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In the presence of a solid-liquid or liquid-air interface, bacteria can choose between a planktonic and a sessile lifestyle. Depending on environmental conditions, cells swimming in close proximity to the interface can irreversibly attach to the surface and grow into three-dimensional aggregates where the majority of cells is sessile and embedded in an extracellular polymer matrix (biofilm). We used microfluidic tools and time lapse microscopy to perform experiments with the polarly flagellated soil bacterium Pseudomonas putida (P. putida), a bacterial species that is able to form biofilms. We analyzed individual trajectories of swimming cells, both in the bulk fluid and in close proximity to a glass-liquid interface. Additionally, surface related growth during the early phase of biofilm formation was investigated. In the bulk fluid, P.putida shows a typical bacterial swimming pattern of alternating periods of persistent displacement along a line (runs) and fast reorientation events (turns) and cells swim with an average speed around 24 micrometer per second. We found that the distribution of turning angles is bimodal with a dominating peak around 180 degrees. In approximately six out of ten turning events, the cell reverses its swimming direction. In addition, our analysis revealed that upon a reversal, the cell systematically changes its swimming speed by a factor of two on average. Based on the experimentally observed values of mean runtime and rotational diffusion, we presented a model to describe the spreading of a population of cells by a run-reverse random walker with alternating speeds. We successfully recover the mean square displacement and, by an extended version of the model, also the negative dip in the directional autocorrelation function as observed in the experiments. The analytical solution of the model demonstrates that alternating speeds enhance a cells ability to explore its environment as compared to a bacterium moving at a constant intermediate speed. As compared to the bulk fluid, for cells swimming near a solid boundary we observed an increase in swimming speed at distances below d= 5 micrometer and an increase in average angular velocity at distances below d= 4 micrometer. While the average speed was maximal with an increase around 15% at a distance of d= 3 micrometer, the angular velocity was highest in closest proximity to the boundary at d=1 micrometer with an increase around 90% as compared to the bulk fluid. To investigate the swimming behavior in a confinement between two solid boundaries, we developed an experimental setup to acquire three-dimensional trajectories using a piezo driven objective mount coupled to a high speed camera. Results on speed and angular velocity were consistent with motility statistics in the presence of a single boundary. Additionally, an analysis of the probability density revealed that a majority of cells accumulated near the upper and lower boundaries of the microchannel. The increase in angular velocity is consistent with previous studies, where bacteria near a solid boundary were shown to swim on circular trajectories, an effect which can be attributed to a wall induced torque. The increase in speed at a distance of several times the size of the cell body, however, cannot be explained by existing theories which either consider the drag increase on cell body and flagellum near a boundary (resistive force theory) or model the swimming microorganism by a multipole expansion to account for the flow field interaction between cell and boundary. An accumulation of swimming bacteria near solid boundaries has been observed in similar experiments. Our results confirm that collisions with the surface play an important role and hydrodynamic interactions alone cannot explain the steady-state accumulation of cells near the channel walls. Furthermore, we monitored the number growth of cells in the microchannel under medium rich conditions. We observed that, after a lag time, initially isolated cells at the surface started to grow by division into colonies of increasing size, while coexisting with a comparable smaller number of swimming cells. After 5:50 hours, we observed a sudden jump in the number of swimming cells, which was accompanied by a breakup of bigger clusters on the surface. After approximately 30 minutes where planktonic cells dominated in the microchannel, individual swimming cells reattached to the surface. We interpret this process as an emigration and recolonization event. A number of complementary experiments were performed to investigate the influence of collective effects or a depletion of the growth medium on the transition. Similar to earlier observations on another bacterium from the same family we found that the release of cells to the swimming phase is most likely the result of an individual adaption process, where syntheses of proteins for flagellar motility are upregulated after a number of division cycles at the surface.
Supermassive black holes reside in the hearts of almost all massive galaxies. Their evolutionary path seems to be strongly linked to the evolution of their host galaxies, as implied by several empirical relations between the black hole mass (M BH ) and different host galaxy properties. The physical driver of this co-evolution is, however, still not understood. More mass measurements over homogeneous samples and a detailed understanding of systematic uncertainties are required to fathom the origin of the scaling relations.
In this thesis, I present the mass estimations of supermassive black holes in the nuclei of one late-type and thirteen early-type galaxies. Our SMASHING sample extends from the intermediate to the massive galaxy mass regime and was selected to fill in gaps in number of galaxies along the scaling relations. All galaxies were observed at high spatial resolution, making use of the adaptive-optics mode of integral field unit (IFU) instruments on state-of-the-art telescopes (SINFONI, NIFS, MUSE). I extracted the stellar kinematics from these observations and constructed dynamical Jeans and Schwarzschild models to estimate the mass of the central black holes robustly. My new mass estimates increase the number of early-type galaxies with measured black hole masses by 15%. The seven measured galaxies with nuclear light deficits (’cores’) augment the sample of cored galaxies with measured black holes by 40%. Next to determining massive black hole masses, evaluating the accuracy of black hole masses is crucial for understanding the intrinsic scatter of the black hole- host galaxy scaling relations. I tested various sources of systematic uncertainty on my derived mass estimates.
The M BH estimate of the single late-type galaxy of the sample yielded an upper limit, which I could constrain very robustly. I tested the effects of dust, mass-to-light ratio (M/L) variation, and dark matter on my measured M BH . Based on these tests, the typically assumed constant M/L ratio can be an adequate assumption to account for the small amounts of dark matter in the center of that galaxy. I also tested the effect of a variable M/L variation on the M BH measurement on a second galaxy. By considering stellar M/L variations in the dynamical modeling, the measured M BH decreased by 30%. In the future, this test should be performed on additional galaxies to learn how an as constant assumed M/L flaws the estimated black hole masses.
Based on our upper limit mass measurement, I confirm previous suggestions that resolving the predicted BH sphere-of-influence is not a strict condition to measure black hole masses. Instead, it is only a rough guide for the detection of the black hole if high-quality, and high signal-to-noise IFU data are used for the measurement. About half of our sample consists of massive early-type galaxies which show nuclear surface brightness cores and signs of triaxiality. While these types of galaxies are typically modeled with axisymmetric modeling methods, the effects on M BH are not well studied yet. The massive galaxies of our presented galaxy sample are well suited to test the effect of different stellar dynamical models on the measured black hole mass in evidently triaxial galaxies. I have compared spherical Jeans and axisymmetric Schwarzschild models and will add triaxial Schwarzschild models to this comparison in the future. The constructed Jeans and Schwarzschild models mostly disagree with each other and cannot reproduce many of the triaxial features of the galaxies (e.g., nuclear sub-components, prolate rotation). The consequence of the axisymmetric-triaxial assumption on the accuracy of M BH and its impact on the black hole - host galaxy relation needs to be carefully examined in the future.
In the sample of galaxies with published M BH , we find measurements based on different dynamical tracers, requiring different observations, assumptions, and methods. Crucially, different tracers do not always give consistent results. I have used two independent tracers (cold molecular gas and stars) to estimate M BH in a regular galaxy of our sample. While the two estimates are consistent within their errors, the stellar-based measurement is twice as high as the gas-based. Similar trends have also been found in the literature. Therefore, a rigorous test of the systematics associated with the different modeling methods is required in the future. I caution to take the effects of different tracers (and methods) into account when discussing the scaling relations.
I conclude this thesis by comparing my galaxy sample with the compilation of galaxies with measured black holes from the literature, also adding six SMASHING galaxies, which were published outside of this thesis. None of the SMASHING galaxies deviates significantly from the literature measurements. Their inclusion to the published early-type galaxies causes a change towards a shallower slope for the M BH - effective velocity dispersion relation, which is mainly driven by the massive galaxies of our sample. More unbiased and homogenous measurements are needed in the future to determine the shape of the relation and understand its physical origin.
In dieser Arbeit wurden zwei Themenbereiche bearbeitet: 1. Ellipsometrie an Adsorpionsschichten niedermolekularer Tenside an der Wasser/Luft-Grenzfläche (Ellipsometrie ist geeignet, adsorbierte Mengen von nicht- und zwitterionischen Tensiden zu messen, bei ionischen werden zusätzlich die Gegenionen mit erfaßt; Ellipsometrie mißt sich ändernde Gegenionenverteilung). 2. Ellipsometrische Untersuchung von endadsorbierten Polymerbürsten an der Wasser/Öl-Grenzfläche (Ellipsometrie ist nicht in der Lage, verschiedene Segmentkonzentrationsprofile innerhalb der Bürste aufzulösen, ist aber sehr wohl geeignet, Skalengesetze für Dicken und Drücke in Abhängigkeit von Ankerdichte und Kettenlänge der Polymere zu überprüfen; für in Heptan gequollene Poly-isobuten-Bürsten konnte gezeigt werden, daß sie sich entsprechend den theoretischen Vorhersagen für Bürsten in einem theta-Lösungsmittel verhalten)
Partial synchronous states exist in systems of coupled oscillators between full synchrony and asynchrony. They are an important research topic because of their variety of different dynamical states. Frequently, they are studied using phase dynamics. This is a caveat, as phase dynamics are generally obtained in the weak coupling limit of a first-order approximation in the coupling strength. The generalization to higher orders in the coupling strength is an open problem. Of particular interest in the research of partial synchrony are systems containing both attractive and repulsive coupling between the units. Such a mix of coupling yields very specific dynamical states that may help understand the transition between full synchrony and asynchrony. This thesis investigates partial synchronous states in mixed-coupling systems. First, a method for higher-order phase reduction is introduced to observe interactions beyond the pairwise one in the first-order phase description, hoping that these may apply to mixed-coupling systems. This new method for coupled systems with known phase dynamics of the units gives correct results but, like most comparable methods, is computationally expensive. It is applied to three Stuart-Landau oscillators coupled in a line with a uniform coupling strength. A numerical method is derived to verify the analytical results. These results are interesting but give importance to simpler phase models that still exhibit exotic states. Such simple models that are rarely considered are Kuramoto oscillators with attractive and repulsive interactions. Depending on how the units are coupled and the frequency difference between the units, it is possible to achieve many different states. Rich synchronization dynamics, such as a Bellerophon state, are observed when considering a Kuramoto model with attractive interaction in two subpopulations (groups) and repulsive interactions between groups. In two groups, one attractive and one repulsive, of identical oscillators with a frequency difference, an interesting solitary state appears directly between full and partial synchrony. This system can be described very well analytically.
Variationen der stratosphärischen Residualzirkulation und ihr Einfluss auf die Ozonverteilung
(2006)
Die Residualzirkulation entspricht der mittleren Massenzirkulation und beschreibt die im zonalen Mittel stattfindenden meridionalen Transportprozesse. Die Variationen der Residualzirkulation bestimmen gemeinsam mit dem anthropogen verursachten Ozonabbau die jährlichen Schwankungen der Ozongesamtsäule im arktischen Frühling. In der vorliegenden Arbeit wird die Geschwindigkeit des arktischen Astes der Residualzirkulation aus atmosphärischen Daten gewonnen. Zu diesem Zweck wird das diabatische Absinken im Polarwirbel mit Hilfe von Trajektorienrechnungen bestimmt. Die vertikalen Bewegungen der Luftpakete können mit vertikalen Windfeldern oder entsprechend einem neuen Ansatz mit diabatischen Heizraten angetrieben werden. Die Eingabedaten stammen aus dem 45 Jahre langen Reanalyse-Datensatz des "European Centre for Medium Range Weather Forecast" (ECMWF). Außerdem kann für die Jahre ab 1984 die operationelle ECMWF-Analyse verwendet werden. Die Qualität und Robustheit der Heizraten- und Trajektorienrechnungen werden durch Sensitivitätsstudien und Vergleiche mit anderen Modellen untermauert. Anschließend werden umfangreiche Trajektorienensemble statistisch ausgewertet, um ein detailliertes, zeit- und höhenaufgelöstes Bild des diabatischen Absinkens zu ermitteln. In diesem Zusammenhang werden zwei Methoden entwickelt, um das Absinken gemittelt im Polarwirbel oder als Funktion der äquivalenten Breite zu bestimmen. Es wird gezeigt, dass es notwendig ist den Lagrangeschen auf Trajektorienrechnungen basierenden Ansatz zu verfolgen, da die einfachen Eulerschen Mittel Abweichungen zu den Lagrangeschen Vertikalgeschwindigkeiten aufweisen. Das wirbelgemittelte Absinken wird für einzelne Winter mit dem beobachteten Absinken langlebiger Spurengase und anderen Modellstudien verglichen. Der Vergleich zeigt, dass das Absinken basierend auf den vertikalen Windfeldern der ECMWF-Datensätze den Nettoluftmassentransport durch die Residualzirkulation sehr stark überschätzt. Der neue Ansatz basierend auf den Heizraten ergibt hingegen realistische Ergebnisse und wird aus diesem Grund für alle Rechnungen verwendet. Es wird erstmalig eine Klimatologie des diabatischen Absinkens über einen fast fünf Jahrzehnte umfassenden Zeitraum erstellt. Die Klimatologie beinhaltet das vertikal und zeitlich aufgelöste diabatische Absinken gemittelt über den gesamten Polarwirbel und Informationen über die räumliche Struktur des vertikalen Absinkens. Die natürliche Jahr-zu-Jahr Variabilität des diabatischen Absinkens ist sehr stark ausgeprägt. Es wird gezeigt, dass zwischen der ECMWF-Zeitreihe des diabatischen Absinkens und der Zeitreihe aus einem unabhängig analysierten Temperaturdatensatz hohe Korrelationen bestehen. Erstmals wird der Einfluss von Transportprozessen auf die Ozongesamtsäule im arktischen Frühling direkt quantifiziert. Es wird gezeigt, dass die Jahr-zu-Jahr Variabilität der Ozongesamtsäule im arktischen Frühling zu gleichen Anteilen durch die Variabilität der dynamischen Komponente und durch die Variabilität der chemischen Komponente beeinflusst wird. Die gefundenen Variabilitäten von diabatischem Absinken und Ozoneintrag in hohen Breiten werden mit der vertikalen Ausbreitung planetarer Wellen aus der Troposphäre in die Stratosphäre in Beziehung gesetzt.
Ferroic materials have attracted a lot of attention over the years due to their wide range of applications in sensors, actuators, and memory devices. Their technological applications originate from their unique properties such as ferroelectricity and piezoelectricity. In order to optimize these materials, it is necessary to understand the coupling between their nanoscale structure and transient response, which are related to the atomic structure of the unit cell.
In this thesis, synchrotron X-ray diffraction is used to investigate the structure of ferroelectric thin film capacitors during application of a periodic electric field. Combining electrical measurements with time-resolved X-ray diffraction on a working device allows for visualization of the interplay between charge flow and structural motion. This constitutes the core of this work. The first part of this thesis discusses the electrical and structural dynamics of a ferroelectric Pt/Pb(Zr0.2,Ti0.8)O3/SrRuO3 heterostructure during charging, discharging, and polarization reversal. After polarization reversal a non-linear piezoelectric response develops on a much longer time scale than the RC time constant of the device. The reversal process is inhomogeneous and induces a transient disordered domain state. The structural dynamics under sub-coercive field conditions show that this disordered domain state can be remanent and can be erased with an appropriate voltage pulse sequence. The frequency-dependent dynamic characterization of a Pb(Zr0.52,Ti0.48)O3 layer, at the morphotropic phase boundary, shows that at high frequency, the limited domain wall velocity causes a phase lag between the applied field and both the structural and electrical responses. An external modification of the RC time constant of the measurement delays the switching current and widens the electromechanical hysteresis loop while achieving a higher compressive piezoelectric strain within the crystal.
In the second part of this thesis, time-resolved reciprocal space maps of multiferroic BiFeO3 thin films were measured to identify the domain structure and investigate the development of an inhomogeneous piezoelectric response during the polarization reversal. The presence of 109° domains is evidenced by the splitting of the Bragg peak.
The last part of this work investigates the effect of an optically excited ultrafast strain or heat pulse propagating through a ferroelectric BaTiO3 layer, where we observed an additional current response due to the laser pulse excitation of the metallic bottom electrode of the heterostructure.
Galaxy clusters are the largest known gravitationally bound objects, their study is important for both an intrinsic understanding of their systems and an investigation of the large scale structure of the universe. The multi- component nature of galaxy clusters offers multiple observable signals across the electromagnetic spectrum. At X-ray wavelengths, galaxy clusters are simply identified as X-ray luminous, spatially extended, and extragalactic sources. X-ray observations offer the most powerful technique for constructing cluster catalogues. The main advantages of the X-ray cluster surveys are their excellent purity and completeness and the X-ray observables are tightly correlated with mass, which is indeed the most fundamental parameter of clusters. In my thesis I have conducted the 2XMMi/SDSS galaxy cluster survey, which is a serendipitous search for galaxy clusters based on the X-ray extended sources in the XMM-Newton Serendipitous Source Catalogue (2XMMi-DR3). The main aims of the survey are to identify new X-ray galaxy clusters, investigate their X-ray scaling relations, identify distant cluster candidates, and study the correlation of the X-ray and optical properties. The survey is constrained to those extended sources that are in the footprint of the Sloan Digital Sky Survey (SDSS) in order to be able to identify the optical counterparts as well as to measure their redshifts that are mandatory to measure their physical properties. The overlap area be- tween the XMM-Newton fields and the SDSS-DR7 imaging, the latest SDSS data release at the starting of the survey, is 210 deg^2. The survey comprises 1180 X-ray cluster candidates with at least 80 background-subtracted photon counts, which passed the quality control process. To measure the optical redshifts of the X-ray cluster candidates, I used three procedures; (i) cross-matching these candidates with the recent and largest optically selected cluster catalogues in the literature, which yielded the photometric redshifts of about a quarter of the X-ray cluster candidates. (ii) I developed a finding algorithm to search for overdensities of galaxies at the positions of the X-ray cluster candidates in the photometric redshift space and to measure their redshifts from the SDSS-DR8 data, which provided the photometric redshifts of 530 groups/clusters. (iii) I developed an algorithm to identify the cluster candidates associated with spectroscopically targeted Luminous Red Galaxies (LRGs) in the SDSS-DR9 and to measure the cluster spectroscopic redshift, which provided 324 groups and clusters with spectroscopic confirmation based on spectroscopic redshift of at least one LRG. In total, the optically confirmed cluster sample comprises 574 groups and clusters with redshifts (0.03 ≤ z ≤ 0.77), which is the largest X-ray selected cluster catalogue to date based on observations from the current X-ray observatories (XMM-Newton, Chandra, Suzaku, and Swift/XRT). Among the cluster sample, about 75 percent are newly X-ray discovered groups/clusters and 40 percent are new systems to the literature. To determine the X-ray properties of the optically confirmed cluster sample, I reduced and analysed their X-ray data in an automated way following the standard pipelines of processing the XMM-Newton data. In this analysis, I extracted the cluster spectra from EPIC(PN, MOS1, MOS2) images within an optimal aperture chosen to maximise the signal-to-noise ratio. The spectral fitting procedure provided the X-ray temperatures kT (0.5 - 7.5 keV) for 345 systems that have good quality X-ray data. For all the optically confirmed cluster sample, I measured the physical properties L500 (0.5 x 10^42 – 1.2 x 10^45 erg s-1 ) and M500 (1.1 x 10^13 – 4.9 x 10^14 M⊙) from an iterative procedure using published scaling relations. The present X-ray detected groups and clusters are in the low and intermediate luminosity regimes apart from few luminous systems, thanks to the XMM-Newton sensitivity and the available XMM-Newton deep fields The optically confirmed cluster sample with measurements of redshift and X-ray properties can be used for various astrophysical applications. As a first application, I investigated the LX - T relation for the first time based on a large cluster sample of 345 systems with X-ray spectroscopic parameters drawn from a single survey. The current sample includes groups and clusters with wide ranges of redshifts, temperatures, and luminosities. The slope of the relation is consistent with the published ones of nearby clusters with higher temperatures and luminosities. The derived relation is still much steeper than that predicted by self-similar evolution. I also investigated the evolution of the slope and the scatter of the LX - T relation with the cluster redshift. After excluding the low luminosity groups, I found no significant changes of the slope and the intrinsic scatter of the relation with redshift when dividing the sample into three redshift bins. When including the low luminosity groups in the low redshift subsample, I found its LX - T relation becomes after than the relation of the intermediate and high redshift subsamples. As a second application of the optically confirmed cluster sample from our ongoing survey, I investigated the correlation between the cluster X-ray and the optical parameters that have been determined in a homogenous way. Firstly, I investigated the correlations between the BCG properties (absolute magnitude and optical luminosity) and the cluster global proper- ties (redshift and mass). Secondly, I computed the richness and the optical luminosity within R500 of a nearby subsample (z ≤ 0.42, with a complete membership detection from the SDSS data) with measured X-ray temperatures from our survey. The relation between the estimated optical luminosity and richness is also presented. Finally, the correlation between the cluster optical properties (richness and luminosity) and the cluster global properties (X-ray luminosity, temperature, mass) are investigated.
This thesis is focused on the electronic, spin-dependent and dynamical properties of thin magnetic systems. Photoemission-related techniques are combined with synchrotron radiation to study the spin-dependent properties of these systems in the energy and time domains. In the first part of this thesis, the strength of electron correlation effects in the spin-dependent electronic structure of ferromagnetic bcc Fe(110) and hcp Co(0001) is investigated by means of spin- and angle-resolved photoemission spectroscopy. The experimental results are compared to theoretical calculations within the three-body scattering approximation and within the dynamical mean-field theory, together with one-step model calculations of the photoemission process. From this comparison it is demonstrated that the present state of the art many-body calculations, although improving the description of correlation effects in Fe and Co, give too small mass renormalizations and scattering rates thus demanding more refined many-body theories including nonlocal fluctuations. In the second part, it is shown in detail monitoring by photoelectron spectroscopy how graphene can be grown by chemical vapour deposition on the transition-metal surfaces Ni(111) and Co(0001) and intercalated by a monoatomic layer of Au. For both systems, a linear E(k) dispersion of massless Dirac fermions is observed in the graphene pi-band in the vicinity of the Fermi energy. Spin-resolved photoemission from the graphene pi-band shows that the ferromagnetic polarization of graphene/Ni(111) and graphene/Co(0001) is negligible and that graphene on Ni(111) is after intercalation of Au spin-orbit split by the Rashba effect. In the last part, a time-resolved x-ray magnetic circular dichroic-photoelectron emission microscopy study of a permalloy platelet comprising three cross-tie domain walls is presented. It is shown how a fast picosecond magnetic response in the precessional motion of the magnetization can be induced by means of a laser-excited photoswitch. From a comparision to micromagnetic calculations it is demonstrated that the relatively high precessional frequency observed in the experiments is directly linked to the nature of the vortex/antivortex dynamics and its response to the magnetic perturbation. This includes the time-dependent reversal of the vortex core polarization, a process which is beyond the limit of detection in the present experiments.
Magnetorotational instability (MRI) is one of the most important and most common instabilities in astrophysics. Today it is widely accepted that it serves as a major source of turbulent viscosity in accretion disks, the most energy efficient objects in the universe. The importance of the MRI for astrophysics has been realized only in recent fifteen years. However, originally it was discovered much earlier, in 1959, in a very different context. Theoretical flow of a conducting liquid confined between differentially rotating cylinders in the presence of an external magnetic field was analyzed. The central conclusion is that the additional magnetic field parallel to the axis of rotation can destabilize otherwise stable flow. Theory of non-magnetized fluid motion between rotating cylinders has much longer history, though. It has been studied already in 1888 and today such setup is usually referred as a Taylor-Couette flow. To prove experimentally the existence of MRI in a magnetized Taylor-Couette flow is a demanding task and different MHD groups around the world try to achieve it. The main problem lies in the fact that laboratory liquid metals which are used in such experiments are characterized by small magnetic Prandtl number. Consequently rotation rates of the cylinders must be extremely large and vast amount of technical problems emerge. One of the most important difficulties is an influence of plates enclosing the cylinders in any experiment. For fast rotation the plates tend to dominate the whole flow and the MRI can not be observed. In this thesis we discuss a special helical configuration of the applied magnetic field which allows the critical rotation rates to be much smaller. If only the axial magnetic field is present, the cylinders must rotate with angular velocities corresponding to Reynolds numbers of order Re ≈ 10^6. With the helical field this number is dramatically reduced to Re ≈ 10^3. The azimuthal component of the magnetic field can be easily generated by letting an electric current through the axis of rotation, In a Taylor-Couette flow the (primary) instability manifests itself as Taylor vortices. The specific geometry of the helical magnetic field leads to a traveling wave solution and the vortices are drifting in a direction determined by rotation and the magnetic field. In an idealized study for infinitely long cylinders this is not a problem. However, if the cylinders have finite length and are bounded vertically by the plates the situation is different. In this dissertation it is shown, with use of numerical methods, that the traveling wave solution also exists for MHD Taylor-Couette flow at finite aspect ratio H/D, H being height of the cylinders, D width of the gap between them. The nonlinear simulations provide amplitudes of fluid velocity which are helpful in designing an experiment. Although the plates disturb the flow, parameters like the drift velocity indicate that the helical MRI operates in this case. The idea of the helical MRI was implemented in a very recent experiment PROMISE. The results provided, for the first time, an evidence that the (helical) MRI indeed exists. Nevertheless, the influence of the vertical endplates was evident and the experiment can be, in principle, improved. Exemplary methods of reduction of the end-effect are here proposed. Near the vertical boundaries develops an Ekman-Hartmann layer. Study of this layer for the MHD Taylor-Couette system as well as its impact on the global flow properties is presented. It is shown that the plates, especially if they are conducting, can disturb the flow far more then previously thought also for relatively slow rotation rates.
We calculate the additional carbon emissions as a result of the conversion of natural land in a process of urbanisation; and the change of carbon flows by “urbanised” ecosystems, when the atmospheric carbon is exported to the neighboring territories, from 1980 till 2050 for the eight regions of the world. As a scenario we use combined UN and demographic model′s prognoses for regional total and urban population growth. The calculations of urban areas dynamics are based on two models: the regression model and the Gamma-model. The urbanised area is sub-divided on built-up, „green“ (parks, etc.) and informal settlements (favelas) areas. The next step is to calculate the regional and world dynamics of carbon emission and export, and the annual total carbon balance. Both models give similar results with some quantitative differences. In the first model, the world annual emissions attain a maximum of 205 MtC/year between 2020-2030. Emissions will then slowly decrease. The maximum contributions are given by China and the Asia and Pacific regions. In the second model, world annual emissions increase to 1.25 GtC in 2005, beginning to decrease afterwards. If we compare the emission maximum with the annual emission caused by deforestation, 1.36GtC per year, then we can say that the role of urbanised territories (UT) is of a comparable magnitude. Regarding the world annual export of carbon by UT, we observe its monotonous growth by three times, from 24 MtC to 66 MtC in the first model, and from 249 MtC to 505 MtC in the second one. The latter, is therefore comparable to the amount of carbon transported by rivers into the ocean (196-537 MtC). By estimating the total balance we find that urbanisation shifts the total balance towards a “sink” state. The urbanisation is inhibited in the interval 2020-2030, and by 2050 the growth of urbanised areas would almost stop. Hence, the total emission of natural carbon at that stage will stabilise at the level of the 1980s (80 MtC per year). As estimated by the second model, the total balance, being almost constant until 2000, then starts to decrease at an almost constant rate. We can say that by the end of the XXI century, the total carbon balance will be equal to zero, when the exchange flows are fully balanced, and may even be negative, when the system begins to take up carbon from the atmosphere, i.e., becomes a “sink”.
Organic solar cells (OSCs) represent a new generation of solar cells with a range of captivating attributes including low-cost, light-weight, aesthetically pleasing appearance, and flexibility. Different from traditional silicon solar cells, the photon-electron conversion in OSCs is usually accomplished in an active layer formed by blending two kinds of organic molecules (donor and acceptor) with different energy levels together.
The first part of this thesis focuses on a better understanding of the role of the energetic offset and each recombination channel on the performance of these low-offset OSCs. By combining advanced experimental techniques with optical and electrical simulation, the energetic offsets between CT and excitons, several important insights were achieved: 1. The short circuit current density and fill-factor of low-offset systems are largely determined by field-dependent charge generation in such low-offset OSCs. Interestingly, it is strongly evident that such field-dependent charge generation originates from a field-dependent exciton dissociation yield. 2. The reduced energetic offset was found to be accompanied by strongly enhanced bimolecular recombination coefficient, which cannot be explained solely by exciton repopulation from CT states. This implies the existence of another dark decay channel apart from CT.
The second focus of the thesis was on the technical perspective. In this thesis, the influence of optical artifacts in differential absorption spectroscopy upon the change of sample configuration and active layer thickness was studied. It is exemplified and discussed thoroughly and systematically in terms of optical simulations and experiments, how optical artifacts originated from non-uniform carrier profile and interference can manipulate not only the measured spectra, but also the decay dynamics in various measurement conditions. In the end of this study, a generalized methodology based on an inverse optical transfer matrix formalism was provided to correct the spectra and decay dynamics manipulated by optical artifacts.
Overall, this thesis paves the way for a deeper understanding of the keys toward higher PCEs in low-offset OSC devices, from the perspectives of both device physics and characterization techniques.
The solar tachocline is a thin transition layer between the solar radiative zone rotating uniformly and the solar convection zone, which has a mainly latitudinal differential rotation profile. This layer has a thickness of less than $0.05R_{\sun}$ and is subject to extreme radial as well as latitudinal shears. Helioseismological estimates put this layer at roughly $0.7R_{\sun}$. The tachocline mostly resides in the sub-adiabatic, non-turbulent radiative interior, except for a small overlap with the convection zone on the top. Many proposed dynamo mechanisms involve strong toroidal magnetic fields in this transition region. The exact mechanisms behind the formation of such a thin layer is still disputed. A very plausible mechanism is the one involving a weak, relic poloidal magnetic field trapped inside the radiative zone, which is responsible for expelling differential rotation outwards. This was first proposed by \citet{RK97}. The present work develops this idea with numerical simulations including additional effects like meridional circulation. It is shown that a relic field of 1~Gauss or smaller would be sufficient to explain the observed thickness of the tachocline. The stability of the solar tachocline is addressed as the next part of the problem. It is shown that the tachocline is stable up to a differential rotation of 52\% in the absence of magnetic fields. This is a new finding as compared to the earlier two dimensional models which estimated the solar differential rotation (about 28\%) to be marginally stable or even unstable. The changed stability limit is attributed to the changed stability criterion of the 3-dimensional model which also involves radial gradients of the angular velocity. In the presence of toroidal magnetic field belts, the lowest non-axisymmetric mode is shown to be the most unstable one for the radiative part of the tachocline. It is estimated that the tachocline would become unstable for toroidal fields exceeding about 100~Gauss. With both formation and stability questions satisfactorily addressed, this work presents the most comprehensive analysis of the physical processes in the solar tachocline to date.
Wasserdampf in der Stratosphäre und Troposphäre ist eines der wichtigsten atmosphärischen Treibhausgase. Neben seiner Bedeutung für das Klima hat es großen Einfluss auf die Bildung von polaren stratosphärischen Wolken sowie auf die atmosphärische Chemie. Weltweit erstmalig soll innerhalb eines Forscherverbundes in Deutschland ein leistungsstarkes, mobiles, abtastendes Wasserdampf-DIAL zur dreidimensional hochaufgelösten Messung des atmosphärischen Wasserdampfs entwickelt werden. Mit dem Wasserdampf-DIAL können Wasserdampfkonzentrationen in der Atmosphäre mit hoher zeitlicher und räumlicher Auflösung gemessen werden. Das DIAL basiert auf einem Titan-Saphir-Laser oder einem dazu alternativen OPO-Laser (optisch parametrischer Oszillator). Der für das optische Pumpen dieser Laser nötige Pumplaser wurde im Rahmen dieser Arbeit in der Arbeitsgruppe Nichtlineare Optik des Instituts für Physik der Universität Potsdam entwickelt. Ein hochauflösendes, mobiles DIAL erfordert einen Pumplaser mit großen Pulsenergien, guter Strahlqualität und einer hohen Effizienz. Um diese Ziele zu erreichen, wurde ein MOPA-System (Master Oscillator Power Amplifier) mit Frequenzstabilisierung auf der Basis von doppelbrechungskompensierten, transversal diodengepumpten Laserstäben entwickelt und untersucht. Auf dem Weg dahin wurden unterschiedliche Realisierungsmöglichkeiten des MOPA-Systems geprüft. Im Rahmen dessen wurden die Festkörperlasermaterialien Yb:YAG [1], kerndotierte Nd:YAG-Keramik [2] und herkömmliches Nd:YAG vorgestellt und hinsichtlich ihrer Eignung für dieses MOPA-System untersucht. Nachdem die Entscheidung für Nd:YAG als laseraktives Material gefallen war, konnte darauf aufbauend die Konzeptionierung des Lasersystems auf der Basis von Verstärkungsrechnungen vorgenommen werden. Die entwickelte Verstärkungsrechnung trägt den Tatbeständen von realen Systemen Rechnung, indem radiusabhängige Intensitäten und eine radiale, nicht homogene Inversionsdichte berücksichtigt werden. Die Frequenzstabilisierung des gepulsten Oszillators (Frequenzstabilität von 1 MHz) wurde mittels des Pound-Drever-Hall-Verfahrens vorgenommen. Mit der Heterodynmethode wird die Frequenzstabilität des Oszillators gemessen. Nach Untersuchungen über verschiedene Konfigurationen für lineare und ringförmige Oszillatoren, wurde ein Ringoszillator mit zwei Laserköpfen aufgebaut, in welchen von außen mit einem Laser fester Frequenz eingestrahlt wird. Dieser emittiert bei einer Wiederholrate von 400 Hz eine Pulsenergie von Eout = 21 mJ bei nahezu beugungsbegrenzter Strahlqualität (M2 < 1,2). Die Verstärkung dieser Laserpulse erfolgte zunächst durch eine Vorverstärkerstufe und anschließend durch zwei doppelbrechungskompensierte Hauptverstärker im Doppeldurchgang. Eine gute Strahlqualität (M2 = 1,75) konnte unter anderem erzielt werden, indem der Doppeldurchgang durch die Hauptverstärker mit einem phasenkonjugierenden Spiegel (SF6), auf der Basis der stimulierten Brillouin Streuung, realisiert wurde. Der entwickelte Laser emittiert Pulse mit einer Länge von 25 ns und einer Energie von 250 mJ. Insgesamt wurde ein bisher einmaliges Lasersystem entwickelt. In der Literatur sind die erreichte Frequenzstabilität, Strahlqualität und Leistung in dieser Kombination bisher nicht dokumentiert. In der Zukunft soll durch den Einsatz von kerndotierten, keramischen Lasermaterialien, höheren Pumpleistungen der Hauptverstärker und phasenkonjugierenden Spiegeln aus Quarz die Pulsenergie des Systems weiter erhöht werden. [1] M. Ostermeyer, A. Straesser, “Theoretical investigation of Yb:YAG as laser material for nanosecond pulse emission with large energies in the joule range”, Optics Communications, Vol. 274, pp. 422-428 (2007) [2] A. Sträßer and M. Ostermeyer, “Improving the brightness of side pumped power amplifiers by using core doped ceramic rods”, Optics Express, Vol. 14, pp. 6687- 6693 (2006)
In this thesis we utilize resolved stellar populations to improve our understanding of galaxy formation and evolution. In the first part we improve a method for metallicity determination of faint old stellar systems, in the second and third part we analyze the individual history of six nearby disk galaxies outside the Local Group.
A New Calibration of the Color Metallicity Relation of Red Giants for HST data:
It is well known, that the color distribution of stars on the the Red Giant Branch (RGB) can be used to determine metallicities of old stellar populations that have only shallow photometry. Based on the largest sample of globular clusters ever used for such studies, we quantify the relation between metallicity and color in the widely used HST ACS filters F606W and F814W.
We use a sample of globular clusters from the ACS Globular Cluster Survey and measure their RGB color at given absolute magnitudes to derive the color-metallicity relation. We find a clear relation between metallicity and RGB color; we investigate the scatter and the uncertainties in this relation and show its limitations. A comparison with isochrones shows reasonably good agreement with BaSTI models, a small offset to Dartmouth models, and a larger offset to Padua models.
Even for the best globular cluster data available, the metallicity of a simple stellar population can be determined from the RGB alone only with an accuracy of 0.3 dex for [M/H]<-1, and 0.15 dex for [M/H]>-1. For mixed populations, as they are observed in external galaxies, the uncertainties will be even larger due to uncertainties in extinction, age, etc. Therefore caution is necessary when interpreting photometric metallicities.
The Structural History of Nearby Low Mass Disk Galaxies:
We study the individual evolution histories of three nearby, low-mass, edge-on galaxies (IC5052, NGC4244, NGC5023).
Using the color magnitude diagrams of resolved stellar populations, we construct star count density maps for populations of different ages and analyze the change of structural parameters with stellar age within each galaxy.
The three galaxies show low vertical heating rates, which are much lower than the heating rate of the Milky Way. This indicates that heating agents, as giant molecular clouds and spiral structure are weak in low mass galaxies.
We do not detect a separate thick disk in any of the three galaxies, even though our observations cover a larger range in equivalent surface brightness than any integrated light study. While scaleheights increase with age, each population can be well described by a single disk. Only two of the galaxies contain a very weak additional component, which we identify as the faint halo. The mass of these faint halos is less than 1% of the mass of the disk.
All populations in the three galaxies exhibit no or only little flaring. While this finding is consistent with previous integrated light studies, it poses strong constraints on galaxy formation models, because most theoretical simulations often find strong flaring due to interactions or radial migration.
Furthermore, we find breaks in the radial profiles of all three galaxies. The radii of these breaks are independent of age, and the break strength is decreasing with age in two of the galaxies (NGC4244 and NGC5023). This is consistent with break formation models, that combine a star formation cutoff with radial migration. The differing behavior of IC5052 can be explained by a recent interaction or minor merger.
The Structural History of Massive Disk Galaxies:
We extend the structural analysis of stellar populations with distinct ages to three massive galaxies, NGC891, NGC4565 and NGC7814. While confusion effects due to the high stellar number densities in their central region, and the prominent dust lanes inhibit an detailed analysis of the radial profiles, we can study their vertical structure.
These massive galaxies also have a slower heating than the Milky Way, comparable to the low mass galaxies. This can be traced back to their already thick young populations and thick layers of their interstellar medium.
We do not find a clear separate thick disk in any of these three galaxies; all populations can be described by a single disk plus a S\'ersic bulge/halo component. In contrast to the low mass galaxies, we cannot rule out the presence of thick disks in the massive galaxies, because of the strong influence of the halo, that might hide the possible contribution of the thick disk to the vertical star count profiles. However, the faintness of the possible thick disks still points to problems in the earlier ubiquitous findings of thick disks in external galaxies.
Bestimmung von Ozonabbauraten über der Arktis und Antarktis mittels Ozonsonden- und Satellitendaten
(2005)
Diese Arbeit beschäftigt sich mit der chemischen Ozonzerstörung im arktischen und antarktischen stratosphärischen Polarwirbel. Diese wird durch Abbauprodukte von anthropogen emittierten Fluorchlorkohlenwasserstoffen und Halonen, Chlor- und Bromradikale, verursacht. Studien in denen der gemessene und modellierte Ozonabbau verglichen wird zeigen, dass die Prozeße bekannt sind, der quantitative Verlauf allerdings nicht vollständig verstanden ist. Die Prozesse, die zur Ozonzerstörung führen sind in beiden Polarwirbeln ähnlich. Allerdings fällt als Konsequenz unterschiedlicher meteorologischer Bedingungen der chemische Ozonabbau im arktischen Polarwirbel weniger drastisch aus als über der Antarktis. Der arktische Polarwirbel ist im Mittel stärker dynamisch gestört als der antarktische und weist eine stärkere Jahr-zu-Jahr Variabilität auf. Das erschwert die Messung des chemischen Ozonabbaus. Zur Trennung des chemischen Ozonabbaus von der dynamischen Umverteilung des Ozons im arktischen Polarwirbel wurde die Matchmethode entwickelt. Bei dieser Methode werden Luftpakete innerhalb des Polarwirbels mehrfach beprobt, um den chemischen Anteil der Ozonänderung zu quantifizieren. Zur Identifizierung von doppelt beprobten Luftpaketen werden Trajektorien aus Windfeldern berechnet. Können zwei Messungen im Rahmen bestimmter Qualitätskriterien durch eine Trajektorie verbunden werden, kann die Ozondifferenz zwischen beiden Sondierungen berechnet und als chemischer Ozonabbau interpretiert werden. Eine solche Koinzidenz wird Match genannt. Der Matchmethode liegt ein statistischer Ansatz zugrunde, so dass eine Vielzahl solcher doppelt beprobter Luftmassen vorliegen muss, um gesicherte Aussagen über die Ozonzerstörung gewinnen zu können. So erhält man die Ozonzerstörung in einem bestimmten Zeitintervall, also Ozonabbauraten. Um die Anzahl an doppelt beprobten Luftpackten zu erhöhen wurde eine aktive Koordinierung der Ozonsondenaufstiege entwickelt. Im Rahmen dieser Arbeit wurden Matchkampagnen während des arktischen Winters 2002/2003 und zum ersten Mal während eines antarktischen Winter (2003) durchgeführt. Aus den gewonnenen Daten wurden Ozonabbauraten in beiden Polarwirbeln bestimmt. Diese Abbauraten dienen zum einen der Evaluierung von Modellen, ermöglichen aber auch den direkten Vergleich von Ozonabbauraten in beiden Polarwirbeln. Der Winter 2002/2003 war zu Beginn durch sehr tiefe Temperaturen in der mittleren und unteren Stratosphäre charakterisiert, so dass die Matchkampagne Ende November gestartet wurde. Ab Januar war der Polarwirbel zeitweise stark dynamisch gestört. Die Kampagne ging bis Mitte März. Für den Höhenbereich von 400 bis 550 K potentieller Temperatur (15-23 km) konnten Ozonabbauraten und der Verlust in der Gesamtsäule berechnet werden. Die Ozonabbauraten wurden in verschiedenen Tests auf ihre Stabilität überprüft. Der antarktische Polarwirbel war vom Beginn des Winters bis Mitte Oktober 2003 sehr kalt und stellte Ende September kurzzeitig den Rekord für die größte bisher aufgetretene Ozonloch-Fläche ein. Es konnten für den Kampagnenzeitraum, Anfang Juni bis Anfang Oktober, Ozonabbauraten im Höhenbereich von 400 bis 550 K potentieller Temperatur ermittelt werden. Der zeitliche Verlauf des Ozonabbaus war dabei auf fast allen Höhenniveaus identisch. Die Zunahme des Sonnenlichtes im Polarwirbel mit der Zeit führt zu einem starken Anwachsen der Ozonabbauraten. Ab Mitte September gingen die Ozonabbauraten auf Null zurück, da bis zu diesem Zeitpunkt das gesamte Ozon zwischen ca. 14 und 21 km zerstört wurde. Im letzten Teil der Arbeit wird ein neuer Algorithmus auf Basis der multivariaten Regression vorgestellt, mit dem Ozonabbauraten aus Ozonprofilen verschiedener Sensoren gleichzeitig berechnet werden können. Dabei können neben der Ozonabbaurate die systematischen Fehler zwischen den einzelnen Sensoren bestimmt werden. Dies wurde exemplarisch am antarktischen Winter 2003 für das 475 K potentielle Temperatur Niveau gezeigt. Neben den Ozonprofilen der Sonden wurden Daten von zwei Satellitenexperimenten verwendet. Die mit der multivariaten Matchtechnik berechneten Ozonabbauraten stimmen gut mit den Ozonabbauraten der Einzelsensor-Matchansätze überein.
Soft nanocomposites with enhanced electromechanical response for dielectric elastomer actuators
(2011)
Electromechanical transducers based on elastomer capacitors are presently considered for many soft actuation applications, due to their large reversible deformation in response to electric field induced electrostatic pressure. The high operating voltage of such devices is currently a large drawback, hindering their use in applications such as biomedical devices and biomimetic robots, however, they could be improved with a careful design of their material properties. The main targets for improving their properties are increasing the relative permittivity of the active material, while maintaining high electric breakdown strength and low stiffness, which would lead to enhanced electrostatic storage ability and hence, reduced operating voltage. Improvement of the functional properties is possible through the use of nanocomposites. These exploit the high surface-to-volume ratio of the nanoscale filler, resulting in large effects on macroscale properties. This thesis explores several strategies for nanomaterials design. The resulting nanocomposites are fully characterized with respect to their electrical and mechanical properties, by use of dielectric spectroscopy, tensile mechanical analysis, and electric breakdown tests. First, nanocomposites consisting of high permittivity rutile TiO2 nanoparticles dispersed in thermoplastic block copolymer SEBS (poly-styrene-coethylene-co-butylene-co-styrene) are shown to exhibit permittivity increases of up to 3.7 times, leading to 5.6 times improvement in electrostatic energy density, but with a trade-off in mechanical properties (an 8-fold increase in stiffness). The variation in both electrical and mechanical properties still allows for electromechanical improvement, such that a 27 % reduction of the electric field is found compared to the pure elastomer. Second, it is shown that the use of nanofiller conductive particles (carbon black (CB)) can lead to a strong increase of relative permittivity through percolation, however, with detrimental side effects. These are due to localized enhancement of the electric field within the composite, which leads to sharp reductions in electric field strength. Hence, the increase in permittivity does not make up for the reduction in breakdown strength in relation to stored electrical energy, which may prohibit their practical use. Third, a completely new approach for increasing the relative permittivity and electrostatic energy density of a polymer based on 'molecular composites' is presented, relying on chemically grafting soft π-conjugated macromolecules to a flexible elastomer backbone. Polarization caused by charge displacement along the conjugated backbone is found to induce a large and controlled permittivity enhancement (470 % over the elastomer matrix), while chemical bonding, encapsulates the PANI chains manifesting in hardly any reduction in electric breakdown strength, and hence resulting in a large increase in stored electrostatic energy. This is shown to lead to an improvement in the sensitivity of the measured electromechanical response (83 % reduction of the driving electric field) as well as in the maximum actuation strain (250 %). These results represent a large step forward in the understanding of the strategies which can be employed to obtain high permittivity polymer materials with practical use for electro-elastomer actuation.
Auf der Grundlage von Sonnenphotometermessungen an drei Messstationen (AWIPEV/ Koldewey in Ny-Ålesund (78.923 °N, 11.923 °O) 1995–2008, 35. Nordpol Driftstation – NP-35 (84.3–85.5 °N, 41.7–56.6 °O) März/April 2008, Sodankylä (67.37 °N, 26.65 °O) 2004–2007) wird die Aerosolvariabilität in der europäischen Arktis und deren Ursachen untersucht. Der Schwerpunkt liegt dabei auf der Frage des Zusammenhanges zwischen den an den Stationen gemessenen Aerosolparametern (Aerosol optische Dicke, Angström Koeffizient, usw.) und dem Transport des Aerosols sowohl auf kurzen Zeitskalen (Tagen) als auch auf langen Zeitskalen (Monate, Jahre). Um diesen Zusammenhang herzustellen, werden für die kurzen Zeitskalen mit dem Trajektorienmodell PEP-Tracer 5-Tage Rückwärtstrajektorien in drei Starthöhen (850 hPa, 700 hPa, 500 hPa) für die Uhrzeiten 00, 06, 12 und 18 Uhr berechnet. Mit Hilfe der nicht-hierarchischen Clustermethode k-means werden die berechneten Rückwärtstrajektorien dann zu Gruppen zusammengefasst und bestimmten Quellgebieten und den gemessenen Aerosol optischen Dicken zugeordnet. Die Zuordnung von Aerosol optischer Dicke und Quellregion ergibt keinen eindeutigen Zusammenhang zwischen dem Transport verschmutzter Luftmassen aus Europa oder Russland bzw. Asien und erhöhter Aerosol optischer Dicke. Dennoch ist für einen konkreten Einzelfall (März 2008) ein direkter Zusammenhang von Aerosoltransport und hohen Aerosol optischen Dicken nachweisbar. In diesem Fall gelangte Waldbrandaerosol aus Südwestrussland in die Arktis und konnte sowohl auf der NP-35 als auch in Ny-Ålesund beobachtet werden. In einem weiteren Schritt wird mit Hilfe der EOF-Analyse untersucht, inwieweit großskalige atmosphärische Zirkulationsmuster für die Aerosolvariabilität in der europäischen Arktis verantwortlich sind. Ähnlich wie bei der Trajektorienanalyse ist auch die Verbindung der atmosphärischen Zirkulation zu den Photometermessungen an den Stationen in der Regel nur schwach ausgeprägt. Eine Ausnahme findet sich bei der Betrachtung des Jahresganges des Bodendruckes und der Aerosol optischen Dicke. Hohe Aerosol optische Dicken treten im Frühjahr zum einen dann auf, wenn durch das Islandtief und das sibirische Hochdruckgebiet Luftmassen aus Europa oder Russland/Asien in die Arktis gelangen, und zum anderen, wenn sich ein kräftiges Hochdruckgebiet über Grönland und weiten Teilen der Arktis befindet. Ebenso zeigt sich, dass der Übergang zwischen Frühjahr und Sommer zumindest teilweise bedingt ist durch denWechsel vom stabilen Polarhoch im Winter und Frühjahr zu einer stärker von Tiefdruckgebieten bestimmten arktischen Atmosphäre im Sommer. Die geringere Aerosolkonzentration im Sommer kann zum Teil mit einer Zunahme der nassen Deposition als Aerosolsenke begründet werden. Für Ny-Ålesund wird neben den Transportmustern auch die chemische Zusammensetzung des Aerosols mit Hilfe von Impaktormessungen an der Zeppelinstation auf dem Zeppelinberg (474m ü.NN) nahe Ny-Ålesund abgeleitet. Dabei ist die positive Korrelation der Aerosoloptischen Dicke mit der Konzentration von Sulfationen und Ruß sehr deutlich. Beide Stoffe gelangen zu einem Großteil durch anthropogene Emissionen in die Atmosphäre. Die damit nachweisbar anthropogen geprägte Zusammensetzung des arktischen Aerosols steht im Widerspruch zum nicht eindeutig herstellbaren Zusammenhang mit dem Transport des Aerosols aus Industrieregionen. Dies kann nur durch einen oder mehrere gleichzeitig stattfindende Transformationsprozesse (z. B. Nukleation von Schwefelsäurepartikeln) während des Transportes aus den Quellregionen (Europa, Russland) erklärt werden.
Organische Halbleiter besitzen neue, bemerkenswerte Materialeigenschaften, die sie für die grundlegende Forschung wie auch aktuelle technologische Entwicklung (bsw. org. Leuchtdioden, org. Solarzellen) interessant werden lassen. Aufgrund der starken konformative Freiheit der konjugierten Polymerketten führt die Vielzahl der möglichen Anordnungen und die schwache intermolekulare Wechselwirkung für gewöhnlich zu geringer struktureller Ordnung im Festkörper. Die Morphologie hat gleichzeitig direkten Einfluss auf die elektronische Struktur der organischen Halbleiter, welches sich meistens in einer deutlichen Reduktion der Ladungsträgerbeweglichkeit gegenüber den anorganischen Verwandten zeigt. So stellt die Beweglichkeit der Ladungen im Halbleiter einen der limitierenden Faktoren für die Leistungsfähigkeit bzw. den Wirkungsgrad von funktionellen organischen Bauteilen dar. Im Jahr 2009 wurde ein neues auf Naphthalindiimid und Bithiophen basierendes Dornor/Akzeptor Copolymer vorgestellt [P(NDI2OD‑T2)], welches sich durch seine außergewöhnlich hohe Ladungsträgermobilität auszeichnet. In dieser Arbeit wird die Ladungsträgermobilität in P(NDI2OD‑T2) bestimmt, und der Transport durch eine geringe energetischer Unordnung charakterisiert. Obwohl dieses Material zunächst als amorph beschrieben wurde zeigt eine detaillierte Analyse der optischen Eigenschaften von P(NDI2OD‑T2), dass bereits in Lösung geordnete Vorstufen supramolekularer Strukturen (Aggregate) existieren. Quantenchemische Berechnungen belegen die beobachteten spektralen Änderungen. Mithilfe der NMR-Spektroskopie kann die Bildung der Aggregate unabhängig von optischer Spektroskopie bestätigt werden. Die Analytische Ultrazentrifugation an P(NDI2OD‑T2) Lösungen legt nahe, dass sich die Aggregation innerhalb der einzelnen Ketten unter Reduktion des hydrodynamischen Radius vollzieht. Die Ausbildung supramolekularen Strukturen nimmt auch eine signifikante Rolle bei der Filmbildung ein und verhindert gleichzeitig die Herstellung amorpher P(NDI2OD‑T2) Filme. Durch chemische Modifikation der P(NDI2OD‑T2)-Kette und verschiedener Prozessierungs-Methoden wurde eine Änderung des Kristallinitätsgrades und gleichzeitig der Orientierung der kristallinen Domänen erreicht und mittels Röntgenbeugung quantifiziert. In hochauflösenden Elektronenmikroskopie-Messungen werden die Netzebenen und deren Einbettung in die semikristallinen Strukturen direkt abgebildet. Aus der Kombination der verschiedenen Methoden erschließt sich ein Gesamtbild der Nah- und Fernordnung in P(NDI2OD‑T2). Über die Messung der Elektronenmobilität dieser Schichten wird die Anisotropie des Ladungstransports in den kristallographischen Raumrichtungen von P(NDI2OD‑T2) charakterisiert und die Bedeutung der intramolekularen Wechselwirkung für effizienten Ladungstransport herausgearbeitet. Gleichzeitig wird deutlich, wie die Verwendung von größeren und planaren funktionellen Gruppen zu höheren Ladungsträgermobilitäten führt, welche im Vergleich zu klassischen semikristallinen Polymeren weniger sensitiv auf die strukturelle Unordnung im Film sind.
Gold at the nanoscale
(2020)
In this cumulative dissertation, I want to present my contributions to the field of plasmonic nanoparticle science. Plasmonic nanoparticles are characterised by resonances of the free electron gas around the spectral range of visible light. In recent years, they have evolved as promising components for light based nanocircuits, light harvesting, nanosensors, cancer therapies, and many more.
This work exhibits the articles I authored or co-authored in my time as PhD student at the University of Potsdam. The main focus lies on the coupling between localised plasmons and excitons in organic dyes. Plasmon–exciton coupling brings light–matter coupling to the nanoscale. This size reduction is accompanied by strong enhancements of the light field which can, among others, be utilised to enhance the spectroscopic footprint of molecules down to single molecule detection, improve the efficiency of solar cells, or establish lasing on the nanoscale. When the coupling exceeds all decay channels, the system enters the strong coupling regime. In this case, hybrid light–matter modes emerge utilisable as optical switches, in quantum networks, or as thresholdless lasers. The present work investigates plasmon–exciton coupling in gold–dye core–shell geometries and contains both fundamental insights and technical novelties. It presents a technique which reveals the anticrossing in coupled systems without manipulating the particles themselves. The method is used to investigate the relation between coupling strength and particle size. Additionally, the work demonstrates that pure extinction measurements can be insufficient when trying to assess the coupling regime. Moreover, the fundamental quantum electrodynamic effect of vacuum induced saturation is introduced. This effect causes the vacuum fluctuations to diminish the polarisability of molecules and has not yet been considered in the plasmonic context.
The work additionally discusses the reaction of gold nanoparticles to optical heating. Such knowledge is of great importance for all potential optical applications utilising plasmonic nanoparticles since optical excitation always generates heat. This heat can induce a change in the optical properties, but also mechanical changes up to melting can occur. Here, the change of spectra in coupled plasmon–exciton particles is discussed and explained with a precise model. Moreover, the work discusses the behaviour of gold nanotriangles exposed to optical heating. In a pump–probe measurement, X-ray probe pulses directly monitored the particles’ breathing modes. In another experiment, the triangles were exposed to cw laser radiation with varying intensities and illumination areas. X-ray diffraction directly measured the particles’ temperature. Particle melting was investigated with surface enhanced Raman spectroscopy and SEM imaging demonstrating that larger illumination areas can cause melting at lower intensities. An elaborate methodological and theoretical introduction precedes the articles. This way, also readers without specialist’s knowledge get a concise and detailed overview of the theory and methods used in the articles. I introduce localised plasmons in metal nanoparticles of different shapes. For this work, the plasmons were mostly coupled to excitons in J-aggregates. Therefore, I discuss these aggregates of organic dyes with sharp and intense resonances and establish an understanding of the coupling between the two systems. For ab initio simulations of the coupled systems, models for the systems’ permittivites are presented, too. Moreover, the route to the sample fabrication – the dye coating of gold nanoparticles, their subsequent deposition on substrates, and the covering with polyelectrolytes – is presented together with the measurement methods that were used for the articles.
The current generation of ground-based instruments has rapidly extended the limits of the range accessible to us with very-high-energy (VHE) gamma-rays, and more than a hundred sources have now been detected in the Milky Way. These sources represent only the tip of the iceberg, but their number has reached a level that allows population studies. In this work, a model of the global population of VHE gamma-ray sources based on the most comprehensive census of Galactic sources in this energy regime, the H.E.S.S. Galactic plane survey (HGPS), will be presented. A population synthesis approach was followed in the construction of the model. Particular attention was paid to correcting for the strong observational bias inherent in the sample of detected sources. The methods developed for estimating the model parameters have been validated with extensive Monte Carlo simulations and will be shown to provide unbiased estimates of the model parameters. With these methods, five models for different spatial distributions of sources have been constructed. To test the validity of these models, their predictions for the composition of sources within the sensitivity range of the HGPS are compared with the observed sample. With one exception, similar results are obtained for all spatial distributions, showing that the observed longitude profile and the source distribution over photon flux are in fair agreement with observation. Regarding the latitude profile and the source distribution over angular extent, it becomes apparent that the model needs to be further adjusted to bring its predictions in agreement with observation. Based on the model, predictions of the global properties of the Galactic population of VHE gamma-ray sources and the prospects of the Cherenkov Telescope Array (CTA) will be presented.
CTA will significantly increase our knowledge of VHE gamma-ray sources by lowering the threshold for source detection, primarily through a larger detection area compared to current-generation instruments. In ground-based gamma-ray astronomy, the sensitivity of an instrument depends strongly, in addition to the detection area, on the ability to distinguish images of air showers produced by gamma-rays from those produced by cosmic rays, which are a strong background. This means that the number of detectable sources depends on the background rejection algorithm used and therefore may also be increased by improving the performance of such algorithms. In this context, in addition to the population model, this work presents a study on the application of deep-learning techniques to the task of gamma-hadron separation in the analysis of data from ground-based gamma-ray instruments. Based on a systematic survey of different neural-network architectures, it is shown that robust classifiers can be constructed with competitive performance compared to the best existing algorithms. Despite the broad coverage of neural-network architectures discussed, only part of the potential offered by the
application of deep-learning techniques to the analysis of gamma-ray data is exploited in the context of this study. Nevertheless, it provides an important basis for further research on this topic.
Ziel dieser Arbeit ist die phänomenologische Untersuchung der Feuchteempfindlichkeit der elektrischen Eigenschaften dünner Polymerschichten. Diese Untersuchungen stellen gleichzeitig Vorarbeiten zur Entwicklung von Prototypen von zwei polymeren Dünnschicht-Feuchtesensoren dar, die sich durch die spezielle Auswahl der feuchtesensitiven Materialien jeweils durch eine besondere Eigenschaft gegenüber kommerziellen Massenprodukten auszeichnen. Ziel der Entwicklungsarbeiten für den ersten Prototypen war die Konstruktion eines schnellen Feuchtesensors, der plötzliche und sprunghafte Feuchteänderungen in der umgebenden Atmosphäre möglichst rasch detektieren kann. Dafür wurden dünne Schichten von Poly-DADMAC auf Interdigitalstrukturen aufgebracht, die einen möglichst direkten Kontakt zwischen feuchtesensitiver Schicht und umgebender, feuchter Atmosphäre gewährleisten. Als Messgrößen dienten die Wechselstromgrößen Widerstand und Kapazität der Schichten. Die Feuchtekennlinien der Schichten zeigen gute Konstanz und hohe Reproduzierbarkeit. Der Widerstand der Schichten ändert sich durch den Einfluss von Feuchte je nach Schichtdicke um 3 bis 5 Größenordnungen und eignet sich als Messgröße für die Feuchtigkeit im gesamten Feuchtebereich. Die Hysterese der Filme konnte auf kleiner als 2,5% r.F. bestimmt werden, die Reproduzierbarkeit auf besser als 1% r.F. Die Ansprechzeit der Schichten lässt sich schichtdickenabhängig zu 1 bis 10 Sekunden bestimmen. Hierbei zeigen besonders die dünnen Schichten kurze Ansprechzeiten. Zielstellung für den zweiten Feuchtesensor war die Entwicklung eines Prototypen, dessen sensitive Schicht sich biostatisch und biozid verhält, so dass er in biotischen Umgebungen eingesetzt werden kann. Es wurden fünf Polysulfobetaine synthetisiert, deren Biozidität und Biostatik mit dem Kontakttest nach Rönnpagel, dem ISO846-Test und Abbautests bestimmt wurde. Zwei Polymere – Poly-DMMAAPS (BT2) und Poly-[MSA-Styren-Sulfobetain] (BT5) – erwiesen sich als ausreichend biozid und biostatisch. Schichten dieser Polymere wurden auf Interdigitalstrukturen aufgezogen, anschließend wurden die Kennlinien dieser Proben aufgenommen. Die Messwerte zeigen für beide Polymere gute Konstanz und eine hohe Reproduzierbarkeit. BT2-Proben sind zwischen 20% und 80% r.F. besonders empfindlich und zeigen über einen Monat keine Langzeitdrift. Vernetzte Proben zeigen bis 50°C keinen temperaturbedingten Abfall der Feuchteempfindlichkeit. Der Einsatz vernetzter BT5-Schichten als kapazitiver Feuchtesensor ist bis etwa 70°C möglich, die Schichten sind selbst nach Lagerung im Hochvakuum und mehrfacher Betauung stabil. Damit liegen zwei funktionsfähige Prototypen von Feuchtesensoren vor, für die die meisten Kennwerte denen von vergleichbaren kommerziellen Feuchtesensoren entsprechen. Gleichzeitig zeichnen sie sich aber durch eine sehr niedrige Ansprechzeit bzw. eine ausreichende Lebensdauer unter biotischen Bedingungen aus.
Despite remarkable progress made in the past century, which has revolutionized our understanding of the universe, there are numerous open questions left in theoretical physics. Particularly important is the fact that the theories describing the fundamental interactions of nature are incompatible. Einstein's theory of general relative describes gravity as a dynamical spacetime, which is curved by matter and whose curvature determines the motion of matter. On the other hand we have quantum field theory, in form of the standard model of particle physics, where particles interact via the remaining interactions - electromagnetic, weak and strong interaction - on a flat, static spacetime without gravity. A theory of quantum gravity is hoped to cure this incompatibility by heuristically replacing classical spacetime by quantum spacetime'. Several approaches exist attempting to define such a theory with differing underlying premises and ideas, where it is not clear which is to be preferred. Yet a minimal requirement is the compatibility with the classical theory, they attempt to generalize. Interestingly many of these models rely on discrete structures in their definition or postulate discreteness of spacetime to be fundamental. Besides the direct advantages discretisations provide, e.g. permitting numerical simulations, they come with serious caveats requiring thorough investigation: In general discretisations break fundamental diffeomorphism symmetry of gravity and are generically not unique. Both complicates establishing the connection to the classical continuum theory. The main focus of this thesis lies in the investigation of this relation for spin foam models. This is done on different levels of the discretisation / triangulation, ranging from few simplices up to the continuum limit. In the regime of very few simplices we confirm and deepen the connection of spin foam models to discrete gravity. Moreover, we discuss dynamical, e.g. diffeomorphism invariance in the discrete, to fix the ambiguities of the models. In order to satisfy these conditions, the discrete models have to be improved in a renormalisation procedure, which also allows us to study their continuum dynamics. Applied to simplified spin foam models, we uncover a rich, non--trivial fixed point structure, which we summarize in a phase diagram. Inspired by these methods, we propose a method to consistently construct the continuum theory, which comes with a unique vacuum state.
Gasausströmungen, oft in der Form hoch kollimierter Jets, sind ein allgegenwärtiges Phänomen bei der Geburt neuer Sterne. Emission von stossangeregtem molekularem Wasserstoff bei Wellenlängen im nahen Infrarotbereich ist ein Merkmal ihrer Existenz und auch in eingebetteten, im Optischen obskurierten Ausströmungen generell gut zu beobachten. In dieser Arbeit werden die Resultate einer von Auswahleffekten freien, empfindlichen, grossflächigen Suche nach solchen Ausströmungen von Protosternen in der v=1-0 S(1) Linie molekularen Wasserstoffs bei einer Wellenlänge von 2.12 µm vorgestellt. Die Durchmusterung umfasst eine Fläche von etwa einem Quadratgrad in der Orion A Riesenmolekülwolke. Weitere Daten aus einem grossen Wellenlängenbereich werden benutzt, um die Quellen der Ausströmungen zu identifizieren. Das Ziel dieser Arbeit ist es, eine Stichprobe von Ausströmungen zu bekommen, die so weit wie möglich frei von Auswahleffekten ist, um die typischen Eigenschaften protostellarer Ausströmungen und deren Entwicklung festzustellen, sowie um die Rückwirkung der Ausströmungen auf die umgebende Wolke zu untersuchen. Das erste Ergebnis ist, dass Ausströmungen in Sternentstehungsgebieten tatsächlich sehr häufig sind: mehr als 70 Jet-Kandidaten werden identifiziert. Die meisten zeigen eine sehr irreguläre Morphologie anstelle regulärer oder symmetrischer Strukturen. Dies ist auf das turbulente, klumpige Medium zurückzuführen, in das sich die Jets hineinbewegen. Die Ausrichtung der Jets ist zufällig verteilt. Insbesondere gibt es keine bevorzugte Ausrichtung der Jets parallel zum grossräumigen Magnetfeld in der Wolke. Das legt nahe, dass die Rotations- und Symmetrieachse in einem protostellaren System durch zufällige, turbulente Bewegung in der Wolke bestimmt wird. Mögliche Ausströmungsquellen werden für 49 Jets identifiziert; für diese wird der Entwicklungsstand und die bolometrische Leuchtkraft abgeschätzt. Die Jetlänge und die H2 Leuchtkraft entwickeln sich gemeinsam mit der Ausströmungsquelle. Von null startend, dehnen sich die Jets schnell bis auf eine Länge von einigen Parsec aus und werden dann langsam wieder kürzer. Sie sind zuerst sehr leuchtkräftig, die H2 Helligkeit nimmt aber im Lauf der protostellaren Entwicklung ab. Die Längen- und H2 Leuchtkraftentwicklung lässt sich im Wesentlichen durch eine zuerst sehr hohe, dann niedriger werdende Massenausflussrate erklären, die auf eine zuerst sehr hohe, dann niedriger werdende Gasakkretionsrate auf den Protostern schliessen lässt (Akkretion und Ejektion sind eng verknüpft!). Die Längenabnahme der Jets erfordert eine ständig wirkende Abbremsung der Jets. Ein einfaches Modell einer simultanen Entwicklung eines Protosterns, seiner zirkumstellaren Umgebung und seiner Ausströmung (Smith 2000) kann die gemessenen H2- und bolometrischen Leuchtkräfte der Jets und ihrer Quellen reproduzieren, unter der Annahme, dass die starke Akkretionsaktivität zu Beginn der protostellaren Entwicklung mit einer überproportional hohen Massenausflussrate verbunden ist. Im Durchmusterungsgebiet sind 125 dichte Molekülwolkenkerne bekannt (Tatematsu et al. 1993). Jets (bzw. Sterne) entstehen in ruhigen Wolkenkernen, d.h. solchen mit einem niedrigen Verhältnis von interner kinetischer Energie zu gravitativer potentieller Energie; dies sind die Wolkenkerne höherer Masse. Die Wolkenkerne mit Jets haben im Mittel grössere Linienbreiten als die ohne Jets. Dies ist darauf zurückzuführen, dass sie bevorzugt in den massereicheren Wolkenkernen zu finden sind, welche generell eine grössere Linienbreite haben. Es gibt keinen Hinweis auf stärkere interne Bewegungen in Wolkenkernen mit Jets, die durch eine Wechselwirkung der Jets mit den Wolkenkernen erzeugt sein könnte. Es gibt, wie von der Theorie vorausgesagt, eine Beziehung zwischen der Linienbreite der Wolkenkerne und der H2 Leuchtkraft der Jets, wenn Jets von Klasse 0 und Klasse I Protosternen separat betrachtet werden; dabei sind Klasse 0 Jets leuchtkräftiger als Klasse I Jets, was ebenfalls auf eine zeitabhängige Akkretionsrate mit einer frühzeitigen Spitze und einem darauffolgenden Abklingen hinweist. Schliesslich wird die Rückwirkung der Jetpopulation auf eine Molekülwolke unter der Annahme strikter Vorwärtsimpulserhaltung betrachtet. Die Jets können auf der Skala einer ganzen Riesenmolekülwolke und auf den Skalen von Molekülwolkenkernen nicht genügend Impuls liefern, um die abklingende Turbulenz wieder anzuregen. Auf der mittleren Skala von molekularen Klumpen, mit einer Grösse von einigen parsec und Massen von einigen hundert Sonnenmassen liefern die Jets jedoch genügend Impuls in hinreichend kurzer Zeit, um die Turbulenz “am Leben zu erhalten” und können damit helfen, einen Klumpen gegen seinen Kollaps zu stabilisieren.
Actin is one of the most highly conserved proteins in eukaryotes and distinct actin-related proteins with filament-forming properties are even found in prokaryotes. Due to these commonalities, actin-modulating proteins of many species share similar structural properties and proposed functions. The polymerization and depolymerization of actin are critical processes for a cell as they can contribute to shape changes to adapt to its environment and to move and distribute nutrients and cellular components within the cell. However, to what extent functions of actin-binding proteins are conserved between distantly related species, has only been addressed in a few cases. In this work, functions of Coronin-A (CorA) and Actin-interacting protein 1 (Aip1), two proteins involved in actin dynamics, were characterized. In addition, the interchangeability and function of Aip1 were investigated in two phylogenetically distant model organisms. The flowering plant Arabidopsis thaliana (encoding two homologs, AIP1-1 and AIP1-2) and in the amoeba Dictyostelium discoideum (encoding one homolog, DdAip1) were chosen because the functions of their actin cytoskeletons may differ in many aspects. Functional analyses between species were conducted for AIP1 homologs as flowering plants do not harbor a CorA gene.
In the first part of the study, the effect of four different mutation methods on the function of Coronin-A protein and the resulting phenotype in D. discoideum was revealed in two genetic knockouts, one RNAi knockdown and a sudden loss-of-function mutant created by chemical-induced dislocation (CID). The advantages and disadvantages of the different mutation methods on the motility, appearance and development of the amoebae were investigated, and the results showed that not all observed properties were affected with the same intensity. Remarkably, a new combination of Selection-Linked Integration and CID could be established.
In the second and third parts of the thesis, the exchange of Aip1 between plant and amoeba was carried out. For A. thaliana, the two homologs (AIP1-1 and AIP1-2) were analyzed for functionality as well as in D. discoideum. In the Aip1-deficient amoeba, rescue with AIP1-1 was more effective than with AIP1-2. The main results in the plant showed that in the aip1-2 mutant background, reintroduced AIP1-2 displayed the most efficient rescue and A. thaliana AIP1-1 rescued better than DdAip1. The choice of the tagging site was important for the function of Aip1 as steric hindrance is a problem. The DdAip1 was less effective when tagged at the C-terminus, while the plant AIP1s showed mixed results depending on the tag position. In conclusion, the foreign proteins partially rescued phenotypes of mutant plants and mutant amoebae, despite the organisms only being very distantly related in evolutionary terms.
Investigation of tropospheric arctic aerosol and mixed-phase clouds using airborne lidar technique
(2005)
An Airborne Mobile Aerosol Lidar (AMALi) was constructed and built at Alfred-Wegener-Institute for Polar and Marine Research (AWI) in Potsdam, Germany for the lower tropospheric aerosol and cloud research under tough arctic conditions. The system was successfully used during two AWI airborne field campaigns, ASTAR 2004 and SVALEX 2005, performed in vicinity of Spitsbergen in the Arctic. The novel evaluation schemes, the Two-Stream Inversion and the Iterative Airborne Inversion, were applied to the obtained lidar data. Thereby, calculation of the particle extinction and backscatter coefficient profiles with corresponding lidar ratio profiles characteristic for the arctic air was possible. The comparison of these lidar results with the results of other in-situ and remote instrumentation (ground based Koldewey Aerosol Raman Lidar (KARL), sunphotometer, radiosounding, satellite imagery) allowed to provided clean contra polluted (Arctic Haze) characteristics of the arctic aerosols. Moreover, the data interpretation by means of the ECMWF Operational Analyses and small-scale dispersion model EULAG allowed studying the effects of the Spitsbergens orography on the aerosol load in the Planetary Boundary Layer. With respect to the cloud studies a new methodology of alternated remote AMALi measurements with the airborne in-situ cloud optical and microphysical parameters measurements was proved feasible for the low density mixed-phase cloud studies. An example of such approach during observation of the natural cloud seeding (feeder-seeder phenomenon) with ice crystals precipitating into the lower supercooled stratocumulus deck were discussed in terms of the lidar signal intensity profiles and corresponding depolarisation ratio profiles. For parts of the cloud system characterised by almost negligible multiple scattering the calculation of the particle backscatter coefficient profiles was possible using the lidar ratio information obtained from the in-situ measurements in ice-crystal cloud and water cloud.
The two hallmark features of Brownian motion are the linear growth < x2(t)> = 2Ddt of the mean squared displacement (MSD) with diffusion coefficient D in d spatial dimensions, and the Gaussian distribution of displacements. With the increasing complexity of the studied systems deviations from these two central properties have been unveiled over the years. Recently, a large variety of systems have been reported in which the MSD exhibits the linear growth in time of Brownian (Fickian) transport, however, the distribution of displacements is pronouncedly non-Gaussian (Brownian yet non-Gaussian, BNG). A similar behaviour is also observed for viscoelastic-type motion where an anomalous trend of the MSD, i.e., <x2(t)> ~ ta, is combined with a priori unexpected non-Gaussian distributions (anomalous yet non-Gaussian, ANG). This kind of behaviour observed in BNG and ANG diffusions has been related to the presence of heterogeneities in the systems and a common approach has been established to address it, that is, the random diffusivity approach.
This dissertation explores extensively the field of random diffusivity models. Starting from a chronological description of all the main approaches used as an attempt of describing BNG and ANG diffusion, different mathematical methodologies are defined for the resolution and study of these models. The processes that are reported in this work can be classified in three subcategories, i) randomly-scaled Gaussian processes, ii) superstatistical models and iii) diffusing diffusivity models, all belonging to the more general class of random diffusivity models. Eventually, the study focuses more on BNG diffusion, which is by now well-established and relatively well-understood. Nevertheless, many examples are discussed for the description of ANG diffusion, in order to highlight the possible scenarios which are known so far for the study of this class of processes.
The second part of the dissertation deals with the statistical analysis of random diffusivity processes. A general description based on the concept of moment-generating function is initially provided to obtain standard statistical properties of the models. Then, the discussion moves to the study of the power spectral analysis and the first passage statistics for some particular random diffusivity models. A comparison between the results coming from the random diffusivity approach and the ones for standard Brownian motion is discussed. In this way, a deeper physical understanding of the systems described by random diffusivity models is also outlined.
To conclude, a discussion based on the possible origins of the heterogeneity is sketched, with the main goal of inferring which kind of systems can actually be described by the random diffusivity approach.
Galaxies are observational probes to study the Large Scale Structure. Their gravitational motions are tracers of the total matter density and therefore of the Large Scale Structure. Besides, studies of structure formation and galaxy evolution rely on numerical cosmological simulations. Still, only one universe observable from a given position, in time and space, is available for comparisons with simulations. The related cosmic variance affects our ability to interpret the results. Simulations constrained by observational data are a perfect remedy to this problem. Achieving such simulations requires the projects Cosmic flows and CLUES. Cosmic flows builds catalogs of accurate distance measurements to map deviations from the expansion. These measures are mainly obtained with the galaxy luminosity-rotation rate correlation. We present the calibration of that relation in the mid-infrared with observational data from Spitzer Space Telescope. Resulting accurate distance estimates will be included in the third catalog of the project. In the meantime, two catalogs up to 30 and 150 Mpc/h have been released. We report improvements and applications of the CLUES' method on these two catalogs. The technique is based on the constrained realization algorithm. The cosmic displacement field is computed with the Zel'dovich approximation. This latter is then reversed to relocate reconstructed three-dimensional constraints to their precursors' positions in the initial field. The size of the second catalog (8000 galaxies within 150 Mpc/h) highlighted the importance of minimizing the observational biases. By carrying out tests on mock catalogs, built from cosmological simulations, a method to minimize observational bias can be derived. Finally, for the first time, cosmological simulations are constrained solely by peculiar velocities. The process is successful as resulting simulations resemble the Local Universe. The major attractors and voids are simulated at positions approaching observational positions by a few megaparsecs, thus reaching the limit imposed by the linear theory.
The non-linear behaviour of the atmospheric dynamics is not well understood and makes the evaluation and usage of regional climate models (RCMs) difficult. Due to these non-linearities, chaos and internal variability (IV) within the RCMs are induced, leading to a sensitivity of RCMs to their initial conditions (IC). The IV is the ability of RCMs to realise different solutions of simulations that differ in their IC, but have the same lower and lateral boundary conditions (LBC), hence can be defined as the across-member spread between the ensemble members.
For the investigation of the IV and the dynamical and diabatic contributions generating the IV four ensembles of RCM simulations are performed with the atmospheric regional model HIRHAM5. The integration area is the Arctic and each ensemble consists of 20 members. The ensembles cover the time period from July to September for the years 2006, 2007, 2009 and 2012. The ensemble members have the same LBC and differ in their IC only. The different IC are arranged by an initialisation time that shifts successively by six hours. Within each ensemble the first simulation starts on 1st July at 00 UTC and the last simulation starts on 5th July at 18 UTC and each simulation runs until 30th September. The analysed time period ranges from 6th July to 30th September, the time period that is covered by all ensemble members. The model runs without any nudging to allow a free development of each simulation to get the full internal variability within the HIRHAM5.
As a measure of the model generated IV, the across-member standard deviation and the across-member variance is used and the dynamical and diabatic processes influencing the IV are estimated by applying a diagnostic budget study for the IV tendency of the potential temperature developed by Nikiema and Laprise [2010] and Nikiema and Laprise [2011]. The diagnostic budget study is based on the first law of thermodynamics for potential temperature and the mass-continuity equation. The resulting budget equation reveals seven contributions to the potential temperature IV tendency.
As a first study, this work analyses the IV within the HIRHAM5. Therefore, atmospheric circulation parameters and the potential temperature for all four ensemble years are investigated. Similar to previous studies, the IV fluctuates strongly in time. Further, due to the fact that all ensemble members are forced with the same LBC, the IV depends on the vertical level within the troposphere, with high values in the lower troposphere and at 500 hPa and low values in the upper troposphere and at the surface. By the same reason, the spatial distribution shows low values of IV at the boundaries of the model domain.
The diagnostic budget study for the IV tendency of potential temperature reveals that the seven contributions fluctuate in time like the IV. However, the individual terms reach different absolute magnitudes. The budget study identifies the horizontal and vertical ‘baroclinic’ terms as the main contributors to the IV tendency, with the horizontal ‘baroclinic’ term producing and the vertical ‘baroclinic’ term reducing the IV. The other terms fluctuate around zero, because they are small in general or are balanced due to the domain average.
The comparison of the results obtained for the four different ensembles (summers 2006, 2007, 2009 and 2012) reveals that on average the findings for each ensemble are quite similar concerning the magnitude and the general pattern of IV and its contributions. However, near the surface a weaker IV is produced with decreasing sea ice extent. This is caused by a smaller impact of the horizontal 'baroclinic' term over some regions and by the changing diabatic processes, particularly a more intense reducing tendency of the IV due to condensative heating. However, it has to be emphasised that the behaviour of the IV and its dynamical and diabatic contributions are influenced mainly by complex atmospheric feedbacks and large-scale processes and not by the sea ice distribution.
Additionally, a comparison with a second RCM covering the Arctic and using the same LBCs and IC is performed. For both models very similar results concerning the IV and its dynamical and diabatic contributions are found. Hence, this investigation leads to the conclusion that the IV is a natural phenomenon and is independent from the applied RCM.
In this work we investigated ultrafast demagnetization in a Heusler-alloy. This material belongs to the halfmetal and exists in a ferromagnetic phase. A special feature of investigated alloy is a structure of electronic bands. The last leads to the specific density of the states. Majority electrons form a metallic like structure while minority electrons form a gap near the Fermi-level, like in semiconductor. This particularity offers a good possibility to use this material as model-like structure and to make some proof of principles concerning demagnetization. Using pump-probe experiments we carried out time-resolved measurements to figure out the times of demagnetization. For the pumping we used ultrashort laser pulses with duration around 100 fs. Simultaneously we used two excitation regimes with two different wavelengths namely 400 nm and 1240 nm. Decreasing the energy of photons to the gap size of the minority electrons we explored the effect of the gap on the demagnetization dynamics. During this work we used for the first time OPA (Optical Parametrical Amplifier) for the generation of the laser irradiation in a long-wave regime. We tested it on the FETOSPEX-beamline in BASSYII electron storage ring. With this new technique we measured wavelength dependent demagnetization dynamics. We estimated that the demagnetization time is in a correlation with photon energy of the excitation pulse. Higher photon energy leads to the faster demagnetization in our material. We associate this result with the existence of the energy-gap for minority electrons and explained it with Elliot-Yaffet-scattering events. Additionally we applied new probe-method for magnetization state in this work and verified their effectivity. It is about the well-known XMCD (X-ray magnetic circular dichroism) which we adopted for the measurements in reflection geometry. Static experiments confirmed that the pure electronic dynamics can be separated from the magnetic one. We used photon energy fixed on the L3 of the corresponding elements with circular polarization. Appropriate incidence angel was estimated from static measurements. Using this probe method in dynamic measurements we explored electronic and magnetic dynamics in this alloy.
The near-Earth space environment is a highly complex system comprised of several regions and particle populations hazardous to satellite operations. The trapped particles in the radiation belts and ring current can cause significant damage to satellites during space weather events, due to deep dielectric and surface charging. Closer to Earth is another important region, the ionosphere, which delays the propagation of radio signals and can adversely affect navigation and positioning. In response to fluctuations in solar and geomagnetic activity, both the inner-magnetospheric and ionospheric populations can undergo drastic and sudden changes within minutes to hours, which creates a challenge for predicting their behavior. Given the increasing reliance of our society on satellite technology, improving our understanding and modeling of these populations is a matter of paramount importance.
In recent years, numerous spacecraft have been launched to study the dynamics of particle populations in the near-Earth space, transforming it into a data-rich environment. To extract valuable insights from the abundance of available observations, it is crucial to employ advanced modeling techniques, and machine learning methods are among the most powerful approaches available. This dissertation employs long-term satellite observations to analyze the processes that drive particle dynamics, and builds interdisciplinary links between space physics and machine learning by developing new state-of-the-art models of the inner-magnetospheric and ionospheric particle dynamics.
The first aim of this thesis is to investigate the behavior of electrons in Earth's radiation belts and ring current. Using ~18 years of electron flux observations from the Global Positioning System (GPS), we developed the first machine learning model of hundreds-of-keV electron flux at Medium Earth Orbit (MEO) that is driven solely by solar wind and geomagnetic indices and does not require auxiliary flux measurements as inputs. We then proceeded to analyze the directional distributions of electrons, and for the first time, used Fourier sine series to fit electron pitch angle distributions (PADs) in Earth's inner magnetosphere. We performed a superposed epoch analysis of 129 geomagnetic storms during the Van Allen Probes era and demonstrated that electron PADs have a strong energy-dependent response to geomagnetic activity. Additionally, we showed that the solar wind dynamic pressure could be used as a good predictor of the PAD dynamics. Using the observed dependencies, we created the first PAD model with a continuous dependence on L, magnetic local time (MLT) and activity, and developed two techniques to reconstruct near-equatorial electron flux observations from low-PA data using this model.
The second objective of this thesis is to develop a novel model of the topside ionosphere. To achieve this goal, we collected observations from five of the most widely used ionospheric missions and intercalibrated these data sets. This allowed us to use these data jointly for model development, validation, and comparison with other existing empirical models. We demonstrated, for the first time, that ion density observations by Swarm Langmuir Probes exhibit overestimation (up to ~40-50%) at low and mid-latitudes on the night side, and suggested that the influence of light ions could be a potential cause of this overestimation. To develop the topside model, we used 19 years of radio occultation (RO) electron density profiles, which were fitted with a Chapman function with a linear dependence of scale height on altitude. This approximation yields 4 parameters, namely the peak density and height of the F2-layer and the slope and intercept of the linear scale height trend, which were modeled using feedforward neural networks (NNs). The model was extensively validated against both RO and in-situ observations and was found to outperform the International Reference Ionosphere (IRI) model by up to an order of magnitude. Our analysis showed that the most substantial deviations of the IRI model from the data occur at altitudes of 100-200 km above the F2-layer peak. The developed NN-based ionospheric model reproduces the effects of various physical mechanisms observed in the topside ionosphere and provides highly accurate electron density predictions.
This dissertation provides an extensive study of geospace dynamics, and the main results of this work contribute to the improvement of models of plasma populations in the near-Earth space environment.
Via their powerful radiation, stellar winds, and supernova explosions, massive stars (Mini & 8 M☉) bear a tremendous impact on galactic evolution. It became clear in recent decades that the majority of massive stars reside in binary systems. This thesis sets as a goal to quantify the impact of binarity (i.e., the presence of a companion star) on massive stars. For this purpose, massive binary systems in the Local Group, including OB-type binaries, high mass X-ray binaries (HMXBs), and Wolf-Rayet (WR) binaries, were investigated by means of spectral, orbital, and evolutionary analyses.
The spectral analyses were performed with the non-local thermodynamic equillibrium (non-LTE) Potsdam Wolf-Rayet (PoWR) model atmosphere code. Thanks to critical updates in the calculation of the hydrostatic layers, the code became a state-of-the-art tool applicable for all types of hot massive stars (Chapter 2). The eclipsing OB-type triple system δ Ori served as an intriguing test-case for the new version of the PoWR code, and provided key insights regarding the formation of X-rays in massive stars (Chapter 3). We further analyzed two prototypical HMXBs, Vela X-1 and IGR J17544-2619, and obtained fundamental conclusions regarding the dichotomy of two basic classes of HMXBs (Chapter 4). We performed an exhaustive analysis of the binary R 145 in the Large Magellanic Cloud (LMC), which was claimed to host the most massive stars known. We were able to disentangle the spectrum of the system, and performed an orbital, polarimetric, and spectral analysis, as well as an analysis of the wind-wind collision region. The true masses of the binary components turned out to be significantly lower than suggested, impacting our understanding of the initial mass function and stellar evolution at low metallicity (Chapter 5). Finally, all known WR binaries in the Small Magellanic Cloud (SMC) were analyzed. Although it was theoretical predicted that virtually all WR stars in the SMC should be formed via mass-transfer in binaries, we find that binarity was not important for the formation of the known WR stars in the SMC, implying a strong discrepancy between theory and observations (Chapter 6).
The origin and structure of magnetic fields in the Galaxy are largely unknown. What is known is that they are essential for several astrophysical processes, in particular the propagation of cosmic rays. Our ability to describe the propagation of cosmic rays through the Galaxy is severely limited by the lack of observational data needed to probe the structure of the Galactic magnetic field on many different length scales. This is particularly true for modelling the propagation of cosmic rays into the Galactic halo, where our knowledge of the magnetic field is particularly poor.
In the last decade, observations of the Galactic halo in different frequency regimes have revealed the existence of out-of-plane bubble emission in the Galactic halo. In gamma rays these bubbles have been termed Fermi bubbles with a radial extent of ≈ 3 kpc and an azimuthal height of ≈ 6 kpc. The radio counterparts of the Fermi bubbles were seen by both the S-PASS telescopes and the Planck satellite, and showed a clear spatial overlap. The X-ray counterparts of the Fermi bubbles were named eROSITA bubbles after the eROSITA satellite, with a radial width of ≈ 7 kpc and an azimuthal height of ≈ 14 kpc. Taken together, these observations suggest the presence of large extended Galactic Halo Bubbles (GHB) and have stimulated interest in exploring the less explored Galactic halo.
In this thesis, a new toy model (GHB model) for the magnetic field and non-thermal electron distribution in the Galactic halo has been proposed. The new toy model has been used to produce polarised synchrotron emission sky maps. Chi-square analysis was used to compare the synthetic skymaps with the Planck 30 GHz polarised skymaps. The obtained constraints on the strength and azimuthal height were found to be in agreement with the S-PASS radio observations.
The upper, lower and best-fit values obtained from the above chi-squared analysis were used to generate three separate toy models. These three models were used to propagate ultra-high energy cosmic rays. This study was carried out for two potential sources, Centaurus A and NGC 253, to produce magnification maps and arrival direction skymaps. The simulated arrival direction skymaps were found to be consistent with the hotspots of Centaurus A and NGC 253 as seen in the observed arrival direction skymaps provided by the Pierre Auger Observatory (PAO).
The turbulent magnetic field component of the GHB model was also used to investigate the extragalactic dipole suppression seen by PAO. UHECRs with an extragalactic dipole were forward-tracked through the turbulent GHB model at different field strengths. The suppression in the dipole due to the varying diffusion coefficient from the simulations was noted. The results could also be compared with an analytical analogy of electrostatics. The simulations of the extragalactic dipole suppression were in agreement with similar studies carried out for galactic cosmic rays.
Unter atmosphärischen Zirkulationsregimen versteht man bevorzugte quasi-stationäre Zustände der atmosphärischen Zirkulation auf der planetaren Skala, die für eine bis mehrere Wochen persistieren können. Klimaänderungen, ob natürlich entstanden oder anthropogen verursacht, äußern sich in erster Linie durch Änderungen der Auftrittswahrscheinlichkeiten der natürlichen Regime. In der vorliegenden Arbeit wurden dynamische Mechanismen des Regimeverhaltens und der dekadischen Klimavariabilität der Atmosphäre bei Abwesenheit zeitlich veränderlicher externer Einflussfaktoren untersucht. Das Hauptwerkzeug dafür war ein quasi-geostrophisches Dreischichtenmodell der winterlichen atmosphärischen Zirkulation auf der Nordhemisphäre, das eine spektrale T21-Auflösung, einen orographischen und einen zeitlich konstanten thermischen Antrieb mit nicht-zonalen Anteilen besitzt. Ein solches Modell vermag großskalige atmosphärische Strömungsvorgänge außerhalb der Tropen mit einiger Genauigkeit zu simulieren. Nicht berücksichtigt werden Feuchteprozesse, die Wechselwirkung der Atmosphäre mit anderen Teilen des Klimasystems sowie anthropogene Einflüsse. Für das Dreischichtenmodell wurde ein automatisiertes, iteratives Verfahren zur Anpassung des thermischen Modellantriebs neu entwickelt. Jede Iteration des Verfahrens besteht aus einer Testintegration des Modells, ihrer Auswertung, dem Vergleich der Ergebnisse mit den NCEP-NCAR-Reanalysedaten aus den Wintermonaten Dezember, Januar und Februar sowie einer auf diesem Vergleich basierenden Antriebskorrektur. Nach Konvergenz des Verfahrens stimmt das Modell sowohl bezüglich des zonal gemittelten Klimazustandes als auch bezüglich der zeitgemittelten nicht-zonalen außertropischen diabatischen Erwärmung nahezu perfekt mit den wintergemittelten Reanalysedaten überein. In einer 1000-jährigen Simulation wurden die beobachtete mittlere Zirkulation im Winter sowie ihre Variabilität realitätsnah reproduziert, insbesondere die Arktische Oszillation (AO) und ihre vertikale Ausdehnung. Der AO-Index des Modells weist deutliche dekadische Schwankungen auf, die allein durch die interne Modelldynamik bedingt sind. Darüber hinaus zeigt das Modell ein Regimeverhalten, das gut mit den Beobachtungsdaten übereintimmt. Es besitzt ein Regime, das in etwa der negativen Phase der Nordatlantischen Oszillation (NAO) entspricht und eines, das der positiven Phase der AO ähnelt. Eine weit verbreitete Hypothese ist die näherungsweise Übereinstimmung zwischen Regimen und stationären Lösungen der Bewegungsgleichungen. In der vorliegenden Arbeit wurde diese Hypothese für das Dreischichtenmodell überprüft, mit negativem Resultat. Es wurden mittels eines Funktionalminimierungsverfahrens sechs verschiedene stationäre Zustände gefunden. Diese sind allesamt durch eine äußerst unrealistische Zirkulation gekennzeichnet und sind daher weit vom Modellattraktor entfernt. Fünf der sechs Zustände zeichnen sich durch einen extrem starken subtropischen Jet in der mittleren und obereren Modellschicht aus. Da die Ursache des Regimeverhaltens des Dreischichtenmodells nach wie vor unklar war, wurde auf ein einfacheres Modell, nämlich ein barotropes Modell mit T21-Auflösung zurückgegriffen. Für die Anpassung des Oberflächenantriebs wurde eine modifizierte Form der iterativen Prozedur verwendet. Die zeitgemittelte Zirkulation des barotropen Modells stimmt sehr gut mit der zeitlich und vertikal gemittelten Zirkulation des Dreischichtenmodells überein. Das dominierende räumliche Muster der Variabilität besitzt eine AO-ähnliche Struktur. Zudem besitzt das barotrope Modell zwei Regime, die näherungsweise der positiven und negativen Phase der AO entsprechen und somit auch den Regimen des Dreischichtenmodells ähneln. Im Verlauf der Justierung des Oberflächenantriebs konnte beobachtet werden, dass die zwei Regime des barotropen Modells durch die Vereinigung zweier koexistierender Attraktoren entstanden. Der wahrscheinliche Mechanismus der Attraktorvereinigung ist eine Randkrise eines der beiden Attraktoren, gefolgt von einer explosiven Bifurkation des anderen Attraktors. Es wird die Hypothese aufgestellt, dass der beim barotropen Modell vorgefundene Mechanismus der Regimeentstehung für atmosphärische Zirkulationsmodelle mit realitätsnahem Regimeverhalten Allgemeingültigkeit besitzt. Gestützt wird die Hypothese durch vier Experimente mit dem Dreischichtenmodell, bei denen jeweils der Parameter der Bodenreibung verringert und die Antriebsanpassung wiederholt wurde. Bei diesen Experimenten erhöhte sich die Persistenz und die Separiertheit der Regime bei abnehmender Reibung drastisch und damit auch der Anteil dekadischer Zeitskalen an der Variabilität. Die Zunahme der Persistenz der Regime ist charakteristisch für die Annäherung an eine inverse innere Krise, deren Existenz aber nicht nachgewiesen werden konnte.
Eumelanin ist ein Fluorophor mit teilweise recht ungewöhnlichen spektralen Eigenschaften. Unter anderem konnten in früheren Veröffentlichungen Unterschiede zwischen dem 1- und 2-photonen-angeregtem Fluoreszenzspektrum beobachtet werden, weshalb im nichtlinearen Anregungsfall ein schrittweiser Anregungsprozess vermutet wurde. Um diese und weitere optische Eigenschaften des Eumelanins besser zu verstehen, wurden in der vorliegenden Arbeit vielfältige messmethodische Ansätze der linearen und nichtlinearen Optik an synthetischem Eumelanin in 0,1M NaOH verfolgt. Aus den Ergebnissen wurde ein Modell abgeleitet, welches die beobachteten photonischen Eigenschaften konsistent beschreibt. In diesem kaskadierten Zustandsmodell (Kaskaden-Modell) wird die aufgenommene Photonenenergie schrittweise von Anregungszuständen hoher Übergangsenergien zu Anregungszuständen niedrigerer Übergangsenergien transferiert. Messungen der transienten Absorption ergaben dominante Anteile mit kurzen Lebensdauern im ps-Bereich und ließen damit auf eine hohe Relaxationsgeschwindigkeit entlang der Kaskade schließen. Durch Untersuchung der nichtlinear angeregten Fluoreszenz von verschieden großen Eumelanin-Aggregaten konnte gezeigt werden, dass Unterschiede zwischen dem linear und nichtlinear angeregten Fluoreszenzspektrum nicht nur durch einen schrittweisen Anregungsprozess bei nichtlinearer Anregung sondern auch durch Unterschiede in den Verhältnissen der Quantenausbeuten zwischen kleinen und großen Aggregaten beim Wechsel von linearer zu nichtlinearer Anregung begründet sein können. Durch Bestimmung des Anregungswirkungsquerschnitts und der Anregungspulsdauer-Abhängigkeit der nichtlinear angeregten Fluoreszenz von Eumelanin konnte jedoch ein schrittweiser 2-Photonen-Anregungsprozess über einen Zwischenzustand mit Lebendsdauern im ps-Bereich nachgewiesen werden.
Im Rahmen der vorliegenden Arbeit ist es erstmals gelungen, mit einem ps-Pumplaser (10 ps) Weißlicht mit einer spektralen Breite von mehr als einer optischen Oktave in einer mikrostrukturierten Faser (MSF) bei einer Pumpwellenlänge von 1064 nm zu generieren. Es ließ sich, abgesehen von nichtkonvertierten Resten der Pumpstrahlung, ein unstrukturiertes und zeitlich stabiles Weißlichtspektrum von 700 nm bis 1650 nm generieren. Die maximale Ausgangsleistung dieser Weißlichtstrahlung betrug 3,1 W. Es konnten sehr gute Einkoppeleffizienzen von maximal 62 % erzielt werden. Die an der Weißlichterzeugung beteiligten dispersiven und nichtlinear optischen Effekte, wie z.B. Selbstphasenmodulation, Vierwellenmischung, Modulationsinstabilitäten oder Solitoneneffekte, werden detailliert theoretisch untersucht und erläutert. Die Arbeit beinhaltet ebenfalls eine umfangreiche Beschreibung der Wirkungsweise und Eigenschaften von mikrostrukturierten Fasern mit einem festen Faserkern. Aufgrund der großen Variationsvielfalt des mikrostrukturierten Fasermantels und der damit verbundenen Wellenleitereigenschaften ergeben sich, insbesondere für die Anwendung in der nichtlinearen Optik, eine Reihe von interessanten Eigenschaften. Es wurden insgesamt vier verschiedene mikrostrukturierte Fasern experimentell untersucht. Für die Interpretation der experimentellen Ergebnisse ist die Pulsausbreitung der ps-Pumppulse in einer dispersiven, nichtlinear optischen Faser anhand der verallgemeinerten nichtlinearen Schrödinger-Gleichung berechnet worden. Durch einen Vergleich der Berechnungen mit den Messdaten ließen sich verstärkte Modulationsinstabilitäten und verschiedene Solitoneneffekte als hauptsächlich für die Weißlichterzeugung bei ps-Anregungspulsen verantwortlich identifizieren. Auf der Basis der durchgeführten Untersuchungen wurde in Kooperation mit der Fa. Jenoptik Laser, Optik, Systeme GmbH eine kompakte und leistungsstarke Weißlichtquelle entwickelt. Diese wurde erfolgreich in einer Kohärenztomographiemessung (Optical Coherence Tomography - OCT) getestet: Es konnte in ex vivo-Untersuchungen gezeigt werden, dass sich mit dieser ps-Weißlichtquelle eine hohe Eindringtiefe von ca. 400 µm in die Netzhaut eines Affen erreichen lässt.
In Germany more than 200.000 persons die of cancer every year, which makes it the second most common cause of death. Chemotherapy and radiation therapy are often combined to exploit a supra-additive effect, as some chemotherapeutic agents like halogenated nucleobases sensitize the cancerous tissue to radiation. The radiosensitizing action of certain therapeutic agents can be at least partly assigned to their interaction with secondary low energy electrons (LEEs) that are generated along the track of the ionizing radiation. In the therapy of cancer DNA is an important target, as severe DNA damage like double strand breaks induce the cell death. As there is only a limited number of radiosensitizing agents in clinical practice, which are often strongly cytotoxic, it would be beneficial to get a deeper understanding of the interaction of less toxic potential radiosensitizers with secondary reactive species like LEEs. Beyond that LEEs can be generated by laser illuminated nanoparticles that are applied in photothermal therapy (PTT) of cancer, which is an attempt to treat cancer by an increase of temperature in the cells. However, the application of halogenated nucleobases in PTT has not been taken into account so far. In this thesis the interaction of the potential radiosensitizer 8-bromoadenine (8BrA) with LEEs was studied. In a first step the dissociative electron attachment (DEA) in the gas phase was studied in a crossed electron-molecular beam setup. The main fragmentation pathway was revealed as the cleavage of the C-Br bond. The formation of a stable parent anion was observed for electron energies around 0 eV. Furthermore, DNA origami nanostructures were used as platformed to determine electron induced strand break cross sections of 8BrA sensitized oligonucleotides and the corresponding nonsensitized sequence as a function of the electron energy. In this way the influence of the DEA resonances observed for the free molecules on the DNA strand breaks was examined. As the surrounding medium influences the DEA, pulsed laser illuminated gold nanoparticles (AuNPs) were used as a nanoscale electron source in an aqueous environment. The dissociation of brominated and native nucleobases was tracked with UV-Vis absorption spectroscopy and the generated fragments were identified with surface enhanced Raman scattering (SERS). Beside the electron induced damage, nucleobase analogues are decomposed in the vicinity of the laser illuminatednanoparticles due to the high temperatures. In order to get a deeper understanding of the different dissociation mechanisms, the thermal decomposition of the nucleobases in these systems was studied and the influence of the adsorption kinetics of the molecules was elucidated. In addition to the pulsed laser experiments, a dissociative electron transfer from plasmonically generated ”hot electrons” to 8BrA was observed under low energy continuous wave laser illumination and tracked with SERS. The reaction was studied on AgNPs and AuNPs as a function of the laser intensity and wavelength. On dried samples the dissociation of the molecule was described by fractal like kinetics. In solution, the dissociative electron transfer was observed as well. It turned out that the timescale of the reaction rates were slightly below typical integration times of Raman spectra. In consequence such reactions need to be taken into account in the interpretation of SERS spectra of electrophilic molecules. The findings in this thesis help to understand the interaction of brominated nucleobases with plasmonically generated electrons and free electrons. This might help to evaluate the potential radiosensitizing action of such molecules in cancer radiation therapy and PTT.
In der vorliegenden Dissertation wird eine Beschreibung der Phasendynamik irregulärer Oszillationen und deren Wechselwirkungen vorgestellt. Hierbei werden chaotische und stochastische Oszillationen autonomer dissipativer Systeme betrachtet. Für eine Phasenbeschreibung stochastischer Oszillationen müssen zum einen unterschiedliche Werte der Phase zueinander in Beziehung gesetzt werden, um ihre Dynamik unabhängig von der gewählten Parametrisierung der Oszillation beschreiben zu können. Zum anderen müssen für stochastische und chaotische Oszillationen diejenigen Systemzustände identifiziert werden, die sich in der gleichen Phase befinden. Im Rahmen dieser Dissertation werden die Werte der Phase über eine gemittelte Phasengeschwindigkeitsfunktion miteinander in Beziehung gesetzt. Für stochastische Oszillationen sind jedoch verschiedene Definitionen der mittleren Geschwindigkeit möglich. Um die Unterschiede der Geschwindigkeitsdefinitionen besser zu verstehen, werden auf ihrer Basis effektive deterministische Modelle der Oszillationen konstruiert. Hierbei zeigt sich, dass die Modelle unterschiedliche Oszillationseigenschaften, wie z. B. die mittlere Frequenz oder die invariante Wahrscheinlichkeitsverteilung, nachahmen. Je nach Anwendung stellt die effektive Phasengeschwindigkeitsfunktion eines speziellen Modells eine zweckmäßige Phasenbeziehung her. Wie anhand einfacher Beispiele erklärt wird, kann so die Theorie der effektiven Phasendynamik auch kontinuierlich und pulsartig wechselwirkende stochastische Oszillationen beschreiben. Weiterhin wird ein Kriterium für die invariante Identifikation von Zuständen gleicher Phase irregulärer Oszillationen zu sogenannten generalisierten Isophasen beschrieben: Die Zustände einer solchen Isophase sollen in ihrer dynamischen Entwicklung ununterscheidbar werden. Für stochastische Oszillationen wird dieses Kriterium in einem mittleren Sinne interpretiert. Wie anhand von Beispielen demonstriert wird, lassen sich so verschiedene Typen stochastischer Oszillationen in einheitlicher Weise auf eine stochastische Phasendynamik reduzieren. Mit Hilfe eines numerischen Algorithmus zur Schätzung der Isophasen aus Daten wird die Anwendbarkeit der Theorie anhand eines Signals regelmäßiger Atmung gezeigt. Weiterhin zeigt sich, dass das Kriterium der Phasenidentifikation für chaotische Oszillationen nur approximativ erfüllt werden kann. Anhand des Rössleroszillators wird der tiefgreifende Zusammenhang zwischen approximativen Isophasen, chaotischer Phasendiffusion und instabilen periodischen Orbits dargelegt. Gemeinsam ermöglichen die Theorien der effektiven Phasendynamik und der generalisierten Isophasen eine umfassende und einheitliche Phasenbeschreibung irregulärer Oszillationen.
Supermassive black holes are a fundamental component of the universe in general and of galaxies in particular. Almost every massive galaxy harbours a supermassive black hole (SMBH) in its center. Furthermore, there is a close connection between the growth of the SMBH and the evolution of its host galaxy, manifested in the relationship between the mass of the black hole and various properties of the galaxy's spheroid component, like its stellar velocity dispersion, luminosity or mass. Understanding this relationship and the growth of SMBHs is essential for our picture of galaxy formation and evolution. In this thesis, I make several contributions to improve our knowledge on the census of SMBHs and on the coevolution of black holes and galaxies. The first route I follow on this road is to obtain a complete census of the black hole population and its properties. Here, I focus particularly on active black holes, observable as Active Galactic Nuclei (AGN) or quasars. These are found in large surveys of the sky. In this thesis, I use one of these surveys, the Hamburg/ESO survey (HES), to study the AGN population in the local volume (z~0). The demographics of AGN are traditionally represented by the AGN luminosity function, the distribution function of AGN at a given luminosity. I determined the local (z<0.3) optical luminosity function of so-called type 1 AGN, based on the broad band B_J magnitudes and AGN broad Halpha emission line luminosities, free of contamination from the host galaxy. I combined this result with fainter data from the Sloan Digital Sky Survey (SDSS) and constructed the best current optical AGN luminosity function at z~0. The comparison of the luminosity function with higher redshifts supports the current notion of 'AGN downsizing', i.e. the space density of the most luminous AGN peaks at higher redshifts and the space density of less luminous AGN peaks at lower redshifts. However, the AGN luminosity function does not reveal the full picture of active black hole demographics. This requires knowledge of the physical quantities, foremost the black hole mass and the accretion rate of the black hole, and the respective distribution functions, the active black hole mass function and the Eddington ratio distribution function. I developed a method for an unbiased estimate of these two distribution functions, employing a maximum likelihood technique and fully account for the selection function. I used this method to determine the active black hole mass function and the Eddington ratio distribution function for the local universe from the HES. I found a wide intrinsic distribution of black hole accretion rates and black hole masses. The comparison of the local active black hole mass function with the local total black hole mass function reveals evidence for 'AGN downsizing', in the sense that in the local universe the most massive black holes are in a less active stage then lower mass black holes. The second route I follow is a study of redshift evolution in the black hole-galaxy relations. While theoretical models can in general explain the existence of these relations, their redshift evolution puts strong constraints on these models. Observational studies on the black hole-galaxy relations naturally suffer from selection effects. These can potentially bias the conclusions inferred from the observations, if they are not taken into account. I investigated the issue of selection effects on type 1 AGN samples in detail and discuss various sources of bias, e.g. an AGN luminosity bias, an active fraction bias and an AGN evolution bias. If the selection function of the observational sample and the underlying distribution functions are known, it is possible to correct for this bias. I present a fitting method to obtain an unbiased estimate of the intrinsic black hole-galaxy relations from samples that are affected by selection effects. Third, I try to improve our census of dormant black holes and the determination of their masses. One of the most important techniques to determine the black hole mass in quiescent galaxies is via stellar dynamical modeling. This method employs photometric and kinematic observations of the galaxy and infers the gravitational potential from the stellar orbits. This method can reveal the presence of the black hole and give its mass, if the sphere of the black hole's gravitational influence is spatially resolved. However, usually the presence of a dark matter halo is ignored in the dynamical modeling, potentially causing a bias on the determined black hole mass. I ran dynamical models for a sample of 12 galaxies, including a dark matter halo. For galaxies for which the black hole's sphere of influence is not well resolved, I found that the black hole mass is systematically underestimated when the dark matter halo is ignored, while there is almost no effect for galaxies with well resolved sphere of influence.
The mystery of the origin of cosmic rays has been tackled for more than hundred years and is still not solved. Cosmic rays are detected with energies spanning more than 10 orders of magnitude and reaching energies up to ~10²¹ eV, far higher than any man-made accelerator can reach. Different theories on the astrophysical objects and processes creating such highly energetic particles have been proposed.
A very prominent explanation for a process producing highly energetic particles is shock acceleration. The observation of high-energy gamma rays from supernova remnants, some of them revealing a shell like structure, is clear evidence that particles are accelerated to ultrarelativistic energies in the shocks of these objects. The environments of supernova remnants are complex and challenge detailed modelling of the processes leading to high-energy gamma-ray emission.
The study of shock acceleration at bow shocks, created by the supersonic movement of individual stars through the interstellar medium, offers a unique possibility to determine the physical properties of shocks in a less complex environment. The shocked medium is heated by the stellar and the shock excited radiation, leading to thermal infrared emission. 28 bow shocks have been discovered through their infrared emission. Nonthermal radiation in radio and X-ray wavelengths has been detected from two bow shocks, pointing to the existence of relativistic particles in these systems. Theoretical models of the emission processes predict high-energy and very high-energy emission at a flux level in reach of current instruments. This work presents the search for gamma-ray emission from bow shocks of runaway stars in the energy regime from 100MeV to ~100TeV.
The search is performed with the large area telescope (LAT) on-board the Fermi satellite and the H.E.S.S. telescopes located in the Khomas Highland in Namibia. The Fermi-LAT was launched in 2008 and is continuously scanning the sky since then. It detects photons with energies from 20MeV to over 300 GeV and has an unprecedented sensitivity. The all-sky coverage allows us to study all 28 bow shocks of runaway stars listed in the E-BOSS catalogue of infrared bow shocks. No significant emission was detected from any of the objects, although predicted by several theoretical models describing the non-thermal emission of bow shocks of runaway stars.
The H.E.S.S. experiment is the most sensitive system of imaging atmospheric Cherenkov telescopes. It detects photons from several tens of GeV to ~100TeV. Seven of the bow shocks have been observed with H.E.S.S. and the data analysis is presented in this thesis. The analyses of the very-high energy data did not reveal significant emission from any of the sources either.
This work presents the first systematic search for gamma-ray emission from bow shocks of runaway stars. For the first time Fermi-LAT data was specifically analysed to reveal emission from bow shocks of runaway stars. In the TeV regime no searches for emission from theses objects have been published so far, the study presented here is the first in this energy regime. The level of the gamma-ray emission from bow shocks of runaway stars is constrained by the calculated upper limits over six orders in magnitude in energy.
The upper limits calculated for the bow shocks of runaway stars in the course of this work, constrain several models. For the best candidate, ζ Ophiuchi, the upper limits in the Fermi-LAT energy range are lower than the predictions by a factor ~5. This challenges the assumptions made in this model and gives valuable input for further modelling approaches.
The analyses were performed with the software packages provided by the H.E.S.S. and Fermi collaborations. The development of a unified analysis framework for gamma-ray data, namely GammaLib/ctools, is rapidly progressing within the CTA consortium. Recent implementations and cross-checks with current software frameworks are presented in the Appendix.
In der vorliegenden Arbeit wird die planetare Grenzschicht in Ny-Ålesund, Spitzbergen, sowohl bezüglich kleinskaliger („mikrometeorologischer“) Effekte als auch in ihrer Kopplung mit der Synoptik untersucht. Dazu werden verschiedene Beobachtungsdaten aus der Säule und in Bodennähe zusammengezogen und bewertet. Die so gewonnenen Datensätze werden dann zur Validierung eines nicht-hydrostatischen, regionalen Klimamodells genutzt. Weiterhin werden orographisch bedingte Einflüsse, die Untergrundbeschaffenheit und die lokale Heterogenität der Unterlage untersucht. Hierzu werden meteorologische Größen, wie die Variabilität der Temperatur und insbesondere die jährliche Windverteilung in Bodennähe untersucht und es erfolgt ein Vergleich von in-situ gemessenen turbulenten Flüssen von den Eddy-Kovarianz-Messkomplexen bei Ny-Ålesund und im Bayelva-Tal unter demselben Aspekt. Es zeigt sich, dass der Eddy-Kovarianz-Messkomplex im Bayelva-Tal sehr stark durch eine orographisch bedingte Kanalisierung der Strömung beeinflusst ist und sich nicht für Vergleiche mit regionalen Klimamodellen mit horizontalen Auflösungen von <1km eignet. Die hohe Bodenfeuchte im Bayelva-Tal führt zudem zu einem deutlich kleineren Bowen-Verhältnis, als es für diese Region zu erwarten ist. Der Eddy-Kovarianz-Messkomplex bei Ny-Ålesund erweist sich hingegen als geeigneter für solche Modellvergleiche, aufgrund der typischen, küstennahen Windverteilung und des repräsentativen Footprints. Letzteres wird durch die Bestimmung der Footprint-Klimatologie des Jahres 2013 mit einem aktuellen Footprint-Modell erarbeitet.
Weiterhin wird die Auswirkung von (Anti-) Zyklonen über den Archipel auf die zeitliche Variabilität der lokalen Grenzschichteigenschaften untersucht und bewertet. Dazu wird ein Zyklonen-Detektions-Algorithmus auf ERA-Interim-Reanalysedatensätze angewendet, wodurch die Häufigkeit von nahezu ideal konzentrischen Hoch- und die Tiefdruckgebieten für drei Jahre bestimmt wird. Aus dieser Verteilung werden insgesamt drei interessante Zeiträume zu verschiedenen Jahreszeiten ausgewählt und im Rahmen von Prozessstudien die lokalen bodennahen meteorologischen Messungen, der turbulente Austausch an der Oberfläche und die Grenzschichtdynamik in der Säule untersucht. Die zeitliche Variabilität der dynamischen Grenzschichtstabilität in der Säule wird anhand von zeitlich hoch aufgelösten vertikalen Profilen der Bulk-Richardson-Zahl aus Kompositprofilen aus Fernerkundungsinstrumenten (Radiometer, Wind-LIDAR) sowie Mastdaten (BSRN-Mast) untersucht und die Grenzschichthöhe ermittelt. Aus diesen Analysen ergibt sich eine deutliche Abhängigkeit der thermischen Stabilität beim Durchzug von Fronten, eine damit einhergehende erhebliche Abhängigkeit der Grenzschichtdynamik und der Grenzschichthöhe sowie des turbulenten Austauschs von der zeitlichen Variabilität der Windgeschwindigkeit in der Säule.
Auf Grundlage der Standortanalysen und Prozessstudien erfolgt ein Vergleich der bodennahen Messungen und den Beobachtungen aus der Säule, sowohl von den genannten Fernerkundungsinstrumenten als auch von In-situ-Messungen (Radiosonden) für den Zeitraum einer Radiosondierungskampagne mit dem nicht-hydrostatischen, regionalen Klimamodel WRF (ARW). Auf Grundlage der Fragestellung, inwieweit aktuelle Schemata die Grenzschichtcharakteristika in orographisch stark gegliedertem Gelände in der Arktis reproduzieren können, werden zwei Grenzschichtparametrisierungsschemata mit verschiedenen Ordnungen der Schließung validiert. Hierzu wird die zeitliche Variabilität der Temperatur, der Feuchte und des Windfeldes in der Säule bis 2000m in den Simulationen mit den Beobachtungsdaten vergleichen. Es wird gezeigt, dass durch Modifikation der Initialwertfelder eine sehr gute Übereinstimmung zwischen den Simulationen und den Beobachtungen bereits bei einer horizontalen Auflösung von 1km erreicht werden kann und die Wahl des Grenzschichtschemas nur untergeordneten Einfluss hat. Hieraus werden Ansätze der Weiterentwicklung der Parametrisierungen, aber auch Empfehlungen bezüglich der Initialwertfelder, wie der Landmaske und der Orographie, vorgeschlagen.
Donor-acceptor (D-A) copolymers have revolutionized the field of organic electronics over the last decade. Comprised of a electron rich and an electron deficient molecular unit, these copolymers facilitate the systematic modification of the material's optoelectronic properties. The ability to tune the optical band gap and to optimize the molecular frontier orbitals as well as the manifold of structural sites that enable chemical modifications has created a tremendous variety of copolymer structures. Today, these materials reach or even exceed the performance of amorphous inorganic semiconductors. Most impressively, the charge carrier mobility of D-A copolymers has been pushed to the technologically important value of 10 cm^{2}V^{-1}s^{-1}. Furthermore, owed to their enormous variability they are the material of choice for the donor component in organic solar cells, which have recently surpassed the efficiency threshold of 10%. Because of the great number of available D-A copolymers and due to their fast chemical evolution, there is a significant lack of understanding of the fundamental physical properties of these materials. Furthermore, the complex chemical and electronic structure of D-A copolymers in combination with their semi-crystalline morphology impede a straightforward identification of the microscopic origin of their superior performance. In this thesis, two aspects of prototype D-A copolymers were analysed. These are the investigation of electron transport in several copolymers and the application of low band gap copolymers as acceptor component in organic solar cells. In the first part, the investigation of a series of chemically modified fluorene-based copolymers is presented. The charge carrier mobility varies strongly between the different derivatives, although only moderate structural changes on the copolymers structure were made. Furthermore, rather unusual photocurrent transients were observed for one of the copolymers. Numerical simulations of the experimental results reveal that this behavior arises from a severe trapping of electrons in an exponential distribution of trap states. Based on the comparison of simulation and experiment, the general impact of charge carrier trapping on the shape of photo-CELIV and time-of-flight transients is discussed. In addition, the high performance naphthalenediimide (NDI)-based copolymer P(NDI2OD-T2) was characterized. It is shown that the copolymer posses one of the highest electron mobilities reported so far, which makes it attractive to be used as the electron accepting component in organic photovoltaic cells.\par Solar cells were prepared from two NDI-containing copolymers, blended with the hole transporting polymer P3HT. I demonstrate that the use of appropriate, high boiling point solvents can significantly increase the power conversion efficiency of these devices. Spectroscopic studies reveal that the pre-aggregation of the copolymers is suppressed in these solvents, which has a strong impact on the blend morphology. Finally, a systematic study of P3HT:P(NDI2OD-T2) blends is presented, which quantifies the processes that limit the efficiency of devices. The major loss channel for excited states was determined by transient and steady state spectroscopic investigations: the majority of initially generated electron-hole pairs is annihilated by an ultrafast geminate recombination process. Furthermore, exciton self-trapping in P(NDI2OD-T2) domains account for an additional reduction of the efficiency. The correlation of the photocurrent to microscopic morphology parameters was used to disclose the factors that limit the charge generation efficiency. Our results suggest that the orientation of the donor and acceptor crystallites relative to each other represents the main factor that determines the free charge carrier yield in this material system. This provides an explanation for the overall low efficiencies that are generally observed in all-polymer solar cells.
Additive manufacturing (AM) processes enable the production of metal structures with exceptional design freedom, of which laser powder bed fusion (PBF-LB) is one of the most common. In this process, a laser melts a bed of loose feedstock powder particles layer-by-layer to build a structure with the desired geometry. During fabrication, the repeated melting and rapid, directional solidification create large temperature gradients that generate large thermal stress. This thermal stress can itself lead to cracking or delamination during fabrication. More often, large residual stresses remain in the final part as a footprint of the thermal stress. This residual stress can cause premature distortion or even failure of the part in service. Hence, knowledge of the residual stress field is critical for both process optimization and structural integrity.
Diffraction-based techniques allow the non-destructive characterization of the residual stress fields. However, such methods require a good knowledge of the material of interest, as certain assumptions must be made to accurately determine residual stress. First, the measured lattice plane spacings must be converted to lattice strains with the knowledge of a strain-free material state. Second, the measured lattice strains must be related to the macroscopic stress using Hooke's law, which requires knowledge of the stiffness of the material. Since most crystal structures exhibit anisotropic material behavior, the elastic behavior is specific to each lattice plane of the single crystal. Thus, the use of individual lattice planes in monochromatic diffraction residual stress analysis requires knowledge of the lattice plane-specific elastic properties. In addition, knowledge of the microstructure of the material is required for a reliable assessment of residual stress.
This work presents a toolbox for reliable diffraction-based residual stress analysis. This is presented for a nickel-based superalloy produced by PBF-LB. First, this work reviews the existing literature in the field of residual stress analysis of laser-based AM using diffraction-based techniques. Second, the elastic and plastic anisotropy of the nickel-based superalloy Inconel 718 produced by PBF-LB is studied using in situ energy dispersive synchrotron X-ray and neutron diffraction techniques. These experiments are complemented by ex situ material characterization techniques. These methods establish the relationship between the microstructure and texture of the material and its elastic and plastic anisotropy. Finally, surface, sub-surface, and bulk residual stress are determined using a texture-based approach. Uncertainties of different methods for obtaining stress-free reference values are discussed.
The tensile behavior in the as-built condition is shown to be controlled by texture and cellular sub-grain structure, while in the heat-treated condition the precipitation of strengthening phases and grain morphology dictate the behavior. In fact, the results of this thesis show that the diffraction elastic constants depend on the underlying microstructure, including texture and grain morphology. For columnar microstructures in both as-built and heat-treated conditions, the diffraction elastic constants are best described by the Reuss iso-stress model. Furthermore, the low accumulation of intergranular strains during deformation demonstrates the robustness of using the 311 reflection for the diffraction-based residual stress analysis with columnar textured microstructures. The differences between texture-based and quasi-isotropic approaches for the residual stress analysis are shown to be insignificant in the observed case. However, the analysis of the sub-surface residual stress distributions show, that different scanning strategies result in a change in the orientation of the residual stress tensor. Furthermore, the location of the critical sub-surface tensile residual stress is related to the surface roughness and the microstructure. Finally, recommendations are given for the diffraction-based determination and evaluation of residual stress in textured additively manufactured alloys.
In this thesis, the two prototype catalysts Fe(CO)₅ and Cr(CO)₆ are investigated with time-resolved photoelectron spectroscopy at a high harmonic setup. In both of these metal carbonyls, a UV photon can induce the dissociation of one or more ligands of the complex. The mechanism of the dissociation has been debated over the last decades. The electronic dynamics of the first dissociation occur on the femtosecond timescale.
For the experiment, an existing high harmonic setup was moved to a new location, was extended, and characterized. The modified setup can induce dynamics in gas phase samples with photon energies of 1.55eV, 3.10eV, and 4.65eV. The valence electronic structure of the samples can be probed with photon energies between 20eV and 40eV. The temporal resolution is 111fs to 262fs, depending on the combination of the two photon energies.
The electronically excited intermediates of the two complexes, as well as of the reaction product Fe(CO)₄, could be observed with photoelectron spectroscopy in the gas phase for the first time. However, photoelectron spectroscopy gives access only to the final ionic states. Corresponding calculations to simulate these spectra are still in development. The peak energies and their evolution in time with respect to the initiation pump pulse have been determined, these peaks have been assigned based on literature data. The spectra of the two complexes show clear differences. The dynamics have been interpreted with the assumption that the motion of peaks in the spectra relates to the movement of the wave packet in the multidimensional energy landscape. The results largely confirm existing models for the reaction pathways. In both metal carbonyls, this pathway involves a direct excitation of the wave packet to a metal-to-ligand charge transfer state and the subsequent crossing to a dissociative ligand field state. The coupling of the electronic dynamics to the nuclear dynamics could explain the slower dissociation in Fe(CO)₅ as compared to Cr(CO)₆.
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.
Uncertainty about the sensitivity of the climate system to changes in the Earth’s radiative balance constitutes a primary source of uncertainty for climate projections. Given the continuous increase in atmospheric greenhouse gas concentrations, constraining the uncertainty range in such type of sensitivity is of vital importance. A common measure for expressing this key characteristic for climate models is the climate sensitivity, defined as the simulated change in global-mean equilibrium temperature resulting from a doubling of atmospheric CO2 concentration. The broad range of climate sensitivity estimates (1.5-4.5°C as given in the last Assessment Report of the Intergovernmental Panel on Climate Change, 2001), inferred from comprehensive climate models, illustrates that the strength of simulated feedback mechanisms varies strongly among different models. The central goal of this thesis is to constrain uncertainty in climate sensitivity. For this objective we first generate a large ensemble of model simulations, covering different feedback strengths, and then request their consistency with present-day observational data and proxy-data from the Last Glacial Maximum (LGM). Our analyses are based on an ensemble of fully-coupled simulations, that were realized with a climate model of intermediate complexity (CLIMBER-2). These model versions cover a broad range of different climate sensitivities, ranging from 1.3 to 5.5°C, and have been generated by simultaneously perturbing a set of 11 model parameters. The analysis of the simulated model feedbacks reveals that the spread in climate sensitivity results from different realizations of the feedback strengths in water vapour, clouds, lapse rate and albedo. The calculated spread in the sum of all feedbacks spans almost the entire plausible range inferred from a sampling of more complex models. We show that the requirement for consistency between simulated pre-industrial climate and a set of seven global-mean data constraints represents a comparatively weak test for model sensitivity (the data constrain climate sensitivity to 1.3-4.9°C). Analyses of the simulated latitudinal profile and of the seasonal cycle suggest that additional present-day data constraints, based on these characteristics, do not further constrain uncertainty in climate sensitivity. The novel approach presented in this thesis consists in systematically combining a large set of LGM simulations with data information from reconstructed regional glacial cooling. Irrespective of uncertainties in model parameters and feedback strengths, the set of our model versions reveals a close link between the simulated warming due to a doubling of CO2, and the cooling obtained for the LGM. Based on this close relationship between past and future temperature evolution, we define a method (based on linear regression) that allows us to estimate robust 5-95% quantiles for climate sensitivity. We thus constrain the range of climate sensitivity to 1.3-3.5°C using proxy-data from the LGM at low and high latitudes. Uncertainties in glacial radiative forcing enlarge this estimate to 1.2-4.3°C, whereas the assumption of large structural uncertainties may increase the upper limit by an additional degree. Using proxy-based data constraints for tropical and Antarctic cooling we show that very different absolute temperature changes in high and low latitudes all yield very similar estimates of climate sensitivity. On the whole, this thesis highlights that LGM proxy-data information can offer an effective means of constraining the uncertainty range in climate sensitivity and thus underlines the potential of paleo-climatic data to reduce uncertainty in future climate projections.
In this thesis, dynamical structures and manifolds in closed chaotic flows will be investigated. The knowledge about the dynamical structures (and manifolds) of a system is of importance, since they provide us first information about the dynamics of the system - means, with their help we are able to characterize the flow and maybe even to forecast it`s dynamics. The visualization of such structures in closed chaotic flows is a difficult and often long-lasting process. Here, the so-called 'Leaking-method' will be introduced, in examples of simple mathematical maps as the baker- or sine-map, with which we are able to visualize subsets of the manifolds of the system`s chaotic saddle. Comparisons between the visualized manifolds and structures traced out by chemical or biological reactions superimposed on the same flow will be done in the example of a kinematic model of the Gulf Stream. It will be shown that with the help of the leaking method dynamical structures can be also visualized in environmental systems. In the example of a realistic model of the Mediterranean Sea, the leaking method will be extended to the 'exchange-method'. The exchange method allows us to characterize transport between two regions, to visualize transport routes and their exchange sets and to calculate the exchange times. Exchange times and sets will be shown and calculated for a northern and southern region in the western basin of the Mediterranean Sea. Furthermore, mixing properties in the Earth mantle will be characterized and geometrical properties of manifolds in a 3dimensional mathematical model (ABC map) will be investigated.
Populärwissenschaftlicher Abstract: Bislang gibt es in der beobachtenden optischen Astronomie zwei verschiedene Herangehensweisen: Einerseits werden Objekte durch Kameras abbildend erfaßt, andererseits werden durch die wellenlängenabhängige Zerlegung ihres Lichtes Spektren gewonnen. Das Integral - Field - Verfahren ist eine relativ neue Technik, welche die genannten Beobachtungsmethoden vereint. Das Objektbild im Teleskopfokus wird in räumlich zerlegt und jedes Ortselement einem gemeinsamen Spektrografen zugeführt. Hierdurch wird das Objekt nicht nur zweidimensional räumlich erfaßt, sondern zusätzlich die spektrale Kompenente als dritte Dimension erhalten, weswegen das Verfahren auch als 3D-Methode bezeichnet wird. Anschaulich kann man sich das Datenresultat als eine Abbildung vorstellen, in der jeder einzelne Bildpunkt nicht mehr nur einen Intensitätswert enthält, sondern gleich ein ganzes Spektrum. Diese Technik ermöglicht es, ausgedehnte Objekte im Unterschied zu gängigen Spaltspektrografen komplett zu erfassen. Die besondere Stärke der Methode ist die Möglichkeit, die Hintergrundkontamination der unmittelbaren Umgebung des Objektes zu erfassen und in der Auswertung zu berücksichtigen. Durch diese Fähigkeit erscheint die 3D-Methode prädestiniert für den durch moderne Großteleskope erschlossenen Bereich der extragalaktischen Stellarastronomie. Die detaillierte Untersuchung aufgelöster stellare Populationen in nahegelegenen Galaxien ist erst seit kurzer Zeit dank der Fortschritte mit modernen Grossteleskopen und fortschrittlicher Instrumentierung möglich geworden. Wegen der Bedeutung für die Entstehung und Evolution von Galaxien werden diese Arbeiten zukünftig weiter an Bedeutung gewinnen. In der vorliegenden Arbeit wurde die Integral-Field-Spektroskopie an zwei planetarischen Nebeln in der nächstgelegenen großen Spiralgalaxie M31 (NGC 224) getestet, deren Helligkeiten und Koordinaten aus einer Durchmusterung vorlagen. Hierzu wurden Beobachtungen mit dem MPFS-Instrument am russischen 6m - Teleskop in Selentschuk/Kaukasus sowie mit INTEGRAL/WYFFOS am englischen William-Herschel-Teleskop auf La Palma gewonnen. Ein überraschendes Ergebnis war, daß eins der beiden Objekte falsch klassifiziert wurde. Sowohl die meßbare räumliche Ausdehnung des Objektes als auch das spektrale Erscheinungsbild schlossen die Identität mit einem planetarischen Nebel aus. Mit hoher Wahrscheinlichkeit handelt es sich um einen Supernovaüberrest, zumal im Rahmen der Fehler an gleicher Stelle eine vom Röntgensatelliten ROSAT detektierte Röntgenquelle liegt. Die in diesem Projekt verwendeten Integral-Field-Instrumente wiesen zwei verschiedene Bauweisen auf, die sich miteinander vergleichen ließen. Ein Hauptkritikpunkt der verwendeten Instrumente war ihre geringe Lichtausbeute. Die gesammelten Erfahrung fanden Eingang in das Konzept des derzeit in Potsdam in der Fertigung befindlichen 3D-Instruments PMAS (Potsdamer Multi - Apertur - Spektrophotometer), welcher zunächst für das 3.5m-Teleskop des Calar - Alto - Observatoriums in Südspanien vorgesehen ist. Um die Effizienz dieses Instrumentes zu verbessern, wurde in dieser Arbeit die Kopplung der zum Bildrasterung verwendeten Optik zu den Lichtleitfasern im Labor untersucht. Die Untersuchungen zur Maximierung von Lichtausbeute und Stabilität zeigen, daß sich die Effizienz durch Auswahl einer geeigneten Koppelmethode um etwa 20 Prozent steigern lässt.
In this thesis we use the gravitational lensing effect as a tool to tackle two rather different cosmological topics: the nature of the dark matter in galaxy halos, and the rotation of the universe. Firstly, we study the microlensing effect in the gravitational lens systems Q0957+561 and Q2237+0305. In these systems the light from the quasar shines directly through the lensing galaxy. Due to the relative motion of the quasar, the lensing galaxy, and the observer compact objects in the galaxy or galaxy halo cause brightness fluctuations of the light from the background quasar. We compare light curve data from a monitoring program of the double quasar Q0957+561 at the 3.5m telescope at Apache Point Observatory from 1995 to 1998 (Colley, Kundic & Turner 2000) with numerical simulations to test whether the halo of the lensing galaxy consists of massive compact objects (MACHOs). This test was first proposed by Gott (1981). We can exclude MACHO masses from 10^-6 M_sun up to 10^-2 M_sun for quasar sizes of less than 3x10^14 h_60^-0.5 cm if the MACHOs make up at least 50% of the dark halo. Secondly, we present new light curve data for the gravitationally lensed quadruple quasar Q2237+0305 taken at the 3.5m telescope at Apache Point Observatory from June 1995 to January 1998. Although the images were taken under variable, often poor seeing conditions and with coarse pixel sampling, photometry is possible for the two brighter quasar images A and B with the help from HST observations. We find independent evidence for a brightness peak in image A of 0.4 to 0.5 mag with a duration of at least 100 days, which indicates that microlensing has taken place in the lensing galaxy. Finally, we use the weak gravitational lensing effect to put limits on a class of Goedel-type rotating cosmologies described by Korotky & Obukhov (1996). In weak lensing studies the shapes of thousands of background galaxies are measured and averaged to reveal coherent gravitational distortions of the galaxy shapes by foreground matter distributions, or by the large-scale structure of space-time itself. We calculate the predicted shear as a function of redshift in Goedel-type rotating cosmologies and compare this to the upper limit on cosmic shear gamma_limit of approximately 0.04 from weak lensing studies. We find that Goedel-type models cannot have larger rotations omega than H_0=6.1x10^-11 h_60/year if this shear limit is valid for the whole sky.
The atmosphere over the Arctic Ocean is strongly influenced by the distribution of sea ice and open water. Leads in the sea ice produce strong convective fluxes of sensible and latent heat and release aerosol particles into the atmosphere. They increase the occurrence of clouds and modify the structure and characteristics of the atmospheric boundary layer (ABL) and thereby influence the Arctic climate.
In the course of this study aircraft measurements were performed over the western Arctic Ocean as part of the campaign PAMARCMIP 2012 of the Alfred Wegener Institute for Polar and Marine Research (AWI). Backscatter from aerosols and clouds within the lower troposphere and the ABL were measured with the nadir pointing Airborne Mobile Aerosol Lidar (AMALi) and dropsondes were launched to obtain profiles of meteorological variables. Furthermore, in situ measurements of aerosol properties, meteorological variables and turbulence were part of the campaign. The measurements covered a broad range of atmospheric and sea ice conditions.
In this thesis, properties of the ABL over Arctic sea ice with a focus on the influence of open leads are studied based on the data from the PAMARCMIP campaign. The height of the ABL is determined by different methods that are applied to dropsonde and AMALi backscatter profiles. ABL heights are compared for different flights representing different conditions of the atmosphere and of sea ice and open water influence. The different criteria for ABL height that are applied show large variation in terms of agreement among each other, depending on the characteristics of the ABL and its history. It is shown that ABL height determination from lidar backscatter by methods commonly used under mid-latitude conditions is applicable to the Arctic ABL only under certain conditions. Aerosol or clouds within the ABL are needed as a tracer for ABL height detection from backscatter. Hence an aerosol source close to the surface is necessary, that is typically found under the present influence of open water and therefore convective conditions. However it is not always possible to distinguish residual layers from the actual ABL. Stable boundary layers are generally difficult to detect.
To illustrate the complexity of the Arctic ABL and processes therein, four case studies are analyzed each of which represents a snapshot of the interplay between atmosphere and underlying sea ice or water surface. Influences of leads and open water on the aerosol and clouds within the ABL are identified and discussed. Leads are observed to cause the formation of fog and cloud layers within the ABL by humidity emission. Furthermore they decrease the stability and increase the height of the ABL and consequently facilitate entrainment of air and aerosol layers from the free troposphere.
Stars are born in turbulent molecular clouds that fragment and collapse under the influence of their own gravity, forming a cluster of hundred or more stars. The star formation process is controlled by the interplay between supersonic turbulence and gravity. In this work, the properties of stellar clusters created by numerical simulations of gravoturbulent fragmentation are compared to those from observations. This includes the analysis of properties of individual protostars as well as statistical properties of the entire cluster. It is demonstrated that protostellar mass accretion is a highly dynamical and time-variant process. The peak accretion rate is reached shortly after the formation of the protostellar core. It is about one order of magnitude higher than the constant accretion rate predicted by the collapse of a classical singular isothermal sphere, in agreement with the observations. For a more reasonable comparison, the model accretion rates are converted to the observables bolometric temperature, bolometric luminosity, and envelope mass. The accretion rates from the simulations are used as input for an evolutionary scheme. The resulting distribution in the Tbol-Lbol-Menv parameter space is then compared to observational data by means of a 3D Kolmogorov-Smirnov test. The highest probability found that the distributions of model tracks and observational data points are drawn from the same population is 70%. The ratios of objects belonging to different evolutionary classes in observed star-forming clusters are compared to the temporal evolution of the gravoturbulent models in order to estimate the evolutionary stage of a cluster. While it is difficult to estimate absolute ages, the realtive numbers of young stars reveal the evolutionary status of a cluster with respect to other clusters. The sequence shows Serpens as the youngest and IC 348 as the most evolved of the investigated clusters. Finally the structures of young star clusters are investigated by applying different statistical methods like the normalised mean correlation length and the minimum spanning tree technique and by a newly defined measure for the cluster elongation. The clustering parameters of the model clusters correspond in many cases well to those from observed ones. The temporal evolution of the clustering parameters shows that the star cluster builds up from several subclusters and evolves to a more centrally concentrated cluster, while the cluster expands slower than new stars are formed.