@phdthesis{Zoeller1999,
  author    = {Z{\"o}ller, Gert},
  title     = {Analyse raumzeitlicher Muster in Erdbebendaten},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0000122},
  school      = {Universit{\"a}t Potsdam},
  year      = {1999},
  abstract  = {Die vorliegende Arbeit besch{\"a}ftigt sich mit der Charakterisierung von Seismizit{\"a}t anhand von Erdbebenkatalogen. Es werden neue Verfahren der Datenanalyse entwickelt, die Aufschluss dar{\"u}ber geben sollen, ob der seismischen Dynamik ein stochastischer oder ein deterministischer Prozess zugrunde liegt und was daraus f{\"u}r die Vorhersagbarkeit starker Erdbeben folgt. Es wird gezeigt, dass seismisch aktive Regionen h{\"a}ufig durch nichtlinearen Determinismus gekennzeichent sind. Dies schließt zumindest die M{\"o}glichkeit einer Kurzzeitvorhersage ein. Das Auftreten seismischer Ruhe wird h{\"a}ufig als Vorl{\"a}uferphaenomen f{\"u}r starke Erdbeben gedeutet. Es wird eine neue Methode pr{\"a}sentiert, die eine systematische raumzeitliche Kartierung seismischer Ruhephasen erm{\"o}glicht. Die statistische Signifikanz wird mit Hilfe des Konzeptes der Ersatzdaten bestimmt. Als Resultat erh{\"a}lt man deutliche Korrelationen zwischen seismischen Ruheperioden und starken Erdbeben. Gleichwohl ist die Signifikanz daf{\"u}r nicht hoch genug, um eine Vorhersage im Sinne einer Aussage {\"u}ber den Ort, die Zeit und die St{\"a}rke eines zu erwartenden Hauptbebens zu erm{\"o}glichen.},
  language  = {en}
}
@phdthesis{Uyaver2004,
  author    = {Uyaver, Sahin},
  title     = {Simulation of annealed polyelectrolytes in poor solvents},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0001488},
  school      = {Universit{\"a}t Potsdam},
  year      = {2004},
  abstract  = {Polymere sind lange kettenartige Molek{\"u}le. Sie bestehen aus vielen elementaren chemischen Einheiten, den Monomeren, die durch kovalente Bindungen aneinander gekettet sind. Polyelektrolyte sind Polymere, die ionisierbare Monomeren enthalten. Aufgrund ihrer speziellen Eigenschaften sind Polyelektrolyte sowohl in der Molekular- und Zellbiologie von großen Bedeutung als auch in der Chemie großtechnisch relevant. Verglichen mit ungeladenen Polymeren sind Polyelektrolyte theoretisch noch wenig verstanden. Insbesondere gilt dies f{\"u}r Polyelektrolyte in sogenanntem schlechten L{\"o}sungsmittel. Ein schlechtes L{\"o}sungsmittel bewirkt eine effektive Anziehung zwischen den Monomeren. F{\"u}r Polyelektrolyte in schlechtem L{\"o}sungsmittel kommt es daher zu einer Konkurrenz zwischen dieser Anziehung und der elektrostatischen Abstoßung. Geladene Polymere werden im Rahmen der chemischen Klassifikation in starke und schwache Polyelektrolyte unterschieden. Erstere zeigen vollst{\"a}ndige Dissoziation unabh{\"a}ngig vom pH-Wert der L{\"o}sung. Die Position der Ladungen auf der Kette wird ausschließlich w{\"a}hrend der Polymersynthese festgelegt. In der Physik spricht man deshalb von Polyelektrolyten mit eingefrorener Ladungsverteilung (quenched polyelectrolytes). Im Falle von schwachen Polyelektrolyten ist die Ladungsdichte auf der Kette nicht konstant, sondern wird durch der pH-Wert der L{\"o}sung kontrolliert. Durch Rekombinations- und Dissoziationsprozesse sind die Ladungen auf der Kette beweglich. Im allgemeinen stellt sich eine inhomogene Gleichgewichtsverteilung ein, die mit der Struktur der Kette gekoppelt ist. Diese Polymere werden deshalb auch Polyelektrolyte mit Gleichgewichtsladungsverteilung (annealed polyelectrolytes) genannt. Wegen des zus{\"a}tzlichen Freiheitsgrades in der Ladungsverteilung werden eine Reihe ungew{\"o}hnlicher Eigenschaften theoretisch vorhergesagt. Mit Hilfe von Simulationen ist es zum ersten Mal gelungen, zu zeigen daß 'annealed' Polyelektrolyte in relativ schlechtem L{\"o}sungsmittel einen diskontinuierlichen Phasen{\"u}bergang durchlaufen, wenn ein kritischer pH-Werts der L{\"o}sung {\"u}berschritten wird. Bei diesem Phasen{\"u}bergang, gehen die Polyelektolyte von einer schwach geladenen kompakten globul{\"a}ren Struktur zu einer stark geladenen gestreckten Konfiguration {\"u}ber. Aufgrund theoretischer Vorhersagen wird erwartet, daß die globul{\"a}re Struktur in weniger schlechtem L{\"o}sungsmittel instabil wird und sich eine Perlenkettenkonfiguration ausbildet. Diese Vorhersage konnte f{\"u}r 'annealed' Polyelektrolyte mit den durchgef{\"u}hrten Simulationen zum ersten Mal best{\"a}tigt werden - inzwischen auch durch erste experimentelle Ergebnisse. Schließlich zeigen die Simulationen auch, daß annealed Polyelektrolyte bei einer kritischen Salzkonzentration in der L{\"o}sung einen scharfen {\"U}bergang zwischen einem stark geladenen gestreckten Zustand und einem schwach geladenen globul{\"a}ren Zustand aufweisen, wiederum in {\"U}bereinstimmung mit theoretischen Erwartungen.},
  language  = {en}
}
@phdthesis{Maraun2006,
  author    = {Maraun, Douglas},
  title     = {What can we learn from climate data? : Methods for fluctuation, time/scale and phase analysis},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-9047},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {Since Galileo Galilei invented the first thermometer, researchers have tried to understand the complex dynamics of ocean and atmosphere by means of scientific methods. They observe nature and formulate theories about the climate system. Since some decades powerful computers are capable to simulate the past and future evolution of climate. Time series analysis tries to link the observed data to the computer models: Using statistical methods, one estimates characteristic properties of the underlying climatological processes that in turn can enter the models. The quality of an estimation is evaluated by means of error bars and significance testing. On the one hand, such a test should be capable to detect interesting features, i.e. be sensitive. On the other hand, it should be robust and sort out false positive results, i.e. be specific. This thesis mainly aims to contribute to methodological questions of time series analysis with a focus on sensitivity and specificity and to apply the investigated methods to recent climatological problems. First, the inference of long-range correlations by means of Detrended Fluctuation Analysis (DFA) is studied. It is argued that power-law scaling of the fluctuation function and thus long-memory may not be assumed a priori but have to be established. This requires to investigate the local slopes of the fluctuation function. The variability characteristic for stochastic processes is accounted for by calculating empirical confidence regions. The comparison of a long-memory with a short-memory model shows that the inference of long-range correlations from a finite amount of data by means of DFA is not specific. When aiming to infer short memory by means of DFA, a local slope larger than \$\alpha=0.5\$ for large scales does not necessarily imply long-memory. Also, a finite scaling of the autocorrelation function is shifted to larger scales in the fluctuation function. It turns out that long-range correlations cannot be concluded unambiguously from the DFA results for the Prague temperature data set. In the second part of the thesis, an equivalence class of nonstationary Gaussian stochastic processes is defined in the wavelet domain. These processes are characterized by means of wavelet multipliers and exhibit well defined time dependent spectral properties; they allow one to generate realizations of any nonstationary Gaussian process. The dependency of the realizations on the wavelets used for the generation is studied, bias and variance of the wavelet sample spectrum are calculated. To overcome the difficulties of multiple testing, an areawise significance test is developed and compared to the conventional pointwise test in terms of sensitivity and specificity. Applications to Climatological and Hydrological questions are presented. The thesis at hand mainly aims to contribute to methodological questions of time series analysis and to apply the investigated methods to recent climatological problems. In the last part, the coupling between El Nino/Southern Oscillation (ENSO) and the Indian Monsoon on inter-annual time scales is studied by means of Hilbert transformation and a curvature defined phase. This method allows one to investigate the relation of two oscillating systems with respect to their phases, independently of their amplitudes. The performance of the technique is evaluated using a toy model. From the data, distinct epochs are identified, especially two intervals of phase coherence, 1886-1908 and 1964-1980, confirming earlier findings from a new point of view. A significance test of high specificity corroborates these results. Also so far unknown periods of coupling invisible to linear methods are detected. These findings suggest that the decreasing correlation during the last decades might be partly inherent to the ENSO/Monsoon system. Finally, a possible interpretation of how volcanic radiative forcing could cause the coupling is outlined.},
  subject      = {Spektralanalyse <Stochastik>},
  language  = {en}
}
@phdthesis{Kappe2006,
  author    = {Kappe, Philip},
  title     = {Design and investigation of the emission dynamics of a mode-locked SBS-laser oscillator},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-11514},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {The primary objective of this work was to develop a laser source for fundamental investigations in the field of laser - materials interactions. In particular it is supposed to facilitate the study of the influence of the temporal energy distribution such as the interaction between adjacent pulses on ablation processes. Therefore, the aim was to design a laser with a highly flexible and easily controllable temporal energy distribution. The laser to meet these demands is an SBS-laser with optional active mode-locking. The nonlinear reflectivity of the SBS-mirror leads to a passive Q-switching and issues ns-pulse bursts with µs spacing. The pulse train parameters such as pulse duration, pulse spacing, pulse energy and number of pulses within a burst can be individually adjusted by tuning the pump parameters and the starting conditions for the laser. Another feature of the SBS-reflection is phase conjugation, which leads to an excellent beam quality thanks to the compensation of phase distortions. Transverse fundamental mode operation and a beam quality better than 1.4 times diffraction limited can be maintained for average output powers of up to 10 W. In addition to the dynamics on a ns-timescale described above, a defined splitting up of each ns-pulse into a train of ps-pulses can be achieved by additional active mode-locking. This twofold temporal focussing of the intensity leads to single pulse energies of up to 2 mJ at pulse durations of approximately 400 ps which corresponds to a pulse peak power of 5 MW. While the pulse duration is of the same order of magnitude as those of other passively Q-switched lasers with simultaneous mode-locking, the pulse energy and pulse peak power exceeds the values of these systems found in the literature by an order of magnitude. To the best of my knowledge the laser presented here is the first implementation of a self-starting mode-locked SBS-laser oscillator. In order to gain a better understanding and control of the transient output of the laser two complementary numerical models were developed. The first is based on laser rate equations which are solved for each laser mode individually while the mode-locking dynamics are calculated from the resultant transient spectrum. The rate equations consider the mean photon densities in the resonator, therefore the propagation of the light inside the resonator is not properly displayed. The second model, in contrast, introduces a spatial resolution of the resonator and hence the propagation inside the resonator can more accurately be considered. Consequently, a mismatch between the loss modulation frequency and the resonator round trip time can be conceived. The model calculates all dynamics in the time domain and therefore the spectral influences such as the Stokes-shift have to be neglected. Both models achieve an excellent reproduction of the ns-dynamics that are generated by the SBS-Q-switch. Separately, each model fails to reproduce all aspects of the ps-dynamics of the SBS-laser in detail. This can be attributed to the complexity of the numerous physical processes involved in this system. But thanks to their complementary nature they provide a very useful tool for investigating the various influences on the dynamics of the mode-locked SBS-laser individually. These aspects can eventually be recomposed to give a complete picture of the mechanisms which govern the output dynamics. Among the aspects under scrutiny were in particular the start resonator quality which determines the starting condition for the SBS-Q-switch, the modulation depth of the AOM and the phonon lifetime as well as the Brillouin-frequency of the SBS-medium. The numerical simulations and the experiments have opened several doors inviting further investigations and promising a potential for further improvement of the experimental results: The results of the simulations in combination with the experimental results which determined the starting conditions for the simulations leave no doubt that the bandwidth generation can primarily be attributed to the SBS-Stokes-shift during the buildup of the Q-switch pulse. For each resonator round trip, bandwidth is generated by shifting a part of the revolving light in frequency. The magnitude of the frequency shift corresponds to the Brillouin-frequency which is a constant of the SBS material and amounts in the case of SF6 to 240 MHz. The modulation of the AOM merely provides an exchange of population between spectrally adjacent modes and therefore diminishes a modulation in the spectrum. By use of a material with a Brillouin-frequency in the GHz range the bandwidth generation can be considerably accelerated thereby shortening the pulse duration. Also, it was demonstrated that yet another nonlinear effect of the SBS can be exploited: If the phonon lifetime is short compared to the resonator round trip time we obtain a modulation in the SBS-reflectivity that supports the modulation of the AOM. The application of an external optical feedback by a conventional mirror turns out to be an alternative to the AOM in synchronizing the longitudinal resonator modes. The interesting feature about this system is that it is ― although highly complex in the physical processes and the temporal output dynamics ― very simple and inexpensive from a technical point of view. No expensive modulators and no control electronics are necessary. Finally, the numerical models constitute a powerful tool for the investigation of emission dynamics of complex laser systems on arbitrary timescales and can also display the spectral evolution of the laser output. In particular it could be demonstrated that differences in the results of the complementary models vanish for systems of lesser complexity.},
  language  = {en}
}
@phdthesis{Streibel2005,
  author    = {Streibel, Martin Albert Gerhard},
  title     = {Bestimmung von Ozonabbauraten {\"u}ber der Arktis und Antarktis mittels Ozonsonden- und Satellitendaten},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-6570},
  school      = {Universit{\"a}t Potsdam},
  year      = {2005},
  abstract  = {Diese Arbeit besch{\"a}ftigt sich mit der chemischen Ozonzerst{\"o}rung im arktischen und antarktischen stratosph{\"a}rischen 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 vollst{\"a}ndig verstanden ist. Die Prozesse, die zur Ozonzerst{\"o}rung f{\"u}hren sind in beiden Polarwirbeln {\"a}hnlich. Allerdings f{\"a}llt als Konsequenz unterschiedlicher meteorologischer Bedingungen der chemische Ozonabbau im arktischen Polarwirbel weniger drastisch aus als {\"u}ber der Antarktis. Der arktische Polarwirbel ist im Mittel st{\"a}rker dynamisch gest{\"o}rt als der antarktische und weist eine st{\"a}rkere Jahr-zu-Jahr Variabilit{\"a}t 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 Ozon{\"a}nderung zu quantifizieren. Zur Identifizierung von doppelt beprobten Luftpaketen werden Trajektorien aus Windfeldern berechnet. K{\"o}nnen zwei Messungen im Rahmen bestimmter Qualit{\"a}tskriterien 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 {\"u}ber die Ozonzerst{\"o}rung gewinnen zu k{\"o}nnen. So erh{\"a}lt man die Ozonzerst{\"o}rung in einem bestimmten Zeitintervall, also Ozonabbauraten. Um die Anzahl an doppelt beprobten Luftpackten zu erh{\"o}hen wurde eine aktive Koordinierung der Ozonsondenaufstiege entwickelt. Im Rahmen dieser Arbeit wurden Matchkampagnen w{\"a}hrend des arktischen Winters 2002/2003 und zum ersten Mal w{\"a}hrend eines antarktischen Winter (2003) durchgef{\"u}hrt. Aus den gewonnenen Daten wurden Ozonabbauraten in beiden Polarwirbeln bestimmt. Diese Abbauraten dienen zum einen der Evaluierung von Modellen, erm{\"o}glichen 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 Stratosph{\"a}re charakterisiert, so dass die Matchkampagne Ende November gestartet wurde. Ab Januar war der Polarwirbel zeitweise stark dynamisch gest{\"o}rt. Die Kampagne ging bis Mitte M{\"a}rz. F{\"u}r den H{\"o}henbereich von 400 bis 550 K potentieller Temperatur (15-23 km) konnten Ozonabbauraten und der Verlust in der Gesamts{\"a}ule berechnet werden. Die Ozonabbauraten wurden in verschiedenen Tests auf ihre Stabilit{\"a}t {\"u}berpr{\"u}ft. Der antarktische Polarwirbel war vom Beginn des Winters bis Mitte Oktober 2003 sehr kalt und stellte Ende September kurzzeitig den Rekord f{\"u}r die gr{\"o}ßte bisher aufgetretene Ozonloch-Fl{\"a}che ein. Es konnten f{\"u}r den Kampagnenzeitraum, Anfang Juni bis Anfang Oktober, Ozonabbauraten im H{\"o}henbereich von 400 bis 550 K potentieller Temperatur ermittelt werden. Der zeitliche Verlauf des Ozonabbaus war dabei auf fast allen H{\"o}henniveaus identisch. Die Zunahme des Sonnenlichtes im Polarwirbel mit der Zeit f{\"u}hrt zu einem starken Anwachsen der Ozonabbauraten. Ab Mitte September gingen die Ozonabbauraten auf Null zur{\"u}ck, da bis zu diesem Zeitpunkt das gesamte Ozon zwischen ca. 14 und 21 km zerst{\"o}rt 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 k{\"o}nnen. Dabei k{\"o}nnen neben der Ozonabbaurate die systematischen Fehler zwischen den einzelnen Sensoren bestimmt werden. Dies wurde exemplarisch am antarktischen Winter 2003 f{\"u}r 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-Matchans{\"a}tze {\"u}berein.},
  subject      = {Ozon},
  language  = {de}
}
@phdthesis{Boroudjerdi2005,
  author    = {Boroudjerdi, Hoda},
  title     = {Charged polymer-macroion complexes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-6282},
  school      = {Universit{\"a}t Potsdam},
  year      = {2005},
  abstract  = {This work explores the equilibrium structure and thermodynamic phase behavior of complexes formed by charged polymer chains (polyelectrolytes) and oppositely charged spheres (macroions). Polyelectrolyte-macroion complexes form a common pattern in soft-matter physics, chemistry and biology, and enter in numerous technological applications as well. From a fundamental point of view, such complexes are interesting in that they combine the subtle interplay between electrostatic interactions and elastic as well as entropic effects due to conformational changes of the polymer chain, giving rise to a wide range of structural properties. This forms the central theme of theoretical studies presented in this thesis, which concentrate on a number of different problems involving strongly coupled complexes, i.e. complexes that are characterized by a large adsorption energy and small chain fluctuations. In the first part, a global analysis of the structural phase behavior of a single polyelectrolyte-macroion complex is presented based on a dimensionless representation, yielding results that cover a wide range of realistic system parameters. Emphasize is made on the interplay between the effects due to the polyelectrolytes chain length, salt concentration and the macroion charge as well as the mechanical chain persistence length. The results are summarized into generic phase diagrams characterizing the wrapping-dewrapping behavior of a polyelectrolyte chain on a macroion. A fully wrapped chain state is typically obtained at intermediate salt concentrations and chain lengths, where the amount of polyelectrolyte charge adsorbed on the macroion typically exceeds the bare macroion charge leading thus to a highly overcharged complex. Perhaps the most striking features occur when a single long polyelectrolyte chain is complexed with many oppositely charged spheres. In biology, such complexes form between DNA (which carries the cell's genetic information) and small oppositely charged histone proteins serving as an efficient mechanism for packing a huge amount of DNA into the micron-size cell nucleus in eucaryotic cells. The resultant complex fiber, known as the chromatin fiber, appears with a diameter of 30~nm under physiological conditions. Recent experiments indicate a zig-zag spatial arrangement for individual DNA-histone complexes (nucleosome core particles) along the chromatin fiber. A numerical method is introduced in this thesis based on a simple generic chain-sphere cell model that enables one to investigate the mechanism of fiber formation on a systematic level by incorporating electrostatic and elastic contributions. As will be shown, stable complex fibers exhibit an impressive variety of structures including zig-zag, solenoidal and beads-on-a-string patterns, depending on system parameters such as salt concentration, sphere charge as well as the chain contour length (per sphere). The present results predict fibers of compact zig-zag structure within the physiologically relevant regime with a diameter of about 30~nm, when DNA-histone parameters are adopted. In the next part, a numerical method is developed in order to investigate the role of thermal fluctuations on the structure and thermodynamic phase behavior of polyelectrolyte-macroion complexes. This is based on a saddle-point approximation, which allows to describe the experimentally observed reaction (or complexation) equilibrium in a dilute solution of polyelectrolytes and macroions on a systematic level. This equilibrium is determined by the entropy loss a single polyelectrolyte chain suffers as it binds to an oppositely charged macroion. This latter quantity can be calculated from the spectrum of polyelectrolyte fluctuations around a macroion, which is determined by means of a normal-mode analysis. Thereby, a stability phase diagram is obtained, which exhibits qualitative agreement with experimental findings. At elevated complex concentrations, one needs to account for the inter-complex interactions as well. It will be shown that at small separations, complexes undergo structural changes in such a way that positive patches from one complex match up with negative patches on the other. Furthermore, one of the polyelectrolyte chains may bridge between the two complexes. These mechanisms lead to a strong inter-complex attraction. As a result, the second virial coefficient associated with the inter-complex interaction becomes negative at intermediate salt concentrations in qualitative agreement with recent experiments on solutions of nucleosome core particles.},
  subject      = {Biopolymere},
  language  = {en}
}
@phdthesis{NarayananNair2006,
  author    = {Narayanan Nair, Arun Kumar},
  title     = {Molecular dynamics simulations of polyelectrolyte brushes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-7005},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {This thesis studies strong, completely charged polyelectrolyte brushes. Extensive molecular dynamics simulations are performed on different polyelectrolyte brush systems using local compute servers and massively parallel supercomputers. The full Coulomb interaction of charged monomers, counterions, and salt ions is treated explicitly. The polymer chains are anchored by one of their ends to a uncharged planar surface. The chains are treated under good solvent conditions. Monovalent salt ions (1:1 type) are modelled same as counterions. The studies concentrate on three different brush systems at constant temperature and moderate Coulomb interaction strength (Bjerrum length equal to bond length): The first system consists of a single polyelectrolyte brush anchored with varying grafting density to a plane. Results show that chains are extended up to about 2/3 of their contour length. The brush thickness slightly grows with increasing anchoring density. This slight dependence of the brush height on grafting density is in contrast to the well known scaling result for the osmotic brush regime. That is why the result obtained by simulations has stimulated further development of theory as well as new experimental investigations on polyelectrolyte brushes. This observation can be understood on a semi-quantitative level using a simple scaling model that incorporates excluded volume effects in a free-volume formulation where an effective cross section is assigned to the polymer chain from where couterions are excluded. The resulting regime is called nonlinear osmotic brush regime. Recently this regime was also obtained in experiments. The second system studied consists of polyelectrolyte brushes with added salt in the nonlinear osmotic regime. Varying salt is an important parameter to tune the structure and properties of polyelectrolytes. Further motivation is due to a theoretical scaling prediction by Pincus for the salt dependence of brush thickness. In the high salt limit (salt concentration much larger than counterion concentration) the brush height is predicted to decrease with increasing external salt, but with a relatively weak power law showing an exponent -1/3. There is some experimental and theoretical work that confirms this prediction, but there are other results that are in contradiction. In such a situation simulations are performed to validate the theoretical prediction. The simulation result shows that brush thickness decreases with added salt, and indeed is in quite good agreement with the scaling prediction by Pincus. The relation between buffer concentration and the effective ion strength inside the brush at varying salt concentration is of interest both from theoretical as well as experimental point of view. The simulation result shows that mobile ions (counterions as well as salt) distribute nonhomogeneously inside and outside of the brush. To explain the relation between the internal ion concentration with the buffer concentration a Donnan equilibrium approach is employed. Modifying the Donnan approach by taking into account the self-volume of polyelectrolyte chains as indicated above, the simulation result can be explained using the same effective cross section for the polymer chains. The extended Donnan equilibrium relation represents a interesting theoretical prediction that should be checked by experimental data. The third system consist of two interacting polyelectrolyte brushes that are grafted to two parallel surfaces. The interactions between brushes are important, for instance, in stabilization of dispersions against flocculation. In the simulations pressure is evaluated as a function of separation D between the two grafting planes. The pressure behavior shows different regimes for decreasing separation. This behavior is in qualitative agreement with experimental data. At relatively weak compression the pressure behavior obtained in the simulation agrees with a 1/D power law predicted by scaling theory. Beyond that the present study could supply new insight for understanding the interaction between polyelectrolyte brushes.},
  subject      = {Molekulardynamik},
  language  = {en}
}
@phdthesis{Kucklaender2006,
  author    = {Kuckl{\"a}nder, Nina},
  title     = {Synchronization via correlated noise and automatic control in ecological systems},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-10826},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {<img src="http://vg00.met.vgwort.de/na/806c85cec18906a64e06" width="1" height="1" alt=""> Subject of this work is the possibility to synchronize nonlinear systems via correlated noise and automatic control. The thesis is divided into two parts. The first part is motivated by field studies on feral sheep populations on two islands of the St. Kilda archipelago, which revealed strong correlations due to environmental noise. For a linear system the population correlation equals the noise correlation (Moran effect). But there exists no systematic examination of the properties of nonlinear maps under the influence of correlated noise. Therefore, in the first part of this thesis the noise-induced correlation of logistic maps is systematically examined. For small noise intensities it can be shown analytically that the correlation of quadratic maps in the fixed-point regime is always smaller than or equal to the noise correlation. In the period-2 regime a Markov model explains qualitatively the main dynamical characteristics. Furthermore, two different mechanisms are introduced which lead to a higher correlation of the systems than the environmental correlation. The new effect of "correlation resonance" is described, i. e. the correlation yields a maximum depending on the noise intensity. In the second part of the thesis an automatic control method is presented which synchronizes different systems in a robust way. This method is inspired by phase-locked loops and is based on a feedback loop with a differential control scheme, which allows to change the phases of the controlled systems. The effectiveness of the approach is demonstrated for controlled phase synchronization of regular oscillators and foodweb models.},
  subject      = {Markov-Prozess},
  language  = {en}
}
@phdthesis{Yin2010,
  author    = {Yin, Fan},
  title     = {Mathematic approaches for the calibration of the CHAMP satellite magnetic field measurements},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-41201},
  school      = {Universit{\"a}t Potsdam},
  year      = {2010},
  abstract  = {CHAMP (CHAllenging Minisatellite Payload) is a German small satellite mission to study the earth's gravity field, magnetic field and upper atmosphere. Thanks to the good condition of the satellite so far, the planned 5 years mission is extended to year 2009. The satellite provides continuously a large quantity of measurement data for the purpose of Earth study. The measurements of the magnetic field are undertaken by two Fluxgate Magnetometers (vector magnetometer) and one Overhauser Magnetometer (scalar magnetometer) flown on CHAMP. In order to ensure the quality of the data during the whole mission, the calibration of the magnetometers has to be performed routinely in orbit. The scalar magnetometer serves as the magnetic reference and its readings are compared with the readings of the vector magnetometer. The readings of the vector magnetometer are corrected by the parameters that are derived from this comparison, which is called the scalar calibration. In the routine processing, these calibration parameters are updated every 15 days by means of scalar calibration. There are also magnetic effects coming from the satellite which disturb the measurements. Most of them have been characterized during tests before launch. Among them are the remanent magnetization of the spacecraft and fields generated by currents. They are all considered to be constant over the mission life. The 8 years of operation experience allow us to investigate the long-term behaviors of the magnetometers and the satellite systems. According to the investigation, it was found that for example the scale factors of the FGM show obvious long-term changes which can be described by logarithmic functions. The other parameters (offsets and angles between the three components) can be considered constant. If these continuous parameters are applied for the FGM data processing, the disagreement between the OVM and the FGM readings is limited to \pm1nT over the whole mission. This demonstrates, the magnetometers on CHAMP exhibit a very good stability. However, the daily correction of the parameter Z component offset of the FGM improves the agreement between the magnetometers markedly. The Z component offset plays a very important role for the data quality. It exhibits a linear relationship with the standard deviation of the disagreement between the OVM and the FGM readings. After Z offset correction, the errors are limited to \pm0.5nT (equivalent to a standard deviation of 0.2nT). We improved the corrections of the spacecraft field which are not taken into account in the routine processing. Such disturbance field, e.g. from the power supply system of the satellite, show some systematic errors in the FGM data and are misinterpreted in 9-parameter calibration, which brings false local time related variation of the calibration parameters. These corrections are made by applying a mathematical model to the measured currents. This non-linear model is derived from an inversion technique. If the disturbance field of the satellite body are fully corrected, the standard deviation of scalar error \triangle B remains about 0.1nT. Additionally, in order to keep the OVM readings a reliable standard, the imperfect coefficients of the torquer current correction for the OVM are redetermined by solving a minimization problem. The temporal variation of the spacecraft remanent field is investigated. It was found that the average magnetic moment of the magneto-torquers reflects well the moment of the satellite. This allows for a continuous correction of the spacecraft field. The reasons for the possible unknown systemic error are discussed in this thesis. Particularly, both temperature uncertainties and time errors have influence on the FGM data. Based on the results of this thesis the data processing of future magnetic missions can be designed in an improved way. In particular, the upcoming ESA mission Swarm can take advantage of our findings and provide all the auxiliary measurements needed for a proper recovery of the ambient magnetic field.},
  language  = {en}
}
@phdthesis{GamezLopez2006,
  author    = {G{\´a}mez L{\´o}pez, Antonio Juan},
  title     = {Application of nonlinear dimensionality reduction to climate data for prediction},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-10956},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {This Thesis was devoted to the study of the coupled system composed by El Ni{\~n}o/Southern Oscillation and the Annual Cycle. More precisely, the work was focused on two main problems: 1. How to separate both oscillations into an affordable model for understanding the behaviour of the whole system. 2. How to model the system in order to achieve a better understanding of the interaction, as well as to predict future states of the system. We focused our efforts in the Sea Surface Temperature equations, considering that atmospheric effects were secondary to the ocean dynamics. The results found may be summarised as follows: 1. Linear methods are not suitable for characterising the dimensionality of the sea surface temperature in the tropical Pacific Ocean. Therefore they do not help to separate the oscillations by themselves. Instead, nonlinear methods of dimensionality reduction are proven to be better in defining a lower limit for the dimensionality of the system as well as in explaining the statistical results in a more physical way [1]. In particular, Isomap, a nonlinear modification of Multidimensional Scaling methods, provides a physically appealing method of decomposing the data, as it substitutes the euclidean distances in the manifold by an approximation of the geodesic distances. We expect that this method could be successfully applied to other oscillatory extended systems and, in particular, to meteorological systems. 2. A three dimensional dynamical system could be modeled, using a backfitting algorithm, for describing the dynamics of the sea surface temperature in the tropical Pacific Ocean. We observed that, although there were few data points available, we could predict future behaviours of the coupled ENSO-Annual Cycle system with an accuracy of less than six months, although the constructed system presented several drawbacks: few data points to input in the backfitting algorithm, untrained model, lack of forcing with external data and simplification using a close system. Anyway, ensemble prediction techniques showed that the prediction skills of the three dimensional time series were as good as those found in much more complex models. This suggests that the climatological system in the tropics is mainly explained by ocean dynamics, while the atmosphere plays a secondary role in the physics of the process. Relevant predictions for short lead times can be made using a low dimensional system, despite its simplicity. The analysis of the SST data suggests that nonlinear interaction between the oscillations is small, and that noise plays a secondary role in the fundamental dynamics of the oscillations [2]. A global view of the work shows a general procedure to face modeling of climatological systems. First, we should find a suitable method of either linear or nonlinear dimensionality reduction. Then, low dimensional time series could be extracted out of the method applied. Finally, a low dimensional model could be found using a backfitting algorithm in order to predict future states of the system.},
  subject      = {Nichtlineare Dynamik},
  language  = {en}
}