Fakultät für Geowissenschaften - Digitale Hochschulschriften der LMU

The possibility of using accurate numerical methods to simulate seismic wavefields on unstructured meshes for complex rheologies is explored. In particular, the Discontinuous Galerkin (DG) finite element method for seismic wave propagation is extended to the rheological types of viscoelasticity, anisotropy and poroelasticity. First is presented the DG method for the elastic isotropic case on tetrahedral unstructured meshes. Then an extension to viscoelastic wave propagation based upon a Generalized Maxwell Body formulation is introduced which allows for quasi-constant attenuation through the whole frequency range. In the following anisotropy is incorporated in the scheme for the most general triclinic case, including an approach to couple its effects with those of viscoelasticity. Finally, poroelasticity is incorporated for both the propagatory high-frequency range and for the diffusive low-frequency range.

For all rheology types, high-order convergence is achieved simultaneously in space and time for three-dimensional setups. Applications and convergence tests verify the proper accuracy of the approach. Due to the local character of the DG method and the use of tetrahedral meshes, the presented schemes are ready to be applied for large scale problems of forward wave propagation modeling of seismic waves in setups highly complex both geometrically and physically.

A homogeneous design for landfill bodies is generally agreed. However the manner in which waste is deposited may result in a sequence of layers that causes inhomogeneity. The goal of this research was to investigate the influences of such inhomogeneities on long-term leaching of highly soluble salts and ecotoxic species.

This long-term leaching of was observed for 25 months. Laboratory column tests and field experiments (test bodies and lysimeters) were performed with municipal solid waste incineration residues. Laboratory columns were irrigated with tap water. Control field experiments were exposed to natural precipitation. Due to the fact that municipal solid waste incineration residues are continually landfilled on monofills, the percolating landfill-leachates are highly saline. Therefore extended experiments were carried out and these were treated with saline solutions: either solely or in addition to natural precipitation. Highly saline irrigation-media artificial leachates produced in the lab, actual landfill leachate or a concentrate from reverse osmosis was used, depending on the experiment. Besides irrigation, the application of residues, as the top or intermediate layers, provided continuous supply of highly saline solutions.

Commonly, column experiments are conducted under water-saturated conditions. For this research however, unsaturated conditions were chosen to understand real landfill conditions.

All experiments were performed as parallel experiments. One test had a uniform-grain setup and acted as a control. The application of a fine-grained bottom ash layer within a column filled mainly with coarse-grained bottom ash provided the inhomogeneous setup. Grain size changeover as a barrier layer within a column should change the permeability along the profile of the column. In some cases the barrier layer was compacted. The results of long-term the solid sample and leachate investigations pointed out that the application of a barrier layer by means of grain size changeover had mainly physical effects. With the control experiment, water contents of solid samples increased in general from the top of the experiments to the basis. In contrast, the following was observed for the application of a barrier layer:

 impounding of leachate,

 slowdown of leachate percolation time,

 increased water retention capacity.

Mainly the zone within the barrier layer showed the highest water content. A general observation was that the setting beneath the barrier layer was much drier. Another observation was that irrigation with saline water enhances water retention within the column. Additionally model experiments with plastic shots pointed out that the irrigation with small amount of water intensifies the physical effect of the barrier layer. Unsaturated water conditions which are common in landfills together with reduced permeability provide the basis for salt accumulations around the zone of the fine grained ash layer. An investigation on the distribution of the elements along the profile showed that impounding of the leachate at the barrier layer is linked to higher eluate soluble species concentrations: the tendency of accumulation was observable especially for the zone within and beneath the barrier layer and in the near-bottom samples for the control as well as extended experiments.

Concerning a uniform setup the salt distribution along the profile was homogeneous up to gradual. In general the observations indicated that the application of a barrier layer by means of grain size changeover impounds the leachate. Thus, increased concentrations of different species of saline solutions in combination with changing water contents within the layers caused precipitation of the highly soluble salts out of the pore solution. The formation of salt accumulations is time-dependent. Most of the chemical and mineralogical progressions occurred only after a longer period:

 tendencies for the leachate progression changed several times

Die vorliegende Arbeit behandelt Fragen aus dem interdisziplinären Gebiet der Nanowissenschaften durch Untersuchungen mittels Rastertunnelmikroskopie und Computerchemie. Sie steht im Kontext der Entwicklung nanotechnologischer Herstellungsverfahren, die sich auf die "bottom-up"- Fertigungsstrategie beziehen. Diese

Strategie verfolgt das Ziel, aus einzelnen elementaren Bausteinen (z.B. Molekülen) grössere funktionelle Strukturen und Systeme kontrolliert zusammenzusetzen.

Kern dieser Arbeit ist die Vorstellung eines neuartigen Strukturbildungsprozesses auf molekularer Ebene und die Erschliessung dessen Potentials.

Für diesen Prozess wird der Begriff "supramolekulare Festphasenbenetzung" vorgeschlagen.

Damit wird ausgedrückt, dass die Ergebnisse als eine neue Bedingung für supramolekulare, spontane Strukturbildung (engl. self-assembly) interpretiert werden, die bei Raumtemperatur an der Grenze zwischen zwei festen Phasen stattfindet. Das vorgestellte Modell beschreibt diesen Prozess durch Nanokristalle, die – in einer Matrix suspendiert – bei Kontakt mit einer Kristalloberfläche ein Verhalten zeigen, das trotz vorhandener Festkörpereigenschaften (kristalline Ordnung) dem Verhalten

flüssiger Tropfen bei der Benetzung von Oberflächen verwandt ist.

Darauf aufbauend wird das technologische Potential des neuen Prozesses erschlossen:

1. Adsorbatstrukturen von einer Reihe organischer Halbleiter werden erstmals beschrieben. Damit wird zudem gezeigt, dass sich durch supramolekulare Festphasenbenetzung

unlösliche Halbleitermoleküle sehr einfach und unter Umgebungsbedingungen geordnet adsorbieren lassen – ein Ergebnis, das sonst nur mit grossen Aufwand (z.B. Molekularstrahlepitaxie im Vakuum) möglich wäre.

2. Ein Erklärungsmodell wird entwickelt, mit dem sich die bislang unverstandene Möglichkeit molekularer Datenspeicherung mittels PTCDA- Moleküle theoretisch

erklären und auf weitere, unter (1) vorgestellte Moleküle erweitern lässt.

3. Die Entwicklung eines Nanofabrikationskonzeptes wird vorgestellt, das eine lokale Kontrolle des Wachstums von Nanostrukturen ermöglicht. Der Vorteil gegenüber einer klassischen, Molekül für Molekül durchgeführten Nanostrukturierung liegt darin, dass durch die Spitze eines Rastertunnelmikroskops allein die Information über Wachstumsrichtungen in das System lokal einzubringen

ist, die eigentliche Bildung der Strukturen jedoch durch selbständig ablaufende und somit qualitativ und zeitlich hoche¢ziente Wachstumsprozesse stattfindet

("geführtes Wachstum"). Damit lässt sich die bisherige Beschränkung von self-assembly auf streng periodische Strukturen durchbrechen und die vordefinierte

Bildung komplexer Strukturen erreichen.

4. Ein Verfahren wird vorgestellt, das eine lokale Adsorption von Molekülen zu geordneten Schichten innerhalb einer Lage fremder Moleküle erlaubt und somit den Aufbau heterogener Adsorbatschichten ermöglicht.