scholarly journals Fixation time in evolutionary graphs: a mean field approach

2018 ◽  
Author(s):  
Mahdi Hajihashemi ◽  
Keivan Aghababaei Samani
Keyword(s):  
Analytical Method ◽  
Transition Matrix ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Fixation Time ◽  
Field Approach ◽  
Moran Process ◽  
Structured Population ◽  
Population Structures

A novel analytical method is proposed for calculation of average fixation and extinction times of mutants in a general structured population of two types of species. The method is based on Markov chains and uses a mean field approximation to calculate the corresponding transition matrix. Analytical results are compared with the results of simulation of the Moran process on a number of population structures.

scholarly journals MEAN FIELD APPROACH TO THE GIANT WORMHOLE PROBLEM

1994 ◽  
Vol 03 (02) ◽  
pp. 421-430
Author(s):  
A. GAMBA ◽  
I. KOLOKOLOV ◽  
M. MARTELLINI
Keyword(s):  
Free Energy ◽  
Probability Density ◽  
Time Distribution ◽  
Mean Field ◽  
Field Approximation ◽  
Space Time ◽  
Mean Field Approximation ◽  
Field Approach

We introduce a gaussian probability density for the space-time distribution of worm-holes, thus taking effectively into account wormhole interaction. Using a mean-field approximation for the free energy, we show that giant wormholes are probabilistically suppressed in a homogenous isotropic “large” universe.

A MEAN FIELD APPROACH TO THE COLORED HUBBARD MODEL

2001 ◽  
Vol 16 (11) ◽  
pp. 2003-2008
Author(s):  
TOBIAS BAIER ◽  
EIKE BICK
Keyword(s):  
Mean Field ◽  
Scalar Fields ◽  
Field Approximation ◽  
Square Lattice ◽  
Mean Field Approximation ◽  
Antiferromagnetic Order ◽  
Expectation Values ◽  
Field Approach ◽  
Antiferromagnetic Ordering ◽  
Measured Phase Diagram

By subdividing a 2d square lattice into plaquettes containing 4 lattice sites each, the Hubbard Hamiltonian is reformulated in terms of different "colored" fermion species. This makes it possible to describe e.g. antiferromagnetic order or d-wave superconductivity in terms of expectation values of composite scalar fields. A suitable mean field approximation indeed reproduces qualitatively the measured phase diagram and shows a competition between phases with antiferromagnetic ordering and dx2-y2-superconductivity at low temperatures.

HARD-CORE SLAVE-BOSON DESCRIPTION OF GENERALIZED FLUX PHASES

1991 ◽  
Vol 05 (01n02) ◽  
pp. 119-130 ◽  
Author(s):  
Franco Nori ◽  
Gergely T. Zimanyi ◽  
Elihu Abrahams
Keyword(s):  
Electron Gas ◽  
Mean Field ◽  
Hard Core ◽  
Frustration Effect ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Field Approach ◽  
Average Flux ◽  
Quantum Antiferromagnet ◽  
The Continuum

Through a hard-core slave-boson mean-field approach to the t-J model, which describes the dynamics of holes moving in a quantum antiferromagnet, we investigate its generalized flux phases. We first study the motion of an electron gas for arbitrary fillings and fields and establish the linear proportionality between the filling factor and the optimal flux with high accuracy. Using this result, we show that if the hard-core nature of the hole bosons is taken into account, then the slave-boson mean-field approximation for the t-J Hamiltonian allows for a solution where both the spinons and the holons experience an average flux of one flux quantum per particle. This enables them to achieve the lowest possible energy within the manifold of spatially-uniform flux states. In the case of the continuum model, this is possible only for certain fractional fillings and we suggest that the system may react to this frustration effect by phase separation.

The Determination of the Magnetoelectric Coupling Coefficient in Ferroelectric–Ferromagnetic Composite Based on PZT–Ferrite

2013 ◽  
Vol 58 (4) ◽  
pp. 1401-1403 ◽  
Author(s):  
J.A. Bartkowska ◽  
R. Zachariasz ◽  
D. Bochenek ◽  
J. Ilczuk
Keyword(s):  
Dielectric Permittivity ◽  
Coupling Coefficient ◽  
Mean Field ◽  
Field Approximation ◽  
Theoretical Description ◽  
Magnetoelectric Coupling ◽  
Mean Field Approximation ◽  
Dielectric Measurements ◽  
Temperature Dependences ◽  
Multiferroic Composite

Abstract In the present work, the magnetoelectric coupling coefficient, from the temperature dependences of the dielectric permittivity for the multiferroic composite was determined. The research material was ferroelectric-ferromagnetic composite on the based PZT and ferrite. We investigated the temperature dependences of the dielectric permittivity (") for the different frequency of measurement’s field. From the dielectric measurements we determined the temperature of phase transition from ferroelectric to paraelectric phase. For the theoretical description of the temperature dependence of the dielectric constant, the Hamiltonian of Alcantara, Gehring and Janssen was used. To investigate the dielectric properties of the multiferroic composite this Hamiltonian was expressed under the mean-field approximation. Based on dielectric measurements and theoretical considerations, the values of the magnetoelectric coupling coefficient were specified.

scholarly journals Hexagonal-Shaped Spin Crossover Nanoparticles Studied by Ising-Like Model Solved by Local Mean Field Approximation

2021 ◽  
Vol 7 (5) ◽  
pp. 69
Author(s):  
Catherine Cazelles ◽  
Jorge Linares ◽  
Mamadou Ndiaye ◽  
Pierre-Richard Dahoo ◽  
Kamel Boukheddaden
Keyword(s):  
Spin Crossover ◽  
Hexagonal Lattice ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Ligand Field ◽  
Order And Disorder ◽  
The Matrix ◽  
Local Mean ◽  
Parameter Values

The properties of spin crossover (SCO) nanoparticles were studied for five 2D hexagonal lattice structures of increasing sizes embedded in a matrix, thus affecting the thermal properties of the SCO region. These effects were modeled using the Ising-like model in the framework of local mean field approximation (LMFA). The systematic combined effect of the different types of couplings, consisting of (i) bulk short- and long-range interactions and (ii) edge and corner interactions at the surface mediated by the matrix environment, were investigated by using parameter values typical of SCO complexes. Gradual two and three hysteretic transition curves from the LS to HS states were obtained. The results were interpreted in terms of the competition between the structure-dependent order and disorder temperatures (TO.D.) of internal coupling origin and the ligand field-dependent equilibrium temperatures (Teq) of external origin.

Geometrical and Transport Properties of Disordered Fibre Networks: Analytical Results

1997 ◽  
Vol 11 (20) ◽  
pp. 867-875 ◽  
Author(s):  
A. A. Rodríaguez ◽  
E. Medina
Keyword(s):  
Probability Distribution ◽  
Transport Properties ◽  
Geometrical Structure ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Fracture Networks ◽  
Simplified Models ◽  
Fibre Density ◽  
Line Network

We study novel geometrical and transport properties of a 2D model of disordered fibre networks. To assess the geometrical structure we determine, analytically, the probability distribution for the number of fibre intersections and resulting segment sizes in the network as a function of fibre density and length. We also determine, numerically, the probability distribution of pore perimeters and areas. We find a non-monotonous behavior of the perimeter distribution whose main features can be explained by solving for two simplified models of the line network. Finally we formulate a mean field approximation to conduction, above the percolation threshold, using the derived results. Relevance of the results to fracture networks will be discussed.

Dynamical friction in a mean field approximation

1983 ◽  
Vol 97 (2) ◽  
pp. 435-452 ◽  
Author(s):  
Henry E. Kandrup
Keyword(s):  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Dynamical Friction

Exact Critical Temperature by Mean-Field Approximation

1992 ◽  
Vol 61 (12) ◽  
pp. 4356-4366 ◽  
Author(s):  
Adam Lipowski ◽  
Masuo Suzuki
Keyword(s):  
Critical Temperature ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation
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