共查询到20条相似文献,搜索用时 31 毫秒
1.
A. Möbius 《Zeitschrift für Physik B Condensed Matter》1990,80(2):213-223
A detailed phenomenological re-analysis of previously published conductivity data, (T, x), is presented. It was shown in [1] that the cusp-like low-temperature contribution can be described by
wherep=0.19±0.03. Starting from this result, two furtherT dependent contributions are separated: The high-temperature region is dominated by a positive contribution ht (T, x), which is approximately independent ofx, nearly linear inT above 100 K and nearly quadratic inT below 30 K. ForT 4 K, there is a small deviation, increasing withT, from the superposition of the above mechanisms. The relation between
, being negative, and theT independent part,
, exhibits a singularity,
where
and=0.68±0.05 –(p–0.19). This singularity should be related to the metal-semiconductor transition, taking place atT
c
0.14. The quantity
should be interpreted as minimum metallic conductivity. The limitingT dependences asxx
c
+0 agrees quantitatively with that one obtained previously for the activated region,xx
c
–0. Extrapolation of the phenomenological model obtained leads to the hypothesis that the interplay of
and ht could be the main origin of the temperature coefficient changing its sign in the Mooijregion, at
tc=0. The model enables several trend predictions concerning the value of
tc=0. 相似文献
2.
T. Nattermann M. Feigelman I. Lyuksyutov 《Zeitschrift für Physik B Condensed Matter》1991,84(3):353-359
We analyze the influence of thermal and frozen-in disorder on the flux line (FL) density
close to the lower critical fieldH
c1. Arguments which consider the steric repulsion of fluctuating FLs give
with the roughness exponent of a single FL andd the space dimensionality. We show by a phenomenological scaling approach and a renormalization group treatment, that this is correct only fordd
c
=2/–1, i.e. for
. Ford>d
c
the steric FL repulsion at scales more than some critical one is irrelevant and
. For disordered superconductorsd
c
=2 and
ford=2, 3. We also found the melting line for a FL lattice in the presence of frozen-in impurities close toH
c1. 相似文献
3.
Horng-Tzer Yau 《Communications in Mathematical Physics》1996,181(2):367-408
Let
denote the grand canonical Gibbs measure of a lattice gas in a cube of sizeL with the chemical potential and a fixed boundary condition. Let
be the corresponding canonical measure defined by conditioning
on
. Consider the lattice gas dynamics for which each particle performs random walk with rates depending on near-by particles. The rates are chosen such that, for everyn andL fixed,
is a reversible measure. Suppose that the Dobrushin-Shlosman mixing conditions holds for
forall chemical potentials . We prove that
for any probability densityf with respect to
; here the constant is independent ofn orL andD denotes the Dirichlet form of the dynamics. The dependence onL is optimal.Research partially supported by U.S. National Science Foundations grant 9403462, Sloan Foundation Fellowship and David and Lucile Packard Foundation Fellowship. 相似文献
4.
Neutrinoless double-beta decay within Minimal Supersymmetric Standard Model with gauge mediated supersymmetry breaking is considered. Limits on R-parity breaking constant
coming from non-observability of 0 in 76Ge are found. The dependence of
on different parameters at the messenger scale M are shown, with special attention paid to nuclear part of calculations. We have found that
strongly depends on the effective supersymmetry breaking scale only and deduced limits imposed on this non-standard parameter by the germanium experiment. 相似文献
5.
Let (M, g) be a pseudo-Riemannian manifold and
the space of densities of degree on M. Denote
the space of differential operators from
to
of order k and S
k
with = – the corresponding space of symbols. We construct (the unique) conformally invariant quantization map
. This result generalizes that of Duval and Ovsienko. 相似文献
6.
R. D. S. Yadava 《Zeitschrift für Physik B Condensed Matter》1992,86(1):93-99
An analysis of the ac conductivity ac(), and the ac dielectric constant, (), of the metal-insulator percolation systems is presented in the critical regime near the transition threshold. It is argued that the polarization and relaxation of the finite fractal metallic clusters play dominant roles in controlling the dynamic response of the system on both sides of the threshold. The relaxation time constant of a fractal cluster is shown to scale with its size as
withd
t
= 4 – 2d +d
c
+ /, whered is tge Euclidean dimension, andd
c
, , and are the scaling indices for the charging, the dc conductivity, and the correlation length respectively. The average time dependent response of the system is shown to scale with a new time scale
, where is the correlation length and 0 is a microscopic time constant. It is shown that at frequencies
and
with /dt 1, in close agreement with experiments. The effects of the anomalous transport along the infinite cluster and the medium polarizability are also discussed. 相似文献
7.
We study the initial value problem for the two-dimensional nonlinear nonlocal Schrödinger equations i ut + u = N(v), (t, x, y) R3, u(0, x, y) = u0(x, y), (x, y) R2 (A), where the Laplacian = 2
x + 2
y, the solution u is a complex valued function, the nonlinear term N = N1 + N2 consists of the local nonlinear part N1(v) which is cubic with respect to the vector v=(u,ux,uy,\overline{u},\overline{u}_{x},\overline{u}_{y}) in the neighborhood of the origin, and the nonlocal nonlinear part N2(v) =(v, – 1
x Kx(v)) + (v, – 1
y Ky(v)), where (, ) denotes the inner product,
and the vectors Kx (C4(C6; C))6 and Ky (C4(C6; C))6 are quadratic with respect to the vector v in the neighborhood of the origin. We assume that the components K(2)
x = K(4)
x 0, K(3)
y = K(6)
y 0. In particular, Equation (A) includes two physical examples appearing in fluid dynamics. The elliptic–hyperbolic Davey–Stewartson system can be reduced to Equation (A) with
, and all the rest components of the vectors Kx and Ky are equal to zero. The elliptic–hyperbolic Ishimori system is involved in Equation (A), when
, and
. Our purpose in this paper is to prove the local existence in time of small solutions to the Cauchy problem (A) in the usual Sobolev space, and the global-in-time existence of small solutions to the Cauchy problem (A) in the weighted Sobolev space under some conditions on the complex conjugate structure of the nonlinear terms, namely if N(ei v) = ei N(v) for all R. 相似文献
8.
Hugo Parr 《Zeitschrift für Physik B Condensed Matter》1976,25(4):359-361
We have calculated analytically the superheating fieldH
sh
for bulk superconductors, correct to second order in. We find
, which agrees well with numerical computations for<0.5. The surface order parameter is
, and the penetration depth is
. 相似文献
9.
We use the recursion method to calculate the vibrational density of states
of site percolation clusters slightly above the percolation threshold. It is found that
is proportional to at long wavelengths. At shorter length scales,
is proportional to
, with the fraction dimension
. The cross-over from phonon to fraction regime is characterized by a rapid rise in
in agreement with effective medium calculations. 相似文献
10.
A locally finite, causal, and quantal substitute for a locally Minkowskian principal fiber bundle
of modules of Cartan differential forms over a bounded region X of a curved C
-smooth spacetime manifold M with structure group G that of orthochronous Lorentz transformations L
+ := SO(1,3), is presented.
is usually regarded as the kinematical structure of classical Lorentzian gravity when the latter is viewed as a Yang-Mills type of gauge theory of a sl(2, {})-valued connection 1-form
. The mathematical structure employed to model this replacement of
is a principal finitary spacetime sheaf
of quantum causal sets
with structure group G
n, which is a finitary version of the continuous group G of local symmetries of General Relativity, and a finitary Lie algebra g
n-valued connection 1-form
on it, which is a section of its subsheaf
.
is physically interpreted as the dynamical field of a locally finite quantum causality, whereas its associated curvature
as some sort of finitary and causal Lorentzian quantum gravity. 相似文献
11.
A presence of a Meissner-Ochsenfeld effect in a gas of spin 1/2 fermions with an interaction
, where
is a volume of a region
in real space which is taken by thesystem and
with
,
satisfying Fermi anticommutation relations, is investigated. The effect proves to be weaker than in BCS by a factor 3/4 at T = 0, implying a greater penetration depth
of external magnetic field. V
4 is nonzero only within a thin layer of 1-fermion energies around the chemical potential .Received: 14 June 2004, Published online: 12 October 2004PACS:
74.20.-z Theories and models of superconducting state - 74.20.Fg BCS theory and its development 相似文献
12.
C. P. Boyer E. G. Kalnins Willard Miller Jr. 《Communications in Mathematical Physics》1978,59(3):285-302
We present a complete list of all separable coordinate systems for the equations
and
with special emphasis on nonorthogonal coordinates. Applications to general relativity theory are indicated. 相似文献
13.
R. Akers G. Alexander J. Allison N. Altekamp K. Ametewee K. J. Anderson S. Anderson S. Arcelli S. Asai D. Axen et al. 《Zeitschrift fur Physik C Particles and Fields》1995,67(3):365-378
The forward-backward asymmetry of
has been measured using approximately 2.15 million hadronicZ
0 decays collected at the LEP e+e– collider with the OPAL detector. A lifetime tag technique was used to select an enriched
event sample. The measurement of the
asymmetry was then performed using a jet charge algorithm to determine the direction of the primary quark. Values of:
相似文献
14.
Brovchenko I. Geiger A. Oleinikova A. 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,44(3):345-358
The phase behavior of fluids near weakly attractive substrates is studied by computer simulations of the coexistence curve of a Lennard-Jones (LJ) fluid confined in a slitlike pore. The temperature dependence of the density profiles of the LJ fluid was used to study the surface critical behavior. A universal critical behavior of the local order parameter, defined as the difference between the local densities of the coexisting liquid and vapor phases at some distance
from the pore walls,
, is observed in a wide temperature range and found to be consistent with the surface critical behavior of the Ising model. Near the surface the dependence of the order parameter on the reduced temperature
obeys a scaling law ~1 with a critical exponent 1 of about 0.8, corresponding to the
surface transition. A crossover from bulk-like to surface-like critical behavior occurs, when the distance to the surface is about twice the correlation length at the given temperature. Relations between the
and
transitions in Ising systems and the surface critical behavior of fluids are discussed. 相似文献
15.
16.
Surface structures in the Te/Ni(111) system are revealed by using reflection high-energy electron diffraction combined with X-ray and ultraviolet photoelectron spectroscopies. At a 0.33 mono-layer (ML)-Te/Ni(111) surface, a reversible structural phase transition is observed with a transition temperature Tc of 380
C. The diffraction pattern from the low temperature phase is accompanied by streaks. The high and low temperature phases are characterized by
and
rectangle, respectively. The mechanism of the phase transition is explained by the order-disorder transition with a rumpled chain model. Both 0.51 ML- and 0.44 ML-Te/Ni(111) surfaces exhibit the complex diffraction patterns accompanied by diffuse streaks. These surface structures are characterized by the
rectangle and
, respectively. All diffuse streaks obtained at the above surfaces are consistently interpreted in the view of the ill-ordered arrangements of the well-ordered
linear chains. It is shown that the
linear structure is the key in the Te/Ni(111) system.Received: 1 December 2003, Published online: 20 April 2004PACS:
61.14.Hg Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED) - 68.65.-k Low-dimensional, mesoscopic, and nanoscale systems: structure and nonelectronic properties - 64.60.Cn Order-disorder transformations; statistical mechanics of model systems 相似文献
17.
For Lax-pair isospectral deformations whose associated spectrum, for given initial data, consists of the disjoint union of a finitely denumerable discrete spectrum (solitons) and a continuous spectrum (continuum), the matrix Riemann–Hilbert problem approach is used to derive the leading-order asymptotics as
of solutions
to the Cauchy problem for the defocusing nonlinear Schrödinger equation (
NLSE),
, with finite-density initial data
18.
P. Abreu W. Adam E. Agasi I. Ajinenko R. Aleksan G. D. Alekseev P. P. Allport S. Almehed F. M. L. Almeida S. J. Alvsvaag et al. 《Zeitschrift fur Physik C Particles and Fields》1995,66(3):341-354
The forward-backward asymmetries for the processes
and
at theZ resonance are measured using identifiedD
*± mesons. In 905,000 selected hadronic events, taken in 1991 and 1992 with the DEL-PHI detector at LEP, 4757D
*+D
0+ decays are reconstructed. Thec andb quark forward-backward asymmetries are determined to be:
|
设为首页 | 免责声明 | 关于勤云 | 加入收藏 |
Copyright©北京勤云科技发展有限公司 京ICP备09084417号 |