@misc{ThoelertHoermannAntreichetal.2017,
  author    = {Thoelert, Steffen and H{\"o}rmann, Ulrich and Antreich, Felix and Meurer, Michael},
  title     = {Ionospheric effects on high gain antenna GNSS measurements},
  series = {Proceedings of the 30th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2017)},
  journal   = {Proceedings of the 30th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2017)},
  publisher = {Instituite of Navigation},
  address   = {Washington},
  issn      = {2331-5911},
  doi       = {10.33012/2017.15343},
  pages     = {3368 -- 3374},
  year      = {2017},
  abstract  = {The ionospheric delay of global navigation satellite systems (GNSS) signals typically is compensated by adding a single correction value to the pseudorange measurement of a GNSS receiver. Yet, this neglects the dispersive nature of the ionosphere. In this context we analyze the ionospheric signal distortion beyond a constant delay. These effects become increasingly significant with the signal bandwidth and hence more important for new broadband navigation signals. Using measurements of the Galileo E5 signal, captured with a high gain antenna, we verify that the expected influence can indeed be observed and compensated. A new method to estimate the total electron content (TEC) from a single frequency high gain antenna measurement of a broadband GNSS signal is proposed and described in detail. The received signal is de facto unaffected by multi-path and interference because of the narrow aperture angle of the used antenna which should reduce the error source of the result in general. We would like to point out that such measurements are independent of code correlation, like in standard receiver applications. It is therefore also usable without knowledge of the signal coding. Results of the TEC estimation process are shown and discussed comparing to common TEC products like TEC maps and dual frequency receiver estimates.},
  language  = {en}
}
@phdthesis{Avila2011,
  author    = {Avila, Gast{\´o}n},
  title     = {Asymptotic staticity and tensor decompositions with fast decay conditions},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-54046},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Corvino, Corvino and Schoen, Chruściel and Delay have shown the existence of a large class of asymptotically flat vacuum initial data for Einstein's field equations which are static or stationary in a neighborhood of space-like infinity, yet quite general in the interior. The proof relies on some abstract, non-constructive arguments which makes it difficult to calculate such data numerically by using similar arguments. A quasilinear elliptic system of equations is presented of which we expect that it can be used to construct vacuum initial data which are asymptotically flat, time-reflection symmetric, and asymptotic to static data up to a prescribed order at space-like infinity. A perturbation argument is used to show the existence of solutions. It is valid when the order at which the solutions approach staticity is restricted to a certain range. Difficulties appear when trying to improve this result to show the existence of solutions that are asymptotically static at higher order. The problems arise from the lack of surjectivity of a certain operator. Some tensor decompositions in asymptotically flat manifolds exhibit some of the difficulties encountered above. The Helmholtz decomposition, which plays a role in the preparation of initial data for the Maxwell equations, is discussed as a model problem. A method to circumvent the difficulties that arise when fast decay rates are required is discussed. This is done in a way that opens the possibility to perform numerical computations. The insights from the analysis of the Helmholtz decomposition are applied to the York decomposition, which is related to that part of the quasilinear system which gives rise to the difficulties. For this decomposition analogous results are obtained. It turns out, however, that in this case the presence of symmetries of the underlying metric leads to certain complications. The question, whether the results obtained so far can be used again to show by a perturbation argument the existence of vacuum initial data which approach static solutions at infinity at any given order, thus remains open. The answer requires further analysis and perhaps new methods.},
  language  = {en}
}
@misc{Winkler2011,
  type      = {Master Thesis},
  author    = {Winkler, Michael},
  title     = {Thinning and turbulence in aqueous films},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-53107},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {This thesis covers the topic "Thinning and Turbulence in Aqueous Films". Experimental studies in two-dimensional systems gained an increasing amount of attention during the last decade. Thin liquid films serve as paradigms of atmospheric convection, thermal convection in the Earth's mantle or turbulence in magnetohydrodynamics. Recent research on colloids, interfaces and nanofluids lead to advances in the developtment of micro-mixers (lab-on-a-chip devices). In this project a detailed description of a thin film experiment with focus on the particular surface forces is presented. The impact of turbulence on the thinning of liquid films which are oriented parallel to the gravitational force is studied. An experimental setup was developed which permits the capturing of thin film interference patterns under controlled surface and atmospheric conditions. The measurement setup also serves as a prototype of a mixer on the basis of thermally induced turbulence in liquid thin films with thicknesses in the nanometer range. The convection is realized by placing a cooled copper rod in the center of the film. The temperature gradient between the rod and the atmosphere results in a density gradient in the liquid film, so that different buoyancies generate turbulence. In the work at hand the thermally driven convection is characterized by a newly developed algorithm, named Cluster Imaging Velocimetry (CIV). This routine determines the flow relevant vector fields (velocity and deformation). On the basis of these insights the flow in the experiment was investigated with respect to its mixing properties. The mixing characteristics were compared to theoretical models and mixing efficiency of the flow scheme calculated. The gravitationally driven thinning of the liquid film was analyzed under the influence of turbulence. Strong shear forces lead to the generation of ultra-thin domains which consist of Newton black film. Due to the exponential expansion of the thin areas and the efficient mixing, this two-phase flow rapidly turns into the convection of only ultra-thin film. This turbulence driven transition was observed and quantified for the first time. The existence of stable convection in liquid nanofilms was proven for the first time in the context of this work.},
  language  = {en}
}
@phdthesis{Malik2011,
  author    = {Malik, Nishant},
  title     = {Extremes in events and dynamics : a nonlinear data analysis perspective on the past and present dynamics of the Indian summer monsoon},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-58016},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {To identify extreme changes in the dynamics of the Indian Summer Monsoon (ISM) in the past, I propose a new approach based on the quantification of fluctuations of a nonlinear similarity measure, to identify regimes of distinct dynamical complexity in short time series. I provide an analytical derivation for the relationship of the new measure with the dynamical invariants such as dimension and Lyapunov exponents of the underlying system. A statistical test is also developed to estimate the significance of the identified transitions. Our method is justified by uncovering bifurcation structures in several paradigmatic models, providing more complex transitions compared with traditional Lyapunov exponents. In a real world situation, we apply the method to identify millennial-scale dynamical transitions in Pleistocene proxy records of the south Asian summer monsoon system. We infer that many of these transitions are induced by the external forcing of solar insolation and are also affected by internal forcing on Monsoonal dynamics, i.e., the glaciation cycles of the Northern Hemisphere and the onset of the tropical Walker circulation. Although this new method has general applicability, it is particularly useful in analysing short palaeo-climate records. Rainfall during the ISM over the Indian subcontinent occurs in form of enormously complex spatiotemporal patterns due to the underlying dynamics of atmospheric circulation and varying topography. I present a detailed analysis of summer monsoon rainfall over the Indian peninsular using Event Synchronization (ES), a measure of nonlinear correlation for point processes such as rainfall. First, using hierarchical clustering I identify principle regions where the dynamics of monsoonal rainfall is more coherent or homogenous. I also provide a method to reconstruct the time delay patterns of rain events. Moreover, further analysis is carried out employing the tools of complex network theory. This study provides valuable insights into the spatial organization, scales, and structure of the 90th and 94th percentile rainfall events during the ISM (June to September). I furthermore analyse the influence of different critical synoptic atmospheric systems and the impact of the steep Himalayan topography on rainfall patterns. The presented method not only helps in visualising the structure of the extremeevent rainfall fields, but also identifies the water vapor pathways and decadal-scale moisture sinks over the region. Furthermore a simple scheme based on complex networks is presented to decipher the spatial intricacies and temporal evolution of monsoonal rainfall patterns over the last six decades. Some supplementary results on the evolution of monsoonal rainfall extremes over the last sixty years are also presented.},
  language  = {de}
}
@misc{Fischer2012,
  type      = {Master Thesis},
  author    = {Fischer, Jost},
  title     = {{\"U}ber Synchronisationsph{\"a}nomene nichtlinearer akustischer Oszillatoren},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-63618},
  school      = {Universit{\"a}t Potsdam},
  year      = {2012},
  abstract  = {In dieser Arbeit werden die Effekte der Synchronisation nichtlinearer, akustischer Oszillatoren am Beispiel zweier Orgelpfeifen untersucht. Aus vorhandenen, experimentellen Messdaten werden die typischen Merkmale der Synchronisation extrahiert und dargestellt. Es folgt eine detaillierte Analyse der {\"U}bergangsbereiche in das Synchronisationsplateau, der Ph{\"a}nomene w{\"a}hrend der Synchronisation, als auch das Austreten aus der Synchronisationsregion beider Orgelpfeifen, bei verschiedenen Kopplungsst{\"a}rken. Die experimentellen Befunde werfen Fragestellungen nach der Kopplungsfunktion auf. Dazu wird die Tonentstehung in einer Orgelpfeife untersucht. Mit Hilfe von numerischen Simulationen der Tonentstehung wird der Frage nachgegangen, welche fluiddynamischen und aero-akustischen Ursachen die Tonentstehung in der Orgelpfeife hat und inwiefern sich die Mechanismen auf das Modell eines selbsterregten akustischen Oszillators abbilden l{\"a}sst. Mit der Methode des Coarse Graining wird ein Modellansatz formuliert.},
  language  = {de}
}
@phdthesis{Orgis2014,
  author    = {Orgis, Thomas},
  title     = {Unstetige Galerkin-Diskretisierung niedriger Ordnung in einem atmosph{\"a}rischen Multiskalenmodell},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-70687},
  school      = {Universit{\"a}t Potsdam},
  year      = {2014},
  abstract  = {Die Dynamik der Atmosph{\"a}re der Erde umfasst einen Bereich von mikrophysikalischer Turbulenz {\"u}ber konvektive Prozesse und Wolkenbildung bis zu planetaren Wellenmustern. F{\"u}r Wettervorhersage und zur Betrachtung des Klimas {\"u}ber Jahrzehnte und Jahrhunderte ist diese Gegenstand der Modellierung mit numerischen Verfahren. Mit voranschreitender Entwicklung der Rechentechnik sind Neuentwicklungen der dynamischen Kerne von Klimamodellen, die mit der feiner werdenden Aufl{\"o}sung auch entsprechende Prozesse aufl{\"o}sen k{\"o}nnen, notwendig. Der dynamische Kern eines Modells besteht in der Umsetzung (Diskretisierung) der grundlegenden dynamischen Gleichungen f{\"u}r die Entwicklung von Masse, Energie und Impuls, so dass sie mit Computern numerisch gel{\"o}st werden k{\"o}nnen. Die vorliegende Arbeit untersucht die Eignung eines unstetigen Galerkin-Verfahrens niedriger Ordnung f{\"u}r atmosph{\"a}rische Anwendungen. Diese Eignung f{\"u}r Gleichungen mit Wirkungen von externen Kr{\"a}ften wie Erdanziehungskraft und Corioliskraft ist aus der Theorie nicht selbstverst{\"a}ndlich. Es werden n{\"o}tige Anpassungen beschrieben, die das Verfahren stabilisieren, ohne sogenannte „slope limiter" einzusetzen. F{\"u}r das unmodifizierte Verfahren wird belegt, dass es nicht geeignet ist, atmosph{\"a}rische Gleichgewichte stabil darzustellen. Das entwickelte stabilisierte Modell reproduziert eine Reihe von Standard-Testf{\"a}llen der atmosph{\"a}rischen Dynamik mit Euler- und Flachwassergleichungen in einem weiten Bereich von r{\"a}umlichen und zeitlichen Skalen. Die L{\"o}sung der thermischen Windgleichung entlang der mit den Isobaren identischen charakteristischen Kurven liefert atmosph{\"a}rische Gleichgewichtszust{\"a}nde mit durch vorgegebenem Grundstrom einstellbarer Neigung zu(barotropen und baroklinen)Instabilit{\"a}ten, die f{\"u}r die Entwicklung von Zyklonen wesentlich sind. Im Gegensatz zu fr{\"u}heren Arbeiten sind diese Zust{\"a}nde direkt im z-System(H{\"o}he in Metern)definiert und m{\"u}ssen nicht aus Druckkoordinaten {\"u}bertragen werden.Mit diesen Zust{\"a}nden, sowohl als Referenzzustand, von dem lediglich die Abweichungen numerisch betrachtet werden, und insbesondere auch als Startzustand, der einer kleinen St{\"o}rung unterliegt, werden verschiedene Studien der Simulation von barotroper und barokliner Instabilit{\"a}t durchgef{\"u}hrt. Hervorzuheben ist dabei die durch die Formulierung von Grundstr{\"o}men mit einstellbarer Baroklinit{\"a}t erm{\"o}glichte simulationsgest{\"u}tzte Studie des Grades der baroklinen Instabilit{\"a}t verschiedener Wellenl{\"a}ngen in Abh{\"a}ngigkeit von statischer Stabilit{\"a}t und vertikalem Windgradient als Entsprechung zu Stabilit{\"a}tskarten aus theoretischen Betrachtungen in der Literatur.},
  language  = {de}
}
@phdthesis{Theves2013,
  author    = {Theves, Matthias},
  title     = {Bacterial motility and growth in open and confined environments},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-70313},
  school      = {Universit{\"a}t Potsdam},
  year      = {2013},
  abstract  = {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.},
  language  = {en}
}
@phdthesis{Prokhorov2015,
  author    = {Prokhorov, Boris E.},
  title     = {High-latitude coupling processes between thermospheric circulation and solar wind driven magnetospheric currents and plasma convection},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-92353},
  school      = {Universit{\"a}t Potsdam},
  pages     = {117},
  year      = {2015},
  abstract  = {The high-latitudinal thermospheric processes driven by the solar wind and Interplanetary Magnetic Field (IMF) interaction with the Earth magnetosphere are highly variable parts of the complex dynamic plasma environment, which represent the coupled Magnetosphere - Ionosphere - Thermosphere (MIT) system. The solar wind and IMF interactions transfer energy to the MIT system via reconnection processes at the magnetopause. The Field Aligned Currents (FACs) constitute the energetic links between the magnetosphere and the Earth ionosphere. The MIT system depends on the highly variable solar wind conditions, in particular on changes of the strength and orientation of the IMF. In my thesis, I perform an investigation on the physical background of the complex MIT system using the global physical - numerical, three-dimensional, time-dependent and self-consistent Upper Atmosphere Model (UAM). This model describes the thermosphere, ionosphere, plasmasphere and inner magnetosphere as well as the electrodynamics of the coupled MIT system for the altitudinal range from 80 (60) km up to the 15 Earth radii. In the present study, I developed and investigated several variants of the high-latitudinal electrodynamic coupling by including the IMF dependence of FACs into the UAM model. For testing, the various variants were applied to simulations of the coupled MIT system for different seasons, geomagnetic activities, various solar wind and IMF conditions. Additionally, these variants of the theoretical model with the IMF dependence were compared with global empirical models. The modelling results for the most important thermospheric parameters like neutral wind and mass density were compared with satellite measurements. The variants of the UAM model with IMF dependence show a good agreement with the satellite observations. In comparison with the empirical models, the improved variants of the UAM model reproduce a more realistic meso-scale structures and dynamics of the coupled MIT system than the empirical models, in particular at high latitudes. The new configurations of the UAM model with IMF dependence contribute to the improvement of space weather prediction.},
  language  = {en}
}
@phdthesis{Schroeder2016,
  author    = {Schr{\"o}der, Henning},
  title     = {Ultrafast electron dynamics in Fe(CO)5 and Cr(CO)6},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-94589},
  school      = {Universit{\"a}t Potsdam},
  pages     = {v, 87},
  year      = {2016},
  abstract  = {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.},
  language  = {en}
}
@phdthesis{Rezanezhad2016,
  author    = {Rezanezhad, Vahid},
  title     = {Inversion of the 2004 M6.0 Parkfield Earthquake Coseismic Offsets by Partition Model},
  school      = {Universit{\"a}t Potsdam},
  pages     = {83},
  year      = {2016},
  language  = {en}
}