Publication Server of Constructor University Library
Not a member yet
858 research outputs found
Sort by
A geometric approach to the study of (g, k)-modules of finite type
No full textLet g be a semisimple Lie algebra over C and k be a reductive in g subalgebra. We say that a simple g-module M is a (g; k)-module if as a k-module M is a direct sum of finite-dimensional k-modules. We say that a simple (g; k) module M is of finite type if all k-isotypic components of M are finite-dimensional. To a simple g-module M one assigns interesting invariants V(M), V(M) and L(M) reflecting the 'directions of growth of M'. In this work we prove that, for a given pair (g; k), the set of possible such invariants is finite. Let K be a reductive Lie group with Lie algebra k. We say that a K-variety X is K-spherical if X has an open orbit of a Borel subgroup of K. Let W be a finite-dimensional K-module. The set of flags (W_1,..., W_s) of W with fixed dimensions (n_1;...; ns) is a homogeneous space of the group GL(W). We call such a variety partial W-flag variety. In this work we classify all K-spherical partial W-flag varieties. We say that a simple (g; k)-module is bounded if there exists constant C_M such that, for any simple k-module E, the isotypic component of E in M is a direct sum of not more than C_M-copies of E. To any simple sl(W)-module one assigns a partial W-flag variety. In this thesis we prove that a simple (sl(W); k)-module is bounded if and only if the corresponding partial W-flag variety is K-spherical. Moreover, we prove that the pair (sl(W); k) admits an infinite-dimensional simple bounded module if and only if P(W) is a K-spherical variety. For four particular case we say more about category of bounded modules and the set of simple bounded modules
Airport Benchmarking An Efficiency Analysis of European Airports from an Economic and Managerial Perspective
No full textSubsequent to airline deregulation, an increasing commercialization, privatization and restructuring gradually changed a sovereign operated airport industry to modern business enterprises. Where market power was likely to be exploited, airports may now face competition with nearby airports or other transport modes. Consequently airport benchmarking became popular for comparisons with competitors and to assess efficiency changes resulting from the structural change. Within academic benchmarking a number of studies emerged utilizing parametric and non-parametric approaches to estimate the productivity and efficiency of airports. Building on the limitations and discussions from previous research the general objective of this thesis is to further the understanding of the airport industry and to improve airport benchmarking in order to enhance its usefulness for managerial, political and regulatory purposes. Particular emphasis is given on the consideration of the heterogeneous character of airports and how to explain efficiency difference across airports. The cumulative thesis presents the results of three research articles. The first article provides a survey on the methods, data and findings of empirical research from the current literature in airport benchmarking. The survey indicates substantial progress in the methodological application however many issues still remain unresolved such as the appropriate measurement of capital. The second article assesses the combined impact of ownership form, economic regulation and competition on airport performance and pricing in order to search for the most desirable combination. Australian and European are analyzed using non-parametric data envelopment analysis (DEA) in a first stage efficiency measurement and regression analysis in a second stage environmental study. The results reveal that airports not facing competition should be regulated to increase cost efficiency and prevent exploitation of market power. However, in a competitive setting, regulation inhibits airports of any ownership from operating efficiently. Nevertheless, unregulated private airports appear to remain profit-maximizer within competition. The third article aims to improve the airport benchmarking process. Most previous studies either treat the airport production technology as a black box or separate terminal and airside activities, assessing them individually. This research analyzes European airports as a single unit due to the direct complementarities but opening the black box through network DEA. Combined with dynamic clustering appropriate benchmarks are identified based on pre-defined characteristics. Compared to basic DEA models, the results of the network DEA structure provide more meaningful benchmarks with comparable peer units and target values that are achievable in the medium term
Bacterial habitat differentiation in cold- and warm-water coral reef ecosystems
No full textCoral reef ecosystems, often called "rainforests of the sea", represent structurally complex and dynamic environments in both shallow and deep ocean realms, which harbor a unique plethora of organisms. However, only little is known about the role these biodiversity hotspots play as habitat for the "unseen majority" in the oceans: microbial communities. The general aim of this thesis was therefore to advance hitherto existing knowledge of microbial diversity in warm and, particularly, cold-water coral reef ecosystems by exploring bacterial community variation and potential environmental drivers across a combination of different ecological (organizational, temporal, spatial) scales - with explicit focus on the importance of microbial habitat differentiation. For this purpose, molecular techniques, such as high-throughput DNA fingerprinting, and a suite of multivariate statistical tools were applied. The first study focused on principle patterns of bacterial community structure associated with the cold-water coral Lophelia pertusa. The coral and environment-specific structuring of bacterial communities was assessed under both natural (reef) and controlled (aquarium) conditions by targeting four distinct microbial habitats: coral skeleton surface, coral mucus, ambient seawater and proximal sediment. In the second study, intra- and inter-reef variations in bacterial community structure of four cold-water coral reef ecosystems were investigated in a multi-scale survey spanning five levels of ecological reef organization (microbial habitat type, coral species and color, reef zoning, reef boundary, reef site) by focusing on the cold-water corals Lophelia pertusa and Madrepora oculata. In the third study, the importance of permeable carbonate and silicate reef sands as specific microbial habitats in a warm-water coral reef ecosystem was assessed. The two sand types were compared for their potential to promote differences in bacterial diversity and biomass, while also taking into account the influence of season and space. The presented methods and findings shall contribute to investigations of microbial community shifts in response to environmental changes and anthropogenic pressures in coral reef ecosystems.Korallenriff-Ökosysteme, auch “Regenwälder der Meere“ genannt, sind strukturell komplexe und dynamische Lebensräume in flachen und tiefen Meereszonen, die eine einzigartige Vielfalt an Organismen beherbergen. Jedoch ist wenig bekannt über die Rolle, welche diese sog. Biodiversitäts-Hotspots als Lebensraum für die „unsichtbare Mehrheit“ in den Meeren spielt: mikrobielle Gemeinschaften. Ziel dieser Doktorarbeit war es daher, den bisherigen Kenntnisstand der mikrobiellen Ökologie in Warm- und speziell Kaltwasserkorallenriff-Ökosystemen durch die Untersuchung ihrer bakteriellen Zusammensetzung und potenziellen Umwelteinflüsse über verschiedene ökologische (Riff-organisatorische, zeitliche, räumliche) Skalen zu erweitern – mit explizitem Schwerpunkt auf der Differenzierung mikrobieller Habitate. Dafür wurden molekulare Methoden, wie die Erstellung von DNA-Fingerabdrücken, und eine Reihe multivariater statistischer Analysen angewandt.
In der ersten Studie wurde die Korallen- und Umwelt-spezifische Strukturierung bakterieller Gemeinschaften unter natürlichen (Riff) und kontrollierten (Aquarium) Bedingungen in vier unterschiedlichen mikrobiellen Habitaten an der Kaltwasserkoralle Lophelia pertusa untersucht: Korallenskelett-Oberfläche, Korallenschleim, Meerwasser und Sediment. In der zweiten Studie wurde die intra- und inter-spezifische Variabilität in der bakteriellen Gemeinschaftsstruktur von vier Kaltwasserkorallenriff-Ökosystemen untersucht. Der multiple-Skalen Ansatz umfasste fünf ökologische Ebenen (mikrobielles Habitat, Korallenart, Korallenfarbe, Riffzonierung, Riffgrenze, Riffstandort), mit Fokus auf den Korallen Lophelia pertusa und Madrepora oculata. In der dritten Studie wurde die Bedeutung permeabler Karbonat- und Silikat-Riffsande als spezifische mikrobielle Habitate in einem Warmwasserkorallenriff-Ökosystem untersucht. Die Sande wurden bzgl. ihres Potenzials verglichen, Unterschiede in bakterieller Diversität und Biomasse zu begünstigen, auch unter Berücksichtigung von Jahreszeit und räumlicher Anordnung. Die vorgestellten Methoden und Ergebnisse sollen einen Beitrag zur Untersuchung mikrobieller Gemeinschaften unter Umweltveränderungen und anthropogenem Stress in Korallenriff-Ökosystemen leisten
Participation and Democracy: Dynamics, Causes and Consequences of Elite-Challenging Activities
No full textThis empirical study focuses on the expanded political action repertoire of citizens in democracies, examining three aspects of elite-challenging activities: their dynamics over time, their determinants and their democratic consequences. Elite-challenging activities are short-term, issue-oriented forms of participation from below, ranging from petitioning to demonstrating to engaging in acts of political consumerism. Covering 70 societies that vary greatly in their economic, social and political characteristics, the study tests competing hypotheses derived from several theoretical approaches in participation research and democratic theory. The analyses are based on a broad empirical database, combining information from different large-scale cross-national surveys (ESS 2002-04, EVS/WVS 1981-2005, Pol. Action Study 1974). The study yields the following results. First, it contradicts the thesis of declining citizen activism in contemporary democracies. Second, it confirms that elite-challenging activities do not proceed at the expense of other forms of political participation (voting, conventional participation) or social activities. Third, contrary to the social capital approach, elite-challenging activities are a result of the productivity of social capital (networks and trust), both at the individual and societal level, and not an indication of declining social capital. Fourth, in line with modernization theory, participation in elite-challenging activities is driven by individual characteristics (self-expression values and political interest) and societal opportunity structures/resources (modernization). Finally, the study argues that elite-challenging participation is beneficial for democracy: Elite-challenging activities are mainly exercised by those who value democracy for its process, not material benefits. Moreover, in societies where pressure from below is high, elite behavior tends to be more transparent and less corrupt
On root Fernando-Kac subalgebras of finite type
No full textLet g be a finite-dimensional Lie algebra and M be a g-module. The Fernando-Kac subalgebra of g associated to M is the subset gsubsetg of all elements xin g which act locally finitely on M. A subalgebra lsubset g for which there exists an irreducible module M with g[M]=l is called a Fernando-Kac subalgebra of g. A Fernando-Kac subalgebra of g is of finite type if in addition M can be chosen to have finite Jordan-Hölder l-multiplicities. Under the assumption that g is simple, I. Penkov has conjectured an explicit combinatorial criterion describing all Fernando-Kac subalgebras of finite type which contain a Cartan subalgebra. The thesis proves this conjecture for g not equal to E_8
Analysis and modelling of charge transport properties in organic field-effect transistors
No full textPrinted organic electronics for flexible, low-cost and large-area applications require solution-processable semiconductors with sufficiently high performance. Many of these soluble semiconductors are organic polymers. Charge transport mechanisms in these disordered systems differ from those in crystalline semiconductors, and various models exist for their description. In this work, top-gate organic field-effect transistors (OFETs) on flexible and transparent plastic foil substrates with solution-processed organic gate insulator are used to investigate on charge transport features in the widely used poly-thiophene P3HT (poly(3-hexyl thiophene)). In addition to standard transistor parameters such as charge carrier mobility and threshold voltage, the modeling takes into account features like bulk current and the charge carrier density dependence of the mobility. These parameters are analyzed upon their variation with temperature, semiconductor layer thickness or changes in the composure of the insulator and its solvent, in order to achieve a comprehensive description. In addition, a model is elaborated and experimentally verified that predicts, from the charge carrier mobility and the contact resistance as well as the parasitic capacitances, the maximum frequency of an OFET, a crucial parameter for any application. Having been realized in the frame of an industrial cooperation aiming for suitable materials for printed electronics, the thesis includes the implementation of a high-quality material test and analysis setup, with which different semiconductor/insulator systems are evaluated, also with respect to the parameters found to be crucial in the modeling section, with the goal of achieving not only high mobility for good on-current, but also suitable threshold voltage and bulk conductivity for low off-current
Data Integration for Marine Ecological Genomics
No full textMany aspects of life can only be explained in their ecological context. This was recognized more than a hundred years ago by Haeckel: "Ecology is the entire science of the relations of an organism to its environment to which we can count in a broader sense all conditions of existence". Molecular methods developed over the last 20 years have revealed the diversity and functioning of microbial communities and their crucial role in ecosystem functioning.
Metagenomics, defined as "the functional and sequence-based analysis of the collective microbial genomes contained in an environmental sample" (Riesenfeld et al. 2004), allows researchers to perform cultivation-independent studies of the microbial world on the DNA level. Basic questions like "How does the environment influence the gene content?", and "How does the functional potential encoded therein influence the capacity of a microbial community to interact with the environment?" can be addressed now. Metagenomics can be used to test the hypothesis that genes with no known function are conserved in certain microbial communities and may be important for their ecological adaptation and survival. However, systematic management of data is a crucial prerequisite to achieve a holistic picture of the complex interactions in the microbial realm, on basic ecological questions like "Who is out there?" and "What are they doing?" for relating sequence data to ecological data.
The results of this thesis are genomic data standardization, software architecture development and implementation of an integrated framework for ecological genomics. The centerpiece is the integrated Microbial Ecological Genomics Database (MegDb). Tools have been developed using geo-referenced DNA sequence data of MegDb. This proofs MegDb suitable for ecological genomics based on standards such as the "Minimum Information about a Genome Sequence" recommendation by the Genomic Standards Consortium
Authoritarian socialization experience and acculturation dysfunction among young immigrants to Western Europe : the role of a negative existential position
No full textThis dissertation is a report on research, which was implemented during 2006 - 2009 at Jacobs University in Bremen, Germany. The scope of this study encompasses two areas of social psychology: the Authoritarian Personality theory and acculturation research. It was a quantitative research (N = 1318), which focused on four different groups (three immigrant groups and one - native (ethnic) Germans). This research used a theoretical framework of Transactional Analysis which was, so to say, “imported” from practical psychology. It examined the relevance of Transactional Analysis’ theoretical framework within the context of Authoritarian Personality research and Acculturation research. Valuable empirical findings were gathered in both fields. Thus, by means of statistical data analysis, acculturation patterns among three immigrant groups in Germany were examined, as well as a newly introduced concept – Acculturation Dysfunction. Within the Authoritarian Personality research, a new conceptual approach to the Authoritarian Personality understanding and formation was introduced, and a core concept of the Transactional Analysis – Negative Existential Position – in the Authoritarian Personality formation was empirically tested. The two main hypotheses, determined for this research, were confirmed; numerous additional empirical findings were obtained, which can serve as abundant material for further research in both research fields
A Comparative Analysis of Array Models for Databases
No full textWhile the database collection types set, list, and record have received in-depth attention, the fourth type, array, is still far from being integrated into database modeling. Due to this lack of attention there is only insufficient array support by today's database technology. This is surprising given that large, multi-dimensional arrays have manifold practical applications in earth sciences (such as remote sensing and climate modeling), life sciences (such as microarray data and human brain imagery), and many more areas. Consequently, flexible retrieval today is supported on metadata, but not on the observation and simulation data themselves.
To overcome this, large, multi-dimensional arrays as first-class database citizens have been studied by various groups worldwide. Several formalisms and languages tailored for use in array databases have been proposed and more or less completely implemented, sometimes even in operational use.
In the attempt towards a consolidation of the field we compare four important array models, AQL, AML, ARRAY ALGEBRA, and RAM. As it turns out, ARRAY ALGEBRA is capable of expressing all other models, and additionally offers functionality not present in the other models. We show this by mapping all approaches to ARRAY ALGEBRA. This establishes a common representation suitable for comparison and allows us discussing the commonalities and differences found. Finally, we show feasibility of conceptual array models for describing optimization and architecture
Window design for multivariate Gabor frames on lattices
No full textConstructive design of Gabor frame windows is rare, and most results come from the one-dimensional case. The connection between the geometry of fundamental domains of lattices and Gabor systems was explored first in a series of papers by Han and Wang [HW01], [HW04]. We build upon these results to construct Gabor frames with smooth and compactly supported window functions in higher dimensions. For this purpose we study pairs of lattices with equal density allowing compact and star-shaped fundamental domains. Concrete examples are provided and the results are extended to other special class of lattices. In addition, we make observations on the intricate behavior of Gabor systems with multivariate Gaussian windows