1,715 research outputs found
Thermal Operators in Ising Percolation
We discuss a new cluster representation for the internal energy and the
specific heat of the d-dimensional Ising model, obtained by studying the
percolation mapping of an Ising model with an arbitrary set of
antiferromagnetic links. Such a representation relates the thermal operators to
the topological properties of the Fortuin-Kasteleyn clusters of Ising
percolation and is a powerful tool to get new exact relations on the
topological structure of FK clusters of the Ising model defined on an arbitrary
graph.Comment: 17 pages, 2 figures. Improved version. Major changes in the text and
in the notations. A missing term added in the specific heat representatio
Glassy behavior of the site frustrated percolation model
The dynamical properties of the site frustrated percolation model are
investigated and compared with those of glass forming liquids. When the density
of the particles on the lattice becomes high enough, the dynamics of the model
becomes very slow, due to geometrical constraints, and rearrangement on large
scales is needed to allow relaxation. The autocorrelation functions, the
specific volume for different cooling rates, and the mean square displacement
are evaluated, and are found to exhibit glassy behavior.Comment: 8 pages, RevTeX, 11 fig
Dynamic heterogeneities in attractive colloids
We study the formation of a colloidal gel by means of Molecular Dynamics
simulations of a model for colloidal suspensions. A slowing down with gel-like
features is observed at low temperatures and low volume fractions, due to the
formation of persistent structures. We show that at low volume fraction the
dynamic susceptibility, which describes dynamic heterogeneities, exhibits a
large plateau, dominated by clusters of long living bonds. At higher volume
fraction, where the effect of the crowding of the particles starts to be
present, it crosses over towards a regime characterized by a peak. We introduce
a suitable mean cluster size of clusters of monomers connected by "persistent"
bonds which well describes the dynamic susceptibility.Comment: 4 pages, 4 figure
Off equilibrium response function in the one dimensional random field Ising model
A thorough numerical investigation of the slow dynamics in the d=1 random
field Ising model in the limit of an infinite ferromagnetic coupling is
presented. Crossovers from the preasymptotic pure regime to the asymptotic
Sinai regime are investigated for the average domain size, the autocorrelation
function and staggered magnetization. By switching on an additional small
random field at the time tw the linear off equilibrium response function is
obtained, which displays as well the crossover from the nontrivial behavior of
the d=1 pure Ising model to the asymptotic behavior where it vanishes
identically.Comment: 12 pages, 10 figure
Static and dynamic heterogeneities in irreversible gels and colloidal gelation
We compare the slow dynamics of irreversible gels, colloidal gels, glasses
and spin glasses by analyzing the behavior of the so called non-linear
dynamical susceptibility, a quantity usually introduced to quantitatively
characterize the dynamical heterogeneities. In glasses this quantity typically
grows with the time, reaches a maximum and then decreases at large time, due to
the transient nature of dynamical heterogeneities and to the absence of a
diverging static correlation length. We have recently shown that in
irreversible gels the dynamical susceptibility is instead an increasing
function of the time, as in the case of spin glasses, and tends asymptotically
to the mean cluster size. On the basis of molecular dynamics simulations, we
here show that in colloidal gelation where clusters are not permanent, at very
low temperature and volume fractions, i.e. when the lifetime of the bonds is
much larger than the structural relaxation time, the non-linear susceptibility
has a behavior similar to the one of the irreversible gel, followed, at higher
volume fractions, by a crossover towards the behavior of glass forming liquids.Comment: 9 pages, 3 figure
Un acercamiento a la Universidad Nacional de Salta : Orígenes, debates y reflexiones
La ponencia que aquí se presenta, tiene como objetivo presentar el caso de la Universidad Nacional de Salta, delineando ligeramente sus orígenes, su trayectoria institucional y sus luchas a fin de poder puntualizar sobre la situación actual que atraviesa esta casa de altos estudios. Afirmamos que el proceso que se transita actualmente, no debe entenderse aisladamente, sino en articulación con las distintas instituciones del mismo tipo a lo largo del territorio nacional; por lo que pretendemos: a) contextualizar la posición de la U.N.Sa. dentro del sistema universitario argentino, b) reconocer a los agentes que en ella participan, c)tratar las luchas recientes que en ella se vivieron. A partir de esa caracterización, creemos, es posible abordar críticamente la situación actual, reconociendo el avance de las políticas neoliberales y con ello, las adherencias y resistencias que se generan en el ámbito universitario. A modo de conclusión, intentaremos reflexionar sobre los desafíos de la educación superior en el momento actua
- …