Universität Stuttgart
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Item Open Access Mechanistic studies on the DNA methyltransferases DNMT3A and DNMT3B(2021) Dukatz, Michael; Jeltsch, Albert (Prof. Dr.)In this work, both regulatory and catalytic mechanisms of de novo methyltransferases were investigated, which include interactions with other proteins and the specific recognition of the substrate sequence. Another part of this work strived to elucidate how enzymatic generation of 3-methylcytosine by DNMT3A can occur.Item Open Access Temperaturbestimmung von Lithium Ionen Zellen mittels künstlicher neuronaler Netze basierend auf Daten der elektrochemischen Impedanzspektroskopie(2025) Ströbel, Marco; Birke, Kai Peter (Prof. Dr.-Ing.)Item Open Access Defined polymer architectures enabled by yttrium-mediated ring-opening polymerization of renewable lactones(2025) Hornberger, Lea-Sophie; Buchmeiser, Michael R. (Prof. Dr.)Although global plastic production exceeds 410 million tons annually, less than 0.7 % currently originates from bio-based sources. Given the finite fossil resources and the low biodegradability of conventional plastics, the development of polymers from renewable feedstocks offers considerable potential. This highlights the largely unexploited opportunities offered by renewable monomers. Ring-opening polymerization (ROP) enables the synthesis of polyesters with precise control over molar mass, polydispersity, and architecture, while reversible-deactivation radical polymerization (RDRP) techniques such as atom transfer radical polymerization (ATRP) provide complementary strategies for post-polymerization modification of functional polyesters. This dissertation employs aminoalkoxy bis(phenolate) yttrium complexes for the controlled ROP of lactones from renewable resources, systematically expanding the accessible monomer scope from small, strained four-membered rings to unstrained macrolactones and functional seven-membered terpene-derived lactones. In the first part, the entropy-driven ROP of the 16-membered macrolactone ω pentadecalactone (PDL) was achieved under controlled conditions, affording high-molar-mass poly(ω-pentadecalactone) (PPDL) with moderate polydispersities. Its aliphatic backbone makes PPDL a promising sustainable analogue to polyolefins. Sequential block copolymerization with the four-membered racemic β-butyrolactone (BBL) yielded semi-crystalline materials that integrate the crystalline domains of both homopolymers, enabling tunable material properties. The second part investigated the effect of substitution pattern and stereochemistry on the polymerization kinetics and mechanism of the seven-membered terpene-based (-)-menthide and (+)-carvomenthide, which differ only in the relative positions of their substituents. Kinetic analysis combined with density functional theory (DFT) calculations revealed that subtle stereoelectronic differences strongly impact activation parameters, propagation rates, and susceptibility to side reactions. In (-)-menthide, the isopropyl group adjacent to the reactive ester moiety introduces steric hindrance and increases the activation, whereas the reduced steric demand near the ester in (+)-carvomenthide enables faster propagation but also promotes side reactions. These findings provide valuable guidelines for the rational design of terpene-based lactones. The third part focused on trans (+)-dihydrocarvide (DHC), a seven-membered lactone bearing a pendant isopropenyl group. ROP of DHC produced amorphous poly(dihydrocarvide) (PDHC) with full retention of the double bond. Block copolymerization with semi-crystalline PPDL or syndiotactic poly(3-hydroxybutyrate) (PHB) introduced crystallinity and phase separation. The pendant double bonds in PDHC were further functionalized via thiol-ene chemistry to generate ATRP macroinitiators, enabling orthogonal grafting-from polymerizations of ethyl acrylate that afforded high-density polyester-based brush architectures. Overall, the combination of yttrium-mediated ROP with orthogonal post-polymerization techniques enables the construction of renewable polyester architectures such as block and graft copolymers that integrate amorphous, semi-crystalline, and functional segments. This modular approach offers a versatile platform to tailor thermal, mechanical, and functional properties, providing new opportunities for advanced biomedical and high-performance materials.Item Open Access Improving usability of gaze and voice based text entry systems(2023) Sengupta, Korok; Staab, Steffen (Prof. Dr.)Item Open Access Zur optimalen Standortplatzierung von leistungselektronischen Kompensationsvorrichtungen : ein Beitrag zum Problem der Spannungsstützung in ausgedehnten Verbundsystemen(2025) Lisin, Wladimir; Scheffknecht, Günter (Prof. Dr. techn.)Behandelt wird ein NP-hartes Zuordnungsproblem. Die Lösung dieses Problems versteht sich als Antwort auf die Frage nach der optimalen Platzierung von leistungselektronischen Kompensationsvorrichtungen - den sog. FACTS. Die Güte einer Platzierungswahl bemisst sich dann am dynamischen Antwortverhalten infolge ausgelöster Netzfehler. Eine adäquate Abwägung zwischen Geräteanzahl und den dazu erforderlichen Aufwendungen überführt die Aufgabe in eine Pareto-optimale Mehrzielsuche. Des Weiteren ist die Frage nach einer optimalen Standortwahl zugleich auch ein fallvariables Problem, da die individuellen Netznutzungsfälle auch jeweils individuelle Probleminstanzen definieren. Zu ermitteln sind schließlich Ort, Art, Anzahl und die Auslegung von Parametern der Dynamikmodelle der dabei platzierten Anlagen. Konstruiert wurde hierzu ein modulares Bestimmungsverfahren. Die Gütebewertung ermittelter Konfigurationen erfolgt mithilfe von Lastflussberechnungen im detaillierten Netzmodell des europäischen Stromverbundsystems. Die ermittelte Lösung ist schließlich ein aus optimal-korrespondierenden Ort-Geräte-Paaren erweiterter Netz-Anlagen-Park, der bei optimal bestimmten Installationsorten, der optimal bestimmten Anzahl jeder verwendeten Geräteart sowie der optimalen, ortsgebundenen Parametrierung ihrer jeweiligen Dynamikmodelle das anfängliche Systemverhalten eines ausgewählten Netzgebiets bzgl. Stabilität und Robustheit in optimaler Weise verbessert.Item Open Access User experience with the technology of virtual reality in the context of training and learning in vocational education(2021) Guo, Qi; Zinn, Bernd (Prof. Dr.)The virtual reality (VR) technology, with its features of simulation, interaction, and gamification, as well as the various technical aspects of input and output for movements and feedback, provides learners in the VR training and learning environment with the perception of immersion, spatial presence, and flow experience. Based on the theoretical research findings in terms of the learning processes and the learning motivation, the design and development of a VR training and learning environment should adhere to the principles of the UX design and the didactical design. This presented research focuses on the generation of an explanatory and description knowledge about user experience with virtual reality technology in the context of training and learning in virtual environments. Based on the current development of VR technology, as well as the significant application areas, two empirical studies (VILA and VPSL) on the user experience of learners and (prospective) teachers with different types of virtual reality technologies in the field of vocational education are conducted. To test the user experience in the virtual reality training and learning environment, several aspects related to the user experience will be analyzed, including usability of the application, spatial presence, learning motivation, and flow experience of the students. Based on the literature review, the empirical studies, as well as practical experience in the development of the VR training and learning environments, the recommendations for the design, development, evaluation, and implementation of the VR training and learning environments are discussed. With regards to the further implementation of the applications, the requirements from the technological, administrative, and didactical perspectives are discussed. The limitations in the current research, as well as the directions for further research, are outlined.Item Open Access Numerische Untersuchungen zum Dichtmechanismus von Radial-Wellendichtungen(Stuttgart : Institut für Maschinenelemente, 2025) Grün, Jeremias; Bauer, Frank (apl. Prof. Dr.-Ing.)In numerous applications, the tribological system rotary shaft seal is subjected to various dynamic loads on multiple scales. Trends and challenges towards electromobility have further increased the exposure of rotary shaft seals to extreme operating conditions and loads. The associated increasing demand for shorter development times with simultaneously growing requirements and changing conditions make the use of numerical models for the simulation of tribological systems inevitable. Within the scope of this study, a multiscale model has been developed for the transient simulation of the lubrication and sealing mechanism of rotary shaft seals. A multiscale finite element model divided into two subdomains provides the computation of the structural mechanics. The macroscopic subdomain is utilized to compute the large deformations of the sealing ring during mounting, while the second subdomain is used to determine the microscopic distortions of the surface roughness on the sealing edge. An efficient and automated modeling approach allows the direct integration of physical surface measurement data into the numerical model. A transient computational fluid dynamics model enables the simulation of the dynamic flow processes in the sealing gap on the microscale. Lubricant film thickness equations serve as an indirect coupling between structural mechanics and fluid mechanics. The temperature dependence of the lubricant data is taken into account in the fluid mechanics model and in the determination of the sealing gap height. An empirical model is introduced, in conjunction with the computational fluid dynamics model, to account for mixed lubrication effects, considering only the viscous portion of friction. Established test rig experiments, extended experimental approaches, and data from previous work validate and verify the developed and applied methods. The numerical analyses demonstrate reasonable outcomes and a high level of consistency between the numerical simulation results and experimental data across the scales under consideration. Deviations between the simulation and experimental results increase as the scale moves from macroscale to microscale, potentially due to various factors that have a more significant influence on the microscale and extrapolation errors. In conclusion, the multiscale analyses provide unique insights into the complex flow dynamics in the sealing gap of rotary shaft seals. This presents clear evidence of the active dynamic lubrication and sealing mechanism. Additionally, the model presents various possibilities for extension and application to other tribological problems.Item Open Access Techno-economic analysis of an instrument mix to decarbonize the electricity sector(Stuttgart : Universität Stuttgart, Institut für Energiewirtschaft und Rationelle Energieanwendung, 2024) Gillich, Annika; Hufendiek, Kai (Prof. Dr.-Ing.)Die Politiklandschaft zur Bekämpfung des Klimawandels wird zunehmend komplexer und damit auch ihre Analyse. Diese Arbeit liefert einen Beitrag zur Bewältigung dieser Aufgabe, indem drei Kerninstrumente zur Dekarbonisierung des Stromsektors, nämlich CO2-Bepreisung, Förderung von erneuerbaren Energien und Kohleausstieg, systematisch bewertet werden. Dabei werden in drei Einzelanalysen ökonomische, technologische und Verteilungseffekte auf der Erzeugungsseite betrachtet, sowie Wechselwirkungen zwischen den Instrumenten. Die erste der Analysen beschäftigt sich mit ökonomischen Effekten eines Kohleausstiegs, der parallel zum EU ETS wirkt (sogenannte „overlapping policies“). Die zweite Analyse zeigt die kurzfristigen Effekte der drei Instrumente auf Marktpreise und Deckungsbeiträge einzelner Technologien auf. In der dritten Analyse wird die langfristige Rentabilität der Technologien in einem iterativen Ansatz untersucht, unter der Annahme von unzureichenden Knappheitspreisen im realen Markt. In allen drei Analysen kommt das lineare, systemkostenoptimierende Strommarktmodell E2M2 zum Einsatz, das für die jeweilige Fragestellung geeignet adaptiert wird. Die aus diesen Analysen abgeleiteten zentralen Empfehlungen für die Gestaltung eines Politikmixes im Stromsektor sind: Erstens sollte die Anzahl an Politikinstrumenten so gering wie möglich gehalten werden. Und zweitens sollte sich die Gestaltung und die Bewertung eines Instrumentenmix an dessen theoretisch optimalem Ergebnis orientieren. Die Berücksichtigung dieser Empfehlungen kann dazu beitragen, dass der Politikmix zur Dekarbonisierung des Stromsektors in Zukunft besser geeignet ist, die Klimaziele so effizient wie möglich zu erreichen.Item Open Access High quality graphene for magnetic sensing(2022) Herlinger, Patrick; Smet, Jurgen (Dr.)In this thesis, we investigated the reliable fabrication of high quality graphene and its use as Hall transducer material. Charged impurities and random strain fluctuations were identified as main culprits that deteriorate the electrical properties of graphene devices. It was shown that these extrinsic sources of disorder can be reduced through optimized device processing steps as well as the use of a proper substrate material for graphene such as hexagonal boron nitride (hBN). This insulating material is atomically flat and possesses a very low intrinsic density of charged impurities. By performing Raman spectroscopy and electrical transport measurements, both without and with applied magnetic field, on a large number of different types of graphene devices, it was demonstrated that the encapsulation of graphene between hexagonal boron nitride thin films is the best way to obtain high quality graphene devices. However, even for these hBN-encapsulated devices, we still observed a notable sample-to-sample variation of the electrical properties. Therefore, we developed a post-processing technique that allows us to improve the electrical properties of such devices both significantly and reliably. Since our technique is applied after device fabrication, we could also demonstrate its beneficial effect by comparing one and the same device before and after treatment. We then assessed the application of such high quality graphene as Hall transducer material. The dependencies on and between all relevant operating parameters were explored. This allowed us to develop a deep understanding and empirical model for graphene Hall elements, including the interplay between thermal and 1/f noise in these devices. All key performance indicators for Hall sensors were measured and their typical values reported. For comparable device dimensions, hBN-encapsulated graphene Hall elements were found to have the potential to become a strong competitor to existing materials that are used in today's commercial Hall sensors. Unfortunately, the large-scale fabrication of hBN thin films still remains an unresolved challenge for the industrialization of large area, high quality graphene Hall elements. Also, the Si CMOS integration demands further development. Even though the application of graphene in Hall devices is promising, as shown in this work, this use case alone does likely not justify the significant efforts and investments we expect to be necessary to industrialize the fabrication of high quality graphene devices. Instead, these efforts and costs must be shared by developing a common technology platform for 2D materials that can address several commercially attractive applications where graphene or another 2D material offers superior performance as well. We hope that the insights provided in this work can help to accelerate this process.Item Open Access Porosity and permeability alterations in processes of biomineralization in porous media - microfluidic investigations and their interpretation(Stuttgart : Eigenverlag des Instituts für Wasser- und Umweltsystemmodellierung der Universität Stuttgart, 2022) Weinhardt, Felix; Class, Holger (apl. Prof. Dr.-Ing)Motivation: Biomineralization refers to microbially induced processes resulting in mineral formations. In addition to complex biomineral structures frequently formed by marine organisms, like corals or mussels, microbial activities may also indirectly induce mineralization. A famous example is the formation of stromatolites, which result from biofilm activities that locally alter the chemical and physical properties of the environment in favor of carbonate precipitation. Recently, biomineralization gained attention as an engineering application. Especially with the background of global warming and the objective to reduce CO2 emissions, biomineralization offers an innovative and sustainable alternative to the usage of conventional Portland cement, whose production currently contributes significantly to global CO2 emissions. The most widely used method of biomineralization in engineering applications, is ureolytic calcium carbonate precipitation, which relies on the hydrolysis of urea and the subsequent precipitation of calcium carbonate. The hydrolysis of urea at moderate temperatures is relatively slow and therefore needs to be catalyzed by the enzyme urease to be practical for applications. Urease can be extracted from plants, for example from ground jack beans, and the process is consequently referred to as enzyme-induced calcium carbonate precipitation (ECIP). Another method is microbially induced calcium carbonate precipitation (MICP), which uses ureolytic bacteria that produce the enzyme in situ. EICP and MICP applications allow for producing various construction materials, stabilizing soils, or creating hydraulic barriers in the subsurface. The latter can be used, for example, to remediate leakages at the top layer of gas storage reservoirs, or to contain contaminant plumes in aquifers. Especially when remediating leakages in the subsurface, the most crucial parameter to be controlled is its intrinsic permeability. A valuable tool for predicting and planning field applications is the use of numerical simulation at the scale of representative elementary volumes (REV). For that, the considered domain is subdivided into several REV’s, which do not resolve the pore space in detail, but represent it by averaged parameters, such as the porosity and permeability. The porosity describes the ratio of the pore space to the considered bulk volume, and the permeability quantifies the ease of fluid flow through a porous medium. A change in porosity generally also affects permeability. Therefore, for REV-scale simulations, constitutive relationships are utilized to describe permeability as a function of porosity. There are several porosity-permeability relationships in the literature, such as the Kozeny-Carman relationship, Verma-Pruess, or simple power-law relationships. These constitutive relationships can describe individual states but usually do not include the underlying processes. Different boundary conditions during biomineralization may influence the course of porosity-permeability relationships. However, these relationships have not yet been adequately addressed. Pore-scale simulations are, in principle, very well suited to investigate pore space changes and their effects on permeability systematically. However, these simulations also rely on simplifications and assumptions. Therefore, it is essential to conduct experimental studies to investigate the complex processes during calcium carbonate precipitation in detail at the pore scale. Recent studies have shown that microfluidic methods are particularly suitable for this purpose. However, previous microfluidic studies have not explicitly addressed the impact of biomineralization on hydraulic effects. Therefore, this work aims to identify relevant phenomena at the pore scale to conclude on the REV-scale parameters, porosity and permeability, and their relationship. Contributions: This work comprises three publications. First, a suitable microfluidic setup and workflow were developed in Weinhardt et al. [2021a] to study pore space changes and the associated hydraulic effects reliably. This paper illustrated the benefits and insights of combining optical microscopy and micro X-ray computed tomography (micro XRCT) with hydraulic measurements in microfluidic chips. The elaborated workflow allowed for quantitative analysis of the evolution of calcium carbonate precipitates in terms of their size, shape, and spatial distribution. At the same time, their influence on differential pressure could be observed as a measure of flow resistance. Consequently, porosity and permeability changes could be determined. Along with this paper, we published two data sets [Weinhardt et al., 2021b, Vahid Dastjerdi et al., 2021] and set the basis for two other publications. In the second publication [von Wolff et al., 2021], the simulation results of a pore-scale numerical model, developed by Lars von Wolff, were compared to the experimental data of the first paper [Weinhardt et al., 2021b]. We observed a good agreement between the experimental data and the model results. The numerical studies complemented the experimental observations in allowing for accurate analysis of crystal growth as a function of local velocity profiles. In particular, we observed that crystal aggregates tend to grow toward the upstream side, where the supply of reaction products is higher than on the downstream side. Crystal growth during biomineralization under continuous inflow is thus strongly dependent on the locally varying velocities in a porous medium. In the third publication [Weinhardt et al., 2022a], we conducted further microfluidic experiments based on the experimental setup and workflow of the first contribution and published another data set [Weinhardt et al., 2022b]. We used microfluidic cells with a different, more realistic pore structure and investigated the influence of different injection strategies. We found that the development of preferential flow paths during EICP application may depend on the given boundary conditions. Constant inflow rates can lead to the development of preferential flow paths and keep them open. Gradually reduced inflow rates can mitigate this effect. In addition, we concluded that the coexistence of multiple calcium carbonate polymorphs and their transformations could influence the temporal evolution of porosity-permeability relationships.