共查询到20条相似文献,搜索用时 46 毫秒
1.
Domingos H. U. Marchetti 《Journal of statistical physics》1990,61(3-4):909-911
A simple argument is presented by which one can show that the critical inverse temperature
c
of a two-dimensional Coulomb gas (standard or hard-core) with activityz satisfies
, where
in the low-activity limit. Previous results yield
. 相似文献
2.
C. Chris Wu 《Journal of statistical physics》1996,88(5-6):1399-1408
We consider an inhomogeneous contact process on a tree
of degreek, where the infection rate at any site isλ, the death rate at any site in
isδ (with 0 <δ ⩽ 1) and that at any site in
is 1. Denote by
the critical value for thehomogeneous model (i.e.,δ=1) on
and byϑ(δ, λ) the survival probability of the inhomogeneous model on
. We prove that whenk > 4, if
, a subtree embedded in
, with 1 ⩽σ ⩽ √k, then three existsδ
c
σ
strictly between (
) and 1 such that (
) whenδ >δ
c
σ
andϑ(δ, λ
c(
) > 0 whenδ <δ
c
σ
; ifS={o}, the origin of
, then
for anyδ ε (0, 1). 相似文献
3.
We study one-dimensional Brownian motion with constant drift toward the origin and initial distribution concentrated in the strictly positive real line. We say that at the first time the process hits the origin, it is absorbed. We study the asymptotic behavior, ast, ofm
t
, the conditional distribution at time zero of the process conditioned on survival up to timet and on the process having a fixed value at timet. We find that there is a phase transition in the decay rate of the initial condition. For fast decay rate (subcritical case)m
t
is localized, in the critical casem
t
is located around
, and for slow rates (supercritical case)m
t
is located aroundt. The critical rate is given by the decay of the minimal quasistationary distribution of this process. We also study in each case the asymptotic distribution of the process, scaled by
, conditioned as before. We prove that in the subcritical case this distribution is a Brownian excursion. In the critical case it is a Brownian bridge attaining 0 for the first time at time 1, with some initial distribution. In the supercritical case, after centering around the expected value—which is of the order oft—we show that this process converges to a Brownian bridge arriving at 0 at time 1 and with a Gaussian initial distribution. 相似文献
4.
The time correlation function
(t)=Re<[c(t), c
(0)]>, which is related to the dipole spectrum and is the main focus of quantum molecular time scale generalized Langevin equation theory, is calculated for the Hamiltonian system in which a single oscillator is coupled by a nonlinear Davydov term to a chain of oscillators comprising a phonon heat bath. An exact expression for
(t) is obtained. At long times we find that the time correlation function decays as a small power law atT=0K, but switches to exponential decay at higher temperature. This is a new result and bears on the long-standing issue of the existence of long-time tails. 相似文献
5.
G. F. Zharkov 《Central European Journal of Physics》2004,2(1):220-240
The self-consistent solutions of the nonlinear Ginzburg-Landau equations, which describe the behavior of a superconducting
mesoscopic cylinder in an axial magnetic field H (provided there are no vortices inside the cylinder), are studied. Different, vortex-free states (M-, e-, d-, p-), which exist in a superconducting cylinder, are described. The critical fields (H
1, H
2, H
p
, H
i
, H
r
), at which the first or second order phase transitions between different states of the cylinder occur, are found as functions
of the cylinder radius R and the GL-parameter
. The boundary
, which divides the regions of the first and second order (s, n)-transitions in the icreasing field, is found. It is found that at R→∞ the critical value, is
. The hysteresis phenomena, which appear when the cylinder passes from the normal to superconducting state in the decreasing
field, are described. The connection between the self-consistent results and the linearized theory is discussed. It is shown
that in the limiting case
and R ≫ λ (λ is the London penetration length) the self-consistent solution (which correponds to the socalled metastable p-state) coincides with the analitic solution found from the degenerate Bogomolnyi equations. The reason for the existence
of two critical GL-parameters
and
in, bulk superconductors is discussed.
An erratum to this article is available at. 相似文献
6.
We have examined the influence of parametric noise on the solution behavioru(t, x) of a nonlinear initial value() problem arising in cell kinetics. In terms of ensemble statistics, the eventual limiting solution mean
and variance
are well-characterized functions of the noise statistics, and
and
depend on . When noise is continuously present along the trajectory,
and
are independent of the noise statistics and . However, in their evolution toward
and
, both
u
(t, x) and
u
2
(t, x) depend on the noise and. 相似文献
7.
8.
An approximation procedure for the solution of stochastic nonlinear equations, which was derived from a variational principle in a previous paper, is applied to the problem of a particle that diffuses in a symmetric bistable potential starting from the point of unstable equilibrium. The second moment
and variance
for the particle's position
are calculated as functions of the timet. Good agreement is found with results recently obtained by Baibuzet al. from an approximate evaluation of a path integral expression for the probability density. 相似文献
9.
Defining the ratiosr
p
=σ(vp →vx)/σ(vp →μ
−
x) and
we obtain the bounds 0.28 ⩽r
p
⩽ 0.61 and
using only the parton model and the data of CDHS group with iron target. We also give the complete set of parton-model relations
which would allow the determination of all the neutral-current coupling constants from inclusive cross sections alone. 相似文献
10.
Gely F. Zharkov 《Central European Journal of Physics》2005,3(1):77-103
Self-consistent solutions of the nonlinear Ginzburg-Landau (GL) equations are investigated numerically for a superconducting
(SC) cylinder, placed in an axial magnetic field, with a single vortex on the axis (m=1). Two modes, which show the original state of the cylinder, SC or normal (s
0 andn
0), are studied. The field increase (FI) and the field decrease (FD) regimes are studied. The critical fields destroying the
SC state withm=1 are found in both regimes. It is shown that in a cylinder of radiusR and GL-parameter ϰ, there exist a number of solutions depending only on the radial co-ordinater corresponding to different states such as M,e, d, p,i, n,
,n
*, and the state diagram on the plane of the variables (ϰ,R) is described. The critical fields corresponding to intrastate transitions and the onset of hysteresis are obtained. The
critical fieldH
0(R) dividing the paramagnetic and diamagnetic states of the cylinder withm=1 is determined. The limiting fields of supercooling or superheating of the normal state at which the restoration of the
SC state occurs are established. It is shown, that (in both casesm=1,0) there exist two critical parameters,
and
, which divide bulk SC into three groups (with
and
), in accordance with the behavior in a magnetic field. The parameters
and
mark the boundary for the existence of a supercooled normal
-state in FD-regime and a superheated SC M-state in FI-regime respectively. It is shown, that the value
, which was claimed in a number of papers as related to type-I superconductors, is illusory.
We regret to inform that Professor Gely Zharkov passed away on 9th July 2004. 相似文献
11.
We report numerical data obtained on the special-purpose computer PERCOLA for the exponent
of the electrical conductivity of 2D percolation. The extrapolation yields
and a correction to the scaling exponent=1.2±0.2. 相似文献
12.
R. Orbach 《Hyperfine Interactions》1989,49(1-4):325-333
The excitation dynamics of site diluted magnets can be described at low energies (long length scales) by magnons, and above
a crossover frequency, ωc, (short length scales) by fractons. The density of fracton states is given by
, where
is the fracton dimensionality. Dilution gives rise to a characteristic length ξ∝(p−p
c)ν, wherep
c is the critical concentration for (magnetic) percolation. The crossover frequency ωc is proportional to ξ-1[1+(θ/2)], where θ is the rate at which the diffusion constant decays with distance for diffusion on an equivalent network. A fractal
dimensionD describes the density of magnetic sites on the infinite network, and
. For percolating networks,
for all dimensions ≥2. Neutron scattering structure factor measurements by Uemura and Birgeneau compare well with calculations
using fracton concepts.
Magnons are extended at low energies, while the fracton states are geometrically localized, with a wave function envelope
proportional to exp
. Here,
is the fracton length scale at frequency ω. The exponentd
ϕ lies between 1 andd
min, the chemical length index (of the order of 1.6 in three dimensions). The localization of the magnetic excitations causes
a spread in the NMR relaxation rates. A given nuclear moment will experience only a limited set of fracton excitations, resulting
in an overall non-exponential decay of the NMR relaxation signal. When strong cross-relaxation is present, the relaxation
will be exponential, but the temperature dependence will be strongly altered from the concentrated result. 相似文献
13.
A. Heintz 《Journal of statistical physics》1998,90(3-4):663-695
The paper is concerned with the Enskog equation with a constant high density factor for large initial data in L
1(R
n). The initial boundary value problem is investigated for bounded domains with irregular boundaries. The proof of an H-theorem for the case of general domains and boundary conditions is given. The main result guarantees the existence of global solutions of boundary value problems for large initial data with all v-moments initially finite and domains having boundary with finite Hausdorff measure and satisfying a cone condition. Existence and uniqueness are first proved for the case of bounded velocities. The solution has finite norm
where q = (t
0, x) is taken on all possible n-dimensional planes Q(v) in R
n+l intersecting a fixed point and orthogonal to vectors (1, v), v R
n. 相似文献
14.
We consider the diffusion of a particle at Xt in a drift field derived from a smooth potential of the formV+B, whereV is periodic andB is a bump of compact support. With no bump,B=0, the mean squared displacementE(t) E |X
t
– X0|2 =D(V)t +C +O(e
–t
),>0, in any dimension. WhenB0, we establish in one dimension the asymptotic expansion
, 0, ast. Our analysis relies on the Nash estimates developed in previous work for the transition density of the process and their consequences for the analytic structure,of the Laplace transform
ofE(t). 相似文献
15.
D. H. D. West V. J. McBrierty C. F. G. Delaney 《Applied Physics A: Materials Science & Processing》1975,7(3):171-174
The decay time τl ofo-Ps by the electron pickoff process has been measured in polystyrene as a function of molecular weight. For samples below
their glass transition temperature τl is essentially independent of
. In the low molecular weight region,
, τl increased with decreasing
in line with earlier theoretical predictions. The overall behaviour reflects closely the dependence of free volume on
. The effects of molecular motion on τl are examined and it is concluded that the decay time is insensitive to such motions in polystyrene below the melting point,
in contrast to what is observed in polytetrafluoroethylene. 相似文献
16.
In this paper we construct the equilibrium states of Dyson's vector-valued hierarchical model with parameter
at low temperatures and describe their large-scale limit. The analogous problems for
<c<2 and 1<c<
were solved in our papers [1] and [2]. In the present case the large-scale limit is similar to the case
<c<2, i.e. it is a Gaussian self-similar field with long-range dependence in the direction orthogonal to and a field consisting of independent Gaussian random variables in the direction parallel with the magnetization. The main difference between the two cases is that now the normalizing factor in the direction of the magnetization contains, beside the square-root of the volume, a logarithmic term too.Dedicated to Roland Dobrushin 相似文献
17.
Explicit evaluation of the following parameters has been carried out in the extraU (1) superstring inspired model: (i) As Mz2 varies from 555 GeV to 620 GeV and (m
t) CDF = 175.6 ± 5.7 GeV (Table 1): (a) SNew varies from -0.100 ± 0.089 to -0.130 ± 0.090, (b) TNew varies from -0.098 ± 0.097 to -0.129 ± 0.098, (c) UNew varies from -0.229 ± 0.177 to -0.253 ± 0.206, (d) Τz varies from 2.487 ± 0.027 to 2.486 ± 0.027, (e) ALR varies from 0.0125 ± 0.0003 to 0.0126 ± 0.0003, (f) A
FB
b
remains constant at 0.0080 ± 0.0007. Almost identical values are obtained for (m
t)D0 = 169 GeV (see table 2). (ii) Triple gauge boson vertices (TGV) contributions: AsMz
2 varies from 555 GeV to 620 GeV and (m
t) CDF = 175.6 ±5.7 GeV. (a)√s = 500 GeV, asymptotic case:
varies from -0.301 to -0.179;
varies from -0.622 to -0.379;
varies from +0.0061 to 0.0056;
varies from -3.691 to -2.186.
varies from +0.270 to +0.118;
varies from +0.552 to 0.238;
varies from +0.0004 to +0.0002;
remains constant at -0.110. (b)√s = 700 GeV, asymptotic case:
varies from -0.297 to -0.176;
varies from -0.609 to -0.370;
varies from -0.0082 to -0.0078;
varies from -3.680 to -2.171.√s = 700 GeV, nonasymptotic case:
varies from -0.173 to -0.299;
varies from-0.343 to -0.591;
varies from -0.005 to -0.011;
remains constant at -0.110.
The pattern of form factors values for√s = 1000, 1200 GeV is almost identical to that of√s= 700 GeV. Further the values of the form factors for (m
t)D0 (=169 GeV) follow identical pattern as that of (m
t) CDF form factors values (see tables 5, 6, 9, 10).
We conclude that the values of all the form factors with the exception of these of
,
are comparable or larger than theS, T values and therefore the TGV contributions are important while deciding the use of extraU (1) model for doing physics beyond standard model. 相似文献
18.
An estimation of the mass difference of
system with heavy quark symmetry formalism is presented. The effective Hamiltonian describing the transition
(whereh=b forB
d
0
-system) is considered in a manifest left right symmetric (MLRS) model along with contribution from neutral Higgs boson. We
use the spin and flavor symmetry for heavy quarks to obtain the transition matrix element 〈B
d
0
|ℋeff(x)|
d
0
〉 in terms of Isgur-Wise function. Assuming thatB
d
0
and
states are at rest, we find that Isgur-Wise function turns out to be unity. However using the experimental values of ΔM
K and
as input, we find thatM
R=835 GeV andM
H⩾2·9 TeV. 相似文献
19.
V. V. Skobelev 《Russian Physics Journal》1999,42(2):136-141
Switching on an external electromagnetic field opens a neutrino decay channel of a hypothetical pseudoscalar particle, an
axion, which plays an important role in modern field theory. We obtain exact expressions in the one-loop approximation for
the probability of the
decay into a massless neutrino in a crossed fieldF and study the asymptotic behavior by the nature of the parameter
.
Moscow State Industrial University, Moscow. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 42, No. 2,
pp. 8–12, February, 1999. 相似文献
20.
Guido A. Raggio 《Letters in Mathematical Physics》1982,6(3):233-236
It is shown that for normal states ρ and φ of a W
*-algebra
, where P(.,.) is the transition probability considered by Uhlmann [1], and ζ(ω) is the vector in the natural positive cone of some
standard faithful representation of A, associated with the normal state ω. The above inequality is equivalent to:
, where d(.,.) is the Bures distance function [5]. 相似文献