The phenomenon of friction is on the one hand useful, for example for walking, which would not be so easy without friction, and on the other hand disturbing, for example in wheel bearings, where it slows down desired motion. Therefore, the origin and effect of friction is under intense research. One main point in this work is the analytic investigation of the coupling between friction force and (torsion) friction torque of a sliding and spinning disk. The local friction force at a contact area element was chosen to be an algebraic function of the local relative velocity with an exponent α > 0. It could be shown, that for α < 1 sliding and torsion friction dynamically reduce each other, while for α > 1 they amplify each other. In case of α = 1 sliding and torsion friction are decoupled. With respect to the velocity ratio of sliding and angular velocity, the final motion mode has been investigated, i.e. whether both motions stop together or whether one motion gets dominant. For α < 1 both motions stop together, while for α > 1 it depends on the initial velocity ratio. The mass distribution and contact area radius, which are encoded in the key parameter C of the corresponding differential equation, are the second important influence on the final motion mode. A phase diagram shows for given values C and α the possible final motion modes. The influence of an inhomogenous pressure distribution within the contact area on the coupling was investigated exemplarily for α = 0 with a cylinder as object. In contrast to the disk (homogenous pressure distribution) the cylinder is deflected from its initial sliding direction. In this context the motion of a curling rock on ice is discussed, as it is deflected towards the opposite direction compared to that of the cylinder. Another focal point is the investigation of the role of friction torques (rolling and torsion friction) in the compaction of nano-powders. For this three dimensional contact dynamics simulations with phenomenologically chosen contact laws were performed. With this it could be shown that torsion and rolling friction contribute significantly to the final porosity. Furthermore, these contributions of torsion and rolling friction are independent of each other and can be represented by a sum. In the chapter Conclusions and Outlook a brief introduction on recent research of atomic scale torsion friction is presented.

In this thesis, several stochastic models are investigated, which are subjected to irreversible dynamics. Motivation for the presented work stems, on the one hand, from particular physical systems under consideration, which are modeled by the studied stochastic processes. Besides that, the models discussed in this thesis are, on the other hand, generally interesting from the point of view of statistical physics, since they describe systems far from thermodynamic equilibrium. Interesting properties to be encountered are, e.g., dynamical scaling behavior or continuous phase transitions. The first issue to be addressed, is the investigation of irreversibly aggregating systems, where the main emphasis is laid on aggregation of monopolarly charged clusters suspended in a fluid. For this purpose, rate equations are analyzed and Brownian dynamics simulations are performed. It is shown that the system crosses over from power-law cluster growth to sub-logarithmic cluster growth. Asymptotically, the cluster size distribution evolves towards a universal scaling form, which implies a 'self-focussing' of the size distribution. Another emphasis of this thesis is the investigation of nonequilibrium critical phenomena, in particular, the study of phase transitions into absorbing states (states that may be reached irreversibly). To this end, the continuous nonequilibrium phase transition of directed percolation, which serves as a paradigm for absorbing-state phase transitions, is analyzed by a novel approach. Despite the lack of a partition function for directed percolation, this novel approach follows the ideas of Yang-Lee theory of equilibrium statistical mechanics, by investigating the complex roots of the survival probability. Stochastic models such as directed percolation mimic spreading processes, e.g., the spreading of an infectious disease. The effect of long-time memory, which is not included in directed percolation and which corresponds to immunization in epidemic spreading, is investigated through an appropriate model. This model includes dynamical percolation (perfect immunization) as a special case, as well as directed percolation (no immunization). The critical behavior of this model is studied by means of Monte Carlo simulations, in particular for weak immunization. A further generalization is investigated, which allows spontaneous mutations and different species of spreading agents (pathogens). Restricting the analysis to perfect immunization and two spatial dimensions, it is shown by Monte Carlo simulations, that immunization leads to a crossover from dynamical to directed percolation. Other properties of this model are discussed in detail.

In order to characterize the spin-reorientation transition (SRT), i. e. the change of the easy axis of the magnetization, of ultrathin Ni/Cu(100)- and Fe/Ni/Cu(100)-films the magnetic domain structure was imaged as a function of the Ni and Fe layer thickness, respectively, by using spin-polarized low energy electron microscopy (SPLEEM) during the film growth in ultrahigh vacuum at 300 K. Whereas the size of the domains at the SRT of Ni/Cu(100) is some micrometers, the domain structure of the Fe/Ni-films breaks up into a pattern of 180 nm wide stripe domains. It was shown that the SRT of both Ni/Cu(100) and Fe/Ni/Cu(100) proceeds via a spiral-like rotation of the magnetization within the domains. A discontinuous SRT via coexisting in-plane and out-of-plane magnetized stripe domains is not observed for the film systems.

The realization of integrated-optic broadband wavelength devision multiplexer for separation of 1.31µm and 1.55µm wavelength window is demonstrated based on the well known arrayed waveguide structure. Broadband characteristic with passband greater than 100nm is achieved by using low diffraction order (m = 1, 2). The number of arrayed waveguides is W = 13 and W= 7 respectively. Structure parameters especially those for the star coupler region are derived by use of the transfer-matrix formalism for layered media and the wide-angle finite difference beam propagation method. Prototypes of these structures where realised as doped silica on silicon substrate by using standard plasma enhanced chemical vapor deposition (PECVD) and reactive ion etching (RIE) techniques. The waveguide structure is based on a 7x7µm waveguide core with refractive index difference Dn = 0.005 with reference to a 20µm buffer and cladding layer. Phosphor and Boron were used as dopands of each silica layer to achieve proper adjustment of phys ical layer properties, i.e. refractive index and transformation temperature. Codopand Boron is used to open a selective thermal postprocessing of deposited layers to overcome inhomogeneous PECVD cladding layer deposition on the RIE structured waveguide

In recent years a new class of one-dimensional cellular automata (CA) models has attracted much attention. These so-called mass transport models can be characterized as nonequilibrium stochastic processes. In the presented thesis a new model of this class, the Asymmetric Multi Occupation Process (AMOP) is considered. This CA model was first introduced with open boundary conditions to simulate Internet data transport. It is defined on a one-dimensional lattice equipped with buffers of finite size that can be occupied by at most B particles. The local dynamics are implemented by the totally asymmetric shift of discrete mass variables respectively particles under consideration of hard-core repulsion and parallel dynamics. In the first part of this work the AMOP with periodic boundary conditions is investigated by means of numerical as well as analytical considerations. Regarding deterministic model dynamics the influence of finite buffer and system sizes onto the fundamental diagram (FD), i.e., flow-density relation is analyzed. Furthermore, for stochastic movement the FDs obtained by numerical simulations are compared with analytical results derived by Mean-Field (MF) approaches and a 2-cluster approximation. In the second part the AMOP with open boundary conditions is investigated in the context of boundary induced phase transitions. In case of deterministic bulk dynamics an analytical exact representation of the system inflow as well as the outflow is presented in dependence of the buffer size. As a result the deterministic phase diagram derived by numerical simulations could be verified by analytical considerations. Regarding stochastic particle movement the phase diagram is obtained by Monte Carlo simulations. In both cases it is shown that the jammed phase is strongly enlarged for increasing buffer sizes. Finally, in the third part of this thesis the influence of interacting boundaries on the model dynamics is analyzed. Therefore, a new fall back inflow strategy is introduced in order to stabilize high flow states and thus prevent the system from a complete jamming. Precisely, the inflow is determined by the state of the last site of the system. As a result the phase diagrams of the deterministic and the stochastic model obtained by means of numerical simulations are presented. Two new phases could be identified a free-flow as well as a jammed phase both characterized by a striped microscopic pattern. Especially in the arising striped jammed regime system flow and mean velocity are drastically enlarged compared to generic inflow strategies. Here, the fall back strategy is capable to prevent the system from a complete jamming. Thus, the introduced inflow procedure represents an effective strategy for establishing reliable connections.

This thesis will give an overview about the connection of physics and economy in special view of human behavior in traffic scenarios. Main topic is the human decision making process in a two-route-choice scenario. In three main Experiments, human players had to decide between two routes which connect two cities. The first experiment is defined by a pure Nash-equilibrium and 18 participants, the second experiment is similar, but alternating construction sites on both routes were added. Experiment 1 and 2 are played over 200 periods. The third experiment is a minority game with mixed equilibria and 9 participants. Experiment 3 was played over 100 periods. Furthermore the first experiment was extended to a larger group of players up to 90 persons. For every experiment two treatments with 6 observations were played. The treatments differ in the given information to the participants before they choose between the two routes. In the first treatment the information about the own travel time was given, additionally in the second treatment the information about travel times on both routes were given. The second part of the thesis describes the statistical data and illustrates the results. Two main results are that the equilibrium was not stable in the experiments, the fluctuations persists to the end of every observation. Further on two player types were found and explained in this chapter. In the third part of this thesis an extended payoff-sum model is described and explained. Simulations using this reinforcement learning model were run and show the reproducibility of the empirical data. In the conclusions the main results are shown and discussed.

The present work investigates the interaction between buckminsterfullerene molecules (C60) and silicon surfaces as well as the influence of buckminsterfullerenes on metal/silicon interfaces. The knowledge about the mechanism of surface/molecule interaction between the technologically important semiconductor Si and C60 molecules may lead to new applications of fullerenes. In this context the present study compares the adsorption and the growth mechanisms as well as the desorption of C60 molecules which were evaporated onto well-prepared Si(111)-7x7-, Si(111):H-1x1- and Si(111):Ag-(sqrt(3) x sqrt(3))R30°-surfaces using Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) under ultra-high vacuum conditions. The electronic structure of C60-covered Si(111)-7x7-, Si(111)-1x1-, Si(111):H-1x1-and Si(111):Ag-(sqrt(3) x sqrt(3))R30°-surfaces was investigated using ultraviolet and X-ray photoelectron spectroscopy (UPS, XPS). From these experiments the molecule/surface interaction mechanisms can be identified. Crystalline C60 is a new semiconductor material. Therefore, evaporating C60 onto Si surfaces builds up a semiconductor heterostructure. The electronic properties of this heterostructure are characterized by the band discontinuities at the C60/Si interface. Using UPS and XPS the valence-band discontinuity at this semiconductor/semiconductor interface were determined. Additionally, metal/Si contacts were produced on initially clean silicon surfaces which were covered with distinct amounts of C60 before Ag-, Pb- or Pd-contacts were evaporated. The transport properties of these contacts were studied by current-voltage-chracteristics to determine the influence of C60-layers on the Schottky barrier heights of the metal/Si contacts.

Metamagnets have been playing an important role as model systems in the physics of phase transitions for 30 years. Especially the isolating substances FeCl2 and FeBr2 have attracted much interest both in experimental and theoretical physics. In this thesis we focus on experimental investigations of Fe1-xMgxBr2 with x = 0 and 0.05. By SQUID-magnetometry, SQUID-susceptometry, elastic neutron scattering and calorimetry we studied the magnetic phase boundaries and especially the recently found new phase transition at H=H1(T) (Aruga Katori et al. 1996). Also we arrived to a physical understanding of the non-critical fluctuations at H=H-(T) in terms of a smeared 2-dimensional phase transition of the spin down sublattice.

In the present thesis the structural and magnetic properties of 3d transition metals and their alloys have been investigated within the framework of density functional methods. The calculations have been made mainly to understand magneto-volume instabilities and martensitic phase transformations in iron-nickel and iron-manganese alloys. Many aspects of the alloys can already be understood from the discussion of elemental iron, which forms the essential part of this work. A simple thermodynamical approach combined with the ab-initio results allows the discussion of the physical properties to be extended to finite temperatures. The thermal expansion coefficients calculated within this model coincide well with experiment. Besides the magnetic iron alloys the nonmagnetic Al-Cu-Zn system has been investigated. This ternary alloy undergoes several martensitic phase transformations and spinodal decomposition has also been observed on the Al-Zn-rich side of the phase diagram. The spinodal decomposition is relieved by incommensurable ordering if the aluminium atoms are increasingly replaced by copper. The mixing behavior and the structural phase stability at T = 0 K are obtained from ab initio electronic structure calculations for ordered compounds. The experimental trends are well reproduced. - In dieser Arbeit werden die strukturellen und magnetischen Eigenschaften von 3d-Übergangsmetallen und ihren Verbindungen mit Hilfe verschiedener Methoden der Dichtefunktionaltheorie behandelt. Dabei werden insbesondere Magnetovolumen-Instabilitäten und martensitische Phasenübergänge in Eisen-Nickel und Eisen-Mangan-Verbindungen diskutiert. Einen zentralen Punkt der Arbeit bildet die Untersuchung von elementarem Eisen, da viele Eigenschaften der Legierungen bereits dadurch verstanden werden können. Die Verknüpfung der ab-initio-Ergebnisse mit einem einfachen thermodynamischen Ansatz ermöglicht eine Diskussion bei endlichen Temperaturen. Die im Rahmen dieses Modells berechneten thermischen Ausdehnungskoeffizienten zeigen bereits eine gute Übereinstimmung mit den experimentellen Daten. Neben den Eisenlegierungen wird das nichtmagnetische System Al-Cu-Zn untersucht, welches in bestimmten Konzentrationsbereichen ebenfalls martensitische Phasenübergänge aufweist und auf der Al-Zn-Seite spinodale Entmischung zeigt, die mit zunehmender Substitution von Aluminium durch Kupfer in inkommensurable Ordnung übergeht. An Hand von ab-initio-Berechnungen der elektronischen Struktur geordneter Verbindungen wird das Mischungsverhalten sowie die strukturelle Phasenstabilität des Systems für T = 0 K untersucht. Die Ergebnisse spiegeln die experimentell gefundenen Tendenzen gut wieder.

Particles in granular systems collide inelasticly and kinetic energy is dissipated in the granular system. Granular temperature measures the unordered relative motion of the particles. As a result of the inelastic collisions granular temperature decreases, this process is called collisional cooling. In most cases granular particles are charged. This thesis studies the influence of electrical charges on the collisional cooling by using computer simulations and kinetic theory. It is shown, that electrical charge modifies the dissipation rate by a Boltzmann-factor. The energy barrier of the Boltzmann-factor is given by the electrostatic interaction of two colliding particles. In dense systems this energy barrier is reduced due to the interactions with the particles, that do not take part in the collision. A quantitative expression is given for the effective reduction of the energy barrier. The results found for homogeneous systems is expanded for the local description of inhomogeneous systems.