共查询到20条相似文献,搜索用时 15 毫秒
1.
A. Bershadskii 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):381-382
It is shown that a dimension-invariant form for fractal dimension D of random systems (where d is Euclidean dimension of the embedding space) is in good agreement with results of numerical simulations performed by different
authors for critical (p=p
c
) and subcritical (p<p
c
) percolation, for lattice animals, and for different aggregation processes.
Received: 9 July 1998 / Revised and Accepted: 12 July 1998 相似文献
2.
R. Neffati J. Rault 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(2):205-210
By differential Scanning Calorimetry (DSC), at low heating rate and using a technique of fractionation, we have measured the
equilibrium DSC signal (heat flow) J
q
0 of two families of porous glass saturated with water. The shape of the DSC peak obtained by these techniques is dependent
on the sizes distribution of the pores. For porous glass with large pore size distribution, obtained by sol-gel technology,
we show that in the domain of ice melting, the heat flow Jq is related to the melting temperature depression of the solvent, ΔT
m , by the scaling law: J
q
0∼ΔT
m
- (1 + D). We suggest that the exponent D is of the order of the fractal dimension of the backbone of the pore network and we discuss the influence of the variation
of the melting enthalpy with the temperature on the value of this exponent. Similar D values were obtained from small angle neutron scattering and electronic energy transfer measurements on similar porous glass.
The proposed scaling law is explained if one assumes that the pore size distribution is self similar. In porous glass obtained
from mesomorphic copolymers, the pore size distribution is very sharp and therefore this law is not observed. One concludes
that DSC, at low heating rate ( q? 2°C/min) is the most rapid and less expensive method for determining the pore distribution and the fractal exponent of a porous
material.
Received 23 July 1999 and Received in final form 16 February 2001 相似文献
3.
J. Asikainen S. Majaniemi M. Dubé J. Heinonen T. Ala-Nissila 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):253-263
We consider the dynamical scaling and kinetic roughening of single-valued interfaces propagating in 2D fractal media. Assuming
that the nearest-neighbor height difference distribution function of the fronts obeys Lévy statistics with a well-defined
algebraic decay exponent, we consider the generalized scaling forms and derive analytic expressions for the local scaling
exponents. We show that the kinetic roughening of the interfaces displays intrinsic anomalous scaling and multiscaling in
the relevant correlation functions. We test the predictions of the scaling theory with a variety of well-known models which
produce fractal growth structures. Results are in excellent agreement with theory. For some models, we find interesting crossover
behavior related to large-scale structural instabilities of the growing aggregates.
Received 22 May 2002 Published online 19 November 2002 相似文献
4.
Z. Bo D. Loggia L. Xiaorong G. Vasseur H. Ping 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(4):631-637
Two dimensional simulations of percolation are
realized on square networks of pore throats with a random
capillary pressure distribution. We analyse the influence of a
destabilizing gravity field (g) and of the
standard deviation of the distribution of the capillary pressure thresholds
(Wt). The fragmentation process is not taken into account in this study.
For an increase of g or/and when Wt decreases, two
transitions are analyzed with three different regimes
displacement patterns: Invasion percolation, invasion
percolation in a gradient, and invasion in a pure
gradient. The transitions are controlled both by the ratio
g/Wt and by the sample size (L). A scaling law between the
saturation at the percolation threshold and g/Wt
allows delineating the three regimes in agreement with
theoretical argument of the percolation in a gradient. 相似文献
5.
The unique structure of a set of self-assembled porous silica materials was
characterized through a combined small-angle scattering (CSAS) method using
small- and ultra-small angle neutron scattering as well as small-angle X-ray
scattering. The porous silica specimens investigated were prepared by a
sol-gel method under the presence of alkylketene dimer (AKD) template
particles and through calcination, which leads to the development of porous
silica having a mass-fractal structure over length scales from ~ 100 nm
to ~ 10 μm. Furthermore, the specimens posses a hierarchical
structure, which consist of a fractal porous structure, and also contain
primary silica particles less than 10 nm in size, which form a continuous
silica matrix. To characterize these complex structures, observation over a
broad range of length scales is indispensable. We propose a CSAS technique
that serves this purpose well. 相似文献
6.
Rottereau M Gimel JC Nicolai T Durand D 《The European physical journal. E, Soft matter》2003,11(1):61-64
We present off-lattice Monte Carlo simulations of site-bond percolation of semi-penetrable spheres or, equivalently, of hard
spheres with a finite bond range. We will show that the crucial parameter is the effective volume fraction ( φe), i.e. the volume that is occupied or within the bond range of at least one particle. For the equivalent system of semi-penetrable
spheres 1 - φe is the porosity. The bond percolation threshold (p
b) can be described in terms of φe by a simple analytical expression: log(φe)/log(φec) + log(p
b)/log(p
bc) = 1, with p
bc = 0.12 independent of the bond range and φec a constant that decreases with increasing bond range.
Received: 10 March 2003 / Accepted: 23 April 2003 / Published online: 21 May 2003
RID="a"
ID="a"e-mail: jean-christophe.gimel@univ-lemans.fr 相似文献
7.
The static structure factor (S(q)) of dispersions and gels of disk-like mineral colloids (Laponite) was investigated using time- and ensemble-averaged light
scattering. The evolution of S(q) in time after increasing the ionic strength of well-dispersed Laponite suspensions shows that Laponite aggregates and forms
fractal clusters. The structure of the aggregates does not depend on the ionic strength, but the rate of growth increases
very strongly with the ionic strength. At concentrations below about 3 g/l (0.12% v/v) the aggregates sediment while at higher
concentrations space-filling gels are formed. The gels are homogeneous on length scales larger than the correlation length
which decreases strongly with decreasing ionic strength and increasing concentration. However, the local structure is the
same, independent of the concentration and the ionic strength.
Received 6 August 2000 and Received in final form 16 March 2001 相似文献
8.
M.A. Jafarizadeh 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(1):103-112
Using the symmetry of (
d
+1)-simplex fractals with decimation number b
=2, the current distribution has been determined. Then using the renormalization group technique, based on the independent Schur's
invariant polynomials of current distributions, the multifractal spectrum of even moments of current distributions has been
evaluated analytically up to order six for an arbitrary value of d. Also the scaling exponents of order 8 and order 10 have been calculated numerically up to d
=30.
Received: 19 November 1997 / Revised: 21 January 1998 / Accepted: 9 February 1998 相似文献
9.
P. Poulin J. Bibette D.A. Weitz 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):277-281
Aggregation mechanisms of emulsions at high initial volume fractions () is studied using light scattering. We use emulsion droplets which can be made unstable towards aggregation by a temperature
quench. For deep quenches and , the aggregation mechanism is identified as diffusion-limited cluster aggregation (DLCA). An ordering of the clusters, which
is reflected by a peak in the scattering intensity, is shown to result from the intercluster separation, exhibiting different
scaling than that observed at lower volume fractions. This manifests an increasing similarity to spinodal decomposition observed
as is increased. For and shallow quenches, different mechanisms, closer to spinodal decomposition, are observed. These results allow the subtle
boundaries between DLCA and spinodal decomposition to be explored.
Received: 7 April 1998 / Revised: 19 August 1998 / Accepted: 21 August 1998 相似文献
10.
A. Saichev D. Sornette 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(3):377-401
We report an empirical determination of the
probability density functions Pdata(r) (and
its cumulative version)
of the number r of earthquakes in finite space-time windows
for the California catalog, over fixed spatial boxes 5 ×5 km2,
20 ×20 km2 and 50 ×50 km2
and time intervals
and 1000 days. The data can
be represented by asymptotic power law tails together with several
cross-overs. These observations are
explained by a simple stochastic branching process previously studied by
many authors, the ETAS (epidemic-type aftershock sequence) model which
assumes that each earthquake can trigger other earthquakes
(“aftershocks”). An aftershock sequence results in this model from the
cascade of aftershocks of each past earthquake. We develop the full
theory in terms of generating functions for describing the space-time
organization of earthquake sequences and develop several approximations
to solve the equations.
The calibration of the theory to the empirical observations
shows that it is essential to augment the ETAS model by taking account
of the pre-existing frozen heterogeneity of spontaneous earthquake
sources. This seems natural in view of the complex multi-scale nature of
fault networks, on which earthquakes nucleate.
Our extended theory is able to account for the empirical
observation but some discrepancies, especially for the shorter time windows,
point to limits of both our theoretical approach and of the ETAS model. 相似文献
11.
We introduce a solid-on-solid growth process which evolves by random deposition of dimers, surface diffusion, and evaporation
of monomers from the edges of plateaus. It is shown that the model exhibits a robust transition from a smooth to a rough phase.
The roughening transition is driven by an absorbing phase transition at the bottom layer of the interface, which displays
the same type of critical behavior as the pair contact process with diffusion 2A↦3A, 2A↦.
Received 14 October 2002 Published online 14 February 2003
RID="a"
ID="a"e-mail: Haye.Hinrichsen@physik.uni-wuppertal.de 相似文献
12.
J.E. Santos U.C. Täuber 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):423-440
Second-order phase transitions in a non-equilibrium liquid-gas model with reversible mode couplings, i.e., model H for binary-fluid critical dynamics, are studied using dynamic field theory and the renormalization group. The system
is driven out of equilibrium either by considering different values for the noise strengths in the Langevin equations describing
the evolution of the dynamic variables (effectively placing these at different temperatures), or more generally by allowing
for anisotropic noise strengths, i.e., by constraining the dynamics to be at different temperatures in d
|| - and d
⊥-dimensional subspaces, respectively. In the first, isotropic case, we find one infrared-stable and one unstable renormalization group fixed point. At the stable fixed point, detailed
balance is dynamically restored, with the two noise strengths becoming asymptotically equal. The ensuing critical behavior
is that of the standard equilibrium model H. At the novel unstable fixed point, the temperature ratio for the dynamic variables
is renormalized to infinity, resulting in an effective decoupling between the two modes. We compute the critical exponents
at this new fixed point to one-loop order. For model H with spatially anisotropic noise, we observe a critical softening only in the d
⊥-dimensional sector in wave vector space with lower noise temperature. The ensuing effective two-temperature model H does
not have any stable fixed point in any physical dimension, at least to one-loop order. We obtain formal expressions for the
novel critical exponents in a double expansion about the upper critical dimension d
c = 4 - d
|| and with respect to d
|| , i.e., about the equilibrium theory.
Received 4 April 2002 Published online 13 August 2002 相似文献
13.
R. Mélin S. Peysson 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):169-176
A Bethe-Peierls treatment to dilution in frustrated magnets and spin liquids is given. A spin glass phase is present at low
temperatures and close to the percolation point as soon as frustration takes a finite value in the dilute magnet model; the
spin glass phase is reentrant inside the ferromagnetic phase. An extension of the model is given, in which the spin glass/ferromagnet
phase boundary is shown not to reenter inside the ferromagnetic phase asymptotically close to the tricritical point whereas
it has a turning point at lower temperatures. We conjecture similar phase diagrams to exist in finite dimensional models not
constraint by a Nishimori's line. We increase frustration to study the effect of dilution in a spin liquid state. This provides
a “minimal” ordering by disorder from an Ising paramagnet to an Ising spin glass.
Received 9 April 1999 and Received in final form 27 September 1999 相似文献
14.
H. Chamati 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(2):241-249
The finite-size critical properties of the (n) vector ϕ4 model, with long-range interaction decaying algebraically with the interparticle distance r like r
-d - σ, are investigated. The system is confined to a finite geometry subject to periodic boundary condition. Special attention
is paid to the finite-size correction to the bulk susceptibility above the critical temperature T
c. We show that this correction has a power-law nature in the case of pure long-range interaction i.e. 0 < σ < 2 and it turns out to be exponential in case of short-range interaction i.e.σ = 2. The results are valid for arbitrary dimension d, between the lower ( d
< = σ) and the upper ( d
> = 2σ) critical dimensions.
Received 2 July 2001 and Received in final form 4 Septembre 2001 相似文献
15.
E. Nogueira Jr. R.F.S. Andrade S. Coutinho 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(3):373-382
The role of the geometric fluctuations on the multifractal properties of the local magnetization of aperiodic ferromagnetic
Ising models on hierarchical lattices is investigated. The geometric fluctuations are introduced by generalized Fibonacci
sequences. The local magnetization is evaluated via an exact recurrent procedure encompassing real space renormalization group decimation. The symmetries of the local magnetization
patterns induced by the aperiodic couplings is found to be strongly (weakly) different, with respect to the ones of the corresponding
homogeneous systems, when the geometric fluctuations are relevant (irrelevant) to change the critical properties of the system.
At the criticality, the measure defined by the local magnetization is found to exhibit a non-trivial F(α) spectra being shifted to higher values of α when relevant geometric fluctuations are considered. The critical exponents
are found to be related with some special points of the F(α) function and agree with previous results obtained by the quite distinct transfer matrix approach.
Received 2 April 2001 and Received in final form 14 August 2001 相似文献
16.
L. Raymond J.-M. Laugier S. Schäfer G. Albinet 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(3):355-364
Binary disordered systems are usually obtained by mixing two ingredients in variable proportions: conductor and insulator,
or conductor and super-conductor. They present very specific properties, in particular the second-order percolation phase
transition, with its fractal geometry and the multi-fractal properties of the current moments. These systems are naturally
modeled by regular bi-dimensional or tri-dimensional lattices, on which sites or bonds are chosen randomly with given probabilities.
The two significant parameters are the ratio h = σ
1/σ of the complex conductances, σ and σ
1, of the two components, and their relative abundances p (or, respectively, 1 - p). In this article, we calculate the impedance of the composite by two independent methods: the so-called spectral method,
which diagonalises Kirchhoff's Laws via a Green function formalism, and the Exact Numerical Renormalization method (ENR). These methods are applied to mixtures of
resistors and capacitors (R-C systems), simulating e.g. ionic conductor-insulator systems, and to composites constituted of resistive inductances and capacitors (LR-C systems),
representing metal inclusions in a dielectric bulk. The frequency dependent impedances of the latter composites present very
intricate structures in the vicinity of the percolation threshold. In this paper, we analyse the LR-C behavior of compounds
formed by the inclusion of small conducting clusters (“n-legged animals”) in a dielectric medium. We investigate in particular their absorption spectra who present a pattern of sharp
lines at very specific frequencies of the incident electromagnetic field, the goal being to identify the signature of each
animal. This enables us to make suggestions of how to build compounds with specific absorption or transmission properties
in a given frequency domain.
Received 16 August 2002 Published online 14 February 2003
RID="a"
ID="a"e-mail: laurent.raymond@l2mp.fr
RID="b"
ID="b"e-mail: steffen.schaefer@l2mp.fr
RID="c"
ID="c"UMR CNRS 6137 相似文献
17.
Y. V. Ivanenko N. I. Lebovka N. V. Vygornitskii 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):469-480
The stochastic Eden model of charged particles aggregation in two-dimensional systems is presented. This model is governed
by the following two parameters: screening length of electrostatic interaction, , and short-range attraction energy, E. Different patterns of finite and infinite aggregates are observed. They are of the following morphology types: linear or
linear with bending, worm-like, DBM (dense-branching morphology), DBM with nucleus, and compact Eden-like. The transition
between the different modes of growth is studied and phase diagram of the growth structures is obtained in co-ordinates. The detailed aggregate structure analysis, including analysis of their scaling properties, is presented. The
scheme of the internal inhomogeneous structure of aggregates is proposed.
Received 2 September 1998 and Received in final form 15 January 1999 相似文献
18.
A nanosecond scale in situ probe reveals that a bulk linear polymer undergoes a sharp phase transition as a function of the degree of conversion, as
it nears the glass transition. The scaling behaviour is in the same universality class as percolation. The exponents γ and
β are found to be 1.7±0.1 and 0.41±0.01 in agreement with the best percolation results in three dimensions.
Received 29 August 2002
RID="a"
ID="a"e-mail: erzan@gursey.gov.tr e-mail: erzan@itu.edu.tr 相似文献
19.
C.B. Yang X. Cai 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(3):375-379
A new type of spatio-temporal correlation function for the process approaching the self-organized criticality is investigated
within the Bak-Sneppen model for biological evolution. In terms of the “directional shorter distance” between the two sites
with minimum fitness at two successive updates, the correlation function is defined and studied numerically for the nearest-
and random-neighbor versions of the model. Qualitatively different behaviors of the jump of the minimal site in the two models
are presented, and the behaviors of the correlation functions are shown also different.
Received 14 April 2001 and Received in final form 28 June 2001 相似文献
20.
M. Bauer O. Golinelli 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(3):339-352
We study both numerically and analytically what happens to a random graph of average connectivity α when its leaves and their
neighbors are removed iteratively up to the point when no leaf remains. The remnant is made of isolated vertices plus an induced
subgraph we call the core. In the thermodynamic limit of an infinite random graph, we compute analytically the dynamics of leaf removal, the number
of isolated vertices and the number of vertices and edges in the core. We show that a second order phase transition occurs
at α = e = 2.718 ... : below the transition, the core is small but above the transition, it occupies a finite fraction of
the initial graph. The finite size scaling properties are then studied numerically in detail in the critical region, and we
propose a consistent set of critical exponents, which does not coincide with the set of standard percolation exponents for
this model. We clarify several aspects in combinatorial optimization and spectral properties of the adjacency matrix of random
graphs.
Received 31 January 2001 and Received in final form 26 June 2001 相似文献