共查询到20条相似文献,搜索用时 15 毫秒
1.
F.A. Tamarit S.A. Cannas C. Tsallis 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(4):545-548
We consider biological evolution as described within the Bak and Sneppen 1993 model. We exhibit, at the self-organized critical
state, a power-law sensitivity to the initial conditions, calculate the associated exponent, and relate it to the recently
introduced nonextensive thermostatistics. The scenario which here emerges without tuning strongly reminds of that of the tuned onset of chaos in say logistic-like one-dimensional maps. We also calculate the dynamical exponent z.
Received: 5 November 1997 / Received in final form: 11 November 1997 / Accepted: 19 November 1997 相似文献
2.
L.-H. Tang P. Smilauer D.D. Vvedensky 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):409-412
Two types of mechanisms are proposed for mound coarsening during unstable epitaxial growth: stochastic, due to deposition
noise, and deterministic, due to mass currents driven by surface energy differences. Both yield the relation H=(RWL)2 between the typical mound height W, mound size L, and the film thickness H. An analysis of simulations and experimental data shows that the parameter R saturates to a value which discriminates sharply between stochastic () and deterministic () coarsening. We derive a scaling relation between the coarsening exponent 1/z and the mound-height exponent which, for a saturated mound slope, yields .
Received: 11 November 1997 / Revised in final form: 28 November 1997 /
Accepted: 28 November 1997 相似文献
3.
E. Del Gado L. de Arcangelis A. Coniglio 《The European physical journal. E, Soft matter》2000,2(4):359-365
Within a recently introduced model based on the bond-fluctuation dynamics, we study the viscoelastic behaviour of a polymer
solution at the gelation threshold. We here present the results of the numerical simulation of the model on a cubic lattice:
the percolation transition, the diffusion properties and the time autocorrelation functions have been studied. From both the
diffusion coefficients and the relaxation times critical behaviour a critical exponent k for the viscosity coefficient has been extracted: the two results are comparable within the errors giving , in close agreement with the Rouse model prediction and with some experimental results. In the critical region below the
transition threshold the time autocorrelation functions show a long-time tail which is well fitted by a stretched exponential
decay.
Received 20 December 1999 and Received in final form 18 February 2000 相似文献
4.
K.J. Wiese 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(3):269-272
The dynamical scaling properties of selfavoiding polymerized membranes with internal dimension D are studied using model A dynamics. It is shown that the theory is renormalizable to all orders in perturbation theory and
that the dynamical scaling exponent z is given by . This result applies especially to membranes (D=2) but also to polymers (D=1).
Received: 5 September 1997 / Accepted: 17 November 1997 相似文献
5.
P. Sen S. Dasgupta D. Stauffer 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(1):107-110
The dynamical critical exponent z of the Ising antiferromagnet under the constraint of a fixed zero magnetization is verified by Monte Carlo simulations to
be compatible with that of the usual Glauber dynamics of model A, while for positive magnetization the exponent seems different.
We also determine the diffusivity of the magnetization and finite size effects.
Received: 18 June 1997 / Revised: 28 July 1997 / Accepted: 13 October 1997 相似文献
6.
E. Rastelli A. Tassi 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(3):341-347
Ferromagnetic spin chains of a hexagonal lattice coupled by a weak antiferromagnetic interaction J1 develop a helix arrangement if the intrachain antiferromagnetic NNN exchange J2 is sufficiently large. We show that the classical minimum energy spin configuration is an umbrella when an external magnetic field is applied. The scenario is dramatically changed by quantum fluctuations. Indeed we find
that the zero point motion forces the spins in a plane containing the magnetic field so that classical expectation is deceptive
for our model. Our result is obtained by controlled expansion in the low field-long wavelength modulation limit.
Received: 9 September 1997 / Revised: 15 October 1997 / Accepted: 17 November 1997 相似文献
7.
L. Bányai H. Haug P. Gartner 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(2):209-213
We compute numerically the time dependent retarded Green function of the polaron within the self-consistent RPA approximation.
The results show an approximately Gaussian behaviour at t=0 changing at later times its concavity to an exponential decay, as it has been predicted in the approximate form of an inverse
hyperbolic cosine function. The result contrasts with the non-selfconsistent RPA, where the exponential decay is only a transitory
behaviour and the asymptotics is rather oscillatory. Our conclusions are significant in the context of the quantum kinetics
with LO-phonons, where the transition from an intitially coherent scattering kinetics to a Markov kinetics with energy conservation
is controlled by the time behaviour of the retarded Green function.
Received: 18 September 1997 / Revised: 24 October 1997 / Accepted: 6 November 1997 相似文献
8.
H. Rieger R. Juhász F. Iglói 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(3):409-412
We study random XY and (dimerized) XX spin-1/2 quantum spin chains at their quantum phase transition driven by the anisotropy and dimerization, respectively. Using
exact expressions for magnetization, correlation functions and energy gap, obtained by the free fermion technique, the critical
and off-critical (Griffiths-McCoy) singularities are related to persistence properties of random walks. In this way we determine
exactly the decay exponents for surface and bulk transverse and longitudinal correlations, correlation length exponent and
dynamical exponent.
Received 26 September 1999 相似文献
9.
S. Cueille C. Sire 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(1):111-127
We define a block persistence probability p
l
(t) as the probability that the order parameter integrated on a block of linear size l has never changed sign since the initial time in a phase-ordering process at finite temperature T<T
c
. We argue that in the scaling limit of large blocks, where z is the growth exponent (), is the global (magnetization) persistence exponent and f(x) decays with the local (single spin) exponent for large x. This scaling is demonstrated at zero temperature for the diffusion equation and the large-n model, and generically it can be used to determine easily from simulations of coarsening models. We also argue that and the scaling function do not depend on temperature, leading to a definition of at finite temperature, whereas the local persistence probability decays exponentially due to thermal fluctuations. These
ideas are applied to the study of persistence for conserved models. We illustrate our discussions by extensive numerical results.
We also comment on the relation between this method and an alternative definition of at finite temperature recently introduced by Derrida [Phys. Rev. E 55, 3705 (1997)].
Received: 25 February 1998 / Revised: 24 July 1998 / Accepted: 27 July 1998 相似文献
10.
M. Reuhl P. Nielaba K. Binder 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(2):225-232
,Static and dynamic properties of the Potts model on the simple cubic lattice with nearest neighbor -interaction are obtained from Monte Carlo simulations in a temperature range where full thermal equilibrium still can be
achieved (). For a lattice size L
= 16, in this range finite size effects are still negligible, but the data for the spin glass susceptibility agree with previous
extrapolations based on finite size scaling of very small lattices. While the static properties are compatible with a zero
temperature transition, they certainly do not prove it. Unlike the Ising spin glass, the decay of the time-dependent order
parameter is compatible with a simple Kohlrausch function, , while a power law prefactor cannot be distinguished. The Kohlrausch exponent y
(
T
) decreases from at [0pt] to at [0pt] however. The relaxation time is compatible with the exponential divergence postulated by McMillan for spin glasses at their lower critical dimension,
but the exponent that can be extracted still differs significantly from the theoretical value, . Thus the present results support the conclusion that the Potts spin glass in d
= 3 dimensions differs qualitatively from the Ising spin glass.
Received: 8 October 1997 / Accepted: 27 November 1997 相似文献
11.
A. Svorenčík F. Slanina 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(4):453-462
Inspired by order-book models of financial fluctuations, we
investigate the Interacting gaps model, which is the schematic
one-dimensional system mimicking the order-book dynamics. We find by
simulations the power-law tail in return distribution, power-law decay
of volatility autocorrelation with exponent 0.5 and Hurst exponent
close to 1/2. Surprisingly, when we make a mean-field
approximation, i.e. replace the one-dimensional system by
effectively infinite-dimensional one, we obtain analytically the
return exponent 5/2, in perfect accord with one-dimensional simulations. 相似文献
12.
H.K. Janssen K. Oerding F. van Wijland H.J. Hilhorst 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(1):137-145
We consider two stochastic processes, the Gribov process and the general epidemic process, that describe the spreading of
an infectious disease. In contrast to the usually assumed case of short-range infections that lead, at the critical point,
to directed and isotropic percolation respectively, we consider long-range infections with a probability distribution decaying
in d dimensions with the distance as . By means of Wilson's momentum shell renormalization-group recursion relations, the critical exponents characterizing the
growing fractal clusters are calculated to first order in an -expansion. It is shown that the long-range critical behavior changes continuously to its short-range counterpart for a decay
exponent of the infection .
Received: 17 July 1998 / Revised: 20 July 1998 / Accepted: 28 July 1998 相似文献
13.
R. Schorr H. Rieger 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(3):347-354
We consider the optimal paths in a d-dimensional lattice, where the bonds have isotropically correlated random weights. These paths can be interpreted as the ground state configuration of a simplified polymer model in a random
potential. We study how the universal scaling exponents, the roughness and the energy fluctuation exponent, depend on the
strength of the disorder correlations. Our numerical results using Dijkstra's algorithm to determine the optimal path in directed
as well as undirected lattices indicate that the correlations become relevant if they decay with distance slower than 1/r in d = 2 and 3. We show that the exponent relation 2ν - ω = 1 holds at least in d = 2 even in case of correlations. Both in two and three dimensions, overhangs turn out to be irrelevant even in the presence
of strong disorder correlations.
Received 20 December 2002 / Received in final form 10 April 2003 Published online 20 June 2003
RID="a"
ID="a"e-mail: schorr@lusi.uni-sb.de 相似文献
14.
T. Schenkel A.V. Barnes A.V. Hamza D.H. Schneider 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(3):297-302
Cluster ion emission from a variety of surfaces upon impact of highly charged ions is investigated by time-of-flight secondary
ion mass spectrometry. The yield of cluster ions as a function of cluster size for and surface follow a power law decline with exponent approaching the -2 limit of the ”equilibrium” and ”shock wave” cluster emission
models. While the decline of the cluster ion emission with cluster size is an exponential decay for highly oriented pyrolytic
graphite upon impact, the decline is more gradual than for impact, such that at the relative cluster yield is 1000 times higher.
Received: 22 April 1997 / Revised: 29 December 1997 / Accepted: 19 January 1998 相似文献
15.
K.J. Wiese 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(3):273-276
The dynamical scaling properties of selfavoiding polymerized membranes with internal dimension D embedded into d dimensions are studied including hydrodynamical interactions. It is shown that the theory is renormalizable to all orders
in perturbation theory and that the dynamical scaling exponent z is given by z=d. The crossover to the region, where the membrane is crumpled swollen but the hydrodynamic interaction irrelevant is discussed.
The results apply as well to polymers (D=1) as to membranes (D=2).
Received: 5 September 1997 / Accepted: 17 November 1997 相似文献
16.
H. Hinrichsen H.M. Koduvely 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):257-264
The local persistence probability P
l
(t) that a site never becomes active up to time t, and the global persistence probability P
g
(t) that the deviation of the global density from its mean value does not change its sign up to time t are studied in a (1+1)-dimensional directed percolation process by Monte-Carlo simulations. At criticality, starting from
random initial conditions, P
l
(t) decays algebraically with the exponent . The value is found to be independent of the initial density and the microscopic details of the dynamics, suggesting is an universal exponent. The global persistence exponent is found to be equal or larger than . This contrasts with previously known cases where . It is shown that in the special case of directed-bond percolation, P
l
(t) can be related to a certain return probability of a directed percolation process with an active source (wet wall).
Received: 15 December 1997 / Revised: 6 April 1998 / Accepted: 29 May 1998 相似文献
17.
K. Ghosh A. Dutta J.K. Bhattacharjee 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):219-221
We calculate using diagrammatic perturbation theory in the two-loop approximation, the specific heat exponent for the classical N-vector model in a random external field for spatial dimension (D) lying between four and six. The calculation supports the modified hyperscaling , where is the correlation length exponent.
Received: 18 March 1998 / Revised: 17 April 1998 / Accepted: 21 April 1998 相似文献
18.
G. Basappa N.V. Madhusudana 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(2):179-187
We present experimental studies on the effect of strong electric fields on the nematogen p-cyanophenyl p-n-heptyl benzoate
which has the strongly polar cyano end group and a large positive dielectric anisotropy. We use a local temperature measurement
to take into account heating effects and an electrical impedance analysis to determine both the dielectric constant () and the resistance (R) of the sample. We also measure the higher harmonic responses of the medium. The new results obtained in this study are: (i)
a detailed temperature dependence of the terms which describe (a) the quenching of macroscopic thermal fluctuations of the
nematic director and (b) the enhancement of the orientational order parameter due to Kerr effect, (ii) clear evidence for
the critical divergence of susceptibility as reflected in the third harmonic signal, (iii) an unusual enhancement of the conductivity
which shows a large peak just below the critical point , (iv) a significant peak in the second harmonic signal at and (v) evidence for a field induced nematic-nematic transition well inside the nematic range. We argue that the results
(iii)-(v) indicate the presence of polar short range order in the medium and hence support a molecular model in which such an order has been proposed.
Received: 15 July 1997 / Received in final form: 24 September 1997 / Accepted: 29 October 1997 相似文献
19.
P. Boccaccio L. Vannucci R.A. Ricci G. Vannini R. Dona I. Massa J.P. Coffin P. Fintz G. Guillaume F. Jundt F. Rami P. Wagner 《The European Physical Journal A - Hadrons and Nuclei》1998,1(4):399-406
We studied the sequential binary decay of the systems 32S+45Sc, 76Ge, 89Y, 59Co, 63Cu and 19F+63Cu induced by collisions at ≃6 MeV·A. The two stages of the process have reaction-times compatible with the dynamics of different mechanisms. The study of the
excitation energy partition shows that the reaction mechanism of the first step has influence on the de-excitation of the
primary fragments producing two decay components which have different time scale.
Received: 25 March 1997 / Revised version: 2 December 1997 相似文献
20.
We present a series of rigorous examples of the Kondo lattice model that exhibit full ferromagnetism in the ground state.
The models are defined in one-, two- and three-dimensional lattices, and are characterized by a range of hopping terms, specific
electron filling, and large ferromagnetic coupling. Our examples show that a sufficient strong but finite exchange coupling
between conduction electrons and localized spins could overcome the competition from mobility of a finite density of electrons
and drive the system from a paramagnetic phase to a ferromagnetic phase. We also establish a relation of ferromagnetism between
the Hubbard model and Kondo lattice model. Meanwhile some rigorous results on ferromagnetism in the corresponding Hubbard
model are presented.
Received: 10 September 1997 / Revised: 15 October 1997 / Accepted: 17 October 1997 相似文献