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1.
J.M. de Araújo F.A. da Costa F.D. Nobre 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):661-667
A spin-1 model, appropriated to study the competition between bilinear (J
ij
S
i
S
j
) and biquadratic (K
ij
S
i
2
S
j
2) random interactions, both of them with zero mean, is investigated. The interactions are infinite-ranged and the replica
method is employed. Within the replica-symmetric assumption, the system presents two phases, namely, paramagnetic and spin-glass,
separated by a continuous transition line. The stability analysis of the replica-symmetric solution yields, besides the usual
instability associated with the spin-glass ordering, a new phase due to the random biquadratic couplings between the spins.
Received 18 May 1999 and Received in final form 20 October 1999 相似文献
2.
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
3.
K.J. Wiese M. Kardar 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):187-190
We introduce a generalization of the O(N) field theory to N-colored membranes of arbitrary inner dimension D. The O(N) model is obtained for , while leads to self-avoiding tethered membranes (as the O(N) model reduces to self-avoiding polymers). The model is studied perturbatively by a 1-loop renormalization group analysis,
and exactly as .Freedom to choose the expansion point D, leads to precise estimates of critical exponents of the O(N) model. Insights gained from this generalization include a conjecture on the nature of droplets dominating the 3d-Ising model at criticality; and the fixed point governing the random bond Ising model.
Received: 15 October 1998 / Accepted: 4 November 1998 相似文献
4.
S. Galam A. Mauger 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(2):255-258
An universal invariant for site and bond percolation thresholds ( and respectively) is proposed. The invariant writes where and are positive constants, and d the space dimension. It is independent of the coordination number, thus exhibiting a topology invariance at any d. The formula is checked against a large class of percolation problems, including percolation in non-Bravais lattices and
in aperiodic lattices as well as rigid percolation. The invariant is satisfied within a relative error of for all the twenty lattices of our sample at d=2, d=3, plus all hypercubes up to d=6.
Received: 7 July 1997 / Accepted: 5 November 1997 相似文献
5.
A.E. Allahverdyan Th.M. Nieuwenhuizen D.B. Saakian 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):317-335
In a p-spin interaction spherical spin-glass model both the spins and the couplings are allowed to change with time. The spins are
coupled to a heat bath with temperature T, while the coupling constants are coupled to a bath having temperature TJ. In an adiabatic limit (where relaxation time of the couplings is much larger that of the spins) we construct a generalized
two-temperature thermodynamics. It involves entropies of the spins and the coupling constants. The application for spin-glass
systems leads to a standard replica theory with a non-vanishing number of replicas, n=T/T
J
. For p>2 there occur at low temperatures two different glassy phases, depending on the value of n. The obtained first-order transitions have positive latent heat, and positive discontinuity of the total entropy. This is
an essentially non-equilibrium effect. The dynamical phase transition exists only for n<1. For p=2 correlation of the disorder (leading to a non-zero n) removes the known marginal stability of the spin glass phase. If the observation time is very large there occurs no finite-temperature
spin glass phase. In this case there are analogies with the non-equilibrium (aging) dynamics. A generalized fluctuation-dissipation
relation is derived.
Received 12 July 1999 and Received in final form 8 December 1999 相似文献
6.
H. Chamati D.M. Danchev N.S. Tonchev 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):307-316
A d-dimensional quantum model system confined to a general hypercubical geometry with linear spatial size L and “temporal size” 1/T ( T - temperature of the system) is considered in the spherical approximation under periodic boundary conditions. For a film
geometry in different space dimensions , where is a parameter controlling the decay of the long-range interaction, the free energy and the Casimir amplitudes are given.
We have proven that, if , the Casimir amplitude of the model, characterizing the leading temperature corrections to its ground state, is . The last implies that the universal constant of the model remains the same for both short, as well as long-range interactions, if one takes the normalization factor for
the Gaussian model to be such that . This is a generalization to the case of long-range interaction of the well-known result due to Sachdev. That constant differs
from the corresponding one characterizing the leading finite-size corrections at zero temperature which for is .
Received 3 June 1999 and Received in final form 16 August 1999 相似文献
7.
J. Kaupužs R. Mahnke 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):793-800
A stochastic approach based on the Master equation is proposed to describe the process of formation and growth of car clusters
in traffic flow in analogy to usual aggregation phenomena such as the formation of liquid droplets in supersaturated vapour.
By this method a coexistence of many clusters on a one-lane circular road has been investigated. Analytical equations have
been derived for calculation of the stationary cluster distribution and related physical quantities of an infinitely large
system of interacting cars. If the probability per time (or p) to decelerate a car without an obvious reason tends to zero in an infinitely large system, our multi-cluster model behaves
essentially in the same way as a one-cluster model studied before. In particular, there are three different regimes of traffic
flow (free jet of cars, coexisting phase of jams and isolated cars, highly viscous heavy traffic) and two phase transitions
between them. At finite values of p the behaviour is qualitatively different, i.e., there is no sharp phase transition between the free jet of cars and the coexisting phase. Nevertheless, a jump-like phase
transition between the coexisting phase and the highly viscous heavy traffic takes place both at and at a finite p. Monte-Carlo simulations have been performed for finite roads showing a time evolution of the system into the stationary
state. In distinction to the one-cluster model, a remarkable increasing of the average flux has been detected at certain densities
of cars due to finite-size effects.
Received 17 September 1999 相似文献
8.
X.S. Chen V. Dohm D. Stauffer 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):699-704
Using field theory and Monte Carlo (MC) simulation we investigate the finite-size effects of the magnetization M for the three-dimensional Ising model in a finite cubic geometry with periodic boundary conditions. The field theory with
infinite cutoff gives a scaling form of the equation of state where is the reduced temperature, h is the external field and L is the size of system. Below and at the theory predicts a nonmonotonic dependence of f(x,y) with respect to at fixed and a crossover from nonmonotonic to monotonic behaviour when y is further increased. These results are confirmed by MC simulation. The scaling function f(x,y) obtained from the field theory is in good quantitative agreement with the finite-size MC data. Good agreement is also found
for the bulk value at .
Received 20 July 1999 and Received in final form 11 November 1999 相似文献
9.
D.H.E. Gross E.V. Votyakov 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):115-126
Traditionally, phase transitions are defined in the thermodynamic limit only. We discuss how phase transitions of first order
(with phase separation and surface tension), continuous transitions and (multi)-critical points can be seen and classified
for small systems. “Small” systems are systems where the linear dimension is of the characteristic range of the interaction
between the particles; i.e. also astrophysical systems are “small” in this sense. Boltzmann defines the entropy as the logarithm of the area of the surface in the mechanical N-body phase space at total energy E. The topology of S(E,N) or more precisely, of the curvature determinant allows the classification of phase transitions without taking the thermodynamic limit. Micro-canonical thermo-statistics
and phase transitions will be discussed here for a system coupled by short range forces in another situation where entropy
is not extensive. The first calculation of the entire entropy surface S(E,N) for the diluted Potts model (ordinary (q=3)-Potts model plus vacancies) on a square lattice is shown. The regions in {E,N} where D>0 correspond to pure phases, ordered resp. disordered, and D<0 represent transitions of first order with phase separation and “surface tension”. These regions are bordered by a line
with D=0. A line of continuous transitions starts at the critical point of the ordinary (q=3)-Potts model and runs down to a branching point Pm. Along this line vanishes in the direction of the eigenvector of D with the largest eigen-value . It characterizes a maximum of the largest eigenvalue . This corresponds to a critical line where the transition is continuous and the surface tension disappears. Here the neighboring
phases are indistinguishable. The region where two or more lines with D=0 cross is the region of the (multi)-critical point. The micro-canonical ensemble allows to put these phenomena entirely
on the level of mechanics.
Received 18 October 1999 and received in final form 17 November 1999 相似文献
10.
F. Baffioni F. Rosati 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(3):439-447
The mean field spin glass model is analyzed by a combination of exact methods and a simple Ansatz. The method exploited is general, and can be applied to others disordered mean field models such as, e.g., neural networks. It is well known that the probability measure of overlaps among replicas carries the whole physical content
of these models. A functional order parameter of Parisi type is introduced by rigorous methods, according to previous works
by F. Guerra. By the Ansatz that the functional order parameter is the correct order parameter of the model, we explicitly find the full overlap distribution.
The physical interpretation of the functional order parameter is obtained, and ultrametricity of overlaps is derived as a
natural consequence of a branching diffusion process. It is shown by explicit construction that ultrametricity of the 3-replicas
overlap distribution together with the Ghirlanda-Guerra relations determines the distribution of overlaps among s replicas, for any s, in terms of the one-overlap distribution.
Received 14 February 2000 相似文献
11.
F.A. da Costa J.M de Araújo 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(2):313-316
The zero-temperature TAP equations for the spin-1 Ghatak-Sherrington model are investigated. The spin-glass energy density
(ground state) is determined as a function of the anisotropy crystal field D for a large number of spins. This allows us to locate a first-order transition between the spin-glass and paramagnetic phases
within a good accuracy. The total number of solutions is also determined as a function of D.
Received 25 November 1999 相似文献
12.
13.
L. Zhang W. L. Zhong C. L. Wang Y. P. Peng Y. G. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):565-573
The size effect of the dielectric properties and the barrier height was investigated in the ferroelectric solid solution BaxSr1-xTiO3 system. The decrease of the grain size causes the suppression of the ferroelectricity, and the increase of the relaxation
frequency. Barrier heights increase with increasing grain size. The result is analogous to magnetic phase transitions in nanocrystals
and other solid-solid phase transitions in nanocrystals. It suggests a general rule that may be of use in the discovery of
new metastable phases. An explanation of this phenomenon was given by an electric potential model that agrees well with the
experimental results. For BaxSr1-xTiO3 system, the decrease of xcauses the decrease of the barrier height.
Received 3 August 1998 and Received in final form 22 November 1998 相似文献
14.
O. Golinelli 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):145-155
We study the statistics of meanders, i.e. configurations of a road crossing a river through n bridges, and possibly winding around the source, as a toy model for compact folding of polymers. We introduce a Monte-Carlo
method which allows us to simulate large meanders up to n=400. By performing large n extrapolations, we give asymptotic estimates of the connectivity per bridge R=3.5018(3), the configuration exponent , the winding exponent and other quantities describing the shape of meanders.
Received 21 June 1999 相似文献
15.
X.S. Chen V. Dohm 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):687-703
We reexamine the range of validity of finite-size scaling in the lattice model and the field theory below four dimensions. We show that general renormalization-group arguments based on the renormalizability of
the theory do not rule out the possibility of a violation of finite-size scaling due to a finite lattice constant and a finite
cutoff. For a confined geometry of linear size L with periodic boundary conditions we analyze the approach towards bulk critical behavior as at fixed for where is the bulk correlation length. We show that for this analysis ordinary renormalized perturbation theory is sufficient. On
the basis of one-loop results and of exact results in the spherical limit we find that finite-size scaling is violated for
both the lattice model and the field theory in the region . The non-scaling effects in the field theory and in the lattice model differ significantly from each other.
Received 5 February 1999 相似文献
16.
17.
M. Stebelski M. Lisowski E. Zipper 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(2):215-222
Quantum coherence of electrons interacting via the magnetostatic coupling and confined to a mesoscopic cylinder is discussed. The electromagnetic response of a system is
studied. It is shown that the electromagnetic kernel has finite low frequency limit what implies infinite conductivity. It
means that part of the electrons is in a coherent state and the system can be in general described by a two-fluid model. The
coherent behavior is determined by the interplay between finite size effects and the correlations coming from the magnetostatic
interactions (the interaction is considered in the mean field approximation). The related persistent currents depend on the
geometry of the Fermi surface. If the Fermi surface has some flat portions the self-sustaining currents can be obtained. The
relation of the quantum coherent state in mesoscopic cylinders to other coherent phenomena is discussed.
Received: 9 July 1997 / Revised: 19 September 1997 / Accepted: 4 November 1997 相似文献
18.
M. Leadbeater R.A. Römer M. Schreiber 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(4):643-652
We present calculations of the localisation length, , for two interacting particles (TIP) in a one-dimensional random potential, presenting its dependence on disorder, interaction
strength U and system size. is computed by a decimation method from the decay of the Green function along the diagonal of finite samples. Infinite sample
size estimates are obtained by finite-size scaling. For U=0 we reproduce approximately the well-known dependence of the one-particle localisation length on disorder while for finite
U, we find that with varying between and . We test the validity of various other proposed fit functions and also study the problem of TIP in two different random potentials
corresponding to interacting electron-hole pairs. As a check of our method and data, we also reproduce well-known results
for the two-dimensional Anderson model without interaction.
Received 19 June 1998 and Received in final form 29 October 1998 相似文献
19.
S. Krishnamurthy A. Tanguy S. Roux 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):149-153
The depinning transition of a front moving in a time-independent random potential is studied. The temporal development of
the overall roughness w(L,t) of an initially flat front, , is the classical means to have access to the dynamic exponent. However, in the case of front propagation in quenched disorder
via extremal dynamics, we show that the initial increase in front roughness implies an extra dependence over the system size
which comes from the fact that the activity is essentially localized in a narrow region of space. We propose an analytic expression
for the exponent and confirm this for different models (crack front propagation, Edwards-Wilkinson model in a quenched noise etc.).
Received 27 August 1999 相似文献
20.
S. De Toro Arias X. Waintal J.-L. Pichard 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):149-158
The interplay between the quantum interferences responsible for one particle localization over a length L1, and the partial dephasing induced by a local interaction of strength U with another particle leading to partial delocalization over a length L
2
> L
1
, is illustrated by a study of the motion of two particles put close to each other at the initial time. Localization is reached
in two steps. First, before the time t1 necessary to propagate over L1, the interaction slows down the ballistic motion. On the contrary, after t1 the interaction favors a very slow delocalization, characterized by a spreading of the center of mass, until L2 is reached. This slow motion is related to the absence of quantum chaos in this one dimensional model, the interaction being
only able to induce weaker chaos with critical spectral statistics. Under appropriate initial conditions, the motion remains
invariant under the duality transformation mapping the behavior at small U onto the behavior at large U.
Received 24 August 1998 相似文献