Calendar of Physics Talks Vienna

Relativistic Bondi-Michel accretion: global vs. homoclinic solutions
Speaker:Patryk Mach (Cracow)
Abstract:Lunchseminar:A spherically symmetric accretion model introduced by Bondi in 1952 belongs to classical textbook models of theoretical astrophysics. Its general relativistic version is due to Michel, who considered spherically symmetric, purely radial, stationary flow of perfect fluid in the Schwarzschild spacetime. Solutions of the Bondi-Michel flow are usually parametrized by fixing asymptotic values of the density and the speed of sound at infinity; they extend smoothly from infinity up to the horizon of the black hole (and below). In contrast to that, local solutions, that cannot be extended to infinity, were recently discovered in the cosmological context. They correspond to homoclinic orbits on phase diagrams of the radial velocity vs. radius (say). More surprisingly, they also appear in the standard Bondi-Michel model for polytropic fluids with polytropic exponents larger than 5/3.
Date: Mon, 22.06.2015
Time: 13:00
Duration: 60 min
Location:Arbeitsgruppe Gravitation, Währinger Strasse 17, common room, 1. Stock
Contact:P.T. Chrusciel

Der Schutz geistigen Eigentums
Speaker:Dipl.-Ing. Michael Lackner (Der Schutz geistigen Eigentums)
Abstract:Es wird ein Überblick mit Konzentration auf technischen, gewerblichen Rechtsschutz gegeben. Nach einem kurzen Einblick in verschiedene Schutzmöglichkeiten folgt eine Einführung in das Patentrecht. Was ist die Aufgabe und die Möglichkeit eines Patentes, welche Anforderungen sind zu erfüllen? Patentämter können bei der täglichen Arbeit unterstützen und helfen. Patente sollen auch den Forschergeist beflügeln. Sie sind eine Bereicherung für Industrie und Forschung, ein staatlich gefördertes Privileg. Aber was kann ich überhaupt patentieren?
Date: Tue, 23.06.2015
Time: 16:00
Location:Technische Universität Wien, Institut für Angewandte Physik, E134 yellow tower „B“, 5th floor, Seminarraum 134A (room number DB05L03) 1040 Wien, Wiedner Hauptstraße 8-10
Contact:Ao.Univ.Prof. Dr. Peter Mohn

Rod-like Colloids in External Electric Fields
Speaker:Prof. Dr. Jan K.G. Dhont (Institute of Complex Systems, Forschungszentrum Jülich)
Date: Tue, 23.06.2015
Time: 17:30
Duration: 60 min
Location:Lise-Meitner-Hörsaal, Fakultät für Physik, Universität Wien, 1090 Wien, Strudlhofgasse 4 / Boltzmanngasse 5, 1. Stock

A positive Bondi--type mass in asymptotically de Sitter spacetimes
Speaker:Laszlo Szabados (Budapest)
Abstract:A Bondi-type mass, associated with a cut of the conformal boundary of asymptotically de Sitter spacetimes is suggested. This is based on the integral of the Nester-Witten 2-form and the Witten-type positivity argument on a spacelike hypersurface intersecting the conformal boundary in the cut. It is shown that this integral (1.) can be finite only if the boundary value of the Witten spinor at the cut solves the 2-surface twistor equation, (2.) is positive if the matter fields satisfy the dominant energy condition on the spacelike hypersurface, and (3.) its vanishing is equivalent to the local de Sitter nature of the domain of dependence of the hypersurface. However, this integral gives a well defined notion of mass only in the presence of some extra structure. In particular, when the cut is non-contorted, the integral yields an invariant analogous to the Bondi mass, which is positive
Date: Thu, 25.06.2015
Time: 14:00
Duration: 60 min
Location:Arbeitsgruppe Gravitation, Währinger Strasse 17, Seminarraum A, 2. Stock, 1090 Wien
Contact:P.T. Chrusciel