共查询到20条相似文献,搜索用时 898 毫秒
1.
We investigate the critical behaviour of an epidemical model in a diffusive population mediated by a static vector environment on a 2D network. It is found that this model presents a dynamical phase transition from disease-free state to endemic state with a finite population density. Finite-size and short-time dynamic scaling relations are used to determine the critical population density and the critical exponents characterizing the behaviour near the critical point. The results are compatible with the universality class of directed percolation coupled to a conserved diffusive field with equal diffusion constants. 相似文献
2.
Through using the methods of
finite-size effect and short time dynamic scaling, we study the critical
behavior of parasitic disease spreading process in a diffusive population
mediated by a static vector environment. Through comprehensive analysis of
parasitic disease spreading we find that this model presents a dynamical
phase transition from disease-free state to endemic state with a finite
population density. We determine the critical population density, above which
the system reaches an epidemic spreading stationary state. We also perform a
scaling analysis to determine the order parameter and critical relaxation
exponents. The results show that the model does not belong to the usual
directed percolation universality class and is compatible with the class of
directed percolation with diffusive and conserved
fields. 相似文献
3.
A New Approach about Determining the Phase Transition Point in Variational-Cumulant Expansion
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Based on Variational-cumulant expansion (VCE), through calculating Polyakov line in the SU(2) gauge model at finite temperature and considering the similarity of finite size interaction in VCE method with the finite volume effect in Monte Carlo (MC) simulation, a new approach is adopted to determine the critical couplings for the deconfinement phase transition. New results of VCE which are close to MC data manifest that new approach is much more effective than the traditional one and show that VCE analysis is consistent with MC simulation. 相似文献
4.
We investigate the critical behavior of a stochastic lattice model describing a General Epidemic Process. By means of a Monte Carlo procedure, we simulate the model on a regular square lattice and follow the spreading of an epidemic process with immunization. A finite size scaling analysis is employed to determine the critical point as well as some critical exponents. We show that the usual scaling analysis of the order parameter moment ratio does not provide an accurate estimate of the critical point. Precise estimates of the critical quantities are obtained from data of the order parameter variation rate and its fluctuations. Our numerical results corroborate that this model belongs to the dynamic isotropic percolation universality class. We also check the validity of the hyperscaling relation and present data collapse curves which reinforce the accuracy of the estimated critical parameters. 相似文献
5.
6.
We study hierarchical network models which have recently been introduced to approximate the Chalker-Coddington model for the integer quantum Hall effect (A.G. Galstyan and M.E. Raikh, PRB 5 (1997) 1422; Arovas et al., PRB 56 (1997) 4751). The hierarchical structure is due to a recursive method starting from a finite elementary cell. The localization-delocalization transition occurring in these models is displayed in the flow of the conductance distribution under increasing system size. We numerically determine this flow, calculate the critical conductance distribution, the critical exponent of the localization length, and the multifractal exponents of critical eigenstates. 相似文献
7.
Non-perturbative flow equations within an effective linear sigma model coupled to constituent quarks for two quark flavours are derived and solved. A heat kernel regularization is employed for a renormalization group improved effective potential. We determine the initial values of the coupling constants in the effective potential at zero temperature. Solving the evolution equations with the same initial values at finite temperature in the chiral limit, we find a second-order phase transition at Tc≈150 MeV. Due to the smooth decoupling of massive modes, we can directly link the low-temperature four-dimensional theory to the three-dimensional high-temperature theory. We calculate the equation of state in the chiral limit and for finite pion masses and determine universal critical exponents. 相似文献
8.
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
9.
The fully finite spherical model 总被引:2,自引:0,他引:2
A lattice sum technique is applied to the constraint equation of the finite size mean spherical model. It is shown that this allows the investigation of the model over a wide range of temperatures, for a wide range of system sizes. Correlation lengths and susceptibilities are shown to obey crossover scaling aroundT=0 below the lower critical dimension, and finite size scaling between the lower and upper critical dimensions. Universal scaling forms are suggested for the lower critical dimension. At and above the upper critical dimension, the behavior is identical to that of finite sized mean field theory. The scaling at and above the upper critical dimension is shown to be modified by the existence of a dangerous irrelevant variable which also governs the failure of hyperscaling. Implications for phenomenological renormalization experiments are discussed. Numerical results of scaling are displayed. 相似文献
10.
We study the response of an adsorbed monolayer under a driving force as a model of sliding friction phenomena between two crystalline surfaces with a boundary lubrication layer. Using Langevin-dynamics simulation, we determine the nonlinear response in the direction transverse to a high symmetry direction along which the layer is already sliding. We find that below a finite transition temperature there exist a critical depinning force and hysteresis effects in the transverse response in the dynamical state when the adlayer is sliding smoothly along the longitudinal direction. 相似文献
11.
Elena Agliari Angelica Pachon Pablo M. Rodriguez Flavia Tavani 《Journal of statistical physics》2017,169(4):846-875
We consider the Maki–Thompson model for the stochastic propagation of a rumour within a population. In this model the population is made up of “spreaders”, “ignorants” and “stiflers”; any spreader attempts to pass the rumour to the other individuals via pair-wise interactions and in case the other individual is an ignorant, it becomes a spreader, while in the other two cases the initiating spreader turns into a stifler. In a finite population the process will eventually reach an equilibrium situation where individuals are either stiflers or ignorants. We extend the original hypothesis of homogenously mixed population by allowing for a small-world network embedding the model, in such a way that interactions occur only between nearest-neighbours. This structure is realized starting from a k-regular ring and by inserting, in the average, c additional links in such a way that k and c are tuneable parameters for the population architecture. We prove that this system exhibits a transition between regimes of localization (where the final number of stiflers is at most logarithmic in the population size) and propagation (where the final number of stiflers grows algebraically with the population size) at a finite value of the network parameter c. A quantitative estimate for the critical value of c is obtained via extensive numerical simulations. 相似文献
12.
In non-destructive testing (NDT), the intensity of laser pulses may be temporally modulated to improve the signal-to-noise ratio of ultrasonic signals. The purpose of this work is to determine the time scale on which hyperbolic heat conduction effects are significant in ultrasonic displacements and stresses for temporally modulated laser pulses, under the assumption that the heat wave speed equals the longitudinal wave speed. A one-dimensional model with a finite train of heat flux pulses is investigated. Using the Green and Lindsay model, it is found that the critical modulation frequency in steel, above which hyperbolic heat conduction effects will become signficant, is 2.26 GHz. A dimensionless factor is given to calculate critical modulation frequencies in other isotropic materials. The signal enhancement potential of temporal intensity modulation is apparent in the numerical results. 相似文献
13.
14.
Charged vortex solutions are found iri a (2+1)-dimensional Abelian Higgs model with Chern- Simons term at finite temperature. It is shown that there exists a finite critical temperature at which vortices disappear and it implies that the system changes fiom superconducting state to normal state at this critical temperature. 相似文献
15.
The dynamic critical behavior of semi-infinite model C near the special and ordinary transitions is investigated using field theoretic renormalization-group approach. It is shown that the dynamic surface quantities have different critical behavior aginst their bulk analogues and their scaling laws can be expressed entirely in terms of static (bulk and surface) exponents and dynamic exponents. It is found that at the critical point the surface transport coefficient reaches a finite value via a cusplike singularity and the surface-bulk transport coefficient diverges, but the bulk transport coefficient remains finite as that of the infinite model C. 相似文献
16.
Instabilities in population dynamics 总被引:1,自引:0,他引:1
K. Sznajd-Weron 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(1):183-187
Biologists have long known that the smaller the population, the more susceptible it is to extinction from various causes.
Biologists define minimum viable population size (MVP), which is the critical population size, below which the population has a very small chance to survive. There are several
theoretical models for predicting the probability that a small population will become extinct. But these models either embody
unrealistic assumptions or lead to currently unresolved mathematical problems. In other popular models of population dynamics,
like the logistic model, MVP does not exist. In this paper we find the existence of such a critical concentration in a simple
model of evolution. We solve this model by a mean field theory and show, in one and two dimensions, the existence of the critical
adaptation and concentration below which a population dies out. We also show that, like in the logistic model, above the critical
value a population reaches its carrying capacity. Moreover, in the two-dimensional case we find - the so common in biological
models - periodic solutions and their biffurcations.
Received 15 February 2000 相似文献
17.
E. Ben-Naim F. Vazquez S. Redner 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(4):531-538
We model the dynamics of social structure by a simple interacting particle
system. The social standing of an individual agent is represented by an
integer-valued fitness that changes via two offsetting processes. When two
agents interact one advances: the fitter with probability p and the less
fit with probability 1-p. The fitness of an agent may also decline with
rate r. From a scaling analysis of the underlying master equations for
the fitness distribution of the population, we find four distinct social
structures as a function of the governing parameters p and r. These
include: (i) a static lower-class society where all agents have finite
fitness; (ii) an upwardly-mobile middle-class society; (iii) a hierarchical
society where a finite fraction of the population belongs to a middle class
and a complementary fraction to the lower class; (iv) an egalitarian
society where all agents are upwardly mobile and have nearly the same
fitness. We determine the basic features of the fitness distributions in
these four phases. 相似文献
18.
Phenomenological renormalization of finite lattice data is used to locate the critical line of an asymmetric eight-vertex model. This model reduces at a special point to a loop gas on the square lattice. The critical fugacity of the loop gas is estimated to be 2.373±0.001, whereas the correlation exponent appears to be Ising-like. 相似文献
19.
《Physics letters. [Part B]》1987,188(2):219-225
We investigate the structure of the linear differential operators whose solutions determine the four-point correlations of primary operators in the d = 2 conformally invariant SU(2) α-model with Wess-Sumino term and the d = 2 critical statistical systems with central Virasoro charge smaller than one. Factorisation properties of the differential operators are related to a finite closure of the operator algebras. We recover the selection and fusion rules of Fateev, Zamolodchikov and Gepner, Witten for the SU(2) α-model. It is outlined how the results of the SU(2) model can be used for the identification of closed operator algebras in the statistical model. 相似文献
20.
PAN Gui-Jun ZHANG Duan-Ming SUN Hong-Zhang YIN Yan-Ping 《理论物理通讯》2005,44(3):483-486
We present a stochastic critical slope sandpile model, where the amount of grains that fall in an overturning event is stochastic variable. The model is local, conservative, and Abelian. We apply the moment analysis to evaluate critical exponents and finite size scaling method to consistently test the obtained results. Numerical results show that this model, Oslo model, and one-dimensional Abelian Manna model have the same critical behavior although the three models have different stochastic toppling rules, which provides evidences suggesting that Abelian sandpile models with different stochastic toppling rules are in the same universality class. 相似文献