OPUS Online Publikationen der Universität Stuttgart
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Crystal structure of (3R,1S′,2S′)-3-[1-benzyloxy-2,3-isopropylidenedioxypropyl]-2-methyltetrahydro-1,2-oxazole, C17H25NO4
No full textC17H25NO4, monoclinic, P1211 (no. 4), a = 8.547(3) Å, b = 9.176(2) Å, c = 11.166(2) Å, β = 102.24(2)°, V = 855.8 Å3, Z = 2, Rgt(F) = 0.053, wRref(F2) = 0.137, T = 293 K.Fonds der Chemischen Industri
Das Einbindungsverhalten von Alkaliverbindungen in Additive beim Einsatz von Biomassen in Staubfeuerungen
No full textDie weltweit steigende Nachfrage nach Energie sowie die zunehmende Diskussion um die Einsparung von Kohlendioxid bei der Erzeugung von Wärme und elektrischer Energie rücken konventionelle Kraftwerke, bei denen aus fossilen Brennstoffen Strom und ggf. Wärme erzeugt werden, in den Fokus. Durch den von der Politik beschlossenen Ausstieg aus der Atomkraft und der Verstromung von Kohle wird die Versorgungslage in vielen Teilen Deutschlands schwieriger.
Die erneuerbaren Energien, wie z.B. die Nutzung von Solar und Windkraft, können ohne geeignete Speicherlösungen aufgrund der zeitlichen Fluktuation des Energieangebots diese Lücke nur bedingt schließen. Zudem liegen die großen Windparks, die das Potential haben große konventionelle Kraftwerke zu ersetzen, vorwiegend an den Küsten in Norddeutschland. Aufgrund der begrenzten Kapazität der Übertragungsnetze kann die hier erzeugte Energie jedoch nur bedingt zu den industriellen Zentren wie im Ruhrgebiet und Süddeutschland transportiert werden.
Daher bietet es sich an, die bestehenden Steinkohlefeuerungen, denen durch den geplanten Ausstieg aus der Kohleverstromung die Betriebsgrundlage entzogen wird, auf Biomasse umzustellen.
Aufgrund der großen Brennstoffmengen sowie der im Einsatz befindlichen Staubfeuerungstechnik ist nicht jede Biomasse geeignet. Maßgeblich ist die Verfügbarkeit, die Energiedichte sowie die Nutzbarkeit in einer Staubfeuerung. Als aussichtsreich aufgrund der Energiedichte, die mit Trockenbraunkohle vergleichbar ist, haben sich hier Pellets aus Holz und Agrarreststoffen wie z.B. Sonnenblumenkernschalen gezeigt.
Durch die Lage der Steinkohlekraftwerke an der Küste oder Flüssen, die bisher bereits für den Transport der Kohle verwendet werden, ist die Logistik für den Transport von Biomasse in Form von Pellets bereits vorhanden.
Die notwendigen Modifikationen der bestehenden Kraftwerksblöcke begrenzen sich überwiegend auf die Brennstoffvorbereitung. Hier werden angepasste Brennstoffmühlen benötigt, die den Verbund der Biomassefaser im Pellet wieder auflösen.
Der Einsatz von Biomasse in konventionellen Staubfeuerungen bietet den Vorteil, dass der Brennstoff als CO2-neutral gilt, da die freigesetzten Mengen dem entsprechen, was die Pflanzen während ihres Wachstums aus der Atmosphäre abgeschieden haben. Zudem führt der Einsatz von Biomassen zu einer deutlichen Reduktion der aus dem Verbrennungsprozess anfallenden Aschemassenströme.
Neben den Vorteilen birgt der Einsatz von Biomassen auch diverse Nachteile. So enthalten die meisten Biomassen deutlich höhere Konzentrationen an Phosphor und Alkalimetallen, die im Bereich der Feuerung und des Dampferzeugers durch Korrosion zu Schäden und höheren Betriebskosten führen, und in den nachgeschalteten Aggregaten der Rauchgasreinigung ebenfalls negative Auswirkungen haben. Dies gilt besonders für den SCR-DeNOx-Katalysator, im Folgenden DeNOx-Katalysator genannt, der in den meisten Staubfeuerungen zur Reduktion der Stickoxide aus dem Verbrennungsprozess verbaut ist. Dieser Katalysator besteht in der Regel aus einer Matrix aus Titandioxid, die mit aktiven Komponenten wie z.B. Vanadiumpentoxid dotiert ist. So führen Phosphorverbindungen zu einem Verkleben der Poren und somit zu einer Reduktion der Katalysatoroberfläche. Dieser Prozess ist jedoch mit geeigneten Maßnahmen reversibel. Im Gegensatz dazu ist die Deaktivierung des Katalysators, die durch Kaliumverbindungen hervorgerufen wird, nicht umkehrbar.
Aus diesem Grund beschäftigt sich diese Arbeit mit dem Einfluss von Additiven, die dem Verbrennungsprozess zugegeben werden, um die negativen Effekte auf den Katalysator zu reduzieren. Hierzu gibt es in der Literatur unterschiedlichste Ansätze, wobei in dieser Arbeit der Ansatz der Einbindung in alumino-silikatische Strukturen anhand von experimentellen Untersuchungen näher betrachtet wird.
Die Arbeit gliedert sich in drei Teile, beginnend mit der Charakterisierung der Brennstoffe und Additive im Labormaßstab. Im zweiten Teil werden, basierend auf den Daten aus den Untersuchen, die im ersten Teil durchgeführt wurden, Berechnungen mit FactSageTM zum Freisetzungs- bzw. Einbindungsverhalten der Alkaliverbindungen durchgeführt. Im dritten Teil der Arbeit folgen anschließend Untersuchungen an einem Flugstromreaktor sowie einer Staubfeuerung, um unter realen Bedingungen die Aussagen des zweiten Teils der Arbeit zu verifizieren. Neben den Analysen, die direkt während der Versuchsreihen erfolgten, wie z.B. Emissionsmessungen, wurden auch Asche- und Katalysatorproben im Nachgang mittels Rasterelektronenmikroskop untersucht und ausgewertet.
Die Untersuchungen zeigen, dass durch den Einsatz von Additiven auf aluminosilikatischer Basis eine schnelle und stabile Einbindung des im Brennstoff gebundenen Kaliums im Bereich der Verbrennungsreaktion erfolgt.
Zudem hat sich gezeigt, dass ebenfalls im Brennstoff vorkommende Chlorverbindungen, aufgrund des fehlenden Reaktionspartners Kalium, zu einer erhöhten HCl-Konzentration im Verbrennungsabgas führen. Dies kann, neben Emissionsproblemen bei Unterschreiten des Säuretaupunkts, zur Korrosion mit metallischen Werkstoffen führen.
Die gewonnenen Erkenntnisse aus den Versuchsreihen zeigen, dass beim Einsatz von Additiven auf alumino-silikatischer Basis die Bildung von Kaliumchlorid bei der thermischen Umwandlung der untersuchten Biomassen deutlich reduziert und das Kalium stabil in das Additiv eingebunden werden kann
Repeat DNA methylation is modulated by adherens junction signaling
No full textThrough its involvement in gene transcription and heterochromatin formation, DNA methylation regulates how cells interact with their environment. Nevertheless, the extracellular signaling cues that modulate the distribution of this central chromatin modification are largely unclear. DNA methylation is highly abundant at repetitive elements, but its investigation in live cells has been complicated by methodological challenges. Utilizing a CRISPR/dCas9 biosensor that reads DNA methylation of human α-satellite repeats in live cells, we here uncover a signaling pathway linking the chromatin and transcriptional state of repetitive elements to epithelial adherens junction integrity. Specifically, we find that in confluent breast epithelial cell monolayers, α-satellite repeat methylation is reduced by comparison to low density cultures. This is coupled with increased transcriptional activity at repeats. Through comprehensive perturbation experiments, we identify the junctional protein E-cadherin, which links to the actin cytoskeleton, as a central molecular player for signal relay into the nucleus. Furthermore, we find that this pathway is impaired in cancer cells that lack E-cadherin and are not contact-inhibited. This suggests that the molecular connection between cell density and repetitive element methylation could play a role in the maintenance of epithelial tissue homeostasis.Baden-Württemberg Stiftung (Baden-Württemberg Foundation)Massachusetts Institute of Technology International Science and Technology Initiatives-Germany seed fun
Practical assessment of the architecture refactoring helper : a case study on an industrial commercial project
No full textContext. This thesis pertains to the field of software architecture evolution, focusing on the migration of legacy monolithic applications to microservice-based architectures using a tool-supported, quality-driven method, in particular the Architecture Refactoring Helper [Fri24a].
Problem. Monolithic applications that grow large often decrease developer productivity [VGC+15]. Organizations that want to migrate their monoliths towards microservices previously had no guidance to find a Service Identification Approach that aligns with their demands [Her24; Kno23]3.3.
Objective. This thesis, wants to validate the applicability of the Architecture Refactoring Helper [Fri24a] in constrained real-world environments, through a collaborative case study with the LF Consult GmbH [LF 24], by performing a proof of concept decomposition on a subcomponent of the 3LiterPPS-Server®. Additionally, this thesis suggests improvements for the shortcomings found.
Method. During this thesis, we conducted a scenario-based architecture review with developers and the software architect, as well as a preference review with LF Consult GmbH’s [LF 24] Head of Development and Support, to configure the Architecture Refactoring Helper [Fri24a]. Afterward, we used different configurations to query for Service Identification Approaches. After attaining the highest-ranked applicable SIAs, we performed the proof-of-concept decomposition, compared, and evaluated the candidate services. Lastly, we evaluated the Architecture Refactoring Helper, suggested improvements, and discussed threats to validity.
Result. The ARH’s [Fri24a] phased methodology systematically narrowed over one hundred SIAs to the Service Cutter [GKGZ16a] approach, yielding reproducible service candidates for the Dispo component in the 3LiterPPS-Server®, while revealing limitations in match aggregation, preference weighting, and UI clarity.
Conclusion. The ARH [Fri24a] proves valuable for structured migration planning under realistic constraints, though enhancements in metric expressiveness, preference exclusion, and weighting, and interface usability are recommended to strengthen decision support.Kontext. Diese Arbeit betrifft das Gebiet der Evolution von Softwarearchitekturen und konzentriert sich auf die Migration monolithischer Altsysteme zu microservice-basierten Architekturen mittels eines toolgestützten, qualitätsgetriebenen Verfahrens, insbesondere des Architecture Refactoring Helper [Fri24a].
Problem. Monolithische Anwendungen, die stark anwachsen, verringern häufig die Produktivität der Entwickler [VGC+15]. Organisationen, die ihre Monolithen zu Microservices migrieren möchten, verfügten bislang über keine Anleitung zur Auswahl eines Service Identification Approach, der ihren Anforderungen entspricht [Her24; Kno23]3.3.
Ziel. Diese Arbeit soll die Anwendbarkeit des Architecture Refactoring Helper [Fri24a] unter realen, eingeschränkten Rahmenbedingungen validieren, indem in einer kollaborativen Fallstudie mit der LF Consult GmbH [LF 24] eine Proof-of-Concept-Dekomposition einer Subkomponente des 3LiterPPS-Server® durchgeführt wird. Zusätzlich werden Verbesserungen für die festgestellten Schwachstellen vorgeschlagen.
Methode. Im Rahmen dieser Arbeit wurden ein szenariobasiertes Architektur-Review mit Entwicklern und dem Softwarearchitekten sowie ein Präferenz-Review mit dem Leiter für Entwicklung und Support der LF Consult GmbH [LF 24] durchgeführt, um den Architecture Refactoring Helper [Fri24a] zu konfigurieren. Anschließend wurden mit unterschiedlichen Konfigurationen Service Identification Approaches abgefragt. Nach der Auswahl der am besten bewerteten anwendbaren SIAs erfolgte die Proof-of-Concept-Dekomposition, der Vergleich und die Evaluierung der Kandidatenservices. Abschließend wurde der Architecture Refactoring Helper evaluiert, Verbesserungsvorschläge formuliert und Bedrohungen der Validität diskutiert.
Ergebnis. Die phasenweise Methodik des ARH [Fri24a] reduzierte systematisch über hundert SIAs auf den Service-Cutter-Ansatz [GKGZ16a] und lieferte reproduzierbare Servicekandidaten für die Dispo-Komponente im 3LiterPPS-Server®, während Einschränkungen bei der Trefferaggregierung, Präferenzgewichtung und Benutzeroberflächenklarheit aufgezeigt wurden.
Schlussfolgerung. Der ARH [Fri24a] erweist sich als wertvolles Instrument für eine strukturierte Migrationsplanung unter realistischen Rahmenbedingungen. Zur Stärkung der Entscheidungsunterstützung werden jedoch Erweiterungen der Metrikausdrucksfähigkeit, Mechanismen zum Ausschluss und zur Gewichtung von Präferenzen sowie Benutzbarkeitsverbesserungen der Benutzeroberfläche empfohlen
Residential mobility decisions of Anglophone migrants in Douala, Cameroon
No full textWhat are the drivers for domestic migration and intra-urban mobility in a Sub-Sahara African context? This study analyses this aspect by looking at residential mobility decisions of Anglophone migrants in Douala. The paper presents factors that influenced migrants to move to, within and out of Douala, as well as what made them decide to stay. Based on a framework of drivers of migration (Black et al., 2011), these factors are analysed at macro-, meso- and micro-level. We argue that at the macro-level, it is mostly political, economic, socio-cultural and security-related factors that influence Anglophone migrants’ residential mobility decisions. At the meso-level, language and ethnicity, social networks and technological advances seemingly facilitate moving decisions, whereas at the micro-level, we argue that it is not only individual or household characteristics, but also events that influence the decision to move. Apart from individual preferences, life course events and external forces playing out at micro-level, these also relate to place attachment and migration aspirations.Projekt DEA
Customer and managerial perspectives on personalization along the customer journey
No full textAdvances in technology have transformed the way consumers engage with brands, enabling companies to manage an increasing number of connected touchpoints and collect vast amounts of customer data for personalization. In response, many companies strive to holistically implement personalization along the customer journey - tailoring each touchpoint to individual preferences and behaviors across the customer journey. While the potential benefits are substantial, including improved satisfaction, loyalty, and marketing efficiency, companies face significant challenges related to data integration, consumer privacy, and the complexity of orchestrating multiple touchpoints. Existing research has primarily examined personalization in digital environments, with little focus on comparing different touchpoints, and only a few studies have examined the extent to which consumer responses to personalized touchpoints change over time and across contexts. Against this backdrop, this dissertation addresses two overarching research questions: 1) How should companies implement personalization in their
touchpoints across the customer journey from a management and consumer perspective? 2) What are consumer responses to personalized customer journeys?
Three publications approach these questions from complementary methodological perspectives. Publication 1 combines a systematic literature review and conceptual synthesis to integrate existing personalization research with a customer experience (management) lens. It highlights the multidimensional nature of personalized touchpoints and how both positive and negative customer outcomes emerge. Publication 2 uses a qualitative research methodology - combining expert interviews and customer focus groups - to explore how managers and consumers perceive personalized omnichannel customer journeys. This work
introduces two design concepts for personalized customer journeys: scope and intensity. It shows that personalization requires balancing company capabilities with consumer preferences, thereby viewing personalization as a co-created process rather than a purely company-driven initiative. Publication 3 uses scenario-based experiments with repeated measures and mixed ANOVA to examine how consumers evaluate the trade-offs of personalization (i.e., the personalization-privacy-calculus) across different touchpoints (branded vs. employee-operated; online vs. offline) and different customer journey stages. The results suggest that privacy concerns remain relatively stable over time but vary significantly by touchpoint type. The findings show that a one-size-fits-all approach to personalization
across all touchpoints in the customer journey can lead to suboptimal results. Instead, effective personalization requires a nuanced, context-sensitive strategy that considers both business constraints (e.g., data integration challenges, resource availability) and consumer expectations (e.g., desired level of personalization, privacy protections).
Collectively, these papers make a theoretical contribution by bridging previously separate areas of personalization, customer journey, customer experience (management), and omnichannel research. They offer novel frameworks to guide future empirical studies. Managerially, they provide practical guidance for tailoring personalization efforts, from identifying which touchpoints merit investment to dynamically adjusting personalization intensity to individual consumer preferences to transparently addressing privacy concerns. In doing so, this dissertation advances the theory and practice of holistic personalization along the customer journey - providing actionable insights for academics and practitioners alike
Self-pumping transpiration cooling : a joint experimental and numerical study
No full textA joint experimental and numerical study is presented to close the current gap in fully coupled data and modeling capabilities for self-pumping transpiration cooling (SPTC). An experimental setup was developed to investigate the effects of the porous medium properties, the flow conditions, and the interactions between solid and coolant on SPTC. Additionally, a two-reference-point, locally emissivity-corrected evaluation methodology for analyzing infrared (IR) measurements was developed, which is valid for quasi-steady evaporation regimes and achieves a better repeatability. For the numerical simulations, we developed an upscaling workflow with pore-network models derived from micro computed tomography (CT) data to accurately describe effective representative elementary volume (REV)-scale parameters and relations. Using upscaled properties, we created a non-isothermal, two-phase Darcy-scale model for the porous medium and modeled free-flow with Reynolds-averaged Navier-Stokes equations, employing an shear stress transport (SST) k-ωturbulence closure to capture near-wall shear stress effects. Coupling conditions ensured mass, momentum, and energy transfer at the interface. The experimental results show a high reproducibility and new insights for the surface temperature at SPTC with the new IR method. The comparison between experimental and numerical results show good agreements. The developed simulation workflow is a major step toward creating a digital twin of an experimental SPTC system. This work lays the foundation for investigating the influence of parameters on SPTC systems and optimizing their efficiency.Projekt DEALUniversität Stuttgar
Influence of ionic liquid film thickness and flow rate on macrocyclization efficiency and selectivity in supported ionic liquid‐liquid phase catalysis
No full textSupported ionic‐liquid phase (SILP) technology in a biphasic setting with n ‐heptane as the transport phase was applied to the Ru‐alkylidene‐N‐heterocyclic carbene (NHC) catalyzed macrocyclization of α , ω ‐dienes to elucidate the effect of ionic liquid (IL)‐film thickness, flow rate as well as substrate and product concentration on macrocyclization efficiency, and Z ‐selectivity. To understand the molecular‐level behavior of the substrates and products at the n ‐heptane/IL interphase, atomistic molecular dynamics simulations were conducted and correlated with experimental observations. The thickness of the IL layer strongly influences the Z/E ratio of the products in that a thin IL layer favors higher Z/E ratios by confining the catalyst between the pore wall and the liquid‐liquid interphase whereas a thick IL layer favors formation of the E ‐product and Ru‐hydride catalyzed isomerization reactions. Also, macrocyclization efficiency, expressed by the ratio of oligomers/macromonocycle (O/MMC), is influenced both by the flow rate and the thickness of the IL layer.Deutsche Forschungsgemeinschaf
Continuation of periodic orbits in conservative hybrid dynamical systems and its application to mechanical systems with impulsive dynamics
No full textIn autonomous differential equations where a single first integral is present, periodic orbits are well-known to belong to one-parameter families, parameterized by the first integral’s values.This paper shows that this characteristic extends to a broader class of conservative hybrid dynamical systems (cHDSs).We study periodic orbits of a cHDS, introducing the concept of a hybrid first integral to characterize conservation in these systems. Additionally, our work presents a methodology that utilizes numerical continuation methods to generate these periodic orbits, building upon the concept of normal periodic orbits introduced by Sepulchre and MacKay (1997). We specifically compare state-based and time-based implementations of an cHDS as an important application detail in generating periodic orbits. Furthermore, we showcase the continuation process using exemplary conservative mechanical systems with impulsive dynamics.Deutsche Forschungsgemeinschaf
From muscle spindle to spinal cord : a modelling approach of the hierarchical organization in sensorimotor control
No full textThe muscle spindle is an essential proprioceptor, significantly involved in sensing limb position and movement. Although biological spindle models exist for years, the gold-standard for motor control in biomechanics are still sensors built of homogenized spindle output models due to their simpler combination with neuro-musculoskeletal models. The performance of new studies that consider different structures of the hierarchical sensorimotor control system, implementing physiologically-motivated neuromechanical models aligned to proprioception, is essential to enable a more holistic understanding about movement. The incorporation of more biological proprioceptive and neuronal circuit models to muscles can make neuro-musculoskeletal systems more appropriate to investigate and elucidate motor control.
Therefore, initially, this doctoral dissertation presents a more physiological model of the muscle spindle that considers the individual characteristics of involved tissue compartments, aligned to the advantage of easy integration into large-scale musculoskeletal models. Different stretches in the intrafusal fibers were simulated in the model's variations following the spindle afferent recorded in previous experiments in feline soleus muscle. Additionally, the proposed enhanced Hill-type spindle models had their parameters extensively optimized to match the experimental conditions, and the resulting model was validated against data from rats’ triceps surae muscle. As result, the model exhibits a stable and valid prediction of experimentally observed muscle spindle responses. At the same time, it presents a well-tuned Hill-type model as muscle spindle fibers – accounting for real sarcomere force-length and force-velocity aspects - and its activation dynamics is similar to the one applied to Hill-type model for extrafusal fibers, making it more easily integrated in multi-body simulations.
Furthermore, this dissertation aims to demonstrate that the afferent firings from the muscle spindle model can be processed by neuronal networks and are important for motor control. Hence, the spindle model was integrated to a previous implemented extrafusal fiber model, inside of the demoa multi-body simulation framework. This structure composed by extrafusal (muscle) and intrafusal (spindle) fibers replaced the muscle-tendon units (MTUs) of a prior developed arm model composed by two degrees of freedom and six MTUs, into the same simulation framework. Additionally, a spinal cord model, based on literature, was implemented in the Nest spiking neural network simulator. The spinal network has 6 neurons per muscle - alpha, dynamic gamma and static gamma motoneurons, together with Ia, propriospinal and Renshaw interneurons – and their respective physiological connections. The coupling between demoa and Nest simulators was implemented using a Cython interface. The spinal cord network - in its two variations of complete and simpler circuitry (including only Renshaw pathway, without spindle proprioception) - had its synaptic weights optimized to perform a center-out reaching task using the musculoskeletal model, without and with perturbation (increment of lower arm segment in 1 kg). As result, the complete spinal cord circuitry learned how to successfully reach all the evaluated targets without and with perturbation, demonstrating the sensorimotor control learning in the environment formed from muscle spindle to spinal circuitry, encompassing the two simulators. On the other hand, the simpler spinal cord circuitry did not succeed in the task of reach all the targets, also demonstrating reduced performance with perturbation. Moreover, the spindle afferent synapses in the complete circuitry were intensified for the higher targets (considered more difficult under gravity) when comparing the scenarios without and with perturbation. Therefore, the muscle spindle connections were strengthened for difficult targets under perturbation, highlighting the importance of spindle proprioception in these more difficult scenarios, as well as indicated by the circuitry that does not consider proprioception and did not show a similar successful performance.
Finally, this dissertation offers a novel possibility of neuro-musculoskeletal modelling environment formed with demoa and Nest simulators. Future outlook includes the integration of the musculoskeletal and spinal cord models with higher-level models of Central Nervous System, aligned to further sophisticated details of the current modelling, to allow a more comprehensive understanding of sensorimotor behavior