In festen azobenzenhaltigen Polymeren wurde bei Bestrahlung mit blauem Licht ein makroskopischer Materialtransport beobachtet. Um die Dynamik der Gitterentstehung zu verfolgen, wurde am Speicherring für Synchrotronstrahlung ein Gitterschreibaufbau errichtet. Damit konnte erstmals in dieser Arbeit die Gitterbildungsgeschwindigkeit in-situ simultan mit Röntgen- und Lichtstreuung untersucht werden. Mit Hilfe einer speziellen Anpassung der Röntgenstreutheorie konnten sehr gute Übereinstimmungen von theoretischen Berechnungen mit den Messergebnissen erzielt werden. Dabei konnte nachgewiesen werden, dass sich zeitgleich mit einem Oberflächengitter auch ein Dichtegitter entwickelt. Durch die Trennung beider Streuanteile ließ sich die Dynamik der Strukturentstehungen bestimmen. Des weiteren konnte erstmals mit Hilfe der Photoelektronenspektroskopie die molekulare Orientierung an der Oberfläche eines Oberflächengitters nachgewiesen werden. Die Bewegungsursache kann auf einen Impulsübertrag während der Isomerisierung zurückgeführt werden, während die Bewegungsrichtung durch den elektrischen Feldvektor festgelegt wird. Die Theorie der Gitterentstehung konnte verbessert werden. / Solid azobenzene containing polymers show a macroscopic material transport under illumination with blue light. A writing setup was constructed at a synchrotron beamline in order to investigate the dynamics of the grating formation. With this setup it was possible to record the grating velocity for the first time simultaneously with x-ray and laser light scattering. <br /> A very good consistency could be achieved between the experiments and a suitable accomodation of the x-ray scattering theory. The theory reveals, that a density grating develops simultaneously with a surface grating. By separation of both parts the dynamics was determined for the density and the surface grating.<br /> The molecular ordering was determined at the surface with photoelectron spectroscopy. A momentum transfer could be identified as the source of the movement while the electric field defines the direction of the movement. The theory of the grating formation was improved.

The aim of this project was to develop a numerical model simulating the global transport of air pollution. The model currently used by SMHI, the Swedish Meteorological and Hydrological Institute, was intended to perform such simulations at regional scales. However, the usage of a grid based on longitudes and latitudes makes this model work poorly in global simulations. The problem with this grid is that the nodes are concentrated near the North and South Poles. Due to this characteristic, the Courant, Friedrich and Lewy-condition for numerical stability puts a sharp bound on the timestep length. In order to keep the transport algorithms stable, the timestep length has to be very small. To avoid too short timesteps, we adopted a new kind of grid. In principle, we defined the global grid on the surface of a cube. By replacing straight lines on the cube with great circles we took the curvature of the Earth into account. The result was almost equal distances between the nodes, and thus we were able to use an acceptable timestep length. / Målet med detta examensarbete var att utveckla en datormodell för global transportsimulering av luftföroreningar. Den modell som hittills använts av SMHI, Sveriges meterologiska och hydrologiska institut, utvecklades för att göra transportsimuleringar över begränsade områden. Detta innebar att ett gitter baserat på latituder och longituder kunde utnyttjas. Problemet som uppkommer då detta gitter används i globala simuleringar är att noderna ligger alltför tätt i närheten av polerna. Enligt CFL-villkoret för numerisk stabilitet så kommer då de numeriska algoritmer som simulerar vindtransport att bli instabila i polarområdena om inte tidssteglängden görs mycket liten. För att undvika en alltför kort tidssteglängd så har vi i detta projekt begagnat oss av ett nytt slags gitter. Grundideen bakom det nya gittret var att utgå från en numerisk metod definierad på en kub. För att tillämpa metoden på en sfär så ersatte vi kubens räta linjer med storcirklar till sfären. Resultatet blev en någorlunda jämn geografisk spridning av beräkningsnoderna, vilket innebar att en godtagbar tidssteglängd kunde användas.

In this work I present a 23Na/51V-NMR study of sodium vanadate as pure compound, and the influence of very small amounts of Sodium substitution by Calcium and Lithium is reported and discussed. The measurements of spin-lattice relaxation for 23Na and 51V are also presented. The sodium vanadate is found to have a double phase transition. The two transitions are close together and take place around 34 K. Above the transition temperature there is one V site in the mixed oxidation state 4.5+ and there is one Na site. A consistency for a number of un-doped and very slightly doped samples of three vanadium valences is argued, confirming a charge ordering transition at transition temperature, in good qualitative agreement with Bernert’s model and as well in quantitative and qualitative agreement with Sawa’s monoclinic structure. Below the transition temperature sodium is found to have ten sites. The number of the Na site is continuously developed with decreasing the temperature below transition temperature. This continues development of the Na sites demonstrates that the second transition is continues. The detailed spin-lattice relaxation rate for 23Na in both, the pure and the doped samples, in transition region, provided evidence for a non-symmetric and complex transition peak structure which we relate to the onset of more than one transition occurring at slightly different temperatures. This scales with the transition temperature reduction provided by lithium and calcium doping. The two transitions (i.e. dimerization and charge ordering) are intimately related. We investigated the spin-gap by means of Vanadium and Sodium spin-lattice relaxation temperature dependence well below transition temperature. The analysis of the single crystal data reveals a significant anisotropy in the nature of the gap, which is sensitive to Calcium and Lithium doping, indicating that is constrained to the ladder plane.

In this work the interaction between a spatial localized and time periodic state (discrete breather) and small amplitude plane waves is studied.

Besides attenuation, dispersion is the major limiting factor in high data rate fiber optical transmission systems. Dispersion compensation techniques have to be deployed in order to increase the data bandwidth or the reach of fiber optical links. Typically fixed value dispersion compensators are used. However at channel bit rates of 40 GBit/s and beyond adjustable residual dispersion compensator modules (DCM) are needed to guarantee an error free transmission under changing environmental conditions. In this thesis dispersion techniques were investigated which exploit the special propagation properties of higher order modes in custom-designed optical fibers. After a short introduction of state-of-the-art dispersion techniques and their parameters (chapter 2) the modeling and calculation of propagation properties of a particular mode in an optical fiber with an arbitrary, rotation-symmetric refractive index profile is shown (chapter 3). A converter from the fundamental mode and back is needed in order to exploit the propagation properties of a higher order mode (HOM). In this work long-period gratings (LPG) were considered as mode converters (chapter 4) as they can excite selective and nearly lossless a higher order mode. The modeling und calculation of these gratings, based on the fiber calculation of chapter 3, is presented in the first part of chapter 4. Afterwards the manufacturing methods developed during this work are introduced. The spectral properties of realized long-period gratings are discussed and the influence of such factors as strain and temperature on tuning the mode conversion is shown. A dispersion compensator type utilizing only the waveguide dispersion of a certain mode in a custom few mode fiber (FMF) is the subject of chapter 5. The working principle, the fiber design process and first measurements of a realized HOM-DCM with almost completely coupling FMF-LPG are presented. Subsequently the principle of a novel dispersion compensator with an arbitrary dispersion function for a higher or the fundamental mode is explained. In chapter 6 another type of dispersion compensator is investigated consisting of equally distributed long-period gratings along an optical fiber. The fiber pieces between the gratings create a certain time delay between the fundamental mode and the considered higher order mode. It is shown in simulations and in an experiment, that by tuning the mode conversion of each grating and the optical phase relation between the two signal paths in each fiber piece this finite impulse filter structure is so adjusted to function as a tunable residual dispersion compensator.

Adaptive anisotropic refinement of finite element meshes allows to reduce the computational effort required to achieve a specified accuracy of the solution of a PDE problem. We present a new approach to adaptive refinement and demonstrate that this allows to construct algorithms which generate very flexible and efficient anisotropically refined meshes, even improving the convergence order compared to adaptive isotropic refinement if the problem permits.

Die vorliegende Arbeit beschreibt die Entwicklung eines Drucksensorkatheters auf Basis von Faser-Bragg-Gittern. Dazu werden der medizinische Hintergrund aus technischer Sicht strukturiert dargelegt und bereits verfügbare Messmethoden für Manometrieuntersuchungen erörtert. Der Stand der Technik bei Faser-Bragg-Gitter basierten Sensoren und deren Auswertegeräten wird im Zusammenhang mit den aus dem medizinischen Hintergrund und dem Vergleich mit den anderen Messmethoden erwachsenden Anforderungen dargestellt. Die Entwicklung eines zweistufigen für die Herstellung mittels Koextrusion geeigneten Mantels für die optischen Fasern wird beschrieben. Mehrere Funktionsmuster für einen Drucksensorkatheter werden experimentell charakterisiert und die Ergebnisse hinsichtlich der Medizineignung bewertet.

Darmstadt, Techn. University, Diss., 2007.

University, Diss., 2001--Freiburg (Breisgau). / Parallelt.: A-posteriori-Fehlerabschätzungen und adaptive Methoden für konvektionsdominante Transportprozesse.

Universiẗat, Diss., 2003--Heidelberg.