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Studies on optimization problems with dynamically arriving information
No full textIn today’s fast-paced world, transportation planning, e-commerce, smart manufacturing, emergency services, and financial markets operate in real-time environments where dynamically arriving information must be integrated on-the-fly into decision-making. Research produced online algorithms ranging from myopic reoptimization (Reopt) to learning-based anticipation methods. However, given the complexity of real-world problems, optimal decision policies remain unknown, and effectiveness is often assessed through simulations against simple benchmarks, leaving improvement potential and robustness uncertain.
This dissertation proposes effective online policies using classical and innovative analytical and computational evaluation methods, establishing performance bounds and comparisons to optimal solutions. It designs algorithmic frameworks for two dynamic optimization problems: the Online Order Batching, Sequencing, and picker Routing Problem (OOBSRP) in warehousing and the Traveling Salesman Problem with a Truck and a Drone under Incomplete Information (TSP-DI), for disaster relief. Given the importance of automation in real-time environments, a strong emphasis is placed on robotic solutions.
For the OOBSRP with manual and robotic carts, we prove that Reopt is asymptotically optimal with probability one under broad stochastic conditions. From a worst-case perspective, no policy can improve Reopt by more than 50%, as it is shown to be asymptotically two-competitive. A computational study confirms that Reopt’s gaps to the complete-information optimum are small, e.g. averaging less than 5% for a cost-minimization objective. A pattern analysis of Complete-Information Optimal Solutions (CIOSs), generated with dynamic programming algorithms, identifies simple algorithmic enhancements – like eliminating waiting, intervention, or strategic relocation – that further reduce costs and delivery times. These findings suggest limited benefits of anticipatory (including AI-based) algorithms in OOBSRP.
Conversely, for TSP-DI, where road blockages reveal dynamically, Reopt performs poorly in the worst case, as we reveal its exponentially growing competitive ratio. We show that policies delaying deliveries for drone surveillance are significantly superior in competitive ratio. A proposed hybrid policy achieves best average and worst-case results in experiments. Using battery-limited drones introduces a challenging static subproblem within these policies, classified as Drone Routing Problems with Energy Replenishment (DRP-E). We develop a Very Large-Scale Neighborhood Search (VLNS) and an exact method for generic DRP-Es. VLNS searches an exponential-sized neighborhood of a promising solution entirely in polynomial runtime, making it ideal for real-time policies or intensification in metaheuristics.
This dissertation underscores the importance of analytical guarantees and comparisons to the optimum in online algorithm design, as policy effectiveness often diverges from intuition and varies significantly across problems
Strengthening Security Foundations in Next-G Wireless Telecommunication Systems
No full textDigital transformation fundamentally impacts our everyday lives and creates significant efficiency gains in the economy. At the same time, however, it is also increasing the complexity of wireless networks, particularly in the case of the sixth generation (6G) mobile communications standard. The use of different technologies in these networks poses an increasing challenge and increases the risk of security threats and vulnerabilities. Wireless communication networks are particularly vulnerable to cyber attacks as they are an integral part of critical infrastructures. Robust methods must, therefore, be developed to overcome these challenges.
Consequently, this dissertation is focused on the security fundamentals of next-generation (Next-G) wireless telecommunication systems. It addresses the security challenges resulting from emerging and innovative concepts within these systems. We use case studies for in-depth investigation and analysis, with a particular focus on the Open Radio Access Network (O-RAN) approach. The aim of this concept is to enable open and interoperable network architectures, in contrast to traditional RAN systems, which are often proprietary and manufacturer-specific. In this respect, it is essential to address fundamental questions, like the efficient assessment of the threat landscape, the impact of potential attacks, and the mechanisms that can be used to ensure security at the system level.
Initially, an empirical approach is developed to analyze threats within telecommunications systems, such as the O-RAN. The procedure we have developed enables automated, programmatically executable vulnerability management. This methodology is further enhanced by integrating Natural Language Processing (NLP), leading to the creation of a fully automated, iteratively executable framework for security analysis within O-RANs. The framework allows for the direct incorporation of our methods into the deployment process, facilitating rapid and efficient comparison of all components against the latest security vulnerabilities. The current approach of fully deploying all components in virtualized environments, such as cloud infrastructures, introduces new and unprecedented security challenges. In response, we investigate current deployment strategies within the O-RAN infrastructure and establish best practices to mitigate these security issues.
In the course of the dissertation, we identify security vulnerabilities in wireless telecommunication systems by executing different attack scenarios. We present a detailed procedure for carrying out the attacks as well as effective methodologies for detecting or avoiding the vulnerabilities we have identified. In the first study, we analyze the security of a key component, the Near-Real-Time RAN Intelligent Controller (Near-RT RIC), within O-RAN. We show how a subscription Denial of Service (DoS) attack can render current implementations of this component unusable. In the second analysis, we investigate the robustness of new standards in wireless networks against jamming attacks using the open-source connectivity standard Matter.
The final section of this dissertation explores innovative security research approaches for enhancing the system security of future communication systems. Initially, a novel concept is introduced that facilitates the comprehensive and efficient management and assurance of security within O-RAN systems through the use of Security Platforms (SPs). Furthermore, two developed methodologies for this approach are presented: firstly, a method for programmatically analyzing eXtended Applications (xApps) to identify vulnerabilities, and secondly, an approach for conducting comparative assessments of these vulnerabilities. Additionally, a strategy is proposed to ensure that only secure xApps, such as those that have been pre-tested, are deployed for use in Near-RT RIC.
Overall, this dissertation makes an important contribution to the research of security principles for next-generation wireless telecommunication systems. With the help of our approaches for a better and more concrete assessment of threats in such networks, we directly contribute to a clearer and better manageable picture of the vulnerability landscape. Our two publications on vulnerability research also provide valuable insights for securing future problems in the respective areas. In summary, with our approaches to system security, with which security principles can be implemented and integrated into modern system approaches such as O-RAN, we contribute to ensuring a secure transition to 6G
The 2008 Beijing Olympic Games as a City and Nation Branding Tool: An Interdisciplinary Analysis of the Image of International Opinion Leaders
No full textThis dissertation examines the 2008 Beijing Olympic Games as a tool of city and nation branding, analyzing their role within China's broader soft power strategy and their impact on international perceptions of Beijing and China. Drawing from urban geography, political geography, international relations, and marketing theory, the study explores how mega-events contribute to the construction of national identity and global image.
Using a mixed-methods approach, the research combines qualitative interviews with 16 international diplomats in Beijing and an online survey of 40 foreign journalists who lived and worked in China during the Olympiad. The analysis focuses on two dimensions of image: the city of Beijing and the nation of China.
The findings indicate that the 2008 Summer Olympic Games did not fundamentally alter China's international image. While the event successfully projected an image of modernization, efficiency, and confidence, pre-existing concerns about political control and human rights persisted. For Beijing, the Olympics enhanced its visibility as a global city but also highlighted tensions between its traditional identity and its modern aspirations. The media's framing played a decisive role in shaping these perceptions.
Overall, the study concludes that the Beijing Olympics functioned as a significant yet limited instrument of soft power. They reinforced China's global presence and urban development goals but fell short of transforming its international reputation. The research contributes to understanding how mega-events operate as strategic tools of geopolitical communication and branding in the context of globalization
The Asymptotic Behavior of Birkhoff- and Lacunary Sums
No full textThis doctoral thesis consists of three independently published research articles on the asymptoic behaviour of Lacunary- and Birkhoff sums. The former are sums formed by periodic functions and exponentially growing sequences of natural numbers. The corresponding summands often exhibit behavior typical of independent and identically distributed random variables. The methods used are of an analytical and probabilistic nature. The Birkhoff sums considered in this work are generated by the Kronecker sequence and by discontinuous functions. The methods employed are from the field of metric number theory, specifically classical results from continued fraction theory are utilized
La littérature migratoire au féminin à l’interface entre l’«Orient» et l’«Occident»
No full textCe volume collectif se questionne comment les contacts et les conflits entre l’« Orient » et l’« Occident » se reflètent dans les textes narratifs des femmes écrivains. Les contributrices examinent dans quelle mesure le fait d’être une femme donne lieu à différentes perceptions de soi et de l’autre, et dans quelle mesure les formes internes et externes d’orientalisme jouent un rôle à cet égard. Elles explorent dans quelle mesure les images de soi et de l’autre, les images orientales et occidentales des femmes et des rôles stéréotypés du genre entrent en contact ou en conflit dans ces textes, et quelles conséquences cela a sur l’identité des femmes dans l’entre-deux entre la culture d’origine et la culture d’accueil. Dans un post-orientalisme, si les problématiques culturelles, linguistiques, religieuses et idéologiques sont au centre de nos préoccupations, les autrices accordent également une attention particulière à la manière dont les femmes écrivains étudiées, elles-mêmes voyageuses et migrantes, transcendent la critique du colonialisme traditionnel, récréent et font comprendre un Orient dont l’image et la signification se renouvelle et se rafraîchit constamment
Berufswahlmotivation Lehramt: Ein weltweit ähnliches Phänomen? Eine international vergleichende Studie
No full textIm Angesicht eines weltweiten Lehrkräftemangels (OECD, 2018b; UNESCO, 2023) wird in der empirischen Forschung der Berufswahlmotivation Lehramtsstudierender ein großer Stellenwert beigemessen (Butler, 2017). Es handelt sich beim Lehrkräftemangel aktuell um ein weltweites Phänomen, das weder nur Deutschland oder nur westliche Länder betrifft (UNESCO, 2023).
In den letzten zwanzig Jahren haben sich einige theoretische Modelle zur Berufswahlmotivation spezifisch für das Lehramt etabliert, dazu zählen das FIT-Choice-Projekt (Richardson und Watt, 2007), Femola (Retelsdorf und Möller, 2012) und STeaM (Weiß und Kiel, 2013).
In dieser Arbeit wird das FIT-Choice-Modell (Richardson und Watt, 2007) verwendet, um die Berufswahlmotive eines internationalen Samples Lehramtsstudierender zu zwei Zeitpunkten zu betrachten. Das Modell stellt mit seinen Bezugstheorien (Eccles und Wigfield, 2002; Ryan und Deci, 2000) sowohl die theoretische als auch die empirische Fundierung dieser Arbeit dar. Neben diesem werden Professionalisierungstheorien (vor allem der kompetenztheoretische Ansatz nach Baumert und Kunter, 2011a) und die Habitustheorie (Bourdieu, 1982) zur Interpretation der Ergebnisse herangezogen. Strukturmerkmale der einzelnen Länder ermöglichen ein kultursensitives Vorgehen.
Zu zwei Zeitpunkten (Studienbeginn und Studienende) wurden an 5 Universitäten in Deutschland, Österreich, der Schweiz, Südafrika und Israel mit einem Skalenfragebogen insgesamt n= 1157 Studierende (Studienbeginn n= 835, Studienende n= 322) zu ihren Berufswahlmotiven und Einstellungen befragt. Diese wurden in Zusammenhang gebracht mit der Länderzugehörigkeit, ihrer sozialen Herkunft sowie ihren pädagogischen Vorerfahrungen. Zudem wurden im deutschen Sample zum Ende des Studiums offene Fragen ergänzt, um Begründungslinien für die Berufswahl in Erfahrung zu bringen.
Mit dem spezifischen Sample wurde das Desiderat der Ländererweiterung um nicht- westliche Länder (Watt, Richardson und Smith, 2017) bearbeitet, ebenso mit den offenen Fragen das Desiderat nach der Verbindung von quantitativen und qualitativen Ansätzen (Watt und Richardson, 2015).
Mit der Arbeit können die Hauptergebnisse der Forschung mit den FIT-Choice-Skalen bestätigt werden. Die Betrachtung von Subgruppen innerhalb der Länder gab einen Einblick zu Berufswahlmotiven marginalisierter Gruppen und den Grenzen von global anzuwen-denden (westlichen) Erhebungsinstrumenten. Die Arbeit leistet außerdem einen Beitrag zum Diskurs um den Einfluss von pädagogischen Vorerfahrungen in der Berufswahlmotivationsforschung, zudem werden Ergänzungen für den FIT-Choice-Fragebogen für die „Gen Z“ vorgeschlagen
Tight Hamilton cycles with high discrepancy
No full textIn this paper, we study discrepancy questions for spanning subgraphs of k-uniform hypergraphs. Our main result is that, for any integers k ≥ 3 and r ≥ 2, any r-colouring of the edges of a k-uniform n-vertex hypergraph G with minimum (k−1)-degree δ(G) ≥ (1/2+o(1))n contains a tight Hamilton cycle with high discrepancy, that is, with at least n/r +� (n) edges of one colour. The minimum degree condition is asymptotically best possible and our theorem also implies a corresponding result for perfect matchings.
Our tools combine various structural techniques such as Turán-type problems and hypergraph shadows with probabilistic techniques such as random walks and the nibble method. We also propose several intriguing problems for future research
Abschlussbericht zu "Erzählung, Erwartung, Erfahrung. Behinderung im zeitgenössischen europäischen Theater und Film"
No full textDas Projekt EEE (429281822) setzt sich zum Ziel, die Wirkung von Theateraufführungen und Filmen mit Darsteller:innen mit „geistiger“ Behinderung auf die Vorstellungsbilder von „geistiger“ Behinderung systematisch darzustellen.
Das Fortsetzungsprojekt EEEM hat zum Ziel, die Ergebnisse des Forschungsprojektes EEE niedrigschwellig einer breiten Öffentlichkeit zu vermitteln.Closing report on "Narration, expectation, experience. Disability in contemporary European theatre and film"
The aim of the project EEE (429281822) is to systematically present the effect of theatre performances and films with actors with learning difficulties on perceptions of intellectual disabilities.
The aim of the EEEM follow-up project was to communicate the results of the research project to a broad public in a low-threshold way
Social Networking Sites as Intermediaries of Authoritarian State Propaganda: How Facebook and VK Disseminated Predominantly Kremlin-Friendly Political Content Before and During Russia’s Full-Scale Invasion of Ukraine
No full textPrevious research on Russia’s use of social networking sites to influence foreign audiences has primarily focused on US-based platforms, such as Twitter and Facebook, the activities of Russia’s “troll farms”, as well as Russia’s foreign broadcasters, RT and Sputnik, and their audiences. By contrast, little research has examined the global reach of Russia’s state-aligned domestic news content, specifically on US- and Russia-based social networking sites that significantly differ in the level of the Kremlin’s control over information flows, and how the activities of novel Russian disinformation production organizations support this reach. In my dissertation, I addressed these gaps in the extant research literature in the fields of political communication, social media, and Russia studies in four distinct research papers focusing on the reach of and engagement with Russian-speaking political content, including Russia’s domestic news content, and the activities of ANO Dialog, Russia’s novel disinformation production organization with close links to the Russian government, on US-based Facebook and Russia-based VK. To do so, I used innovative qualitative, quantitative, and computational research methods to create knowledge on Russia’s informational influence on the two platforms before and after the start of Russia’s full-scale invasion of Ukraine in February 2022. The findings highlight that, despite differing levels of Kremlin control, both of the social networking sites studied functioned as conduits for the dissemination of Russian-speaking, predominantly Kremlin-friendly political content, including state-aligned domestic news. This content reached audiences both within Russia and abroad in the lead-up to and during the full-scale war in Ukraine. While VK primarily served Russia’s users, Facebook disseminated Russia’s state-aligned news mostly to audiences outside Russia, particularly in former Soviet countries, in the lead-up to the invasion. During the war, Facebook continued to host critical perspectives on Russia’s war crimes, in contrast to VK, where such content was blocked. However, Facebook was banned in Russia in March 2022, limiting domestic access to dissenting views. With the war ongoing as of May 2025 and organizations such as ANO Dialog intensifying their efforts to influence both domestic and foreign audiences on platforms such as VK and Facebook, it is likely that Russia will further strengthen its information control
On optimal error rates for strong approximation of stochastic differential equations with irregular drift coefficients
No full textIn this dissertation we study strong approximation of stochastic differential equations (SDEs) with irregular drift coefficients at the final time point or globally in time by methods that use only finitely many evaluations of the driving Brownian motion. We show the optimality of well-known methods, such as the Euler-Maruyama scheme or a transformed Milstein scheme, for classes of piecewise Lipschitz continuous, Hölder continuous and Sobolev regular drift coefficients. To do this, we derive the optimal error rates for the different classes of irregular drift coefficients. Furthermore, we show that the solution of an SDE with piecewise Hölder continuous drift coefficient has a regular local density, which is used in the proofs of the lower bounds