The 10 most recently published documents
This dissertation explores key challenges and innovations in contemporary asset management through three self-contained empirical essays. Each paper examines a distinct but interrelated topic in portfolio construction, contributing to a more resilient and practically viable approach to investing.
Paper 1: The Performance of Risk-Based Asset Allocation in Downward Markets – An Empirical Examination
The first paper investigates the effectiveness of risk-based portfolio strategies – such as minimum variance, equal risk contribution, and risk parity – during periods of market stress. Motivated by the shortcomings of return-optimized models in crisis periods, the paper conducts an extensive backtest using a multi-asset dataset across several downturns. It finds that risk-based strategies consistently offer superior downside protection and more stable performance compared to traditional approaches. These results underscore the robustness of risk-focused allocations when facing uncertain or volatile markets.
Paper 2: A Performance “Horse Race”: Does Anything Beat the 1/N Portfolio?
The second paper revisits the enduring puzzle of the 1/N (equal-weighted) portfolio's performance. Despite its simplicity, previous research has shown it often rivals or outperforms optimized strategies. Using an expanded dataset and robust methodology,
this paper compares a wide range of portfolio construction techniques – including mean-variance optimization and shrinkage methods – against the 1/N benchmark. The findings reaffirm the strong performance of the naïve strategy, particularly when estimation error and real-world frictions are considered. While some optimized models perform better in specific contexts, none dominate consistently.
Paper 3: Index Tracking in Crisis Periods – An Empirical Investigation of the German DAX Index
The third paper shifts focus to passive investment strategies, specifically the accuracy and stability of index tracking during market crises. Using the German DAX as a case study, the paper compares multiple tracking approaches – such as constrained regression and relative optimization – under both normal and crisis conditions. Results reveal that tracking performance deteriorates notably in turbulent markets, with simpler, constraint-based methods offering more consistent tracking accuracy. This highlights the limitations of passive strategies under stress and points to the need for more adaptive frameworks.
Hunting is typically regarded and publicly often criticized as a rather archaic and outdated process of tracking and shooting an animal. However, it can also be understood in a more symbolic way. As a superordinate term, hunting can be referred to as a practice of going after or chasing a specific desire – be it a material object, a living being or immaterialities. One thing that has gained a special value in today´s modern(ised) world, is the experience of seemingly “original” nature and animals – often phrased under the term “the wild”. More and more people can be found participating in a variety of practices of hunting “the wild”, influenced by certain desires, motivations, and geographical imaginations at predestined places.
While there already is a great range of research revolving around what is understood as wilderness, it is rarely discussed how these varying desires and seemingly pre-existing configurations come into practice and thereby shape the places of “the wild”. Therefore, this project aims at dissecting elements of practices and imaginations revolving around “the wild” and place them in a wider context of postcolonial discussions. Furthermore, it wants to contribute to a practice-based approach to better understand desire as well as the process of succeeding at its fulfillment and its volatility. As tools, a variety of ethnographic methods like observatory participation, go-along interviews or hanging outs is used and complemented by semi-structured interviews to capture different practices and types of hunting “the wild”.
Ash dieback, a disease caused by the fungal pathogen Hymenoscyphus fraxineus, is severely threatening the existence of the European common ash (Fraxinus excelsior L.). The invasive pathogen leads to progressive symptoms such as leaf loss, shoot dieback, and stem necrosis, often resulting in high mortality in affected forest stands. While these visual symptoms are well documented, finer-scale physiological and morphological leaf responses remain largely unexplored. Ash dieback symptom severity is typically assessed through time-intensive field-based ratings; however, remote sensing technologies such as Unmanned Aerial Vehicles (UAVs) offer new opportunities for large-scale, remote assessment of disease impact. Therefore, this dissertation applies a multiscale and multisensory approach to assess the effects of ash dieback.
The main research questions were:
(1) Does ash dieback, beyond visible symptoms such as leaf loss and shoot dieback, also induce fine-scale morphological and physiological alterations in the leaves of infected ash trees?
(2) Can multisensory UAV data and the thereof calculated vegetation indices detect different degrees of damage caused by ash dieback?
(3) What level of segmentation accuracy is required to ensure reliable estimation of mean vege-tation index values for individual ash tree crowns?
Field investigations were carried out at four study sites in 2022 and 2023, combining visual vitality assessments with detailed analyses of leaf physiology and morphology in ash trees affected by ash dieback. The examined leaf traits included chlorophyll fluorescence, chlorophyll content, Specific Leaf Area (SLA), leaf thickness, and Fluctuating Asymmetry (FA), all of which were evaluated in relation to visually assessed damage severity. In addition, at two of the sites, repeated UAV-based aerial surveys were conducted from May to October over two consecutive years to capture the whole vegetation period of the common ash, using RGB, multispectral and thermal sensors. Complementing this, close-range multispectral images of individual tree crowns were acquired in 2023 to provide higher spatial resolution data for detailed crown analysis.
In Publication 1 of this dissertation, physiological and morphological leaf traits were investigated in relation to visually assessed disease severity. Among the measured traits, SLA exhibited the most consistent and significant correlation with increasing damage severity, highlighting a potential link between leaf morphology and ash dieback.
In Publication 2 a novel UAV-based monitoring workflow that utilizes RGB and multispectral imagery is introduced to classify ash dieback severity via vegetation index thresholds. The study demonstrated that both RGB and multispectral indices, particularly the Green-Red Vegetation Index (GRVI) and Difference Vegetation Index (DVI), can effectively distinguish between mildly and severely damaged trees. The combination of both multispectral and RGB indices achieved a combined classification accuracy of 77.2 %.
Publication 3 explored the influence of ash tree crown segmentation precision on vegetation index reliability. A newly developed fine segmentation method, based on unsupervised machine learning, successfully excluded non-foliar elements such as ground pixels and canopy gaps, improving spectral data interpretation. Although mean vegetation index values per crown did not differ significantly between coarse and fine segmentation, vegetation index heterogeneity increased with disease severity, emphasizing the added value of detailed crown delineation for detecting subtle stress patterns.
Collectively, these studies contribute a scalable and interdisciplinary framework that bridges leaf-level physiological and morphological measurements with crown-level spectral data and machine learning–based crown segmentation. They further demonstrate how UAV-based remote sensing can be effectively integrated into long-term conservation strategies for Fraxinus excelsior L. This work underscores the importance of combining plant physiology, remote sensing, and machine learning to advance forest health monitoring and offers practical insights for the conservation of Fraxinus excelsior L. under ongoing disease pressure.
Konflikte entstehen oftmals, wenn eine Person das Verhalten einer anderen als Verletzung persönlicher oder sozialer Normen, als Vertrauensbruch oder als Ungerechtigkeit wahrnimmt. Entscheidend für den weiteren Verlauf der Interaktion ist die Reaktion der betroffenen Person auf diese wahrgenommene Transgression. Die vorliegende Dissertation untersucht daher ausgewählte personale und situationale Einflussfaktoren auf diese individuellen Reaktionen. Diese Faktoren werden in vier Publikationen aus unterschiedlichen Perspektiven beleuchtet, um spezifische Ansatzpunkte zur Prävention und Deeskalation von Konflikten zu identifizieren.
In Publikation 1 stehen individuelle Macht- und Gerechtigkeitsmotive im Fokus, die zur Entwicklung von Rachebedürfnissen nach einem Vertrauensbruch in engen Beziehungen beitragen. Es zeigt sich, dass Personen mit starken Macht- und Gerechtigkeitsmotiven eher zu überproportionalen Racheformen neigen. Zudem bevorzugen gerechtigkeitsorientierte Personen eine indirekte Bestrafung durch Dritte oder das Schicksal gegenüber einem gänzlichen Racheverzicht.
Publikation 2 widmet sich produktiven konfliktbezogenen Einstellungen und Verhaltensweisen und bestätigt die Wirksamkeit einer videobasierten Intervention zur Stärkung ebendieser. Durch diese präventive Maßnahme können produktive konfliktbezogene Überzeugungen sowie flexibles Konfliktverhalten über längere Zeit gestärkt werden, während sich negativ erlebte Emotionen in Konflikten nicht signifikant verändern.
Publikation 3 bestätigt durch qualitative Interviews die differenziellen Zusammenhänge zwischen verschiedenen Dimensionen organisationaler (Un-)Gerechtigkeit und diversen Vertrauensdynamiken in der interorganisationalen Zusammenarbeit. Darauf aufbauend wird exemplarisch gezeigt, dass nur positiv, nicht aber negativ erlebte Emotionen die Beziehung zwischen erlebter informationaler Gerechtigkeit und wahrgenommener Vertrauenswürdigkeit vermitteln.
In Publikation 4 wird die Bedeutung der wahrgenommenen Aufrichtigkeit einer Bitte um Verzeihung in kollegialen Arbeitsbeziehungen untersucht. Demnach reduziert eine Bitte um Verzeihung Rache- und Vermeidungsmotivationen und erhöht wohlwollende Tendenzen nur dann, wenn sie als aufrichtig empfunden wird. Wird die Aufrichtigkeit in Frage gestellt, bleiben die Motivationen wie bei fehlender Bitte um Verzeihung bestehen.
In der Gesamtschau erweitern diese Befunde das bisherige Verständnis von Konfliktdynamiken und bieten vielfältige Ansatzpunkte für die Prävention und Deeskalation konflikthafter Situationen.
Unaccompanied young refugees (UYRs) are exposed to multiple stressors before, during, and after flight, placing them at heightened risk for mental health disorders such as post-traumatic stress symptoms (PTSS), depression, and anxiety. As UYRs are usually placed in residential group homes in the Child and Youth Welfare System (CYWS) in Germany, it is important to analyze the role of the institutional environment on UYR’s mental health, as well as the symptom recognition and agreement with their caregivers concerning the symptomatology and how psychotherapeutic treatment can be facilitated. This dissertation synthesizes findings from three publications examining these research questions.
The first publication found that lower caregiver workload predicted reduced PTSS, depression, and anxiety, while UYR-specific accommodation was linked to lower PTSS after one year. Additionally, open group climate, defined as a supportive, warm, responsive, and respectful atmosphere, mediated the effect between physical facility characteristics (accommodation quality) and PTSS, depression, and anxiety, as well as between living in a UYR-specific group and PTSS and depression. The second publication showed low but statistically significant agreement between self- and caregiver reports, with self-reports consistently yielding higher scores regarding PTSS. Greater disagreement was associated with comorbid symptoms and shorter facility stays. The third publication qualitatively identified structured training programs, supportive caregivers and facilities, and skilled interpreters as key facilitators for psychotherapeutic treatment of UYRs from the perspective of psychotherapists.
Overall, this dissertation underscores the necessity of specialization across all fields. This includes trauma-informed care in UYRs-specific groups, widespread mental health screenings, training for caregivers and interpreters, and adequate staffing to ensure symptom recognition and service accessibility. Strengthening local partnerships between CYWS facilities and psychotherapists, along with implementing outreach approaches, can enhance access to mental health care. Policymakers must uphold facility standards, invest in staff resources, and support financial measures for interpreters and evidence-based interventions.
Die Arbeit befasst sich mit dem Ansinnen, verschiedene Facetten von Gerechtigkeit zu betrachten und Konzeptionen von Gerechtigkeit sowie die daraus erfolgenden Ableitungen zu illuminieren. Dabei wird die Fragestellung behandelt, ob das Individuum eine Rolle einnehmen kann, die sich darauf bezieht, durch das eigene Wirken als Person einen wesentlichen Beitrag für Gerechtigkeit leisten zu können. Durch die Wahl einer Perspektive, die Gerechtigkeit als Tugend, als die wertvollste Einflussgröße für die Implementierung von Gerechtigkeit, annimmt, wird der Vorstellungsrahmen von Tugend examiniert. Dazu werden implizite und explizite Aspekte, die das Verständnis von Tugend umgeben, dargestellt und ein aktualisiertes Verständnis von Tugend präsentiert. Gerechtigkeit wird als Desiderat eines individuellen Bildungsprozesses verstanden, bei dem Anerkennung eine formative Rolle einnimmt. Für das Feld von Coaching und Beratung wird ein Rahmen gespannt, der das Verständnis des Autors von Coaching und Beratung einordnet. Dies geschieht in kritischer Auseinandersetzung mit einem alternativen Beispiel aus der Coaching-Literatur, welches eine Form der Kompetenzförderung für Gerechtigkeit beschreibt, und mit der Anknüpfung an Gedankenlinien aus der systemischen Sichtweise. So wird einerseits die Rolle des Coaches und Beraters, als die eines Bildungsbegleitenden, fokussiert und andererseits die Wirkung einer Resonanzerfahrung auf das Individuum, die zu positiven Veränderungen hinsichtlich einer Gerechtigkeitsorientierung führen kann. Der Autor konstatiert, dass die Verbindung von Anerkennung mit einer personalen Tugendverfolgung ein wirksames theoretisches Konstrukt anbietet, das ein hohes Maß an Umsetzungspotenz für die menschliche Lebensführung eröffnet.
Guided walking tours are peculiar forms of urban walking that have an intentional and designed performative nature, which is accomplished through the engagement of a ‘guide’ and ‘participants’. The narrative structure of the walking tours connects different tourist sites, heritage sites, and sites of memorials together and employs diverse practices of narration, historical imagination, and walkability as an epistemic practice to produce knowledge. This predesigned narrative material, however, is not directly absorbed as knowledge but is used by participants for their own process of sense and meaning-making that occurs together with walking.
With the epistemic focus on walking, the thesis investigates the under-studied sense-making processes from the members' perspective. This is achieved by an ethnographic participant observation study of walking tours in the cities of Delhi and Berlin. The thesis addresses a wider objective through a methodological and reflexive practice of thick comparison within urban ethnography to develop and create a praxeological mode to understand how comparison within transnational research can be initiated and practiced beyond pre-defined quantified parameters. The idea is to keep practices at the center and, through thick comparison, produce comparability as opposed to following and adding to the already existing normative and hegemonic national-based epistemologies.
The thesis, with a post-colonial approach, attempts to show how the comparison between Delhi and Berlin can reveal urban nuances and practices that add to a thicker and more diverse understanding of urban theories and concepts while rendering them ever-evolving. In doing so, the project makes a case for thick comparison as a mode of research expanding it beyond a method and engages with the post-colonial discourse through empirically praxeologising the object of research. The central notion of my dissertation is that sense-making and knowledge production during walking are always indexical, temporal, performative, and situated in place and, therefore, can be best studied through the analytical concept of practicing place.
Unaccompanied young refugees (UYRs) encounter a multitude of stressors prior to, during and after their flight. Consequently, they demonstrate elevated levels of psychological distress and are vulnerable to the development of mental disorders, particularly post-traumatic stress disorder (PTSD). A treatment manual that has a broad evidence base and is also suitable for the treatment of young unaccompanied refugees, is trauma-focused cognitive behavioral therapy, which was established by Cohen, Mannarino and Deblinger (2006, 2017). Despite the existence of empirically validated treatment modalities for pediatric PTSD, UYRs frequently fail to receive sufficient psychotherapeutic care. Consequently, there is a necessity to identify factors that can lead to successful psychotherapeutic treatment on the patients, psychotherapists, and the healthcare system level.
The present dissertation sought to explore four main questions. The initial publication is a metaanalysis. We found substantial improvement in PTSD symptoms, depression, anxiety, and grief for young patients who participated in TF-CBT, with favorable post-treatment outcomes when compared to all control conditions. The second publication posits that a web-based training approach for TF-CBT results in substantial knowledge gain among its users and is an accessible training method of training for mental health care professionals. The third publication employed qualitative analysis to ascertain the factors that facilitate effective psychotherapy with UYRs, as perceived by psychotherapists. The identified factors encompass the presence of structured training programs, the availability of supportive caregivers and facilities, and the availability of skilled interpreters. At the patient level, the fourth publication identified age, length of stay in the host-country, and the severity of PTSD symptoms as significant correlates with the intention to utilize psychotherapeutic care. The severity of PTSD symptoms emerged as the sole significant predictor of the intention, and utilization was exclusively associated with the expressed intention.
This dissertation underscores the need for continuous implementation and dissemination of knowledge among all levels of the actors involved in the process of psychotherapeutic care of UYRs. At the practitioner level, the ongoing provision of structured training in evidence-based manuals is imperative, as their efficacy in practice has been well-documented. Addressing individual barriers faced by patients and their caregivers, including self-stigma and a lack of knowledge about mental illness, through targeted interventions and educational initiatives is also essential. Additionally, it is important to address structural barriers that impede the utilization of these services.
Hintergrund: Die Einführung von Pflegerobotik setzt ein umfassendes Verständnis für die Auswirkungen dieser Technologien auf die Pflegebeziehung und -praxis voraus. Der Fokus dieser Dissertation liegt auf dem Einsatz des robotischen Systems VEMOTION®, welches zur Frühmobilisation von Intensivpatient*innen genutzt werden kann. Die vorliegende Arbeit vereint die Disziplinen Pflegewissenschaft und Soziologie in einem interdisziplinären Ansatz und zielt darauf ab, soziale und organisatorische Dynamiken, die durch die Einführung von solchen Technologien entstehen, zu verstehen. Der Schwerpunkt des Forschungsprojekts liegt auf der Perspektive des mobilisierenden Fachpersonals
hinsichtlich der Auswirkungen auf Pflegepraxis und -beziehungen. Die Akteur-Netzwerk-Theorie (ANT) wird hierfür als eine Art Meta-Methode mit der Absicht, die komplexen Interaktionen zwischen den Akteuren begreifen zu können, eingesetzt.
Methode: Im Rahmen der kumulativ verfassten Dissertation wurden vier Artikel zu der genannten Thematik veröffentlicht. Diese bedienen sich einer interdisziplinären Methodik, die ein Scoping Review mit den ethnografischen Ansätzen Beobachtungen, Interviews und Gruppendiskussionen kombiniert. Die Methoden wurden agnostisch motiviert ausgewählt, das heißt, dass die Methodenauswahl und -durchführung jeweils darauf ausgerichtet war, ein umfassendes Verständnis der untersuchten Themen zu erlangen und die Forschungsfragen ausführlich zu beantworten. Das Scoping Review bietet einen
Überblick über die bestehende Literatur zum Einsatz von Frühmobilisationsrobotik. Die ethnografischen Methoden geben tiefere Einblicke in die Pflegepraxis und die Auswirkungen des Einsatzes des robotischen Systems auf das mobilisierende Fachpersonal.
Ergebnisse: Die Ergebnisse zeigen, dass das System VEMOTION® der Firma ReActive
Robotics GmbH vor allem der physischen Entlastung des Fachpersonals dient. Es werden aber auch neue Herausforderungen identifiziert, die eine sorgfältige Anpassung der Arbeitsabläufe und eine starke interprofessionelle Zusammenarbeit voraussetzen. Die Forschung unterstreicht Veränderungen in der Pflegebeziehung die durch die Einführung von Frühmobilisationsrobotik entstehen und hebt die Bedeutung der ANT hervor, um die Einführung und Nutzung von Technologien in der Pflegepraxis kritisch zu reflektieren.
Fazit: Die vorliegende Arbeit verdeutlicht die Bedeutung einer interdisziplinären Herangehensweise, die pflegewissenschaftliche und techniksoziologische Perspektiven vereint, um die komplexen sozialen Wechselwirkungen zwischen den Akteuren und organisatorischen Prozessen bei der Einführung von Frühmobilisationsrobotik zu verstehen. Zukünftige Forschungen sollten die Patient*innenperspektive stärker einbeziehen und langfristige Effekte auf die Pflegebeziehungen sowie die Qualität der Gesundheitsversorgung
untersuchen. Die Arbeit betont die Rolle der ANT als wertvolles Instrument zur
Analyse der Wechselwirkungen innerhalb der Pflegebeziehung und zur Förderung einer umfassenden Integration technologischer Innovationen in die Pflegepraxis.
Background: Self-regulated learning (SRL) has been identified as fundamental for learning in computer-based learning environments (CBLEs) and lifelong learning. One way to effectively support SRL in CBLEs was shown to be metacognitive prompting, a form of support which aims at activating strategies that are not used spontaneously. Young learners in lower secondary schools were found to possess basic forms of metacognitive SRL skills, however, in CBLEs, they were observed to experience difficulties in using them.
Aim and Method: To gain in-depth insights into the effects of metacognitive prompting in young learners, in the research in the present thesis, two empirical studies were conducted to explore young learners’ prompted and unprompted SRL activities and the relation to recall and transfer learning performance.
In the first study, prompted (n = 17) and unprompted (n = 16) 6th grade students were compared in their SRL activities by means of the think-aloud method during a 30-minutes learning session in the CBLE. Furthermore, process mining to analyze the sequential structure of the SRL activities and a recall knowledge test to assess learning performance were used.
In the second study, 6th grade students received metacognitive prompts (n = 38) or no prompts (n = 34) to investigate their metacognitive SRL activities using self-reports and their online learning behavior during a three weeks learning period using trace data. Also, their recall and transfer learning performance was measured.
Results: The results show that learning with metacognitive prompts, in the first study, lead to higher domain-general metacognitive SRL activities, and in the second study, to higher self-reported metacognitive SRL activities. The prompts did not yield significant differences in learning performance. However, in the second study, prior performance level was identified as a significant moderator influencing the interaction between the prompts and transfer learning performance.
Conclusion: In the present research, adaptive metacognitive prompting was shown to be a promising tool to support young learners in their metacognitive SRL activities in an authentic CBLE. Future research is needed to more precisely understand young learners’ needs for adaptive SRL support in CBLEs, focusing particularly on low achieving young learners. The present research highlights the developmental perspective of SRL in metacognitive prompting for young learners and draws conclusions in terms of prompt compliance and prompt design. Future directions within adaptivity in CBLEs and SRL support are discussed.
