Universität Stuttgart
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Item Open Access Visuelle Analyse gemeinsamer Sequenzen(2020) Galuschka, MarcelIn den sozialen Medien verbreiten sich Texte schnell. Dieses Phänomen lässt sich auch in historischen Zeitungsartikeln erkennen. Forscher aus der Literaturwissenschaft und der Kulturwissenschaft befassen sich mit diesem Thema und untersuchen eine Menge von Texten. In dieser Arbeit erstellen wir dazu einen Prototyp, mit welchem es möglich ist, diese Texte untereinander zu vergleichen und zwei Texte im Vergleich genauer zu betrachten. Außerdem diskutieren wir hier, aus welchem Grund wir diese Darstellung gewählt und wie wir diese verwirklicht haben. Darüber hinaus haben wir diesen Prototyp einer Literaturwissenschaftlerin vorgestellt, welche mit diesem sprachliche Veränderungen zwischen den Texten erkennen kann.Item Open Access Exploring tailored fiber placement in biocomposite modular structures(2025) Petrš, Jan; Spyridonos, Evgenia; Grabowska, Paulina; Grisin, Benjamin; Carosella, Stefan; Middendorf, Peter; Dahy, HanaaItem Open Access Efficient simulation of challenging PDE problems on CPU and GPU clusters(2021) Schirwon, Malte; Göddeke, Dominik (Prof. Dr.)The main contribution of this dissertation is to show how efficient parallelization techniques for numerical simulations of partial differential equations (PDEs) can be developed and which aspects have to be considered in order to obtain the best possible performance. For this purpose, the target platforms range from high-performance workstations to small clusters and up to supercomputers. In particular, we focus on platforms accelerated by graphics cards. We emphasize that the efficient numerical simulation of PDE problems comprises and combines, in novel ways, aspects from numerical analysis, numerical methods (algorithmics, data structures and other areas more related to computer science) and hardware details. Many models in science, engineering and economics are based on systems of PDEs. The choice of modeling techniques, the implementation of numerical solution techniques, as well as the chosen target platform limit the accuracy and the duration of the simulation. Increasing the accuracy and/or reducing the duration of the simulation is usually not possible without efficient software. Based on three application scenarios, we adapt already existing methodologies and algorithms to the target platforms or change the way they are implemented in order to achieve optimal efficiency. As a guiding scheme, we consider the challenging case of unstructured data and schemes. The first application is the wave propagation in optical fibers. We present an MPI-parallel implementation that is particularly suitable for small clusters. %Here, we change the numerical method and the implementation technique to increase efficiency and decrease runtime. The second application scenario is the flow in porous media. Based on both applications, we develop implementation techniques that increase their efficiency. Furthermore, we present an adapted version of a neighborhood algorithm that further increases the efficiency for current graphics cards. The increased efficiency and reduced runtime allows to perform more complex simulations. %For example, higher resolutions can be simulated or more physical parameters can be included. One of theses applications is considered to be the third application, which is seismic wave propagation and waveform inversion. The feasibility of developing efficient implementations for computationally powerful target platforms permits us to consider the inversion of seismic waves in viscoelastic materials. In particular, we present an inversion scheme that also allows us to determine the damping parameters of the viscoelastic material. In addition, regularization methods and a modified solver method are presented, which can be used for a more efficient solution of such problems.Item Open Access Manipulating wetting and pore filling by wall transparency(2025) Kondrat, Svyatoslav; Schimmele, Lothar; Giacomello, Alberto; Tasinkevych, Mykola; Dietrich, S.Atomically thin walls become increasingly prevalent in modern technologies. Exhibiting a unique property-transparency to interparticle interactions-such walls influence processes as diverse as capacitive energy storage, electron transfer, and wetting. However, the impact of wall transparency on wetting and capillary phenomena remains poorly understood. Herein, we employ classical density functional theory to explore how van der Waals interactions across thin solid walls affect capillarity and substrate wetting. Our findings demonstrate that a fluid-filled, sidewise-open channel beneath a thin wall can drastically enhance the lyophobicity of the wall (hydrophobicity if fluid is water), up to the point of effectively transforming lyophilic surfaces into lyophobic ones. Conversely, a fluid covering a thin wall can convert capillary condensation to drying and induce unusual capillary phases within the channel. These findings highlight the potential of wall transparency as a tool for manipulating channel filling and wetting behaviors, emphasizing its significance for interfacial phenomena and fluid adsorption in porous materials.Item Open Access Introducing tree-based-regression models for prediction of hard rock TBM performance with consideration of rock type(2022) Salimi, Alireza; Rostami, Jamal; Moormann, Christian; Hassanpour, JafarPrediction of machine performance is a fundamental step for planning, cost estimation/control and selection of the machine type when using a tunnel boring machine (TBM). Penetration rate (PR) and machine utilization (U) are the two principal measures of TBM performance for evaluating the feasibility of using a machine in a given ground condition. However, despite the widespread use of TBMs and established track records, accurate estimation of machine performance could still be a challenge, particularly in complex geological conditions. Since different types of rocks have varied texture (cementation and grain size), and respond differently to cutting forces in the TBM tunnelling, incorporating the effects of rock type in performance prediction models can improve the accuracy of the estimates. The aim of this study was to develop models for predicting penetration rate of hard rock TBMs in different types of rock based on field penetration index (FPI), using multivariable regression analysis and machine learning algorithm, including classification and regression tree (CART). The proposed models offer estimated FPIs in different rock types, rock strength, and rock mass properties in the form of graphs (diagrams), which can be used to estimate TBM penetration rate. The proposed models have been developed based on the analysis of a comprehensive database of TBM performance in various rock types and offers more accurate estimates of machine performance by incorporating many of the key parameters available in typical geotechnical reports and contract documents. The models also exhibit sensitivity to rock mass parameters for predicting the penetration rate.Item Open Access Konzept für eine sichere und benutzerfreundliche Authentifizierung für industrielle Produktionsanlagen(Stuttgart : Fraunhofer Verlag, 2020) Borisov, Alexander; Verl, Alexander (Prof. Dr.-Ing. Dr. h.c. mult.)Die Anzahl und die Schwere der Angriffe auf industrielle Komponenten nehmen von Jahr zu Jahr stark zu. Gleichzeitig steigt der Grad der Vernetzung der Anlagen weiter an und vergrößert dadurch nochmals die mögliche Angriffsfläche. Die aktuelle Situation bezüglich IT-Sicherheit in der fertigenden Industrie erfordert eine dringende Verbesserung der vorhandenen IT-Sicherheitsmaßnahmen. Insbesondere weisen die existierenden Authentifizierungsmöglichkeiten in der Industrie mehrere Defizite auf. Die Sicherheit der zurzeit eingesetzten Methoden, ihre Benutzerfreundlichkeit und auch der monetäre Aufwand für den Betrieb sind bei zahlreichen Anwendungen nicht zufriedenstellend. Seitens der Industrie und auch der Forschungsgemeinschaft besteht daher der Bedarf, bessere Authentifizierungsverfahren zu entwickeln. Die Erforschung einer neuen Authentifizierungsmöglichkeit für eine industrielle Anwendung bildet den Hauptteil der vorliegenden Arbeit. Die in dieser Arbeit erarbeitete Authentifizierungsmethode basiert auf der Verwendung von zeitbasierten Einmalschlüsseln, die über eine speziell entwickelte App im Smartphone des Benutzers generiert werden. Dabei findet eine beidseitige und eine Zwei-Faktor-Authentifizierung statt. Die Authentifizierungsinformationen werden zudem über die Verbindung des Smartphones an den Server übertragen. Die Lösung weist somit eine hohe Benutzerfreundlichkeit, starke Sicherheit und geringe Betriebskosten auf. Diese Eigenschaften wurden im Rahmen dieser Arbeit experimentell bestätigt und in einer Benutzerstudie nachgewiesen. Darüber hinaus wurde in der Arbeit gezeigt, wie die entwickelte Authentifizierungslösung in eine IT-Sicherheitsarchitektur eines Werkes integriert werden kann. Die vorliegende Arbeit leistet somit einen Beitrag zur Verbesserung der IT-Sicherheit in der produzierenden Industrie und kann für die Institute der angewandten Forschung sowie auch für die Entwicklungsabteilungen der Industrieunternehmen von Bedeutung sein.Item Open Access A numerical method for the generation of hierarchical Poisson Voronoi microstructures applied in micromechanical finite element simulations : part I: method(2020) Schneider, Y.; Weber, U.; Wasserbäch, W.; Zielke, R.; Schmauder, S.; Tillmann, W.Poisson Voronoi (PV) tessellations as artificial microstructures are widely used in investigations of material deformation behaviors. However, a PV structure usually describes a relative homogeneous field. This work presents a simple numerical method for generating 2D/3D artificial microstructures based on hierarchical PV tessellations. If grains/particles of a phase cover a large size span, the concept of “artificial phases” can be used to create a more realistic size distribution. From case to case, detailed microstructural features cannot be directly achieved by commercial or free softwares, but they are necessary for a deep or thorough study of the material deformation behavior. PV tessellations created in our process can fulfill individual requirements from material designs. Another reason to use PV tessellations is due to the limited experimental data. Concerning the application of PV microstructures, four examples are given. The FE models and results will be presented in consecutive works, i.e. “part II: applications”.Item Open Access Low-field chip-based Overhauser dynamic nuclear polarization platforms(2026) Yang, Qing; Anders, Jens (Prof. Dr.)Item Open Access Multiphoton quantum interference at ultracompact inverse-designed multiport beam splitter(2025) Huang, Shiang-Yu; Kumar, Shreya; Huster, Jeldrik; Augenstein, Yannick; Rockstuhl, Carsten; Barz, StefanieItem Open Access GeSn‐on‐Si avalanche photodiodes with high responsivity and low dark current(2025) Wanitzek, Maurice; Ramachandra, Harishnarayan; Spieth, Christian; Daus, Alwin; Schulze, Jörg; Oehme, MichaelGeSn‐on‐Si avalanche photodiodes (APDs) are emerging as a promising solution for low‐light detection in the short‐wave infrared (SWIR) spectral range, including applications in imaging and telecommunications. In this work, key challenges such as high dark current and limited responsivity are addressed by demonstrating devices, which combine low noise with high signal amplification, while remaining compatible with silicon‐based technology. GeSn‐on‐Si APDs with various Sn concentrations up to 1.9% are fabricated and characterized. The GeSn layers are grown pseudomorphically on Ge virtual substrates on Si wafers using molecular beam epitaxy. The devices comprise a double‐mesa structure and exhibit a dark current dominated by a perimeter leakage path, independent of the Sn content. A dark current below 1 µA is maintained up to the onset of avalanche breakdown, marking a significant improvement compared to prior work. A record‐high responsivity of 14.7 A W -1 is achieved at 1550 nm for the APD with 1.9% Sn. Through impulse response measurements, the 3‐dB bandwidth is determined to 1.2 GHz on devices with an 80 µm diameter, resulting in a responsivity‐bandwidth‐product of 17.6 A W -1 GHz -1 . These results highlight the potential of GeSn‐on‐Si APDs for high‐performance, low‐light applications in the SWIR range.