共查询到20条相似文献,搜索用时 46 毫秒
1.
L. Gauvin J. Vannimenus J.-P. Nadal 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(2):293-304
The collective behavior in a variant of Schelling’s segregation model is characterized with methods borrowed from statistical
physics, in a context where their relevance was not conspicuous. A measure of segregation based on cluster geometry is defined
and several quantities analogous to those used to describe physical lattice models at equilibrium are introduced. This physical
approach allows to distinguish quantitatively several regimes and to characterize the transitions between them, leading to
the building of a phase diagram. Some of the transitions evoke empirical sudden ethnic turnovers. We also establish links
with ‘spin-1’ models in physics. Our approach provides generic tools to analyze the dynamics of other socio-economic systems. 相似文献
2.
T. Boutreux H.A. Makse P.-G. de Gennes 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(1):105-115
We present the generalization of the minimal model for surface flows of granular mixtures, proposed by Boutreux and de Gennes
[J. Phys. I France 6, 1295 (1996)]. The minimal model was valid for grains differing only in their surface properties. The present model also
takes into account differences in the size of the grains. We apply the model to study segregation in two-dimensional silos
of mixtures of grains differing in size and/or surface properties. When the difference in size is small, the model predicts
that a continuous segregation appears in the static phase during the filling of a silo. When the difference in size is wide,
we take into account the segregation of the grains in the rolling phase, and the model predicts complete segregation and stratification
in agreement with experimental observations.
Received 9 September 1998 and Received in final form 4 November 1998 相似文献
3.
V.A. Pryamitsyn A.N. Semenov T.C.B. McLeish 《The European physical journal. E, Soft matter》2001,4(2):161-171
An analytical one-dimensional model of the microphase separation in symmetric diblock copolymers is developed. Three stages
of the process of the microphase segregation of a quenched diblock copolymer system into a lamella structure are predicted.
The first stage involves a fast increase of the amplitude of the quasi-periodical lamella structure (with the average wave
vector q0) up to a nearly equilibrium value; the second stage is a slow phase diffusion process which is characterized by increasing
coherency of the lamella structure; the third stage is the slow process of the lamella swelling, which is driven by the thermally
activated process of the spontaneous deletion of excessive lamellas, the lamella size increasing from the initial value 2π/q
0 to the equilibrium 2π/q
eq > 2π/q
0 during the process. The last two stages are described with the specially introduced coarse-grained “amplitude-phase” approximation.
It is shown that the relaxation of the gradient of the phase of the lamellar structure is the slowest relaxation process and,
thus, can be used as an effective order parameter of the lamellar structure at the later stages of the microphase segregation.
Received 10 March 2000 and Received in final form 5 June 2000 相似文献
4.
Lizette González-Lee 《Physica A》2008,387(1):145-158
Assuming the aggregates of a single chiral component as a pure phase, chiral segregation can be considered as a coexistence of two phases, therefore the formalisms of phase transitions in Statistical Mechanics can be applied. That is, chiral segregation can be considered as phase equilibrium. The standard mechanism to understand phase equilibrium considers the complete van der Waals forces, including repulsions and attractions. However, during the last few years, a particular kind of fluid-fluid equilibrium, explained in terms of only excluded volume effects, has gained important interest. This kind of phenomenon is known as depletion forces. In this paper, the contribution of these two mechanisms is investigated. In order to analyze the effect that repulsions and attractions have on chiral segregation we study a two-dimensional model, bent hard needles model. In one case only infinitely repulsive interactions are considered while in the second case, one and two Lennard-Jones (LJ) sites are added to model the complete van der Waals forces. In the first case, because of the nature of the model, the cause for chiral segregation is due to excluded volume effects that appear when the density of the system is sufficiently high. In the second case, the model proposed is more complex and besides the density the temperature also affects the phase separation. Monte Carlo simulations in the Gibbs ensemble (GMC) are used to perform this comparison. As a result, the segregation phase diagram is obtained for the infinitely repulsive model and that with two LJ sites. The important conclusions are that for some particular molecular geometries, repulsions are not able to produce chiral segregation at all, independently of density. However, when attractions are included the effect of repulsion is complemented and phase separation can be achieved even for those molecular geometries where infinitely repulsions were not able. 相似文献
5.
P. Fronczak A. Fronczak J. A. Hołyst 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):133-139
We study a model of network with clustering and desired node
degree. The original purpose of the model was to describe optimal
structures of scientific collaboration in the European Union. The
model belongs to the family of exponential random graphs. We show
by numerical simulations and analytical considerations how a very
simple Hamiltonian can lead to surprisingly complicated and
eventful phase diagram. 相似文献
6.
G. Bouglet C. Ligoure 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(1):137-147
Small angle X-ray and neutron scattering data on an effective three-component lamellar phase composed of water, a non adsorbing
water-soluble polymer (polyvynilpyrolidone), fluid membranes, made from a mixture of a cationic surfactant (cetylpiridiumchloride)
and a cosurfactant (hexanol), are presented for various membrane as well as polymer concentrations. The data are fitted with
a recently proposed model which takes into account the geometry and the fluctuations of these periodic structures. This allows
a quantitative study of the polymer contribution to the smectic compression modulus of the lamellar phase. Four different regimes of polymer confinement are expected. The associated variations in are compared to a recent theoretical model, which predicts the polymer-mediated contribution to the smectic compression modulus.
Received 20 January 1998 相似文献
7.
L.I. Salminen M.J. Alava K.J. Niskanen 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,37(3):369-374
A differential cluster variation method (DCVM) is proposed for analysis of spinoidal decomposition in alloys. In this method, lattice symmetry operations in the presence of an infinitesimal composition gradient are utilized to deduce the connection equations for the correlation functions and to reduce the number of independent variables in the cluster variation analysis. Application of the method is made to calculate the gradient energy coefficient in the Cahn-Hilliard free energy function and the fastest growing wavelength for spinodal decomposition in Al-Li alloys. It is shown that the gradient coefficient of congruently ordered Al-Li alloys is much larger than that of the disordered system. In such an alloy system, the calculated fastest growing wavelength is approximately 10 nm, which is an order of magnitude larger than the experimentally observed domain size. This may provide a theoretical explanation why spinodal decomposition after a congruent ordering is dominated by the antiphase boundaries.Received: 17 November 2003, Published online: 2 April 2004PACS:
64.75. + g Solubility, segregation, and mixing; phase separation - 81.30.-t Phase diagrams and microstructures developed by solidification and solid-solid phase transformations - 05.70.Ln Nonequilibrium and irreversible thermodynamics 相似文献
8.
We study the role of dislocation loops defects on the elasticity of lamellar phases by investigating the variation of the
lamellar elastic constants, ˉ and K, induced by the proliferation of these defects. We focus our interest on one particular lamellar phase made up of a mixture
of C12E5 and DMPC in water, which is already well-characterised. This lamellar phase undergoes a second-order (or weakly first-order)
lamellar-to-nematic phase transition at about 19°C and dislocation loops are seen to proliferate within the lamellar structure when temperature is decreased below 30°C. The values of both elastic constants of this given lamellar phase are measured as a function of temperature, approaching
the lamellar-to-nematic transition, with the help of Quasi-Elastic Light Scattering (QELS) on oriented lamellar phases. Very
surprisingly we observe a strong and rapid increase in both ˉ and K as the lamellar-to-nematic transition temperature is approached. These increases are seen to start as soon as dislocation
loops can be observed in the lamellar phase. We interpret our results as being the consequence of the appearance and proliferation
of dislocation loops within the lamellar structure. According to a simple model we developped we show that ˉ and K are proportional to the density of dislocation loops in the lamellar phase. 相似文献
9.
H.A. Makse 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):271-276
We study the segregation of granular mixtures in two-dimensional silos using a recently proposed set of coupled equations
for surface flows of grains. We study the thick flow regime, where the grains are segregated in the rolling phase. We incorporate
this dynamical segregation process, called kinematic sieving, free-surface segregation or percolation, into the theoretical
formalism and calculate the profiles of the rolling species and the concentration of grains in the bulk in the steady state.
Our solution shows the segregation of the mixture with the large grains being found at the bottom of the pile in qualitative
agreement with experiments.
Received: 6 July 1998 / Revised and Accepted: 13 August 1998 相似文献
10.
The optical properties of the quarter-filled single-band CDW systems
have been reexamined in the model with the electron-phonon coupling
related to the variations of electron site energies.
It appears that the indirect, electron-mediated coupling
between phase phonons and external electromagnetic fields
vanishes for symmetry reasons, at variance with the infrared selection
rules used in the generally accepted microscopic theory.
It is shown that the phase phonon modes and the electric fields
couple directly, with the coupling constant proportional to the
magnitude of the charge-density wave.
The single-particle contributions to the optical
conductivity tensor are determined for the ordered CDW state
and the related weakly doped metallic state by means of the Bethe-Salpeter
equations for elementary electron-hole excitations.
It turns out that this gauge-invariant approach establishes
a clear connection between the effective numbers of residual,
thermally activated and bound charge carriers.
Finally, the relation between these numbers and the activation energy of dc
conductivity and the optical CDW gap scale is explained in the way consistent
with the conductivity sum rules. 相似文献
11.
Equilibrium phase coexistence between two chemical species implies the equality of the chemical potentials and of the osmotic
pressures. We study this problem on a deformable membrane when one type of the molecules serves as anchor for polymeric chains
immersed in the surrounding medium (considered as a good solvent). We derive the general conditions for phase coexistence
when both the curvature of the membrane and the density field of the anchor molecule are free to adjust themselves. We show
that curvature favors phase segregation. Our model predicts that membranes decorated with polymeric chains exhibit new shape
bifurcations without equivalent in fixed density systems.
Received: 26 November 2002 / Accepted: 2 April 2003 / Published online: 12 May 2003
RID="a"
ID="a"e-mail: nicolas@drfmc.ceng.cea.fr
RID="b"
ID="b"e-mail: bfourcade@cea.fr 相似文献
12.
T. Boutreux 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):419-424
We present the generalization of a theoretical model for segregation of granular mixtures due to surface flows, published
in J. Phys. I France 6, 1295 (1996). Our generalized model is valid for grains differing by their size and/or their surface properties; in the present
paper, we describe the case of two species with the same surface properties but two different sizes. The rolling stream is
assumed to be homogeneous. Exchanges between the grains at rest and the rolling stream are modelized via binary collisions.
The model predicts that during the filling of a two-dimensional silo, continuous segregation appears inside the static phase: small (respectively large) grains tend to stop uphill (respectively downhill), although
both species remain present everywhere. This fits the observations when the size difference between the species is small.
When the size difference is large, a different regime is observed. We argue that in this case, segregation occurs directly inside the rolling stream.
Received: 25 February 1998 / Received in final form and Accepted: 6 July 1998 相似文献
13.
G.G. Pereira 《The European physical journal. E, Soft matter》2002,7(3):273-289
The inherent nanoscale morphologies of self-organizing diblock copolymer melts are now being investigated for a variety of
technological applications. To obtain global, well-oriented, regular patterns requires suitably confining and aligning the
melt between two flat plates. Here we consider such confinement for an asymmetrical diblock melt, which forms columns of the
minority phase in a matrix of the majority phase. We investigate this system with a combination of numerical simulations and
strong segregation theory and make suggestions as to when perpendicular orientation should prevail over parallel orientation
of the columns.
Received 22 May 2001 and Received in final form 14 February 2002 相似文献
14.
A. T. Lawniczak X. Tang 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(1-2):231-236
We explore packet traffic dynamics in a data network model near phase
transition point from free flow to congestion. The model of data network is an
abstraction of the Network Layer of the OSI (Open Systems Interconnect)
Reference Model of packet switching networks. The Network Layer is responsible
for routing packets across the network from their sources to their
destinations and for control of congestion in data networks. Using the model
we investigate spatio-temporal packets traffic dynamics near the phase
transition point for various network connection topologies, and static and
adaptive routing algorithms. We present selected simulation results and
analyze them. 相似文献
15.
L. Ramos P. Fabre F. Nallet C.-Y.D. Lu 《The European physical journal. E, Soft matter》2000,1(4):285-299
We investigate, using quasi-elastic light scattering, some features of the long-wavelength, low-frequency modes of the hexagonal
phase often encountered in the study of lyotropic (surfactant-solvent) systems. The hexagonal phase is swollen by an oil-based
ferrofluid, allowing magnetically aligned samples to be prepared. We show experimentally the anisotropy of the two lowest-frequency
modes. We develop a model which predicts that these slow modes are associated to particle diffusion and tube motion. With
the help of microscopic as well as phenomenological analyses, we suggest that the latter presumably corresponds to a peristaltic
mode. Confinement effects on the one-dimensional, Brownian diffusion of the colloids along the tube axis together with the
coupling between the two modes are studied experimentally, varying the tube diameter to particle size ratio.
Received 7 July 1999 相似文献
16.
S. Xiao W. Hu W. Luo Y. Wu X. Li H. Deng 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(4):479-484
In the present paper, the surface and size effects on the
alloying ability and phase stability of immiscible alloy
nanoparticles have been studied with calculating the heats of
formation of Au-Pt alloy nanoparticles from the single element
nanoparticles of their constituents (Au and Pt) with a simple
thermodynamic model and an analytic embedded atom method. The
results indicated that, besides the similar compositional dependence
of heat of formation as in bulk alloys, the heat of formation of
alloy nanoparticles exhibits notable size-dependence, and there
exists a competition between size effect and compositional effect on
the heat of formation of immiscible system. Contrary to the positive
heat of formation for bulk-immiscible alloys, a negative heat of
formation may be obtained for the alloy nanoparticles with a small
size or dilute solute component, which implies a promotion of the
alloying ability and phase stability of immiscible system on a
nanoscale. The surface segregation results in an extension of the
size range of particles with a negative heat of formation. The
molecular dynamics simulations have indicated that the structurally
and compositionally homogeneous AuPt nanoparticles tend to form a
core-shell structure with temperature increasing. 相似文献
17.
G. Pawłowski 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(4):471-479
The extended Hubbard model in the atomic limit (AL-EHM) on a square lattice with periodic boundary conditions is studied with
use of the Monte Carlo (MC) method. Within the grand canonical ensemble the phase and order-order boundaries for charge orderings
are obtained. The phase diagrams include three types of charge ordered phases and the nonordered phase. The system exhibits
very rich structure and shows unusual multicritical behavior.
In the limiting case of tij=0, the EHM is equivalent to the pseudospin model with single-ion anisotropy
, exchange interaction W in an effective magnetic field
. This classical spin model is analyzed using the MC method for the canonical ensemble. The phase diagram is compared with
the known results for the Blume-Capel model. 相似文献
18.
P. H. Chavanis 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(2):179-208
We study a general class of nonlinear mean field
Fokker-Planck equations in relation with an effective generalized
thermodynamical (E.G.T.) formalism. We show that these equations describe
several physical systems such as: chemotaxis of bacterial
populations, Bose-Einstein condensation in the canonical ensemble,
porous media, generalized Cahn-Hilliard equations, Kuramoto model,
BMF model, Burgers equation, Smoluchowski-Poisson system for
self-gravitating Brownian particles, Debye-Hückel theory of
electrolytes, two-dimensional turbulence... In particular, we show
that nonlinear mean field Fokker-Planck equations can provide
generalized Keller-Segel models for the chemotaxis of
biological populations. As an example, we introduce a new model of
chemotaxis incorporating both effects of anomalous diffusion and
exclusion principle (volume filling). Therefore, the notion of
generalized thermodynamics can have applications for concrete
physical systems. We also consider nonlinear mean field
Fokker-Planck equations in phase space and show the passage from
the generalized Kramers equation to the generalized Smoluchowski
equation in a strong friction limit. Our formalism is simple and
illustrated by several explicit examples corresponding to Boltzmann,
Tsallis, Fermi-Dirac and Bose-Einstein entropies among others. 相似文献
19.
Saikat Chakraborty Prabhu R. Nott J. Ravi Prakash 《The European physical journal. E, Soft matter》2000,1(4):265-273
This paper considers the segregation of a granular mixture in a rotating drum. Extending a recent kinematic model for grain
transport on sandpile surfaces to the case of rotating drums, an analysis is presented for radial segregation in the rolling
regime, where a thin layer is avalanching down while the rest of the material follows rigid body rotation. We argue that segregation
is driven not just by differences in the angle of repose of the species, as has been assumed in earlier investigations, but
also by differences in the size and surface properties of the grains. The cases of grains differing only in size (slightly
or widely) and only in surface properties are considered, and the predictions are in qualitative agreement with observations.
The model yields results inconsistent with the assumptions for more general cases, and we speculate on how this may be corrected.
Received 4 June 1999 and Received in final form 28 September 1999 相似文献
20.
We present a phase field model on buckling membranes to analyze phase separation and budding on soft membranes. By numerically
integrating dynamic equations, it turns out that the formation of caps is greatly influenced by the presence of a little excess
area due to the surface area constraint. When cap-shaped domains are created, domain coalescence is mainly observed not between
domains with same budding directions, but between domains with opposite budding directions, because the bending energy between
two domains is larger in the former case. Although we do not introduce spontaneous curvature like Helfrich model, we obtain
some suggestions related to the slow dynamics of the phase separation on vesicles. 相似文献