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From: Sonia Wellens <[EMAIL PROTECTED]>
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Date: Friday, August 26, 2005, 9:41:50 AM
Subject: [Norton AntiSpam] Séminaires McEWEN et CHUA
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Mesdames et messieurs les professeurs,
Je vous prie de trouver ci-attaché deux annonces de
séminaires,
l'un aura lieu le vendredi 2 septembre 2005 à 16h
l'autre le vendredi 16 septembre 2005 à 16h
tous deux à la Salle Solvay, Bâtiment NO, Campus
Plaine, U.L.B.
Bien à vous,
Sonia Wellens,
Secrétaire
--
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Sonia Wellens
Université Libre de Bruxelles (CP 231)
Campus Plaine, Boulevard du Triomphe
B-1050 Bruxelles, Belgique
Phone 32 2 650 55 35 - Fax 32 2 650 57 67
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Interdisciplinary Centre for Nonlinear Phenomena and Complex Systems
Universite Libre de Bruxelles
Seminaire
Salle Solvay, Bat. NO, Campus Plaine, U.L.B.
Vendredi 2 septembre 2005 de 16:00 a 17 :00
Jean-Sabin McEWEN
Dalhousie University
Canada
Kinetic lattice gas models for adsorption, desorption and diffusion in
adsorbates : An investigation using diagonalization methods, Monte Carlo
simulations and density functional theory
Abstract:
This talk consists of several projects which investigate adsorbate systems in
or away from equilibrium and the influence of lateral interactions on their
measurable properties.
We use the kinetic lattice gas model to study adsorption and desorption
processes as well as hopping for a finite, homogeneous one-dimensional
adsorbate with nearest-neighbor interactions and periodic boundary conditions.
We solve the complete set of linear ordinary differential equations of motion
of all adsorbate correlation functions and obtain their eigenvalues and
eigenvectors. We examine the effect of hopping and adsorption processes on the
desorption kinetics by calculating the desorption rate, correlation functions
and eigenvalues. We generalize the above problem to deal with the time
evolution of N particles on Ns sites in a 1-d inhomogeneous adsorbate with
hopping processes only. The eigenvalue spectrum is analysed in momentum space
from which the diffusion coefficient for the adsorbate is obtained as well as
its complete time evolution.
A comprehensive theory of the adsorption of CO on Ru(0001) is then developed to
describe the equilibrium properties and the adsorption and desorption kinetics,
using a generalization of the theory developed in one dimension to two. The
basis is a multi-site kinetic lattice gas model with site exclusion and lateral
interactions between CO molecules out to second-neighbor unit cells. The theory
is such that it reproduces all available experimental data in a consistent
manner. Results are compared to an analysis where all relevant site-binding
energies and interactions of CO molecules are calculated within density
functional theory (DFT).
Equilibrium fluctuations of islands of adsorbed O atoms on Ru(0001) observed
with scanning tunneling microscopy (STM) are then analysed. The observed
ramified (2x2)-O islands point to complex interactions between the O atoms
which are modeled with a lattice gas model and DFT. The DFT calculations show
that, in addition to pair-wise attractive interactions between third nearest
neighbors, a repulsive three-body interaction exists between these.
_________________________________________________________
Interdisciplinary Centre for Nonlinear Phenomena and Complex Systems
Universite Libre de Bruxelles
Seminaire
Salle Solvay, Bat. NO, Campus Plaine, U.L.B.
Vendredi 16 septembre 2005 a 16:00
Professeur Leon CHUA
University of California, Berkeley, U.S.A.
International Francqui chair Professor, K.U. Leuven
LOCAL ACTIVITY IS THE ORIGIN OF COMPLEXITY
Abstract:
Many scientists have struggled to uncover the elusive origin of "complexity",
and its many equivalent jargons, such as emergence, self-organization,
synergetics, collective behaviors, slaving principle, non-equilibrium
phenomenon, etc. They have provided some qualitative, but not quantitative,
characterizations of numerous fascinating examples from many disciplines. For
example, Schrodinger had identified "the exchange of energy" from open systems
as a necessary condition for complexity. Prigogine has argued for the need to
introduce a new principle of nature which he dubbed "the instability of the
homogeneous". Turing had proposed "symmetry breaking" as an origin of
morphogenesis. Smale had asked what "axiomatic" properties must a
reaction-diffusion system possess to make the Turing interacting system
oscillate.
The purpose of this lecture is to show that all of the jargons and issues cited
above are mere manifestations of a new fundamental principle called local
activity, which is mathematically precise and easily testable. The local
acitivity theorem provides the quantitative characterization of Prigogine's
"instability of the homogeneous" and Smale's quest for an axiomatic principle
on Turing instability.
Among other things, a mathematical proof will be given which shows none of the
complexity-related jargons cited above is possible without local activity.
Explicit mathematical criteria will be given to identify a relatively small
subset of the locally-active parameter region called the edge of chaos where
most complex phenomena emerge.
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Carlos Gershenson...
Centrum Leo Apostel, Vrije Universiteit Brussel
Krijgskundestraat 33. B-1160 Brussels, Belgium
http://homepages.vub.ac.be/~cgershen/
"Describing and understanding problems will not solve them..."
