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Modulare thermische Modellierung und Unsicherheitsanalyse von Getriebemotor-Baukästen
Full text linkAntriebssysteme sind im Betrieb stark durch thermische Randbedingungen, insbesondere Temperaturgrenzwerte, eingeschränkt. In der Projektierung werden thermische Betrachtungen meist durch die separate Analyse einzelner Antriebskomponenten durchgeführt. Eine ganzheitliche thermische Modellierung des Gesamtsystems ermöglicht umfassendere und präzisere Aussagen über das Systemverhalten.
In dieser Arbeit wird ein Baukastensystem entwickelt, das den modularen Aufbau des Gesamtsystems aus einzelnen Komponenten ermöglicht. Es werden Modelle für die verschiedenen Antriebskomponenten erstellt und ein Algorithmus entwickelt, der diese Einzelkomponenten automatisiert zu einem Gesamtsystem zusammenführt. Der Fokus der Modellbildung liegt auf der präzisen Abbildung des makroskopischen Systemverhaltens, wobei Unsicherheiten durch Fertigungsschwankungen, Messfehler und physikalisch vereinfachte Modelle berücksichtigt werden.
Um die Verluste von Modellen in verschiedenen Betriebsbereichen genau zu bestimmen, wird eine automatisierte Methode zur Messung von Wirkungsgraden entwickelt. Diese Methode ermöglicht eine präzise Aufteilung in einzelne Verlustkomponenten und deren Unsicherheiten, indem die Temperaturen während des Messvorgangs in einem engen Temperaturband gehalten werden. Der entwickelte Messablauf gewährleistet eine stabile Temperatur, was zu genaueren und zuverlässigeren Ergebnissen führt.
Zur Validierung der Modelle werden Messungen unterschiedlicher Lastprofile für einen Solomotor und einen Getriebemotor durchgeführt. Ein Vergleich der Messergebnisse mit den Vorhersagen des thermischen Modells, einschließlich der berechneten Unsicherheiten im Temperaturverlauf, zeigt, dass die Messergebnisse innerhalb des berechneten Konfidenzintervalls liegen
An Automated Approach to Generating Card-Based Cryptographic Protocols
Full text linkCard-based cryptographic protocols provide a simple and illustrative way of performing multi-party computation without computers, but instead use just a set of playing cards. A lot of research has been done on finding minimal protocols, with respect to the number of cards or the number of protocol steps, for various functions. To automate the process of finding new card-based protocols, Koch, Schrempp, and Kirsten (2021) employed the technique of software bounded model checking for a symbolic program that implements the basic actions and states. The bounded model checker is then used to synthesize a secure protocol by automatically generating a bounded (symbolic) program run, or, if there exists no such run, prove impossibility within the given bounds.
In this thesis, we evaluate and extend the above technique for a generalization to more boolean functions, for an introduction of modularity so that (more) complex protocols can be found more efficiently, and finally for using bitwise datatype encodings so that finding protocols can be done more efficiently. From the increased efficiency and more universal applicability, we were able to extend the scope of the automated approach for generating card-based protocols to further impossibility proofs and various more protocols, for which some of them had already been found manually (but not formally verified) within literature
A micromechanical investigation of plasticity in ordered NbMoCrTiAl and disordered TaNbHfZrTi refractory compositionally complex alloys at room temperature
Full text linkRefractory compositionally complex alloys (RCCAs) are known for their exceptional high-temperature resistance. However, their inherent brittleness at room temperature limits broader practical applications. To explore the effects of microstructure and loading conditions on their deformation behavior, micromechanical experiments, including microbending and micropillar compression tests, were performed on two representative RCCAs: equimolar NbMoCrTiAl (ordered B2 crystal structure) and TaNbHfZrTi (disordered A2 crystal structure). Both alloys demonstrated significant plastic deformation, with strains exceeding 40% at room temperature. Despite prior reports of limited ductility in NbMoCrTiAl at the millimeter scale, our micropillar compression tests on single-crystalline pillars oriented along 100 and 110 reveal substantial plasticity. The dominant deformation mechanisms in NbMoCrTiAl were identified as crystallographic slip and cross-slip of screw dislocations. By contrast, TaNbHfZrTi exhibited a broader range of mechanisms, including screw dislocation slip and a high density of non-screw dislocations, accompanied by kink band formation and activation of high-order slip planes, which collectively contribute to its remarkable ductility among the highest reported for body-centered cubic RCCAs. The atomic size mismatch inherent in compositionally complex alloys enhances dislocation mobility, while the random distribution of elements promotes the formation of edge segments, further improving ductility. These findings highlight the critical role of microstructural characteristics in tailoring the deformation behavior of RCCAs for room-temperature applications
Effect of Ionomer-to-Carbon Ratio on PEMFC Carbon Corrosion: An Electrochemical Study
Full text linkThis study investigates the effect of the ionomer-to-carbon (I/C) weight ratio in polymer electrolyte membrane fuel cell (PEMFC) cathode catalyst layers (CCLs) on carbon corrosion during high-potential accelerated stress tests (ASTs). Membrane electrode assemblies (MEAs) with I/C ratios of 0.5, 0.85, and 1.2 were analyzed using polarization curves, cyclic voltammetry, limiting current measurements, and electrochemical impedance spectroscopy. Impedance data analysis, based on distribution of relaxation times and transmission line modeling, showed that higher I/C ratios (0.85 and 1.2) exhibit superior beginning-of-life (BoL) performance due to lower ionic resistance in the CCL. However, the MEA with a lower I/C ratio (0.5) exhibited a performance improvement of up to 35% during initial AST cycles and enhanced carbon corrosion resistance. Compared to BoL, performance improved significantly due to a 28%–46% reduction in charge transfer resistance and a 91% reduction in ionic resistance. These findings emphasize the trade-off between BoL performance and long-term durability when determining the optimal I/C ratio. They also underscore the need for further investigation into how the I/C ratio influences CCL structure and electrochemistry. Optimizing the I/C ratio has the potential to substantially improve PEMFC electrode performance and durability, guiding the design of more resilient catalyst layers
Testing lepton non-unitarity with the next generation of (Germanium-based) CENS reactor experiments
Full text linkCoherent elastic neutrino-nucleus scattering (CENS) has been experimentally confirmed using neutrinos from pion decay at rest, solar neutrinos and reactor antineutrinos. Future CENS experiments will foreseeable lead to precision measurements which will be a powerful tool to search for new physics beyond the Standard Model. In this work, we investigate possible deviations from unitarity in the leptonic mixing matrix that controls the propagation of active neutrinos. Such deviations may originate from the mixing with additional gauge singlet fermions and depending on their mass scale and mixing, the resulting phenomenology can differ substantially. We explore two well-motivated regimes: the \textit{seesaw limit}, where the new fermions are heavy and kinematically inaccessible, leading to effective deviations from unitarity in the active sector; and the \textit{light sterile limit}, where they are light enough to be produced and participate in neutrino propagation and scattering processes. We show how these scenarios modify both CENS and elastic neutrino--electron scattering (ES), and we present the corresponding sensitivity projections for a future CENS reactor experiment obtained by upscaling the CONUS+ experiment, which reported the first observation of reactor CENS. We identify the leading experimental systematics relevant for such an upscaling and demonstrate the resulting capability to probe TeV-scale new physics. Our results highlight the strong potential of CENS to test the structure of the lepton sector and to search for physics beyond the Standard Model
Application of the homogeneous relaxation model for flash boiling under sub-atmospheric pressures
Full text linkFlashing two-phase flows under sub-atmospheric outlet conditions in a converging–diverging nozzle are investigated using the Homogeneous Relaxation Model (HRM) within a two-phase mixture flow framework. The main objectives of this study are to conduct an in-depth investigation of low-temperature, low-pressure flash evaporation, which is essential in flash-based wastewater purification and power generation systems that utilize low-grade waste heat as an energy source, and to support the improvement of a proof-of-concept experimental setup currently being established in our laboratory through the findings of this study.
The numerical results demonstrate that the mathematical model accurately reproduces pressure and void fraction distributions reported in the literature. It also captures key flashing features—including pressure undershoots, vapor generation delays, and pressure recovery—through the relaxation-time formulation. The results indicate that flashing flow in a converging–diverging nozzle is characterized by a sharp pressure drop near the throat, followed by rapid vapor generation and partial pressure recovery in the diverging section. This behaviour is primarily governed by nozzle geometry and the large disparity in specific volumes between the liquid and vapor phases. Vapor generation increases markedly at higher inlet pressures and temperatures, driven by the greater availability of superheat energy. The simulations further reveal that the mass flow rate is highly sensitive to inlet conditions: elevated inlet temperatures intensify vapor generation and consequently reduce mass flow rate, whereas achieving both high vapor production and high mass flow rates requires sufficiently high inlet pressures. The model also predicts shorter flash-delay distances at higher pressures, indicating an earlier onset of phase change, while longer delays occur at elevated temperatures due to increased metastability. Additionally, pressure undershoots become more pronounced with higher inlet temperatures, whereas their dependence on inlet pressure is negligible. It is found that, under fixed inlet conditions, lower sub-atmospheric back pressures enhance steam generation and promote pressure recovery after the nozzle throat, while simultaneously reducing the mass flow rate and the magnitude of pressure undershoots
Spatiotemporal Detection and Uncertainty Visualization of Atmospheric Blocking Events
Full text linkAtmospheric blocking events are quasi-stationary high-pressure systems that disrupt the typical paths of polar and subtropical air currents, often producing prolonged extreme weather events such as summer heat waves or winter cold spells. Despite their critical role in shaping mid-latitude weather, accurately modeling and analyzing blocking events in long meteorological records remains a significant challenge. To address this challenge, we present an uncertainty visualization framework for detecting and characterizing atmospheric blocking events. First, we introduce a geometry-based detection and tracking method, evaluated on both pre-industrial climate model simulations (UKESM) and reanalysis data (ERA5), which represent historical Earth observations assimilated from satellite and station measurements onto regular numerical grids using weather models. Second, we propose a suite of uncertainty-aware summaries: contour boxplots that capture representative boundaries and their variability, frequency heatmaps that encode occurrences, and 3D temporal stacks that situate these patterns in time. Third, we demonstrate our framework in a case study of the 2003 European heatwave, mapping the spatiotemporal occurrences of blocking events using these summaries. Collectively, these uncertainty visualizations reveal where blocking events are most likely to occur and how their spatial footprints evolve over time. We envision our framework as a valuable tool for climate scientists and meteorologists: by analyzing how blocking frequency, duration, and intensity vary across regions and climate scenarios, it supports both the study of historical blocking events and the assessment of scenario-dependent climate risks associated with changes in extreme weather linked to blocking
Fine tuning of long-range interactions to describe the binding of adamantane and diamantane derivatives to a Cucurbit[7]uril-based synthetic receptor: Insights from metadynamics simulations
No full textHigh-affinity host–guest systems, such as Cucurbit[n]uril (CBn) macrocycles, are vital across various scientific and technological fields—such as targeted drug delivery, smart (self-healing) materials, sensitive biosensors, and molecular diagnostics—due to their exceptional molecular recognition capabilities. Molecular simulation (MS)-based predictions of ligands’ binding poses and affinities on the macrocycles would greatly help optimize such host–guest systems. Yet, the poor accuracy of force fields (FFs) for these synthetic receptors has limited the applicability of MS thus far. Here, we demonstrate that incorporating electron density-derived Lennard-Jones parameters and charges into FFs can drastically improve the accuracy of free-energy calculations for these systems. As a test case, we focus on five adamantane derivatives and two diamantane derivatives in complex with one of the macrocycles, CB7. Our free energies of binding, calculated via multiple-walker well-tempered funnel metadynamics, turned out to be in fair agreement with the experiment for all the adamantane molecules. For the larger diamantane molecules, we still observe a discrepancy with experiments, which calls for deeper investigation. Overall, the calculations also provide insights into the binding mechanism and the role of the solvent. In particular, the chemical structures of the ligands and the ion strength play an important role in the binding process
A Global Analysis of Cyber Threats to the Energy Sector: “Currents of Conflict” from a geopolitical perspective"
No full textThe escalating frequency and sophistication of cyber threats increased the need for their comprehensive understanding. This paper explores the intersection of geopolitical dynamics, cyber threat intelligence analysis, and advanced detection technologies, with a focus on the energy domain. We leverage generative artificial intelligence to extract and structure information from raw cyber threat descriptions, enabling enhanced analysis, which yields new insights, providing actionable information to researchers, policy makers, and cybersecurity professionals
