Particle-wall collision statistics in the open circular billiard

In the open circular billiard particles are placed initially with a uniform distribution in their positions inside a planar circular vesicle. They all have velocities of the same magnitude, whose initial directions are also uniformly distributed. No particle-particle interactions are included, only specular elastic collisions of the particles with the wall of the vesicle. The particles may escape through an aperture with an angle $2\delta$. The collisions of the particles with the wall are characterized by the angular position and the angle of incidence. We study the evolution of the system considering the probability distributions of these variables at successive times $n$ the particle reaches the border of the vesicle. These distributions are calculated analytically and measured in numerical simulations. For finite apertures $\delta<\pi/2$, a particular set of initial conditions exists for which the particles are in periodic orbits and never escape the vesicle. This set is of zero measure, but the selection of angular momenta close to these orbits is observed after some collisions, and thus the distributions of probability have a structure formed by peaks. We calculate the marginal distributions up to $n=4$, but for $\delta>\pi/2$ a solution is found for arbitrary $n$. The escape probability as a function of $n^{-1}$ decays with an exponent 4 for $\delta>\pi/2$ and evidences for a power law decay are found for lower apertures as well.Comment: 11 pages, 14 figures. Typos corrected and two new figures added, figure captions changed and additional discussions added. Version accepted for publication in Physica

Serien ohne Modelle : Architektur gefühlsecht

Wissenschaftliches Kolloquium vom 27. bis 30. Juni 1996 in Weimar an der Bauhaus-Universität zum Thema: ‚Techno-Fiction. Zur Kritik der technologischen Utopien

Wachstum von Winterweizen bei Gärrestdüngung und unterschiedlichen Kleegrasmanagement

Wheat performance and yields were tested in field an experiment regarding pre-crop management and fertilization with biogas digestate. Digestate fertilization led to an increased nitrogen uptake, higher yield and higher protein content. The yield increases were due to denser stands related to earlier fertilization. Recycling nitrogen from the harvested and digested clover-grass increased yield 50 % compared to mulching the above-ground biomass

Mechatronic Coupling System for Cooperative Manufacturing with Industrial Robots

Rising product variants and shortened product life cycles require more flexible and universally utilizable production systems and machines. Consequently, it can be expected that the importance of industrial robots in production will continuously increase, due to their suitability to take over the role of a universal production machine. However, robots are not yet able to fulfill this role. Industrial use of robots has so far been limited mainly to simple transport and handling tasks in the context of human-robot collaboration as well as highly repetitive automated tasks in the context of manufacturing and assembly. For universal use, robots must be capable to perform more demanding tasks in manufacturing with higher requirements on mechanical stiffness and accuracy. Therefore, this paper presents a mechatronic system to couple two robots to a parallel kinematic system to temporarily increase the mechanical stiffness. The coupled state of the robots allows load sharing, higher process forces and eventually higher precision. The overall goal is to enable robots to perform more demanding manufacturing tasks and thus to be utilized in a wider range of applications. Design requirements, the development approach and optimization methods of the first coupling module prototype will be presented and discussed. The next development steps, a future demonstration system and possible use cases for the coupling module will be shown in the outlook

Theory of a Magnetically-Controlled Quantum-Dot Spin Transistor

We examine transport through a quantum dot coupled to three ferromagnetic leads in the regime of weak tunnel coupling. A finite source-drain voltage generates a nonequilibrium spin on the otherwise non-magnetic quantum dot. This spin accumulation leads to magnetoresistance. A ferromagnetic but current-free base electrode influences the quantum-dot spin via incoherent spin-flip processes and coherent spin precession. As the dot spin determines the conductance of the device, this allows for a purely magnetic transistor-like operation. We analyze the effect of both types of processes on the electric current in different geometries.Comment: 7 pages, 6 figure