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Multimedia retrieval is an essential part of today's world. This situation is observable in industrial domains, e.g., medical imaging, as well as in the private sector, visible by activities in manifold Social Media platforms. This trend led to the creation of a huge environment of multimedia information retrieval services offering multimedia resources for almost any user requests. Indeed, the encompassed data is in general retrievable by (proprietary) APIs and query languages, but unfortunately a unified access is not given due to arising interoperability issues between those services. In this regard, this thesis focuses on two application scenarios, namely a medical retrieval system supporting a radiologist's workflow, as well as an interoperable image retrieval service interconnecting diverse data silos. The scientific contribution of this dissertation is split in three different parts: the first part of this thesis improves the metadata interoperability issue. Here, major contributions to a community-driven, international standardization have been proposed leading to the specification of an API and ontology to enable a unified annotation and retrieval of media resources. The second part issues a metasearch engine especially designed for unified retrieval in distributed and heterogeneous multimedia retrieval environments. This metasearch engine is capable of being operated in a federated as well as autonomous manner inside the aforementioned application scenarios. The remaining third part ensures an efficient retrieval due to the integration of optimization techniques for multimedia retrieval in the overall query execution process of the metasearch engine.
This thesis addresses some of the algorithmic and numerical challenges associated with the computation of approximate border bases, a generalisation of border bases, in the context of the oil and gas industry. The concept of approximate border bases was introduced by D. Heldt, M. Kreuzer, S. Pokutta and H. Poulisse in "Approximate computation of zero-dimensional polynomial ideals" as an effective mean to derive physically relevant polynomial models from measured data. The main advantages of this approach compared to alternative techniques currently in use in the (hydrocarbon) industry are its power to derive polynomial models without additional a priori knowledge about the underlying physical system and its robustness with respect to noise in the measured input data. The so-called Approximate Vanishing Ideal (AVI) algorithm which can be used to compute approximate border bases and which was also introduced by D. Heldt et al. in the paper mentioned above served as a starting point for the research which is conducted in this thesis. A central aim of this work is to broaden the applicability of the AVI algorithm to additional areas in the oil and gas industry, like seismic imaging and the compact representation of unconventional geological structures. For this purpose several new algorithms are developed, among others the so-called Approximate Buchberger Möller (ABM) algorithm and the Extended-ABM algorithm. The numerical aspects and the runtime of the methods are analysed in detail - based on a solid foundation of the underlying mathematical and algorithmic concepts that are also provided in this thesis. It is shown that the worst case runtime of the ABM algorithm is cubic in the number of input points, which is a significant improvement over the biquadratic worst case runtime of the AVI algorithm. Furthermore, we show that the ABM algorithm allows us to exercise more direct control over the essential properties of the computed approximate border basis than the AVI algorithm. The improved runtime and the additional control turn out to be the key enablers for the new industrial applications that are proposed here. As a conclusion to the work on the computation of approximate border bases, a detailed comparison between the approach in this thesis and some other state of the art algorithms is given. Furthermore, this work also addresses one important shortcoming of approximate border bases, namely that central concepts from exact algebra such as syzygies could so far not be translated to the setting of approximate border bases. One way to mitigate this problem is to construct a "close by" exact border bases for a given approximate one. Here we present and discuss two new algorithmic approaches that allow us to compute such close by exact border bases. In the first one, we establish a link between this task, referred to as the rational recovery problem, and the problem of simultaneously quasi-diagonalising a set of complex matrices. As simultaneous quasi-diagonalisation is not a standard topic in numerical linear algebra there are hardly any off-the-shelf algorithms and implementations available that are both fast and numerically adequate for our purposes. To bridge this gap we introduce and study a new algorithm that is based on a variant of the classical Jacobi eigenvalue algorithm, which also works for non-symmetric matrices. As a second solution of the rational recovery problem, we motivate and discuss how to compute a close by exact border basis via the minimisation of a sum of squares expression, that is formed from the polynomials in the given approximate border basis. Finally, several applications of the newly developed algorithms are presented. Those include production modelling of oil and gas fields, reconstruction of the subsurface velocities for simple subsurface geometries, the compact representation of unconventional oil and gas bodies via algebraic surfaces and the stable numerical approximation of the roots of zero-dimensional polynomial ideals.
Contributing to the still scarce European evidence this thesis examines in detail different aspects of equity styles and systematic liquidity in Europe and their role with respect to European stocks and mutual funds. First, a consistent set of European style indices is outlined from which risk factors like market excess return, size, valuation and momentum, but also novel idiosyncratic risk and systematic liquidity factors are derived. The daily 2002 to 2009 time period examined contains the recent financial crisis. As based on a stochastic discount factor GMM based analysis, liquidity is found to help to price European stocks and a decrease in common liquidity during the recent period of market stress reveals the role of liquidity as a state variable of hedging concern to investors. Moreover, the risk factors including liquidity and idiosyncratic risk are found to be relevant in mutual fund performance evaluation as indicated by significant risk exposures of a set of mutual funds with European investment focus. However, regarding different models the risk-adjusted net performance of these funds is mainly found to be indistinguishable from zero, being in line with equilibrium models of fund performance. Furthermore, the dynamic abilities of fund managers with respect to liquidity and risk factor timing are examined by conducting unconditional as well as time-varying analyses based on a Kalman filter approach. The results reveal dynamics in the risk exposures of mutual funds, but evidence on daily risk factor timing is weak with respect to established risk factors as well as liquidity. Finally, the evidence that both liquidity and idiosyncratic risk affect the cross-section of asset returns suggests that both risk factors capture different return characteristics. As motivated by models of price discovery processes, liquidity might capture transaction costs, while idiosyncratic risk seems to capture effects of price discovery.
The dissertation consists of three self-contained essays, with a focus on empirical capital market research. The first essay "Time-Varying Conditional Market Returns: Is Variance or Tail-Risk Priced", empirically investigates the question whether there is a positive relationship between aggregate market tail risk and expected returns. Based on the classical risk return trade-off, intuition suggests a statistically positive relationship between aggregate market tail risk and expected returns. The paper contributes to previous literature in several ways. First it offers an statistically well founded method for aggregate tail risk estimation in relying on EVT. In the second place it empirically determines a positive relationship between lagged aggregate market tail risk and market returns, based on a time-series approach, which can be further characterized by a non-linear dependence structure. The second essay "Credit Cycle Dependent Spread Determinants in Emerging Sovereign Debt Markets", empirically estimates non-linear dependence structures of determinants of changes in sovereign bond spreads. Empirical results of the paper clearly identify a non-linear influence of determinants of changes in emerging markets sovereign credit spreads. The statistical and economical significance as well as the sign of some determinants changes with respect to the underlying sovereign credit cycle. The third paper "Modeling the Dependence Structure between Aggregate Market Tail Risk and Expected Returns" takes on the results of the first paper regarding the non-linear positive dependence structure between aggregate market tail risk and expected returns. In order to implement a more profound analysis of the non-linear pattern, the paper employs several copula functions to model the conditional bivariate time series dependence structure. The inspection of the empirical results clearly indicates the Clayton copula function to provide the best formula describing the conditional dependence structure.
This thesis investigates the suitability of state-of-the-art protocols for large-scale and long-term environmental event monitoring using wireless sensor networks based on the application scenario of early forest fire detection. By suitable combination of energy-efficient protocol mechanisms a novel communication protocol, referred to as cross-layer message-merging protocol (XLMMP), is developed. Qualitative and quantitative protocol analyses are carried out to confirm that XLMMP is particularly suitable for this application area. The quantitative analysis is mainly based on finite-source retrial queues with multiple unreliable servers. While this queueing model is widely applicable in various research areas even beyond communication networks, this thesis is the first to determine the distribution of the response time in this model. The model evaluation is mainly carried out using Markovian analysis and the method of phases. The obtained quantitative results show that XLMMP is a feasible basis to design scalable wireless sensor networks that (1) may comprise hundreds of thousands of tiny sensor nodes with reduced node complexity, (2) are suitable to monitor an area of tens of square kilometers, (3) achieve a lifetime of several years. The deduced quantifiable relationships between key network parameters — e.g., node size, node density, size of the monitored area, aspired lifetime, and the maximum end-to-end communication delay — enable application-specific optimization of the protocol.
Decentralised Service Location, i.e. finding an application communication endpoint based on a Distributed Hash Table (DHT), is a fairly new concept. The precise security implications of this approach have not been studied in detail. More importantly, a detailed analysis regarding the applicability of existing security solutions to this concept has not been conducted. In many cases existing client-server approaches to security may not be feasible. In addition, to understand the necessity for such an analysis, it is key to acknowledge that Decentralised Service Location has some unique security requirements compared to other P2P applications such as filesharing or live streaming. This thesis concerns the security challenges for Decentralised Service Location. The goals of our work are on the one hand to precisely understand the security requirements and research challenges for Decentralised Service Location, and on the other hand to develop and evaluate corresponding security mechanisms. The thesis is organised as follows. First, fundamentals are explained and the scope of the thesis is defined. Decentralised Service Location is defined and P2PSIP is explained technically as a prototypical example. Then, a security analysis for P2PSIP is presented. Based on this security analysis, security requirements for Decentralised Service Location and the corresponding research challenges -- i.e. security concerns not suitably mitigated by existing solutions -- are derived. Second, several decentralised solutions are presented and evaluated to tackle the security challenges for Decentralised Service Location. We present decentralised algorithms to enable availability of the DHTs lookup service in the presence of adversary nodes. These algorithms are evaluated via simulation and compared to analytical bounds. Further, a cryptographic approach based on self-certifying identities is illustrated and discussed. This approach enables decentralised integrity protection of location-bindings. Finally, a decentralised approach to assess unknown identities is introduced. The approach is based on a Web-of-Trust model. It is evaluated via prototypical implementation. Finally, the thesis closes with a summary of the main contributions and a discussion of open issues.
Up to a few years ago, the typical operation of a distributed architecture was modelled as the enactment of a collaborative protocol by networked nodes. In this context, all nodes were under the system designer’s control, faithfully executing the programmed behaviour. However, today’s networks are often characterized by a free aggregation of nodes. Thus, the possibility increases that a selfish party operates a node, which may violate the collaborative protocol in order to increase a personal benefit. If such violations differ from the system goals they can even be considered as attack. Current fault-tolerance techniques may weaken the harmful impact to some degree but they cannot necessarily prevent them. Furthermore, the several architectures differ in their fault-tolerance capabilities. This emphasizes the need for a systematic approach to achieve collaboration in distributed systems. In this PhD thesis we consider the problem of attaining a targeted level of collaboration in a distributed architecture deployed over rational selfish-driven nodes, which have interest in deviating from the communication protocol to increase a personal benefit. In order to reach this goal and to cover a broad spectrum of systems, we do not modify the architecture or communication protocol itself. Instead, we add a monitoring logic to inspect a node’s behaviour in terms of the correct interaction with the system. With this approach, the system designer needs to contrast several aspects such as the specific environmental circumstances, the inspection effort or the node’s individual preferences. Furthermore, he should consider the fact that each agent could be aware of the other agents’ preferences and selfishness, and perform strategic choices consequently. The natural frame for modelling such complex, interdependent and possibly interactive decision landscape is Game Theory (GT). In this context, the monitoring setup proposed in this thesis corresponds to a class of GT models known as Inspection Games (IG). Such games were introduced 1962 in their simplest formulation by Dresher in the context of non-proliferation treatises and arm control. They model the general situation where one inspector verifies through inspections the correct behaviour of another party, called inspectee. However, inspections are costly and the inspector’s resources are limited. Hence, a complete surveillance is not possible and an inspector will try to minimize the inspections. Finally, a game strategy combination (violating/inspecting or not) that is considered optimal by the parties represents a Nash equilibrium for the game. In this thesis, the initial IG model is enriched by the possibility of false negatives, i.e. the probability that a violation is not detected during an inspection. Both the initial and the enriched model remain abstract and can thus easily find interdisciplinary application. However, as solution approach in this thesis considering the context of distributed systems, it models the network participants’ strategy choice. As outcome, the IG model enables to calculate system parameters in order to shift the Nash equilibrium to the desired target collaboration. The approach is designed as framework. It can be therefore applied to any architecture considering, any selfish goal and any reliability technique. For sake of concreteness, we will discuss the IG approach by means of the illustrative case of a Publish/Subscribe (pub/sub) architecture. In this way messages over the communication infrastructure will have a specific associated semantics. The Inspection Game approach of this thesis secures the whole collaborative protocol in order to attain a correctly working system up to a specific degree (in the sense of collaboration). This represents a completely new way in terms of reliability mechanisms. Hence, this thesis can be considered as fundamental research. In order to enable a broad application, the generality of this approach is supported by further contributions. This is among others the software library RCourse for practical robustness evaluations of overlay networks and a simulation environment for further research of the abstract IG model. All developments will finally be published as open source software.
In his famous paper Gersho stressed that the codecells of optimal quantizers asymptotically make an equal contribution to the distortion of the quantizer. Motivated by this fact, we investigate in this paper quantizers in the scalar case, where each codecell contributes with exactly the same portion to the quantization error. We show that such quantizers of Gersho type - or Gersho quantizers for short - exist for non-atomic scalar distributions. As a main result we prove that Gersho quantizers are asymptotically optimal.
The dissertation "Three Essays on Credit Risk with a Special Focus on the Subprime Financial Crisis" consists of three self-contained essays. At the core of the dissertation is the market for credit risk and its role during and after the recent subprime financial crisis. In particular, it is dedicated to the following research questions: - What are the causes of the subprime financial crisis? - Which role did credit markets and credit derivatives play during the crisis? - How might the crisis be resolved? - What is the impact of the crisis on market participants perception of credit risk? - How can complex credit derivatives be modeled in a way that allows an understanding of their inherent risk?
In this thesis a new approach to building product recommender systems is introduced. By using a customer-centric dialogue, the customers' preferences are elicited. These are the basis for inferring utility estimations about the desired technical properties of the products in question. Systems built this way can both operate autonomously, e.g., in an online store, and support a salesperson directly at the point-of-sale. The core of the approach is formed by a layered domain description that models customer stereotypes and needs, product attributes, the products themselves, and the causal interrelations between customer and product properties. Maintenance of the domain description, i.e., keeping the model up-to-date in face of frequent changes, is facilitated by the clear separation of concerns provided by the layered structure. In fact, the most frequently used class of updates can be handled in an entirely automated way if some constraints are satisfied. On a high level of abstraction, the system behavior is described by State Charts that are parameterized according to the domain description. Those parts of the system description where State Charts would be too imprecise are implemented by separate components realizing the required complex semantics. From the domain description, a Bayesian network is generated that forms the core of the inference engine of the recommender system. The network essentially controls the system-initiated dialogue flow and the recommendation process. Due to the characteristics of Bayesian networks, it is possible to respond to user-initiated dialogue steps in a natural way. Moreover, an explanation of the current recommendation can be generated without having to explicitly encode additional information in the modeling layer. Finally, a database structure and the SQL queries necessary to obtain recommendations can be inferred from the corresponding parts of the domain description. Instantiation of the system to a specific business domain is supported by a dedicated maintenance application that hides the complexities of the underlying algorithms. Thus, day-to-day system updates by non-technical domain experts, e.g., product managers, are facilitated. The developed concepts were implemented in cooperation with a local industry partner who intends to apply the recommender system in the field of mobile communications.
This dissertation builds on the economic research about M&A and the effects on the merging plants' performance. In particular, the objective of this thesis is to shed some light on questions about causal effects of M&A on plants' performance, taking firm heterogeneity into account. Since there is no typical merger (Tichy, 2001) it distinguishes between acquiring and target plants, and between horizontal and non-horizontal mergers. The thesis focuses on two major research questions: do plants with specific characteristics self-select in merger activity, and is there a causal effect of M&A on the merging plants' performance parameters, in particular on labor productivity, employment, and skill-intensity? The results allow drawing some conclusions about the reasons why plants merge. The thesis consists of four chapters. All contributions have in common that they focus on questions about the effects of M&A on plant performance. That is, the thesis does not discuss questions about the effects of M&A on industry and aggregation concentration levels, or the effects of M&A on social welfare. Each chapter in this thesis can be read separately, because they are based on stand-alone papers. Hence, all chapters have their own introduction and conclusion. The structure and storyline of this thesis and the interaction of the chapters are as follows: the first chapter is a survey about M&A and acts as an introduction to this research field. The second chapter describes propensity score matching as a newer microeconometric evaluation method and explains its implementation in the econometric computer software STATA. In a certain sense, the second chapter serves as a preparation for a better understanding of the econometric analysis performed in chapters three and four, which form the heart of the thesis. They both discuss questions about self-selection of plants into merger activity, and questions about causal effects on plants' performance. In particular, the third chapter focuses on the effects on merging plants' labor productivity, while the fourth chapter focuses on the effects on both employment and skill-intensity. Even if both chapters discuss the effects on different performance parameters, they are similar with respect to motivation, structure, and estimation strategy. Hence, there is some inevitable overlapping between these two chapters which are based on stand-alone papers as mentioned above
IMPACT 2013 in Berlin, Germany (in conjuction with HiPEAC 2013) is the third workshop in a series of international workshops on polyhedral compilation techniques. The previous workshops were held in Chamonix, France (2011) in conjuction with CGO 2011 and Paris, France (2012) in conjuction with HiPEAC 2012.
This work investigates the intertemporal portfolio optimization of professional portfolio managers. It analyzes whether the special conditions of delegation in which portfolio managers make investment decisions - compensation depending on assets under management, capital flow depending on past performance, and influence on prices - can explain the observable investment patterns of portfolio managers. It further evaluates optimal portfolio policies from the primary investor’s perspective.
The introduction of the economic reform program, Doi Moi, in 1986 opened the door for private sector development in Vietnam, as well as the country’s integration into the world economy. As Hanoi is the national political centre, it occupies an important role in Vietnam’s transformation process. The capital has become a major hub for socio-economic development. Whereas “Hanoi was renowned for its quiet streets in the 1980s” (Drummond 2000: 2382), nowadays it is characterised by its bustling street life. Public spaces, such as streets and sidewalks, are appropriated by private individuals for mostly small-scale economic activities. Existing green parks are privatised in order to cater to the growing demand for leisure space. At the same time, official spaces like Ba Dinh Square or Ly Thai To Square are occupied by Hanoi’s residents for sports and gatherings. Thomas (2002: 1621) regards this a contestation of the state-defined landscape by local people. In other words, the state’s defining power for the urban image is challenged by a multiplicity of spatial producers. This thesis focuses on the development of public spaces in Hanoi. Using the frame of an emic reconstruction , major themes such as changes in power relations between state and society and their reflection in the city’s physical environment are explored. Embedded in the discipline of urban sociology, this thesis aims to contribute to the discussion about the correlation between the public sphere as a sociological/political category and the materiality and practices of public space. According to Sennett (2008), the public sphere is a crucial element of urbanism. Furthermore, as Eisenstadt and Schluchter (20021: 12) indicate, there is a strong relationship between the public sphere and civil society, along with political and economic liberalisation. Therefore, the question remains whether public spaces in Hanoi are an expression of a public sphere or a prerequisite for its development.
The capacity of a society to adapt and cope with disasters is generally discussed under the term resilience. It is a concept that entered vulnerability research recently and that will still need further theoretical underpinning and empirical grounding. The vulnerability context of urban poor can be approached from different angles, such as urbanism or development studies. My thesis has the aim to contribute to a better understanding of resilience within vulnerability research. I decided to follow recent approaches in vulnerability research for two reasons. First, integrated vulnerability concepts highlight the value of interdisciplinary approaches. Second, the integrated vulnerability discourse offers a analytical framework that can be modified and applied to the empirical study of vulnerability in Jakarta's kampungs. In chapter two I will introduce the theoretical embedding of the analytical framework. This will be necessary, as disaster research in social science is a relatively young research stream. Terms such as disasters, catastrophes and hazards are often used synonymously. Moreover, different definitions of vulnerability and resilience lead to diverse applications of the concepts. Thus, I would like to outline some aspects of disaster research in social science and present the definitions I will apply in this thesis. Moreover, at the end of chapter two, I will refine my research question and present the methodological framework I use for the analysis of my empirical data. The integrated vulnerability framework is pointing out the importance of the temporal and spatial scale in vulnerability analysis. In chapter three, I will therefore provide the temporal and spatial embedding of my research by presenting a historical perspective on Jakarta. Since it is not possible to present almost 500 years of city history in one chapter, I will concentrate on two aspects. The first focus will be put on the origin and development of Jakarta's kampungs. The second focus will be put on the flood situation. Accordingly, I will shortly present the different phases of Jakarta's history. In each phase I will point out the aspects relevant for kampungs and aspects that will be relevant in regards to the flood situation. Finally, I will conclude how the situation of the kampungs and its dwellers changed over time. In addition to that, I will discuss the historical development of flood risk in a separate section in order to contribute to a better understanding of recent flooding. Since the integrated vulnerability framework is a place based approach, I would like to introduce the theoretical discussion on urbanism and space in chapter four. I will show that the analytical value of the concept of slum in approaching the local level in Jakarta's kampungs is limited. I will also present the concept of informality as it is often discussed in the context of slums and urban poverty. Moreover, I will argue that informality is an integral part of megacities in developing countries and it reflects processes of self-organisation on a local level. Aspects of social organisations are, again, also important for a vulnerability analysis. I will then link the concepts of institutions and social capital in order to show how social organisation can be approached as a resource for communities. I will conclude the chapter with models of social space, particularly the concept of locality, that will provide a framework for structuring and analysing the empirical field data. In chapter five and six, I will leave the theoretical discussion and present the data I collected during my empirical research in two kampung. Chapter five will begin with a short introduction to the research approach and the methods I used in the research process. Then I will present the field data following the structure provided by the concept of locality which is basically referring to the categories of material space and social organisation. I will add two categories to this structure. In order to link the previous discussion on informality with the empirical research, I will present data on the informal-formal continuum in both research locations. In addition to this I will sum up my empirical findings on how people adapt to and cope with hazards, particularly flooding. I decided to separate description and analysis of my research findings because I would like to first provide a general understanding of the local situation in both research locations in a descriptive way before I analyse and interpret the data. Accordingly, I will analyse and interpret the data in chapter six. The main focus will be put on aspects of space and social organisation so that local communities can be conceptualised. In chapter seven I will finally analyse aspects of vulnerability and resilience by applying the integrated vulnerability framework to my research findings. Lastly, I will briefly summarize the thesis in chapter eight and provide an outlook.
Since any encryption map may be viewed as a polynomial map between finite dimensional vector spaces over finite fields, the security of a cryptosystem can be examined by studying the difficulty of solving large systems of multivariate polynomial equations. Therefore, algebraic attacks lead to the task of solving polynomial systems over finite fields. In this thesis, we study several new algebraic techniques for polynomial system solving over finite fields, especially over the finite field with two elements. Instead of using traditional Gröbner basis techniques we focus on highly developed methods from several other areas like linear algebra, discrete optimization, numerical analysis and number theory. We study some techniques from combinatorial optimization to transform a polynomial system solving problem into a (sparse) linear algebra problem. We highlight two new kinds of hybrid techniques. The first kind combines the concept of transforming combinatorial infeasibility proofs to large systems of linear equations and the concept of mutants (finding special lower degree polynomials). The second kind uses the concept of mutants to optimize the Border Basis Algorithm. We study recent suggestions of transferring a system of polynomial equations over the finite field with two elements into a system of polynomial equalities and inequalities over the set of integers (respectively over the set of reals). In particular, we develop several techniques and strategies for converting the polynomial system of equations over the field with two elements to a polynomial system of equalities and inequalities over the reals (respectively over the set of integers). This enables us to make use of several algorithms in the field of discrete optimization and number theory. Furthermore, this also enables us to investigate the use of numerical analysis techniques such as the homotopy continuation methods and Newton's method. In each case several conversion techniques have been developed, optimized and implemented. Finally, the efficiency of the developed techniques and strategies is examined using standard cryptographic examples such as CTC and HFE. Our experimental results show that most of the techniques developed are highly competitive to state-of-the-art algebraic techniques.
Commutative Gröbner bases have a lot of applications in theory and practice, because they have many nice properties, they are computable, and there exist many efficient improvements of their computations. Non-commutative Gröbner bases also have many useful properties. However, applications of non-commutative Gröbner bases are rarely considered due to high complexity of computations. The purpose of this study was to improve the computation of non-commutative Gröbner bases and investigate the applications of non-commutative Gröbner bases. Gröbner basis theory in free monoid rings was carefully revised and Gröbner bases were precisely characterized in great detail. For the computations of Gröbner bases, the Buchberger Procedure was formulated. Three methods, say interreduction on obstructions, Gebauer-Möller criteria, and detecting redundant generators, were developed for efficiently improving the Buchberger Procedure. Further, the same approach was applied to study Gröbner basis theory in free bimodules over free monoid rings. The Buchberger Procedure was also formulated and improved in this setting. Moreover, J.-C. Faugere's F4 algorithm was generalized to this setting. Finally, many meaningful applications of non-commutative Gröbner bases were developed. Enumerating procedures were proposed to semi-decide some interesting undecidable problems. All the examples in the thesis were computed using the package gbmr of the computer algebra system ApCoCoA. The package was developed by the author. It contains dozens of functions for Gröbner basis computations and many concrete applications. The package gbmr and a collection of interesting examples are available at http://www.apcocoa.org/.
This qualitative approach to research develops a case oriented design in order to examine risks of corruption in public procurement. The method involves expert interviews as the most important data collection tool and explains how to examine the information by means of a qualitative content analyze. In order to develop rigor results, the concepts of external validity, construct validity, internal validity and reliability are applied. The research design was adopted in two field investigations: A first project focuses on the challenges and chances for anticorruption when awarding contracts in a competitive dialogue. For this purpose, data was collected in an investigation of the German construction market. The results are presented in form of 16 propositions, also including policy recommendations and approaches for reform. In the framework of a further case based research project, the paper analyzes the organizational structure and working process of "China's Tangible Construction Market" (TCM). The TCM is an administrative institution where a bid inviter can register in order to announce a public need and conduct a procurement procedure at a fixed location. The analysis of expert interviews conducted during an investigation of the Chinese construction market shows that the TCM offers strong institutional support that can be helpful to curb corruption in public procurement
Thomas Bernhard and the air crash on Tettelham in 1944. "It was a spectacle of unrelieved tragedy".
(2012)
In his autobiographical essay "Ein Kind" (A Child) the Austrian writer Thomas Bernhard (1931-1998)describes the downing of a heavy World War II USAIRFORCE bomber at Tettelham near Traunstein in Upper Bavaria in 1944. The scene of the crash is now headed by a chapel and some reminiscenses of the crews' fate. Although the event is still vivid in the local history, it was not known that Thomas Bernhard had been a keen eyewitness.
This thesis investigates, how placement variations of electronic devices influence the possibility of using sensors integrated in those devices for context recognition. The vast majority of context recognition research assumes well defined, fixed sen- sor locations. Although this might be acceptable for some application domains (e.g. in an industrial setting), users, in general, will have a hard time coping with these limitations. If one needs to remember to carry dedicated sensors and to adjust their orientation from time to time, the activity recognition system is more distracting than helpful. How can we deal with device location and orientation changes to make context sensing mainstream? This thesis presents a systematic evaluation of device placement effects in context recognition. We first deal with detecting if a device is carried on the body or placed somewhere in the environ- ment. If the device is placed on the body, it is useful to know on which body part. We also address how to deal with sensors changing their position and their orientation during use. For each of these topics some highlights are given in the following. Regarding environmental placement, we introduce an active sampling ap- proach to infer symbolic object location. This approach requires only simple sensors (acceleration, sound) and no infrastructure setup. The method works for specific placements such as "on the couch", "in the desk drawer" as well as for general location classes, such as "closed wood compartment" or "open iron sur- face". In the experimental evaluation we reach a recognition accuracy of 90% and above over a total of over 1200 measurements from 35 specific locations (taken from 3 different rooms) and 12 abstract location classes. To derive the coarse device placement on the body, we present a method solely based on rotation and acceleration signals from the device. It works independent of the device orientation. The on-body placement recognition rate is around 80% over 4 min. of unconstrained motion data for the worst scenario and up to 90% over a 2 min. interval for the best scenario. We use over 30 hours of motion data for the analysis. Two special issues of device placement are orientation and displacement. This thesis proposes a set of heuristics that significantly increase the robustness of motion sensor-based activity recognition with respect to sen- sor displacement. We show how, within certain limits and with modest quality degradation, motion sensor-based activity recognition can be implemented in a displacement tolerant way. We evaluate our heuristics first on a set of synthetic lower arm motions which are well suited to illustrate the strengths and limits of our approach, then on an extended modes of locomotion problem (sensors on the upper leg) and finally on a set of exercises performed on various gym machines (sensors placed on the lower arm). In this example our heuristic raises the dis- placed recognition rate from 24% for a displaced accelerometer, which had 96% recognition when not displaced, to 82%.