2 - Theses

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  • Publication
    Open Access
    The role of interindividual differences in task-based approach-avoidance behavior
    (UB HSU, 2024-06-17)
    Fricke, Kim L.
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    Helmut-Schmidt-Universität / Universität der Bundeswehr Hamburg
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    Vogel, Susanne
    Approach and avoidance are evolutionary highly conserved mechanisms of survival, realized by approaching rewarding and avoiding punishing stimuli in one’s environment. In the laboratory, approach-avoidance behaviors are often measured using experimental tasks. In this thesis, the relationship of interindividual differences with behavioral outcomes of those so-called approach-avoidance tasks was investigated. Firstly, the literature on approach-avoidance tasks and interindividual differences was systematically reviewed. Secondly, the influences of the stress mediators cortisol and noradrenaline as well as self-reported interindividual differences was investigated with a pharmacologically validated approach-avoidance conflict paradigm in a double-blind study with healthy participants. Lastly, the approach-avoidance conflict paradigm was compared to two more established approach-avoidance tasks, the joystick and manikin tasks, in their efficacy to relate to self-reported interindividual differences. Both, systematic review and the conducted research indicates that relationships between task-based approach-avoidance measures and interindividual differences are ambiguous in nature with few exceptions, e.g. in the case of specific phobias. The approach-avoidance conflict paradigm was not affected by the stress mediators, but related to self-reported behavioral inhibition, physical aggression and verbal aggression whereas the joystick and manikin tasks did not. Even those findings appear to be ambiguous, as while interactions of aggression were found in the comparison study, they were not in the pharmacological study, possibly due to a lack of power. Internal consistency measures of all three tasks indicated subpar consistencies for joystick and manikin task and robust consistencies of approach-avoidance conflict paradigm measures. Potential reasons such as differences in the level of abstraction between task and trait measures, particularities of the task designs as well as ideas to resolve or improve them, for example, by employing more ecologically valid designs, are discussed.
  • Publication
    Open Access
    Governance-Transformationen und neue Formen des Policymaking am Beispiel der Digitalisierung von (schulischer) Bildung in Deutschland
    (UB HSU, 2024)
    Förschler, Lea-Annina
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    Helmut-Schmidt-Universität / Universität der Bundeswehr Hamburg
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    Macgilchrist, Felicitas
  • Publication
    Open Access
    Developing high-capacity sustainable materials for hydrogen storage
    (UB HSU, 2024)
    Shang, Yuanyuan
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    Helmut-Schmidt-Universität / Universität der Bundeswehr Hamburg
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    Pundt, Astrid
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    In this thesis, the development of sustainable materials for hydrogen storage is studied. Four model types of hydrogen storage materials are included in this work, which are the complex metal hydride NaAlH₄, solid solution room temperature FeTi alloys, compositionally complex alloys (CCAs), and the reactive hydrides composite (RHC) 2NaBH₄ + MgH₂. The first part of this thesis focuses on developing a complex metal hydride of NaAlH₄ by using waste Al alloy as raw material. The synthesised less pure NaAlH₄ exhibits good reversible hydrogen capacity, whereas the pure NaAlH₄ is not reversible. The second part of this thesis is devoted to developing a FeTi-based metal hydride by using waste steel and Ti alloy scraps as raw materials. Astonishingly, at 50 °C and 100 bar of H₂, the hydrogen storage capacities measured for the FeTi alloys synthesised from recycled scraps are extremely close to the value measured for the pure FeTi. In the third part of this thesis, the hydrogen storage properties of some CCAs are investigated, which further helps in screening the suitable types of waste metal alloys to be used as raw materials. With the synthesised hydrogen storage materials, the main issues are kinetic and thermodynamic tuning. The selected waste steels, Ti alloys, Mg alloys, and Al alloys, are just examples of the vast variety of scrap materials potentially useful for synthesising sustainable hydrogen storage materials. In addition, the influence of single impurities cannot be distinguished. Therefore, the RHC system of 2NaBH₄ + MgH₂ was chosen as a model system to study the effects of well-defined additives on hydrogen storage performances, as can be seen in the last part of this thesis. This work shows that by using waste metal scraps instead of high-purity elements as raw materials, the carbon footprint and costs are tremendously reduced for producing hydrogen storage materials without deteriorating the hydrogen storage properties. This work opens a new path to the development of environmentally sustainable alloys for hydrogen storage purposes.
  • Publication
    Open Access
    Untersuchung zu modularen Hochspannungsschaltern in Sonderanwendungen der Leistungselektronik
    (UB HSU, 2024-05-17)
    Kemper, Johannes
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    Helmut-Schmidt-Universität / Universität der Bundeswehr Hamburg
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    Die vorliegende Arbeit befasst sich mit der Aufgabe, einen Hochspannungsschalter zu entwickeln. Zu den Herausforderungen der Aufgabenstellung gehörten das wiederholte, schnelle Schalten einer unterschiedlich hohen Spannung mit der Möglichkeit eines kontrollierten bidirektionalen Stromflusses. Der realisierte Schalter erweitert den Stand der Technik dahingehend, dass er einen Leistungshalbleiter im linearen Bereich ansteuert, um die Spannungssymmetrie in einer Reihenschaltung zu ermöglichen. Das Gesamtsystem aus Schalter und Ansteuerung kann hinsichtlich der Spannungsfestigkeit zu jedem Zeitpunkt skalierbar werden. Die Treiberschaltungen beziehen ihre Energie aus dem Lastkreis parasitär und besitzen eine Stromaufnahme von weniger als 1mA im statischen Zustand. Für die Ansteuerung wird eine analoge Schaltung verwendet, die durch den Einsatz von diskreten Standardkomponenten eine hohe Verfügbarkeit der Bauteile sicherstellt.
  • Publication
    Open Access
    Diversity and (in)equality in organizations
    (UB HSU, 2024-05-08) ; ;
    Helmut-Schmidt-Universität / Universität der Bundeswehr Hamburg
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    Rastetter, Daniela
    Despite extensive legal and organizational measures to promote diversity, inequalities in organizations, e.g. based on gender, class, or sexual orientation, persist or are (re)produced. This cumulative dissertation comprises six manuscripts that examine issues of diversity and inequality in organizations from a critical perspective. What are differences and inequalities and how are they maintained and (re)produced in daily work practices? The focus is on different aspects of doing difference and diversity as well as on specific contexts of work, management and organization, such as equal participation through e-voice in a digital alternative organization, intersections of gender and class in service work in the luxury segment, barriers and success factors for women’s entrepreneurship in the hospitality and tourism industry, and gay leaders in management. In the dissertation’s frame, the studies’ research perspectives and their critical, politicizing aim are reflected in order to position them within the research field of Critical Management Studies with a focus on diversity and (in)equality as well as in the field of Critical Diversity Studies with a focus on management and organizations.