1,820 research outputs found
Thermodynamic description of a dynamical glassy transition
For the dynamical glassy transition in the -spin mean field spin glass
model a thermodynamic description is given. The often considered marginal
states are not the relevant ones for this purpose. This leads to consider a
cooling experiment on exponential timescales, where lower states are accessed.
The very slow configurational modes are at quasi-equilibrium at an effective
temperature. A system independent law is derived that expresses their
contribution to the specific heat. -scaling in the aging regime of
two-time quantities is explained.Comment: 5 pages revte
Thermodynamics of the glassy state: effective temperature as an additional system parameter
A system is glassy when the observation time is much smaller than the
equilibration time. A unifying thermodynamic picture of the glassy state is
presented. Slow configurational modes are in quasi-equilibrium at an effective
temperature. It enters thermodynamic relations with the configurational entropy
as conjugate variable. Slow fluctuations contribute to susceptibilities via
quasi-equilibrium relations, while there is also a configurational term.
Fluctuation-dissipation relations also involve the effective temperature.
Fluctuations in the energy are non-universal, however. The picture is supported
by analytically solving the dynamics of a toy model.Comment: 5 pages, REVTEX. Phys. Rev. Lett, to appea
Memory Effects in the Standard Model for Glasses
The standard model of glasses is an ensemble of two-level systems interacting
with a thermal bath. The general origin of memory effects in this model is a
quasi-stationary but non-equilibrium state of a single two-level system, which
is realized due to a finite-rate cooling and very slow thermally activated
relaxation. We show that single particle memory effects, such as negativity of
the specific heat under reheating, vanish for a sufficiently disordered
ensemble. In contrast, a disordered ensemble displays a collective memory
effect [similar to that described by Kovacs for glassy polymers], where
non-equilibrium features of the ensemble are monitored via a macroscopic
observable. An experimental realization of the effect can be used to further
assess the consistency of the model.Comment: 4 pages, 6 figure
Rigid supersymmetry with boundaries
We construct rigidly supersymmetric bulk-plus-boundary actions, both in
-space and in superspace. For each standard supersymmetric bulk action a
minimal supersymmetric bulk-plus-boundary action follows from an extended -
or -term formula. Additional separately supersymmetric boundary actions can
be systematically constructed using co-dimension one multiplets (boundary
superfields). We also discuss the orbit of boundary conditions which follow
from the Euler-Lagrange variational principle.Comment: 28 pages, JHEP clas
Food, nutrition & behaviour : research for healthy eating, healthy living
This brochure illustrates this range of research activities in the domain of food and nutrition, lifestyle and health. It does so by providing examples of collaboration of Wageningen UR with partners in the public and private sector
Even-visiting random walks: exact and asymptotic results in one dimension
We reconsider the problem of even-visiting random walks in one dimension.
This problem is mapped onto a non-Hermitian Anderson model with binary
disorder. We develop very efficient numerical tools to enumerate and
characterize even-visiting walks. The number of closed walks is obtained as an
exact integer up to 1828 steps, i.e., some walks. On the analytical
side, the concepts and techniques of one-dimensional disordered systems allow
to obtain explicit asymptotic estimates for the number of closed walks of
steps up to an absolute prefactor of order unity, which is determined
numerically. All the cumulants of the maximum height reached by such walks are
shown to grow as , with exactly known prefactors. These results
illustrate the tight relationship between even-visiting walks, trapping models,
and the Lifshitz tails of disordered electron or phonon spectra.Comment: 24 pages, 4 figures. To appear in J. Phys.
Split supersymmetry and the role of a light fermion in a supergravity-based scenario
We investigate split supersymmetry (SUSY) within a supergravity framework,
where local SUSY is broken by the F-term of a hidden sector chiral superfield
X. With reasonably general assumptions, we show that the fermionic component of
X will always have mass within a Tev. Though its coupling to the observable
sector superfields is highly suppressed in Tev scale SUSY, we show that it can
be enhanced by many orders in split SUSY, leading to its likely participation
in accelerator phenomenology.We conclude with a specific example of such a
scenario in a string based supergravity model.Comment: 12 Pages, Latex, Title changed, version thoroughly revise
Locating a weak change using diffuse waves (LOCADIFF) : theoretical approach and inversion procedure
We describe a time-resolved monitoring technique for heterogeneous media. Our
approach is based on the spatial variations of the cross-coherence of coda
waveforms acquired at fixed positions but at different dates. To locate and
characterize a weak change that occurred between successive acquisitions, we
use a maximum likelihood approach combined with a diffusive propagation model.
We illustrate this technique, called LOCADIFF, with numerical simulations. In
several illustrative examples, we show that the change can be located with a
precision of a few wavelengths and its effective scattering cross-section can
be retrieved. The precision of the method depending on the number of source
receiver pairs, time window in the coda, and errors in the propagation model is
investigated. Limits of applications of the technique to real-world experiments
are discussed.Comment: 11 pages, 14 figures, 1 tabl
Self-Dual Conformal Supergravity and the Hamiltonian Formulation
In terms of Dirac matrices the self-dual and anti-self-dual decomposition of
a conformal supergravity is given and a self-dual conformal supergravity theory
is developed as a connection dynamic theory in which the basic dynamic variabes
include the self-dual spin connection i.e. the Ashtekar connection rather than
the triad. The Hamiltonian formulation and the constraints are obtained by
using the Dirac-Bergmann algorithm.
PACS numbers: 04.20.Cv, 04.20.Fy,04.65.+
"Optical conductance fluctuations: diagrammatic analysis in Landauer approach and non-universal effects"
The optical conductance of a multiple scattering medium is the total
transmitted light of a diffuse incoming beam. This quantity, very analogous to
the electronic conductance, exhibits universal conductance fluctuations. We
perform a detailed diagrammatic analysis of these fluctuations. With a
Kadanoff-Baym technique all the leading diagrams are systematically generated.
A cancellation of the short distance divergencies occurs, that yields a well
behaved theory. The analytical form of the fluctuations is calculated and
applied to optical systems. Absorption and internal reflections reduce the
fluctuations significantly.Comment: 25 pages Revtex 3.0, 18 seperate postscript figure
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