Spectral Model Reduction as Preconditioner and Adaptive Solver Component in Chemical Reaction Systems

Die vorliegende Arbeit besch\"aftigt sich mit der Analyse und der Anwendung der Reduktionsmechanismen QSSA und ILDM, die beide im Rahmen der Modellierung von chemischen Verbrennungsprozessen entwickelt worden sind. Beide Mechanismen reduzieren die Anzahl der zu modellierenden Spezies erheblich, was eine bedeutende Kostenersparnis bei der numerischen Behandlung zur Folge hat. Der dadurch entstehende systematische Fehler bedingt, dass eine so erhaltene L\"osung nicht notwendigerweise eine L\"osung des detaillierten Problems ist. In einigen Anwendungen f\"uhrt der reduzierte L\"osungsweg daher zu physikalisch fragw\"urdigen Ergebnissen. Ein Schwerpunkt dieser Arbeit ist daher die Untersuchung der Anwendbarkeit dieser Reduktionsmechanismen als Vorkonditionierer f\"ur L\"oser von station\"aren Problemen. Diese Art der Anwendung impliziert die Konvergenz der Berechnungen zu einem physikalisch sinn\-vollen Grenzwert, gegeben dass Konvergenz vorliegt. Ungl\"ucklicherweise kann gezeigt werden, dass Konvergenz mit den Reduktionsmechanismen als Vorkonditionierer unter keinen Umst\"anden vorliegen kann. Ein weiterer Untersuchungsschwerpunkt liegt in der adaptiven Anwendung der Reduktions\-mechanismen bei instation\"aren Problemen. Mit so vielen reduzierten Zeitschritten wie m\"oglich und so wenigen detaillierten Schritten wie n\"otig soll eine zuvor vorgegebene Genauig\-keit erreicht werden. Mit Hilfe der Technik der dualen L\"osungen kann ein Verfahren ent\-wickelt werden, das eine L\"osung liefert, die um einen beliebig kleinen Faktor von der detailliert gerechneten L\"osung abweicht. Das Verfahren ist so konstruiert, dass mit gleichem Rechenaufwand auch die Zeitschrittweite adaptiv gesteuert werden kann

Sourcing a Unique Man-in-the-Moon Bead

Chemical analysis of a unique black bead found in Turkey that depicts the four phases of the moon reveals it most likely originated in the Fichtelgebirge region of Bavaria at some time prior to the early 19th century

Autoencoder Attractors for Uncertainty Estimation

The reliability assessment of a machine learning model's prediction is an important quantity for the deployment in safety critical applications. Not only can it be used to detect novel sceneries, either as out-of-distribution or anomaly sample, but it also helps to determine deficiencies in the training data distribution. A lot of promising research directions have either proposed traditional methods like Gaussian processes or extended deep learning based approaches, for example, by interpreting them from a Bayesian point of view. In this work we propose a novel approach for uncertainty estimation based on autoencoder models: The recursive application of a previously trained autoencoder model can be interpreted as a dynamical system storing training examples as attractors. While input images close to known samples will converge to the same or similar attractor, input samples containing unknown features are unstable and converge to different training samples by potentially removing or changing characteristic features. The use of dropout during training and inference leads to a family of similar dynamical systems, each one being robust on samples close to the training distribution but unstable on new features. Either the model reliably removes these features or the resulting instability can be exploited to detect problematic input samples. We evaluate our approach on several dataset combinations as well as on an industrial application for occupant classification in the vehicle interior for which we additionally release a new synthetic dataset.Comment: This paper is accepted at IEEE International Conference on Pattern Recognition (ICPR), 202

Dislocation multiplication by cross-slip and glissile reaction in a dislocation based continuum formulation of crystal plasticity

Modeling dislocation multiplication due to interaction and reactions on a mesoscopic scale is an important task for the physically meaningful description of stage II hardening in face centered cubic crystalline materials. In recent Discrete Dislocation Dynamics simulations it is observed that dislocation multiplication is exclusively the result of mechanisms, which involve dislocation reactions between different slip systems. These findings contradict multiplication models in dislocation based continuum theories, in which density increase is related to plastic slip on the same slip system. An application of these models for the density evolution on individual slip systems results in self-replication of dislocation density. We introduce a formulation of dislocation multiplication in a dislocation based continuum formulation of plasticity derived from a mechanism-based homogenization of cross-slip and glissile reactions in three-dimensional face-centered cubic systems. As a key feature, the presented model includes the generation of dislocations based on an interplay of dislocation density on different slip systems. This particularly includes slip systems with vanishing shear stress. The results show, that the proposed dislocation multiplication formulation allows for a physically meaningful microstructural evolution without self-replication of dislocations density. The results are discussed in comparison to discrete dislocation dynamics simulations exposing the coupling of different slip systems as the central characteristic for the increase of dislocation density on active and inactive slip systems. (C) 2019 Elsevier Ltd. All rights reserved

Hybrid sideways/longitudinal swimming in the monoflagellate Shewanella oneidensis: from aerotactic band to biofilm

Shewanella oneidensis MR-1 are facultative aerobic electroactive bacteria, with an appealing potential for sustainable energy production and bioremediation. They gather around air sources, forming aerotactic bands and biofilms. Though accumulation is crucial to technological exploitation, their collective behaviour remains poorly reported. Here we establish a comprehensive framework for the study of aerotaxis, unveiling a novel hybrid locomotion pattern. Despite having only one flagellum, MR-1 combine motility features of mono- and multiflagellate bacteria, alternating longitudinal fast and sideways slow swimming. The adaptive tuning of the resulting bimodal velocity distributions fulfils different biological functions, such as aerotaxis and confinement. Overall, we reveal the mechanisms underlying the aerotactic collective behaviour of MR-1, in the process leading from accumulation to biofilm formatio

Relations of the German almost perfect scale-revised and short almost perfect scale with the big five personality facets

The Almost Perfect Scale-Revised (APS-R) and its short form (SAPS) are among the most-established multidimensional perfectionism measures. Yet, investigations into the APS-R/SAPS nomological networks have mainly been limited to the level of broader personality traits. This reliance on trait-level associations hampers the conceptual understanding of perfectionism traits by masking more complex relations with specific cognitive, emotional, and behavioral tendencies (personality facets). In this study, we validated German versions of the APS-R and SAPS and assessed their relations with the Big Five personality facets in two samples (NSample 1 = 305 university students; NSample 2 = 467 community adults). Both scales displayed satisfactory psychometric properties, convergent and criterion-related validity. Analyses on the level of the Big Five personality facets revealed complex and nuanced patterns of relations. These findings provide new insights into the APS-R and SAPS nomological networks and facilitate the conceptual distinction between the APS-R subscales