@phdthesis{Ahnert2010, author = {Ahnert, Karsten}, title = {Compactons in strongly nonlinear lattices}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-48539}, school = {Universit{\"a}t Potsdam}, year = {2010}, abstract = {In the present work, we study wave phenomena in strongly nonlinear lattices. Such lattices are characterized by the absence of classical linear waves. We demonstrate that compactons - strongly localized solitary waves with tails decaying faster than exponential - exist and that they play a major role in the dynamics of the system under consideration. We investigate compactons in different physical setups. One part deals with lattices of dispersively coupled limit cycle oscillators which find various applications in natural sciences such as Josephson junction arrays or coupled Ginzburg-Landau equations. Another part deals with Hamiltonian lattices. Here, a prominent example in which compactons can be found is the granular chain. In the third part, we study systems which are related to the discrete nonlinear Schr{\"o}dinger equation describing, for example, coupled optical wave-guides or the dynamics of Bose-Einstein condensates in optical lattices. Our investigations are based on a numerical method to solve the traveling wave equation. This results in a quasi-exact solution (up to numerical errors) which is the compacton. Another ansatz which is employed throughout this work is the quasi-continuous approximation where the lattice is described by a continuous medium. Here, compactons are found analytically, but they are defined on a truly compact support. Remarkably, both ways give similar qualitative and quantitative results. Additionally, we study the dynamical properties of compactons by means of numerical simulation of the lattice equations. Especially, we concentrate on their emergence from physically realizable initial conditions as well as on their stability due to collisions. We show that the collisions are not exactly elastic but that a small part of the energy remains at the location of the collision. In finite lattices, this remaining part will then trigger a multiple scattering process resulting in a chaotic state.}, language = {en} } @phdthesis{Blessmann2010, author = {Bleßmann, Daniela}, title = {Der Einfluss der Dynamik auf die stratosph{\"a}rische Ozonvariabilit{\"a}t {\"u}ber der Arktis im Fr{\"u}hwinter}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-51394}, school = {Universit{\"a}t Potsdam}, year = {2010}, abstract = {Der fr{\"u}hwinterliche Ozongehalt ist ein Indikator f{\"u}r den Ozongehalt im Sp{\"a}twinter/Fr{\"u}hjahr. Jedoch weist dieser aufgrund von Absinkprozessen, chemisch bedingten Ozonabbau und Wellenaktivit{\"a}t von Jahr zu Jahr starke Schwankungen auf. Die vorliegende Arbeit zeigt, dass diese Variabilit{\"a}t weitestgehend auf dynamische Prozesse w{\"a}hrend der Wirbelbildungsphase des arktischen Polarwirbels zur{\"u}ckgeht. Ferner wird der bisher noch ausstehende Zusammenhang zwischen dem fr{\"u}h- und sp{\"a}twinterlichen Ozongehalt bez{\"u}glich Dynamik und Chemie aufgezeigt. F{\"u}r die Untersuchung des Zusammenhangs zwischen der im Polarwirbel eingeschlossenen Luftmassenzusammensetzung und Ozonmenge wurden Beobachtungsdaten von Satellitenmessinstrumenten und Ozonsonden sowie Modellsimulationen des Lagrangschen Chemie/Transportmodells ATLAS verwandt. Die {\"u}ber die Fl{\"a}che (45-75°N) und Zeit (August-November) gemittelte Vertikalkomponente des Eliassen-Palm-Flussvektors durch die 100hPa-Fl{\"a}che zeigt eine Verbindung zwischen der fr{\"u}hwinterlichen wirbelinneren Luftmassenzusammensetzung und der Wirbelbildungsphase auf. Diese ist jedoch nur f{\"u}r die untere Stratosph{\"a}re g{\"u}ltig, da die Vertikalkomponente die sich innerhalb der Stratosph{\"a}re {\"a}ndernden Wellenausbreitungsbedingungen nicht erfasst. F{\"u}r eine verbesserte H{\"o}hendarstellung des Signals wurde eine neue integrale auf der Wellenamplitude und dem Charney-Drazin-Kriterium basierende Gr{\"o}ße definiert. Diese neue Gr{\"o}ße verbindet die Wellenaktivit{\"a}t w{\"a}hrend der Wirbelbildungsphase sowohl mit der Luftmassenzusammensetzung im Polarwirbel als auch mit der Ozonverteilung {\"u}ber die Breite. Eine verst{\"a}rkte Wellenaktivit{\"a}t f{\"u}hrt zu mehr Luft aus niedrigeren ozonreichen Breiten im Polarwirbel. Aber im Herbst und Fr{\"u}hwinter zerst{\"o}ren chemische Prozesse, die das Ozon ins Gleichgewicht bringen, die interannuale wirbelinnere Ozonvariablit{\"a}t, die durch dynamische Prozesse w{\"a}hrend der arktischen Polarwirbelbildungsphase hervorgerufen wird. Eine Analyse in Hinblick auf den Fortbestand einer dynamisch induzierten Ozonanomalie bis in den Mittwinter erm{\"o}glicht eine Absch{\"a}tzung des Einflusses dieser dynamischen Prozesse auf den arktischen Ozongehalt. Zu diesem Zweck wurden f{\"u}r den Winter 1999-2000 Modelll{\"a}ufe mit dem Lagrangesche Chemie/Transportmodell ATLAS gerechnet, die detaillierte Informationen {\"u}ber den Erhalt der k{\"u}nstlichen Ozonvariabilit{\"a}t hinsichtlich Zeit, H{\"o}he und Breite liefern. Zusammengefasst, besteht die dynamisch induzierte Ozonvariabilit{\"a}t w{\"a}hrend der Wirbelbildungsphase l{\"a}nger im Inneren als im {\"A}ußeren des Polarwirbels und verliert oberhalb von 750K potentieller Temperatur ihre signifikante Wirkung auf die mittwinterliche Ozonvariabilit{\"a}t. In darunterliegenden H{\"o}henbereichen ist der Anteil an der urspr{\"u}nglichen St{\"o}rung groß, bis zu 90\% auf der 450K. Innerhalb dieses H{\"o}henbereiches {\"u}ben die dynamischen Prozesse w{\"a}hrend der Wirbelbildungsphase einen entscheidenden Einfluss auf den Ozongehalt im Mittwinter aus.}, language = {de} } @phdthesis{Chirvasa2010, author = {Chirvasa, Mihaela}, title = {Finite difference methods for 1st Order in time, 2nd order in space, hyperbolic systems used in numerical relativity}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-42135}, school = {Universit{\"a}t Potsdam}, year = {2010}, abstract = {This thesis is concerned with the development of numerical methods using finite difference techniques for the discretization of initial value problems (IVPs) and initial boundary value problems (IBVPs) of certain hyperbolic systems which are first order in time and second order in space. This type of system appears in some formulations of Einstein equations, such as ADM, BSSN, NOR, and the generalized harmonic formulation. For IVP, the stability method proposed in [14] is extended from second and fourth order centered schemes, to 2n-order accuracy, including also the case when some first order derivatives are approximated with off-centered finite difference operators (FDO) and dissipation is added to the right-hand sides of the equations. For the model problem of the wave equation, special attention is paid to the analysis of Courant limits and numerical speeds. Although off-centered FDOs have larger truncation errors than centered FDOs, it is shown that in certain situations, off-centering by just one point can be beneficial for the overall accuracy of the numerical scheme. The wave equation is also analyzed in respect to its initial boundary value problem. All three types of boundaries - outflow, inflow and completely inflow that can appear in this case, are investigated. Using the ghost-point method, 2n-accurate (n = 1, 4) numerical prescriptions are prescribed for each type of boundary. The inflow boundary is also approached using the SAT-SBP method. In the end of the thesis, a 1-D variant of BSSN formulation is derived and some of its IBVPs are considered. The boundary procedures, based on the ghost-point method, are intended to preserve the interior 2n-accuracy. Numerical tests show that this is the case if sufficient dissipation is added to the rhs of the equations.}, language = {en} } @phdthesis{Fang2010, author = {Fang, Peng}, title = {Preparation and investigation of polymer-foam films and polymer-layer systems for ferroelectrets}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-48412}, school = {Universit{\"a}t Potsdam}, year = {2010}, abstract = {Piezoelectric materials are very useful for applications in sensors and actuators. In addition to traditional ferroelectric ceramics and ferroelectric polymers, ferroelectrets have recently become a new group of piezoelectrics. Ferroelectrets are functional polymer systems for electromechanical transduction, with elastically heterogeneous cellular structures and internal quasi-permanent dipole moments. The piezoelectricity of ferroelectrets stems from linear changes of the dipole moments in response to external mechanical or electrical stress. Over the past two decades, polypropylene (PP) foams have been investigated with the aim of ferroelectret applications, and some products are already on the market. PP-foam ferroelectrets may exhibit piezoelectric d33 coefficients of 600 pC/N and more. Their operating temperature can, however, not be much higher than 60 °C. Recently developed polyethylene-terephthalate (PET) and cyclo-olefin copolymer (COC) foam ferroelectrets show slightly better d33 thermal stabilities, but usually at the price of smaller d33 values. Therefore, the main aim of this work is the development of new thermally stable ferroelectrets with appreciable piezoelectricity. Physical foaming is a promising technique for generating polymer foams from solid films without any pollution or impurity. Supercritical carbon dioxide (CO2) or nitrogen (N2) are usually employed as foaming agents due to their good solubility in several polymers. Polyethylene propylene (PEN) is a polyester with slightly better properties than PET. A "voiding + inflation + stretching" process has been specifically developed to prepare PEN foams. Solid PEN films are saturated with supercritical CO2 at high pressure and then thermally voided at high temperatures. Controlled inflation (Gas-Diffusion Expansion or GDE) is applied in order to adjust the void dimensions. Additional biaxial stretching decreases the void heights, since it is known lens-shaped voids lead to lower elastic moduli and therefore also to stronger piezoelectricity. Both, contact and corona charging are suitable for the electric charging of PEN foams. The light emission from the dielectric-barrier discharges (DBDs) can be clearly observed. Corona charging in a gas of high dielectric strength such as sulfur hexafluoride (SF6) results in higher gas-breakdown strength in the voids and therefore increases the piezoelectricity. PEN foams can exhibit piezoelectric d33 coefficients as high as 500 pC/N. Dielectric-resonance spectra show elastic moduli c33 of 1 - 12 MPa, anti-resonance frequencies of 0.2 - 0.8 MHz, and electromechanical coupling factors of 0.016 - 0.069. As expected, it is found that PEN foams show better thermal stability than PP and PET. Samples charged at room temperature can be utilized up to 80 - 100 °C. Annealing after charging or charging at elevated temperatures may improve thermal stabilities. Samples charged at suitable elevated temperatures show working temperatures as high as 110 - 120 °C. Acoustic measurements at frequencies of 2 Hz - 20 kHz show that PEN foams can be well applied in this frequency range. Fluorinated ethylene-propylene (FEP) copolymers are fluoropolymers with very good physical, chemical and electrical properties. The charge-storage ability of solid FEP films can be significantly improved by adding boron nitride (BN) filler particles. FEP foams are prepared by means of a one-step procedure consisting of CO2 saturation and subsequent in-situ high-temperature voiding. Piezoelectric d33 coefficients up to 40 pC/N are measured on such FEP foams. Mechanical fatigue tests show that the as-prepared PEN and FEP foams are mechanically stable for long periods of time. Although polymer-foam ferroelectrets have a high application potential, their piezoelectric properties strongly depend on the cellular morphology, i.e. on size, shape, and distribution of the voids. On the other hand, controlled preparation of optimized cellular structures is still a technical challenge. Consequently, new ferroelectrets based on polymer-layer system (sandwiches) have been prepared from FEP. By sandwiching an FEP mesh between two solid FEP films and fusing the polymer system with a laser beam, a well-designed uniform macroscopic cellular structure can be formed. Dielectric resonance spectroscopy reveals piezoelectric d33 coefficients as high as 350 pC/N, elastic moduli of about 0.3 MPa, anti-resonance frequencies of about 30 kHz, and electromechanical coupling factors of about 0.05. Samples charged at elevated temperatures show better thermal stabilities than those charged at room temperature, and the higher the charging temperature, the better is the stability. After proper charging at 140 °C, the working temperatures can be as high as 110 - 120 °C. Acoustic measurements at frequencies of 200 Hz - 20 kHz indicate that the FEP layer systems are suitable for applications at least in this range.}, language = {en} } @phdthesis{Fix2010, author = {Fix, Dmitri}, title = {Lokalkorrosion auf Aluminium: Nicht-invasive in-situ-Observation von Lochkorrosion}, address = {Potsdam}, pages = {124 S.}, year = {2010}, language = {de} } @phdthesis{Ganesan2010, author = {Ganesan, Lakshmi Meena}, title = {Coupling of the electrical, mechanical and optical response in polymer/liquid-crystal composites}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-41572}, school = {Universit{\"a}t Potsdam}, year = {2010}, abstract = {Micrometer-sized liquid-crystal (LC) droplets embedded in a polymer matrix may enable optical switching in the composite film through the alignment of the LC director along an external electric field. When a ferroelectric material is used as host polymer, the electric field generated by the piezoelectric effect can orient the director of the LC under an applied mechanical stress, making these materials interesting candidates for piezo-optical devices. In this work, polymer-dispersed liquid crystals (PDLCs) are prepared from poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) and a nematic liquid crystal (LC). The anchoring effect is studied by means of dielectric relaxation spectroscopy. Two dispersion regions are observed in the dielectric spectra of the pure P(VDF-TrFE) film. They are related to the glass transition and to a charge-carrier relaxation, respectively. In PDLC films containing 10 and 60 wt\% LC, an additional, bias-field-dependent relaxation peak is found that can be attributed to the motion of LC molecules. Due to the anchoring effect of the LC molecules, this relaxation process is slowed down considerably, when compared with the related process in the pure LC. The electro-optical and piezo-optical behavior of PDLC films containing 10 and 60 wt\% LCs is investigated. In addition to the refractive-index mismatch between the polymer matrix and the LC molecules, the interaction between the polymer dipoles and the LC molecules at the droplet interface influences the light-scattering behavior of the PDLC films. For the first time, it was shown that the electric field generated by the application of a mechanical stress may lead to changes in the transmittance of a PDLC film. Such a piezo-optical PDLC material may be useful e.g. in sensing and visualization applications. Compared to a non-polar matrix polymer, the polar matrix polymer exhibits a strong interaction with the LC molecules at the polymer/LC interface which affects the electro-optical effect of the PDLC films and prevents a larger increase in optical transmission.}, language = {en} } @phdthesis{Klasczyk2010, author = {Klasczyk, Benjamin}, title = {Interactions of ions with membranes}, address = {Potsdam}, pages = {116 S.}, year = {2010}, language = {en} } @phdthesis{Kralemann2010, author = {Kralemann, Bj{\"o}rn Christian}, title = {Die Rekonstruktion invarianter Phasenmodelle aus Daten}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-45057}, school = {Universit{\"a}t Potsdam}, year = {2010}, abstract = {Ziel dieser Arbeit ist die {\"U}berwindung einer Differenz, die zwischen der Theorie der Phase bzw. der Phasendynamik und ihrer Anwendung in der Zeitreihenanalyse besteht: W{\"a}hrend die theoretische Phase eindeutig bestimmt und invariant unter Koordinatentransformationen bzw. gegen{\"u}ber der jeweils gew{\"a}hlten Observable ist, f{\"u}hren die Standardmethoden zur Absch{\"a}tzung der Phase aus gegebenen Zeitreihen zu Resultaten, die einerseits von den gew{\"a}hlten Observablen abh{\"a}ngen und so andererseits das jeweilige System keineswegs in eindeutiger und invarianter Weise beschreiben. Um diese Differenz deutlich zu machen, wird die terminologische Unterscheidung von Phase und Protophase eingef{\"u}hrt: Der Terminus Phase wird nur f{\"u}r Variablen verwendet, die dem theoretischen Konzept der Phase entsprechen und daher das jeweilige System in invarianter Weise charakterisieren, w{\"a}hrend die observablen-abh{\"a}ngigen Absch{\"a}tzungen der Phase aus Zeitreihen als Protophasen bezeichnet werden. Der zentrale Gegenstand dieser Arbeit ist die Entwicklung einer deterministischen Transformation, die von jeder Protophase eines selbsterhaltenden Oszillators zur eindeutig bestimmten Phase f{\"u}hrt. Dies erm{\"o}glicht dann die invariante Beschreibung gekoppelter Oszillatoren und ihrer Wechselwirkung. Die Anwendung der Transformation bzw. ihr Effekt wird sowohl an numerischen Beispielen demonstriert - insbesondere wird die Phasentransformation in einem Beispiel auf den Fall von drei gekoppelten Oszillatoren erweitert - als auch an multivariaten Messungen des EKGs, des Pulses und der Atmung, aus denen Phasenmodelle der kardiorespiratorischen Wechselwirkung rekonstruiert werden. Abschließend wird die Phasentransformation f{\"u}r autonome Oszillatoren auf den Fall einer nicht vernachl{\"a}ssigbaren Amplitudenabh{\"a}ngigkeit der Protophase erweitert, was beispielsweise die numerischen Bestimmung der Isochronen des chaotischen R{\"o}ssler Systems erm{\"o}glicht.}, language = {de} } @phdthesis{Krobath2010, author = {Krobath, Heinrich}, title = {Binding cooperativity and domain energies of membrane adhesion receptors}, address = {Potsdam}, pages = {106 S. : graph. Darst.}, year = {2010}, language = {en} } @phdthesis{Ksianzou2010, author = {Ksianzou, Viachaslau}, title = {Second-order nonlinear optical interactions and cascading effects in thinorganic films}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-49186}, school = {Universit{\"a}t Potsdam}, year = {2010}, abstract = {The presented work describes new concepts of fast switching elements based on principles of photonics. The waveguides working in visible and infra-red ranges are put in a basis of these elements. And as materials for manufacturing of waveguides the transparent polymers, dopped by molecules of the dyes possessing second order nonlinear-optical properties are proposed. The work shows how nonlinear-optical processes in such structures can be implemented by electro-optical and opto-optical control circuit signals. In this paper we consider the complete cycle of fabrication of several types of integral photonic elements. The theoretical analysis of high-intensity beam propagation in media with second-order optical nonlinearity is performed. Quantitative estimations of necessary conditions of occurrence of the nonlinear-optical phenomena of the second order taking into account properties of used materials are made. The paper describes the various stages of manufacture of the basic structure of the integrated photonics: a planar waveguide. Using the finite element method the structure of the electromagnetic field inside the waveguide in different modes was analysed. A separate part of the work deals with the creation of composite organic materials with high optical nonlinearity. Using the methods of quantum chemistry, the dependence of nonlinear properties of dye molecules from its structure were investigated in details. In addition, the paper discusses various methods of inducing of an optical nonlinearity in dye-doping of polymer films. In the work, for the first time is proposed the use of spatial modulation of nonlinear properties of waveguide according Fibonacci law. This allows involving several different nonlinear optical processes simultaneously. The final part of the work describes various designs of integrated optical modulators and switches constructed of organic nonlinear optical waveguides. A practical design of the optical modulator based on Mach-Zehnder interferometer made by a photolithography on polymer film is presented.}, language = {en} }