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Die vorliegende Arbeit betrachtet Partizipation aus einer interaktionalen Perspektive und nimmt zunächst eine interdisziplinär orientierte Begriffsbestimmung vor. Daran anschließend werden anhand einer Längsschnittstudie Entwicklungsbedingungen sozialer Partizipationskompetenzen im Vorschulalter untersucht und Förderempfehlungen abgeleitet. Partizipation (Teilhabe) soll in Kontexten wie Schule oder Arbeitswelt Entscheidungen demokratisch legitimieren, individuelle Ressourcen ausschöpfen und soziale Grundbedürfnisse des Menschen befriedigen. Ein engeres Verständnis von sozialer Partizipation aus einer interaktionalen Perspektive erfordert die Beteiligung an den Aktivitäten einer bereits bestehenden Gruppe und die Aushandlung eigener Interessen innerhalb dieser Gruppe und wird in der Arbeit als Prozess anhand dreier Phasen (Anbahnung, Projektierung und Realisierung) dargestellt. Im Vorschulalter werden wichtige Grundsteine für eine erfolgreiche soziale Entwicklung und für den Erwerb von sozialen Partizipationskompetenzen gelegt. In der vorliegenden Arbeit wurden deshalb die Zusammenhänge und Wechselwirkungen zwischen sozialen Partizipationskompetenzen (Bereitschaft und Fähigkeit) und (1) kognitiven Leistungsparametern (Intelligenz und Perspektivenübernahme), (2) dem Selbstkonzept und (3) dem Konfliktverhalten (Aggression und Schüchternheit) mit 5- bis 7jährigen Kindern mit Hilfe von Kreuzpfadanalysen untersucht. Zudem wurde die Situationsgebundenheit sozialer Partizipationskompetenzen und die Bedeutung struktureller Parameter der Familie und der Kindertageseinrichtung auf explorativer Ebene analysiert. Die Stichprobe bestand aus 334 Kindern (51,5 % weiblich, Altersdurchschnitt zum ersten Messzeitpunkt 5,4 Jahre) in 71 Kindergartengruppen in 21 Kindertageseinrichtungen in vier Bundesländern. Die längsschnittliche Datenanalyse basiert auf drei Messzeitpunkten. Die Ergebnisse zeigen, dass soziale Partizipationskompetenzen über verschiedene Situationen hinweg bedeutsame, aber nur mäßig ausgeprägte, Zusammenhänge aufweisen. Hohe Ausprägungen kognitiver Leistungsparameter gehen mit hohen Erziehereinschätzungen sozialer Partizipationskompetenzen einher. Über die Zusammenhänge hinaus zeigen sich im Längsschnitt bedeutsame Wechselwirkungen zwischen kognitiver Entwicklung und sozialen Partizipationskompetenzen im Vorschulalter. Selbsteinschätzungen zur eigenen Kompetenz hängen im Vorschulalter hingegen nur gering mit Erziehereinschätzungen der sozialen Partizipationskompetenz zusammen. Im Längsschnitt zeigt sich, dass junge Kinder bei der Beurteilung ihrer Kompetenzen zunächst auf soziale Partizipationserfolge zurückgreifen. Später hingegen scheint der Partizipationserfolg dann umgekehrt eher durch das Selbstbild bedingt zu sein. Geringe Partizipationskompetenzen gehen mit hohen Erziehereinschätzungen beim aggressiven (schwach signifikant) und schüchternen Verhalten (mäßig signifikant) einher. Hinsichtlich der Aggression und des schüchternen Verhaltens ergaben sich längsschnittlich betrachtet nur schwache Wechselwirkungen zur sozialen Partizipationskompetenz. Die Kumulation familiärer Belastungssituationen (z.B. Krankheit und akute Finanznot) stellen eine größere Bedrohung für die kindliche Entwicklung dar als der sozio-ökonomische Status der Familie. Mit Blick auf die Förderung sozialer Partizipationskompetenzen lassen sich die Ergebnisse mit einem sozial-konstruktivistischen Ansatz verbinden. Dessen Ziel ist es, intra- und interpersonelle Konflikte auszulösen, deren erfolgreiche Bewältigung produktive Lernprozesse auf kognitiver, emotionaler und behavioraler Ebene anstoßen.
Ziel der Studie war die Untersuchung individueller und familialer Faktoren für den sozialen Status eines Kindes in seiner Schulklasse. Durch die Unterscheidung von Akzeptanz und Einfluss als zweier Hauptdimensionen des sozialen Status konnte die Arbeit aufklären, welche Rolle verschiedene Attribute für das Erreichen von Akzeptanz oder Einfluss spielen. 234 Dritt- und Fünftklässler aus Berliner Grundschulen erhielten soziometrische Maße, durch welche der soziale Status erhoben wurde (Akzeptanz und Einfluss). Individuelle und familiale Faktoren wurden mittels Peernominationen über das Verhalten der Kinder (Fremdurteil), Schulnoten (Lehrerangabe)und Maße des sozio-ökonomischen Status der Eltern (Elternangabe)erhoben. Die Ergebnisse zeigen, dass Akzeptanz positiv mit prosozialem und negativ mit aggressivem Verhalten eines Kindes assoziiert ist. Die Zusammenhänge dieser Verhaltensweisen mit Einfluss wiesen in dieselbe Richtung, waren aber deutlich geringer. Ideenreichtum und Humor hingen mit Akzeptanz und Einfluss gleichermaßen positiv zusammen, sowie Traurigsein gleichermaßen negativ mit beiden Statusdimensionen verbunden war. Das Verhalten eines Kindes vermittelte den Zusammenhang zwischen Merkmalen wie Geschlecht, relativem Alter, Schulnoten und der Akzeptanz und dem Einfluss eines Kindes. Zum Beispiel war die positive Beziehung zwischen Schulnoten und dem sozialen Status überwiegend auf die mit(guten)Schulnoten assoziierten Verhaltensweisen Prosozialität und (geringe) Aggressivität zurückzuführen. Die größere Akzeptanz von Mädchen ließ sich ebenso durch deren größere Prosozialität und geringere Aggressivität erklären. Jungen waren im Hinblick auf ihren Einfluss sowohl am oberen als auch am unteren Ende der Hierarchie überrepräsentiert. Sowohl sehr einflussreiche als auch einflusslose Jungen zeichneten sich durch eine erhöhte Aggressivität aus. Komplexere Analysen wiesen daraufhin, dass Jungen negative Auswirkungen von aggressivem Verhalten durch Humor und Ideenreichtum auf ihren Status kompensieren konnten. Der moderate Zusammenhang zwischen dem elterlichen sozioökonomischen Status und dem sozialen Status des Kindes wurde vollständig durch das Verhalten des Kindes mediiert. Das Elternhaus war wichtiger für die Akzeptanz als für den Einfluss eines Kindes. Kinder mit Migrationshintergrund waren sowohl weniger akzeptiert als auch weniger einflussreich in ihrer Klasse. Elterliche Trennung trug nicht zur sozialen Position eines Kindes bei.
In der wissenschaftlichen Literatur, in der betrieblichen Praxis und in der gesellschaftlichen Diskussion wird wieder zunehmend mehr die Bedeutung der Beschäftigten für den Unternehmenserfolg hervorgehoben und diskutiert. Unternehmen, die zielgerichtet geeignete Managementstrategien mit Blick auf den Umgang mit ihren Beschäftigten einsetzen, werden in bezug auf ihre ökonomische Wertschöpfung als erfolgreicher charakterisiert. Besonders im Bereich Human Resources Management lassen sich erste Belege finden, die es ermöglichen, den ökonomischen Erfolg von Unternehmen kausal auf einzelne Personalmanagementstrategien zurückzuführen. Ziel eigener Untersuchungen in der IT- und Softwarebranche war es, Unternehmenserfolg auf der Grundlage ökonomischer Erfolgsmaße und des subjektiven Erlebens der Beschäftigten in kleinen und mittleren Softwareunternehmen unter besonderer Fokussierung des Human Resources Management und der Unternehmenskultur zu untersuchen.
Artikel 15 Grundgesetz als sozialistische Utopie? Keineswegs. Die Sozialisierungsnorm gibt dem Gesetzgeber ein Instrument an die Hand, um staatliche Gewährleistungsverantwortung mithilfe gemeinwirtschaftlicher Organisationsformen wahrzunehmen. Sozialisierungsmaßnahmen greifen in das Eigentumsgrundrecht ein. Sie treffen zudem auf grundrechtliche Funktionsgarantien einer marktwirtschaftlichen Ordnung und die unionsrechtliche Systemgarantie zugunsten des freien Wettbewerbs. Die Arbeit untersucht daher die verfassungsrechtlichen Anforderungen an die Sozialisierungsgesetzgebung auf Bundes- und Landesebene einschließlich der gerichtlichen Kontrolle. Ferner zeigt die Arbeit auf, wie sich Sozialisierungsgesetze unionsrechtskonform verhalten können.
Water quality in river systems is of growing concern due to rising anthropogenic pressures and climate change. Mitigation efforts have been placed under the guidelines of different governance conventions during last decades (e.g., the Water Framework Directive in Europe). Despite significant improvement through relatively straightforward measures, the environmental status has likely reached a plateau. A higher spatiotemporal accuracy of catchment nitrate modeling is, therefore, needed to identify critical source areas of diffuse nutrient pollution (especially for nitrate) and to further guide implementation of spatially differentiated, cost-effective mitigation measures. On the other hand, the emerging high-frequency sensor monitoring upgrades the monitoring resolution to the time scales of biogeochemical processes and enables more flexible monitoring deployments under varying conditions. The newly available information offers new prospects in understanding nitrate spatiotemporal dynamics. Formulating such advanced process understanding into catchment models is critical for model further development and environmental status evaluation. This dissertation is targeting on a comprehensive analysis of catchment and in-stream nitrate dynamics and is aiming to derive new insights into their spatial and temporal variabilities through the new fully distributed model development and the new high-frequency data.
Firstly, a new fully distributed, process-based catchment nitrate model (the mHM-Nitrate model) is developed based on the mesoscale Hydrological Model (mHM) platform. Nitrate process descriptions are adopted from the Hydrological Predictions for the Environment (HYPE), with considerable improved implementations. With the multiscale grid-based discretization, mHM-Nitrate balances the spatial representation and the modeling complexity. The model has been thoughtfully evaluated in the Selke catchment (456 km2), central Germany, which is characterized by heterogeneous physiographic conditions. Results show that the model captures well the long-term discharge and nitrate dynamics at three nested gauging stations. Using daily nitrate-N observations, the model is also validated in capturing short-term fluctuations due to changes in runoff partitioning and spatial contribution during flooding events. By comparing the model simulations with the values reported in the literature, the model is capable of providing detailed and reliable spatial information of nitrate concentrations and fluxes. Therefore, the model can be taken as a promising tool for environmental scientists in advancing environmental modeling research, as well as for stakeholders in supporting their decision-making, especially for spatially differentiated mitigation measures.
Secondly, a parsimonious approach of regionalizing the in-stream autotrophic nitrate uptake is proposed using high-frequency data and further integrated into the new mHM-Nitrate model. The new regionalization approach considers the potential uptake rate (as a general parameter) and effects of above-canopy light and riparian shading (represented by global radiation and leaf area index data, respectively). Multi-parameter sensors have been continuously deployed in a forest upstream reach and an agricultural downstream reach of the Selke River. Using the continuous high-frequency data in both streams, daily autotrophic uptake rates (2011-2015) are calculated and used to validate the regionalization approach. The performance and spatial transferability of the approach is validated in terms of well-capturing the distinct seasonal patterns and value ranges in both forest and agricultural streams. Integrating the approach into the mHM-Nitrate model allows spatiotemporal variability of in-stream nitrate transport and uptake to be investigated throughout the river network.
Thirdly, to further assess the spatial variability of catchment nitrate dynamics, for the first time the fully distributed parameterization is investigated through sensitivity analysis. Sensitivity results show that parameters of soil denitrification, in-stream denitrification and in-stream uptake processes are the most sensitive parameters throughout the Selke catchment, while they all show high spatial variability, where hot-spots of parameter sensitivity can be explicitly identified. The Spearman rank correlation is further analyzed between sensitivity indices and multiple catchment factors. The correlation identifies that the controlling factors vary spatially, reflecting heterogeneous catchment responses in the Selke catchment. These insights are, therefore, informative in informing future parameter regionalization schemes for catchment water quality models. In addition, the spatial distributions of parameter sensitivity are also influenced by the gauging information that is being used for sensitivity evaluation. Therefore, an appropriate monitoring scheme is highly recommended to truly reflect the catchment responses.
This PhD thesis presents the spatio-temporal distribution of terrestrial carbon fluxes for the time period of 1982 to 2002 simulated by a combination of the process-based dynamic global vegetation model LPJ and a 21-year time series of global AVHRR-fPAR data (fPAR – fraction of photosynthetically active radiation). Assimilation of the satellite data into the model allows improved simulations of carbon fluxes on global as well as on regional scales. As it is based on observed data and includes agricultural regions, the model combined with satellite data produces more realistic carbon fluxes of net primary production (NPP), soil respiration, carbon released by fire and the net land-atmosphere flux than the potential vegetation model. It also produces a good fit to the interannual variability of the CO2 growth rate. Compared to the original model, the model with satellite data constraint produces generally smaller carbon fluxes than the purely climate-based stand-alone simulation of potential natural vegetation, now comparing better to literature estimates. The lower net fluxes are a result of a combination of several effects: reduction in vegetation cover, consideration of human influence and agricultural areas, an improved seasonality, changes in vegetation distribution and species composition. This study presents a way to assess terrestrial carbon fluxes and elucidates the processes contributing to interannual variability of the terrestrial carbon exchange. Process-based terrestrial modelling and satellite-observed vegetation data are successfully combined to improve estimates of vegetation carbon fluxes and stocks. As net ecosystem exchange is the most interesting and most sensitive factor in carbon cycle modelling and highly uncertain, the presented results complementary contribute to the current knowledge, supporting the understanding of the terrestrial carbon budget.
As land-cover conversion continues to expand into ever more remote areas in the humid tropics, montane rainforests are increasingly threatened. In the south Ecuadorian Andes, they are not only subject to man-made disturbances but also to naturally occurring landslides. I was interested in the impact of this ecosystem dynamics on a key parameter of the hydrologic cycle, the soil saturated hydraulic conductivity (synonym: permeability; Ks from here on), because it is a sensitive indicator for soil disturbances. My general objective was to quantify the effects of the regional natural and human disturbances on the saturated hydraulic conductivity and to describe the resulting spatial-temporal patterns. The main hypotheses were: 1) disturbances cause an apparent displacement of the less permeable soil layer towards the surface, either due to a loss of the permeable surface soil after land-sliding, or as a consequence of the surface soil compaction under cattle pastures; 2) ‘recovery’ from disturbance, either because of landslide re-vegetation or because of secondary succession after pasture abandonment, involves an apparent displacement of the less permeable layer back towards the original depth an 3) disturbances cause a simplification of the Ks spatial structure, i.e. the spatially dependent random variation diminishes; the subsequent recovery entails the re-establishment of the original structure. In my first study, I developed a synthesis of recent geostatistical research regarding its applicability to soil hydraulic data, including exploratory data analysis and variogram estimation techniques; I subsequently evaluated the results in terms of spatial prediction uncertainty. Concerning the exploratory data analysis, my main results were: 1) Gaussian uni- and bivariate distributions of the log-transformed data; 2) the existence of significant local trends; 3) no need for robust estimation; 4) no anisotropic variation. I found partly considerable differences in covariance parameters resulting from different variogram estimation techniques, which, in the framework of spatial prediction, were mainly reflected in the spatial connectivity of the Ks-field. Ignoring the trend component and an arbitrary use of robust estimators, however, would have the most severe consequences in this respect. Regarding variogram modeling, I encouraged restricted maximum likelihood estimation because of its accuracy and independence on the selected lags needed for experimental variograms. The second study dealt with the Ks spatial-temporal pattern in the sequences of natural and man-made disturbances characteristic for the montane rainforest study area. To investigate the disturbance effects both on global means and the spatial structure of Ks, a combined design-and model-based sampling approach was used for field-measurements at soil depths of 12.5, 20, and 50 cm (n=30-150/depth) under landslides of different ages (2 and 8 years), under actively grazed pasture, fallows following pasture abandonment (2 to 25 years of age), and under natural forest. Concerning global means, our main findings were 1) global means of the soil permeability generally decrease with increasing soil depth; 2) no significant Ks differences can be observed among landslides and compared to the natural forest; 3) a distinct permeability decrease of two orders of magnitude occurs after forest conversion to pasture at shallow soil depths, and 4) the slow regeneration process after pasture abandonment requires at least one decade. Regarding the Ks spatial structure, we found that 1) disturbances affect the Ks spatial structure in the topsoil, and 2) the largest differences in spatial patterns are associated with the subsoil permeability. In summary, the regional landslide activity seems to affect soil hydrology to a marginal extend only, which is in contrast to the pronounced drop of Ks after forest conversion. We used this spatial-temporal information combined with local rain intensities to assess the partitioning of rainfall into vertical and lateral flowpaths under undisturbed, disturbed, and regenerating land-cover types in the third study. It turned out that 1) the montane rainforest is characterized by prevailing vertical flowpaths in the topsoil, which can switch to lateral directions below 20 cm depth for a small number of rain events, which may, however, transport a high portion of the annual runoff; 2) similar hydrological flowpaths occur under the landslides except for a somewhat higher probability of impermeable layer formation in the topsoil of a young landslide, and 3) pronounced differences in runoff components can be observed for the human disturbance sequence involving the development of near-surface impeding layers for 24, 44, and 8 % of rain events for pasture, a two-year-old fallow, and a ten-year-old fallow, respectively.
The fragmentation of natural habitat caused by anthropogenic land use changes is one of the main drivers of the current rapid loss of biodiversity. In face of this threat, ecological research needs to provide predictions of communities' responses to fragmentation as a prerequisite for the effective mitigation of further biodiversity loss. However, predictions of communities' responses to fragmentation require a thorough understanding of ecological processes, such as species dispersal and persistence. Therefore, this thesis seeks an improved understanding of community dynamics in fragmented landscapes. In order to approach this overall aim, I identified key questions on the response of plant diversity and plant functional traits to variations in species' dispersal capability, habitat fragmentation and local environmental conditions. All questions were addressed using spatially explicit simulations or statistical models. In chapter 2, I addressed scale-dependent relationships between dispersal capability and species diversity using a grid-based neutral model. I found that the ratio of survey area to landscape size is an important determinant of scale-dependent dispersal-diversity relationships. With small ratios, the model predicted increasing dispersal-diversity relationships, while decreasing dispersal-diversity relationships emerged, when the ratio approached one, i.e. when the survey area approached the landscape size. For intermediate ratios, I found a U-shaped pattern that has not been reported before. With this study, I unified and extended previous work on dispersal-diversity relationships. In chapter 3, I assessed the type of regional plant community dynamics for the study area in the Southern Judean Lowlands (SJL). For this purpose, I parameterised a multi-species incidence-function model (IFM) with vegetation data using approximate Bayesian computation (ABC). I found that the type of regional plant community dynamics in the SJL is best characterized as a set of isolated “island communities” with very low connectivity between local communities. Model predictions indicated a significant extinction debt with 33% - 60% of all species going extinct within 1000 years. In general, this study introduces a novel approach for combining a spatially explicit simulation model with field data from species-rich communities. In chapter 4, I first analysed, if plant functional traits in the SJL indicate trait convergence by habitat filtering and trait divergence by interspecific competition, as predicted by community assembly theory. Second, I assessed the interactive effects of fragmentation and the south-north precipitation gradient in the SJL on community-mean plant traits. I found clear evidence for trait convergence, but the evidence for trait divergence fundamentally depended on the chosen null-model. All community-mean traits were significantly associated with the precipitation gradient in the SJL. The trait associations with fragmentation indices (patch size and connectivity) were generally weaker, but statistically significant for all traits. Specific leaf area (SLA) and plant height were consistently associated with fragmentation indices along the precipitation gradient. In contrast, seed mass and seed number were interactively influenced by fragmentation and precipitation. In general, this study provides the first analysis of the interactive effects of climate and fragmentation on plant functional traits. Overall, I conclude that the spatially explicit perspective adopted in this thesis is crucial for a thorough understanding of plant community dynamics in fragmented landscapes. The finding of contrasting responses of local diversity to variations in dispersal capability stresses the importance of considering the diversity and composition of the metacommunity, prior to implementing conservation measures that aim at increased habitat connectivity. The model predictions derived with the IFM highlight the importance of additional natural habitat for the mitigation of future species extinctions. In general, the approach of combining a spatially explicit IFM with extensive species occupancy data provides a novel and promising tool to assess the consequences of different management scenarios. The analysis of plant functional traits in the SJL points to important knowledge gaps in community assembly theory with respect to the simultaneous consequences of habitat filtering and competition. In particular, it demonstrates the importance of investigating the synergistic consequences of fragmentation, climate change and land use change on plant communities. I suggest that the integration of plant functional traits and of species interactions into spatially explicit, dynamic simulation models offers a promising approach, which will further improve our understanding of plant communities and our ability to predict their dynamics in fragmented and changing landscapes.
Among the different meanings carried by numerical information, cardinality is fundamental for survival and for the development of basic as well as of higher numerical skills. Importantly, the human brain inherits from evolution a predisposition to map cardinality onto space, as revealed by the presence of spatial-numerical associations (SNAs) in humans and animals. Here, the mapping of cardinal information onto physical space is addressed as a hallmark signature characterizing numerical cognition.
According to traditional approaches, cognition is defined as complex forms of internal information processing, taking place in the brain (cognitive processor). On the contrary, embodied cognition approaches define cognition as functionally linked to perception and action, in the continuous interaction between a biological body and its physical and sociocultural environment.
Embracing the principles of the embodied cognition perspective, I conducted four novel studies designed to unveil how SNAs originate, develop, and adapt, depending on characteristics of the organism, the context, and their interaction. I structured my doctoral thesis in three levels. At the grounded level (Study 1), I unfold the biological foundations underlying the tendency to map cardinal information across space; at the embodied level (Study 2), I reveal the impact of atypical motor development on the construction of SNAs; at the situated level (Study 3), I document the joint influence of visuospatial attention and task properties on SNAs. Furthermore, I experimentally investigate the presence of associations between physical and numerical distance, another numerical property fundamental for the development of efficient mathematical minds (Study 4).
In Study 1, I present the Brain’s Asymmetric Frequency Tuning hypothesis that relies on hemispheric asymmetries for processing spatial frequencies, a low-level visual feature that the (in)vertebrate brain extracts from any visual scene to create a coherent percept of the world. Computational analyses of the power spectra of the original stimuli used to document the presence of SNAs in human newborns and animals, support the brain’s asymmetric frequency tuning as a theoretical account and as an evolutionarily inherited mechanism scaffolding the universal and innate tendency to represent cardinality across horizontal space.
In Study 2, I explore SNAs in children with rare genetic neuromuscular diseases: spinal muscular atrophy (SMA) and Duchenne muscular dystrophy (DMD). SMA children never accomplish independent motoric exploration of their environment; in contrast, DMD children do explore but later lose this ability. The different SNAs reported by the two groups support the critical role of early sensorimotor experiences in the spatial representation of cardinality.
In Study 3, I directly compare the effects of overt attentional orientation during explicit and implicit processing of numerical magnitude. First, the different effects of attentional orienting based on the type of assessment support different mechanisms underlying SNAs during explicit and implicit assessment of numerical magnitude. Secondly, the impact of vertical shifts of attention on the processing of numerical distance sheds light on the correspondence between numerical distance and peri-personal distance.
In Study 4, I document the presence of different SNAs, driven by numerical magnitude and numerical distance, by employing different response mappings (left vs. right and near vs. distant).
In the field of numerical cognition, the four studies included in the present thesis contribute to unveiling how the characteristics of the organism and the environment influence the emergence, the development, and the flexibility of our attitude to represent cardinal information across space, thus supporting the predictions of the embodied cognition approach. Furthermore, they inform a taxonomy of body-centred factors (biological properties of the brain and sensorimotor system) modulating the spatial representation of cardinality throughout the course of life, at the grounded, embodied, and situated levels.
If the awareness for different variables influencing SNAs over the course of life is important, it is equally important to consider the organism as a whole in its sensorimotor interaction with the world. Inspired by my doctoral research, here I propose a holistic perspective that considers the role of evolution, embodiment, and environment in the association of cardinal information with directional space. The new perspective advances the current approaches to SNAs, both at the conceptual and at the methodological levels.
Unveiling how the mental representation of cardinality emerges, develops, and adapts is necessary to shape efficient mathematical minds and achieve economic productivity, technological progress, and a higher quality of life.
Daylength is one of several parameters controlling flowering time in many plant species. The day length is perceived in leaves, but how the floral signal is transduced to the shoot apex via the phloem to induce flowering remains to be elucidated. This study aimed at the identification of new candidates involved in the induction of flowering by employing three plant species, Arabidopsis thaliana, Sinapis alba and Brassica napus in combination with transcript profiling by Affymetrix chip hybridization, metabolite profiling by gas chromatography – mass spectrometry and targeted protein analysis using antibodies. All analyses were performed on tissue-specific samples and focused on phloem sap or phloem exudates. To find common transcript and metabolite candidates potentially associated with the floral transition, two independent induction systems in Arabidopsis were used: a photoextension system, whereby plants received fourteen additional hours of light, and a parallel dexamethasone-inducible system, which was centered on the induction of the known flowering gene CONSTANS (CO). Identification of signals preceding the CO cascade was possible using the light extension regime, while downstream events dependent on CO activation were compared in both systems. Altogether, a number of interesting transcript and metabolite candidates were identified in both systems with some degree of overlap. Sinapis alba was used to investigate the universality of the floral signals between species. Comparisons of metabolite data revealed a few common candidates that may prove interesting for further studies. In addition, a targeted approach was carried out to investigate the presence of the Flowering Locus T (FT) protein during different stages of flower development using an antibody. Interesting changes in the sizes of antigens from rape phloem were seen and appeared consistent in Arabidopsis and to a lesser extent in Sinapis. Overall, the broad surveying approaches for transcripts and metabolites used in this study revealed several new potential candidates involved in the induction and/or regulation of flowering. As far as the protein work, additional experiments will reveal the link between FT and floral induction as well as its role in maintaining the floral state using the abovementioned plant species.
The Lombok Island is part of the Lesser Sunda Islands (LSI) region – Indonesia, situated along the Sunda-Banda Arcs transition. It lies between zones characterized by the highest intensity geomagnetic anomalies of this region, remarkable as one of the eight most important features provided on the 1st edition of World Digital Magnetic Anomaly Map. The seismicity of this region during the last years is high, while the geological and tectonic structures of this region are still not known in detail. Some local magnetic surveys have been conducted previously during 2004–2005. However, due to the lower accuracy of the used equipment and a limited number of stations, the qualities of the previous measurements are questionable for more interpretations. Thus a more detailed study to better characterize the geomagnetic anomaly -spatially and temporally- over this region and to deeply explore the related regional geology, tectonic and seismicity is needed. The intriguing geomagnetic anomalies over this island region vis-à-vis the socio-cultural situations lead to a study with a special aim to contribute to the assessment of the potential of natural hazards (earthquakes) as well as a new natural resource of energy (geothermal potential).
This study is intended to discuss several crucial questions, including:
i. The real values and the general pattern of magnetic anomalies over the island, as well as their relation to the regional one.
ii. Any temporal changes of regional anomalies over the recent time.
iii. The relationships between the anomalies and the geology and tectonic of this region, especially new insights that can be gained from the geomagnetic observations.
iv. The relationships between the anomalies and the high seismicity of this region, especially some possible links between their variations to the earthquake occurrence.
First, all available geomagnetic data of this region and results of the previous measurements are evaluated. The new geomagnetic surveys carried out in 2006 and 2007/2008 are then presented in detail, followed by the general description of data processing and data quality evaluation. The new results show the general pattern of contiguous negative-positive anomalies, revealing an active arc related subduction region. They agree with earlier results obtained by satellite, aeromagnetic, and marine platforms; and provide a much more detailed picture of the strong anomalies on this island. The temporal characteristics of regional anomalies show a decreasing strength of the dipolar structure, where decreasing of the field intensities is faster than the regional secular variations as defined by the global model (the 10th generation of IGRF). However, some exceptions (increasing of anomalies) have to be noted and further analyzed for several locations.
Thereafter, simultaneous magnetic anomalies and gravity models are generated and interpreted in detail. Three profiles are investigated, providing new insights into the tectonics and geological evolution of the Lombok Island. Geological structure of this island can be divided as two main parts with different consecutive ages: an old part (from late Oligocene to late Miocene) in the South and a younger one (from Pliocene to Holocene) in the North. A new subduction in the back arc region (the Flores Thrust zone) is considered mature and active, showing a tendency of progressive subduction during 2005–2008. Geothermal potential in the northern part of this island can be mapped in more detail using these geomagnetic regional survey data. The earlier estimates of reservoir depth can be confirmed further to a depth of about 800 m. Evaluation of temporal changes of the anomalies gives some possible explanations related to the evolution of the back arc region, large stress accumulations over the LSI region, a specific electrical characteristic of the crust of the Lombok Island region, and a structural discontinuity over this island.
Based on the results, several possible advanced studies involving geomagnetic data and anomaly investigations over the Lombok Island region can be suggested for the future:
i. Monitoring the subduction activity of the back arc region (the Flores Thrust zone) and the accumulated stress over the LSI, that could contribute to middle term hazard assessment with a special attention to the earthquake occurrence in this region. Continuous geomagnetic field measurements from a geomagnetic observatory which can be established in the northern part of the Lombok Island and systematic measurements at several repeat stations can be useful in this regards.
ii. Investigating the specific electrical characteristic (high conductivity) of the crust, that is probably related to some aquifer layers or metal mineralization. It needs other complementary geophysical methods, such as magnetotelluric (MT) or preferably DC resistivity measurements.
iii. Determining the existence of an active structural fault over the Lombok Island, that could be related to long term hazard assessment over the LSI region. This needs an extension of geomagnetic investigations over the neighbouring islands (the Bali Island in the West and the Sumbawa Island in the East; probably also the Sumba and the Flores islands). This seems possible because the regional magnetic lineations might be used to delineate some structural discontinuities, based on the modelling of contrasts in crustal magnetizations.
Biodiversity and intact ecological interactions form the basis for functional and resilient ecosystems that maintain optimal conditions for life on earth. During the second half of the 20th century, especially land-use changes and an intensification of agricultural management caused an unprecedented loss of biodiversity in agroecosystems worldwide. Concerns have been raised that the ongoing loss of biodiversity would ultimately lead to impaired ecological interactions and ecosystem functioning in agricultural landscapes. In order to stop biodiversity loss while producing enough food for a growing world population, we need to gain detailed knowledge on ecological interactions and the functioning of agroecosystems as a whole.
Bats (Chiroptera) represent an important component of global biodiversity, occupy a variety of ecological niches and fulfill numerous ecosystem services. Especially in temperate zone agroecosystems, bats were repeatedly reported to contribute to the reduction of pest insects above intensively managed arable fields. However, bat populations have been decimated by the consequence of land-use intensification which led to their legal protection status in the European Union (Council of Europe, 1979). The increasing number of wind turbines on arable fields poses an additional threat to bats as they might get injured or killed when flying too close to wind turbine blades. Although a large amount of land area is covered by arable fields, not much is known about how bats use the intensively managed agricultural landscape.
In the present thesis, my general aim was to identify the relevance of factors at different spatiotemporal scales for shaping species-specific bat activity above intensively managed arable fields. Therefore, I repeatedly monitored bat activity above open arable fields in a landscape dominated by agriculture which is located in Northeast Brandenburg, Germany. From 2012 to 2014, I recorded echolocation calls of bats on a total of 113 sites using a passive acoustic approach. I obtained a total of 27,779 recordings, identified the recorded echolocation calls manually to species level and calculated species-specific bat activity measures. Depending on the focus of research, I modeled the obtained species-specific activity measures using generalized linear and additive mixed effect models. In Chapter I, I focused on identifying seasonal patterns in several species-specific activity measures of different functional bat groups. In Chapter II, I investigated small-scale effects of landscape elements, such as hedgerows and forest edges, on the flight and foraging activity of different bat species along the edge-field interface. Additionally, I aimed at identifying whether these effects are influenced by small ponds located within arable field and whether these effects change across seasons. In Chapter III, my aim was to investigate the interaction between factors from different spatiotemporal levels on the flight and foraging activity of bats above arable fields. At the small spatial scale, I focused on prey availability, at a large spatial scale on selected parameters which describe landscape characteristics and at the temporal scale on seasonal effects.
The major findings obtained in each chapter can be summarized in the following three points. The first major finding is that not only landscape elements on a small spatial scale, e.g. a hedgerow at the edge of an arable field, but also landscape characteristics on a large spatial scale, e.g. landscape composition, shaped species-specific bat activity above open arable fields. This activity was also strongly influenced by interactions between landscape characteristics and local prey availability. Second, the influence of landscape elements and characteristics on bat activity above arable fields was not constant over time but changed across seasons with the strongest impact during summer as compared to spring and autumn. Third, I found indications of ecosystem service provided by N. noctula and P. nathusii in all three chapters, as especially these bat species were repeatedly found to forage above arable fields. This foraging activity was positively influenced by the proximity to landscape elements at the edge of the arable field but also by the presence of small ponds within the arable field.
In light of the obtained findings, I strongly recommend protecting and most importantly recreating semi-natural landscape elements in the agricultural landscape. Furthermore, I strongly recommend against the construction of wind turbines close to these linear woody vegetation edges as bats were found to be active close to these landscape elements. Additionally, the operation times for wind turbines should be down-regulated during the mating and migration period in autumn due to high bat activity above arable fields. Since bats are considered being good bioindicators, effective conservation measures for bats might contribute to the protection of species from other taxa leading to an overall support of biodiversity in agricultural landscapes. In their entirety, the findings in this thesis contribute to the knowledge of different aspects of bat ecology and shed light on the complex interplay between factors from different spatiotemporal levels that shape bat activity above arable fields. Additionally, they can serve as a basis for the improvement and development of conservation measures for bats in agricultural landscapes.
Spatiotemporal variations of key air pollutants and greenhouse gases in the Himalayan foothills
(2021)
South Asia is a rapidly developing, densely populated and highly polluted region that is facing the impacts of increasing air pollution and climate change, and yet it remains one of the least studied regions of the world scientifically. In recognition of this situation, this thesis focuses on studying (i) the spatial and temporal variation of key greenhouse gases (CO2 and CH4) and air pollutants (CO and O3) and (ii) the vertical distribution of air pollutants (PM, BC) in the foothills of the Himalaya. Five sites were selected in the Kathmandu Valley, the capital region of Nepal, along with two sites outside of the valley in the Makawanpur and Kaski districts, and conducted measurements during the period of 2013-2014 and 2016. These measurements are analyzed in this thesis.
The CO measurements at multiple sites in the Kathmandu Valley showed a clear diurnal cycle: morning and evening levels were high, with an afternoon dip. There are slight differences in the diurnal cycles of CO2 and CH4, with the CO2 and CH4 mixing ratios increasing after the afternoon dip, until the morning peak the next day. The mixing layer height (MLH) of the nocturnal stable layer is relatively constant (~ 200 m) during the night, after which it transitions to a convective mixing layer during the day and the MLH increases up to 1200 m in the afternoon. Pollutants are thus largely trapped in the valley from the evening until sunrise the following day, and the concentration of pollutants increases due to emissions during the night. During afternoon, the pollutants are diluted due to the circulation by the valley winds after the break-up of the mixing layer. The major emission sources of GHGs and air pollutants in the valley are transport sector, residential cooking, brick kilns, trash burning, and agro-residue burning. Brick industries are influential in the winter and pre-monsoon season. The contribution of regional forest fires and agro-residue burning are seen during the pre-monsoon season. In addition, relatively higher CO values were also observed at the valley outskirts (Bhimdhunga and Naikhandi), which indicates the contribution of regional emission sources. This was also supported by the presence of higher concentrations of O3 during the pre-monsoon season.
The mixing ratios of CO2 (419.3 ±6.0 ppm) and CH4 (2.192 ±0.066 ppm) in the valley were much higher than at background sites, including the Mauna Loa observatory (CO2: 396.8 ± 2.0 ppm, CH4:1.831 ± 0.110 ppm) and Waligaun (CO2: 397.7 ± 3.6 ppm, CH4: 1.879 ± 0.009 ppm), China, as well as at an urban site Shadnagar (CH4: 1.92 ± 0.07 ppm) in India.
The daily 8 hour maximum O3 average in the Kathmandu Valley exceeds the WHO recommended value during more than 80% of the days during the pre-monsoon period, which represents a significant risk for human health and ecosystems in the region. Moreover, in the measurements of the vertical distribution of particulate matter, which were made using an ultralight aircraft, and are the first of their kind in the region, an elevated polluted layer at around ca. 3000 m asl. was detected over the Pokhara Valley. The layer could be associated with the large-scale regional transport of pollution. These contributions towards understanding the distributions of key air pollutants and their main sources will provide helpful information for developing management plans and policies to help reduce the risks for the millions of people living in the region.
Spectral fingerprinting
(2015)
Current research on runoff and erosion processes, as well as an increasing demand for sustainable watershed management emphasize the need for an improved understanding of sediment dynamics. This involves the accurate assessment of erosion rates and sediment transfer, yield and origin. A variety of methods exist to capture these processes at the catchment scale. Among these, sediment fingerprinting, a technique to trace back the origin of sediment, has attracted increasing attention by the scientific community in recent years. It is a two-step procedure, based on the fundamental assumptions that potential sources of sediment can be reliably discriminated based on a set of characteristic ‘fingerprint’ properties, and that a comparison of source and sediment fingerprints allows to quantify the relative contribution of each source.
This thesis aims at further assessing the potential of spectroscopy to assist and improve the sediment fingerprinting technique. Specifically, this work focuses on (1) whether potential sediment sources can be reliably identified based on spectral features (‘fingerprints’), whether (2) these spectral fingerprints permit the quantification of relative source contribution, and whether (3) in situ derived source information is sufficient for this purpose. Furthermore, sediment fingerprinting using spectral information is applied in a study catchment to (4) identify major sources and observe how relative source contributions change between and within individual flood events. And finally, (5) spectral fingerprinting results are compared and combined with simultaneous sediment flux measurements to study sediment origin, transport and storage behaviour.
For the sediment fingerprinting approach, soil samples were collected from potential sediment sources within the Isábena catchment, a meso-scale basin in the central Spanish Pyrenees. Undisturbed samples of the upper soil layer were measured in situ using an ASD spectroradiometer and subsequently sampled for measurements in the laboratory. Suspended sediment was sampled automatically by means of ISCO samplers at the catchment as well as at the five major subcatchment outlets during flood events, and stored fine sediment from the channel bed was collected from 14 cross-sections along the main river. Artificial mixtures of known contributions were produced from source soil samples. Then, all source, sediment and mixture samples were dried and spectrally measured in the laboratory. Subsequently, colour coefficients and physically based features with relation to organic carbon, iron oxide, clay content and carbonate, were calculated from all in situ and laboratory spectra. Spectral parameters passing a number of prerequisite tests were submitted to principal component analyses to study natural clustering of samples, discriminant function analyses to observe source differentiation accuracy, and a mixing model for source contribution assessment. In addition, annual as well as flood event based suspended sediment fluxes from the catchment and its subcatchments were calculated from rainfall, water discharge and suspended sediment concentration measurements using rating curves and Quantile Regression Forests. Results of sediment flux monitoring were interpreted individually with respect to storage behaviour, compared to fingerprinting source ascriptions and combined with fingerprinting to assess their joint explanatory potential.
In response to the key questions of this work, (1) three source types (land use) and five spatial sources (subcatchments) could be reliably discriminated based on spectral fingerprints. The artificial mixture experiment revealed that while (2) laboratory parameters permitted source contribution assessment, (3) the use of in situ derived information was insufficient. Apparently, high discrimination accuracy does not necessarily imply good quantification results. When applied to suspended sediment samples of the catchment outlet, the spectral fingerprinting approach was able to (4) quantify the major sediment sources: badlands and the Villacarli subcatchment, respectively, were identified as main contributors, which is consistent with field observations and previous studies. Thereby, source contribution was found to vary both, within and between individual flood events. Also sediment flux was found to vary considerably, annually as well as seasonally and on flood event base. Storage was confirmed to play an important role in the sediment dynamics of the studied catchment, whereas floods with lower total sediment yield tend to deposit and floods with higher yield rather remove material from the channel bed. Finally, a comparison of flux measurements with fingerprinting results highlighted the fact that (5) immediate transport from sources to the catchment outlet cannot be assumed. A combination of the two methods revealed different aspects of sediment dynamics that none of the techniques could have uncovered individually.
In summary, spectral properties provide a fast, non-destructive, and cost-efficient means to discriminate and quantify sediment sources, whereas, unfortunately, straight-forward in situ collected source information is insufficient for the approach. Mixture modelling using artificial mixtures permits valuable insights into the capabilities and limitations of the method and similar experiments are strongly recommended to be performed in the future. Furthermore, a combination of techniques such as e.g. (spectral) sediment fingerprinting and sediment flux monitoring can provide comprehensive understanding of sediment dynamics.
Binaries play an important role in observational and theoretical astrophysics. Since the mass and the chemical composition are key ingredients for stellar evolution, high-resolution spectroscopy is an important and necessary tool to derive those parameters to high confidence in binaries. This involves carefully measured orbital motion by the determination of radial velocity (RV) shifts and sophisticated techniques to derive the abundances of elements within the stellar atmosphere.
A technique superior to conventional cross-correlation methods to determine RV shifts in known as spectral disentangling. Hence, a major task of this thesis was the design of a sophisticated software package for this approach. In order to investigate secondary effects, such as flux and line-profile variations, imprinting changes on the spectrum the behavior of spectral disentangling on such variability is a key to understand the derived values, to improve them, and to get information about the variability itself. Therefore, the spectral disentangling code presented in this thesis and available to the community combines multiple advantages: separation of the spectra for detailed chemical analysis, derivation of orbital elements, derivation of individual RVs in order to investigate distorted systems (either by third body interaction or relativistic effects), the suppression of telluric contaminations, the derivation of variability, and the possibility to apply the technique to eclipsing binaries (important for orbital inclination) or in general to systems that undergo flux-variations.
This code in combination with the spectral synthesis codes MOOG and SME was used in order to derive the carbon 12C/13C isotope ratio (CIR) of the benchmark binary Capella. The observational result will be set into context with theoretical evolution by the use of MESA models and resolves the discrepancy of theory and observations existing since the first measurement of Capella's CIR in 1976.
The spectral disentangling code has been made available to the community and its applicability to completely different behaving systems, Wolf-Rayet stars, have also been investigated and resulted in a published article.
Additionally, since this technique relies strongly on data quality, continues development of scientific instruments to achieve best observational data is of great importance in observational astrophysics. That is the reason why there has also been effort in astronomical instrumentation during the work on this thesis.
In this thesis, I study ultrafast dynamics in perovskite oxides using time resolved broadband spectroscopy. I focus on the observation of coherent phonon propagation by time resolved Brillouin scattering: following the excition of metal transducer films with a femtosecond infrared pump pulse, coherent phonon dynamics in the GHz frequency range are triggered. Their propagation is monitored using a delayed white light probe pulse. The technique is illustrated on various thin films and multilayered samples. I apply the technique to investigate the linear and nonlinear acoustic response in bulk SrTiO_3, which displays a ferroelastic phase transition from a cubic to a tetragonal structural phase at T_a=105 K. In the linear regime, I observe a coupling of the observed acoustic phonon mode to the softening optic modes describing the phase transition. In the nonlinear regime, I find a giant slowing down of the sound velocity in the low temperature phase that is only observable for a strain amplitude exceeding the tetragonality of the material. It is attributed to a coupling of the high frequency phonons to ferroelastic domain walls in the material. I propose a new mechanism for the coupling of strain waves to the domain walls that is only effective for high amplitude strain. A detailed study of the phonon attenuation across a wide temperature range shows that the phonon attenuation at low temperatures is influenced by the domain configuration, which is determined by interface strain. Preliminary measurements on magnetic-ferroelectric multilayers reveal that the excitation fluence needs to be carefully controlled when dynamics at phase transitions are studied.
Galaxies evolve on cosmological timescales and to study this evolution we can either study the stellar populations, tracing the star formation and chemical enrichment, or the dynamics, tracing interactions and mergers of galaxies as well as accretion. In the last decades this field has become one of the most active research areas in modern astrophysics and especially the use of integral field spectrographs furthered our understanding. This work is based on data of NGC 5102 obtained with the panoramic integral field spectrograph MUSE. The data are analysed with two separate and complementary approaches: In the first part, standard methods are used to measure the kinematics and than model the gravitational potential using these exceptionally high-quality data. In the second part I develop the new method of surface brightness fluctuation spectroscopy and quantitatively explore its potential to investigate the bright evolved stellar population.
Measuring the kinematics of NGC 5102 I discover that this low-luminosity S0 galaxy hosts two counter rotating discs. The more central stellar component co-rotates with the large amount of HI gas. Investigating the populations I find strong central age and metallicity gradients with a younger and more metal rich central population. The spectral resolution of MUSE does not allow to connect these population gradients with the two counter rotating discs.
The kinematic measurements are modelled with Jeans anisotropic models to infer the gravitational potential of NGC 5102. Under the self-consistent mass-follows-light assumption none of the Jeans models is able to reproduce the observed kinematics. To my knowledge this is the strongest evidence evidence for a dark matter dominated system obtained with this approach so far. Including a Navarro, Frenk & White dark matter halo immediately solves the discrepancies. A very robust result is the logarithmic slope of the total matter density. For this low-mass galaxy I find a value of -1.75 +- 0.04, shallower than an isothermal halo and even shallower than published values for more massive galaxies. This confirms a tentative relation between total mass slope and stellar mass of galaxies.
The Surface Brightness Fluctuation (SBF) method is a well established distance measure, but due to its sensitive to bright stars also used to study evolved stars in unresolved stellar populations. The wide-field spectrograph MUSE offers the possibility to apply this technique for the first time to spectroscopic data. In this thesis I develop the spectroscopic SBF technique and measure the first SBF spectrum of any galaxy. I discuss the challenges for measuring SBF spectra that rise due to the complexity of integral field spectrographs compared to imaging instruments.
Since decades, stellar population models indicate that SBFs in intermediate-to-old stellar systems are dominated by red giant branch and asymptotic giant branch stars. Especially the later carry significant model uncertainties, making these stars a scientifically interesting target. Comparing the NGC 5102 SBF spectrum with stellar spectra I show for the first time that M-type giants cause the fluctuations. Stellar evolution models suggest that also carbon rich thermally pulsating asymptotic giant branch stars should leave a detectable signal in the SBF spectrum. I cannot detect a significant contribution from these stars in the NGC 5102 SBF spectrum.
I have written a stellar population synthesis tool that predicts for the first time SBF spectra. I compute two sets of population models: based on observed and on theoretical stellar spectra. In comparing the two models I find that the models based on observed spectra predict weaker molecular features. The comparison with the NGC 5102 spectrum reveals that these models are in better agreement with the data.
Spectroscopy at the limit
(2018)
Die Wissenschaftsfreiheit ist ein Grundrecht, dessen Sinn und Auslegung im Rahmen von Reformen des Hochschulsystems nicht nur der Justiz, sondern auch der Wissenschaft selbst immer wieder Anlass zur Diskussion geben, so auch im Zuge der Einführung des so genannten Qualitätsmanagements von Studium und Lehre an deutschen Hochschulen. Die vorliegende Dissertationsschrift stellt die Ergebnisse einer empirischen Studie vor, die mit einer soziologischen Betrachtung des Qualitätsmanagements unterschiedlicher Hochschulen zu dieser Diskussion beiträgt.
Auf Grundlage der Prämisse, dass Verlauf und Folgen einer organisationalen Innovation nur verstanden werden können, wenn der alltägliche Umgang der Organisationsmitglieder mit den neuen Strukturen und Prozessen in die Analyse einbezogen wird, geht die Studie von der Frage aus, wie Akteurinnen und Akteure an deutschen Hochschulen die Qualitätsmanagementsysteme ihrer Organisationen nutzen. Die qualitative inhaltsanalytische Auswertung von 26 Leitfaden-Interviews mit Prorektorinnen und -rektoren, Qualitätsmanagement-Personal und Studiendekaninnen und -dekanen an neun Hochschulen ergibt, dass die Strategien der Akteursgruppen an den Hochschulen im Zusammenspiel mit strukturellen Aspekten unterschiedliche Dynamiken entstehen lassen, mit denen Implikationen für die Lehrfreiheit verbunden sind: Während die Autonomie der Lehrenden durch das Qualitätsmanagement an einigen Hochschulen unterstützt wird, sind sowohl Autonomie als auch Verantwortung für Studium und Lehre an anderen Hochschulen Gegenstand andauernder Konflikte, die auch das Qualitätsmanagement einschließen.
The propagation of test fields, such as electromagnetic, Dirac or linearized gravity, on a fixed spacetime manifold is often studied by using the geometrical optics approximation. In the limit of infinitely high frequencies, the geometrical optics approximation provides a conceptual transition between the test field and an effective point-particle description. The corresponding point-particles, or wave rays, coincide with the geodesics of the underlying spacetime. For most astrophysical applications of interest, such as the observation of celestial bodies, gravitational lensing, or the observation of cosmic rays, the geometrical optics approximation and the effective point-particle description represent a satisfactory theoretical model. However, the geometrical optics approximation gradually breaks down as test fields of finite frequency are considered.
In this thesis, we consider the propagation of test fields on spacetime, beyond the leading-order geometrical optics approximation. By performing a covariant Wentzel-Kramers-Brillouin analysis for test fields, we show how higher-order corrections to the geometrical optics approximation can be considered. The higher-order corrections are related to the dynamics of the spin internal degree of freedom of the considered test field. We obtain an effective point-particle description, which contains spin-dependent corrections to the geodesic motion obtained using geometrical optics. This represents a covariant generalization of the well-known spin Hall effect, usually encountered in condensed matter physics and in optics. Our analysis is applied to electromagnetic and massive Dirac test fields, but it can easily be extended to other fields, such as linearized gravity. In the electromagnetic case, we present several examples where the gravitational spin Hall effect of light plays an important role. These include the propagation of polarized light rays on black hole spacetimes and cosmological spacetimes, as well as polarization-dependent effects on the shape of black hole shadows. Furthermore, we show that our effective point-particle equations for polarized light rays reproduce well-known results, such as the spin Hall effect of light in an inhomogeneous medium, and the relativistic Hall effect of polarized electromagnetic wave packets encountered in Minkowski spacetime.
This thesis is focussed on the electronic properties of the new material class named topological insulators. Spin and angle resolved photoelectron spectroscopy have been applied to reveal several unique properties of the surface state of these materials. The first part of this thesis introduces the methodical background of these quite established experimental techniques.
In the following chapter, the theoretical concept of topological insulators is introduced. Starting from the prominent example of the quantum Hall effect, the application of topological invariants to classify material systems is illuminated. It is explained how, in presence of time reversal symmetry, which is broken in the quantum Hall phase, strong spin orbit coupling can drive a system into a topologically non trivial phase. The prediction of the spin quantum Hall effect in two dimensional insulators an the generalization to the three dimensional case of topological insulators is reviewed together with the first experimental realization of a three dimensional topological insulator in the Bi1-xSbx alloys given in the literature.
The experimental part starts with the introduction of the Bi2X3 (X=Se, Te) family of materials. Recent theoretical predictions and experimental findings on the bulk and surface electronic structure of these materials are introduced in close discussion to our own experimental results. Furthermore, it is revealed, that the topological surface state of Bi2Te3 shares its orbital symmetry with the bulk valence band and the observation of a temperature induced shift of the chemical potential is to a high probability unmasked as a doping effect due to residual gas adsorption.
The surface state of Bi2Te3 is found to be highly spin polarized with a polarization value of about 70% in a macroscopic area, while in Bi2Se3 the polarization appears reduced, not exceeding 50%. We, however, argue that the polarization is most likely only extrinsically limited in terms of the finite angular resolution and the lacking detectability of the out of plane component of the electron spin. A further argument is based on the reduced surface quality of the single crystals after cleavage and, for Bi2Se3 a sensitivity of the electronic structure to photon exposure.
We probe the robustness of the topological surface state in Bi2X3 against surface impurities in Chapter 5. This robustness is provided through the protection by the time reversal symmetry. Silver, deposited on the (111) surface of Bi2Se3 leads to a strong electron doping but the surface state is observed up to a deposited Ag mass equivalent to one atomic monolayer. The opposite sign of doping, i.e., hole-like, is observed by exposing oxygen to Bi2Te3. But while the n-type shift of Ag on Bi2Se3 appears to be more or less rigid, O2 is lifting the Dirac point of the topological surface state in Bi2Te3 out of the valence band minimum at $\Gamma$. After increasing the oxygen dose further, it is possible to shift the Dirac point to the Fermi level, while the valence band stays well beyond. The effect is found reversible, by warming up the samples which is interpreted in terms of physisorption of O2.
For magnetic impurities, i.e., Fe, we find a similar behavior as for the case of Ag in both Bi2Se3 and Bi2Te3. However, in that case the robustness is unexpected, since magnetic impurities are capable to break time reversal symmetry which should introduce a gap in the surface state at the Dirac point which in turn removes the protection. We argue, that the fact that the surface state shows no gap must be attributed to a missing magnetization of the Fe overlayer. In Bi2Te3 we are able to observe the surface state for deposited iron mass equivalents in the monolayer regime. Furthermore, we gain control over the sign of doping through the sample temperature during deposition.
Chapter6 is devoted to the lifetime broadening of the photoemission signal from the topological surface states of Bi2Se3 and Bi2Te3. It is revealed that the hexagonal warping of the surface state in Bi2Te3 introduces an anisotropy for electrons traveling along the two distinct high symmetry directions of the surface Brillouin zone, i.e., $\Gamma$K and $\Gamma$M. We show that the phonon coupling strength to the surface electrons in Bi2Te3 is in nice agreement with the theoretical prediction but, nevertheless, higher than one may expect. We argue that the electron-phonon coupling is one of the main contributions to the decay of photoholes but the relatively small size of the Fermi surface limits the number of phonon modes that may scatter off electrons. This effect is manifested in the energy dependence of the imaginary part of the electron self energy of the surface state which shows a decay to higher binding energies in contrast to the monotonic increase proportional to E$^2$ in the Fermi liquid theory due to electron-electron interaction.
Furthermore, the effect of the surface impurities of Chapter 5 on the quasiparticle life- times is investigated. We find that Fe impurities have a much stronger influence on the lifetimes as compared to Ag. Moreover, we find that the influence is stronger independently of the sign of the doping. We argue that this observation suggests a minor contribution of the warping on increased scattering rates in contrast to current belief. This is additionally confirmed by the observation that the scattering rates increase further with increasing silver amount while the doping stays constant and by the fact that clean Bi2Se3 and Bi2Te3 show very similar scattering rates regardless of the much stronger warping in Bi2Te3.
In the last chapter we report on a strong circular dichroism in the angle distribution of the photoemission signal of the surface state of Bi2Te3. We show that the color pattern obtained by calculating the difference between photoemission intensities measured with opposite photon helicity reflects the pattern expected for the spin polarization. However, we find a strong influence on strength and even sign of the effect when varying the photon energy. The sign change is qualitatively confirmed by means of one-step photoemission calculations conducted by our collaborators from the LMU München, while the calculated spin polarization is found to be independent of the excitation energy. Experiment and theory together unambiguously uncover the dichroism in these systems as a final state effect and the question in the title of the chapter has to be negated: Circular dichroism in the angle distribution is not a new spin sensitive technique.
The current thesis is focused on the properties of graphene supported by metallic substrates and specifically on the behaviour of electrons in such systems. Methods of scanning tunneling microscopy, electron diffraction and photoemission spectroscopy were applied to study the structural and electronic properties of graphene. The purpose of the first part of this work is to introduce the most relevant aspects of graphene physics and the methodical background of experimental techniques used in the current thesis.
The scientific part of this work starts with the extensive study by means of scanning tunneling microscopy of the nanostructures that appear in Au intercalated graphene on Ni(111). This study was aimed to explore the possible structural explanations of the Rashba-type spin splitting of ~100 meV experimentally observed in this system — much larger than predicted by theory. It was demonstrated that gold can be intercalated under graphene not only as a dense monolayer, but also in the form of well-periodic arrays of nanoclusters, a structure previously not reported. Such nanocluster arrays are able to decouple graphene from the strongly interacting Ni substrate and render it quasi-free-standing, as demonstrated by our DFT study. At the same time calculations confirm strong enhancement of the proximity-induced SOI in graphene supported by such nanoclusters in comparison to monolayer gold. This effect, attributed to the reduced graphene-Au distance in the case of clusters, provides a large Rashba-type spin splitting of ~60 meV.
The obtained results not only provide a possible mechanism of SOI enhancement in this particular system, but they can be also generalized for graphene on other strongly interacting substrates intercalated by nanostructures of heavy noble d metals.
Even more intriguing is the proximity of graphene to heavy sp-metals that were predicted to induce an intrinsic SOI and realize a spin Hall effect in graphene. Bismuth is the heaviest stable sp-metal and its compounds demonstrate a plethora of exciting physical phenomena. This was the motivation behind the next part of the current thesis, where structural and electronic properties of a previously unreported phase of Bi-intercalated graphene on Ir(111) were studied by means of scanning tunneling microscopy, spin- and angle-resolved photoemission spectroscopy and electron diffraction. Photoemission experiments revealed a remarkable, nearly ideal graphene band structure with strongly suppressed signatures of interaction between graphene and the Ir(111) substrate, moreover, the characteristic moiré pattern observed in graphene on Ir(111) by electron diffraction and scanning tunneling microscopy was strongly suppressed after intercalation. The whole set of experimental data evidences that Bi forms a dense intercalated layer that efficiently decouples graphene from the substrate. The interaction manifests itself only in the n-type charge doping (~0.4 eV) and a relatively small band gap at the Dirac point (~190 meV). The origin of this minor band gap is quite intriguing and in this work it was possible to exclude a wide range of mechanisms that could be responsible for it, such as induced intrinsic spin-orbit interaction, hybridization with the substrate states and corrugation of the graphene lattice. The main origin of the band gap was attributed to the A-B symmetry breaking and this conclusion found support in the careful analysis of the interference effects in photoemission that provided the band gap estimate of ~140 meV.
While the previous chapters were focused on adjusting the properties of graphene by proximity to heavy metals, graphene on its own is a great object to study various physical effects at crystal surfaces. The final part of this work is devoted to a study of surface scattering resonances by means of photoemission spectroscopy, where this effect manifests itself as a distinct modulation of photoemission intensity. Though scattering resonances were widely studied in the past by means of electron diffraction, studies about their observation in photoemission experiments started to appear only recently and they are very scarce.
For a comprehensive study of scattering resonances graphene was selected as a versatile model system with adjustable properties. After the theoretical and historical introduction to the topic of scattering resonances follows a detailed description of the unusual features observed in the photoemission spectra obtained in this work and finally the equivalence between these features and scattering resonances is proven. The obtained photoemission results are in a good qualitative agreement with the existing theory, as verified by our calculations in the framework of the interference model. This simple model gives a suitable explanation for the general experimental observations.
The possibilities of engineering the scattering resonances were also explored. A systematic study of graphene on a wide range of substrates revealed that the energy position of the resonances is in a direct relation to the magnitude of charge transfer between graphene and the substrate. Moreover, it was demonstrated that the scattering resonances in graphene on Ir(111) can be suppressed by nanopatterning either by a superlattice of Ir nanoclusters or by atomic hydrogen. These effects were attributed to strong local variations of tork function and/or destruction of long-range order of thephene lattice. The tunability of scattering resonances can be applied for optoelectronic devices based on graphene. Moreover, the results of this study expand the general understanding of the phenomenon of scattering resonances and are applicable to many other materials besides graphene.
Expansion und Pluralisierung des Sports lassen sich auch in öffentlichen Arbeitsmarktstatistiken nachweisen. Dies zeigen Analysen öffentlich eingesetzter Berufsverzeichnisse ab 1927 sowie Beschäftigungsdaten, Arbeitslosenzahlen und Daten zu offen gemeldeten Stellen der Bundesagentur für Arbeit. Diese wurden für eine Vielzahl von Sportberufen ab 1997 erstmals ausgewertet. Die Bedeutung von Sportberufen in Berufsverzeichnissen ist gewachsen. Neue Berufe fanden bei entsprechender Arbeitsmarktbedeutung Eingang in die Verzeichnisse. Vereinzelt zeigen sich auch neuere Sporttrends. Ferner gab es seit 1999 eine außergewöhnliche Zunahme geringfügig Beschäftigter in allen betrachteten Berufsordnungen mit Sportberufen, teils auch eine Zunahme der sozialversicherungspflichtig Beschäftigten. Fast ausnahmslos waren die Entwicklungen in beiden Beschäftigungsarten in den untersuchten Berufsordnungen weit günstiger als im übergeordneten Berufsumfeld. Für den überwiegenden Teil der Sportberufe ergab sich ein solches Ergebnis auch bei Betrachtung der Arbeitslosenzahlen, die von Anfang 1998 bis Ende 2004 ausgewertet wurden. Demgegenüber wurden der Bundesagentur für Arbeit für fast alle sportbezogenen Berufsklassen 2006 weniger offene ungeförderte Stellen gemeldet als noch 2000. Diese Entwicklung war jedoch nicht ausschließlich für die Berufsklassen im Sport zu beobachten. So sprechen die Ergebnisse zumindest für eine vergleichsweise gute Arbeitsmarktentwicklung in den meisten untersuchten Sportberufen. Die große Zunahme geringfügiger Beschäftigung zeigt aber, dass hier vor allem keine als Haupterwerbsquelle geeigneten Beschäftigungen entstanden sind. Dies reduziert zugleich die Chancen, mit diesen Berufen Arbeitslosigkeit zu reduzieren.
Spots on stellar surfaces are thought to be stellar analogues of sunspots. Thus, starspots are direct manifestations of strong magnetic fields. Their decay rate is directly related to the magnetic diffusivity, which itself is a key quantity for the deduction of an activity cycle length. So far, no single starspot decay has been observed, and thus no stellar activity cycle was inferred from its corresponding turbulent diffusivity.
We investigate the evolution of starspots on the rapidly-rotating K0 giant XX Triangulum. Continuous high-resolution and phase-resolved spectroscopy was obtained with the robotic 1.2-m STELLA telescope on Tenerife over a timespan of six years. With our line-profile inversion code iMap we reconstruct a total of 36 consecutive Doppler maps. To quantify starspot area decay and growth, we match the observed images with simplified spot models based on a Monte-Carlo approach.
It is shown that the surface of XX Tri is covered with large high-latitude and even polar spots and with occasional small equatorial spots. Just over the course of six years, we see a systematically changing spot distribution with various time scales and morphology such as spot fragmentation and spot merging as well as spot decay and formation.
For the first time, a starspot decay rate on another star than the Sun is determined. From our spot-decay analysis we determine an average linear decay rate of D = -0.067±0.006 Gm^2/day. From this decay rate, we infer a turbulent diffusivity of η_τ = (6.3±0.5) x 10^14 cm^2/s and consequently predict an activity cycle of 26±6 years. The obtained cycle length matches very well with photometric observations.
Our time-series of Doppler maps further enables to investigate the differential rotation of XX Tri. We therefore applied a cross-correlation analysis. We detect a weak solar-like differential rotation with a surface shear of α = 0.016±0.003. This value agrees with similar studies of other RS CVn stars.
Furthermore, we found evidence for active longitudes and flip-flops. Whereas the more active longitude is located in phase towards the (unseen) companion star, the weaker active longitude is located at the opposite stellar hemisphere. From their periodic appearance, we infer a flip-flop cycle of ~2 years. Both activity phenomena are common on late-type binary stars.
Last but not least we redetermine several astrophysical properties of XX Tri and its binary system, as large datasets of photometric and spectroscopic observations are available since its last determination in 1999. Additionally, we compare the rotational spot-modulation from photometric and spectroscopic studies.