10,533 research outputs found
Series Expansion of the Off-Equilibrium Mode Coupling Equations
We show that computing the coefficients of the Taylor expansion of the
solution of the off-equilibrium dynamical equations characterizing models with
quenched disorder is a very effective way to understand the long time
asymptotic behavior. We study the spherical spin glass model, and we
compute the asymptotic energy (in the critical region and down to ) and
the coefficients of the time decay of the energy.Comment: 9 pages, LaTeX, 3 uuencoded figure
On the Effect of Cavitation on the Radial Forces and Hydrodynamic Stiffness of a Centrifugal Pump
The asymmetric flow within a volute exerts a radial force on a centrifugal impeller. The present paper presents experimental measurements of the radial forces on the impeller in the presence of cavitation
Temperature evolution and bifurcations of metastable states in mean-field spin glasses, with connections with structural glasses
The correlations of the free-energy landscape of mean-field spin glasses at
different temperatures are investigated, concentrating on models with a first
order freezing transition. Using a ``potential function'' we follow the
metastable states of the model in temperature, and discuss the possibility of
level crossing (which we do not find) and multifurcation (which we find). The
dynamics at a given temperature starting from an equilibrium configuration at a
different temperature is also discussed. In presence of multifurcation, we find
that the equilibrium is never achieved, leading to aging behaviour at slower
energy levels than usual aging. The relevance of the observed mechanisms for
real structural glasses is discussed, and some numerical simulations of a soft
sphere model of glass are presented.Comment: 16 pages, LaTeX, 10 figures (12 postscript files
Quasispecies evolution in general mean-field landscapes
I consider a class of fitness landscapes, in which the fitness is a function
of a finite number of phenotypic "traits", which are themselves linear
functions of the genotype. I show that the stationary trait distribution in
such a landscape can be explicitly evaluated in a suitably defined
"thermodynamic limit", which is a combination of infinite-genome and strong
selection limits. These considerations can be applied in particular to identify
relevant features of the evolution of promoter binding sites, in spite of the
shortness of the corresponding sequences.Comment: 6 pages, 2 figures, Europhysics Letters style (included) Finite-size
scaling analysis sketched. To appear in Europhysics Letter
Ultrametricity in 3D Edwards-Anderson spin glasses
We perform an accurate test of Ultrametricity in the aging dynamics of the
three dimensional Edwards-Anderson spin glass. Our method consists in
considering the evolution in parallel of two identical systems constrained to
have fixed overlap. This turns out to be a particularly efficient way to study
the geometrical relations between configurations at distant large times. Our
findings strongly hint towards dynamical ultrametricity in spin glasses, while
this is absent in simpler aging systems with domain growth dynamics. A recently
developed theory of linear response in glassy systems allows to infer that
dynamical ultrametricity implies the same property at the level of equilibrium
states.Comment: 4 pages, 5 figure
DYNAMICAL SOLUTION OF A MODEL WITHOUT ENERGY BARRIERS
In this note we study the dynamics of a model recently introduced by one of
us, that displays glassy phenomena in absence of energy barriers. Using an
adiabatic hypothesis we derive an equation for the evolution of the energy as a
function of time that describes extremely well the glassy behaviour observed in
Monte Carlo simulations.Comment: 11 pages, LaTeX, 3 uuencoded figure
Exact summation of vertex corrections to the penetration depth in d-wave superconductors
A variety of experiments suggest that in the cuprates, the low-energy
superconducting quasiparticles undergo forward scattering from extended
impurity potentials. We argue that when such potentials dominate the
scattering, the penetration depth may be computed in a simple zero-angle
scattering approximation (ZSA), in which the vertex corrections to the Meissner
effect may be summed exactly. We find a remarkably simple relationship between
the normal fluid density and the quasiparticle density of states of the
disordered system which holds for every realization of the disorder. We expect
this result to be relevant to the -plane penetration depth in high-purity
single crystals of underdoped YBCO.Comment: 4 pages, submitted to PR
Rotordynamic Forces on Centrifugal Pump Impellers
The asymmetric flow around an impeller in a volute exerts a force upon the impeller. To study the rotordynamic force on an impeller which is vibrating around its machine axis of rotation, the impeller, mounted on a dynamometer, is made to whirl in a circular orbit within the volute. The measured force is expressed as the sum of a steady radial force and an unsteady force due to the eccentric motion of the impeller. These forces were measured in separate tests on a centrifugal pump with radically increased shroud clearance, a two-dimensional impeller, and an impeller with an inducer, the impeller of the HPOTP (High Pressure Oxygen Turbopump) of the SSME (Space Shuttle Main Enginer). In each case, a destabilizing force was observed over a region of positive whirl
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