L-PBF systems that have explicitly been optimized to produce filigree structures. In this way, a higher geometric accuracy and low surface roughness could already be achieved in the as-built condition of L-PBF stents, and the subsequent required surface treatment could be reduced to a minimum. Furthermore, the fatigue strength, the damage behavior, the interaction of the stent with the blood vessel as well as the biocompatibility of L-PBF 316L stents should be investigated. To effectively use numerical models for the development of L-PBF stents, the potential of synthetic L-PBF stent models should also be investigated. The synthetic stent models represent a statistics-based modification of the original stent CAD model (e.g., local variations of strut cross section along strut length). In this way, the effects of L-PBF process-related geometric irregularities could be represented statistically and thus without explicit reconstruction from CT scans. The development of L-PBF stents is a very complex interdisciplinary task in the fields of manufacturing technology, material science, design development and numerical simulation. To establish L-PBF as a reliable alternative to conventional stent fabrication, further research in this area is essential. By providing a method to determine the mechanical properties of L-PBF stents as well as their numerical analysis, this doctoral thesis could contribute to the further development of L-PBF 316L stents, as well as define necessary research aspects for further work.}, language = {en} } @phdthesis{Weber, author = {Weber, Sebastian}, title = {Charakterisierung verschiedener Wassereinspritztechnologien f{\"u}r Ottomotoren}, doi = {10.25673/86462}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:ma9:1-1981185920-884176}, pages = {xvii, 151}, abstract = {Die Reduktion von Kraftstoffverbrauch und Schadstoffemission bei gleichzeitiger Verbesserung der Fahrleistung bei kleinerem Hubraum und reduzierter Zylinderzahl, die erh{\"o}hte Performance und die Kompatibilit{\"a}t mit elektrifizierten Komponenten beschreiben die aktuellen Ziele und Herausforderungen der modernen Ottomotorentwicklung. Um alle Herausforderungen zu erf{\"u}llen, muss ein st{\"o}chiometrischer Betrieb sichergestellt werden. Dabei kann es jedoch an der Volllast zur {\"U}berschreitung thermischer Grenzen im Abgaspfad kommen, weswegen die Abgastemperatur ohne Leistungsverluste abgesenkt werden muss. Die Wassereinspritzung kombiniert Downsizing, Leistungssteigerung und die Verbesserung der Schadstoffemissionen wirkungsvoll miteinander und k{\"o}nnte einen Beitrag zur Erreichung der Klimaziele leisten. Um ein optimales Systemlayout zu erarbeiten, sind prozessuale Betrachtungen oft nicht ausreichend. Vielmehr m{\"u}ssen die Ph{\"a}nomene im Brennraum beobachtet werden. Schwerpunktm{\"a}ßig sind dies die Einbringung des Wassers, der Wandkontakt, die Spray- und Wandfilmverdampfung und somit die Wirksamkeit der Abgastemperaturreduktion und die Verbesserung des indizierten Wirkungsgrads. In einem ersten Schritt werden die Thermodynamik bei Wassereinspritzung analysiert und verschiedene Einspritztechnologien miteinander verglichen. Fokussiert wird die Verbrennung, die Ver{\"a}nderung in den gasf{\"o}rmigen und festen Abgasbestandteilen und die mechanische Belastung der Aggregate durch die Verbesserung der Z{\"u}ndwinkel. Die Mischungseinspritzung {\"u}ber den zentralen Hochdruckinjektor vereint den geringsten Wasserverbrauch mit bestm{\"o}glicher Schwerpunktlage, starker Reduktion des Partikelausstoßes und akzeptabler Erh{\"o}hung der mechanischen Belastung und ist damit das favorisierte Konzept. Neben den prozessualen Betrachtungen werden mit einem optisch zug{\"a}nglichen Versuchstr{\"a}ger zwei laseroptische Messtechniken zur Visualisierung fl{\"u}ssigen Wassers und der spektralen Trennung zwischen Wasser und Kraftstoff entwickelt und validiert. Damit werden die verschiedenen Varianten optisch vermessen und die Sensitivit{\"a}t gegen{\"u}ber ver{\"a}nderten Betriebs- und Randbedingungen ermittelt. Die Sammlereinspritzung zeigt die gr{\"o}ßten Tropfen, gefolgt von der Saugrohr- und der Mischungseinspritzung. Auch hat diese den mit Abstand gr{\"o}ßten Wandkontakt und die geringste Verdampfungsrate, ist zus{\"a}tzlich anf{\"a}llig f{\"u}r zyklische Schwankungen. Die Saugrohreinspritzung kennzeichnen kleine Tropfen, ein konzentriertes Einstr{\"o}men durch den Ventilspalt, ein fl{\"a}chiger Wandfilm auf der Kolbenoberseite und die Verbesserung der Tropfenverdampfung durch Turbulenz und die Nutzung von Phasing. Favorit ist abermals die Mischungseinspritzung. Eine hohe Wandfilm- und unmittelbare Sprayverdampfung kennzeichnen das System, wobei eine Erh{\"o}hung des Einspritzdrucks die Verdampfungsrate signifikant verbessert. Außerdem ist die Einspritzdauer am geringsten und die Reproduzierbarkeit am gr{\"o}ßten, jedoch auch der applikative Aufwand. Am favorisierten System werden weitere Analysen durchgef{\"u}hrt, unter anderem zur Ver{\"a}nderung der Bauteiltemperaturen, der Vergleich mit einer Ethanoleinspritzung oder die vielversprechende Kombination in Form einer Wasser-Ethanol-Mischungseinspritzung. Auf Basis der experimentellen Erkenntnisse wird ein CFD-Verfahren vorgestellt, das die Wassereinspritzung abbildet und somit die Virtualisierung in der Produktentwicklung vorantreibt. Neben der methodischen Vorgehensweise wird das Verfahren validiert und am Einzylinder- und Vollmotorbetriebspunkt vorgestellt. Die auftretenden Unterschiede werden analysiert und ausgew{\"a}hlte Parameteranalysen durchgef{\"u}hrt. Mit den Simulationen kann nachvollzogen werden, wie das Wasser die Zylinderlaufbahn benetzt und mit dem Kolben interagiert. Zusammenfassend charakterisiert diese Arbeit die g{\"a}ngigen Wassereinspritzvarianten auf unterschiedlichen Ebenen, gibt Optimierungsempfehlungen f{\"u}r die bestm{\"o}gliche Medienverdampfung und empfiehlt die Mischungseinspritzung als Systemlayout.}, subject = {Kolbenkraftmaschine}, language = {de} } @phdthesis{Suess, author = {S{\"u}ß, Franz}, title = {The influence of mental stress on the musculoskeletal human back during static posture and trunk motion}, doi = {10.5283/epub.46055}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:355-epub-460554}, pages = {106}, abstract = {The investigation of the influence of mental stress on muscle recruitment of the back and its effect on the intervertebral discs was the main focus of this work. Furthermore, the goal was to develop algorithms to use mental stress as an input parameter in musculoskeletal simulation models. In the first step, a study was designed to investigate the influence of emotional and cognitive stress without kinetic influencing factors during sitting. At the muscular level, emotional stress was found to affect the upper back, while cognitive stress elicited higher muscle activity in the upper and lower back. Using a newly developed algorithm to apply back muscle recruitment changes to static inverse kinematic simulation models, load increases at the discs of up to 189 N on average and up to 907 N at peak were found.Based on the results of the first study, a second dynamic study was designed and conducted. In this case, the focus was on the cognitive stressor and the lower back. Using a dynamometer, subject-specific loads were applied during extension and flexion of the upper back. In contrast to the first study, in the upper back, only the right m. trapezius pars descendens showed a load-induced difference in muscle activity, but the lower back did. To investigate the effects of muscle tone increase in detail, the algorithm developed in the first study was extended to the dynamic case. The use of simulation models allowed the inference of the effects of the purely stress-induced tone increase. For this purpose, the kinetic and muscular effects were isolated and simulated. The study revealed a stress increase of 47\% of the body weight in the L4L5 disc. The final numerical study focused on the general application of muscle activities to inverse kinematic simulation models. This was based on the novel simulation algorithm used in study two and the measured muscle activities. The simulation of the measured muscle activities formed the link between reality and simulation. To simulate the activities, neural networks and gradient boosting regression algorithms were investigated. The latter were found to be better suited to represent the data. However, the data is too small for a detailed statement, especially for loads below 100\%. The results of this work can help to better assess the musculoskeletal effects of psychological stress on the musculoskeletal system and, if necessary, to develop ergonomic prevention strategies. By recognizing stress-related kinematic difference, as well as subsequent prompting of trunk movement, could help prevent long-term effects. When examining any situation, the combination of machine learning and musculoskeletal simulation tools can help examine and minimize the effects of psychological stress.}, language = {en} } @phdthesis{Thumann, author = {Thumann, Philipp}, title = {Lebensdauerbewertung von stoßartig belasteten Werkzeugkomponenten}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:91-diss-20210713-1554721-1-5}, pages = {IV, 143}, abstract = {Die vorliegende Arbeit beinhaltet ein neuartiges Gesamtkonzept zur Betriebsfestigkeitsbewertung von Werkzeugkomponenten unter Ber{\"u}cksichtigung dynamischer Einfl{\"u}sse. Es werden experimentelle Untersuchungen an Proben aus dem Verg{\"u}tungsstahl 42CrMoS4-QT sowie aus den Gusseisen mit Kugelgraphit EN-GJS-600-3 und mit Lamellengraphit EN-GJL-250 durchgef{\"u}hrt. Die Ergebnisse aus den Versuchen dienen zum einen zur allgemeinen Validierung von Betriebsfestigkeitsrechnungen. Zum anderen wird damit die Frequenzabh{\"a}ngigkeit in Bezug auf stoßartige Belastungen untersucht. Neben den validierten Berechnungsmodellen resultiert aus den Versuchungen die Erkenntnis einer ausgepr{\"a}gten Frequenzabh{\"a}ngigkeit, welche in zuk{\"u}nftigen Auslegungsrechnungen ber{\"u}cksichtigt werden muss. Bei Untersuchungen an einem Umform- und Beschneidewerkzeug wird die erarbeitete methodische Vorgehensweise aus den Versuchen angewandt. Es wird eine FE-Simulation eines Gesamtmodells erstellt, welche mit Messungen am Werkzeug validiert wird. Die Untersuchungen am Umform- und Beschneidewerkzeug liefern demnach ein validiertes FE-Simulationsmodell, das neben dem Werkzeug das Pressenmodell und die im Fertigungsprozess zu bearbeitende Platine beinhaltet. Unter Anwendung der Submodelltechnik an einer Einzelkomponente werden geeignete FE-Ergebnisse f{\"u}r eine Betriebsfestigkeitsrechnung generiert. Die Betriebsfestigkeitsrechnung erfolgt nach dem validierten Berechnungsmodell aus den Versuchen. Im Zuge der Analysen am Werkzeug findet das validierte Berechnungsmodell f{\"u}r den Gusswerkstoff EN-GJS-600-3 Anwendung. Die Berechnungsergebnisse korrelieren mit tats{\"a}chlich aufgetretenen Sch{\"a}den an einem Bauteil.}, language = {de} } @article{BrollGoldhackerHahneletal., author = {Broll, Alexander and Goldhacker, Markus and Hahnel, Sebastian and Rosentritt, Martin}, title = {Morphological effects of input data quantity in AI-powered dental crown design}, series = {Journal of dentistry}, volume = {159}, journal = {Journal of dentistry}, publisher = {Elsevier}, doi = {10.1016/j.jdent.2025.105767}, pages = {1 -- 8}, abstract = {OBJECTIVES: This retrospective in vitro study evaluated the impact of input data quantity on the morphology of dental crowns generated by AI-based software. The hypothesis suggests that increased input data quantity improves the quality of generated occlusal surfaces. METHODS: A dataset comprising n=30 patients (11 males, 19 females; age: 22-31 years) was analyzed. Input data was categorized into full dentition (full), quadrant data (quad), and adjacent teeth (adj). AI-based software (Dentbird Crown, Imageworks Inc.) generated crowns for a single lower first molar (36/46). Metrics were proposed to assess the morphology and occlusal relationships of the crowns, with the original tooth as reference. STATISTICS: Friedman Chi-Square tests, Wilcoxon signed rank tests, Kendall correlation and Fligner-Killeen tests (α = 0.05). RESULTS: Full and quad groups provided consistent reconstruction quality with no significant differences in morphology and occlusal relationships. The adj group showed significant (p<0.05) morphological deviations and higher reconstruction failure rates compared to the full and quad groups. Correlations (median: 0.19; min-max range: 0.01-0.54) indicate that the proposed metrics capture distinct morphological and functional crown aspects. CONCLUSION: The software reliably reconstructed crowns with at least quadrant-level input data. Performance declined with reduced input. Full-jaw scans did not enhance accuracy compared to quadrant data. CLINICAL SIGNIFICANCE: Increased input data quantity can improve the accuracy of AI-based restorations. As a result, prosthodontists benefit from predictable, accurate restoration proposals that reduce the need for digital chairside adjustments as well as manual modifications after fabrication. This streamlines clinical workflows and enhances the quality of restorations. Quadrant-level data has proven sufficient to generate high-quality reconstructions. Further input data did not significantly improve the accuracy of the reconstructions. The proposed metrics enable quantitative assessments of morphological and functional restoration quality, supporting reliable AI-driven workflows.}, language = {en} } @article{BrollRosentrittSchlegletal., author = {Broll, Alexander and Rosentritt, Martin and Schlegl, Thomas and Goldhacker, Markus}, title = {A data-driven approach for the partial reconstruction of individual human molar teeth using generative deep learning}, series = {Frontiers in Artificial Intelligence}, volume = {7}, journal = {Frontiers in Artificial Intelligence}, publisher = {Frontiers Media SA}, issn = {2624-8212}, doi = {10.3389/frai.2024.1339193}, abstract = {Background and objectiveDue to the high prevalence of dental caries, fixed dental restorations are regularly required to restore compromised teeth or replace missing teeth while retaining function and aesthetic appearance. The fabrication of dental restorations, however, remains challenging due to the complexity of the human masticatory system as well as the unique morphology of each individual dentition. Adaptation and reworking are frequently required during the insertion of fixed dental prostheses (FDPs), which increase cost and treatment time. This article proposes a data-driven approach for the partial reconstruction of occlusal surfaces based on a data set that comprises 92 3D mesh files of full dental crown restorations.MethodsA Generative Adversarial Network (GAN) is considered for the given task in view of its ability to represent extensive data sets in an unsupervised manner with a wide variety of applications. Having demonstrated good capabilities in terms of image quality and training stability, StyleGAN-2 has been chosen as the main network for generating the occlusal surfaces. A 2D projection method is proposed in order to generate 2D representations of the provided 3D tooth data set for integration with the StyleGAN architecture. The reconstruction capabilities of the trained network are demonstrated by means of 4 common inlay types using a Bayesian Image Reconstruction method. This involves pre-processing the data in order to extract the necessary information of the tooth preparations required for the used method as well as the modification of the initial reconstruction loss.ResultsThe reconstruction process yields satisfactory visual and quantitative results for all preparations with a root mean square error (RMSE) ranging from 0.02 mm to 0.18 mm. When compared against a clinical procedure for CAD inlay fabrication, the group of dentists preferred the GAN-based restorations for 3 of the total 4 inlay geometries.ConclusionsThis article shows the effectiveness of the StyleGAN architecture with a downstream optimization process for the reconstruction of 4 different inlay geometries. The independence of the reconstruction process and the initial training of the GAN enables the application of the method for arbitrary inlay geometries without time-consuming retraining of the GAN.}, language = {en} } @article{OttRosengarthDoenitzetal., author = {Ott, Christian and Rosengarth, Katharina and Doenitz, Christian and Hoehne, Julius and Wendl, Christina and Dodoo-Schittko, Frank and Lang, Elmar Wolfgang and Schmidt, Nils Ole and Goldhacker, Markus}, title = {Preoperative Assessment of Language Dominance through Combined Resting-State and Task-Based Functional Magnetic Resonance Imaging}, series = {Journal of personalized medicine}, volume = {11}, journal = {Journal of personalized medicine}, number = {12}, publisher = {MDPI}, doi = {10.3390/jpm11121342}, abstract = {Brain lesions in language-related cortical areas remain a challenge in the clinical routine. In recent years, the resting-state fMRI (RS-fMRI) was shown to be a feasible method for preoperative language assessment. The aim of this study was to examine whether language-related resting-state components, which have been obtained using a data-driven independent-component-based identification algorithm, can be supportive in determining language dominance in the left or right hemisphere. Twenty patients suffering from brain lesions close to supposed language-relevant cortical areas were included. RS-fMRI and task-based (TB-fMRI) were performed for the purpose of preoperative language assessment. TB-fMRI included a verb generation task with an appropriate control condition (a syllable switching task) to decompose language-critical and language-supportive processes. Subsequently, the best fitting ICA component for the resting-state language network (RSLN) referential to general linear models (GLMs) of the TB-fMRI (including models with and without linguistic control conditions) was identified using an algorithm based on the Dice index. Thereby, the RSLNs associated with GLMs using a linguistic control condition led to significantly higher laterality indices than GLM baseline contrasts. LIs derived from GLM contrasts with and without control conditions alone did not differ significantly. In general, the results suggest that determining language dominance in the human brain is feasible both with TB-fMRI and RS-fMRI, and in particular, the combination of both approaches yields a higher specificity in preoperative language assessment. Moreover, we can conclude that the choice of the language mapping paradigm is crucial for the mentioned benefits.}, language = {en} } @article{BrollGoldhackerHahneletal., author = {Broll, Alexander and Goldhacker, Markus and Hahnel, Sebastian and Rosentritt, Martin}, title = {Generative deep learning approaches for the design of dental restorations: A narrative review}, series = {Journal of Dentistry}, volume = {145}, journal = {Journal of Dentistry}, publisher = {Elsevier}, issn = {0300-5712}, doi = {10.1016/j.jdent.2024.104988}, pages = {10}, abstract = {Objectives: This study aims to explore and discuss recent advancements in tooth reconstruction utilizing deep learning (DL) techniques. A review on new DL methodologies in partial and full tooth reconstruction is conducted. Data/Sources: PubMed, Google Scholar, and IEEE Xplore databases were searched for articles from 2003 to 2023. Study selection: The review includes 9 articles published from 2018 to 2023. The selected articles showcase novel DL approaches for tooth reconstruction, while those concentrating solely on the application or review of DL methods are excluded. The review shows that data is acquired via intraoral scans or laboratory scans of dental plaster models. Common data representations are depth maps, point clouds, and voxelized point clouds. Reconstructions focus on single teeth, using data from adjacent teeth or the entire jaw. Some articles include antagonist teeth data and features like occlusal grooves and gap distance. Primary network architectures include Generative Adversarial Networks (GANs) and Transformers. Compared to conventional digital methods, DL-based tooth reconstruction reports error rates approximately two times lower. Conclusions: Generative DL models analyze dental datasets to reconstruct missing teeth by extracting insights into patterns and structures. Through specialized application, these models reconstruct morphologically and functionally sound dental structures, leveraging information from the existing teeth. The reported advancements facilitate the feasibility of DL-based dental crown reconstruction. Beyond GANs and Transformers with point clouds or voxels, recent studies indicate promising outcomes with diffusion-based architectures and innovative data representations like wavelets for 3D shape completion and inference problems. Clinical significance: Generative network architectures employed in the analysis and reconstruction of dental structures demonstrate notable proficiency. The enhanced accuracy and efficiency of DL-based frameworks hold the potential to enhance clinical outcomes and increase patient satisfaction. The reduced reconstruction times and diminished requirement for manual intervention may lead to cost savings and improved accessibility of dental services.}, language = {en} }