4242 research outputs found
Sort by
Topological dynamics of small degree networks
No full textIn self-organizing networks, structure and dynamics interact in a unique way. Local activity sustained on the network organizes in global dynamic patterns to which the network topology adapts. It is believed that simple organisms lacking neural structures may derive their competence for complex behavior from this type of mechanistic interaction. One such organism is the slime mold Physarum polycephalum, which has emerged as an experimentally accessible model system for self-organizing Transport networks over the recent years. Its remarkable features include the formation of a network structure optimized for transport, and various higher-level behaviors such as efficient foraging decisions and learning. Although significant progress has been made in uncovering these behaviors and the origins of dynamic processes taking place on the network, their relation via structural remodeling still lacks detailed understanding. Combining experimental approaches with modeling and simulation, this work focuses on reorganization of the P. polycephalum network after fragmentation, a process occurring in a percolation transition in an expanding system. Data analysis and modeling are based on a novel method for graph extraction from spatial networks, which regards nodes as extended objects and fixes the number of degree two nodes in a graph. Results suggest that the network formation process is separated into four functionally distinctive phases that are closely related to the topological state. Prominently, topological development is concluded once P. polycephalum reaches a steady state in which it continues to expand while maintaining a constant degree distribution, characterized by nodes of degrees one to four, with a negligible number of large degree nodes. Using this small degree property, analytical solutions to the random graph and configuration models of graph theory are derived. Comparison to experimental data reveals a shift of the percolation transition, which through modeling and Simulation is attributed to active growth processes in the slime mold. A model consisting of a deterministic rate equation and a stochastic master equation is devised based on the concept that the topological evolution can be decomposed into a sequence of elementary processes of four distinct classes, each representing one possible type of interaction between nodes. The model, characterized by a set of rate constants obtained from experimental data, describes the topological Dynamics with excellent accuracy. In a simplified setting, the influence of interaction types is analyzed, and via simulations it is found that system growth shifts the percolation transition according to a power law. Furthermore, the percolation critical exponents are determined, concluding that the simulated master equation model shares a universality class with mean-field percolation, whereas preliminary two-dimensional simulations, and by extension, Network formation in P. polycephalum, are characterized by the exponents for two-dimensional percolation
Longitudinal Perspectives on Ethnic Diversity and Social Cohesion : Mass Media, Neighborhoods and Residential Mobility
Get PDFA growing strand of research in the social sciences demonstrates that social trust and other indicators of social cohesion are lower in ethnically diverse localities. This negative association has reached the status of a stylized fact, an empirical regularity that stimulates a host of empirical and theoretical work that tries to explain, contest and replicate the association. The interest in this association in sociology might be due to the fact that the implications of this broader strand of literature go beyond the local effects of ethnic diversity. They touch upon the question whether immigration affects aggregate societal integration, and thus link to a topic that is of interest to sociologists since the early beginning of the discipline. Against the backdrop of this larger scholarly debate, this thesis is part of a broader research agenda that not only empirically investigates the association between neighborhood diversity and social cohesion itself (see study III), but also focuses on the processes that surround this association. One pillar of this agenda is a focus on processes of ethnic segregation and individual residential choice that create what is later measured as neighborhood ethnic composition (see study II). A second pillar moves the debate on social cohesion to higher levels of analysis by focusing on macro-level sources of group threat such as the national media (see study I). In Study I, Mass Media and Concerns about Immigration in Germany in the 21st Century: Individual-Level Evidence over 15 Years , Christian S. Czymara and I use panel data to analyze how the attention that the topic of migration receives in the mainstream media predicts within individual changes in concerns about immigration in Germany from 2001 to 2015. A particular focus is on the question whether local ethnic composition moderates the media salience effect. In study II, I analyze White Flight for the German case. White Flight is widely known in the U.S. American literature, describing mobility flows of ethnic majority individuals out of neighborhoods with high shares of other ethnic groups. Here, I focus on one plausible mechanism for White Flight: having children. The fact that parents might change their neighborhood preferences strongly after having children is often noted in the literature, but there is still a lack of longitudinal evidence. I address this gap by relying on panel fixed-effects models to account for time-stable neighborhood and household specific traits. Study III deals with a core element of social cohesion: individual social connections to neighbors. Previous studies on the association between ethnic diversity and local social cohesion are mostly cross-sectional. Extending prior research, I add a dynamic element to the analysis: the length of residence in a neighborhood. I empirically show whether the formation of contacts with neighbors over time depends on the ethnic diversity of the neighborhood. However, asking a longitudinal research question also poses empirical challenges. As a potential means to address those issues, I propose a method to deal with possible bias due to selective mobility out of neighborhoods during the period of observation
Placing sensory science in health Research : Correlates of sensory taste perception & preferences, healthy eating and health outcomes in European Children
No full textBased on unique data from a large-scale pan-European cohort study in children, adolescents and their families, the present thesis investigated for the first time factors that may influence sensory taste perception and taste preferences in childhood. This thesis took advantage of the great diversity of food environments across Europe and considered biological/ physiological factors (sex, age, number of fungiform papillae) as well as genetic and familial factors (biological parents, parental consumer attitudes/ education level and dietary habits) simultaneously. Since it is very challenging to obtain valid results about sensory taste perception from children, instruments and test systems were adapted to be used in children with various cultural backgrounds. This thesis analysed sensory test methods to investigate their feasibility and suitability for future large-scale observational studies in young populations. Connecting sensory taste perception with health outcomes presents an innovative research field
Occurrence, reaction and transport behavior of cadmium in groundwater
Get PDFCadmium (Cd) is a non-essential trace element that is widely distributed in the environment. It remains in solution at near neutral pH and is one of the most toxic elements in the environment. There is a lack of information about the processes that control Cd concentration in groundwater. Elevated Cd concentrations can be resultant from a multitude of natural and anthropogenic sources. The goal was to provide a better understanding about the source, transport, and fate of Cd in groundwater through the evaluation of a large hydrogeochemical data set. Above-threshold Cd concentrations were linked to specific groundwater compositions caused by land use in connection with acidification or nitrate. The main parameters affecting Cd mobility were pH and redox potential, which were linked to Cd sorption and release from minerals. Cadmium primarily occurred in shallow groundwater under oxic and autotrophic nitrate reducing conditions. Hydrogeological factors limited Cd retention capacity
Von Deutschland nach Istanbul und doch mit beiden verbunden: Integrationserfahrungen und Migrationsmotive von Deutschländern
Get PDFThis dissertation is concerned with persons who grew up in Germany with Turkish parents, but later migrated to Istanbul. The study, based on interviews analysed using qualitative content analysis, investigates their integration experiences in Germany before the migration and in Turkey afterwards, as well as the motives behind their decision to migrate. For each of these aspects, the structural, social, cultural and identificational dimensions are examined, plus experiences of discrimination. While displaying a high degree of integration into German mainstream society in the other dimensions, the interviewees were often unable to achieve a positive social identity due to the stigmatization of their Turkish parts. In Istanbul, on the other hand, they are able to live out both the German and Turkish aspects of their culture and identity. The intervieweesa tendency towards individualization, biculturality and agency forms the basis of their motivation to move to Turkey. This migration is not an indication of failed integration in Germany, but rather it is the result of a very high degree of integration that led to expectations that Germany was unable to fulfill
Influencer-Marketing auf Instagram : Chancen und Risiken für Destinationsmanagementorganisationen
Get PDFDie vorliegende Arbeit beschäftigt sich mit Influencer-Marketing und der Anwendung entsprechender Maßnahmen im Destinationsbereich. Mit einer eigens durchgeführten, zweiteiligen empirischen Untersuchung sollen Chancen und Risiken von Influencer-Marketing auf Instagram für Destinationsmanagementorganisationen ermittelt werden. Dabei werden die Instagram Accounts an sich betrachtet und Einschätzungen aus Sicht von Influencern und Experten der Destinationsmanagementorganisationen eingeholt. Modellhaft wird das Beispiel der Mitgliedsstädte des Magic Cities Germany e.V. verwendet. In Folge werden der Status Quo der Implementierung von Influencer-Marketing Maßnahmen, der Stellenwert und die zukünftige Entwicklung abgeleitet. Ausgehend von der Untersuchung werden Chancen und Risiken für die Destinationsmanagementorganisationen dargestellt. Abschließend werden entsprechende Handlungsempfehlungen für die Destinationsmanagementorganisationen der Magic Cities entwickelt
Steuerung funktioneller Materialeigenschaften eines Polybenzoxazin-Netzwerks über die Integration von Poly(caprolacton)-Oligomeren
Get PDFThe present dissertation deals with the specific control of the functional properties of a bisphenol A based polybenzoxazine (PBA-a). Therefore, the thermoset was combined with the thermoplastic oligomer poly(caprolactone) (PCL). The influence of covalently integrated versus unbound PCL on polybenzoxazines properties was the main focus of this cumulative work and for that reason systematically analyzed by varying the PCL content in the polymer mixtures. The polyester end groups were functionally modified with a tosyl leaving group. In contrast to the hydroxy-terminated basic structure, the modified PCL could be covalently integrated into benzoxazines network. The copolymers homogeneous morphology observed by scanning electron micrographs of PCL/PBA-a revealed that the covalent incorporation of the polyester chains could prevent phase separation of the components as occurred for the unmodified PCL/PBA-a blend-like structures. A slightly decreased network density, due to the incorporated PCL chains, reduced the brittleness of samples with low contents of modified PCL (wPCL 30 %). Thus, toughness values of up to 1.66 MPa were achieved compared to 0.48 MPa for neat PBA-a. By increasing the content of the tosylated PCL in the samples (wPCL = 30 - 50 %) network density was lowered accordingly, resulting highly flexibilized polymers with an almost 10 times increased elongation at break compared to PBA-a. Due to the macroscopic phase separation, a further increase of the amount of unmodified PCL led to samples with even higher brittleness. Polymers with high levels of tosyl-modified PCL (wPCL = 60 - 80 %) exhibited thermoresponsive shape memory properties, which could be attributed to the presence of both covalently incorporated and free PCL in these samples with mixed bonding mode. The combination of the widened network and increased crystallinity are key factors to the displayed shape memory effect. In this work, benzoxazine networks with variable and functional properties have been successfully prepared due to the covalent integration of PCL oligomers. The deeper understanding of the structure-property relationship will facilitate a broader application of polybenzoxazine based materials
Beyond Us versus Them : Explaining Intergroup Bias in Multiple Categorization
Get PDFThe psychological and sociological explorations of intergroup relations have traditionally focused on understanding prejudice and discrimination along a single dimension of social categorization: We study racism and sexism, anti-immigrant attitudes and homophobia, ageism and Islamophobia. What these studies fail to consider is that in real life, each of us belongs to multiple groups. Sociology experiences a boom of research on intersectionality, whereas psychological accounts of consequences of belonging to multiple social groups are still underdeveloped. This dissertation aims to address this gap by investigating attitude formation in situations in which multiple group memberships of a target person are salient, i.e. in multiple categorization settings. Building on social cognition and intergroup relations literatures, I develop a theoretical framework that (1) differentiates between two routes through which group memberships can affect attitudes: ingroup bias and preference for higher status; (2) places perception of similarity as the main cognitive mechanism linking the information about group memberships of others to attitudes towards them; (3) incorporates individual- and societal-level moderators of the effects of group memberships on attitudes. In a series of studies, I demonstrate the difference between the two types of social categories that operate via the two distinct routes. The groups that provide a sense of community and shared norms, such as ethnicity and religion, operate via the preference for ingroup members. The groups that provide information about status of the person, such as education or occupation, affect attitudes directly via preference for higher status, irrespective of own group membership. I show that perceived similarity mediates the link between group memberships and attitudes for both types of groups. Finally, I demonstrate that both individual and contextual factors moderate the relationships between group memberships and attitudes. On the individual level, importance of group memberships to the perceivera s self-concept and perceived threat from the outgroup are associated with stronger ingroup bias. On the societal level, lower country-level acceptance of cultural diversity is associated with stronger preference for ingroup members on cultural dimensions, and lower income and educational inequality is associated with stronger preference for higher-status others on socioeconomic dimensions. This dissertation brings attention to and opens up new avenues for the study of psychological consequences of the complexity of the social worlds we live in
Maskierte Erfassung und inpaintingbasierte Wiederherstellung von großen Datenvolumen in Systemen mit eingeschränkter Berechnungskapazität
No full textThe exponential growth of the generated data volume, due to the increasing number of participants in data traffic as well as networking, confronts many application-specific systems worldwide with new and future challenges. Based on the large amount, the high speed and the large variety of data, individual problems arise in the acquisition, transmission and processing. Managing such data volumes with traditional data processing approaches is often infeasible to resource-constrained applications, because of limitations of the computational capacity. This thesis focusses on solutions for the processing of high data volumes in systems with limited computational capacity. The key concept is based on a methodology for the asymmetric distribution of computational effort through the use of algorithmic tools in the field of multidimensional digital data restoration (inpainting). The combination of masking for data reduction and inpainting for data recovery opens up the potential to innovative solutions for currently unresolved problems and to improve existing approaches. From the field of medicine, space technology as well as imaging recording media, problems to evaluate the developed solutions of the innovative methodology in this thesis. Furthermore, the approaches are compared to different reference methods. Both, the degree of data reduction and the reconstruction quality of the inpainting-based recovery, serve as figures of merit to evaluate the developed approaches within simulated examinations of the application-specific scenarios
Adaptive Localization and Mapping for Planetary Rovers
Get PDFFuture rovers will be equipped with substantial onboard autonomy as space agencies and industry proceed with missions studies and technology development in preparation for the next planetary exploration missions. Simultaneous Localization and Mapping (SLAM) is a fundamental part of autonomous capabilities and has close connections to robot perception, planning and control. SLAM positively affects rover operations and mission success. The SLAM community has made great progress in the last decade by enabling real world solutions in terrestrial applications and is nowadays addressing important challenges in robust performance, scalability, high-level understanding, resources awareness and domain adaptation. In this thesis, an adaptive SLAM system is proposed in order to improve rover navigation performance and demand. This research presents a novel localization and mapping solution following a bottom-up approach. It starts with an Attitude and Heading Reference System (AHRS), continues with a 3D odometry dead reckoning solution and builds up to a full graph optimization scheme which uses visual odometry and takes into account rover traction performance, bringing scalability to modern SLAM solutions. A design procedure is presented in order to incorporate inertial sensors into the AHRS. The procedure follows three steps: error characterization, model derivation and filter design. A complete kinematics model of the rover locomotion subsystem is developed in order to improve the wheel odometry solution. Consequently, the parametric model predicts delta poses by solving a system of equations with weighed least squares. In addition, an odometry error model is learned using Gaussian processes (GPs) in order to predict non-systematic errors induced by poor traction of the rover with the terrain. The odometry error model complements the parametric solution by adding an estimation of the error. The gained information serves to adapt the localization and mapping solution to the current navigation demands (domain adaptation). The adaptivity strategy is designed to adjust the visual odometry computational load (active perception) and to influence the optimization back-end by including highly informative keyframes in the graph (adaptive information gain). Following this strategy, the solution is adapted to the navigation demands, providing an adaptive SLAM system driven by the navigation performance and conditions of the interaction with the terrain. The proposed methodology is experimentally verified on a representative planetary rover under realistic field test scenarios. This thesis introduces a modern SLAM system which adapts the estimated pose and map to the predicted error. The system maintains accuracy with fewer nodes, taking the best of both wheel and visual methods in a consistent graph-based smoothing approach