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Essays in Development and Political Economics: Infrastructure, the Political Resource Curse, and Technology Spillovers
Full text linkDissolution-Precipitation in Porous Media: Experiments and Modelling
Full text linkThe evolution of porosity due to dissolution/precipitation processes of minerals and the associated change of transport parameters are of major interest for natural geological environments and engineered underground structures. We designed a reproducible and fast to conduct 2D experiment, which is flexible enough to investigate several process couplings implemented in the numerical code OpenGeosys-GEM (OGS-GEM). We investigated advective-diffusive transport of solutes, effect of liquid phase density on advective transport, and kinetically controlled dissolution/precipitation reactions causing porosity changes. In addition, the system allowed to investigate the influence of microscopic (pore scale) processes on macroscopic (continuum scale) transport. A Plexiglas tank of dimension 10 × 10 cm was filled with a 1 cm thick reactive layer consisting of a bimodal grain size distribution of celestite (SrSO4) crystals, sandwiched between two layers of sand. A barium chloride solution was injected into the tank causing an asymmetric flow field to develop. As the barium chloride reached the celestite region, dissolution of celestite was initiated and barite precipitated. Due to the higher molar volume of barite, its precipitation caused a porosity decrease and thus also a decrease in the permeability of the porous medium. The change of flow in space and time was observed via injection of conservative tracers and analysis of effluents. In addition, an extensive post-mortem analysis of the reacted medium was conducted. We could successfully model the flow (with and without fluid density effects) and the transport of conservative tracers with a (continuum scale) reactive transport model. The prediction of the reactive experiments initially failed. Only the inclusion of information from post-mortem analysis gave a satisfactory match for the case where the flow field changed due to dissolution/precipitation reactions. We concentrated on the refinement of post-mortem analysis and the investigation of the dissolution/precipitation mechanisms at the pore scale. Our analytical techniques combined scanning electron microscopy (SEM) and synchrotron X-ray micro-diffraction/micro-fluorescence performed at the XAS beamline (Swiss Light Source). The newly formed phases include an epitaxial growth of barite micro-crystals on large celestite crystals (epitaxial growth) and a nano-crystalline barite phase (resulting from the dissolution of small celestite crystals) with residues of celestite crystals in the pore interstices. Classical nucleation theory, using well-established and estimated parameters describing barite precipitation, was applied to explain the mineralogical changes occurring in our system. Our pore scale investigation showed limits of the continuum scale reactive transport model. Although kinetic effects were implemented by fixing two distinct rates for the dissolution of large and small celestite crystals, instantaneous precipitation of barite was assumed as soon as oversaturation occurred. Precipitation kinetics, passivation of large celestite crystals and metastability of supersaturated solutions, i.e. the conditions under which nucleation cannot occur despite high supersaturation, were neglected. These results will be used to develop a pore scale model that describes precipitation and dissolution of crystals at the pore scale for various transport and chemical conditions. Pore scale modelling can be used to parameterize constitutive equations to introduce pore-scale corrections into macroscopic (continuum) reactive transport models. Microscopic understanding of the system is fundamental for modelling from the pore to the continuum scale
A unified approach to architecture conformance checking
Full text linkArchitectural decisions can be interpreted as structural and behavioral constraints that must be enforced in order to guarantee overarching qualities in a system. Enforcing those constraints in a fully automated way is often challenging and not well supported by current tools. Current approaches for checking architecture conformance either lack in usability or offer poor options for adaptation.
To overcome this problem we analyze the current state of practice and propose an approach based on an extensible, declarative and empirically-grounded specification language. This solution aims at reducing the overall cost of setting up and maintaining an architectural conformance monitoring environment by decoupling the conceptual representation of a user-defined rule from its technical specification prescribed by the underlying analysis tools. By using a declarative language, we are able to write tool-agnostic rules that are simple enough to be understood by untrained stakeholders and, at the same time, can be can be automatically processed by a conformance checking validator.
Besides addressing the issue of cost, we also investigate opportunities for increasing the value of conformance checking results by assisting the user towards the full alignment of the implementation with respect to its architecture. In particular, we show the benefits of providing actionable results by introducing a technique which automatically selects the optimal repairing solutions by means of simulation and profit-based quantification.
We perform various case studies to show how our approach can be successfully adopted to support truly diverse industrial projects. We also investigate the dynamics involved in choosing and adopting a new automated conformance checking solution within an industrial context.
Our approach reduces the cost of conformance checking by avoiding the need for an explicit management of the involved validation tools. The user can define rules using a convenient high-level DSL which automatically adapts to emerging analysis requirements. Increased usability and modular customization ensure lower costs and a shorter feedback loop
Erfassung und Validierung der subjektiven Talentkriterien von Fussballtrainern unter Verwendung eines konstruktivistischen Ansatzes
Full text linkTalentselektionsentscheidungen sind zentraler Teil des Talentförderprozesses im Fussball und werden vorwiegend von Trainern und Trainerinnen gefällt. Aufgrund des Forschungsdefizits zum Talentverständnis wurden in der vorliegenden kumulativen Dissertation die subjektiven Talentkriterien von Experten-Fussballtrainern untersucht. Hierfür wurde unter der Verwendung eines konstruktivistischen Ansatzes ein halbstrukturierter Interviewleitfaden entwickelt. In einer ersten Studie lag der Fokus auf der differenzierten Erfassung der subjektiven Talentkriterien und einem ersten (inhaltlichen) Vergleich der von den Trainern verwendeten Talentmodelle. Zudem wurde die Verwendung einer Repertory Grid Technik getestet. In der zweiten Studie wurde das Studiendesign mit Blick auf die zusätzliche Überprüfung von Reliabilität und Validität der von den Trainern verwendeten Talentmodelle mithilfe der Repertory Grid Technik auf ein Mixed-Method-Design erweitert. Die Ergebnisse aus den beiden Studien mit sechs Experten-Clubtrainern und fünf Junioren-Nationaltrainern der Altersstufen U14 bis U18 geben einen differenzierten Einblick in das subjektive Talentverständnis der befragten Trainer. Über einen Zeitraum von 10 Wochen liessen sich adäquate Reliabilitätskoeffizienten finden. Als Hinweis auf die Validität lieferte eine ganzheitliche Potentialbeurteilung als Kriterium mittlere bis starke Korrelationen mit den Spielerbeurteilungen anhand der Talentkriterien durch die Trainer. Die beiden im Rahmen der Dissertation durchgeführten Studien werden in die sportwissenschaftliche Talentforschung eingeordnet und diskutiert
Information-centric communication in mobile and wireless networks
Full text linkInformation-centric networking (ICN) is a new communication paradigm that has been proposed to cope with drawbacks of host-based communication protocols, namely scalability and security. In this thesis, we base our work on Named Data Networking (NDN), which is a popular ICN architecture, and investigate NDN in the context of wireless and mobile ad hoc networks.
In a first part, we focus on NDN efficiency (and potential improvements) in wireless environments by investigating NDN in wireless one-hop communication, i.e., without any routing protocols. A basic requirement to initiate informationcentric communication is the knowledge of existing and available content names. Therefore, we develop three opportunistic content discovery algorithms and evaluate them in diverse scenarios for different node densities and content distributions. After content names are known, requesters can retrieve content opportunistically from any neighbor node that provides the content. However, in case of short contact times to content sources, content retrieval may be disrupted. Therefore, we develop a requester application that keeps meta information of disrupted content retrievals and enables resume operations when a new content source has been found. Besides message efficiency, we also evaluate power consumption of information-centric broadcast and unicast communication. Based on our findings, we develop two mechanisms to increase efficiency of information-centric wireless one-hop communication. The first approach called Dynamic Unicast (DU) avoids broadcast communication whenever possible since broadcast transmissions result in more duplicate Data transmissions, lower data rates and higher energy consumption on mobile nodes, which are not interested in overheard Data, compared to unicast communication. Hence, DU uses broadcast communication only until a content source has been found and then retrieves content directly via unicast from the same source. The second approach called RC-NDN targets efficiency of wireless broadcast communication by reducing the number of duplicate Data transmissions. In particular, RC-NDN is a Data encoding scheme for content sources that increases diversity in wireless broadcast transmissions such that multiple concurrent requesters can profit from each others’ (overheard) message transmissions.
If requesters and content sources are not in one-hop distance to each other, requests need to be forwarded via multi-hop routing. Therefore, in a second part of this thesis, we investigate information-centric wireless multi-hop communication. First, we consider multi-hop broadcast communication in the context of rather static community networks. We introduce the concept of preferred forwarders, which relay Interest messages slightly faster than non-preferred forwarders to reduce redundant duplicate message transmissions. While this approach works well in static networks, the performance may degrade in mobile networks if preferred forwarders may regularly move away. Thus, to enable routing in mobile ad hoc networks, we extend DU for multi-hop communication. Compared to one-hop communication, multi-hop DU requires efficient path update mechanisms (since multi-hop paths may expire quickly) and new forwarding strategies to maintain NDN benefits (request aggregation and caching) such that only a few messages need to be transmitted over the entire end-to-end path even in case of multiple concurrent requesters. To perform quick retransmission in case of collisions or other transmission errors, we implement and evaluate retransmission timers from related work and compare them to CCNTimer, which is a new algorithm that enables shorter content retrieval times in information-centric wireless multi-hop communication. Yet, in case of intermittent connectivity between requesters and content sources, multi-hop routing protocols may not work because they require continuous end-to-end paths. Therefore, we present agent-based content retrieval (ACR) for delay-tolerant networks. In ACR, requester nodes can delegate content retrieval to mobile agent nodes, which move closer to content sources, can retrieve content and return it to requesters. Thus, ACR exploits the mobility of agent nodes to retrieve content from remote locations. To enable delay-tolerant communication via agents, retrieved content needs to be stored persistently such that requesters can verify its authenticity via original publisher signatures. To achieve this, we develop a persistent caching concept that maintains received popular content in repositories and deletes unpopular content if free space is required. Since our persistent caching concept can complement regular short-term caching in the content store, it can also be used for network caching to store popular delay-tolerant content at edge routers (to reduce network traffic and improve network performance) while real-time traffic can still be maintained and served from the content store
«Am Fremden müssen wir lernen, das Eigene zu erkennen». Kulturelle Differenz, Alterität und Identität in Repräsentationen Tibets und des tibetischen Buddhismus
Full text linkWährend öffentliche Diskussionen um muslimische Einwanderer und Glaubensgemeinschaften im Kontext einer zunehmenden internationalen Problematisierung des Islam von vorwiegend negativen Typisierungen und Pauschalisierungen geprägt sind, offenbart der Blick auf öffentliche Repräsentationen des tibetischen Buddhismus ein geradezu konträres Bild: So gilt Tibet spätestens seit Beginn des zwanzigsten Jahrhunderts bis heute vielfach als positiver weltanschaulicher wie ästhetischer Gegenentwurf zur „westlichen Moderne“, der Buddhismus wird als undogmatische, glücks- und gegenwartsorientierte, ebenso friedfertige wie tolerante und zugleich rational nachvollziehbare Lehre wahrgenommen. Besonders in der Schweiz verfügt die Sympathie für kulturelle und religiöse Traditionen Tibets in Anbetracht der langen Geschichte der Begegnung durch die Aufnahme tibetischer Geflüchteter ab den 1960er Jahren über eine breite Basis.
Die vorliegende Dissertationsschrift widmet sich der systematischen Untersuchung öffentlicher Repräsentationen Tibets, tibetisch-buddhistischer Lehren und Praktiken, prominenter Vertreter tibetisch-buddhistischer Traditionen wie des XIV. Dalai Lama, sowie der tibetischen Diasporagemeinschaft in der Schweiz ab Mitte der 1990er Jahre. Im Rahmen der empirischen Untersuchung gegenwärtiger Darstellungen Tibets und des tibetischen Buddhismus in massenmedial und durch resonanzstarke Akteure vermittelten öffentlichen Diskussionen stehen Deutungen, Narrativen und Wertungen im Fokus, welche an die Präsenz Tibets und des tibetischen Buddhismus außerhalb Asiens geknüpft werden und welche im öffentlichen Raum zirkulieren. Eine diskursanalytische Forschungsperspektive sowie das anhand ausführlicher theoretischer Vorüberlegungen entwickelte Verständnis von Alterität ermöglichen es dabei, den Blick systematisch auf die diskursive Herstellung von Grenzen zum Anderen, und damit auf Repräsentationen jener sozialen Bruchstellen zu richten, an welchen kulturelle bzw. religiöse Differenz erlebt wird und entlang derer sich Vorstellungen des Eigenen entfalten: Die Rekonstruktion symbolisch vermittelter Repräsentationen kultureller Differenz am Beispiel Tibets und des tibetischen Buddhismus erweist sich als Schlüssel, mithilfe dessen neben etablierten Wissensbeständen auch implizite Hintergrundannahmen über grundlegend geteilte Wertorientierungen, gesellschaftliche Ideale sowie gesellschaftliche, nationale wie kulturell-religiöse Identitäten sichtbar gemacht werden können. Anhand der detaillierten Darstellung der Bandbreite möglicher Deutungen und Interpretationsrepertoires zu Lehren und Praktiken buddhistischer Schulrichtungen, zu ihrer Präsenz und Adaption in der Schweiz bzw. „im Westen“, zur tibetisch-buddhistischen Kultur sowie den Lebenswelten der tibetischen Diasporagemeinschaft wird ausgeführt, wie im Rahmen öffentlicher Repräsentationen kulturell-religiöser Differenz um die Deutungsinhalte, normative Beurteilung und kollektive Geltung gesellschaftlicher Werte und Ideale, um Deutungen geteilter sozialer, religiöser wie kultureller Identitäten und damit letztlich um „soziale Konstruktionen von Wirklichkeit“ (Berger/Luckmann 2007 [1966]) gerungen wird. So wird beispielsweise gezeigt, wie unterschiedliche Akteure zur Stützung ihrer jeweiligen Argumente auf normativ aufgeladene Leitideen wie Gewaltlosigkeit, Toleranz, Menschlichkeit, Authentizität, Individualität, Selbstbestimmung, Rationalität, Gleichberechtigung, Solidarität und soziale Integration, Demokratie und Pluralismus sowie damit semantisch verknüpfte Deutungskomplexe Bezug nehmen. Das kulturell beziehungsweise religiös Andere in Gestalt Tibets, des tibetischen Buddhismus sowie der tibetischen Gemeinschaft nimmt damit, wie die Autorin ausführt, vielfach die Rolle eines identitätsstiftenden Interaktionspartners zur Verhandlung gesellschaftlicher Selbstbilder und Wertorientierungen ein
Parsing for agile modeling
Full text linkAgile modeling refers to a set of methods that allow for a quick initial development of an importer and its further refinement. These requirements are not met simultaneously by the current parsing technology. Problems with parsing became a bottleneck in our research of agile modeling.
In this thesis we introduce a novel approach to specify and build parsers. Our approach allows for expressive, tolerant and composable parsers without sacrificing performance. The approach is based on a context-sensitive extension of parsing expression grammars that allows a grammar engineer to specify complex language restrictions. To insure high parsing performance we automatically analyze a grammar definition and choose different parsing strategies for different parts of the grammar.
We show that context-sensitive parsing expression grammars allow for highly composable, tolerant and variable-grained parsers that can be easily refined. Different parsing strategies significantly insure high-performance of parsers without sacrificing expressiveness of the underlying grammars
Elucidating different aspects of speed of information processing: comparison of behavioral response latency and P300 latency in a modified Hick reaction time task
Full text linkThe aim of the present work was to get a more detailed understanding of the functional significance of the P300 latency. P300 latency is often used as measure of stimulus evaluation time. However, the interpretation of P300 latency as stimulus evaluation time was challenged by findings of a P300 latency sensitivity to response-related manipulations. In two studies with samples from two different countries, not only RT, but also P300 latency were used as measures of speed of information processing examining the Hick paradigm. P300 latency has been used as speed of information processing measure before, but to my knowledge never in the Hick task. The advantage of using the Hick paradigm is that the influence of response selection on P300 latency can be systematically investigated while keeping stimulus evaluation constant and minimal. Furthermore, a comparison of P300 latency and RT revealed some more information about the functionality of P300 latency. By contrasting both speed of information processing measures as predictors of intelligence, it was also investigated if RT and P300 latency explain common and/or unique parts of variance in intelligence. The present investigation replicated once more the increase of RT in dependence of the amount of bit of information that needs to be processed. Furthermore, in accordance with the mental speed approach of intelligence, participants with higher intelligence were performing faster in the Hick task than participants with lower intelligence levels. Moreover, this inverse relation between RT and intelligence was enhanced across complexity. In addition, the present work also revealed some new insights about the functional significance of P300 latency. These insights are the following:
1. A clear P300 component was elicited under all four bit conditions, including the 0 bit condition. This indicates that even in simple reaction time tasks some cognitive processing is activated. P300 is often associated with a context updating of the current mental representation in the working memory. Since each stimulus under the 0 bit condition is exactly the same as the previous one, present data suggests that P300 might
have other or additional functions than context updating. One alternative function could be a monitoring role, which is determining the stimulus-response association.
2. P300 latency did increase across bit conditions. This indicates that P300 latency is not only sensitive to manipulations that focus on stimulus evaluation, but also to manipulations focusing on response selection. This finding is not compatible with the idea of P300 latency as an index of stimulus evaluation time.
3. RT and P300 latency are often expected to capture the time of similar underlying processes. Indeed, P300 latency is, similar as RT, increasing across bit conditions. However, P300 latency and RT were not related. This suggests that P300 latency and RT are not reflecting the same aspects of speed of information processing. P300 latency might be proportional to stimulus evaluation time in task that focus on stimulus evaluation. But, as the current results show, it is probably determined by completely different processes than RT. Further research is needed to get a more complex pictures of the determinants of the P300 component.
4. The relation between P300 latency and intelligence is still not clear. Present data does not confirm the suggestion of Houlihan et al. (1998) that the relation of RT and intelligence might be partly mediated by response-related processes. However, there might be other factors like subjective task difficulty and complexity, or the subject’s strategy that play a significant role in individual differences in both, P300 latency and intelligence. Further research is needed to get a more complex pictures of these factors
Applications of Resource-Constrained Project Scheduling in Service Operations Management
Full text linkService companies employ expensive personnel to provide services for their customers. Each service may involve a large number of individual activities that must be executed by the company's personnel. Furthermore, the customers often pay for the services provided once all these activities have been completed. Hence, in general, managers plan the service operations of their companies such that the time required to complete each service is minimized, i.e., the available personnel is utilized in the most efficient way. In this dissertation, we consider two complex planning problems that arise in service operations management: the short-term planning of assessment centers and the scheduling of projects with so-called work-content constraints. Both planning problems consist of a prescribed number of activities that must be executed by the available personnel such that the duration of the service, i.e., the duration of the assessment or the project, is minimized. We interpret these two planning problems as specific applications of the well-known resource-constrained project scheduling problem, and we devise novel solution approaches for the planning problems that are based on concepts and methods from the corresponding project-scheduling literature. For the short-term planning of assessment centers, we devise a multi-pass list-scheduling heuristic and five alternative mixed-integer linear programming formulations. For the scheduling of projects with work-content constraints, we develop a mixed-integer programming-based heuristic. Our computational results indicate that the proposed approaches obtain optimal or near-optimal solutions for the two respective planning problems in a short amount of computation time
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