Plenarvorträge - DPG-Tagungen

Dynamik und Statistische Physik Montag
amounts of liquid. We used the electrowetting effect in order to manipulate
liquid droplets. The droplets were placed either on top of a single
substrate with a stripe electrode, or between two substrates with stripe
electrodes on each side. We studied systematically the behaviour of
the liquid as a function of the applied voltage, the substrate separation,
and the relative orientation of opposed stripe electrodes. The experimental
results are compared to both a simple analytical model as well as
numerical calculations using the Surface Evolver.
DY 17.3 Mo 17:00 H3
Statistische Eigenschaften eines Punktwirbelmodells für die
zweidimensionale Turbulenz — •Oliver Kamps und Rudolf
Friedrich — Institut für Theoretische Physik der Universität Münster,
Wilhelm-Klemm-Strasse 9, 48149 Münster
Ausgehend von einer Punktwirbelbeschreibung einer getriebenen zweidimensionalen
Strömung werden statistische Eigenschaften der Lagrangeschen
Flüssigkeitsdynamik numerisch untersucht. Im Zentrum des Interesses
stehen die Lagrangeschen Wahrscheinlichkeitsverteilungen für Ort
und Geschwindigkeit
DY 17.4 Mo 17:15 H3
Thermal noise in thin liquid films — •Markus Rauscher 1,2 ,
Klaus Mecke 1,2 , and Günther Grün 1,2 — 1 Max-Planck-Institut für
Metallforschung, Stuttgart — 2 ITAP, Universität Stuttgart
Thermal noise becomes more and more important the smaller a system
is. Recent studies of thin film evolution indicate that thermal noise
might influence characteristic time-scales of film dewetting [J. Becker et
at., Nature Materials Vol. 2, 59 (2003)]. Up to now, thin film flow was
only studied with deterministic equations.
We develop a stochastic version of the thin film equation. In the thin
film approximation, the stochastic incompressible hydrodynamic equations
[Landau and Lifshitz, Vol. IV] reduce to the deterministic thin film
equation plus a conserved noise term. We show that the noise term is
consistent with the thermodynamical equilibrium distribution of the film
thickness.
DY 17.5 Mo 17:30 H3
Adsorption of an asymmetric binary mixture at a selective solid
wall — •Dirk Woywod, Jörg Silbermann, and Martin Schoen
— Stranski-Laboratorium für Physikalische und Theoretische Chemie
TU Berlin
Sekretariat TC 7
Strasse des 17.Juni 124
10623 Berlin
DY 20 Fractals and Nonlinearity I
We consider a binary (A-B) mixture fluid near a selective planar homogenous
wall. Using a lattice-gas model and mean-field approximation
to the intrinsic free-energy functional, we obtain a closed expression for
the potential density in the grand canonical ensemble (V, T, µA = µB).
This expression depends on the attraction strength of the fluid-fluid interactions
(ǫAA > ǫBB, ǫAB), the fluid-wall interactions (ǫAW < ǫBW), and
the local densities (ρA, ρB). Minimizing the potential density numerically
gives us access to complete phase diagrams including wetting films [1].
In this presentation, we choose bulk parameters in order to promote the
formation of demixed A-rich liquid phases near coexistence with a gas
phase. Introducing a preference of the wall for molecules of component B,
first-order phase transitions between adsorbed mixed, A-rich and B-rich
films are observed. Besides multiple surface critical points, we also find
a peculiar temperature dependence of the concentration of component B
within a B-rich mixed film.[2]
[1] D. Woywod, M. Schoen, Phys. Rev. E 67, 026122 (2003)
[2] J. Silbermann, D. Woywod, M. Schoen, Phys. Rev E, in press (2003)
DY 17.6 Mo 17:45 H3
Microscopic theory for interfaces of binary liquid mixtures —
•Thorsten Hiester 1,2 and Klaus Mecke 1,2 — 1 Max-Planck-Institut
für Metallforschung, Heisenbergstraße 3, 70569 Stuttgart — 2 Institut
für Theoretische und Angewandte Physik, Pfaffenwaldring 57, 70569
Stuttgart
Binary liquid interfaces, in particular, their nanoscopic structure is still
poorly understood. In addition to capillary waves and density fluctuations
there are simultaneously fluctuations of the composition. Beginning
with a density functional theory for binary mixtures of inhomogeneous
fluids we derive an effective Hamiltonian for interfaces of binary liquid
mixtures beyond the well-known capillary-wave model. Explicit expressions
for the surface tension, the bending ridigities and especially the coupling
constants of compositional capillary waves in terms of two number
densities are obtained. Finally, we make predictions for grazing-incidence
x-ray scattering experiments.
Zeit: Dienstag 09:30–11:15 Raum: H2
Hauptvortrag DY 20.1 Di 09:30 H2
Statistical Physics for Complex Cosmic Structures — •Luciano
Pietronero — Dipartimento di Fisica, Universita’ di Roma La
Sapienza, 00185 - Roma, Italy
The amount of data in the field of astrophysics is growing exponentially
since a few years and it will grow even more in the future. This
situation is producing a dramatic change in which many speculations and
conjectures can finally be tested. This large amount of data permits the
detailed application of concepts from modern statistical physics. For the
galaxy distribution these led to a new general perspective and, in particular,
we presented strong evidence for self-similar and fractal structures
extending to the limits of the data. This led to a large debate in the
field which is nicely described in the recent book: “Discovery of Cosmic
Fractals” by Y. Baryshev and P. Tirikorpi (World Scientific, 2002)
http://www.wspc.com/books/popsci/4896.html. Recently we have extended
the applications of these methods also to the Cosmic Microwave
Background Radiation (which is very smooth) and to the N-body simularions
(which should link the two properties). We provide an overview
of the general situation of a field which represents an ideal playground of
interdisciplinary research between astrophysics and statistical physics.
DY 20.2 Di 10:00 H2
Generalization of Oboukhov’s Model for the Description of
Turbulent Lagrangian Statistics — •Rafaela Hillerbrand and
Rudolph Friedrich — Wilhelm-Klemm-Str. 9, 48149 Münster
Within the Langrangian framework for the description of fluid flows
a model for the stochastic evolution of a particle in a turbulent flow is
introduced. As a fractional Fokker-Planck equation the considered model
takes into account longtime correlations. In this model the Lagrangian
probability distribution function can be stated as an integral transform
of the solution of an ordinary Fokker-Planck equation, where the kernel
of the transformation contains the one-sided Lévy distribution. This
relates the stochastic behavior of a Lagrangian particle to the class of
continuous time random walks.
DY 20.3 Di 10:15 H2
Theoretical and experimental study of feedback-mediated drift
of spiral waves — •Vladimir Zykov and Harald Engel — Technische
Universitaet Berlin, Institut fuer Theoretische Physik, Sekr. PN
7-1, Hardenbergstr. 36, D-10623 Berlin
An efficient method is proposed to determine a velocity field describing
feedback induced drift of spiral waves. This method can be applied to
quite different feedback mechanisms as, for example, the one-channel and
the global feedback. It is shown that a smooth variation of eccentricity of
an elliptical domain subjected to the global feedback induces a cascade
of bifurcations that can drastically change the spiral wave evolution. In
a square shaped domain a set of point attractors appears instead of the
circular resonance attractor typical for a circular domain. These predictions
are in good quantitative agreement with performed numerical integrations
of an excitable reaction-diffusion system and with experimental
data obtained for the light-sensitive Belousov-Zhabotinsky reaction.