Plenarvorträge - DPG-Tagungen

Dynamik und Statistische Physik Donnerstag
DY 44 Granular Systems
Zeit: Donnerstag 14:30–16:00 Raum: H2
Hauptvortrag DY 44.1 Do 14:30 H2
Phase transitions and segregation phenomena in granular systems
— •Christof Krülle — Experimentalphysik V, Universität
Bayreuth, 95440 Bayreuth
For a collection of macroscopic particles, which are agitated by external
forces to perform stochastic movements, a ‘granular temperature’ can
be defined as mean kinetic energy in the center-of-mass system. For describing
the physical properties of this ensemble one can ask – in analogy
to thermodynamic phase transitions: (i) Are there critical temperatures
at which the internal structure undergoes qualitative changes? (ii) Which
order parameters characterize the dynamics of the transition? (iii) What
are the consequences for granular mixtures? We present results from experiments
in granular systems, which are excited by vertical and horizontal
vibrations [1,2]. The transitions between different dynamic states
depend on internal properties of the granulate (e.g. the density of particles)
as well as external parameters of the driving shaker. Peculiar to
granular systems are counterintuitive phenomena, like the crystallization
by increasing the vibration amplitude and thereby the energy input, or
the rise of large particles in a sea of smaller ones (Brazil-nut effect).
For horizontal shaking of a bidisperse system the demixing of small and
large particles is found to occur at the same critical particle density as the
liquid-solid transition, which leads to the conclusion that both phenomena,
segregation and phase transition, are closely related. [1] A.P.J. Breu,
H.-M. Ensner, C.A. Kruelle, and I. Rehberg, Phys. Rev. Lett. 90, 014302
(2003), [2] S. Aumaître, T. Schnautz, C.A. Kruelle, and I. Rehberg, Phys.
Rev. Lett. 90, 114302 (2003).
DY 44.2 Do 15:00 H2
Exploring the phase space of granular material — •Matthias
Schröter, Daniel I. Goldman, and Harry L. Swinney — University
of Texas at Austin
Edwards and Oakeshott (Physica A 157, 1080 (1989)) proposed a thermodynamic
approach to granular media, which is based on the idea that
only a finite number of mechanically stable configurations fit a given
number of particles in a fixed volume. They introduce a temperaturelike
state variable named Compactivity. The only experiment designed
to measure this quantity was done by Nowak et al. (Phys. Rev. E 57, 1971
(1998), who tapped a column of granular material and measured the the
asymptotic density fluctuations. This approach was, however, hampered
by long relaxation times and a small range of achievable densities. We
will show that the spatially homogeneous driving in a fluidized bed avoids
this problem. Our approach allows a test the applicability of the Edwards
hypothesis.
DY 44.3 Do 15:15 H2
Granular surface waves upon circular shaking — •Andreas
Götzendorfer 1 , Almudena Garcia 1 , Christof Krülle 1 ,
Ingo Rehberg 1 , Rafal Grochowski 2 , Peter Walzel 2 , Hamid
Elhor 3 , and Stefan J. Linz 3 — 1 Experimentalphysik V, Universität
Bayreuth — 2 Mechanische Verfahrenstechnik, Universität Dortmund —
3 Theoretische Physik, Universität Münster
DY 46 Poster
We study the behaviour of dry granular material on vibratory conveyors.
These machines are ubiquitous in industry and utilized for transport
of small components, coal pieces, cereal grains, fertilizer granulates,
sands, powders ... It is already known that for vertical sinusoidal vibrations
above a critical shaking intensity the granular material shows
surface waves. In our experiment we superpose the vertical vibration
with a horizontal vibration of the same amplitude and a phase shift of
π/2. That means that the support follows a circular trajectory. For this
kind of shaking non-stationary waves are observed in a certain driving
range. These pattern formation phenomena have a direct impact on the
transport properties of the conveyor and are therefore of importance for
industrial applications.
DY 44.4 Do 15:30 H2
Sound propagation in dense granular media — •Stefan Luding
— Particle Technology, DCT, TUDelft, Julianalaan 136, 2628 BL Delft,
Netherlands
The goal of the presented research is to understand information propagation
in dense assemblies of spherical, polydisperse granular media.
Using a discrete element method (DEM) simulation, the wave propagation
is studied. After relaxation to an isotropic static equilibrium state, a
wave is agitated by moving one side wall. First, the effect of the contact
force-law is examined for a cubic sample; second, the effects of singular
and periodic agitations are studied with Fourier analysis; third, pressure
effects and an-isotropy are examined.
DY 44.5 Do 15:45 H2
Horizontal brazil nut effects in a swirled bowl — •Tobias
Schnautz 1 , Christoph Kruelle 1 , Ricardo Brito 2 und Ingo Rehberg
1 — 1 Experimentalphysik V, Universitaet Bayreuth, D-95440 Bayreuth,
Germany — 2 Dep. Fisica Aplicada I, Universidad Complutense,
28040- Madrid, Spain
We present both, the behavior of a monodisperse layer of spheres, rolling
on a circularly vibrating table, and experimental results on on the
segregation of a binary mixture of spheres. When increasing the filling
fraction, a monodisperse layer of spheres shows two transitions between
states characterized by a different mobility of particles. The critical particle
densities for the liquid-solid transition are found to be independent
of the driving frequency, but decrease with increasing vibration amplitude.
Depending on the material properties, segregation occurs in the
liquid-like and in the solid-like state. The particle velocity distributions
show a transition from two peaks, located symmetrically around zero, to
one single peak at zero. The experimental results are compared with a
simplified two- dimsnional model system.
Zeit: Donnerstag 16:00–18:00 Raum: Poster D
DY 46.1 Do 16:00 Poster D
Period orbit expansion for simple spin systems — •Sarah
Hallerberg 1 , Wolfram Just 2 , and Günter Radons 1 — 1 Institute
of Physics, Chemnitz University of Technology, Chemnitz, Germany
— 2 Department of Mathematics, Queen Mary/University of London,
London, UK
We investigate the properties of zeta functions and the corresponding
expansion in terms of periodic orbits for spin chain models. In particular
we focus on mean field models which display phase transitions. The properties
of the zeta function and the periodic orbit expansion in different
phases and near the phase transition will be investigated by analytical
methods.
DY 46.2 Do 16:00 Poster D
Numerical Results for the Generalized Mittag-Leffler Function
— •Hansjörg Seybold 1 and Rudolf Hilfer 1,2 — 1 ICA-1 Universität
Stuttgart, 70569 Stuttgart, Germany — 2 Institut für Physik, Universität
Mainz, 55099 Mainz, Germany
Results of extensive calculations for the generalized Mittag-Leffler
function Eα,β(z) are given in the complex plane: Discussion of the distribution
of the zeros and the dependency of the parameters α > 0 and
β ∈ R. This function is related to the eigenfunction of the fractional
derivative operator of order α and type α + β(1 − α) [1].
[1] R. Hilfer, Applications of fractional calculus in physics, World Scientific,
Singapore (2000)