TY - JOUR A1 - Harks, Tobias A1 - Schwarz, Julian T1 - Generalized Nash equilibrium problems with mixed-integer variables JF - Mathematical Programming N2 - 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. KW - Generalized Nash equilibrium problem KW - Mixed-integer nonlinear problem KW - Non-convex games KW - Complementarity and equilibrium problems and variational inequalities (finite dimensions) KW - Mixed integer programming KW - Noncooperative games Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:101:1-2405152117292.567771401889 SN - 0025-5610 SN - 1436-4646 VL - 209 IS - 1 SP - 231 EP - 277 PB - Springer Berlin Heidelberg CY - Berlin/Heidelberg ER - TY - JOUR A1 - Venus, Terese E. A1 - Beale, Caroline A1 - Villalba, Roberto T1 - Innovation and networks in the bioeconomy : a case study from the German Coffee Value Chain JF - Circular Economy and Sustainability N2 - The transition to a circular bioeconomy requires innovation across many sectors, but social dynamics within a sector’s network may affect innovation potential. We investigate how network dynamics relate to the perceptions and adoption of bioeconomy innovation using a case study from the food processing sector. Our case study of the German coffee value chain represents a technologically advanced sector with a strong sustainability focus and potential for residue valorization, which is an important dimension of a sustainable circular bioeconomy. We identify three distinct views (pioneers, traditional and limited users) related to residue valorization, map linkages between actors using social network analysis, and highlight barriers to innovation. We collected data through an online survey and semi-structured interviews with key actors in the coffee roasting sector. Within the social network analysis, we find that public waste managers are closely linked to the most influential actors, state actors such as the customs and tax offices can quickly interact with others in the network and promote the spread of information (highest closeness centrality) and specific roasters play an important role as intermediaries for efficient communication (highest betweenness centrality). Finally, we identify four main barriers including the structure of the coffee network, inconsistencies in federal waste regulations, economies of scale, and visions of sustainability. To support a sustainable bioeconomy, we recommend that policy makers revise the primary regulatory frameworks for waste (e.g., German Recycling Act) to clarify how to classify food residues, their disposal structures and broaden their use streams. KW - Bioeconomy KW - Coffee KW - Value chain KW - Germany KW - Social network analysis KW - Residue valorization Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:101:1-2405070852079.655263471225 SN - 2730-597X SN - 2730-5988 VL - 4 IS - 3 SP - 1751 EP - 1772 PB - Springer International Publishing CY - Cham ER - TY - JOUR A1 - Kreuzer, Martin A1 - Long, Le Ngoc A1 - Robbiano, Lorenzo T1 - Re-embeddings of affine algebras via Gröbner fans of linear ideals JF - Beiträge zur Algebra und Geometrie / Contributions to Algebra and Geometry N2 - 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 Gröbner 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. (São 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 Gröbner fan of the linear part of  I . Then we describe a method to compute the Gröbner 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. KW - Re-embedding KW - Optimal embedding KW - Gröbner fan KW - Cotangent space KW - Border basis scheme Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:101:1-2024041316352253862922 SN - 0138-4821 SN - 2191-0383 VL - 65 IS - 4 SP - 827 EP - 851 PB - Springer Berlin Heidelberg CY - Berlin/Heidelberg ER - TY - JOUR A1 - Friedlaender, Tobias A1 - Müller, Anna-Lisa T1 - Grenzregionen in der COVID-19-Pandemie : wie der „Grenzschock“ die Oberrheinregion veränderte JF - Standort N2 - Am Beispiel der trinationalen Oberrheinregion geht dieser Artikel der Frage nach, auf welche Weise sich die im Zuge der COVID-19-Pandemie im Jahr 2020 vollzogenen Grenzschließungen und die damit verbundenen Grenzerfahrungen auf die grenzüberschreitenden Beziehungen von lokalen Akteur*innen in Politik, Wirtschaft und Gesellschaft ausgewirkt haben. Anhand qualitativer Interviewdaten zeigen wir, wie dieser pandemiebedingte „Grenzschock“ aufgenommen und der grenzüberschreitende politische und soziale Zusammenhalt auf die Probe gestellt wurde, wie aber auch die Zusammenarbeit nach einer Zeit der Irritation an die neue Situation angepasst werden konnte. Dabei befand sich die grenzüberschreitende Zusammenarbeit in dieser Zeit in einem Spannungsfeld zwischen politisch-administrativen Vorgaben der jeweiligen nationalen Zentren und den lokal spezifischen Anforderungen einer peripher gelegenen Grenzregion. Die Daten zeigen, dass die Akteur*innen in der Oberrheinregion bei der Überwindung dieses „Grenzschocks“ auf langjährig etablierte Strukturen und Erfahrungen in der grenzüberschreitenden Zusammenarbeit zurückgreifen konnten. Die Erfahrungen während der Pandemie sorgten dabei zudem für neue Impulse für die grenzüberschreitende Zusammenarbeit in der Oberrheinregion und stärkten den politischen Willen dafür auf verschiedenen Ebenen. Damit leistet der Artikel einen explorativen Beitrag zu den Auswirkungen der COVID-19-Pandemie auf Grenzregionen. N2 - Taking the trinational Upper Rhine region as an example, this article explores the ways in which the border closures implemented in the course of the COVID-19 pandemic in 2020 and the associated border experiences have affected cross-border relations of local actors in politics, economy, and society. Using qualitative interview data, we show how this pandemic-related “border shock” was received and how cross-border political and social cohesion was put to the test, but also how cooperation was able to adapt to the new situation after a period of confusion. At the same time, cross-border cooperation during this period was caught in the tension between the political-administrative guidelines of the respective national centers and the locally specific requirements of a peripherally located border region. The data show that the actors in the Upper Rhine region were able to draw on long-established structures and experience in cross-border cooperation to overcome this “border shock.” The experiences during the pandemic also provided new impulses for cross-border cooperation in the Upper Rhine region and strengthened the political will for this at various levels. Thus, the article makes an explorative contribution to the impacts of the COVID-19 pandemic on border regions. KW - Grenzgeographien KW - Krisen KW - Oberrhein KW - Schengenraum KW - Grenzüberschreitende Beziehungen KW - Grenzschließungen KW - Border geographies KW - Crises KW - Upper Rhine KW - Schengen Space KW - Cross-Border Relations KW - Border closures Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:101:1-2024041011254221061098 SN - 0174-3635 SN - 1432-220X VL - 48 IS - 4 SP - 302 EP - 311 PB - Springer Berlin Heidelberg CY - Berlin/Heidelberg ER - TY - CHAP A1 - Meißner, Annekatrin ED - Beck, Birgit ED - Thies, Christian T1 - Armut als Folge globaler Ungerechtigkeit? : zur Relevanz der Ansätze von Sen und Pogge T2 - Beck, Birgit/Thies, Christian (Hgg.): Moral und Recht : philosophische und juristische Beiträge; Passau 2011; 978-3-88849-309-6 N2 - "Unterschiedliche Gerechtigkeitsbegriffe führen zu voneinander abweichenden Schlussfolgerungen über die Art und die Akteure der Verantwortungsübernahme sowie die daraus abzuleitenden Strategien zur Überwindung der globalen Armut. Aus diesem Grund liegt das besondere Erkenntnisinteresse dieses Beitrags in der vergleichenden Analyse der Argumentationsstrukturen und Gerechtigkeitsmodelle zweier Philosophen, welche die entsprechenden Diskurse entscheidend beeinflusst haben - Thomas Pogge und Amartya Sen." KW - Gerechtigkeit KW - Verantwortung KW - Menschenrechte KW - internationale Rahmenordnung Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-18626 VL - 2011 SP - 105 EP - 123 PB - Verlag Karl Stutz CY - Passau ER - TY - JOUR A1 - Prochno, Joscha A1 - Rudolf, Daniel T1 - The minimal spherical dispersion JF - The Journal of Geometric Analysis N2 - We prove upper and lower bounds on the minimal spherical dispersion, improving upon previous estimates obtained by Rote and Tichy in (Anz Österreich 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. KW - Dispersion KW - Expected dispersion KW - Spherical cap KW - Spherical dispersion KW - VC-dimension Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:101:1-2405020842543.936733306281 SN - 1050-6926 SN - 1559-002X VL - 34 IS - 3 PB - Springer US CY - New York ER - TY - JOUR A1 - Hidalgo, Oliver T1 - Von Alemann, Ulrich, Nina Basedahl, Gernot Graeßner, und Sabrina Kovacs (2022): Politische Ideen im Wandel der Zeit BT - Opladen/Toronto: Barbara Budrich/UTB. 279 Seiten. 29,90 € JF - Politische Vierteljahresschrift N2 - "Einführungen in die Politische Theorie und Ideengeschichte, die auch für Studienanfänger*innen verständlich sind und sich zugleich auf der Höhe des Forschungsstands bewegen, sind nach wie vor eine gehörige Herausforderung. Erschwerend kommt hinzu, dass die gängigen autor*innen-, werk- oder diskurszentrierten Formate allesamt ihre blinden Flecken besitzen. Insofern ist die Lösung, die Ulrich von Alemann, Nina Basedahl, Gernot Graeßner und Sabrina Kovacs gefunden haben und die auf eine Kombination aller drei genannten Ansätze hinausläuft, im Prinzip durchaus zu begrüßen." KW - Rezension Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:101:1-2405070854311.077128860665 SN - 0032-3470 SN - 1862-2860 VL - 65 IS - 3 SP - 603 EP - 607 PB - Springer Fachmedien Wiesbaden CY - Wiesbaden ER - TY - JOUR A1 - Wiedel, Fabian T1 - Ehrlich, Gianna Luisa; Der konsumentenbasierte Markenwert von Nachrichtenmedien : Muster der Genese und Wirkung von starken Medienmarken. BT - Wiesbaden: Springer VS 2023. 626 Seiten. Preis: € 79,99. Dissertationsschrift Universität Mainz. JF - Publizistik KW - Buchbesprechung Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:101:1-2405150806439.614902039284 SN - 0033-4006 SN - 1862-2569 VL - 69 IS - 1 SP - 95 EP - 97 PB - Springer Fachmedien Wiesbaden CY - Wiesbaden ER - TY - THES A1 - Klement, Felix T1 - Strengthening Security Foundations in Next-G Wireless Telecommunication Systems N2 - 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. KW - Security KW - Next-G KW - 6G KW - Open RAN Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-18669 ER - TY - JOUR A1 - Dang, Duc-Cuong A1 - Opris, Andre A1 - Sudholt, Dirk T1 - Crossover can guarantee exponential speed-ups in evolutionary multi-objective optimisation JF - Artificial Intelligence (Online ISSN: 1872-7921) N2 - 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. KW - Evolutionary computation KW - Runtime analysis KW - Recombination KW - Multi-objective optimisation KW - Unbiased black-box algorithms KW - Hypermutation Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-18732 VL - 2025 IS - 330 PB - Elsevier CY - Amsterdam ER -