Plasma-Strahlungsquellen Teilvorhaben: Numerische Modellierung von Gleichgewichts- und Nichtgleichgewichtsplasmen. Abschlussbericht

The aim of the joint project of Siemens AG, Erlangen, and the Institute of Theoretical Astrophysics of the University of Tuebingen was the development of modular structured codes for numerical modelling of plasmas in equilibrium and in non-equilibrium states. In close interaction with experiments a deeper insight in the physical processes involved in gas discharges was gained. In the scope of this project the following problems were considered and the corresponding algorithms were developed: 1. Calculation of the electron distribution function with the help of the Boltzmann-Equation, 2. numerical modelling of low-pressure gas discharge including ion sound in planar and cylindrical geometry, and 3. development of a particle-simulation code for global modelling of plasmas. (orig.)SIGLEAvailable from TIB Hannover: F93B1080 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

Theoretische Modelle fuer Gamma-Ray-Burst-Quellen (GRD: GRB-Modelle) Abschlussbericht

Purpose of the proposed theoretical investigations is to get a better physical understanding of the Gamma-Ray-Bursts phenomena by means of GRO data. At the beginning of the current proposal part of the standard model of Gamma-Ray-Bursts was the existence of two different classes of objects, i.e., galactic sources as strongly magnetized neutron stars and extragalactic sources which are connected with colliding neutron stars. In both cases, the central problem is the conversion of the burst energy into high-energy photons. In this project realistic Gamma-Ray-Burst models have been developed, numerically calculated, and compared with GRO observations. (orig.)Available from TIB Hannover: DtF QN1(58,27) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany); Deutsche Agentur fuer Raumfahrtangelegenheiten (DARA) GmbH, Bonn (Germany)DEGerman

Local particle simulations of viscous selfgravitating disks

We present the results of a particle simulation studying the local flow of a viscous, self-gravitating disk in Keplerian motion. Our method is based on Wisdom and Tremain's (1988) local simulation of planetary rings, but includes self-gravity. We implement a new numerical prescription of interparticle viscosity that formally reduces to Navier-Stokes stresses. Inclusion of hydrodynamic Navier-Stokes-type viscous friction is essential for the system to develop a secular instability for high values of the stability parameter (Q > 1). In the framework of a linear perturbation theory wavelength and growth time of the most unstable mode are derived for a ''softened'' potential that is used in the simulation. The objectives of this paper are twofold: Predictions regarding wavelength and growth time of a secular ring instability can be confirmed numerically. Moreover the relative density enhancement in the perturbed regions can be determined in the nonlinear particle simulation; it reaches values twice the unperturbed density. The possible relevance of this mechanism for structuring protoplanetary accretion disks and planetary rings is briefly discussed. (orig.)Available from TIB Hannover: RN 9303(293) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Evolution of protoplanetary disks with condensation and coagulation

We investigate the global evolution of the viscous stage of a turbulent protoplanetary disk. The time-dependent radial development of the nebula is calculated with the help of analytical one-zone models of the vertical structure that relate optical properties of grains to turbulent viscosity. Special attention is given to possible growth of dust particles that cause significant opacity and hence viscosity changes. In the framework of a simple two component model for the dust size population we follow the evolution of the total surface density of the disk. Assuming that grain growth is especially rapid in the main condensation regions (e.g. due to enhanced sticking probabilities) we find significant surface density enhancements in these radially confined regions. Moreover a lower turbulence strength in these regions (e.g. caused by the suppression of thermal convection) leads to a further increase in the density. Possible consequences for planet formation are briefly outlined. (orig.)Available from TIB Hannover: RN 9303(294) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman