Calendar of Physics Talks Vienna

Network Science: From structure to control
Speaker:Albert-László Barabási (Center of Complex Networks Research, Harvard,)
Abstract:Systems as diverse as the world wide web, Internet or the cell are described by highly interconnected networks with amazingly complex topology. Recent studies indicate that these networks are the result of self-organizing processes governed by simple but generic laws, resulting in architectural features that makes them much more similar to each other than one would have expected by chance. I will discuss the order characterizing our interconnected world and its implications to network robustness, and control. Indeed, while control theory offers mathematical tools to steer engineered and natural systems towards a desired state, we lack a framework to control complex self-organized systems. I will discuss a recently developed analytical framework to study the controllability of an arbitrary complex directed network, identifying the set of driver nodes whose time-dependent control can guide the system’s dynamics.
Date: Mon, 13.04.2015
Time: 17:30
Location:TU Wien-Freihaus, Hörsaal 5, 2. Stock, grüner Bereich
Contact:J. Schmiedmayer

Clusters at surfaces: concepts for tuning their stability and activity
Speaker:Ulrich Heiz (Clusters at surfaces: concepts for tuning their stability and activity)
Abstract:The study of size-selected clusters on surfaces has been growing into a vital research field within cluster science and catalysis since the discovery of the astonishing size-dependent activity of small gold clusters for the oxidation of CO in the late nineties. More than one decade of research in a combined effort between theory and experiment has resulted in a detailed understanding of cluster’s structural, electronic, optical, and magnetic properties. Furthermore, several chemical, catalytic, and photocatalytic processes on clusters are understood on a molecular level, today. This exciting advancement was only possible by a parallel development and introduction of novel, state-of-the-art methods, both in experiment and theory. In the first part this talk strategies for optimizing cluster stability against ripening will be presented, where both, the binding of the clusters to the surfac
Date: Tue, 14.04.2015
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:Univ.Prof. Dr. Ulrike Diebold

Chiral power counting of one- and two-body currents, isospin violation, and the pion-nucleon sigma-term
Speaker:Martin Hoferichter (TU Darmstadt)
Abstract:im Rahmen des Teilchenphysikseminar: Nuclear matrix elements are crucial ingredients for the consistent interpretation of direct- detection experiments searching for dark matter. In the talk I will discuss how chiral power counting provides a scheme to organize the calculation of these matrix elements, both concerning the relative scaling of different one-body operators and the suppression of operators where the (putative) dark-matter particle interacts with multiple nucleons. Moreover, I will show how the combination of recent precision measurements in pionic atoms and general constraints from analyticity, unitarity, and crossing symmetry imposed in the form of Roy-Steiner equations leads to a very ccurate determination of the pion-nucleon sigma-term, which measures the scalar matrix ements of up-and down-quarks.
Date: Tue, 14.04.2015
Time: 16:15
Duration: 60 min
Location:Fakultät für Physik, Erwin-Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock
Contact:A. Hoang, H. Neufeld

Introduction to tractor calculus and BGG complexes
Speaker:Callum Sleigh (Universität Wien)
Abstract:im Rahmen des Seminars in Geometric Analysis and Physics (GAP Seminar): Using the example of projective differential geometry, I will give an introduction to a collection of geometric tools known as "the tractor calculus" (following the etymology of 'vector', 'tensor','spinor', 'twistor' etc.) I will show how to use this calculus to construct complexes of invariant differential operators and discuss applications. No knowledge beyond elementary Riemannian geometry will be required.
Date: Thu, 16.04.2015
Time: 11:00
Duration: 60 min
Location:Fakultät für Mathematik, Oskar-Morgenstern-Platz 1,1090 Wien, 2. Stock, Besprechungszimmer
Contact:M. Bauer (Fak. Math, U.V.), V. Branding (Fak. Math, T.U.), D. Fajman (Fak. Phys, U.V.), J. Joudioux (Fak. Phys, U.V.)

Introduction to a Local Thermal Interpretation of the Unruh Effect
Speaker:Albert Georg Passegger (Vienna)
Abstract:im Rahmen des Literaturseminars: Based on the algebraic setting of the Unruh effect discussed in the previous talk ("Algebraic Foundations of the Unruh Effect"), I present recent results by D. Buchholz and C. Solveen on a new interpretation of the thermal aspects of the Unruh effect for scalar free fields. If the notion of temperature is defined using so-called local thermal observables, the local temperature of the Minkowski vacuum is zero also for the accelerated observer. Finally, I mention some open physical questions in this approach.
Date: Thu, 16.04.2015
Time: 14:00
Location:Arbeitsgruppe Gravitation, Währinger Strasse 17, Seminarraum A, 2. Stock, 1090 Wien
Contact:P.T. Chrusciel

Atom interferometry in an optical waveguide”
Speaker:Gordon McDonald ( Quantum Sensors Group, Australian National University)
Abstract: “Atom interferometry is a promising tool for acceleration measurement, with applications to navigation, gravity sensing and magnetic field gradient measurements. In the course of my PhD I have been working on atom interferometry using Bose-Einstein condensates in a horizontal optical waveguide, as a testbed for developing new tools for inertial sensing. The sensitivity to acceleration of an atom interferometer increases with the momentum separation of the two trajectories in the interferometer. We have demonstrated the largest momentum separation to date in an acceleration sensitive atom interferometer of 80 photon recoils between the two interfering paths. We use this large momentum separation to create an interferometer with a faster scaling in acceleration sensitivity than has been shown previously. The sensitivity to acceleration also increases along with the fringe visibility of the interference. We have demonstrated a non-dispersive atom cloud, a bright soliton, in an atom interferometer. The soliton is shown to maximise the fringe visibility and coherence time of the interferometer."
Date: Thu, 16.04.2015
Time: 16:00
Duration: 60 min
Location:Atominstitut, Seminarraum, Stadionallee 2, Wien 2
Contact:J. Schmiedmayer

Prospects for a new Neutron Electric Dipole Moment Search using a Pulsed Beam
Speaker:Florian M. PIEGSA (ETH Zürich, Institute for Particle Physics, Switzerland)
Abstract:Recently, a novel concept to search for a CP-violating neutron electric dipole moment has been presented [F.M. Piegsa, Phys. Rev. C 88, 045502 (2013)]. It employs a pulsed neutron beam instead of the established use of storable ultracold neutrons (UCN). The technique takes advantage of the high peak flux and the time structure of a next-generation pulsed spallation source (e.g. the planned European Spallation Source ESS) to directly measure the previously limiting systematic v×E-effect. Such an experiment would be complementary to experiments with UCN and could compete with their sensitivities. In this talk, I will describe this alternative approach including possible systematic effects and first test experiments.
Date: Fri, 17.04.2015
Time: 15:30
Location:Atominstitut, Hörsaal, Stadionallee 2, Wien 2
Contact:H. Abele