openHSU – Research Showcase

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  • Publication
    Unknown
    Machine scheduling problems with position-dependent availability constraints
    (UB HSU, 2024-06-19) ; ;
    Helmut-Schmidt-Universität / Universität der Bundeswehr Hamburg
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    Machine scheduling problems can be found in any practical environment from logistics to manufacturing, where tasks, called jobs, are completed by assigning them to resources, called machines. In this thesis, we assume that the execution of jobs deteriorates the machine to the point where it may not be in a state to process further jobs, or, more generally, restricts the availability of the machine. Time is often considered to be the main factor in machine deterioration, such as the time elapsed since the start of planning. However, with regard to practice, there are other important factors besides time that can have a significant impact on the machine state. In this work, we concentrate on factors based on the job positions in the scheduling sequence, summarized as position-dependent machine availability constraints. This characteristic can be found in any production or logistics environment where the assignment of the job to the machine determines the availability of the machine to process jobs, rather than the processing time. First, a definition and the existing literature of the superordinate research field of problems with position-dependent availability is given: state-dependent machine availability. In the following, single machine scheduling problems with position-dependent maintenance or with jobs that have to be sequenced at fixed positions are analyzed regarding their complexity. These assumptions represent specific characteristics of position-dependent availability in scheduling. For each assumption, complexity results are presented for single machine scheduling problems minimizing completion time or due date related objective functions. In addition, polynomial-time algorithms are formulated for specific scheduling problems. Finally, we deal with the hybrid flow shop scheduling (HFS) problem that is characterized by a flow shop layout with at least one stage of processing with parallel machines. Priority rules and constructive heuristics are tested and evaluated on 1260 instances for the two-stage no-wait HFS problem with two identical machines on the first stage and one machine on the second stage, which is known to be NP-hard. Furthermore, HFS problems with unrelated machines are assumed, considering setup times on the machines caused by different job families. Constructive heuristics are tested on 960 instances to study the influence of the number of setups on the results for completion time related objective functions.
  • Publication
    Unknown
    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
    Metadata only
    Comparison of two reaction-time-based and one foraging-based behavioral approach-avoidance tasks in relation to interindividual differences and their reliability
    (Springer Nature, 2023-12-16)
    Fricke, Kim
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    Alexander, Nina
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    Vogel,Susanne
    Approaching rewards and avoiding punishments is a fundamental aspect of behavior, yet individuals differ in the extent of these behavioral tendencies. One popular method to assess differences in approach-avoidance tendencies and even modify them, is using behavioral tasks in which spontaneous responses to differently valenced stimuli are assessed (e.g., the visual joystick and the manikin task). Understanding whether these reaction-time-based tasks map onto the same underlying constructs, how they predict interindividual differences in theoretically related constructs and how reliable they are, seems vital to make informed judgements about current findings and future studies. In this preregistered study, 168 participants (81 self-identified men, 87 women) completed emotional face versions of these tasks as well as an alternative, foraging-based paradigm, the approach-avoidance-conflict task, and answered self-report questionnaires regarding anxiety, aggression, depressive symptoms, behavioral inhibition and activation. Importantly, approach-avoidance outcome measures of the two reaction-time-based tasks were unrelated with each other, showed little relation to self-reported interindividual differences and had subpar internal consistencies. In contrast, the approach-avoidance-conflict task was related to behavioral inhibition and aggression, and had good internal consistencies. Our study highlights the need for more research into optimizing behavioral approach-avoidance measures when using task-based approach-avoidance measures to assess interindividual differences.
  • Publication
    Unknown
    The effects of hydrocortisone and yohimbine on human behavior in approach-avoidance conflicts
    (2023-06-14)
    Fricke, Kim
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    Alexander, Nina
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    Krug, Henriette
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    Wehkamp, Kai
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    Vogel, Susanne
    Rationale Balancing approach of positive and avoidance of negative stimuli is essential when faced with approach-avoidance conflicts, e.g., situations with both positive and negative outcomes. This balance is disturbed in several mental disorders, e.g., excessive avoidance in anxiety disorders, and heightened approach in substance use disorders. Since stress is assumed to impact these disorders’ etiology and maintenance, it seems crucial to understand how stress influences behavior in approach-avoidance conflicts. Indeed, some studies suggested altered approach-avoidance behavior under acute stress, but the mechanism underlying these effects is unknown. Objectives Investigate how the pharmacological manipulation of major stress mediators (cortisol and noradrenaline) influences task-based approach-avoidance conflict behavior in healthy individuals. Methods Ninety-six participants (48 women, 48 men) received either 20mg hydrocortisone, 20mg yohimbine, both, or placebo before performing a task targeting foraging under predation in a fully crossed double-blind between-subject design. Moreover, we investigated effects of gender and endogenous testosterone and estradiol levels on approach-avoidance behavior. Results While biological stress markers (cortisol concentration, alpha amylase activity) indicated successful pharmacological manipulation, behavior in approach-avoidance conflicts was not affected as expected. Although yohimbine administration affected risky foraging latency under predation, we found no main effect of hydrocortisone or their interaction on behavior. In contrast, we found gender differences for almost all behavioral outcome measures, which might be explained by differences in endogenous testosterone levels. Conclusions The investigated major stress mediators were not sufficient to imitate previously shown stress effects on approach-avoidance conflict behavior. We discuss potential reasons for our findings and implications for future research.
  • 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
    Unknown
    Where are we heading? Hackathons as a new, relational form of policymaking
    (Routledge, Taylor & Francis, 2024)
    Förschler, Annina
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    Decuypere, Mathias
  • Publication
    Metadata only
    Das "Who is who?" der deutschen Bildungs-Digitalisierungsagenda
    (Budrich, 2018)
    Förschler, Annina
  • Publication
    Metadata only
    P2.13 Korrelation von wiederholten Messungen in einer Modenverwirbelungskammer
    Modenverwirbelungskammern (MVKn) stellen vielfältig verwendbare, reproduzierbare Messumgebungen dar. Grundsätzlich handelt es sich dabei um elektromagnetisch geschirmte Volumina, in denen sog. Modenrührer eingebracht sind, die ein elektromagnetisches Feld „verwirbeln“, sodass ein Prüfling einer definierten aber statistisch variierenden Umgebung ausgesetzt wird. Die Modenrührer in MVKn können schrittweise zwischen den einzelnen Messzeitpunkten oder kontinuierlich verfahren werden. In diesem Beitrag werden die jeweiligen Eigenschaften von wiederholten Messungen, die sowohl bei kontinuierlichem als auch schrittweisem Betrieb der Modenrührer aufgenommen wurden, betrachtet. Mit Hilfe von Korrelationskoeffizenten wird jeweils die Wiederholbarkeit der aufgenommenen Messwertsequenzen insgesamt untersucht. Darüber hinaus wird die Wiederholbarkeit von Fadingeinbrüchen gesondert betrachtet, da diese einen wesentlichen Einfluss auf Funksysteme haben, die mittels einer MVK charakterisiert werden können. Als Ursache für Abweichungen bei Wiederholungen wird abschließend das zeitliche Verhalten bzw. die Streuungen zwischen den Messzeitpunkten betrachtet.