15 Fakultätsübergreifend / Sonstige Einrichtung
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/16
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Item Open Access Particle motion in pulsar magnetospheres(1987) Finkbeiner, Bernd; Ertl, Thomas; Herold, Heinz; Ruder, HannsThis report discusses some new results we found in studying the trajectories of single charged particles in the vacuum magnetosphere of a pulsar using the oblique rotator model. We believe that investigations of individual particles in the vicinity of the star can be useful for a better understanding of some fundamental problems of pulsar physics, e.g. the global structure of the magnetosphere or the pulsar radiation.Item Open Access Rydberg atoms in uniform magnetic fields: uncovering the transition from regularity to irregularity in a quantum system(1986) Wunner, Günter; Woelk, Ulrich; Zech, Ingrid; Zeller, Gudrun; Ertl, Thomas; Geyer, Florian; Schweizer, Wolfgang; Ruder, HannsWe investigate the eigenvalue spectra of hydrogen Rydberg atoms in strong magnetic fields for manifestations of quantum stochasticity and find (i) a smooth transition from a Poisson-type to a Wigner-type distribution of level spacings in the range of energy where classical motion becomes increasingly chaotic, (ii) the occurrence of multiple avoided crossings, and (iii) connected with this, an extreme sensitivity of oscillator strengths, and thus of observable spectra, with respect to small variations of an external parameter, viz., the magnetic field strength.Item Open Access Generation of relativistic particles in pulsar magnetospheres(1985) Herold, Heinz; Ertl, Thomas; Ruder, HannsThe problem - fundamental for the physics of pulsars - of determining the global structure of the magnetosphere in a self-consistent way has not yet been solved satisfactorily. We report on some progress in this direction, which we have achieved by studying the trajectories of individual charged particles in the electromagnetic vacuum fields of an aligned rotator.Item Open Access Effects of radiation damping on particle motion in pulsar vacuum fields(1989) Finkbeiner, Bernd; Herold, Heinz; Ertl, Thomas; Ruder, HannsThe effects of radiation reaction on the motion of charged particles are studied in strong electric and magnetic fields with special attention to the vacuum near-field region of an oblique rotator. For strong radiation damping a local velocity field is derived from the Lorentz-Dirac equation, which efficiently describes the motion of electrons and positrons in the whole range of typical pulsar parameters. The velocity field makes it possible to define regions in the inner magnetosphere, where particle trapping occurs due to the radiation losses. By numerical integration of particle trajectories from the pulsar surface, regions around the magnetic poles are found which are defined by particle emission into the wave zone. The shapes of the escape regions on the pulsar surface are determined to a considerable extent by the presence of the accumulation regions.Item Open Access Numerical modeling of the non-isothermal positive column of an Ar+-laser(1992) Zech, Ingrid; Ertl, Thomas; Herold, Heinz; Ruder, Hanns; Köhler, Walter E.; Tiemann, WilhelmA hydrodynamic description of the positive column is used to study the radial variation of particle densities, drift velocities, temperatures and heat fluxes of electrons, singly-charged ions and neutral atoms and the radial electric field. Elastic collisions between the plasma particles and neutrals as well as Coulomb collisions between ions and electrons are taken into account. The relevant equations to solve are the balance equations of particle densities, momentum, energy and the equations for the heat fluxes for each of the three studied particle types; the Poisson equation has to be added for closure. They form a system of 13 nonlinear differential equations with critical points. One singularity occurs when the ions reach the ion sound velocity which is the case inside the positive column. Therefore, a numerical method for multipoint boundary value problems was used which can also successfully handle removable singular points. The applied relaxation method is an iterative method which demands some preliminary knowledge of the solution looked for. The necessary knowledge can be retrieved from the quasineutral model and from a simplified two-fluid model.Item Open Access Hydrogenic Rydberg atoms in strong magnetic fields: theoretical and experimental spectra in the transition region from regularity to irregularity(1987) Holle, Armin; Wiebusch, Gerd; Main, Jörg; Welge, Karl H.; Zeller, Gudrun; Wunner, Günter; Ertl, Thomas; Ruder, HannsFor deuterium Rydberg atoms in a magnetic field of sim6~T we compare the complete experimental spectrum in the range -190 cm-1 to -20 cm-1 with the positions and oscillator strengths of the corresponding quantum theoretically calculated photoabsorption lines. The agreement is excellent. The range of energy covered extends from the end of thel-mixing regime up to the regions where the approximate integrability of the problem is completely lost, and the corresponding classical system undergoes a transition to chaos.Item Open Access Interactive control of biomechanical animation(1993) Ertl, Thomas; Ruder, Hanns; Allrutz, Ralf; Gruber, Karin; Günther, Michael; Hospach, Frank; Ruder, Margret; Subke, Jörg; Widmayer, KarinPhysics-based animation can be generated by performing a complete dynamical simulation of multibody systems. This leads to the solving of a complex system of differential equations in which biomechanical results for the physics of impacts are incorporated. Motion control is achieved by interactively modifying the internal torques. Realtime response requires the distribution of the workload of the computation between a high-speed compute server and the graphics workstation by means of a remote-procedure call mechanism.Item Open Access Fremde Welten auf dem Graphikschirm : die Bedeutung der Visualisierung für die Astrophysik(1991) Ertl, Thomas; Ruder, Hanns; Geyer, Florian; Herold, Heinz; Kraus, Ute; Münzel, Stefan; Nollert, Hans-Peter; Rebetzky, Andreas; Schweizer, Wolfgang; Zahn, CorvinUnsere Vorstellung von der uns umgebenden Welt ist im wesentlichen durch optische Eindrücke geprägt. Durch die Beschränkungen des menschlichen Auges können wir viele Bereiche nicht direkt visuell wahrnehmen, wie z. B. atomare und kosmische Objekte, mit Lichtgeschwindigkeit ablaufende Vorgänge und elektromagnetische Strahlung außerhalb des sichtbaren Bereichs. Die Menschen versuchen aus diesem Grund seit Jahrhunderten durch kunstvolle Instrumente wie Mikroskope, Fernrohre sowie schnelle und multispektrale Detektoren die Grenzen ihrer Wahrnehmung zu erweitern . Dies ist jedoch aufgrund physikalischer Gesetze nicht im beliebigen Maße möglich. Obwohl auch die Computer selbst diesen grundsätzlichen physikalischen Beschränkungen unterliegen, sind sie doch ein Instrument, um mit Simulationsrechnungen im Rahmen der gültigen physikalischen Gesetze und durch Visualisierung der Ergebnisse diese fremden Welten sichtbar zu machen. Dies soll an einigen Beispielen, bei denen der Graphikschirm als Supermikroskop, als Riesenfernrohr und als Fenster zur Welt von Einstein dient, demonstriert werden.Item Open Access Line-of-sight integration: a powerful tool for visualization of three-dimensional scalar fields(1989) Ruder, Hanns; Ertl, Thomas; Geyer, Florian; Herold, Heinz; Kraus, UteAn easy conceivable but very powerful method for the visualization of three-dimensional scalar fields is described. The way this method works is illustrated by some examples and the computed pictures are compared with the results of other methods of representation.Item Open Access Self-consistent modelling of pulsar magnetospheres(1987) Ertl, Thomas; Herold, Heinz; Finkbeiner, Bernd; Ruder, HannsWe report on some progress that we have achieved by numerically modelling the magnetosphere of an aligned rotator where the rotation axis is parallel to the magnetic axis of the neutron star. Here, the unipolar induction, which should be responsible for populating the magnetosphere with charged particles pulled out from the neutron star surface via field emission can be studied in purity, whereas electromagnetic wave effects are neglected.