@phdthesis{Julka2025, author = {Julka, Sahib}, title = {Towards Data Efficiency and Controllable Representations for Deep Learning in Resource-Constrained Domains}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-16030}, school = {Universit{\"a}t Passau}, pages = {20 ungez{\"a}hlte Seiten, 131 Seiten, 17 ungez{\"a}hlte Seiten}, year = {2025}, abstract = {The deployment of artificial intelligence (AI) in specialised domains such as planetary science and healthcare, as well as in low-resource NLP settings, faces two fundamental challenges: label scarcity and data scarcity. Label scarcity stems from the high cost of expert annotation, the scarcity of domain experts, and the infeasibility of crowdsourcing, particularly in complex tasks requiring specialised knowledge. In parallel, data scarcity stems from the inherent difficulty of acquiring sufficient raw data, whether due to limited observational opportunities, environmental and technical barriers, or stringent privacy constraints. Together, these limitations impede the broader adoption of AI in these fields. Many existing approaches to label efficiency, such as active learning, rely on problem-specific heuristics and often, as a design choice, employ naive uncertainty estimations—typically at the instance level. However, such methods can lead to redundant or suboptimal sample selection by ignoring structural data properties and failing to account for representational diversity. In practice, they often perform no better than random sampling. For data synthesis, generative models face their own set of challenges. Despite their promise for synthetic data generation, these models frequently lack mechanisms to disentangle generative factors at the representation level, limiting their controllability. Additionally, standardised evaluation metrics to assess the quality of disentanglement remain underdeveloped, limiting their practical utility. These limitations highlight the need for advancements in data-efficient machine learning and controllable generative modelling, focusing on domain-specific validity and rigorous evaluation. This thesis contributes to addressing these challenges by proposing tailored solutions in two key directions. First, for data-efficient learning, a deep active learning (DAL) framework is introduced to enhance label efficiency by prioritising the most informative samples for annotation. Unlike traditional per-sample approaches, this framework aggregates uncertainty across larger data segments—such as orbital intervals in planetary science—allowing it to capture contextual variations. This method reduces labelled data requirements by up to 90\% in the case of boundary crossing detection at Mercury's magnetosphere. To further improve sampling diversity, a GAN-based concept drift detection method is integrated into the DAL framework, leveraging uncertainty and diversity together to offer a sampling method that outperforms random sampling. Additionally, foundation models such as the Segment Anything Model (SAM) are employed for zero-shot annotation to generate high-quality pseudo-labels, which are subsequently used to train a domain-specific model via knowledge distillation. This approach significantly enhances data efficiency, reducing the need for annotated samples several times over in the tested scenario of image segmentation for geological mapping. Furthermore, large language models (LLMs) are explored as active annotators for linguistic tasks in low-resource languages, achieving near-baseline performance while reducing annotation costs by up to 40x. Second, the thesis investigates methods to induce controllability in generative models, enabling the production of high-fidelity, controllable synthetic data. Conditional generative adversarial networks (CGANs) and disentangled representation learning techniques (DRL) are explored, particularly in the context of pedestrian trajectory prediction in the mobility domain, where controlled synthesis of diverse motion patterns is critical. Additionally, the work examines existing metrics for evaluating disentanglement and identifies critical limitations in them. A novel metric, the Exclusivity Disentanglement Index (EDI), is proposed as an improved standardised measure. Based on the principle of exclusivity in factor-code relationships, this metric offers advantages over existing alternatives in terms of efficiency and robustness. By advancing data-efficient learning and controllable generation strategies, this thesis aims to bridge the gap between AI's vast potential and its practical adoption in resource-constrained environments. These contributions pave the way for transformative applications in planetary science, healthcare, and beyond, where label and data scarcity have long been barriers to progress.}, language = {en} } @phdthesis{Wilhelm2025, author = {Wilhelm, Sebastian}, title = {Emergency Detection in Private Households Utilizing Existing Data Sources for Human Activity Event Recognition}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-15992}, school = {Universit{\"a}t Passau}, pages = {xvii, 156 Seiten}, year = {2025}, abstract = {In an aging society, the need for efficient emergency detection systems in smart homes is becoming increasingly important. Over 30\% of those aged 65 and older experience at least one fall per year, often resulting in the inability to rise without assistance, leading to 'long lies' lasting hours or even days. Systems for detecting such emergency events usually rely on wearable sensors or specific installations of ambient sensors, which can be intrusive and complex, hindering acceptance. This thesis proposes a novel approach that utilizes existing digital data sources within the residential infrastructure to detect human activities and identify potential emergencies. A survey identifies 44 potential data sources in private households for recognizing human activity. However, extracting activity information often requires complex preprocessing. In this thesis, methodologies are developed for three of these data sources to highlight practical applications: Smart Power Meters, Smart Water Meters, and Home Weather Stations. It is shown that detecting human activities using these sources is feasible in a practical environment, although accuracy and reliability vary. Notably, Smart Water Meters demonstrate high reliability, with a precision of 0.86 and a recall of 1.00, making them particularly suitable for emergency detection. Existing emergency detection methods are not designed to handle uncertain activity data. This thesis introduces a novel approach based on probabilistic activity information, employing an Inactivity Score that provides a probabilistic weighting of inactivity periods based on the reliability of sensor measurements. By analyzing historical Inactivity Scores, anomalies that potentially represent an emergency can be identified. Evaluations across seven datasets show this approach outperforms existing methods, achieving a mean time to detect emergencies of approximately 05:23:28 hours and producing 0.09 false positives per day under noise-free conditions. Moreover, unlike related approaches, the proposed method remains effective with noisy data. This thesis demonstrates that emergencies in private households can be detected using existing data sources from the home infrastructure, offering a cost-effective and non-intrusive solution to enhance the safety and autonomy of the elderly at home.}, language = {de} } @phdthesis{Hasenpflug2025, author = {Hasenpflug, Mareike}, title = {Slice sampling on Riemannian manifolds}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-15903}, school = {Universit{\"a}t Passau}, pages = {iii, 118 Seiten}, year = {2025}, abstract = {This 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.}, language = {en} } @article{GoshDastidarCaelenGranitzer2024, author = {Gosh Dastidar, Kanishka and Caelen, Olivier and Granitzer, Michael}, title = {Machine learning methods for credit card fraud detection : a survey}, series = {IEEE Access}, volume = {2024}, journal = {IEEE Access}, number = {12}, publisher = {IEEE}, address = {New York}, doi = {10.1109/ACCESS.2024.348729}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-15796}, pages = {158939 -- 158965}, year = {2024}, abstract = {The widespread adoption of online payments has been accompanied by a significant increase in fraudulent activities, resulting in billions of dollars in financial losses. As payment providers aim to tackle this with various preventive mechanisms, fraudsters also continuously evolve their methods to remain indistinguishable from genuine actors. This necessitates sophisticated fraud detection tools to supplement these security mechanisms. As the volume of transactions taking place per day is in the millions, relying solely on human investigation is expensive and ultimately unfeasible, leading to an emergence of research into data driven or statistical methods for fraud detection. Over the last decade, this research has evolved to tackle the various particularities of the domain. These include the skewed nature of the data, the evolving user and fraud behavior, and the learning representations of the context in which a transaction takes place. This work aims to provide the community with an in-depth overview of the different directions in which recent research on online fraud detection has focused. We develop a taxonomy of the domain based on these directions and organize our analysis accordingly. For each area, we focus on significant methodological advancements and highlight limitations or gaps in the current state-of-the-art solutions. Through our analysis, it emerges that one of the primary limiting factors that many researchers face is the lack of availability of high-quality credit card data. Therefore, we provide a first step in addressing this issue in the form of a data generation framework using generative adversarial networks (GANs). We hope that this survey serves as a foundation for researchers who want to address the multi-faceted problem of credit card fraud detection.}, language = {en} } @article{LukasczykKroissFraser2023, author = {Lukasczyk, Stephan and Kroiß, Florian and Fraser, Gordon}, title = {An empirical study of automated unit test generation for Python}, series = {Empirical Software Engineering}, volume = {28}, journal = {Empirical Software Engineering}, number = {1}, publisher = {Springer Nature}, address = {Berlin}, doi = {10.1007/s10664-022-10248-w}, url = {http://nbn-resolving.de/urn:nbn:de:101:1-2023081721042349746457}, pages = {1 -- 46}, year = {2023}, abstract = {Various mature automated test generation tools exist for statically typed programming languages such as Java. Automatically generating unit tests for dynamically typed programming languages such as Python, however, is substantially more difficult due to the dynamic nature of these languages as well as the lack of type information. Our P YNGUIN framework provides automated unit test generation for Python. In this paper, we extend our previous work on P YNGUIN to support more aspects of the Python language, and by studying a larger variety of well-established state of the art test-generation algorithms, namely DynaMOSA, MIO, and MOSA. Furthermore, we improved our P YNGUIN tool to generate regression assertions, whose quality we also evaluate. Our experiments confirm that evolutionary algorithms can outperform random test generation also in the context of Python, and similar to the Java world, DynaMOSA yields the highest coverage results. However, our results also demonstrate that there are still fundamental remaining issues, such as inferring type information for code without this information, currently limiting the effectiveness of test generation for Python.}, language = {en} } @article{TrautschErbelHerboldetal.2023, author = {Trautsch, Alexander and Erbel, Johannes and Herbold, Steffen and Grabowski, Jens}, title = {What really changes when developers intend to improve their source code: a commit-level study of static metric value and static analysis warning changes}, series = {Empirical Software Engineering}, volume = {28}, journal = {Empirical Software Engineering}, number = {2}, publisher = {Springer Nature}, address = {Berlin}, doi = {10.1007/s10664-022-10257-9}, url = {http://nbn-resolving.de/urn:nbn:de:101:1-2023032321174386000821}, pages = {1 -- 40}, year = {2023}, language = {en} } @article{Mironchenko2023, author = {Mironchenko, Andrii}, title = {Well-posedness and properties of the flow for semilinear evolution equations}, series = {Mathematics of Control, Signals, and Systems}, volume = {36}, journal = {Mathematics of Control, Signals, and Systems}, number = {3}, publisher = {Springer Nature}, address = {Berlin}, doi = {10.1007/s00498-023-00378-x}, url = {http://nbn-resolving.de/urn:nbn:de:101:1-2024022307494197431619}, pages = {483 -- 523}, year = {2023}, abstract = {We derive conditions for well-posedness of semilinear evolution equations with unbounded input operators. Based on this, we provide sufficient conditions for such properties of the flow map as Lipschitz continuity, bounded-implies-continuation property, boundedness of reachability sets, etc. These properties represent a basic toolbox for stability and robustness analysis of semilinear boundary control systems. We cover systems governed by general C0 -semigroups, and analytic semigroups that may have both boundary and distributed disturbances. We illustrate our findings on an example of a Burgers' equation with nonlinear local dynamics and both distributed and boundary disturbances.}, language = {en} } @article{HerboldTunkel2023, author = {Herbold, Steffen and Tunkel, Steffen}, title = {Differential testing for machine learning: an analysis for classification algorithms beyond deep learning}, series = {Empirical Software Engineering}, volume = {28}, journal = {Empirical Software Engineering}, number = {2}, publisher = {Springer Nature}, address = {Berlin}, doi = {10.1007/s10664-022-10273-9}, url = {http://nbn-resolving.de/urn:nbn:de:101:1-2023033121421148821912}, pages = {1 -- 38}, year = {2023}, abstract = {Differential testing is a useful approach that uses different implementations of the same algorithms and compares the results for software testing. In recent years, this approach was successfully used for test campaigns of deep learning frameworks. There is little knowledge about the application of differential testing beyond deep learning. Within this article, we want to close this gap for classification algorithms. We conduct a case study using Scikit-learn, Weka, Spark MLlib, and Caret in which we identify the potential of differential testing by considering which algorithms are available in multiple frameworks, the feasibility by identifying pairs of algorithms that should exhibit the same behavior, and the effectiveness by executing tests for the identified pairs and analyzing the deviations. While we found a large potential for popular algorithms, the feasibility seems limited because, often, it is not possible to determine configurations that are the same in other frameworks. The execution of the feasible tests revealed that there is a large number of deviations for the scores and classes. Only a lenient approach based on statistical significance of classes does not lead to a huge amount of test failures. The potential of differential testing beyond deep learning seems limited for research into the quality of machine learning libraries. Practitioners may still use the approach if they have deep knowledge about implementations, especially if a coarse oracle that only considers significant differences of classes is sufficient.}, language = {en} } @article{RudolfSchaer2023, author = {Rudolf, Daniel and Sch{\"a}r, Philip}, title = {Dimension-independent spectral gap of polar slice sampling}, series = {Statistics and Computing}, volume = {34}, journal = {Statistics and Computing}, number = {1}, publisher = {Springer Nature}, address = {Berlin}, doi = {10.1007/s11222-023-10335-y}, url = {http://nbn-resolving.de/urn:nbn:de:101:1-2024011821064231531382}, pages = {14 Seiten}, year = {2023}, abstract = {Polar slice sampling, a Markov chain construction for approximate sampling, performs, under suitable assumptions on the target and initial distribution, provably independent of the state space dimension. We extend the aforementioned result of Roberts and Rosenthal (Stoch Model 18(2):257-280, 2002) by developing a theory which identifies conditions, in terms of a generalized level set function, that imply an explicit lower bound on the spectral gap even in a general slice sampling context. Verifying the identified conditions for polar slice sampling yields a lower bound of 1/2 on the spectral gap for arbitrary dimension if the target density is rotationally invariant, log-concave along rays emanating from the origin and sufficiently smooth. The general theoretical result is potentially applicable beyond the polar slice sampling framework.}, language = {en} } @article{WeissgerberBenAmorFelliciousetal.2023, author = {Weißgerber, Thomas and Ben Amor, Mehdi and Fellicious, Christofer and Granitzer, Michael}, title = {PyPads: Transparent Machine Learning Experiment Tracking}, series = {Datenbank-Spektrum}, volume = {24}, journal = {Datenbank-Spektrum}, number = {1}, publisher = {Springer Nature}, address = {Berlin}, doi = {10.1007/s13222-023-00459-w}, url = {http://nbn-resolving.de/urn:nbn:de:101:1-2024021511222778687954}, pages = {53 -- 62}, year = {2023}, abstract = {Despite algorithmic advancements in the field of machine learning, a need for improvement in the infrastructure supporting machine learning development and research has become increasingly apparent. Machine learning experiments usually tend to be more ad-hoc in nature, and results are communicated most often in the form of a publication. Experimental details are often omitted due to size or time constraints, or simply because the complexity in terms of technical setup or parametrization became intractable. Even access to code bases, disregard important properties of the environment and experimental setup, like for example random generators or computing infrastructure. At the same time, tracking and communicating an often inherently exploratory scientific process is a task with considerable effort. We explored different venues to tackle these issues from a data science engineering point of view. The efforts resulted in PyPads, a framework providing an infrastructure to extend experimental setups with logging, communication and analysis features in a mostly non-intrusive way. PyPads can be extended to different Python-based frameworks, utilizing community driven, descriptive metadata in an effort to harmonize library specific logs in an ontology. Meanwhile, we also try to emphasize similarities to practices in software engineering, which have turned out to be essential in practical applications.}, language = {en} } @misc{Mexis2023, type = {Master Thesis}, author = {Mexis, Nico}, title = {A Comprehensive Comparison of Fuzzy Extractor Schemes Employing Different Error Correction Codes}, volume = {2023}, doi = {10.15475/ccfesedecc.2023}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-12914}, school = {Universit{\"a}t Passau}, pages = {vii, 100 Seiten}, year = {2023}, abstract = {This thesis deals with fuzzy extractors, security primitives often used in conjunction with Physical Unclonable Functions (PUFs). A fuzzy extractor works in two stages: The generation phase and the reproduction phase. In the generation phase, an Error Correction Code (ECC) is used to compute redundant bits for a given PUF response, which are then stored as helper data, and a key is extracted from the response. Then, in the reproduction phase, another (possibly noisy) PUF response can be used in conjunction with this helper data to extract the original key. It is clear that the performance of the fuzzy extractor is strongly dependent on the underlying ECC. Therefore, a comparison of ECCs in the context of fuzzy extractors is essential in order to make them as suitable as possible for a given situation. It is important to note that due to the plethora of various PUFs with different characteristics, it is very unrealistic to propose a single metric by which the suitability of a given ECC can be measured. First, we give a brief introduction to the topic, followed by a detailed description of the background of the ECCs and fuzzy extractors studied. Then, we summarise related work and describe an implementation of the ECCs under consideration. Finally, we carry out the actual comparison of the ECCs and the thesis concludes with a summary of the results and suggestions for future work.}, subject = {Vorw{\"a}rtsfehlerkorrektur}, language = {en} } @article{ErdoganHassen, author = {Erdogan, G{\"u}lsah and Hassen, Wiem Fekih}, title = {Charging scheduling of hybrid energy storage systems for EV charging stations}, series = {Energies}, volume = {2023}, journal = {Energies}, number = {16}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/en16186656}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-14128}, pages = {29 Seiten}, abstract = {The growing demand for electric vehicles (EV) in the last decade and the most recent European Commission regulation to only allow EV on the road from 2035 involved the necessity to design a cost-effective and sustainable EV charging station (CS). A crucial challenge for charging stations arises from matching fluctuating power supplies and meeting peak load demand. The overall objective of this paper is to optimize the charging scheduling of a hybrid energy storage system (HESS) for EV charging stations while maximizing PV power usage and reducing grid energy costs. This goal is achieved by forecasting the PV power and the load demand using different deep learning (DL) algorithms such as the recurrent neural network (RNN) and long short-term memory (LSTM). Then, the predicted data are adopted to design a scheduling algorithm that determines the optimal charging time slots for the HESS. The findings demonstrate the efficiency of the proposed approach, showcasing a root-mean-square error (RMSE) of 5.78\% for real-time PV power forecasting and 9.70\% for real-time load demand forecasting. Moreover, the proposed scheduling algorithm reduces the total grid energy cost by 12.13\%.}, language = {en} } @article{FruehwirthJuhosProchno2022, author = {Fr{\"u}hwirth, Lorenz and Juhos, Michael and Prochno, Joscha}, title = {The large deviation behavior of lacunary sums}, series = {Monatshefte f{\"u}r Mathematik}, volume = {2022}, journal = {Monatshefte f{\"u}r Mathematik}, number = {199}, publisher = {Springer Nature}, address = {Berlin}, doi = {10.1007/s00605-022-01733-x}, url = {http://nbn-resolving.de/urn:nbn:de:101:1-2022081723261050522140}, pages = {113 -- 133}, year = {2022}, abstract = {We study the large deviation behavior of lacunary sums (Sn /n)n∈N with Sn :=∑[k=1...n] f (a(k)U), n ∈ |N, where U is uniformly distributed on [0, 1], (a(k))k∈|N is an Hadamard gap sequence, and f : |R → |R is a 1-periodic, (Lipschitz-)continuous mapping. In the case of large gaps, we show that the normalized partial sums satisfy a large deviation principle at speed n and with a good rate function which is the same as in the case of independent and identically distributed random variables U(k), k ∈ |N, having uniform distribution on [0, 1]. When the lacunary sequence (a(k))k∈|N is a geometric progression, then we also obtain large deviation principles at speed n, but with a good rate function that is different from the independent case, its form depending in a subtle way on the interplay between the function f and the arithmetic properties of the gap sequence. Our work generalizes some results recently obtained by Aistleitner, Gantert, Kabluchko, Prochno, and Ramanan [Large deviation principles for lacunary sums, preprint, 2020] who initiated this line of research for the case of lacunary trigonometric sums.}, language = {en} } @article{HarksSchwarz2024, author = {Harks, Tobias and Schwarz, Julian}, title = {Generalized Nash equilibrium problems with mixed-integer variables}, series = {Mathematical Programming}, volume = {209}, journal = {Mathematical Programming}, number = {1}, publisher = {Springer Berlin Heidelberg}, address = {Berlin/Heidelberg}, issn = {0025-5610}, doi = {10.1007/s10107-024-02063-6}, url = {http://nbn-resolving.de/urn:nbn:de:101:1-2405152117292.567771401889}, pages = {231 -- 277}, year = {2024}, abstract = {We consider generalized Nash equilibrium problems (GNEPs) with non-convex strategy spaces and non-convex cost functions. This general class of games includes the important case of games with mixed-integer variables for which only a few results are known in the literature. We present a new approach to characterize equilibria via a convexification technique using the Nikaido-Isoda function. To any given instance of the GNEP, we construct a set of convexified instances and show that a feasible strategy profile is an equilibrium for the original instance if and only if it is an equilibrium for any convexified instance and the convexified cost functions coincide with the initial ones. We develop this convexification approach along three dimensions: We first show that for quasi-linear models, where a convexified instance exists in which for fixed strategies of the opponent players, the cost function of every player is linear and the respective strategy space is polyhedral, the convexification reduces the GNEP to a standard (non-linear) optimization problem. Secondly, we derive two complete characterizations of those GNEPs for which the convexification leads to a jointly constrained or a jointly convex GNEP, respectively. These characterizations require new concepts related to the interplay of the convex hull operator applied to restricted subsets of feasible strategies and may be interesting on their own. Note that this characterization is also computationally relevant as jointly convex GNEPs have been extensively studied in the literature. Finally, we demonstrate the applicability of our results by presenting a numerical study regarding the computation of equilibria for three classes of GNEPs related to integral network flows and discrete market equilibria.}, language = {en} } @article{KreuzerLongRobbiano2024, author = {Kreuzer, Martin and Long, Le Ngoc and Robbiano, Lorenzo}, title = {Re-embeddings of affine algebras via Gr{\"o}bner fans of linear ideals}, series = {Beitr{\"a}ge zur Algebra und Geometrie / Contributions to Algebra and Geometry}, volume = {65}, journal = {Beitr{\"a}ge zur Algebra und Geometrie / Contributions to Algebra and Geometry}, number = {4}, publisher = {Springer Berlin Heidelberg}, address = {Berlin/Heidelberg}, issn = {0138-4821}, doi = {10.1007/s13366-024-00733-2}, url = {http://nbn-resolving.de/urn:nbn:de:101:1-2024041316352253862922}, pages = {827 -- 851}, year = {2024}, abstract = {Given an affine algebra R=K[x1,⋯,xn]/Iover a field  K , where I is an ideal in the polynomial ring P=K[x1,⋯,xn], we examine the task of effectively calculating re-embeddings of  I , i.e., of presentations R=P′/I′such that P′=K[y1,⋯,ym]has fewer indeterminates. For cases when the number of indeterminates  n is large and Gr{\"o}bner basis computations are infeasible, we have introduced the method of Z -separating re-embeddings in Kreuzer et al. (J Algebra Appl 21, 2022) and Kreuzer, et al. (S{\~a}o Paulo J Math Sci, 2022). This method tries to detect polynomials of a special shape in  I which allow us to eliminate the indeterminates in the tuple  Z by a simple substitution process. Here we improve this approach by showing that suitable candidate tuples  Z can be found using the Gr{\"o}bner fan of the linear part of  I . Then we describe a method to compute the Gr{\"o}bner fan of a linear ideal, and we improve this computation in the case of binomial linear ideals using a cotangent equivalence relation. Finally, we apply the improved technique in the case of the defining ideals of border basis schemes.}, language = {en} } @article{ProchnoRudolf2024, author = {Prochno, Joscha and Rudolf, Daniel}, title = {The minimal spherical dispersion}, series = {The Journal of Geometric Analysis}, volume = {34}, journal = {The Journal of Geometric Analysis}, number = {3}, publisher = {Springer US}, address = {New York}, issn = {1050-6926}, doi = {10.1007/s12220-023-01527-z}, url = {http://nbn-resolving.de/urn:nbn:de:101:1-2405020842543.936733306281}, pages = {14 Seiten}, year = {2024}, abstract = {We prove upper and lower bounds on the minimal spherical dispersion, improving upon previous estimates obtained by Rote and Tichy in (Anz {\"O}sterreich Akad Wiss Math Nat Kl 132:3-10, 1995). In particular, we see that the inverse N(ε,d)of the minimal spherical dispersion is, for fixed ε>0, linear in the dimension d of the ambient space. We also derive upper and lower bounds on the expected dispersion for points chosen independently and uniformly at random from the Euclidean unit sphere. In terms of the corresponding inverse N~(ε,d), our bounds are optimal with respect to the dependence on ε.}, language = {en} } @phdthesis{Klement2025, author = {Klement, Felix}, title = {Strengthening Security Foundations in Next-G Wireless Telecommunication Systems}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-18669}, school = {Universit{\"a}t Passau}, pages = {XV, 161 Seiten}, year = {2025}, abstract = {Digital 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.}, language = {en} } @article{DangOprisSudholt2024, author = {Dang, Duc-Cuong and Opris, Andre and Sudholt, Dirk}, title = {Crossover can guarantee exponential speed-ups in evolutionary multi-objective optimisation}, series = {Artificial Intelligence (Online ISSN: 1872-7921)}, volume = {2025}, journal = {Artificial Intelligence (Online ISSN: 1872-7921)}, number = {330}, publisher = {Elsevier}, address = {Amsterdam}, doi = {10.1016/j.artint.2024.104098}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-18732}, pages = {26 Seiten}, year = {2024}, abstract = {Evolutionary algorithms are popular algorithms for multi-objective optimisation (also called Pareto optimisation) as they use a population to store trade-offs between different objectives. Despite their popularity, the theoretical foundation of multi-objective evolutionary optimisation (EMO) is still in its early development. Fundamental questions such as the benefits of the crossover operator are still not fully understood. We provide a theoretical analysis of the well-known EMO algorithms GSEMO and NSGA-II to showcase the possible advantages of crossover: we propose classes of "royal road" functions on which these algorithms cover the whole Pareto front in expected polynomial time if crossover is being used. But when disabling crossover, they require exponential time in expectation to cover the Pareto front. The latter even holds for a large class of black-box algorithms using any elitist selection and any unbiased mutation operator. Moreover, even the expected time to create a single Pareto-optimal search point is exponential. We provide two different function classes, one tailored for one-point crossover and another one tailored for uniform crossover, and we show that some immune-inspired hypermutations cannot avoid exponential optimisation times. Our work shows the first example of an exponential performance gap through the use of crossover for the widely used NSGA-II algorithm and contributes to a deeper understanding of its limitations and capabilities.}, language = {en} } @article{KreuzerWalsh2024, author = {Kreuzer, Martin and Walsh, Florian}, title = {Computing the binomial part of a polynomial ideal}, series = {Journal of Symbolic Computation (Online ISSN: 1095-855X)}, volume = {2024}, journal = {Journal of Symbolic Computation (Online ISSN: 1095-855X)}, number = {124}, publisher = {Elsevier}, address = {Amsterdam}, doi = {10.1016/j.jsc.2024.102298}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-18708}, pages = {30 Seiten}, year = {2024}, abstract = {Given an ideal I in a polynomial ring K[x1,...,xn] over a field K, we present a complete algorithm to compute the binomial part of I, i.e., the subideal Bin(I) of I generated by all monomials and binomials in I. This is achieved step-by-step. First we collect and extend several algorithms for computing exponent lattices in different kinds of fields. Then we generalize them to compute exponent lattices of units in 0-dimensional K-algebras, where we have to generalize the computation of the separable part of an algebra to non-perfect fields in characteristic p. Next we examine the computation of unit lattices in finitely generated K-algebras, as well as their associated characters and lattice ideals. This allows us to calculate Bin(I) when I is saturated with respect to the indeterminates by reducing the task to the 0-dimensional case. Finally, we treat the computation of Bin(I) for general ideals by computing their cellular decomposition and dealing with finitely many special ideals called (s,t)-binomial parts. All algorithms have been implemented in SageMath.}, language = {en} } @article{FruehwirthProchno2024, author = {Fr{\"u}hwirth, Lorenz and Prochno, Joscha}, title = {Sanov-type large deviations and conditional limit theorems for high-dimensional Orlicz balls}, series = {Journal of Mathematical Analysis and Applications (Online ISSN: 1096-0813)}, volume = {2024}, journal = {Journal of Mathematical Analysis and Applications (Online ISSN: 1096-0813)}, number = {536,1}, publisher = {Elsevier}, address = {Amsterdam}, doi = {10.1016/j.jmaa.2024.128169}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-18723}, pages = {25 Seiten}, year = {2024}, abstract = {In this paper, we prove a Sanov-type large deviation principle for the sequence of empirical measures of vectors chosen uniformly at random from an Orlicz ball. From this level-2 large deviation result, in a combination with Gibbs conditioning, entropy maximization and an Orlicz version of the Poincar{\´e}-Maxwell-Borel lemma, we deduce a conditional limit theorem for high-dimensional Orlicz balls. In more geometric parlance, the latter shows that if V1 and V2 are Orlicz functions, then random points in the V1-Orlicz ball, conditioned on having a small V2-Orlicz radius, look like an appropriately scaled V2-Orlicz ball. In fact, we show that the limiting distribution in our Poincar{\´e}-Maxwell-Borel lemma, and thus the geometric interpretation, undergoes a phase transition depending on the magnitude of the V2-Orlicz radius.}, language = {en} } @article{PenaFerrandezSauer2024, author = {Pe{\~n}a Ferr{\´a}ndez, Juan Manuel and Sauer, Thomas}, title = {Stabilized recovery and model reduction for multivariate exponential polynomials}, series = {Journal of Symbolic Computation (Online ISSN: 1095-855X)}, volume = {2024}, journal = {Journal of Symbolic Computation (Online ISSN: 1095-855X)}, number = {125}, publisher = {Elsevier}, address = {Amsterdam}, doi = {10.1016/j.jsc.2024.102313}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-18748}, pages = {20 Seiten}, year = {2024}, abstract = {Recovery of multivariate exponential polynomials, i.e., the multivariate version of Prony's problem, can be stabilized by using more than the minimally needed multiinteger samples of the function. We present an algorithm that takes into account this extra information and prove a backward error estimate for the algebraic recovery method SMILE. In addition, we give a method to approximate data by an exponential polynomial sequence of a given structure as a step in the direction of multivariate model reduction.}, language = {en} } @article{KabluchkoProchnoSonnleitner2024, author = {Kabluchko, Zakhar and Prochno, Joscha and Sonnleitner, Mathias}, title = {A probabilistic approach to Lorentz balls l(^n)(q,1)}, series = {Journal of Functional Analysis (Online ISSN: 1096-0783)}, volume = {2025}, journal = {Journal of Functional Analysis (Online ISSN: 1096-0783)}, number = {288, 1}, publisher = {Elsevier}, address = {Amsterdam}, doi = {10.1016/j.jfa.2024.110682}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-18878}, pages = {32 Seiten}, year = {2024}, abstract = {We develop a probabilistic approach to study the volumetric and geometric properties of unit balls |B(^n)(q,1) of finite-dimensional Lorentz sequence spaces l(^n)(q,1). More precisely, we show that the empirical distribution of a random vector X^(n) uniformly distributed on its volume normalized unit ball converges weakly to a compactly supported symmetric probability distribution with explicitly given density; as a consequence we obtain a weak Poincar{\´e}-Maxwell-Borel principle for any fixed number k in |N of coordinates of X^(n) as n grows infinitly. Moreover, we prove a central limit theorem for the largest coordinate of X^(n), demonstrating a quite different behavior than in the case of the l(^n)(q) balls, where a Gumbel distribution appears in the limit. Finally, we prove a Schechtman-Schmuckenschl{\"a}ger type result for the asymptotic volume of intersections of volume normalized l(^n)(q,1) and l(^n)(p) balls.}, language = {en} } @phdthesis{Zerhoudi2025, author = {Zerhoudi, Saber}, title = {User Simulation in Interactive Information Retrieval : methods and frameworks for simulating complex search behavior}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-18936}, school = {Universit{\"a}t Passau}, pages = {xii, 196 Seiten}, year = {2025}, abstract = {Modern information retrieval (IR) systems, including web search engines and digital libraries, face challenges in simulating realistic user search behavior. Evolving interaction patterns and the integration of AI-powered interfaces make these challenges even harder. Traditional evaluation methods struggle to capture the dynamic nature of user interactions, particularly in complex search tasks and multi-stage information-seeking processes. User simulation offers a promising solution, providing a controlled environment for experimentation and allowing customization to model specific user behaviors and task contexts. This research develops advanced techniques for user simulation in IR, creating more realistic and dynamic models than were previously possible. Key contributions include new methods for representing query reformulation, modeling how information needs change, and measuring the impact of different search environments on simulated user behavior. Specifically, this work introduces contextual Markov models, cognitive state models, and embedding space alignment techniques to accurately represent interactive search behavior. Beyond model development, new evaluation methods and metrics are proposed for assessing the quality of simulated search sessions. These include statistical comparisons of session characteristics and classification-based approaches to distinguish between simulated and real user behavior. Additionally, this work leverages emerging technologies, such as large language models (LLMs) and retrieval-augmented generation, to improve the realism of user search behavior simulation. The practical outcome of this research is a modular and extensible simulation framework. This framework incorporates advanced techniques like user type-specific Markov models, advanced query generation using LLMs, and conversational user models.}, language = {en} } @article{MuellerGronbachYaroslavtseva2024, author = {M{\"u}ller-Gronbach, Thomas and Yaroslavtseva, Larisa}, title = {On the complexity of strong approximation of stochastic differential equations with a non-Lipschitz drift coefficient}, series = {Journal of Complexity (Online ISSN: 1090-2708)}, volume = {2024}, journal = {Journal of Complexity (Online ISSN: 1090-2708)}, number = {85}, publisher = {Elsevier}, address = {Amsterdam}, doi = {10.1016/j.jco.2024.101870}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-18819}, pages = {17 Seiten}, year = {2024}, abstract = {We survey recent developments in the field of complexity of pathwise approximation in p-th mean of the solution of a stochastic differential equation at the final time based on finitely many evaluations of the driving Brownian motion. First, we briefly review the case of equations with globally Lipschitz continuous coefficients, for which an error rate of at least 1/2 in terms of the number of evaluations of the driving Brownian motion is always guaranteed by using the equidistant Euler-Maruyama scheme. Then we illustrate that giving up the global Lipschitz continuity of the coefficients may lead to a non-polynomial decay of the error for the Euler-Maruyama scheme or even to an arbitrary slow decay of the smallest possible error that can be achieved on the basis of finitely many evaluations of the driving Brownian motion. Finally, we turn to recent positive results for equations with a drift coefficient that is not globally Lipschitz continuous. Here we focus on scalar equations with a Lipschitz continuous diffusion coefficient and a drift coefficient that satisfies piecewise smoothness assumptions or has fractional Sobolev regularity and we present corresponding complexity results.}, language = {en} } @article{FekihHassenSchoppikSchieggetal.2024, author = {Fekih Hassen, Wiem and Schoppik, Luis and Schiegg, Sascha and Gerl, Armin}, title = {Power management approach of hybrid energy storage system for electric vehicle charging stations}, series = {Smart Cities}, volume = {7 (2024)}, journal = {Smart Cities}, number = {6}, publisher = {MDPI}, address = {Basel}, issn = {2624-6511}, doi = {10.3390/smartcities7060156}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:m347-opus-6045}, pages = {4025 -- 4051}, year = {2024}, abstract = {The applicability of Hybrid Energy Storage Systems (HESSs) has been shown in multiple application fields, such as Charging Stations (CSs), grid services, and microgrids. HESSs consist of an integration of two or more single Energy Storage Systems (ESSs) to combine the benefits of each ESS and improve the overall system performance. In this work, we propose a novel power management controller called the Hybrid Controller for the efficient HESS's charging and discharging, considering the State of Charge (SoC) of the HESS and the dynamic supply and load. The Hybrid Controller optimises the use of the HESS, i.e., minimises the amount of energy drawn from and discharged to the grid, thus utilising and prioritising the provided Photovoltaic (PV) power. The performance of our proposal was assessed via simulation using various evaluation metrics, i.e., Autarky, charge/discharge cycle, and Self-Consumption (SC), where we defined 24 scenarios in different locations in Germany.}, language = {en} } @article{EpperleinWirth2024, author = {Epperlein, Jeremias and Wirth, Fabian}, title = {The joint spectral radius is pointwise H{\"o}lder continuous}, series = {Linear Algebra and its Applications}, volume = {2025}, journal = {Linear Algebra and its Applications}, number = {704}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1873-1856}, doi = {10.1016/j.laa.2024.09.016}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-19140}, pages = {92 -- 122}, year = {2024}, abstract = {We show that the joint spectral radius is pointwise H{\"o}lder continuous. In addition, the joint spectral radius is locally H{\"o}lder continuous for ε-inflations. In the two-dimensional case, local H{\"o}lder continuity holds on the matrix sets with positive joint spectral radius.}, language = {en} }