scholarly journals Особенности фазовой диаграммы полужестких бозонов на квадратной решетке

2021 ◽  
Vol 63 (9) ◽  
pp. 1361
Author(s):  
В.В. Конев ◽  
Ю.Д. Панов
Keyword(s):  
Mean Field ◽  
Hard Core ◽  
Field Approximation ◽  
Charge Ordering ◽  
Mean Field Approximation ◽  
New Order ◽  
Model Parameters ◽  
Local Correlation ◽  
The Mean ◽  
Limit Form

We investigated the phase diagrams of a system of charged semi-hardcore bosons in the mean-field approximation. It is shown that an increase in the local correlation parameter leads to the transformation of the phase diagram of the system from the form characteristic of hard-core bosons to the limit form with a parabolic dependence of the critical temperature of the charge ordering on the boson concentration. The evolution between these limiting cases depends on the ratio of the model parameters and is accompanied by various effects, including a change in the type of phase transition, the appearance of new order-order transitions, and the appearance of new critical points.

scholarly journals DYNAMICAL MODEL FOR VIRUS SPREAD

Fractals ◽  
1996 ◽  
Vol 04 (02) ◽  
pp. 113-122 ◽  
Author(s):  
G. CAMELO-NETO ◽  
S. COUTINHO
Keyword(s):  
Steady State ◽  
Mean Field ◽  
Field Approximation ◽  
Square Lattice ◽  
Mean Field Approximation ◽  
Model Parameters ◽  
Viral Spread ◽  
Infected Cells ◽  
The Mean ◽  
Density Population

The steady state properties of the mean density population of infected cells in a viral spread is simulated by a general forest like cellular automaton model with two distinct populations of cells (permissive and resistant ones) and studied in the framework of the mean field approximation. Stochastic dynamical ingredients are introduced into this model to mimic cells regeneration (with probability p) and to consider infection processes by other means than contiguity (with probability f). Simulations are carried out on a L×L square lattice taking into consideration the eighth first neighbors. The mean density population of infected cells (Di) is measured as a function of the regeneration probability p, and analyzed for small values of the ratio f/p and for distinct degrees of cell resistance. The results obtained by a mean field like approach recovers the simulations results. The role of the resistant parameter R (R≥2) on the steady state properties, is investigated and discussed in comparison with the R=1 monocell case which corresponds to the self organized critical forest model. The fractal dimension of the dead cells ulcers contours was also estimated and analyzed as a function of the model parameters.

scholarly journals Predicting The Yields Of Species Occupying A Single Trophic Level With Incomplete Information: Two Approximations Based On The Lotka-Volterra Generalized Equations

2021 ◽  
Author(s):  
Hugo Fort
Keyword(s):  
Trophic Level ◽  
Interspecific Interactions ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Model Parameters ◽  
Generalized Equations ◽  
Focal Species ◽  
The Mean ◽  
Common Situation

The linear Lotka-Volterra generalized equations (LLVGE) serve for describing the dynamics of communities of species connected by negative as well as positive interspecific interactions. Here we particularize these LLVGE to the case of a single trophic level community with S >2 species, either artificial or natural. In this case, by estimating the LLVGE parameters from the yields in monoculture and biculture experiments, the LLVGE are able to produce quite accurate predictions for species yields. However, a common situation we face is that we don't know all the parameters appearing in the LLVGE. Indeed, for large values of S, only a fraction of the experiments necessary for estimating the model parameters is commonly carried out. We then analyze which quantitative predictions are possible with an incomplete knowledge of the parameters. We discuss two approximations that allow using these LLVGE as a quantitative tool. First, when we only know a fraction of the model parameters, the mean field approximation allows making predictions on aggregate or average quantities. Second, for cases in which all the interaction parameters involving a particular species are available, we have the focal species approximation for predicting the yield of this focal species.

A NEW FERMION-SPIN TRANSFORMATION TO IMPLEMENT THE CHARGE-SPIN SEPARATION

1993 ◽  
Vol 07 (15) ◽  
pp. 1013-1019 ◽  
Author(s):  
SHIPING FENG ◽  
Z.B. SU ◽  
L. YU
Keyword(s):  
Mean Field ◽  
Hard Core ◽  
Field Approximation ◽  
Degree Of Freedom ◽  
Mean Field Approximation ◽  
Dimensional Case ◽  
Spinless Fermion ◽  
The Mean ◽  
Charge Degree ◽  
Good Agreement

We propose a new fermion-spin transformation to implement the charge-spin separation in the large U Hubbard, or the equivalent t-J model. The charge degree of freedom is represented by a spinless fermion while the spin degree of freedom is represented by a hard-core boson. The local constraint for single occupancy is exactly satisfied. Very good agreement with exact solution is obtained for one-dimensional case in the mean field approximation, regarding the total energy, gapless spinon and holon spectra, and the momentum distribution of physical electrons. The same approximation yields good doping dependence of the staggered magnetization in the two-dimensional case.

QUARK AND SIGMA MASS DEPENDENCE OF NUCLEON PROPERTIES FROM LINEAR SIGMA MODEL

2011 ◽  
Vol 20 (06) ◽  
pp. 1509-1517 ◽  
Author(s):  
T. S. T. ALI
Keyword(s):  
Axial Vector ◽  
Mean Field ◽  
Field Approximation ◽  
Linear Sigma Model ◽  
Mean Field Approximation ◽  
Model Parameters ◽  
Coupling Constant ◽  
Field Equations ◽  
Vector Coupling ◽  
The Mean

The sensitivity of static nucleon properties (magnetic moment, axial-vector coupling constant gA, pion–nucleon coupling constant gπNN and sigma commutator term σπN) to the quark and sigma masses have been investigated in the mean-field approximation. We have solved the field equations in the mean-field approximation with different sets of model parameters. Good results have been obtained in comparison with the other models and experimental data.

The Curie Temperature of the Ferroelectric Superlattice Films with Surface Modification

2009 ◽  
Vol 64 (11) ◽  
pp. 723-728
Author(s):  
Bao-Bing Zheng ◽  
Xiao-Yu Kuang ◽  
Shao-Mei Chang ◽  
Ya-Ru Zhao ◽  
Wen-Qiang Li
Keyword(s):  
Surface Modification ◽  
Ising Model ◽  
Mean Field ◽  
Transverse Field ◽  
Exchange Interactions ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Model Parameters ◽  
Transverse Ising Model ◽  
The Mean

We examine the critical behaviour of a finite alternating ferroelectric superlattice based on the transverse Ising model within the framework of the mean-field approximation. The results indicate that the features of the phase diagrams can be greatly modified by changing the transverse Ising model parameters. The transition temperature of alternating superlattice is described as function of the inter- and intra-layer exchange interactions, the strength of the transverse field, the superlattice thickness and the polarizations. In addition, the effects of surface modification on finite superlattices are also studied.

ON THE VALIDITY OF MEAN-FIELD THEORY FOR ANYONS ON A LATTICE

1992 ◽  
Vol 06 (30) ◽  
pp. 1951-1960 ◽  
Author(s):  
A.A. OVCHINNIKOV ◽  
An. A. OVCHINNIKOV
Keyword(s):  
Large Deviation ◽  
Mean Field Theory ◽  
Mean Field ◽  
Hard Core ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Phase Fluctuations ◽  
Fermi Statistics ◽  
The Mean ◽  
Field Approaches

We examine the validity of the mean-field approximation for anyons on a lattice at high density. The phase fluctuations for a large deviation from the Fermi statistics, in particular for the hard core bosons, are shown to be large. The importance of the phase fluctuations in different fermionic mean-field approaches for the antiferromagnetic Heisenberg model is stressed.

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