861 research outputs found
Jamming phase diagram for frictional particles
The non-equilibrium transition from a fluid-like state to a disordered
solid-like state, known as the jamming transition, occurs in a wide variety of
physical systems, such as colloidal suspensions and molecular fluids, when the
temperature is lowered or the density increased. Shear stress, as temperature,
favors the fluid-like state, and must be also considered to define the system
'jamming phase diagram' [1-4]. Frictionless athermal systems [1], for instance,
can be described by the zero temperature plane of the jamming diagram in the
temperature, density, stress space. Here we consider the jamming of athermal
frictional systems [8-13] such as granular materials, which are important to a
number of applications from geophysics to industry. At constant volume and
applied shear stress[1, 2], we show that while in absence of friction a system
is either fluid-like or jammed, in the presence of friction a new region in the
density shear-stress plane appears, where new dynamical regimes are found. In
this region a system may slip, or even flow with a steady velocity for a long
time in response to an applied stress, but then eventually jams. Jamming in
non-thermal frictional systems is described here by a phase diagram in the
density, shear-stress and friction space
Experimental study of the compaction dynamics for 2D anisotropic granular materials
We present an experimental study of the compaction dynamics for
two-dimensional anisotropic granular systems. Compaction dynamics is measured
at three different scales : (i) the macroscopic scale through the packing
fraction , (ii) the mesoscopic scale through both fractions of aligned
grains and ideally ordered grains , and (iii) the
microscopic scale through both rotational and translational grain mobilities
. The effect of the grain rotations on the compaction dynamics has
been measured. At the macroscopic scale, we have observed a discontinuity in
the late stages of the compaction curve. At the mesoscopic scale, we have
observed the formation and the growth of domains made of aligned grains. From a
microscopic point of view, measurements reveal that the beginning of the
compaction process is essentially related to translational motion of the
grains. The grains rotations drive mainly the process during the latest stages
of compaction.Comment: 8pages, 11 figure
A fast algorithm for backbones
A matching algorithm for the identification of backbones in percolation
problems is introduced. Using this procedure, percolation backbones are studied
in two- to five-dimensional systems containing 1.7x10^7 sites, two orders of
magnitude larger than was previously possible using burning algorithms.Comment: 8 pages, 6 .eps figures. Uses epsfig and ijmpc.sty (included). To
appear in Int. J. Mod. Phys.
Glass transition in granular media
In the framework of schematic hard spheres lattice models for granular media
we investigate the phenomenon of the ``jamming transition''. In particular,
using Edwards' approach, by analytical calculations at a mean field level, we
derive the system phase diagram and show that ``jamming'' corresponds to a
phase transition from a ``fluid'' to a ``glassy'' phase, observed when
crystallization is avoided. Interestingly, the nature of such a ``glassy''
phase turns out to be the same found in mean field models for glass formers.Comment: 7 pages, 4 figure
A graph-theoretic account of logics
A graph-theoretic account of logics is explored based on the general
notion of m-graph (that is, a graph where each edge can have a finite
sequence of nodes as source). Signatures, interpretation structures and
deduction systems are seen as m-graphs. After defining a category freely
generated by a m-graph, formulas and expressions in general can be seen
as morphisms. Moreover, derivations involving rule instantiation are also
morphisms. Soundness and completeness theorems are proved. As a consequence of the generality of the approach our results apply to very different
logics encompassing, among others, substructural logics as well as logics
with nondeterministic semantics, and subsume all logics endowed with an
algebraic semantics
Percolation approach to glassy dynamics with continuously broken ergodicity
We show that the relaxation dynamics near a glass transition with continuous
ergodicity breaking can be endowed with a geometric interpretation based on
percolation theory. At mean-field level this approach is consistent with the
mode-coupling theory (MCT) of type-A liquid-glass transitions and allows to
disentangle the universal and nonuniversal contributions to MCT relaxation
exponents. Scaling predictions for the time correlation function are
successfully tested in the F12 schematic model and facilitated spin systems on
a Bethe lattice. Our approach immediately suggests the extension of MCT scaling
laws to finite spatial dimensions and yields new predictions for dynamic
relaxation exponents below an upper critical dimension of 6
The jamming transition of Granular Media
We briefly review the basics ideas and results of a recently proposed
statistical mechanical approach to granular materials. Using lattice models
from standard Statistical Mechanics and results from a mean field replica
approach and Monte Carlo simulations we find a jamming transition in granular
media closely related to the glass transition in super-cooled liquids. These
models reproduce the logarithmic relaxation in granular compaction and
reversible-irreversible lines, in agreement with experimental data. The models
also exhibit aging effects and breakdown of the usual fluctuation dissipation
relation. It is shown that the glass transition may be responsible for the
logarithmic relaxation and may be related to the cooperative effects underlying
many phenomena of granular materials such as the Reynolds transition.Comment: 18 pages with 6 postscript figures. to appear in J.Phys: Cond. Ma
International Migration and the (Un)happiness Push: Evidence from Polish Longitudinal Data
This article analyzes the impact of (un)happiness on the international migration decision. It uses a rich longitudinal household-level database, the Polish Social Diagnosis, to identify migration intentions, as well as subsequent actual migration, allowing us to overcome the issue of reverse causality present in previous studies of the nexus between happiness and migration. In addition, we assess the role of individual and household levels of happiness on migration behaviors and find that unhappy individuals from unhappy households are significantly more likely to declare their intentions to migrate abroad. In terms of actual migration, however, the unhappiness push significantly affects the odds of international migration only for selected subgroups, such as women and employed individuals. For other individuals, the unhappiness-induced migration plans remain mostly unrealized. Our article shows that push and pull factors, including happiness, might exert heterogenous effects on migration intentions and actual realizations. As a consequence, migration scholars should be careful when drawing conclusions on the determinants of actual migration behaviors by looking at determinants of migration intentions
- …