5,236 research outputs found
What can be learned from the schematic mode-coupling approach to experimental data ?
We propose a detailed investigation of the schematic mode-coupling approach
to experimental data, a method based on the use of simple mode-coupling
equations to analyze the dynamics of supercooled liquids. Our aim here is to
clarify different aspects of this approach that appeared so far uncontrolled or
arbitrary, and to validate the results obtained from previous works. Analyzing
the theoretical foundations of the approach, we first identify the parameters
of the theory playing a key role and obtain simple requirements to be met by a
schematic model for its use in this context. Then we compare the results
obtained from the schematic analysis of a given set of experimental data with a
variety of models and show that they are all perfectly consistent. A number of
potential biases in the method are identified and ruled out by the choice of
appropriate models. Finally, reference spectra computed from the mode-coupling
theory for a model simple liquid are analyzed along the same lines as
experimental data, allowing us to show that, despite the strong simplification
in the description of the dynamics it involves, the method is free from
spurious artifacts and provides accurate estimates of important parameters of
the theory. The only exception is the exponent parameter, the evaluation of
which is hindered, as for other methods, by corrections to the asymptotic laws
of the theory present when the dynamics is known only in a limited time or
frequency range.Comment: 13 pages, 5 figures, revtex4, to appear in J. Chem. Phy
Study of the Depolarized Light Scattering Spectra of Supercooled Liquids by a Simple Mode-Coupling Model
By using simple mode coupling equations, we investigate the depolarized light
scattering spectra of two so-called "fragile" glassforming liquids, salol
(phenylsalicylate) and CKN (Ca_{0.4}K_{0.6}(NO_3)_{1.4}), measured by Cummins
and coworkers. Nonlinear integrodifferential equations for the time evolution
of the density-fluctuations autocorrelation functions are the basic input of
the mode coupling theory. Restricting ourselves to a small set of such
equations, we fit the numerical solution to the experimental spectra. It leads
to a good agreement between model and experiment, which allows us to determine
how a real system explores the parameter space of the model, but it also leads
to unrealistic effective vertices in a temperature range where the theory makes
critical asymptotic predictions. We finally discuss the relevance and the range
of validity of these universal asymptotic predictions when applied to
experimental data on supercooled liquids.Comment: 31 LaTeX pages using overcite.sty, 10 postscript figures, accepted in
J. Chem. Phy
Aging, rejuvenation and memory effects in re-entrant ferromagnets
We have studied the slow dynamics of the ferromagnetic phases of the
re-entrant CdCr_{2x}In_{2-2x}S_4 system for 0.85<x<=1 by means of low frequency
ac susceptibility and magnetization measurements. Experimental procedures
widely used in the investigation of the out-of-equilibrium dynamics of spin
glasses (such as the x=0.85 compound) have been applied to search for aging,
rejuvenation and memory effects, and to test their dependence on the disorder
introduced by dilution of the magnetic ions. Whereas the rejuvenation effect is
found in all studied samples, the memory effect is clearly enhanced for
increasing dilutions. The results support a description of aging in both
ferromagnetic and re-entrant spin-glass phases in terms of hierarchical
reconformations of domain walls pinned by the disorder.Comment: Service de Physique de l'Etat Condense, DRECAM, DSM, CEA Saclay,91191
Gif sur Yvette Cedex, France, 9 pages, including 7 figures, To appear in Eur.
Phys. J. B (2002
Flavor-dependent eigenvolume interactions in a hadron resonance gas
Eigenvolume effects in the hadron resonance gas (HRG) model are studied for
experimental hadronic yields in nucleus-nucleus collisions. If particle
eigenvolumes are different for different hadron species, the excluded volume
HRG (EV-HRG) improves fits to multiplicity data. In particular, using different
mass~-~volume relations for strange and non-strange hadrons we observe a
remarkable improvement in the quality of the fits. This effect appears to be
rather insensitive to other details in the schemes employed in the EV-HRG. We
show that the parameters found from fitting the data of the ALICE Collaboration
in central Pb+Pb collisions at the collision energy ~TeV entail the same improvement for all centralities at the same
collision energy, and for the RHIC and SPS data at lower collision energies.
Our findings are put in the context of recent fits of lattice QCD results.Comment: 4 figure
Entanglement gap, corners, and symmetry breaking
We investigate the finite-size scaling of the lowest entanglement gap δξ in the ordered phase of the two-dimensional quantum spherical model (QSM). The entanglement gap decays as δξ = Ω/pLln(L). This is in contrast with the purely logarithmic behaviour as δξ = π2/ln(L) at the critical point. The faster decay in the ordered phase reflects the presence of magnetic order. We analytically determine the constant Ω, which depends on the low-energy part of the model dispersion and on the geometry of the bipartition. In particular, we are able to compute the corner contribution to Ω, at least for the case of a square corner
Unbounded entanglement production via a dissipative impurity
We investigate the entanglement dynamics in a free-fermion chain initially
prepared in a Fermi sea and subjected to localized losses (dissipative
impurity). We derive a formula describing the dynamics of the entanglement
entropies in the hydrodynamic limit of long times and large intervals. The
result depends only on the absorption coefficient of the effective delta
potential describing the impurity in the hydrodynamic limit. Genuine
dissipation-induced entanglement is certified by the linear growth of the
logarithmic negativity. Finally, in the quantum Zeno regime at strong
dissipation the entanglement growth is arrested (Zeno entanglement death).Comment: 29 pages, 12 figures, 1 appendix. Typos corrected, added reference
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