TY - THES A1 - März, Armin T1 - Three Essays on Understanding Mobile Consumer Behavior: Business Models, Perceptions, and Features N2 - For about a decade, consumers have been carrying the Internet in their pockets. The rapid penetration of modern smartphones has meant that more than two-thirds of the people in the West can access and use online resources, anytime and anywhere. Consumers also can communicate and share their consumption experiences instantaneously. Platforms reach users for time-critical events through highly personal communication channels, in the sense that smartphones serve as constant companions. Many mobile applications and their basic services and contents also are available for free. The digital and mobile worlds thus are changing the very means of communication, suggesting the powerful need for marketing research and practice to find the opportunities and meet the challenges of the mobile Internet. In particular, scientific investigations are required to describe new business models in the free e-service industry and the consumer behavior affected by mobile features. This thesis examines these topics in three essays. Study 1 considers business models that offer their services without charge. Offering services for free is symptomatic of not only mobile apps (90% of all apps are available for free) but the digital economy in general. For companies offering free e-services, this situation raises several important questions, in that, without any access device restrictions, how do customers of free e-services contribute value without paying? What are the nature and dynamics of nonmonetary value contributions by nonpaying customers? With a literature review and interviews with senior executives of free e-service providers, Study 1 presents a comprehensive overview of nonmonetary value contributions in the free e-service sector, including word of mouth, co-production, and network effects. Moreover, adding attention and data into this framework reveals two further aspects that have not been addressed in prior customer value research. By putting the findings in the context of the existing literature on customer value and customer engagement, this study sheds light on the complex processes of value creation in the emerging e-service sector, while advancing marketing and service research in general. Study 2 deepens the findings from the first study; specifically, the focus is on the way that mobile users co-produce content and how this contribution is perceived by recipients in the network. With field data and a scenario experiment, this study demonstrates that recipients appreciate mobile-generated customer reviews fundamentally differently from other reviews. In particular, they discount the helpfulness of mobile reviews, due to their text-specific content and style particularities. The very fact that a review has been identified as written on a mobile device also lowers recipients’ perceptions of its value. Recipients use information about the device as a source cue to assess their compatibility with the review contribution channel. If they perceive themselves as compatible with the method used to generate the review (mobile or non-mobile), recipients regard the review as more helpful, because they attribute the review to the quality of the reviewed subject. If they perceive it as incompatible though, recipients assume that the review reflects the personal dispositions of the reviewer and discount its helpfulness. Finally, Study 3 takes up the attention and cross-market network effects in a mobile setting; these were two nonmonetary dimensions identified by Study 1. Platform providers should develop measures to draw the attention of nonpaying customers to the offers of their paying customers. One attention-grabbing mobile-specific feature is push notifications to the device, which provide information about temporally or spatially relevant events. More concretely, Study 3 investigates how mobile push notifications remind users of upcoming deadlines in online auctions and therefore improve late bidding success. Late bidding is a prevalent strategy, in which bidders submit their bids at the very end of an online auction. This research uses field data about an online auction platform to demonstrate that late bidders use these mobile push notifications more frequently than do bidders with different bidding patterns. Within the group of late bidders, the chance to win an auction increases with their use of push notifications. After a mobile push notification, late bidders submit bids through mobile devices but also through non-mobile channels. Less experienced late bidders also benefit from push notifications, which increase their chances of success. In summary, this dissertation contributes to an enhanced understanding of mobile consumer behavior by using various methods, including qualitative interviews, field observations, and online experiments. From a theoretical perspective, it contributes to current knowledge about nonmonetary costumer value contributions in general and their role in mobile settings in particular. This thesis highlights the role of mobile devices in co-production and perceptions of co-produced content. It also reveals how mobile-specific interactive features, like push notifications, affect late bidding efficiency. Therefore, it specifies the role of mobile devices in cross-market effects, in that they enable the platform to direct the relationship between buyers and sellers. The insights presented herein encourage managers to reevaluate their current practices, think about whether they should label co-produced content as generated through a mobile channel or not, and contemplate whether to develop mobile push notifications as helpful features for users (not as intrusive marketing messages). KW - E-Services KW - Mobile KW - Internet KW - Consumer Behavior KW - Marketing KW - Mobiles Internet KW - Verbraucherverhalten Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-3948 ER - TY - THES A1 - Alsarem, Mazen T1 - Semantic Snippets via Query-Biased Ranking of Linked Data Entities N2 - In our knowledge-driven society, the acquisition and the transfer of knowledge play a principal role. Web search engines are somehow tools for knowledge acquisition and transfer from the web to the user. The search engine results page (SERP) consists mainly of a list of links and snippets (excerpts from the results). The snippets are used to express, as efficiently as possible, the way a web page may be relevant to the query. As an extension of the existing web, the semantic web or “web 3.0” is designed to convert the presently available web of unstructured documents into a web of data consumable by both human and machines. The resulting web of data and the current web of documents coexist and interconnect via multiple mechanisms, such as the embedded structured data, or the automatic annotation. In this thesis, we introduce a new interactive artifact for the SERP: the “Semantic Snippet”. Semantic Snippets rely on the coexistence of the two webs to facilitate the transfer of knowledge to the user thanks to a semantic contextualization of the user’s information need. It makes apparent the relationships between the information need and the most relevant entities present in the web page. The generation of semantic snippets is mainly based on the automatic annotation of the LOD1’s entities in web pages. The annotated entities have different level of impor- tance, usefulness and relevance. Even with state of the art solutions for the automatic annotations of LOD entities within web pages, there is still a lot of noise in the form of erroneous or off-topic annotations. Therefore, we propose a query-biased algorithm (LDRANK) for the ranking of these entities. LDRANK adopts a strategy based on the linear consensual combination of several sources of prior knowledge (any form of con- textual knowledge, like the textual descriptions for the nodes of the graph) to modify a PageRank-like algorithm. For generating semantic snippets, we use LDRANK to find the more relevant entities in the web page. Then, we use a supervised learning algorithm to link each selected entity to excerpts from the web page that highlight the relationship between the entity and the original information need. In order to evaluate our semantic snippets, we integrate them in ENsEN (Enhanced Search Engine), a software system that enhances the SERP with semantic snippets. Finally, we use crowdsourcing to evaluate the usefulness and the efficiency of ENsEN. N2 - In unserer heutigen Wissensgesellschaft spielen der Erwerb und die Weitergabe von Wissen eine zentrale Rolle. Internetsuchmaschinen fungieren als Werkzeuge für den Erwerb und die Weitergabe von Wissen aus dem Web an den Nutzer. Die Ergebnisliste einer Suchmaschine (SERP) besteht grundsätzlich aus einer Liste von Links und Textauszügen (Snippets). Diese Snippets sollen auf möglichst effiziente Weise ausdrücken inwiefern eine Webseite für die Suchanfrage relevant ist. Als Erweiterung des bestehenden Internets, überführt das semantische Web - auch genannt “Web 3.0” - das momentan vorhandene Internet der unstrukturierten Dokumente in ein Internet der Daten, das sowohl von Menschen als auch Maschinen verwendet werden kann. Das neu geschaffene Internet der Daten und das derzeitige Internet der Dokumente existieren gleichzeitig und sie sind über eine Vielzahl von Mechanismen miteinander verbunden, wie beispielsweise über eingebettete strukturierte Daten oder eine automatische Annotation. In dieser Arbeit stellen wir ein neues interaktives Artefakt für das SERP vor: Das “Semantische Snippet”. Semantische Snippets stützen sich auf die Koexistenz der beiden Arten des Internets um mit Hilfe der Kontextualisierung des Informationsbedürfnisses eines Nutzers die Weitergabe von Wissen zu erleichtern. Sie stellen die Verbindung zwischen dem Informationsbedürfnis und den besonders relevanten Entitäten einer Webseite heraus. Die Erzeugung semantischer Snippets basiert überwiegend auf der automatisierten Annotation von Webseiten mit Entitäten aus der Linking Open Data Cloud (LOD). Die annotierten Entitäten besitzen unterschiedliche Ebenen hinsichtlich Wichtigkeit, Nützlichkeit und Relevanz. Selbst bei state-of-the-art Lösungen zur automatisierten Annotation von LOD- Entitäten in Webseiten, gibt es stets ein großes Maß an Rauschen in Form von fehlerhaften oder themenfremden Annotationen. Wir stellen deshalb einen anfragegetriebenen Algorithmus (LDRANK) für das Ranking dieser Entitäten vor. LDRANK setzt eine Strategie ein, die auf der linearen Konsensus-Kombination (engl. linear consensual combination) mehrerer a-priori Wissensquellen (jedwede Art von Kontextwissen, wie beispielsweise die textuelle Beschreibung der Knoten des Graphen) basiert um damit den PageRank-Algorithmus zu modifizieren. Zur Generierung semantischer Snippets finden wir zunächst mit Hilfe von LDRANK die relevantesten Entitäten in einer Webseite. Anschließend verwenden wir ein überwachtes Lernverfahren um jede ausgewählte Entität denjenigen Abschnitten der Webseite zuzuordnen, die die Beziehung zwischen der Entität und dem ursprünglichen Informationsbedarf am besten herausstellt. Um unsere semantischen Snippets zu evaluieren, integrieren wir sie in ENsEN (Enhanced Search Engine), ein Softwaresystem das SERP um semantische Snippets erweitert. Zum Abschluss bewerten wir die Nu ̈tzlichkeit und die Effizienz von ENsEN mittels Crowdsourcing. KW - Semantic Snippets KW - Entity Ranking KW - Web of Data KW - World Wide Web 3.0 KW - Suchmaschine KW - Suchmaschinenoptimierung KW - Ranking Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-3959 ER - TY - THES A1 - Tomashevich, Victor T1 - Fault Tolerance Aspects of Virtual Massive MIMO Systems N2 - Employment of a very large number of antennas is seen as the key technology to provide future users with very high data rates. At the same time, the implementation complexity will rise due to large memories required and sophisticated signal processing algorithms employed. Continuous technology downscaling allows implementation of such complex digital designs. At the same time, its inherent variability and vulnerability to physical disturbances violate the assumption of perfectly reliable hardware operation. This work considers Unique Word OFDM which represents the alternative to the standard Cyclic Prefix OFDM providing superior detection quality. The generalization of Unique Word OFDM to a MIMO system is performed which allows interpretation as a virtual massive MIMO system with only few physical antennas. Detection methods for the introduced generalization are discussed and their performance is quantified. Because of the large memory size required, linear detection represents the cost and performance effective solution. The possible memory errors due to radiation effects or voltage scaling are addressed and the nonlinear MMSE detection algorithm is proposed. This algorithm keeps track of the memory errors and is able to significantly mitigate their effect on the quality of the estimated data. Apart of memory issues, reliability of the actual computational hardware which constitutes the receiver is of concern in this work. An own implementation of the MMSE Sorted Givens Rotations is subjected to transient fault injection. The impact of faults in various parts of the implemented circuit on the detection performance is quantified. Most vulnerable components of the implemented circuit in terms of reliability are identified. Security is another major address of this work, since most current implementations include cryptographic devices. Fault-based attacks on such systems are known to be able to extract the secret key in feasible time. The remaining part of this work addresses such fault injection-based malicious attacks. Countermeasures based on a combination of information and hardware redundancy are considered. Recently introduced robust codes target such attacks by providing guaranteed detection capability. The performance of these codes is assessed by application to actual cryptographic and general purpose circuits. The work introduces metrics that help to identify fault locations in the circuit which could escape detection with high probability. These locations are targeted by transistor resizing that renders fault injection unfeasible. KW - MIMO Systems KW - MIMO KW - Fehlertoleranz Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-4047 ER - TY - THES A1 - Wölfl, Andreas T1 - Data Management in Certified Avionics Systems N2 - Data management is a cornerstone for any kind of information system - including the aerospace and aviation sector. In contrast to conventional domains, software development in the avionics domain must adhere to a legally binding certification process, called qualification. The success of the process depends on compliance with international standards, such as DO-178: Software Considerations in Airborne Systems and Equipment Certification. From a software developer's perspective, challenges arise in terms of methods and tools. Techniques that have a potential impact on the deterministic and predictable execution of avionics software are prohibited. The objective of this thesis' research is to develop a scalable method to realize data-management for multi-variant avionics software under the restrictions and constraints of the domain. Since avionics software faces very long-term life-cycles (up to 75 years), a particular focus is being placed on maintenance and evolution. Based on the insights gained in a semi-structured interview at Airbus Helicopters, industrial established approaches to implement qualified avionics software are assessed at first and compared with respect to strengths and weaknesses for data-management afterwards. As a result, a novel development approach is proposed, combining model-based techniques and product-line technology to derive the source code of highly specific data-management variants, as well as the majority of assets required for the qualification process, from a declarative system specification. In order to demonstrate the practicability of the approach in industry, a framework is presented that is deployed and applied at Airbus Helicopters to generate qualifiable data-management components for the variants of the NH90 helicopter. The maintainability is shown by means of a domain-specific optimization, in which the model-based and generative approach is used to establish safe memory overlays at compile-time. Key findings reveal a substantially reduced memory footprint (29,1% in case of a real-world scenario), as well as an significantly facilitated implementation process, which would not be accomplishable using conventional methods for software development in the avionics domain. N2 - Datenverwaltung ist der Grundstein für jegliche Art von Informationssystemen – so auch in der Luft- und Raumfahrt. Im Unterschied zu konventionellen Domänen unterliegt die Software für Avionik-Systeme einem gesetzlich vorgeschriebenen Zertifizierungsprozess, genannt Qualifizierung. Der Erfolg dieses Vorgangs hängt primär von der Einhaltung internationaler Sicherheitsnormen ab. Aus der Sicht eines Software-Entwicklers ergeben sich hier Herausforderungen hinsichtlich erlaubter Methoden und Werkzeuge, denn Techniken, die den deterministischen Ablauf eines Programms gefährden können, sind verboten. Das Ziel dieser Arbeit ist es, ein skalierbares Verfahren zu entwickeln, um eine Datenmanagement-Komponente unter Einhaltung der Sicherheitsnormen für Avionik-Systeme in mehreren Varianten nicht nur zu realisieren, sondern auch langfristig warten zu können (bis zu 75 Jahre). Basierend auf den Erkenntnissen, die durch ein semi-strukturiertes Entwickler-Interview bei Airbus Helicopters gewonnen wurden, werden industriell etablierte Methoden zur Implementierung und Qualifizierung von Avionik-Software zunächst analysiert und anschließend hinsichtlich ihrer Stärken und Schwächen für Datenmanagement bewertet. Als Resultat wird ein neuartiger Ansatz vorgestellt, der durch eine Kombination aus modellbasierten Methoden und Produktlinien-Technologie, sowohl den Quellcode einer spezifischen Datenmanagement-Variante, als auch weitere Erzeugnisse, die für die Qualifizierung zu erbringen sind, aus einer deklarativen Systemspezifikation ableitet. Als Beispiel für die Praktikabilität des Verfahrens wird die Architektur einer Werkzeugkette vorgestellt, die bei Airbus eingesetzt wird, um qualifizierbare Datenmanagement-Varianten für die eingebettete Software des NH90 Helikopters zu generieren. Die Wartbarkeit wird durch eine domänenspezifische Optimierung demonstriert, die durch den modellbasierten und generativen Ansatz eine sichere Überlappung von Speicherbereichen zur Compile-Zeit ermöglicht. Zu den Ergebnissen zählen nicht nur verringerter Speicherverbrauch (29,1% in einem realen Szenario), sondern auch eine effiziente Umsetzung, die mit den etablierten Methoden zur Software-Entwicklung in der Avionik-Domäne nicht zu erreichen wäre. KW - Avionik KW - Datenverarbeitung Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-5758 ER - TY - THES A1 - Jovanovic, Philipp T1 - Analysis and Design of Symmetric Cryptographic Algorithms N2 - This doctoral thesis is dedicated to the analysis and the design of symmetric cryptographic algorithms. In the first part of the dissertation, we deal with fault-based attacks on cryptographic circuits which belong to the field of active implementation attacks and aim to retrieve secret keys stored on such chips. Our main focus lies on the cryptanalytic aspects of those attacks. In particular, we target block ciphers with a lightweight and (often) non-bijective key schedule where the derived subkeys are (almost) independent from each other. An attacker who is able to reconstruct one of the subkeys is thus not necessarily able to directly retrieve other subkeys or even the secret master key by simply reversing the key schedule. We introduce a framework based on differential fault analysis that allows to attack block ciphers with an arbitrary number of independent subkeys and which rely on a substitution-permutation network. These methods are then applied to the lightweight block ciphers LED and PRINCE and we show in both cases how to recover the secret master key requiring only a small number of fault injections. Moreover, we investigate approaches that utilize algebraic instead of differential techniques for the fault analysis and discuss advantages and drawbacks. At the end of the first part of the dissertation, we explore fault-based attacks on the block cipher Bel-T which also has a lightweight key schedule but is not based on a substitution-permutation network but instead on the so-called Lai-Massey scheme. The framework mentioned above is thus not usable against Bel-T. Nevertheless, we also present techniques for the case of Bel-T that enable full recovery of the secret key in a very efficient way using differential fault analysis. In the second part of the thesis, we focus on authenticated encryption schemes. While regular ciphers only protect privacy of processed data, authenticated encryption schemes also secure its authenticity and integrity. Many of these ciphers are additionally able to protect authenticity and integrity of so-called associated data. This type of data is transmitted unencrypted but nevertheless must be protected from being tampered with during transmission. Authenticated encryption is nowadays the standard technique to protect in-transit data. However, most of the currently deployed schemes have deficits and there are many leverage points for improvements. With NORX we introduce a novel authenticated encryption scheme supporting associated data. This algorithm was designed with high security, efficiency in both hardware and software, simplicity, and robustness against side-channel attacks in mind. Next to its specification, we present special features, security goals, implementation details, extensive performance measurements and discuss advantages over currently deployed standards. Finally, we describe our preliminary security analysis where we investigate differential and rotational properties of NORX. Noteworthy are in particular the newly developed techniques for differential cryptanalysis of NORX which exploit the power of SAT- and SMT-solvers and have the potential to be easily adaptable to other encryption schemes as well. N2 - Diese Doktorarbeit beschäftigt sich mit der Analyse und dem Entwurf von symmetrischen kryptographischen Algorithmen. Im ersten Teil der Dissertation befassen wir uns mit fehlerbasierten Angriffen auf kryptographische Schaltungen, welche dem Gebiet der aktiven Seitenkanalangriffe zugeordnet werden und auf die Rekonstruktion geheimer Schlüssel abzielen, die auf diesen Chips gespeichert sind. Unser Hauptaugenmerk liegt dabei auf den kryptoanalytischen Aspekten dieser Angriffe. Insbesondere beschäftigen wir uns dabei mit Blockchiffren, die leichtgewichtige und eine (oft) nicht-bijektive Schlüsselexpansion besitzen, bei denen die erzeugten Teilschlüssel voneinander (nahezu) unabhängig sind. Ein Angreifer, dem es gelingt einen Teilschlüssel zu rekonstruieren, ist dadurch nicht in der Lage direkt weitere Teilschlüssel oder sogar den Hauptschlüssel abzuleiten indem er einfach die Schlüsselexpansion umkehrt. Wir stellen Techniken basierend auf differenzieller Fehleranalyse vor, die es ermöglichen Blockchiffren zu analysieren, welche eine beliebige Anzahl unabhängiger Teilschlüssel einsetzen und auf Substitutions-Permutations Netzwerken basieren. Diese Methoden werden im Anschluss auf die leichtgewichtigen Blockchiffren LED und PRINCE angewandt und wir zeigen in beiden Fällen wie der komplette geheime Schlüssel mit einigen wenigen Fehlerinjektionen rekonstruiert werden kann. Darüber hinaus untersuchen wir Methoden, die algebraische statt differenzielle Techniken der Fehleranalyse einsetzen und diskutieren deren Vor- und Nachteile. Am Ende des ersten Teils der Dissertation befassen wir uns mit fehlerbasierten Angriffen auf die Blockchiffre Bel-T, welche ebenfalls eine leichtgewichtige Schlüsselexpansion besitzt jedoch nicht auf einem Substitutions-Permutations Netzwerk sondern auf dem sogenannten Lai-Massey Schema basiert. Die oben genannten Techniken können daher bei Bel-T nicht angewandt werden. Nichtsdestotrotz werden wir auch für den Fall von Bel-T Verfahren vorstellen, die in der Lage sind den vollständigen geheimen Schlüssel sehr effizient mit Hilfe von differenzieller Fehleranalyse zu rekonstruieren. Im zweiten Teil der Doktorarbeit beschäftigen wir uns mit authentifizierenden Verschlüsselungsverfahren. Während gewöhnliche Chiffren nur die Vertraulichkeit der verarbeiteten Daten sicherstellen, gewährleisten authentifizierende Verschlüsselungsverfahren auch deren Authentizität und Integrität. Viele dieser Chiffren sind darüber hinaus in der Lage auch die Authentizität und Integrität von sogenannten assoziierten Daten zu gewährleisten. Daten dieses Typs werden in nicht-verschlüsselter Form übertragen, müssen aber dennoch gegen unbefugte Veränderungen auf dem Transportweg geschützt sein. Authentifizierende Verschlüsselungsverfahren bilden heutzutage die Standardtechnologie um Daten während der Übertragung zu beschützen. Aktuell eingesetzte Verfahren weisen jedoch oftmals Defizite auf und es existieren vielfältige Ansatzpunkte für Verbesserungen. Mit NORX stellen wir ein neuartiges authentifizierendes Verschlüsselungsverfahren vor, welches assoziierte Daten unterstützt. Dieser Algorithmus wurde vor allem im Hinblick auf Einsatzgebiete mit hohen Sicherheitsanforderungen, Effizienz in Hardware und Software, Einfachheit, und Robustheit gegenüber Seitenkanalangriffen entwickelt. Neben der Spezifikation präsentieren wir besondere Eigenschaften, angestrebte Sicherheitsziele, Details zur Implementierung, umfassende Performanz-Messungen und diskutieren Vorteile gegenüber aktuellen Standards. Schließlich stellen wir Ergebnisse unserer vorläufigen Sicherheitsanalyse vor, bei der wir uns vor allem auf differenzielle Merkmale und Rotationseigenschaften von NORX konzentrieren. Erwähnenswert sind dabei vor allem die für die differenzielle Kryptoanalyse von NORX entwickelten Techniken, die auf die Effizienz von SAT- und SMT-Solvern zurückgreifen und das Potential besitzen relativ einfach auch auf andere Verschlüsselungsverfahren übertragen werden zu können. KW - cryptography KW - cryptanalysis KW - authenticated encryption KW - NORX KW - fault-based attacks KW - Kryptologie KW - Computersicherheit Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-3319 ER - TY - THES A1 - Ruppert, Julia T1 - Asymptotic Expansion for the Time Evolution of the Probability Distribution Given by the Brownian Motion on Semialgebraic Sets N2 - In this thesis, we examine whether the probability distribution given by the Brownian Motion on a semialgebraic set is definable in an o-minimal structure and we establish asymptotic expansions for the time evolution. We study the probability distribution as an example for the occurrence of special parameterized integrals of a globally subanalytic function and the exponential function of a globally subanalytic function. This work is motivated by the work of Comte, Lion and Rolin, which considered parameterized integrals of globally subanalytic functions, of Cluckers and Miller, which examined parameterized integrals of constructible functions, and by the work of Cluckers, Comte, Miller, Rolin and Servi, which treated oscillatory integrals of globally subanalytic functions. In the one dimensional case we show that the probability distribution on a family of sets, which are definable in an o-minimal structure, are definable in the Pfaffian closure. In the two-dimensional case we investigate asymptotic expansions for the time evolution. As time t approaches zero, we show that the integrals behave like a Puiseux series, which is not necessarily convergent. As t tends towards infinity, we show that the probability distribution is definable in the expansion of the real ordered field by all restricted analytic functions if the semialgebraic set is bounded. For this purpose, we apply results for parameterized integrals of globally subanalytic functions of Lion and Rolin. By establishing the asymptotic expansion of the integrals over an unbounded set, we demonstrate that this expansion has the form of convergent Puiseux series with negative exponents and their logarithm. Subsequently, we get that the asymptotic expansion is definable in an o-minimal structure. Finally, we study the three-dimensional case and give the proof that the probability distribution given by the Brownian Motion behaves like a Puiseux series as time t tends towards zero. As t approaches infinity and the semialgebraic set is bounded, it can be ascertained that the probability distribution has the form of a constructible function by results of Cluckers and Miller and therefore it is definable in an o-minimal structure. If the semialgebraic set is unbounded, we establish the asymptotic expansions and prove that the probability distribution given by the Brownian Motion on unbounded sets has an asymptotic expansion of the form of a constructible function. In consequence of that, the asymptotic expansion is definable in an o-minimal structure. KW - o-minimality KW - asymptotic expansions KW - globally subanalytic sets KW - exponential parameterized integrals KW - Brownian Motion KW - Brownsche Bewegung KW - O-Minimalität KW - Asymptotische Entwicklung Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-5069 ER - TY - THES A1 - Boshe, Patricia T1 - Data Protection Legal Reforms in Africa N2 - This work illustrates reform approaches in Africa using an international legal comparative approach. The research uses Tanzania and Senegal as the primary case studies and France, the United Kingdom and Germany as secondary case studies to illustrate how Europe reformed data protection regimes through the transposition of the EU Data Protection Directive of 1995. Chapter one introduces the work; explaining the forces towards data protection regulations and their basis. Chapter two provides for a ‘back-to-back' comparison in three countries (France, Germany and United Kingdom) against the 1995 Data Protection Directive. The idea behind this chapter is to draw a picture on how the legal culture and the pre-existing notions of the right to privacy inform on data protection legal reforms and determines the nature, contents, context and interpretation of adopted regime for data protection. Eventually, all these aspects affect the nature and extent of protection offered regardless of the substance of the law adopted. Chapter three gives a narrative explanation of nature and perceptions of the right to privacy in Africa and how this may affect data protection reforms in Africa. In the same disposition, African customary legal systems and practices are explained providing a reader with a picture of the overall nature of African systems that makes up an African legal culture. The overview of African privacy perception and legal system is necessary for assessing the workability of any data protection regime to be adopted in Africa which in effect answers the first research question. The chapter draws its rationale from chapter two. In understanding African perceptions of privacy and the African legal culture, one can be able to predict the content and context of the reforms and maybe how the judiciary might interpret the laws based on local perceptions and supporting systems. An overview of the African data protection architecture or rather human right architecture is provided in chapter four; ideally to provide a reader with a picture of the enforcement systems in Africa as a continent. This is followed by chapter five discussing the two major legal systems in Africa; the civil law and the common law system. The chapter also illustrates the position of African landscape in relation to legal harmonization/unification. This aspect is considered necessary because data protection regimes are more focused on legal harmonization and hence the question of how well or to what extent Africa as a continent can bring about harmonization in law became inevitable. Eventually, the chapter offers a comparative mirror analysis of the primary case studies, i.e. Senegal and Tanzania. The analysis is made on the reform approach taken, motivation behind the reforms and on the regime erected (this is done through textual analysis of the law and the draft bill respectively). Chapter six concludes the work by answering research questions based on findings and scrutiny from each chapter. It is concluded that there is a very slim chance for the African States to cling on the cultural defence against the adoption of the Western frameworks for data protection. It is also concluded that, lest Africa becomes an active participant in the global process that informs on data protection challenges and regulations, it faces a danger of becoming a puppet of foreign data protection regulation, which may or may not fit African legal culture. The chapter also illustrates how Africa as a continent and the African States individually have taken up data protection reforms blindly. The motivations for the reforms are vaguely stated and unclear. In the majority of legal instruments, the reforms are not taken as a move towards securing and protecting individual rights rather a purely political move influenced by economic motivations. The reforms are to a large extent, a mere impression to align with global data protection regimes and hence lack the political will to enforce the laws. KW - Data Protection Reforms KW - African Privacy KW - African Legal Reforms KW - African Privacy KW - Data Protection Africa Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-5147 ER - TY - THES A1 - Reislhuber, Josef T1 - Optical Graph Recognition N2 - Graphs are an important model for the representation of structural information between objects. One identifies objects and nodes as well as a binary relation between objects and edges. Graphs have many uses, e. g., in social sciences, life sciences and engineering. There are two primary representations: abstract and visual. The abstract representation is well suited for processing graphs by computers and is given by an adjacency list, an adjacency matrix or any abstract data structure. A visual representation is used by human users who prefer a picture. Common terms are diagram, scheme, plan, or network. The objective of Graph Drawing is to transform a graph into a visual representation called the drawing of a graph. The goal is a “nice” drawing. In this thesis we introduce Optical Graph Recognition. Optical Graph Recognition (OGR) reverses Graph Drawing and transforms a digital image of a graph into an abstract representation. Our approach consists of four phases: Preprocessing where we determine which pixels of an image are part of the graph, Segmentation where we recognize the nodes, Topology Recognition where we detect the edges and Postprocessing where we enrich the recognized graph with additional information. We apply established digital image processing methods and make use of the special property that the image contains nodes that are connected by edges. We have focused on developing algorithms that need as little parameters as possible or to automatically calibrate the parameters. Most false recognition results are caused by crossing edges as this makes tracing the edges difficult and can lead to other recognition errors. We have evaluated hand-drawn and computer-drawn graphs. Our algorithms have a very high recognition rate for computer-drawn graphs, e. g., from a set of 100000 computer-drawn graphs over 90% were correctly recognized. Most false recognition results where observed for hand-drawn graphs as they can include drawing errors and inaccuracies. For universal usability we have implemented a prototype called OGRup for mobile devices like smartphones or tablet computers. With our software it is possible to directly take a picture of a graph via a built in camera, recognize the graph, and then use the result for further processing. Furthermore, in order to gain more insight into the way a person draws a graph by hand, we have conducted a field study. KW - Bildverarbeitung KW - Graphenzeichnen Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-5159 ER - TY - THES A1 - de Ponte Müller, Fabian T1 - Cooperative Relative Positioning for Vehicular Environments N2 - Fahrerassistenzsysteme sind ein wesentlicher Baustein zur Steigerung der Sicherheit im Straßenverkehr. Vor allem sicherheitsrelevante Applikationen benötigen eine genaue Information über den Ort und der Geschwindigkeit der Fahrzeuge in der unmittelbaren Umgebung, um mögliche Gefahrensituationen vorherzusehen, den Fahrer zu warnen oder eigenständig einzugreifen. Repräsentative Beispiele für Assistenzsysteme, die auf eine genaue, kontinuierliche und zuverlässige Relativpositionierung anderer Verkehrsteilnehmer angewiesen sind, sind Notbremsassitenten, Spurwechselassitenten und Abstandsregeltempomate. Moderne Lösungsansätze benutzen Umfeldsensorik wie zum Beispiel Radar, Laser Scanner oder Kameras, um die Position benachbarter Fahrzeuge zu schätzen. Dieser Sensorsysteme gemeinsame Nachteile sind deren limitierte Erfassungsreichweite und die Notwendigkeit einer direkten und nicht blockierten Sichtlinie zum Nachbarfahrzeug. Kooperative Lösungen basierend auf einer Fahrzeug-zu-Fahrzeug Kommunikation können die eigene Wahrnehmungsreichweite erhöhen, in dem Positionsinformationen zwischen den Verkehrsteilnehmern ausgetauscht werden. In dieser Dissertation soll die Möglichkeit der kooperativen Relativpositionierung von Straßenfahrzeugen mittels Fahrzeug-zu-Fahrzeug Kommunikation auf ihre Genauigkeit, Kontinuität und Robustheit untersucht werden. Anstatt die in jedem Fahrzeug unabhängig ermittelte Position zu übertragen, werden in einem neuartigem Ansatz GNSS-Rohdaten, wie Pseudoranges und Doppler-Messungen, ausgetauscht. Dies hat den Vorteil, dass sich korrelierte Fehler in beiden Fahrzeugen potentiell herauskürzen. Dies wird in dieser Dissertation mathematisch untersucht, simulativ modelliert und experimentell verifiziert. Um die Zuverlässigkeit und Kontinuität auch in "gestörten" Umgebungen zu erhöhen, werden in einem Bayesischen Filter die GNSS-Rohdaten mit Inertialsensormessungen aus zwei Fahrzeugen fusioniert. Die Validierung des Sensorfusionsansatzes wurde im Rahmen dieser Dissertation in einem Verkehrs- sowie in einem GNSS-Simulator durchgeführt. Zur experimentellen Untersuchung wurden zwei Testfahrzeuge mit den verschiedenen Sensoren ausgestattet und Messungen in diversen Umgebungen gefahren. In dieser Arbeit wird gezeigt, dass auf Autobahnen, die Relativposition eines anderen Fahrzeugs mit einer Genauigkeit von unter einem Meter kontinuierlich geschätzt werden kann. Eine hohe Zuverlässigkeit in der longitudinalen und lateralen Richtung können erzielt werden und das System erweist 90% der Zeit eine Unsicherheit unter 2.5m. In ländlichen Umgebungen wächst die Unsicherheit in der relativen Position. Mit Hilfe der on-board Sensoren können Fehler bei der Fahrt durch Wälder und Dörfer korrekt gestützt werden. In städtischen Umgebungen werden die Limitierungen des Systems deutlich. Durch die erschwerte Schätzung der Fahrtrichtung des Ego-Fahrzeugs ist vor Allem die longitudinale Komponente der Relativen Position in städtischen Umgebungen stark verfälscht. N2 - Advanced driver assistance systems play an important role in increasing the safety on today's roads. The knowledge about the other vehicles' positions is a fundamental prerequisite for numerous safety critical applications, making it possible to foresee critical situations, warn the driver or autonomously intervene. Forward collision avoidance systems, lane change assistants or adaptive cruise control are examples of safety relevant applications that require an accurate, continuous and reliable relative position of surrounding vehicles. Currently, the positions of surrounding vehicles is estimated by measuring the distance with e.g. radar, laser scanners or camera systems. However, all these techniques have limitations in their perception range, as all of them can only detect objects in their line-of-sight. The limited perception range of today's vehicles can be extended in future by using cooperative approaches based on Vehicle-to-Vehicle (V2V) communication. In this thesis, the capabilities of cooperative relative positioning for vehicles will be assessed in terms of its accuracy, continuity and reliability. A novel approach where Global Navigation Satellite System (GNSS) raw data is exchanged between the vehicles is presented. Vehicles use GNSS pseudorange and Doppler measurements from surrounding vehicles to estimate the relative positioning vector in a cooperative way. In this thesis, this approach is shown to outperform the absolute position subtraction as it is able to effectively cancel out common errors to both GNSS receivers. This is modeled theoretically and demonstrated empirically using simulated signals from a GNSS constellation simulator. In order to cope with GNSS outages and to have a sufficiently good relative position estimate even in strong multipath environments, a sensor fusion approach is proposed. In addition to the GNSS raw data, inertial measurements from speedometers, accelerometers and turn rate sensors from each vehicle are exchanged over V2V communication links. A Bayesian approach is applied to consider the uncertainties inherently to each of the information sources. In a dynamic Bayesian network, the temporal relationship of the relative position estimate is predicted by using relative vehicle movement models. Also real world measurements in highway, rural and urban scenarios are performed in the scope of this work to demonstrate the performance of the cooperative relative positioning approach based on sensor fusion. The results show that the relative position of another vehicle towards the ego vehicle can be estimated with sub-meter accuracy in highway scenarios. Here, good reliability and 90% availability with an uncertainty of less than 2.5m is achieved. In rural environments, drives through forests and towns are correctly bridged with the support of on-board sensors. In an urban environment, the difficult estimation of the ego vehicle heading has a mayor impact in the relative position estimate, yielding large errors in its longitudinal component. KW - Fahrerassistenzsystem Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-5411 ER - TY - RPRT A1 - Heinrich, Horst-Alfred T1 - Test of different structural equation models describing the relationship between nationalism, patriotism, and anti-immigration attitudes: documentation of an empirical study N2 - This paper aims at the documentation of the results of a study dealing with the relationship between in-group and out-group attitudes. The research enquires into the question whether nationalistic, patriotic, and anti-immigration attitudes are only correlated with each other or whether there is a causal relationship. The presentation of the Mplus output together with the correlation and covariance matrices will allow the readers to control the results and, if they want to do it, to test alternative models. KW - Nationalismus KW - Nationale Identität KW - Ausländerfeindlichkeit KW - Patriotismus KW - Strukturgleichungsmodell KW - Theorietest Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-5502 ER - TY - THES A1 - Hanauer, Kathrin T1 - Linear Orderings of Sparse Graphs N2 - The Linear Ordering problem consists in finding a total ordering of the vertices of a directed graph such that the number of backward arcs, i.e., arcs whose heads precede their tails in the ordering, is minimized. A minimum set of backward arcs corresponds to an optimal solution to the equivalent Feedback Arc Set problem and forms a minimum Cycle Cover. Linear Ordering and Feedback Arc Set are classic NP-hard optimization problems and have a wide range of applications. Whereas both problems have been studied intensively on dense graphs and tournaments, not much is known about their structure and properties on sparser graphs. There are also only few approximative algorithms that give performance guarantees especially for graphs with bounded vertex degree. This thesis fills this gap in multiple respects: We establish necessary conditions for a linear ordering (and thereby also for a feedback arc set) to be optimal, which provide new and fine-grained insights into the combinatorial structure of the problem. From these, we derive a framework for polynomial-time algorithms that construct linear orderings which adhere to one or more of these conditions. The analysis of the linear orderings produced by these algorithms is especially tailored to graphs with bounded vertex degrees of three and four and improves on previously known upper bounds. Furthermore, the set of necessary conditions is used to implement exact and fast algorithms for the Linear Ordering problem on sparse graphs. In an experimental evaluation, we finally show that the property-enforcing algorithms produce linear orderings that are very close to the optimum and that the exact representative delivers solutions in a timely manner also in practice. As an additional benefit, our results can be applied to the Acyclic Subgraph problem, which is the complementary problem to Feedback Arc Set, and provide insights into the dual problem of Feedback Arc Set, the Arc-Disjoint Cycles problem. KW - directed graph KW - graph algorithms KW - feedback arc set KW - linear ordering KW - cycle cover KW - Graphentheorie KW - Lineares Ordnungsproblem KW - Schwach besetzte Matrix Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-5524 ER - TY - INPR A1 - Lucke, Robin Jan T1 - How Securitization Theory Can Benefit from Psychology Findings N2 - Securitization Theory has been applied and advanced continuously since the publication of the seminal work “Security – A New Framework for Analysis” by Buzan et al. in 1998. Various extensions, clarifications and definitions have been added over the years. Ontological and epistemological debates as well as debates about the normativity of the concept have taken place, furthering the approach incrementally and adapting it to new empirical cases. This paper aims at contributing to the improvement of the still useful framework in a more general way by amending it with well-established findings from another discipline: Psychology. The exploratory article will point out what elements of Securitization Theory might benefit most from incorporating insights from Psychology and in which ways they might change our understanding of the phenomenon. Some well-studied phenomena in the field of (Social) Psychology, it is argued here, play an important role for the construction and perception of security threats and the acceptance of the audience to grant the executive branch extraordinary measures to counter these threats: availability heuristic, loss-aversion and social identity theory are central psychological concepts that can help us to better understand how securitization works, and in which situations securitizing moves have great or little chances to reverberate. The empirical cases of the 9/11 and Paris terror attacks will serve to illustrate the potential of this approach, allowing for variances in key factors, among them: (point in) time, system of government and ideological orientation. As a hypotheses-generating pilot study, the paper will conclude by discussing further research possibilities in the field of Securitization. KW - Securitization KW - Psychology KW - Copenhagen School KW - Security Studies KW - Securitization Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-6216 ER - TY - THES A1 - Seidler, Anna-Raissa T1 - Changing for the Better? Essays on the Role of Institutional Logics and Information System in Organizational Sustainability Transformations N2 - An increasing number of companies report that eco-sustainable initiatives have a positive impact on firms’ economic performance and concurrently allow the combination of social and commercial goals by optimizing environmental and economic decisions simultaneously. These initiatives are considered an integral part of organizational sustainability transformations, which are a special case of multilayered, complex organizational change efforts that relate to environmental, organizational, and individual factors. Institutional logics and information systems (IS) have shown to be two important perspectives from which to explore mechanisms and processes central to organizational sustainability transformations. Institutional logics offer a unique perspective to investigate organizational change for sustainability because they provide a new approach to organizational change that incorporates macro structures, culture, and agency to explain how actions are enabled or constrained. It thus allows for insights into the complex and miscellaneous interplay of external and internal determinants that govern organizational transformation processes towards sustainability. By providing insights into institutional changes of practice and behaviors, an institutional logic perspective allows for a detailed analysis of organizational transformations. Within these change processes, IS have shown to be an efficient and pervasive tool to leverage sustainability by integrating human and technological factors. Since IS have become a key resource for the encouragement of organizational sustainability transformations, adopting an IS perspective allows for an understanding of mechanisms and processes that enable IS to foster sustainability in organizations. Thus, this dissertation draws on four studies by investigateing an institutional logic perspective as well as an IS perspective to explore organizational sustainability transformations and facilitate an in-depth understanding of organizational, human, and technological factors that encourage sustainability in organizational transformations. KW - Institutional Logics KW - Information Systems KW - Organizational Sustainability Transformations KW - Organizational Change KW - Informationssystem KW - Organisationswandel Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-6330 ER - TY - THES A1 - Kell, Christian T1 - A Structure-based Attack on the Linearized Braid Group-based Diffie-Hellman Conjugacy Problem in Combination with an Attack using Polynomial Interpolation and the Chinese Remainder Theorem N2 - This doctoral thesis is dedicated to improve a linear algebra attack on the so-called braid group-based Diffie-Hellman conjugacy problem (BDHCP). The general procedure of the attack is to transform a BDHCP to the problem of solving several simultaneous matrix equations. A first improvement is achieved by reducing the solution space of the matrix equations to matrices that have a specific structure, which we call here the left braid structure. Using the left braid structure the number of matrix equations to be solved reduces to one. Based on the left braid structure we are further able to formulate a structure-based attack on the BDHCP. That is to transform the matrix equation to a system of linear equations and exploiting the structure of the corresponding extended coefficient matrix, which is induced by the left braid structure of the solution space. The structure-based attack then has an empirically high probability to solve the BDHCP with significantly less arithmetic operations than the original attack. A third improvement of the original linear algebra attack is to use an algorithm that combines Gaussian elimination with integer polynomial interpolation and the Chinese remainder theorem (CRT), instead of fast matrix multiplication as suggested by others. The major idea here is to distribute the task of solving a system of linear equations over a giant finite field to several much smaller finite fields. Based on our empirically measured bounds for the degree of the polynomials to be interpolated and the bit size of the coefficients and integers to be recovered via the CRT, we conclude an improvement of the run time complexity of the original algorithm by a factor of n^8 bit operations in the best case, and still n^6 in the worst case. KW - Linear algebra attack KW - Braid group-based cryptography KW - Row echelon form calculation using polynomial interpolation and the chinese remainder theorem KW - Diffie-Hellman conjugacy problem KW - Kryptologie KW - Zopfgruppe KW - Diffie-Hellman-Algorithmus Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-6476 ER - TY - THES A1 - Mosch, Philipp T1 - Four Essays on Digital Transformation Strategies from the Perspectives of Capital Markets, Incumbents and Start-ups N2 - This dissertation uses four studies to examine the context-contingent strategic factors that are critical to the success of digital transformation strategies from the perspectives of capital markets, incumbents, and start-ups. It focuses on a better understanding of (1) digital innovations and their quantitative evaluation, (2) power disruptions in digitally servitized supply chains, (3) strategic measures and dynamics in digital B2B platform markets, and (4) strategizing by data-driven start-ups in digitalized business networks. Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-11337 ER - TY - THES A1 - Grösbrink, Carl-Friederich T1 - Three Essays on Firm Value and Firm Risk and their Relation to IT-Exposure, Corporate Social Responsibility, and Religiosity N2 - 1. IT-Exposure and Firm Value: We analyze the joint influence of a firm’s information technology (IT)-Exposure and investment behavior on firm value. Estimating a firm’s (partial) IT-Exposure allows for distinguishing between firms with a business model that is challenged by IT above and below market average. Hence, we estimate the annual IT-Exposure of a firm using a 3-factor Fama-French model extended by an IT-proxy. Subsequently, we analyze the relationship with Tobin’s Q in a panel data context, accounting for the relationship between IT-Exposure and investments proxied by R&D as well as CapEx. We use more than 48,000 firm-year observations for firms in the Russell 3000 Index covering the period 1990 to 2018. Although IT-Exposure has a negative impact on firm value, this discount can be overcompensated by up to 2.1 times by sufficient investments through R&D and CapEx, giving a firm with an average Tobin’s Q a premium of 14.8% to 19.2%, while controlling for endogeneity. 2. Corporate Social Responsibility, Risk, and Firm Value: An Unconditional Quantile Regression Approach: This paper examines the impact of corporate social responsibility (CSR) on firm risk, comprising total risk, idiosyncratic risk, and systematic risk, as well as firm value. We focus on analyzing the interrelationships along the entire distribution of the dependent variables, thus estimating an unconditional quantile regression (UQR). The analysis is based on CSR scores from Refinitiv and MSCI, using up to 12,013 firm-year observations over the period 2002 to 2019 for all U.S. companies listed on NYSE, NASDAQ, and AMEX. UQR reveals strongly heterogeneous effects along the unconditional quantiles of the dependent variables, which are reflected in sign changes, magnitude and significance variations. For CSR we find a risk-reducing as well as value-enhancing effect. When applying fixed effects OLS, we can just partly confirm the risk-reducing and value-enhancing effect of CSR shown in the literature. 3. Heterogenous Effects of Religiosity on Firm Risk and Firm Value: An Unconditional Quantile Regression Approach: This paper examines the impact of religiosity on firm risk, comprising total risk, idiosyncratic risk, and systematic risk, as well as firm value. We focus on analyzing the interrelationships along the entire distribution of the dependent variables, thus estimating an unconditional quantile regression (UQR). The analysis is based on all U.S. companies listed on NYSE, NASDAQ, and AMEX for the period from 1980 through 2020. UQR reveals strongly heterogeneous effects along the unconditional quantiles of the dependent variables, which are reflected in sign changes, magnitude and significance variations. Overall, the risk-reducing effect of religiosity is more pronounced in the higher quantiles of the distribution. We further observe a value-reducing as well as value-enhancing religiosity effect. When applying fixed effects OLS, we can confirm the risk-reducing and non-existing value effect of religiosity shown in the literature. The robustness of our results is underpinned by a battery of additional tests. KW - Firm Value KW - Firm Risk KW - IT-Exposure KW - Corporate Social Responsibility KW - Religiosity Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-11558 ER - TY - THES A1 - Seruset, Marco T1 - Three Essays on Price Discovery, Stock Liquidity, and Crash Risk N2 - Abstract 1: This paper investigates whether market quality, uncertainty, investor sentiment and attention, and macroeconomic news affect bitcoin price discovery in spot and futures markets. Over the period December 2017 – March 2019, we find significant time variation in the contribution to price discovery of the two markets. Increases in price discovery are mainly driven by relative trading costs and volume, and by uncertainty to a lesser extent. Additionally, medium-sized trades contain most information in terms of price discovery. Finally, higher news-based bitcoin sentiment increases the informational role of the futures market, while attention and macroeconomic news have no impact on price discovery. Abstract 2: We investigate whether local religious norms affect stock liquidity for U.S. listed companies. Over the period 1997–2020, we find that firms located in more religious areas have higher liquidity, as reflected by lower bid-ask spreads. This result persists after the inclusion of additional controls, such as governance metrics, and further sensitivity and endogeneity analyses. Subsample tests indicate that the impact of religiosity on stock liquidity is particularly evident for firms operating in a poor information environment. We further show that firms located in more religious areas have lower price impact of trades and smaller probability of information-based trading. Overall, our findings are consistent with the notion that religiosity, with its antimanipulative ethos, probably fosters trust in corporate actions and information flows, especially when little is known about the firm. Finally, we conjecture an indirect firm value implication of religiosity through the channel of stock liquidity. Abstract 3: This study shows that higher physical distance to institutional shareholders is associated with higher stock price crash risk. Since monitoring costs increase with distance, the results are consistent with the monitoring theory of local institutional investors. Cross-sectional analyses show that the effect of proximity on crash risk is more pronounced for firms with weak internal governance structures. The significant relation between distance and crash risk still holds under the implementation of the Sarbanes-Oxley Act, however, to a lower extent. Also, the existence of the channel of bad news hoarding is confirmed. Finally, I show that there is heterogeneity in distance-induced monitoring activities of different types of institutions. Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-11563 ER - TY - THES A1 - Lehner, Sabrina T1 - The Asymptotic Behaviour of the Riemann Mapping Function at Analytic Cusps N2 - The well-known Riemann Mapping Theorem states the existence of a conformal map of a simply connected proper domain of the complex plane onto the upper half plane. One of the main topics in geometric function theory is to investigate the behaviour of the mapping functions at the boundary of such domains. In this work, we always assume that a piecewise analytic boundary is given. Hereby, we have to distinguish regular and singular boundary points. While the asymptotic behaviour for regular boundary points can be investigated by using the Schwarz Reflection at analytic arcs, the situation for singular boundary points is far more complicated. In the latter scenario two cases have to be differentiated: analytic corners and analytic cusps. The first part of the thesis deals with the asymptotic behaviour at analytic corners where the opening angle is greater than 0. The results of Lichtenstein and Warschawski on the asymptotic behaviour of the Riemann map and its derivatives at an analytic corner are presented as well as the much stronger result of Lehman that the mapping function can be developed in a certain generalised power series which in turn enables to examine the o-minimal content of the Riemann Mapping Theorem. To obtain a similar statement for domains with analytic cusps, it is necessary to investigate the asymptotic behaviour of a Riemann map at the cusp and based on this result to determine the asymptotic power series expansion. Therefore, the aim of the second part of this work is to investigate the asymptotic behaviour of a Riemann map at an analytic cusp. A simply connected domain has an analytic cusp if the boundary is locally given by two analytic arcs such that the interior angle vanishes. Besides the asymptotic behaviour of the mapping function, the behaviour of its derivatives, its inverse, and the derivatives of the inverse are analysed. Finally, we present a conjecture on the asymptotic power series expansion of the mapping function at an analytic cusp. N2 - Der wohlbekannte Riemannsche Abbildungssatz liefert die Existenz einer konformen Abbildung eines einfach zusammenhängenden, echten Teilgebietes der komplexen Ebene auf die obere Halbebene. Die Untersuchung des Verhaltens solcher Abbildungen am Rand der Gebiete ist ein zentrales Thema der geometrischen Funktionentheorie. In der vorliegenden Arbeit gehen wir stets von einem stückweise analytischen Rand aus. Dabei müssen wir reguläre und singuläre Randpunkte unterscheiden. Während das Verhalten einer Riemann-Abbildung an regulären Randpunkten mit Hilfe des Schwarzschen Spiegelungsprinzips an analytischen Kurvenbögen einfach zu bestimmen ist, gestaltet sich dies in der Situation von singulären Randpunkten sehr viel komplizierter. In diesem Fall müssen wir erneut eine Unterscheidung treffen, nämlich ob es sich um eine analytische Ecke oder eine analytische Spitze handelt. Der erste Teil der Dissertation beschäftigt sich mit dem asymptotischen Verhalten einer Riemann-Abbildung an analytischen Ecken. Eine solche liegt vor, falls der Öffnungswinkel zwischen den analytischen Kurvenstücken an dem singulären Randpunkt größer als 0 ist. Es werden die Ergebnisse von Lichtenstein und Warschawski präsentiert, die sich mit dem Verhalten der Riemann-Abbildung und deren Ableitungen beschäftigt haben, sowie das stärkere Ergebnis von Lehman welches besagt, dass die Abbildung in eine verallgemeinerte Potenzreihe entwickelt werden kann. Unter Verwendung dieses Resultats konnte bereits der o-minimale Gehalt des Riemannschen Abbildungssatzes untersucht werden. Um ein ähnliches Ergebnis für den Fall, dass das Gebiet analytische Spitzen hat, zu erhalten, benötigen wir zunächst das asymptotische Verhalten der Riemann-Abbildung an einer Spitze. Darauf aufbauend kann die asymptotische Reihenentwicklung untersucht werden. Daher zielt der zweite Abschnitt dieser Arbeit darauf ab, das Verhalten der Abbildung an einer Spitze zu bestimmen. Dabei sprechen wir von einer analytischen Spitze, wenn der Rand des Gebietes lokal durch zwei reguläre analytische Bögen gegeben ist, deren Öffnungswinkel verschwindet. Neben dem asymptotischen Verhalten der Abbildung wird auch das Verhalten der Ableitungen, ihrer Umkehrfunktion und deren Ableitungen untersucht. Abschließend präsentieren wir eine Vermutung über die asymptotische Reihenentwicklung der Abbildung an einer analytischen Spitze. KW - Riemann mapping theorem KW - analytic cusp KW - asymptotic behaviour KW - boundary behaviour KW - Geometrische Funktionentheorie KW - Randverhalten KW - Riemannscher Abbildungssatz Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-3587 ER - TY - THES A1 - Petit, Albin T1 - Introducing Privacy in Current Web Search Engines N2 - During the last few years, the technological progress in collecting, storing and processing a large quantity of data for a reasonable cost has raised serious privacy issues. Privacy concerns many areas, but is especially important in frequently used services like search engines (e.g., Google, Bing, Yahoo!). These services allow users to retrieve relevant content on the Internet by exploiting their personal data. In this context, developing solutions to enable users to use these services in a privacy-preserving way is becoming increasingly important. In this thesis, we introduce SimAttack an attack against existing protection mechanism to query search engines in a privacy-preserving way. This attack aims at retrieving the original user query. We show with this attack that three representative state-of-the-art solutions do not protect the user privacy in a satisfactory manner. We therefore develop PEAS a new protection mechanism that better protects the user privacy. This solution leverages two types of protection: hiding the user identity (with a succession of two nodes) and masking users' queries (by combining them with several fake queries). To generate realistic fake queries, PEAS exploits previous queries sent by the users in the system. Finally, we present mechanisms to identify sensitive queries. Our goal is to adapt existing protection mechanisms to protect sensitive queries only, and thus save user resources (e.g., CPU, RAM). We design two modules to identify sensitive queries. By deploying these modules on real protection mechanisms, we establish empirically that they dramatically improve the performance of the protection mechanisms. KW - Privacy KW - Search Engine KW - Unlinkability KW - Indistinguishability KW - Suchmaschine KW - Datensicherung KW - Computersicherheit KW - Privatsphäre Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-4652 ER - TY - THES A1 - Kriegl, Markus T1 - Generalizations and Applications of Border Bases N2 - This doctoral thesis is devoted to generalize border bases to the module setting and to apply them in various ways. First, we generalize the theory of border bases to finitely generated modules over a polynomial ring. We characterize these generalized border bases and show that we can compute them. As an application, we are able to characterize subideal border bases in various new ways and give a new algorithm for their computation. Moreover, we prove Schreyer's Theorem for border bases of submodules of free modules of finite rank over a polynomial ring. In the second part of this thesis, we study the effect of homogenization to border bases of zero-dimensional ideals. This yields the new concept of projective border bases of homogeneous one-dimensional ideals. We show that there is a one-to-one correspondence between projective border bases and zero-dimensional closed subschemes of weighted projective spaces that have no point on the hyperplane at infinity. Applying that correspondence, we can characterize uniform zero-dimensional closed subschemes of weighted projective spaces that have a rational support over the base field in various ways. Finally, we introduce projective border basis schemes as specific subschemes of border basis schemes. We show that these projective border basis schemes parametrize all zero-dimensional closed subschemes of a weighted projective space whose defining ideals possess a projective border basis. Assuming that the base field is algebraically closed, we are able to prove that the set of all closed points of a projective border basis scheme that correspond to a uniform subscheme is a constructive set with respect to the Zariski topology. KW - (generalized) border bases KW - Schreyer's theorem KW - weighted projective spaces KW - zero-dimensional projective schemes KW - uniformity conditions Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:739-opus4-3628 ER -