共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
3.
I. Tifrea M. Crisan 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(2):175-178
We derive the jump in the specific heat at T=T
c
for a superconductor in a non-Fermi liquid model. We took into consideration the two possible limits in this problem: the
spin-charge separation model for a Fermi liquid and the usual non-Fermi liquid model which satisfies the homogeneity relation
for the spectral function , ). We also derive the order parameter behavior for these two cases in the vecinity of the critical temperature.
Received: 25 January 1998 / Revised: 25 March 1998 / Accepted: 25 March 1998 相似文献
4.
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
5.
Two cellular automata models with directed mass flow and internal time scales are studied by numerical simulations. Relaxation
rules are a combination of probabilistic critical height (probability of toppling p) and deterministic critical slope processes with internal correlation time tc equal to the avalanche lifetime, in model A, and ,in model B. In both cases nonuniversal scaling properties of avalanche distributions are found for , where is related to directed percolation threshold in d=3. Distributions of avalanche durations for are studied in detail, exhibiting multifractal scaling behavior in model A, and finite size scaling behavior in model B,
and scaling exponents are determined as a function of p. At a phase transition to noncritical steady state occurs. Due to difference in the relaxation mechanisms, avalanche statistics
at approaches the parity conserving universality class in model A, and the mean-field universality class in model B. We also
estimate roughness exponent at the transition.
Received: 29 May 1998 / Revised: 8 September 1998 / Accepted: 10 September 1998 相似文献
6.
D. Loison K.D. Schotte 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):735-743
The nature of the phase transition for the XY stacked triangular antiferromagnet (STA) is a controversial subject at present. The field theoretical renormalization group
(RG) in three dimensions predicts a first order transition. This prediction disagrees with Monte-Carlo (MC) simulations which
favor a new universality class or a tricritical transition. We simulate by the Monte-Carlo method two models derived from
the STA by imposing the constraint of local rigidity which should have the same critical behavior as the original model. A
strong first order transition is found. Following Zumbach we analyze the second order transition observed in MC studies as
due to a fixed point in the complex plane. We review the experimental results in order to clarify the critical behavior observed.
Received: 18 February 1998 / Revised: 24 April 1998 / Accepted: 30 April 1998 相似文献
7.
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
8.
B. Lobe W. Janke K. Binder 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):283-291
We analyze recently extended high-temperature series expansions for the “Edwards-Anderson” spin-glass susceptibility of the
p-state Potts glass model on d-dimensional hypercubic lattices for the case of a symmetric bimodal distribution of ferro- and antiferromagnetic nearest-neighbor
couplings . In these star-graph expansions up to order 22 in the inverse temperature , the number of Potts states p and the dimension d are kept as free parameters which can take any value. By applying several series analysis techniques to the new series expansions,
this enabled us to determine the critical coupling Kc and the critical exponent of the spin-glass susceptibility in a large region of the two-dimensional (p,d)-parameter space. We discuss the thus obtained information with emphasis on the lower and upper critical dimensions of the
model and present a careful comparison with previous estimates for special values of p and d.
Received: 25 May 1998 / Revised and Accepted: 11 August 1998 相似文献
9.
F. Schinagl H. Iro R. Folk 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(1):113-123
Within mean field approximation we investigate the phase diagrams of magnetic fluids in presence of a magnetic field. In a
finite field the magnetic phase transition is absent, but instead a line of first order liquid-liquid transitions ending in
a critical point occurs for a magnetic interaction, which is sufficiently strong. Varying the magnetic field these critical
points extend from the tricritical point at H=0 to a critical endpoint. For a fluid with Ising spins we calculate the critical lines and several tricritical exponents
analytically. For Heisenberg fluids we obtain the phase diagrams from a numerical solution of the mean field equations of
state.
Received 20 March 1998 相似文献
10.
Y. Shimizu S. Sawada K.S. Ikeda 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(3):365-372
“Spontaneous alloying” observed by Yasuda, Mori et al. for metallic small clusters is simulated using classical Hamiltonian dynamics. Very rapid alloying occurs homogeneously and
cooperatively starting from the solid phase of the cluster if the heat of solution is negative and the size of cluster is
less than a critical size. Analysis of 2D models reveals that the alloying rate obeys an Arrhenius-type law, which predicts
the alloying time much less than second at room temperature. Evidences manifesting that the spontaneous alloying proceeds in the solid phase without melting are
also presented. The simulation reproduces the essential features of the experiments.
Received: 2 March 1998 / Revised: 21 May 1998 / Accepted: 28 May 1998 相似文献
11.
We derive the high temperature series expansions for the two relaxation times of the single spin-flip kinetic Ising model on the square lattice. The series for the linear relaxation time
l
is obtained with 20 non-trivial terms, and the analysis yields 2.183±0.005 as the value of the critical exponent
l
, which is equal to the dynamical critical exponentz in the two-dimensional case. For the non-linear relaxation time we obtain 15 non-trivial terms, and the analysis leads to the results
nl
= 2.08 ± 0.07. The scaling relation
l
–
nl
= ( being the exponent of the order parameter) seems to be fulfilled, though the error bars of
nl
are still quite substantial. In addition, we obtain the series expansion of the linear relaxation time on the honeycomb lattice with 22 non-trivial terms. The result for the critical exponent is close to the value obtained on the square lattice, which is expected from universality. 相似文献
12.
J. Mertz 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,3(1):53-66
We present a simple model for calculating the fluorescence generated by the multi-photon excitation (MPE) of molecules in
solution. The model takes into account internal molecular dynamics such as ground-state depletion due to inter-system crossing
(ISC), as well as external molecular dynamics associated with diffusion into and out of an excitation volume confined in 3-dimensions.
Internal and external molecular dynamics are combined by using a technique of linearization of a modified diffusion equation
which takes into account the possibility of concentration depletion due to photobleaching. In addition, we discuss the phenomenon
of pulse saturation which effectively limits the molecular excitation rate constant in the case of short pulsed excitation.
Our results are specifically applied in the context of fluorescence autocorrelation functions and single-molecule detection.
In the latter case, we discuss some consequences of high-order multi-photon photobleaching. Finally, we include three appendices
to rigorously define the temporal and spatial profiles of an arbitrary excitation beam, and also to discuss some properties
of an exact evaluation of concentration depletion due to photobleaching.
Received: 9 March 1998 / Accepted: 20 April 1998 相似文献
13.
V. Korepin N. Slavnov 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):555-557
We discovered a simple quadratic equation, which relates scattering phases of particles on Fermi surface. We consider one-dimensional
Bose gas and XXZ Heisenberg quantum spin chain.
Received: 4 December 1997 / Accepted: 17 March 1998 相似文献
14.
A. Volmer U. Seifert R. Lipowsky 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):811-823
Wetting phenomena, molecular protrusions of lipid bilayers and membrane stacks under lateral tension provide physical examples
for interacting surfaces with tension. Such surfaces are studied theoretically using functional renormalization and Monte-Carlo
simulations. The critical behavior arising from thermally-excited shape fluctuations is determined both for global quantities
such as the mean separation of these surfaces and for local quantities such as the probabilities for local contacts.
Received: 30 January 1998 / Accepted: 17 March 1998 相似文献
15.
We propose an identification of the conformal field theory underlying Lipatov's spin-chain model of high-energy scattering
in perturbative QCD. It is a twisted N = 2 supersymmetric topological field theory, which arises as the limiting case of the SL(2,R)/U(1) non-linear model that also plays a role in describing the Quantum Hall effect and black holes in string theory. The doubly-infinite
set of non-trivial integrals of motion of the high-energy spin-chain model displayed by Faddeev and Korchemsky are identified
as the Cartan subalgebra of a bosonic sub-symmetry possessed by this topological theory. The renormalization group and an analysis of instanton perturbations
yield some understanding why this particular topological spin-chain model emerges in the high-energy limit, and provide a
new estimate of the asymptotic behaviour of multi-Reggeized-gluon exchange.
Received: 31 August 1998 / Published online: 11 March 1999 相似文献
16.
We present an analytical approach of the dynamics of a polymer when it is quenched from a solvent into a good or bad solvent. The dynamics is studied by means of a Langevin equation, first in the absence of hydrodynamic
effect, then taking into account the hydrodynamic interactions with the solvent. The variation of the radius of gyration is
studied as a function of time. In both cases, for the first stage of collapse or swelling, the evolution is described by a
power law with a characteristic time proportional to N
4/3
(N), where N is the number of monomers, without (with) hydrodynamic interactions. At larger times, scaling laws are derived for the diffusive
relaxation time.
Received: 10 March 1998 / Received in final form: 15 September 1998 / Accepted: 25 September 1998 相似文献
17.
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
18.
G. Chaboussant M.-H. Julien Y. Fagot-Revurat M. Hanson L.P. Lévy C. Berthier M. Horvatic O. Piovesana 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(2):167-181
In a magnetic field, spin-ladders undergo two zero-temperature phase transitions at the critical fields Hc1 and Hc2. An experimental review of static and dynamical properties of spin-ladders close to these critical points is presented. The
scaling functions, universal to all quantum critical points in one-dimension, are extracted from (a) the thermodynamic quantities
(magnetization) and (b) the dynamical functions (NMR relaxation). A simple mapping of strongly coupled spin ladders in a magnetic
field on the exactly solvable XXZ model enables to make detailed fits and gives an overall understanding of a broad class of quantum magnets in their gapless
phase (between Hc1 and Hc2). In this phase, the low temperature divergence of the NMR relaxation demonstrates its Luttinger liquid nature as well as
the novel quantum critical regime at higher temperature. The general behavior close these quantum critical points can be tied
to known models of quantum magnetism.
Received: 13 March 1998 / Received in final form and Accepted: 21 July 1998 相似文献
19.
X.-M. Hu J.-S. Peng 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(2):291-299
On the basis of the nondegenerate quantum-beat laser model, we introduce a coherent field which drives the transition between the upper lasing level and an
auxiliary level. We demonstrate that such a four-level system can produce squeezed two-mode laser without and with inversion.
When the laser is operated well above threshold, the intensity fluctuation in the average mode is reduced below the shot noise
with an optimum Mandel parameter Q=- 1/2. At the same time, the noises in the relative amplitude and the relative phase drop to their vaccum noise levels. Furthermore,
regardless of inversion, noninversion, and transition between inversion and noninversion, the optimum Mandel Q parameter of Q=- 1/2 is retained when the system operates well above threshold. A simple physical explanation of the squeezing mechanism
for two-mode squeezing is given.
Received: 22 December 1997 / Revised: 25 March 1998 / Accepted: 9 September 1998 相似文献
20.
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