Plenarvorträge - DPG-Tagungen

Dynamik und Statistische Physik Donnerstag
DY 46.57 Do 16:00 Poster D
Ruin & Recreate – A Method to Overcome Barriers in the
Energy Landscape — •Johannes J. Schneider — Department of
Physics, Johannes Gutenberg University, Staudinger Weg 7, D-55122
Mainz
When simulating or optimizing a system with Monte Carlo techniques,
usually the so-called Local Search approach is used in which an initial
configuration is iteratively altered by small changes. Therefore, the application
of such a small move leads to a new configuration in the neighborhood
of the current configuration, which is quite similar to it. We showed
in [1] that the application of larger moves leads to better results in shorter
times than the classic Local Search concept. However, these larger moves
we used did not lead to thermal equilibrium, such that they could only
be used for optimization purposes but not for simulating a system at
a given temperature. Now we have altered this approach, such that the
moves lead to a Boltzmann equilibrium at each temperature. Moreover,
as these larger moves change the configuration to a much larger extent
than the small moves, we are able to overcome barriers in the energy
landscape more easily. We will present computational results both for
the classic Local Search and the new Ruin & Recreate approach for a
colloidal system.
[1] G. Schrimpf, J. Schneider, H. Stamm-Wilbrandt, and G. Dueck, J.
Comp. Phys. 159, 139, 2000.
DY 46.58 Do 16:00 Poster D
HP Proteins on Generalized Lattices — •Thomas Vogel,
Michael Bachmann, and Wolfhard Janke — Institut für
Theoretische Physik, Universität Leipzig, Augustusplatz 10/11, 04109
Leipzig, Germany
We investigated HP proteins[1] in three dimensions on simple cubic
lattices and on the fcc lattice. Employing the nPERM algorithm[2] to
selected sequences, we searched for ground states on both lattices and
compared the density of states and the heat capacity of sequences which
are designed on the simple cubic lattice.
PERM is a chain growth algorithm which combines the Rosenbluth
method with the “Go with the Winners” strategy. Population control is
implemented by cloning and pruning growing conformations depending
on variable thresholds which are computed adaptively during the simulation.
[1] K.F. Lau, K.A. Dill, Macromol. 22 (1989) 3986.
[2] H.-P. Hsu, V. Mehra, W. Nadler, P. Grassberger, J. Chem. Phys. 118
(2002) 444.
DY 46.59 Do 16:00 Poster D
Stable multiarmed spiral structure and their interaction in
excitable media — •Maria Inmaculada Rodriguez-Ponce and
Franz Schwabl — Lehrstuhl 5 fuer theoretische Physik, Physik Department,
Technische Universitaet Muenchen (Germany)
We study the dynamic properties and interaction of stable multiarmed
spiral structures in excitable media. The model is based on the equations
that describe the early stage of development in the self-organization of
Dictyostelium discoideum cells. We discuss the stability of the different
patterns, focusing on the interplay between the maximum number of
arms in a multiarmed spiral and the presence of local hetereogeneities
(defects) as well as between excitability properties. The interaction between
structures is analyzed in terms of core drifts and frequency changes.
DY 46.60 Do 16:00 Poster D
Poisoning of membrane patches — •Gerhard Schmid, Igor Goychuk,
and Peter Hänggi — Institut für Physik, Universität Augsburg
We consider the influence of intrinsic channel noise on the spontaneous
spiking activity of poisoned excitable membrane patches by use
of a stochastic generalization of the Hodgkin-Huxley model. Internal
noise stemming from the stochastic dynamics of individual ion channels
is known to affect the collective properties of the whole cluster [1]. In
particular, there exists an optimal size of the membrane patch for which
solely the internal noise causes a most regular spontaneous generation
of action potentials. This phenomenon is termed intrinsic coherence resonance.
In addition to the variation of the size of ion channel clusters,
the living organisms may adopt the densities of ion channels in order
to regulate the spontaneous spiking activity. In our model, we vary the
densities resp. the number of the specific ion channels for a given patch
size. Experimentally, this task could be achieved, e.g., by blocking the
ion channels of a given sort with a specific channel poison. Interestingly,
by poisoning the potassium, or the sodium ion channels in a certain proportion
one can increase, or decrease the regularity of the spike train [2].
This work is supported by DFG (SFB 486).
[1] J.A. White, J.T. Rubinstein, and A.R. Kay, Trends Neurosci. 23, 131
(2000).
[2] G. Schmid, I. Goychuk, and P. Hänggi, Physica A.
DY 46.61 Do 16:00 Poster D
Assortative random networks: Construction and properties —
•Ramon Xulvi-Brunet and Igor M. Sokolov — Newtonstr 15,
D-12489 Berlin
Since recently it got clear that many social networks exhibit assortative
mixing [M. E. J. Newman, Phys. Rev. Lett. 89, 208701 (2002)] so
that the predictions of uncorrelated models might be inadequate. To analyze
the role of assortativity we introduce an algorithm which changes
correlations in a network and produces assortative mixing to a desired
degree. This degree is governed by one parameter p; changing this parameter
one can construct networks ranging from fully random (p = 0)
to totally assortative (p = 1). We apply the algorithm to the Barabási-
Albert scale-free construction and show that the degree of assortativity is
an important parameter governing geometrical and transport properties
of networks. Thus the diameter of the network and the clustering coefficient
increase remarkably with the degree of assortativity. Moreover, the
concentration dependences of the size of giant cluster in the node percolation
problem for uncorrelated and assortative networks are strongly
different [R. Xulvi-Brunet, W. Pietsch, and I. M. Sokolov, Phys. Rev. E
68, 036119 (2003)].
DY 46.62 Do 16:00 Poster D
Two phase flow in porous media — •Toby Joseph 1 and Rudolf
Hilfer 1,2 — 1 ICA-1, Universität Stuttgart, 70569 Stuttgart, Germany
— 2 Institut für Physik, Universität Mainz, 55099 Mainz,Germany
Our understanding of two phase flow in porous media is still very incomplete.
Although Darcy’s law has been modified to deal with two fluids
flowing in a porous medium by introducing extra parameters like the relative
permeabilities, its domain of validity is still a matter of scientific
debate. Moreover, it is well known that the relative permeability curves
are history dependent and even the residual saturations in an invasion
process depends on the way in which the invasion is driven as is clear
from the capillary saturation curves. We present here a micro-to-macro
upscaling that takes into consideration some of these problems.
DY 46.63 Do 16:00 Poster D
Macromolecule- Flow Interaction — •Achim Jung and Christian
Wagner — Experimentalphysik, Universität des Saarlandes
We present measurements on the flow of diluted polymer solutions in
basic flow geometries. Our goal is to connect the statistical conformation
of the macromolecules with macroscopic sample parameters such as shear
or elongational viscosity. An example of basic flow geometry is the extensional
flow in a droplet detachment process where the sample is confined
in the thread between droplet and nozzle. Existing theoretical models are
not able to explain our findings on the elongational viscosity of diluted
polyelectrolyte DNA-solutions in different salinities and thus with different
polymer chain flexibilities. In order to gain more insight into the
microscopic conformations of the macromolecules we are setting up optical
tweezers. The focus of our microscopic studies will be the meaning
of hydrodynamic interaction, an effect that has been neglected in most
of the theoretical predictions of macroscopic material parameters.
DY 46.64 Do 16:00 Poster D
Fluctuation Measurements of a Passive Scalar with Miniaturized
Thermocouples — •Marco Munzel, J. Peinke, and A. Kittel
— Carl von Ossietzky University of Oldenburg, Faculty of Physics,
26111 Oldenburg, Germany
The measurement of thermal fluctuations is important for investigating
transport features of a passive and active scalar in fluids. We present
a thermal sensor based on a miniaturized thermocouple. Its coaxial setup
results from the fabrication as a micropipette normally used in neurobiology.
The glass micropipettes contain a core of platinum or constantan
wire and are coated with gold. The achieved tip diameters are 1µm and
less which enhance the spatial and temporal resolution significantly. Because
of their chemically inert coating, these sensors are applicative for
detecting temperature fluctuations in large variety of liquids and gases.
The sensors were tested in turbulent free-jets of heated water and air.
The presented results are compared to a commercially availiable cold wire