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Bivariate distributional copula regression for mixed non-time-to-event and time-to-event responses
Get PDFWe propose a distributional copula regression modelling approach for bivariate responses comprised of non-commensurate (i.e. mixed) variables. In our case, the margins are a right-censored time-to-event outcome and a non-time-to-event variable. The underlying hazard rate of the time-to-event margin is modelled using discrete-time-to-event (DT) or piecewise-exponential (PW) methods. A flexible statistical model is achieved by relying on the correspondence of the likelihood of the aforementioned time-to-event approaches with well-known univariate distributions. We construct joint bivariate distributions for these mixed responses by means of parametric bivariate copulas. This allows for separate specification of the dependence structure between the margins and their individual distribution functions. All coefficients of the distributional copula regression models considered here are estimated simultaneously via penalized maximum likelihood. We showcase the versatility of our proposed approach in an analysis of red-light running behaviour of E-cyclists by modelling the joint distribution of a mixed response comprised of a binary response and a time-to-event outcome that indicates the time of red traffic light running
Dynamic wetting by concentrated granular suspensions
Get PDFMany functional materials, such as paints and inks used in applications like coating and 3D printing, are concentrated granular suspensions. In such systems, the contact line dynamics and the internal structure of the suspension interact through shear rate dependent viscosity and microstructural rearrangements. The local shear rate increases sharply near moving contact lines, leading to the non-Newtonian rheology of dense suspensions in this region. While hydrodynamic solutions can describe dilute suspensions, their applicability near advancing contact lines in dense suspensions remains unclear. This study quantifies the deviation from the Newtonian solution by systematically varying interparticle interactions through the choice of dispersion medium. We use silica particles suspended in two refractive index-matched fluids: (i) aqueous 2,2′-thiodiethanol (weak interactions) and (ii) aqueous sodium thiocyanate solution (strong interactions). These systems exhibit substantially different rheological responses, shear-thickening and yield-stress behaviour, respectively. Using astigmatism particle tracking velocimetry (APTV), we resolve the three-dimensional trajectories of tracer particles within a drop driven over a substrate, in an arrangement enabling tracking of the internal flows over a long travel distance of the drop. We observe distinct flow behaviours depending on the particle interactions and the resulting suspension rheology. The more the particle interactions play a role, i.e., the more pronounced the non-Newtonian effects, the more strongly the measured flow profiles differ from the Newtonian solution of the hydrodynamic equations. In the case of the shear-thickening suspension, a notable deviation from Newtonian behaviour is observed. Conversely, the yield-stress suspension exhibits plug flow over the substrate, with Newtonian-like behaviour restricted to the yielded region near the substrate
Communication-Free Grid-Supportive Control of Converter-Based ZIP Loads in DC Microgrids
Get PDFIn recent years, DC microgrids have garnered significant attention due to their superior capability in integrating renewable energy sources. However, the predominance of renewables in these systems introduces increased uncertainty in power generation, thereby elevating the risk of load loss. While the integration of energy storage systems is widely regarded as the primary solution to mitigate this issue, load-side grid support has also been proposed as a viable alternative strategy. This paper proposes a communication-free grid-supportive load (GSL) controller for converter-based constant-impedance/current/power (ZIP) loads, enabling local voltage support using only bus-voltage measurements. First, a unified control strategy is introduced that dynamically adjusts the load-side voltage reference via a saturation-plus-hysteresis mechanism, ensuring device safety while enabling grid support. Second, an energy-based restoration scheme is proposed that tracks cumulative power deviations and smoothly returns the load to nominal operation, avoiding rebound transients. Finally, the concept is experimentally validated on a 700V, 14kW DC microgrid. Under a 4 kW load step, the proposed scheme reduces the voltage dip by 12.9% and prevents converter shutdown when the battery reaches its power limit, outperforming a conventional PI-controlled system. The results demonstrate that local, device-embedded control of ZIP loads can deliver effective grid support without requiring communication or additional energy storage
Insights into the operational stability of wide-bandgap perovskite and tandem solar cells under rapid thermal cycling
Get PDFTemperature variations can induce phase transformations and strain in perovskite solar cells (PSCs), undermining their structural stability and device performance. Despite growing interest, the operational stability of triple-cation wide-bandgap (WBG) PSCs and tandem solar cells (TSCs) under rapid solar-thermal cycling remains poorly understood. Here, we investigate the operational stability of WBG PSCs (~1.68 eV) with a champion power conversion efficiency (PCE) of 24.31% and extend the study to TSCs. We find that degradation during device operation under rapid solar-thermal cycling (temperature change rate of 10 °C/min) is independent of passivation and occurs in two distinct regimes: an initial burn-in phase, which accounts for a rapid 60% relative loss in performance, followed by a steady degradation characterized by temperature-dependent fluctuations in photovoltaic parameters. By operando grazing-incidence wide-angle X-ray scattering and photoluminescence measurements, we reveal that temperature-induced strain, phase transition, and the increased non-radiative recombination collectively contribute to the degradation of PSCs. This work advances the understanding of the degradation mechanisms of WBG PSCs and TSCs, providing insights toward improving their operational thermal stability for real-world applications
Inline NMR Detection of Li in Aqueous Solutions Using a Cryogen-Free Magnet at 4.7 T
Get PDFLithium is of major importance for many areas of technology, especially batteries, and is therefore relevant to both the industrial and private sectors. High-performance, ideally inline-compatible analytics are important for economical and environmentally friendly lithium extraction. Nuclear Magnetic Resonance is an established analytical method that has already been used in numerous inline applications. For this study on Li NMR in flow, a cryogen-free magnet with a variable magnetic field was used, whereby a field
strength of 4.7 T was set for the measurements for compatibility reasons. The influences of flow velocity, repetition time, and lithium concentration were investigated in spin echo measurements. This allows for defining limitations and potential fields of application for
the measurement setup. In addition, the possibilities of internal pre-polarization were investigated. The results show that the method and setup are well suited for inline flow measurements on Li and have great potential for expanding the range of application
Freigabeargumentation hochautomatisierter Nutzfahrzeuge im Vergleich zum menschlichen Fahrer
Get PDFDas automatisierte Fahren ist eines der zentralen Forschungs- und Innovationsfelder in der Automobilindustrie. Eine entscheidende Herausforderung ist die Frage, wie Akzeptanzkriterien für die Sicherheit des Systems im Rahmen der Freigabeargumentation definiert werden können. Ziel der Argumentation ist der Nachweis, dass ein hochautomatisiertes Fahrzeug auf Basis gesellschaftlich moralischer Konzepte kein unangemessenes Risiko darstellt.
Kern der Dissertation ist der entwickelte Prozess zur Definition und Anwendung von Akzeptanzkriterien im Vergleich zum menschlichen Fahrer. Die im VVM-Projekt als Goal Structuring Notation (GSN) entwickelte Sicherheitsargumentation wird um die Prozessartifakte erweitert und ermöglicht eine strukturierte und nachverfolgbare Freigabeargumentation in Einklang mit dem szenarienbasierten Testansatz. Dabei werden explizit Akzeptanzkriterien für aggregiertes und szenarienbasiertes Verhalten berücksichtigt, deren Kombination für eine umfassende Absicherung im Vergleich zu einem menschlichen Referenzfahrer notwendig ist. Für die Gewinnung geeigneter Realdaten werden die Operational Design Domain für das System under Test (SuT) und Anforderungen an die Datenquellen für die Akzeptanzkriterien definiert. Die Einordnung der Daten in die szenarienbasierte Struktur der Sicherheitsargumentation erfolgt durch die Anwendung der Methode der Szenarienidentifikation. Um die korrekte Definition und Anwendung sicherzustellen, werden die Akzeptanzkriterien im Rahmen des strukturierten szenarienbasierten Testansatzes definiert, für das SuT angewendet und die Testergebnisse als Nachweis in der GSN eingeordnet.
Die praktische Anwendbarkeit des Prozesses wird für zwei Anwendungsfälle im Umfeld der Absicherung von hochautomatisierten Nutzfahrzeugen nach SAE-Level 4 gezeigt
Constraining four-heavy-quark operators with top-quark, Higgs, and electroweak precision data
Get PDFWe establish constraints on the dimension-six four-heavy-quark operators in the Standard Model Effective Field Theory (SMEFT) by synthesising LHC measurements of top-quark and single-Higgs production with electroweak precision observables. We scrutinise the choice of the γ5 scheme in single-Higgs calculations, demonstrating its non-negligible impact on SMEFT fits
The weakly bound CO molecule adsorbed on the low-index CeO surfaces: A case for a CCSD(T) benchmark study using an embedded-cluster model
Get PDFThe binding energy and the vibrational stretching frequency of the probe molecule CO adsorbed on the low-index CeO surfaces [(100), (110), and (111)] were benchmarked using the coupled-cluster singles, doubles, perturbative triples [CCSD(T)] method, employing an embedded cluster approach. Using the same methodology as for the top configuration of CO on the (111) surface [J. Vázquez Quesada et al., J. Chem. Phys. 161, 224707 (2024)], the best theoretical estimate for the CO frequency on the CeO(100) surface (CO bridge configuration) obtained at the CCSD(T)/def2-TZ/QZVPP level of theory and under low-coverage conditions (2193 cm) is 17 cm larger than the experimental value (1 ML coverage saturation), which is in agreement with previous estimates for the CO adsorption on the CeO(111) surface (12 cm). For the (110) surface, theoretical and experimental data compare differently. The CCSD(T)/def2-TZ/QZVPP values are −7 cm−1 (top configuration) and −21 cm (tilt-x configuration) lower than the two experimental features measured at 2170 cm (negative feature) and 2160 cm (positive feature). MP2 predictions suggest the existence of a case of multiple-configuration dynamics with various almost isoenergetic configurations in a low-coverage situation. The CO harmonic vibrational frequencies were not semi-empirically scaled but explicitly corrected for anharmonic effects, which amount to 25–26 cm with all tested methods. CO adsorption energies of −0.40 ± 0.07 eV, −0.17 ± 0.07 eV, and −0.20 ± 0.07 eV for the (100), (110) (top), and (110) (tilt-x) adsorption sites, respectively, are obtained at the CCSD(T)/def2-TZ/QZVPP level of theory. These results agree well with those proposed for the (111) surface (−0.22 ± 0.07 eV) [J. Vázquez Quesada et al., J. Chem. Phys. 161, 224707 (2024)] and confirm the physisorption character of the adsorption of CO on the three low-index surfaces of CeO
Absolute quantification of gluten protein groups and their relation to wheat baking quality
Get PDFWheat gluten proteins are key determinants of baking quality. While untargeted proteomics enables relative quantification, absolute quantities of specific gluten protein groups are not available so far. We developed a targeted liquid chromatography tandem mass spectrometry (LC-MS/MS) stable isotope dilution assay to quantify eleven individual gluten protein groups based on isotope-labeled internal standards corresponding to selected marker peptides. The comparison of targeted and untargeted measurements revealed differences in protein composition, likely arising from different MS/MS acquisition strategies and protein assignment. We correlated the absolute protein content with baking quality traits in a multiple advanced generation intercross wheat population comprising 394 inbred lines. None of the individual groups correlated strongly with any baking quality trait. Six groups (α-gliadin 2, γ-gliadin 1, low-molecular-weight glutenin subunit (LMW-GS) 3, and high-molecular-weight glutenin subunits (HMW-GS) 2–4) showed weak to moderate associations (r = 0.32–0.64), mainly with grain protein content, sedimentation value, and wet gluten content. LMW-GS 3 represents the rare i-type containing eight cysteine residues. Loaf volume was only weakly to moderately correlated, primarily with HMW-GS 1 (r = 0.41) and HMW-GS 3 (r = 0.40), supporting the superior effect of Dy10. By contrast, HMW-GS 5 (Dx2, Dx5) showed little effect, consistent with a stronger influence of y-type glutenin subunits. Summing up the protein content across groups increased correlation strengths, yet baking quality remains a complex trait shaped by multiple proteins and non-protein factors