143 research outputs found
Dynamics of Ordering of Isotropic Magnets
We study the dynamics of ordering of the nonconserved and conserved
Heisenberg magnet. The dynamics consists of two parts - an irreversible
dissipation into a heat bath and a reversible precession induced by a torque
due to the local molecular field. For quenches both to T=0 and T=T_c, we show
that the torque is irrelevant when the dynamics is nonconserved but relevant
when the dynamics is conserved and is governed by a new nontrivial fixed point.Comment: 7 pages, 5 eps figures. To appear in Physica A as a part of the
proceedings of the StatPhys - Calcutta III, January 1999, Calcutta, India.
Largely a combination of Phys. Rev. E, {\bf 57}, (1998),5069 and
cond-mat/9903041, together with a detailed discussion on multiscalin
Cluster emission and phase transition behaviours in nuclear disassembly
The features of the emissions of light particles (LP), charged particles
(CP), intermediate mass fragments (IMF) and the largest fragment (MAX) are
investigated for as functions of temperature and 'freeze-out'
density in the frameworks of the isospin-dependent lattice gas model and the
classical molecular dynamics model. Definite turning points for the slopes of
average multiplicity of LP, CP and IMF, and of the mean mass of the largest
fragment () are shown around a liquid-gas phase transition temperature
and while the largest variances of the distributions of LP, CP, IMF and MAX
appear there. It indicates that the cluster emission rate can be taken as a
probe of nuclear liquid--gas phase transition. Furthermore, the largest
fluctuation is simultaneously accompanied at the point of the phase transition
as can be noted by investigating both the variances of their cluster
multiplicity or mass distributions and the Campi scatter plots within the
lattice gas model and the molecular dynamics model, which is consistent with
the result of the traditional thermodynamical theory when a phase transition
occurs.Comment: replace nucl-th/0103009 due to the technique problem to access old
versio
Finite size scaling analysis of intermittency moments in the two dimensional Ising model
Finite size scaling is shown to work very well for the block variables used
in intermittency studies on a 2-d Ising lattice. The intermittency exponents so
derived exhibit the expected relations to the magnetic critical exponent of the
model. Email contact: [email protected]: Saclay-T93/063 Email: [email protected]
Moment Analysis and Zipf Law
The moment analysis method and nuclear Zipf's law of fragment size
distributions are reviewed to study nuclear disassembly. In this report, we
present a compilation of both theoretical and experimental studies on moment
analysis and Zipf law performed so far. The relationship of both methods to a
possible critical behavior or phase transition of nuclear disassembly is
discussed. In addition, scaled factorial moments and intermittency are
reviewed.Comment: Caption of Fig.6 was corrected. Review paper for WCI (World Consensus
Initiative) Book "Dynamics and Thermodynamics with Nuclear Degrees of
Freedom", published in Euorpean Physics Journal A as part of the Topical
Volume. 16 pages, 21 figure
A model for nuclear matter fragmentation: phase diagram and cluster distributions
We develop a model in the framework of nuclear fragmentation at thermodynamic
equilibrium which can be mapped onto an Ising model with constant
magnetization. We work out the thermodynamic properties of the model as well as
the properties of the fragment size distributions. We show that two types of
phase transitions can be found for high density systems. They merge into a
unique transition at low density. An analysis of the critical exponents which
characterize observables for different densities in the thermodynamic limit
shows that these transitions look like continuous second order transitions.Comment: 27 pages, 5 figures; comments on microcanonical approach and other
minor corrections added; references added; 1 figure change
Statistical nature of cluster emission in nuclear liquid-vapour phase coexistence
The emission of nuclear clusters is investigated within the framework of
isospin dependent lattice gas model and classical molecular dynamics model. It
is found that the emission of individual cluster which is heavier than proton
is almost Poissonian except near the transition temperature at which the system
is leaving the liquid-vapor phase coexistence and the thermal scaling is
observed by the linear Arrhenius plots which is made from the average
multiplicity of each cluster versus the inverse of temperature in the liquid
vapor phase coexistence. The slopes of the Arrhenius plots, {\it i.e.} the
"emission barriers", are extracted as a function of the mass or charge number
and fitted by the formula embodied with the contributions of the surface energy
and Coulomb interaction. The good agreements are obtained in comparison with
the data for low energy conditional barriers. In addition, the possible
influences of the source size, Coulomb interaction and "freeze-out" density and
related physical implications are discussed
Fractals at T=Tc due to instanton-like configurations
We investigate the geometry of the critical fluctuations for a general system
undergoing a thermal second order phase transition. Adopting a generalized
effective action for the local description of the fluctuations of the order
parameter at the critical point () we show that instanton-like
configurations, corresponding to the minima of the effective action functional,
build up clusters with fractal geometry characterizing locally the critical
fluctuations. The connection between the corresponding (local) fractal
dimension and the critical exponents is derived. Possible extension of the
local geometry of the system to a global picture is also discussed.Comment: To appear in Physical Review Letter
Mapeo litológico y mineralógico del batolito devónico Cerro Áspero, usando imágenes ASTER, Sierras Pampeanas Orientales, Argentina
The present study evaluates ASTER image processing as a technique to assist the lithological and mineralogical mapping oflarge granitic bodies and associated hydrothermal alteration assemblages related to the Cerro Áspero batholith, in Sierra de Comechingones, Argentina. This batholith was formed by the successive emplacement of several sub circular, high-level crust plutons that intruded, in the Upper Devonian, to metamorphic sequences of high to medium grade reworked by shear zones. Each of these plutons developed internal, external and roof units, and dyke swarms. Internal units are composed by porphyritic biotite monzogranites and external, roof units and dyke swarms are dominated by two-mica and muscovite leucocratic monzogranites to quarz-rich alkali-feldspar granites. The main associated mineralizations are W-Mo magmatic-hydrothermaldeposits and postbatholith epithemal fluorite deposits of cretaceous age. Supervised classification, principal component analyses and emissivity calculations were made to identify lithological composition and variations within the different plutons that comprise the Cerro Áspero batholith. This methodology allowed us to have a better and precise mapping of the study area as well as the contacts between the different plutons that comprise the Cerro Áspero batholith. The classification with spectral angle mapper methods allowed to identify the different sectors with hydrothermal alteration (argillic and silicification). The argillic alteration is mainly associated with epithermal fluorite deposits74339440
Hydrodynamic Spinodal Decomposition: Growth Kinetics and Scaling Functions
We examine the effects of hydrodynamics on the late stage kinetics in
spinodal decomposition. From computer simulations of a lattice Boltzmann scheme
we observe, for critical quenches, that single phase domains grow
asymptotically like , with in two dimensions
and in three dimensions, both in excellent agreement with
theoretical predictions.Comment: 12 pages, latex, Physical Review B Rapid Communication (in press
Density dependence of the "symmetry energy" in the lattice gas model
Isoscaling behavior of the statistical emission fragments from the
equilibrated sources with = 30 and = 30, 33, 36 and 39, resepectively,
is investigated in the framework of isospin dependent lattice gas model. The
dependences of isoscaling parameters on source isospin asymmetry,
temperature and freeze-out density are studied and the "symmetry energy" is
deduced from isoscaling parameters. Results show that "symmetry energy"
is insensitive to the change of temperature but follows the power-law
dependence on the freeze-out density . The later gives =
30 if the suitable asymmetric nucleon-nucleon potential
is taken. The effect of strength of asymmetry of nucleon-nucleon interaction
potential on the density dependence of the "symmetry energy" is dicussed.Comment: 5 pages, 4 page
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