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Towards Resilient Protection of Interconnected ICT and Power Systems
No full textDue to the increasing number of distributed renewable energy sources, the distribution grid faces new operational challenges. Information and Communication Technology (ICT) systems can resolve these challenges through grid services that use automation, monitoring, and real-time decision-making, helping maintain an acceptable operational state of the distribution grid. However, the reliance of the power system on the ICT system and vice versa in the so-called smart grid creates interdependencies between the systems, which present new pathways for failure propagation. Therefore, these interdependencies require special attention to ensure stable system operation in the face of these challenges. However, these interdependencies have not been studied extensively in the literature. This thesis investigates approaches to model, quantify and improve the performance and resilience of the smart grid infrastructure.
The interdependencies are formalised as interconnectors, entities that exist in all the connected systems. These interconnectors consist of components from both systems, where the components are modelled as state variables. These state variables determine the interconnector state and the service delivered. Failures represented by a change in state variables may impact the state. These state variables are deployed in a discrete event simulation framework to determine the system performance over time. The simulation result is represented on a two-dimensional state-space diagram depicting the operational state and service delivered. This allows for the resilience analysis of a system under various scenarios. The interdependencies are further investigated by exploring the role of ICT-based grid services in power grids, whose state is defined based on ICT properties, such as latency. These properties are formalised using property graphs. The ICT properties obtained from these graphs are used to parameterise a finite state automaton model of a grid service states, which are then used to determine the state of the entire smart grid. Case studies of state estimation and adaptive protection highlight the application of this approach. The use of ICT in state estimation allows the distinction of a global and perceived view of the power grid, which influences decision-making in the face of challenges.
This thesis further investigates the protection system in detail. The overcurrent protection system is adversely impacted by distributed generation, resulting in undesired phenomena such as protection blinding. This thesis characterises this phenomenon by proposing two indices that capture the protection trip time under the influence of distributed generation. These indices consider the electrical distance between faults, protection and distributed generation. These indices and simulation results identify the worst-impacted locations in the power grid in terms of protection trip time. They also identify fault locations under given assumptions that do not cause protection blinding. ICT can resolve protection blinding by adapting the sensitivity of protection relays. However, since faults must be cleared in a short timeframe, communication delays may adversely impact the fault-clearing time. A discrete event simulation model is proposed to study protection performance in distribution grids. Investigation of time distribution assumptions reveals that the lognormal distribution accurately captures the circuit breaker trip time. The impact of the distributed generation and communication delay on the protection system is determined by measuring fault-clearing times using discrete event simulation. Results show that for the system studied, protection blinding is critical for low impedance faults in grids with high fault levels, while high impedance faults are critical in grids with low fault levels. Moreover, sympathetic tripping is seen at increased distribution grid fault levels and fault impedance. Furthermore, while communication systems reduce fault clearing times, increased delays harm protection systems. Finally, communication system components like sensors can fail, preventing fault detection. This thesis proposes a genetic algorithm-based approach to optimally place redundant sensors, minimising protection blinding under communication uncertainty within a redundancy budget. Results demonstrate the algorithm's effectiveness in optimising redundant sensor locations, reducing system costs, and improving fault tolerance. For the system and scenarios investigated, an average of 60% redundant sensors are relocated, reducing the average protection trip time by 36.65% compared to a baseline approach that does not consider communication uncertainty. This encourages incorporating communication component failure considerations in power system planning
Three Essays on the Interpretability of Random Forests: Methods, Insights, and Innovations
No full textThis thesis examines the interpretability of random forests in three essays, focusing on the discussion of established methods, the presentation of new insights and the provision of innovations. The research aims to bridge the gap between traditional statistical methods and random forests, a data-driven machine learning algorithm, by investigating the ability of random forests to adequately model theoretical concepts compared to parametric methods and developing a new approach for statistical hypothesis testing. The results have implications for various areas of research in which interpretability is crucial for applications. The next three paragraphs summarize the studies presented in this thesis.
The ability of random forests to automatically model interactions without the need for pre-specification is mentioned prominently in many articles and book chapters. Promising empirical results from early work on random forests have substantiated this property, which has led to an increasing popularity of using random forests in the presence of interactions as an alternative to traditional parametric methods. This study reviews the literature of the last 20 years on random forests and interactions. We explore the discussion from its origin in the decision tree literature to early applications of random forests and current research. We identify key research areas and illustrate random forest applications to highlight similarities and differences between disciplines. We also provide a critical examination of the arguments in favor of random forests being able to model interactions automatically. Since the term ``interaction'' is associated with different theoretical concepts, we explain and illustrate the definition of interaction for each research area.
The variable importance of random forests is an easy-to-understand metric that intends to make the predictions of random forests more transparent by assessing the contribution of each covariate to the prediction of the response. However, due to its data-driven nature, the variable importance of random forests may over- or underestimate the importance of a covariate, so that the role of the covariate in the underlying data generating process is not correctly reflected. We present an example of underestimation of importance in the case of interacting covariates. We define an interaction in terms of effect modification, which assumes that the effect of one covariate on the response is modified by values of another covariate. We show that the variable importance of random forests is influenced by the interaction form and the measurement scale of the interacting covariates, so that in some cases the importance of one or even both interacting covariates is underestimated. We illustrate how the split decisions of random forests affect the variable importance values of the interacting covariates.
Variable importance estimates the contribution of a covariate to the performance of a predictive algorithm. Defined as the increase in loss after the random permutation of a covariate, permutation variable importance makes it possible to rank the covariates by importance, but in the absence of a threshold, the distinction between important and unimportant covariates is inherently arbitrary. We show that recent approaches of non-parametric permutation tests for variable importance exceed their nominal type I error level for mutually dependent covariates.
As an alternative we propose a combined variable importance estimate on a sequence of permutations and employ a computationally more efficient bootstrap to derive the respective null distribution and -values. The proposed test can be applied to any predictive algorithm and is remarkably fast. We investigate the control of type I error level and the power of the proposed variable importance test in simulation studies. Even for mutually dependent covariates, our test is conservative and provides power comparable to recent advances in non-parametric permutation tests of variable importance. This study was conducted in collaboration with Matthias Wild
Interpretationen & Konflikte in der Populären Musik - Heino, Gainsbourg, Hendrix und die Seleção : eine interdisziplinäre Untersuchung mit Blick auf die Namenkunde
No full textKennzahlenkatalog Green IT an bayerischen Hochschulen
No full text"Der vorliegende, mit den bayerischen Hochschulen und Universitäten abgestimmte Kennzahlenkatalog für Green IT, dient als Grundlage, um einheitlich Kennzahlen für die bayerischen Rechenzentren zu erfassen und damit einen nachhaltigen IT-Betrieb der Hochschulen zu unterstützen. Durch die Implementierung und Erfassung dieser Kennzahlen werden, die ökologischen Auswirkungen der IT messbargemacht. Dies ermöglicht die Wirksamkeit von Maßnahmen quantitativ zu überprüfen und den IT-Betrieb in eine ökologisch nachhaltige Richtung zu steuern. Im Rahmen des Energieeffizienzgesetzes wird das Einsparen von Energie und Treibhausgasen auch für Hochschulen zunehmend verbindlicher. Der Katalog beschreibt die im Energieeffizienzgesetz geforderten Kennzahlen, enthält eine strukturierte Vorgehensweise zur Implementierung und unterstützt dabei die gesetzlichen Anforderungen einzuhalten." (S. III
Analysis of the practices, structures and processes of translocal mobility systems in Burkina Faso
No full textThis report presents the results of the project “Migration and Translocality in West Africa (MiTra|WA)” with reference to translocal practices in Burkina Faso. Funded by the German Federal Ministry of Education and Research, the study ran from 2022 to 2024. The general objective of the project is to analyse the multiple links between the rural areas of departure and urban reception of migrants as well as the impacts on the development of these localities.
The study employs a mixed-methods approach, combining quantitative and qualitative research methods. The quantitative component consisted of two types of surveys. First, a household survey in the migrants' area of origin (AoO) to identify the migrants’ belonging to these households. In the second phase, a telephone survey was conducted among migrants in the destination areas (AoD). Then, the focus was on socio-economic data as well as translocal interactions and network relationships. The qualitative component consisted of in-depth interviews with key actors in the different areas of departure and destination of migrants. These include migrants, local administrative officials, leaders of NGOs, associations, community and religious leaders.
The results show that migration is a phenomenon experienced by many households in rural areas. There are as many internal migrants as there are international migrants. Of the 537 households surveyed, 405 (75.4%) have at least one migrant. The age structure of migrants shows a predominantly young structure of migrants (82% who are under 40 years old). According to gender, migration is strongly male-dominated (82%). Men are more inclined to international migration (56%). Female migration is precocious. A large proportion of migrants (41%) have no level of education and are mostly single (50%). Translocality, conceptualized in this study as the multifaceted links between the places of departure, transit and residence of migrants, is apprehended through telephone contacts between migrants and their place of origin, in addition to the different forms of mobility: mobility of people, financial resources (remittances), material resources (transfers in kind), intangible resources (ideas, practices, etc.). Exchanges are often bidirectional. Telephone contacts represent 86% of migrants. Migrants visit the household in the area of origin more frequently (41.8%) than they receive household members at their destination (33.9%). More than 66.6% of migrants transfer remittances to their households in rural areas. With regard to the 4-level translocality intensity indicator (Wehner 2022), it can be concluded that over 50% of migrants are located at the two highest levels. Hence, translocality is an important feature of rural-urban migration in Burkina Faso
Transparency and Control about Privacy in Data-Driven Online Services: An Investigation of Design Choices and Users' Data Disclosure Decision-Making
No full textAs modern online services are increasingly data-driven, users’ data disclosure is becoming a decisive factor for the success of companies' business models. Extensive disclosure of personal data raises concerns for users’ privacy that managers of online services and regulators need to address. Implementing transparency and control about an online service’s data practices has become the dominant approach to address these concerns. However, the effects of transparency and control on users’ data disclosure behavior have been found to be ambivalent. While some studies in the field of privacy research confirm that implementing transparency and control features can be an effective means to raise users’ willingness to disclose data, other studies have found only minuscule, and sometimes even opposing effects of transparency and control on users’ disclosure behavior. Such heterogeneous effects not only hinder estimating the consequences of regulatory and managerial efforts aimed at creating transparency and control but also impede generating clear guidelines on how to provide transparency and control in the most effective manner. A closer examination of individuals’ underlying decision-making mechanisms in response to provisions of transparency and control in disclosure decision scenarios may help to improve our understanding of the causes of diverging disclosure behavior. A better understanding of these underlying decisionmaking mechanisms will further help to assess specific designs of transparency and control features and their impact on the business models of online services as well as users’ privacy. Therefore, this thesis explores users’ decision-making mechanisms and behavioral reactions to the provision of transparency and control in data disclosure situations. The thesis consists of four essays that employ different research methods, including systematic literature reviews and quantitative studies. The findings of the essays contribute to a better understanding of the effects of transparency and control on user decision-making in the privacy domain by (1) offering conceptualizations that provide a lens for studying users’ decision-making processes and their disclosure behavior in reaction to transparency and control features (2) examining how different implementations of transparency and control features affect users’ decision-making processes and effort in decision-making which causes differences in users’ disclosure behavior, and (3) by investigating the effects of transparently communicated content and relevant pieces of information in so far underexplored data disclosure scenarios between users and a data-sharing firm network
The relevance of the maximal lactate accumulation rate in diagnostics and training: The example of cross-country skiing and cycling
No full textDie Arbeit beleuchtet die Bedeutung der maximalen Laktatbildungsrate (V̇Lamax) für die Leistungsdiagnostik und die Trainingspraxis.
Für die Sportart Skilanglauf wurde ein neuer Sprinttest zur Bestimmung der V̇Lamax am Skiergometer entwickelt, der sich als reliabel und valide erwiesen hat. Dabei wurden verschiedene Ansätze zur Bestimmung der alaktaziden Zeit genauer betrachtet. Außerdem wurde der Sprinttest am Skiergometer mit dem etablierten Sprinttest am Radergometer verglichen, wobei festgestellt werden konnte, dass die V̇Lamax sportart- und extremitätsspezifisch getestet werden sollte.
Zudem wurde die Auswirkung von Intervalltraining unterschiedlicher Intensität im Radsport untersucht. Hochintensives Ausdauertraining scheint dabei die V̇Lamax zu steigern, wohingegen submaximales Sweetspot-Training die V̇Lamax zu senken scheint
Slice sampling on Riemannian manifolds
No full textThis thesis is concerned with hybrid slice samplers for approximate sampling of distributions on Riemannian manifolds. First for distributions on the Euclidean unit sphere, and then for distributions on general Riemannian manifolds we introduce a geodesic-based hybrid slice sampler, called geodesic slice sampler. Under mild regularity assumptions, we establish reversibility with respect to the target distribution for this sampler and positive semi-definiteness of the corresponding operator. Moreover, on compact Riemannian manifolds we show uniform ergodicity with explicit constants for the geodesic slice sampler if the target distribution has a bounded density with respect to the Riemannian measure.
As an important building block of this sampler, we provide an explicit expression for the shrinkage procedure proposed in (Neal, 2003) in terms of a Markov kernel. We establish that this kernel is reversible with respect to the uniform distribution on the target set and that its corresponding operator is positive semi-definite. Beyond the geodesic slice sampler, we apply these results also to elliptical slice sampling (Murray, Adams, MacKay, 2010) to obtain a proof for its reversibility with respect to the target distribution and positive semi-definiteness of the corresponding operator
Asset Tokenization and Authentication in the Industrial Metaverse
No full textThe Industrial Revolution is a crucial development step in human history that started three centuries ago and is still ongoing. It continually influences and shapes the globalized world. Today, industries account for 20% of carbon dioxide emissions worldwide and require more than a third of global energy consumption.
Current problems, such as climate change, increasing waste, and pollution, require simultaneous optimization across all industrial domains, infrastructure, and systems as they depend on each other. The global industry faces the immense challenges of providing for a surging world population expected to peak in the mid-2080s with 10.4 billion people, as reported by the United Nations. Hence, industries are expected to become less resource-intensive, sustainable, and more resilient to disrupted supply chains while producing for a growing population for the next decades.
The Fourth Industrial Revolution, or Industry 4.0 (I4.0), started around 2010 and is still an ongoing transformation of industrial processes towards digitalization, creating smart factories referring to the digital data integration of the entire manufacturing cycle. I4.0 is incredibly information-intensive and requires immense data to simulate and predict essential operations based on a digital shadow of the factory, a so-called digital twin.
The Metaverse is considered a digitalization megatrend merging digital and physical worlds, creating immersive experiences and new opportunities for interaction and innovation across various sectors and industries. The vision of the Metaverse promotes interconnected and interoperable real-time 3D virtual worlds that can be frictionlessly traversed while sustaining ownership of one's assets under a self-sovereign identity in a decentralized environment without platform lock-ins to a specific ecosystem. Therefore, the Metaverse creates an immersive parallel reality with collective virtually shared spaces for entertainment, social interactions, education, and a new working environment.
The Industrial Metaverse synthesizes Metaverse concepts with current industrial automation, such as I4.0, to deepen the digital-physical convergence by interconnecting internal and external systems to enable decision-making and predictions based on significantly broader knowledge. An Industrial Metaverse factory is entirely mirrored to integrate digital twins of all types of equipment, assets, and other entities that can communicate vertically and horizontally, as well as the knowledge about relevant external systems and industrial core sectors. Through the comprehensive data integration of the Industrial Metaverse, AI-driven applications can predict future events, reducing system and hardware failures. Furthermore, the interconnected virtual environments create a meta-ecosystem for global collaboration, providing spaces for solving complex problems such as engineering and product design tasks, simulation of product twins, and reduced development time and costs. The connected industrial ecosystems create a token-based digital economy for exchanging data, assets, and services cross-metaverse connecting isolated data silos. Sharing digital twin resources and services with other systems enables new innovative applications and growing ecosystems.
The theoretical part of this thesis defines the essential characteristics and key technologies of the Industrial Metaverse to derive a reference architecture for a decentralized system of systems, outlining the fundamental Industrial Metaverse building blocks. Interoperable data exchange, access management, and system communication are critical challenges. Especially interoperability of assets such as 3D files that come in different formats and identities must be ensured to move between virtual environments. The unique fusion of technologies leverages interconnected digital twins in the context of immersion, interaction, and collaboration for secure, autonomous-governed, decentralized industrial applications. Hence, the Industrial Metaverse requires the possibility of exchanging assets, products, and services across all systems in a secure manner. Distributed ledger technology enables tamper-proof transactions of assets and value in a decentralized token economy.
Therefore, we investigate the feasibility of current tokenization methods for industrial assets, in particular, Printed Circuit Board (PCB) designs and 3D models. We contribute methods to create unique fingerprints of PCB designs to enable their exchange in the token economy. We investigate how to bind files in different formats and quality representations to the same token. A robust multi-file binding based on the copper layers of a PCB design was achieved by calculating an adaptive perceptual hash of all files. The adaptive perceptual hash was evaluated against numerous tamperings of the routing layout of a PCB, showing decent resistance to layout changes. The resulting adaptive perceptual hash can be used as an additional identification attribute in a tokenized asset.
Furthermore, assets must be authenticatable and verifiable by marketplaces, manufacturers, and other participants to create trust in a decentralized environment. While assets can be tampered with to manipulate, for example, cryptographic hashes that link the file to the token, perceptual hashes can compute a perceived or functional similarity of two objects instead of the plain file integrity. Without the possibility of verifying and protecting intellectual property, mass adoption of the Metaverse and Industrial Metaverse is unlikely. Therefore, we contribute to detecting tampering attacks on 3D models by introducing a 3D perceptual hash that is robust to a set of mesh manipulations, enabling the trusted exchange and authentication of 3D data in the Metaverse
An exploration of professional self concepts in science communication
No full textThe dissertation explores emerging professional self concepts in the field of science communication. It integrates theories and concepts from a diverse range of disciplines from the sociology of professions to science and technology studies. It also considers organisational contexts and country specifics as major influencing factors and includes these in comparative frameworks. By triangulating data from different sources the dissertation offers broad insights not only into science communication but professionalisation more widely