551 research outputs found
A new proof of the analyticity of the electronic density of molecules
We give a new, short proof of the regularity away from the nuclei of the
electronic density of a molecule obtained in [1,2]. The new argument is based
on the regularity properties of the Coulomb interactions underlined in [3,4]
and on well-known elliptic technics. [1] S. Fournais, M. Hoffmann-Ostenhof, T.
Hoffmann-Ostenhof, T. Oe stergaard Soerensen: The electron density is smooth
away from the nuclei. Comm. Math. Phys. 228, no. 3 (2002), 401-415. [2] S.
Fournais, M. Hoffmann-Ostenhof, T. Hoffmann-Ostenhof, T. Oestergaard Soerensen:
Analyticity of the density of electronic wave functions. Ark. Mat. 42, no. 1
(2004), 87-106. [3] W. Hunziker: Distortion analyticity and molecular
resonances curves. Ann. Inst. H. Poincar\'e, s. A, t. 45, no 4, 339-358 (1986).
[4] M. Klein, A. Martinez, R. Seiler, X.P. Wang: On the Born-Oppenheimer
expansion for polyatomic molecules. Comm. Math. Phys. 143, no. 3, 607-639
(1992). The paper is published in Letters in Mathematical Physics 93, number 1,
pp. 73-83, 2010. The original publication is available at "
www.springerlink.com "
The spectrum of the random environment and localization of noise
We consider random walk on a mildly random environment on finite transitive
d- regular graphs of increasing girth. After scaling and centering, the
analytic spectrum of the transition matrix converges in distribution to a
Gaussian noise. An interesting phenomenon occurs at d = 2: as the limit graph
changes from a regular tree to the integers, the noise becomes localized.Comment: 18 pages, 1 figur
Mesoscale magnetism at the grain boundaries in colossal magnetoresistive films
We report the discovery of mesoscale regions with distinctive magnetic
properties in epitaxial LaSrMnO films which exhibit
tunneling-like magnetoresistance across grain boundaries. By using
temperature-dependent magnetic force microscopy we observe that the mesoscale
regions are formed near the grain boundaries and have a different Curie
temperature (up to 20 K {\it higher}) than the grain interiors. Our images
provide direct evidence for previous speculations that the grain boundaries in
thin films are not magnetically and electronically sharp interfaces. The size
of the mesoscale regions varies with temperature and nature of the underlying
defect.Comment: 4 pages of text, 4 figure
European Research Center for Information Systems (ERCIS):Gründungsveranstaltung Münster, 12. Oktober 2004
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Cluster Monte Carlo study of multi-component fluids of the Stillinger-Helfand and Widom-Rowlinson type
Phase transitions of fluid mixtures of the type introduced by Stillinger and
Helfand are studied using a continuum version of the invaded cluster algorithm.
Particles of the same species do not interact, but particles of different types
interact with each other via a repulsive potential. Examples of interactions
include the Gaussian molecule potential and a repulsive step potential.
Accurate values of the critical density, fugacity and magnetic exponent are
found in two and three dimensions for the two-species model. The effect of
varying the number of species and of introducing quenched impurities is also
investigated. In all the cases studied, mixtures of -species are found to
have properties similar to -state Potts models.Comment: 25 pages, 5 figure
Topological effects in ring polymers: A computer simulation study
Unconcatenated, unknotted polymer rings in the melt are subject to strong
interactions with neighboring chains due to the presence of topological
constraints. We study this by computer simulation using the bond-fluctuation
algorithm for chains with up to N=512 statistical segments at a volume fraction
\Phi=0.5 and show that rings in the melt are more compact than gaussian chains.
A careful finite size analysis of the average ring size R \propto N^{\nu}
yields an exponent \nu \approx 0.39 \pm 0.03 in agreement with a Flory-like
argument for the topologica interactions. We show (using the same algorithm)
that the dynamics of molten rings is similar to that of linear chains of the
same mass, confirming recent experimental findings. The diffusion constant
varies effectively as D_{N} \propto N^{-1.22(3) and is slightly higher than
that of corresponding linear chains. For the ring sizes considered (up to 256
statistical segments) we find only one characteristic time scale \tau_{ee}
\propto N^{2.0(2); this is shown by the collapse of several mean-square
displacements and correlation functions onto corresponding master curves.
Because of the shrunken state of the chain, this scaling is not compatible with
simple Rouse motion. It applies for all sizes of ring studied and no sign of a
crossover to any entangled regime is found.Comment: 20 Pages,11 eps figures, Late
Quantum harmonic oscillator systems with disorder
We study many-body properties of quantum harmonic oscillator lattices with
disorder. A sufficient condition for dynamical localization, expressed as a
zero-velocity Lieb-Robinson bound, is formulated in terms of the decay of the
eigenfunction correlators for an effective one-particle Hamiltonian. We show
how state-of-the-art techniques for proving Anderson localization can be used
to prove that these properties hold in a number of standard models. We also
derive bounds on the static and dynamic correlation functions at both zero and
positive temperature in terms of one-particle eigenfunction correlators. In
particular, we show that static correlations decay exponentially fast if the
corresponding effective one-particle Hamiltonian exhibits localization at low
energies, regardless of whether there is a gap in the spectrum above the ground
state or not. Our results apply to finite as well as to infinite oscillator
systems. The eigenfunction correlators that appear are more general than those
previously studied in the literature. In particular, we must allow for
functions of the Hamiltonian that have a singularity at the bottom of the
spectrum. We prove exponential bounds for such correlators for some of the
standard models
Shadowing Effects on Vector Boson Production
We explore how nuclear modifications to the nucleon structure functions,
shadowing, affect massive gauge boson production in heavy ion collisions at
different impact parameters. We calculate the dependence of , and
production on rapidity and impact parameter to next-to-leading order in
Pb+Pb collisions at 5.5 TeV/nucleon to study quark shadowing at high . We
also compare our Pb+Pb results to the rapidity distributions at 14 TeV.Comment: 25 pages ReVTeX, 12 .eps figures, NLO included, version accepted for
publication in Physical Review
The Effect of Shadowing on Initial Conditions, Transverse Energy and Hard Probes in Ultrarelativistic Heavy Ion Collisions
The effect of shadowing on the early state of ultrarelativistic heavy ion
collisions is investigated along with transverse energy and hard process
production, specifically Drell-Yan, , and production. We
choose several parton distributions and parameterizations of nuclear shadowing,
as well as the spatial dependence of shadowing, to study the influence of
shadowing on relevant observables. Results are presented for Au+Au collisions
at GeV and Pb+Pb collisions at TeV.Comment: Submitted to Phys. Rev.
Work function changes in the double layered manganite La1.2Sr1.8Mn2O7
We have investigated the behaviour of the work function of La1.2Sr1.8Mn2O7 as
a function of temperature by means of photoemission. We found a decrease of 55
+/- 10 meV in going from 60 K to just above the Curie temperature (125 K) of
the sample. Above T_C the work function appears to be roughly constant. Our
results are exactly opposite to the work function changes calculated from the
double-exchange model by Furukawa, but are consistent with other measurements.
The disagreement with double-exchange can be explained using a general
thermodynamic relation valid for second order transitions and including the
extra processes involved in the manganites besides double-exchange interaction.Comment: 6 pages, 4 figures included in tex
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