共查询到20条相似文献,搜索用时 15 毫秒
1.
We investigate kinetics of nematic-isotropic transition by solving the hydrodynamic equations for the nematic tensor order parameter and the fluid velocity in two space dimension (x-y plane). Numerical results indicate that nematic directors tend to align parallel to the x-y plane when hydrodynamic flow is incorporated. Late stage growth exponents, for the correlation length and for the number of topological defects, are not significantly altered by hydrodynamic flow. However, in contrast to the case
without flow, the relation holds well, which may indicate the validity of dynamical scaling for the case with hydrodynamic flow.
Received: 8 September 1997 / Received in final form: 23 October 1997 /Accepted: 3 November 1997 相似文献
2.
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
3.
M. Henkel D. Karevski 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):787-792
The effect of point defects on persistent currents in mesoscopic rings is studied in a simple tight-binding model. Using an
analogy with the treatment of the critical quantum Ising chain with defects, conformal invariance techniques are employed
to relate the persistent current amplitude to the Hamiltonian spectrum just above the Fermi energy. From this, the dependence
of the current on the magnetic flux is found exactly for a ring with one or two point defects. The effect of an aperiodic
modulation of the ring, generated through a binary substitution sequence, on the persistent current is also studied. The flux-dependence
of the current is found to vary remarkably between the Fibonacci and the Thue-Morse sequences.
Received: 4 March 1998 / Revised: 20 April 1998 / Accepted: 30 April 1998 相似文献
4.
H. Hinrichsen M. Howard 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(4):635-643
We introduce a model for the spreading of epidemics by long-range infections and investigate the critical behaviour at the
spreading transition. The model generalizes directed bond percolation and is characterized by a probability distribution for
long-range infections which decays in d spatial dimensions as . Extensive numerical simulations are performed in order to determine the density exponent and the correlation length exponents and for various values of . We observe that these exponents vary continuously with , in agreement with recent field-theoretic predictions. We also study a model for pairwise annihilation of particles with
algebraically distributed long-range interactions.
Received: 4 September 1998 / Accepted: 22 September 1998 相似文献
5.
We have performed small angle neutron scattering experiments on the binary fluid mixture n-C6H14+n-C8F18 imbibed inside porous Vycor glass in the thermodynamic region corresponding to the bulk critical one. The resulting structure
can be represented as the sum of a temperature dependent Lorentzian term and a term describing the interference between the
porous matrix, a shell part richer in one component coating the glass surface, and a core part richer in the other component.
We observe critical fluctuations extending over distances markedly larger than the mean pore size.
Received 20 May 1999 相似文献
6.
B. Borštnik D. Lukman 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(1):113-117
Properties of clusters appearing in the site percolation problem on square and cubic lattices are expressed in a way that
emphasizes the thermodynamic analogy. It is shown that the analog of the specific heat exhibits expected critical behaviour
as a function of the analog of the temperature. The results support the notion that the partition of the specific heat of
Ising systems (Borstnik and Lukman, Phys. Rev. E 60, 2595 (1999)) into the structural and populational component is a meaningful one. Another cluster property which is taken
under the scrutiny is the fractal dimensionality of clusters which also indicates the presence of phase transition.
Received 31 August 1999 and Received in final form 14 February 2000 相似文献
7.
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
8.
A. Rosowsky 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):77-86
An analytical method to compute the site percolation threshold is introduced. This method yields an approximate value of larger or equal to the real value. As examples, the computation of is presented for 4 lattices in 2 dimensions: square, triangular, honeycomb and kagome. The results obtained are 0.592 871
6, 0.5, 0.765 069, 0.654 653 7, to be compared with the real values 0.592 746 0, 0.5, 0.697 043, 0.652 703 6. The method is
not limited to 2 dimensions.
Received 27 July 1999 and Received in final form 29 November 1999 相似文献
9.
E. Brézin C. De Dominicis 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):71-76
The field theory of a short range spin glass with Gaussian random interactions, is considered near the upper critical dimension
six. In the glassy phase, replica symmetry breaking is accompanied with massless Goldstone modes, generated by the breaking
of reparametrization invariance of a Parisi type solution. Twisted boundary conditions are thus imposed at two opposite ends
of the system in order to study the size dependence of the twist free energy. A loop-expansion is performed to first order
around a twisted background. It is found, as expected but it is non trivial, that the theory does renormalize around such
backgrounds, as well as for the bulk. However two main differences appear, in comparison with simple ferromagnetic transitions:
(i) the loop expansion yields a (negative) anomaly in the size dependence of the free energy, thereby lifting the lower critical
dimension to a value greater than two (ii) the free energy is lowered by twisting the boundary conditions. This situation
is common in spin glasses, reflecting the non-positivity of mode multiplicity in replica symmetry breaking, but its physical
meaning is still unclear.
Received 12 April 2002 / Received in final form 30 July 2002 Published online 19 November 2002 相似文献
10.
E. Canessa 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(4):591-594
We make an attempt to map a simple economically motivated model for price evolution [J. Phys. A 33, 3637 (2000)] to the phenomenological renormalization group scaling of stock markets. This mapping gives insight into the
critical exponents and the renormalization group predictions for the log-periodic oscillations preceding some stock market
crashes from the perspective of non-linear changes in `the level of stock'.
Received 7 August 2000 相似文献
11.
Y. Y. Tarasevich V. A. Cherkasova 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(1):97-100
We consider site percolation of dimers (“needles”) on simple cubic lattice. The percolation threshold is estimated as pc
perc ≈ 0.2555 ± 0.0001. The jamming threshold is estimated as pc
jamm = 0.799 ± 0.002. 相似文献
12.
On the genre-fication of music: a percolation approach 总被引:1,自引:0,他引:1
R. Lambiotte M. Ausloos 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(1-2):183-188
We analyze web-downloaded data on
people
sharing their music library. By attributing to each music group usual music genres (Rock, Pop ...),
and analysing correlations between music groups of different genres with percolation-idea based methods,
we probe the reality of these subdivisions and construct a music genre cartography, with a tree representation. We also discuss
an alternative objective way to classify music, that is based on the complex structure of the groups audience. Finally, a
link is drawn with the theory of hidden variables in complex networks. 相似文献
13.
D. Daboul I. Chang A. Aharony 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):303-316
We study the site and bond quantum percolation model on the two-dimensional square lattice using series expansion in the low
concentration limit. We calculate series for the averages of , where T
ij
(E) is the transmission coefficient between sites i and j, for k=0, 1, , 5 and for several values of the energy E near the center of the band. In the bond case the series are of order p14 in the concentration p(some of those have been formerly available to order p10) and in the site case of order p16. The analysis, using the Dlog-Padé approximation and the techniques known as M1 and M2, shows clear evidence for a delocalization
transition (from exponentially localized to extended or power-law-decaying states) at an energy-dependent threshold p
q(E) in the range , confirming previous results (e.g.
and for bond and site percolation) but in contrast with the Anderson model. The divergence of the series for different kis characterized by a constant gap exponent, which is identified as the localization length exponent from a general scaling assumption. We obtain estimates of . These values violate the bound of Chayes et al.
Received 28 February 2000 相似文献
14.
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
15.
A. Gadomski 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):569-571
In this Rapid Note, we show that the problem of growth of molecular superlattice in a fully hydrated dipalmitoylphosphatidylcholine (DPPC) membrane
during the gel-to-subgel phase transformation process is a problem of time scale. There are, in fact, two time scales. The
first is an “integrated” or, in some sense, stagnant time scale, that reflects the well-known isotropic growth effect in the
d-dimensional space, but assigns the problem to be still in a category of Debye relaxation kinetics. The fraction of old (parent)
phase does not suit the Paley-Wiener criterion for relaxation functions, and the time behavior is exclusively due to the geometrical
characteristics of the kinetic process. The second (multi-instantaneous) time scale, in turn, is recognised to be a “broken”
(fractional time derivative) or memory-feeling (dynamic) scale, which carries some very essential physics of the phenomenon
under study, and classifies the problem to be of non-Debye (viz., stretched exponential) nature. It may, in principle, contain all the important effects, like small scale coexistence, presence
of collisions between domains, with possible annihilation and creation of domain boundaries, and/or a headgroup packing, hydration
against lipid mobility behavior, and finally, a multitude of quasi-crystalline states. It turns out, that within the range
of validity of the dynamic scale approximation proposed, the criterion for relaxation functions is very well fulfilled.
Received 30 November 1998 相似文献
16.
On social percolation and small world network 总被引:1,自引:0,他引:1
E. Ahmed H.A. Abdusalam 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):569-571
The social percolation model is generalized to include the propagation of two mutually exclusive competing effects on a one-dimensional
ring and a two-dimensional square lattice. It is shown that the result depends significantly on which effect propagates first
i.e. it is a non-commutative phenomenon. Then the propagation of one effect is studied on a small network. It generalizes the
work of Moore and Newman of a disease spread to the case where the susceptibility of the population is random. Three variants
of the Domany-Kinzel model are given. One of them (delayed) does not have a chaotic region for some value of the delay weight.
Received 24 February 2000 相似文献
17.
A.A. Tarasenko F. Nieto L. Jastrabík C. Uebing 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(2):311-322
A two-dimensional lattice-gas model with square symmetry is investigated by using the real-space renormalization group (RSRG)
approach with blocks of different size and symmetries. It has been shown that the precision of the method depends strongly
not only on the number of sites in the block but also on its symmetry. In general, the accuracy of the method increases with
the number of sites in the block. The minimal relative error in determining the critical values of the interaction parameters
is equal to . Using the RSRG method, we have explored phase diagrams of both a two-dimensional Ising spin model and of a square lattice
gas with lateral interactions between adparticles. We also have investigated the influence of the attractive and repulsive
interactions on both the thermodynamic properties of the lattice gas and the diffusion of adsorbed particles over surface.
We have calculated adsorption isotherms and coverage dependences of the pair correlation function, isothermal susceptibility
and the chemical diffusion coefficient. In addition, we have included in our analysis the interaction of the activated particle
in the saddle point with its nearest neighbors. We have also used Monte Carlo (MC) technique to calculate these dependences.
Despite the fact that both methods constitute very different approaches, the correspondence of the numerical data is surprisingly
good. Therefore, we conclude that the RSRG approach can be applied to characterize the thermodynamic and kinetic properties
of systems of particles with strong lateral interactions.
Received 1st September 1998 and Received in final form 8 March 2000 相似文献
18.
Summary By means of a well-developed method in self-organized criticality, we can obtain the lower bound for the percolation threshold
(p
c) of the corresponding site percolation problem. In some special cases, we have proved that such lower bounds are indeed the
percolation thresholds. We can reproduce some well-known percolation thresholds of various lattices including the Cayley trees
and Kock curves in this framework. 相似文献
19.
F. Iglói D. Karevski H. Rieger 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):613-625
We consider cooperative processes (quantum spin chains and random walks) in one-dimensional fluctuating random and aperiodic
environments characterized by fluctuating exponents . At the critical point the random and aperiodic systems scale essentially anisotropically in a similar fashion: length (L) and time (t) scales are related as . Also some critical exponents, characterizing the singularities of average quantities, are found to be universal functions
of , whereas some others do depend on details of the distribution of the disorder. In the off-critical region there is an important
difference between the two types of environments: in aperiodic systems there are no extra (Griffiths)-singularities.
Received: 5 February 1998 / Accepted: 17 April 1998 相似文献
20.
S. Müller L. Schäfer 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):351-369
We give a detailed analysis of the intersection properties of polymers. Using the renormalization group we provide a full
crossover function for the dependence of the number of intersections in a single polymer on chain length and excluded volume
strength. We compare our results with Monte-Carlo data and with exact calculations for a random walk, finding good agreement
in all respects. Restricting to the vicinity of the eight ternary fixed points we also calculate the number of intersections
between two chains placed at a fixed distance, including the two halves of a block-copolymer. The analysis of these systems
confirms the interpretation of the different contributions to the number of intersections in a single chain. Due to the highly
nontrivial character of the correlations in a polymer chain the correction exponents in both cases however are different.
None of the results can be extracted from any Flory-type estimate.
Received: 1 April 1997 / Revised: 24 October 1997 /
Accepted: 29 January 1998 相似文献