4,334 research outputs found
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
Aging phenomena in spin glass and ferromagnetic phases: domain growth and wall dynamics
We compare aging in a disordered ferromagnet and in a spin glass, by studying
the different phases of a reentrant system. We have measured the relaxation of
the low-frequency ac susceptibility, in both the ferromagnetic and spin-glass
phases of a CdCr_{1.9}In_{0.1}S_4 sample. A restart of aging processes when the
temperature is lowered (`chaos-like' effect) is observed in both phases. The
memory of previous aging at a higher temperature can be retrieved upon
re-heating, but in the ferromagnetic phase it can rapidly be erased by the
growth of ferromagnetic domains. We interpret the behaviour observed in the
ferromagnetic phase in terms of a combination of domain growth and pinned wall
reconformations, and suggest that aging in spin glasses is dominated by such
wall reconformation processes.Comment: SPEC, CEA Saclay, 91191 Gif sur Yvette Cedex, France, to appear in
Europhys. Lett. (2000
Potencialidade do uso de imagens orbitais para detecção de mudanças temporais: estudo de caso no municĂpio de Montenegro-RS, 1993 - 2008.
bitstream/item/36418/1/comunicado-240.pd
Classificação de imagens orbitais com auxĂlio da análise por componentes principais no municĂpio de Montenegro, RS, 2009.
bitstream/item/36320/1/comunicado-242.pd
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