共查询到20条相似文献,搜索用时 656 毫秒
1.
J. Galvan-Miyoshi J. Delgado R. Castillo 《The European physical journal. E, Soft matter》2008,26(4):369-377
We present a critical assessment of the diffusing wave spectroscopy (DWS) technique for obtaining the characteristic lengths
and for measuring the loss and storage moduli of a reasonable well-known wormlike micelle (WM) system. For this purpose, we
tracked the Brownian motion of particles using DWS embedded in a Maxwellian fluid constituted by a wormlike micellar solution
made of cetyltrimethylam-monium bromide (CTAB), sodium salicylate (NaSal), and water. We found that the motion of particles
was governed by the viscosity of the solvent at short times and by the stress relaxation mechanisms of the giant micelles
at longer times. From the time evolution of the mean square displacement of particles, we could obtain for the WM solution
the cage size where each particle is harmonically bound at short times, the long-time diffusion coefficient, and experimental
values for the exponent that accounts for the broad spectrum of relaxation times at the plateau onset time found in the 〈Δr
2(t)〉 vs. time curves. In addition, from the 〈Δr
2(t) vs. time curves, we obtained G′(ω) and G″(ω) for the WM solutions. All the DWS microreological information allowed us to estimate the characteristic lengths of the WM
network. We compare our DWS microrheological results and characteristic lengths with those obtained with mechanical rheometers
at different NaSal/CTAB concentration ratios and temperatures. 相似文献
2.
The correlation of the local density of states 〈ρɛ(r
1)ρɛ + ω(r
2)〉 in quasi-one-dimensional disordered wires in a magnetic field is calculated under the assumption that |r
1 − r
2| is much smaller than the localization length. This amounts to finding the zero mode of the transfer-matrix Hamiltonian for
the supersymmetric σ model, which is done exactly by mapping to the three-dimensional Coulomb problem. Both the regimes of
level repulsion and level attraction are obtained, depending on |r
1 − r
2|. We demonstrate that the correlations of different eigenfunctions in the quasi-one-dimensional and strictly one-dimensional
cases are dissimilar.
The text was submitted by the authors in English. 相似文献
3.
The spectral dependence of the electron-phonon relaxation rate γe−ph(ℏω) in metals is studied in pump-supercontinuum-probe (PSCP) experiments with femtosecond time resolution. Investigation
of this spectral dependence, which exhibits a substantial slowing of the relaxation rate γe−ph(ℏω) near the Fermi level E
F
, using the parametrization γe−ph(ℏω)∝λ〈Ω2〉 (ℏω−E
F
)2 makes it possible to determine directly the electron-phonon interaction parameter λ〈Ω2〉. The parameter λ〈Ω2〉 for YBa2Cu3O7−δ is analyzed using this method.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 5, 329–332 (10 September 1999) 相似文献
4.
Summary The turbulent hydrodynamic diffusion may essentially change the kinetics of the elementary chemical reactions. The much faster
character of the turbulent diffusion and the evolution of the relative displacements of particles in the inertial range according
to the Richardson law, 〈Δr
2〉 ∞t
3, rather than 〈Δr
2〉 ∞t, remove in many cases the ?bottleneck? effects created by the molecular diffusion and seriously influences the diffusioncontrolled
processes. It changes also the Debye screening of the charged particles in the turbulent fluids and the scenario of the Turing
instability. These problems are discussed in our paper. The consideration is based and on the Obukhov's suggestion on the
Markovian character of evolution of liquid particles in turbulent flows. The role of non-Markovian corrections is also briefly
discussed.
To speed up pubblication, the authors of this paper have agreed to not receive the proofs for correction. 相似文献
5.
N. A. Silant’ev 《Journal of Experimental and Theoretical Physics》1997,85(4):712-723
An analysis is made of the relation between accurate formulas for the coefficients of turbulent diffusion D
T and the alpha effect α
T for a magnetic field in the Lagrange and Euler representations. It is shown that the quadratic term with respect to α
T in the diffusion coefficient derived by Moffatt and Kraichnan is incorrect and should be dropped. First, a numerical solution
of the nonlinear equation (DIA equation) for the Green function is presented, describing the transport of a magnetic field
for the case of incompressible, uniform, isotropic, steady-state turbulence possessing helicity. These solutions are used
to calculate the steady-state coefficients D
T and α
T for various values of the parameters ξ
0=u
0
σ
0/R
0, a=H
0/u
0
2
p
0, σ
0/σ
1, and R
0/R
1, where u
0, σ
0, and R
0 are the characteristic velocity, lifetime, and scale of the turbulent pulsations, and H
0, σ
1, and R
1 are similar values describing the helicity of the medium h(1,2)=〈u(1)· (∇×u(2))〉, and the parameter α characterizes the degree of helicity. The DIA values of D
T and α
T and the self-consistent values of these quantities calculated using the Green tensor in the diffusion approximation are in
qualitative agreement. It is shown that the coefficient of turbulent diffusion is always positive for all the types of turbulence
studied. Nonsteady-state values of D
T(t) and α
T(t) calculated by a self-consistent method are given.
Zh. éksp. Teor. Fiz. 112, 1312–1331 (October 1997) 相似文献
6.
D. M. Sedrakyan D. A. Badalyan V. M. Gasparyan A. Zh. Khachatryan 《Journal of Experimental and Theoretical Physics》1997,84(2):317-321
We find the dependence of the ensemble-averaged resistance, 〈ρ
L〉, of a one-dimensional chain consisting of periodically spaced random delta-function potentials of the chain length L, the incident-electron energy, and the chain disorder parameter w. We show that generally the 〈ρ
L〉 vs L dependence can be written as a sum of three exponential functions, two of which tend to zero as L℩∞. Hence the asymptotic expression for 〈ρ
L〉 is always an exponential function of L. Such an expression for 〈ρ
L〉 means that the electronic states are indeed localized and makes it possible (which is important) to find the dependence
of the localization radius on the incident-electron energy and the force with which an electron interacts with the sites of
the chain. We also derive a recurrence representation for 〈ρ
L〉, which proves convenient in numerical calculations.
Zh. éksp. Teor. Fiz. 111, 575–584 (February 1997) 相似文献
7.
Viktor Bezák 《Czechoslovak Journal of Physics》1999,49(7):1017-1025
The time evolution of a random surfacez=h(r, t) (r=x, y) formed by a deposition process of the Edwards-Wilkinson type is discussed. The discussion is based on the author’s former
derivation of the autocorrelation functionA
h(|r − r′|,t, t′)=〈h(r,t)h(r′,t′)〉 of the height functionh(r,t) under the assumption of a stochastic initial condition [V. Bezák: Acta Physica Univ. Comenianae39 (1998) 135]. Under the assumption of a steady (non-zero) deposition rate, the varianceσ
h
2
(t)=〈[h(r,t)]2〉 increases logarithmically in time whilst the correlation lengthl
h(t) of the height functionh(r,t) increases as ∼t
1/2. Therefore, the ratioσ
h(t)/l
h
(t) tends to zero and the surfacez=h(r,t) does always tend towards a smoothened appearance.
This work has been supported by the Slovak Grant Agency VEGA under contract No. 1/4319/97. 相似文献
8.
J. K. Baria 《Czechoslovak Journal of Physics》2004,54(4):469-485
A model pseudopotential depending on an effective core radius but otherwise parameter free is used to study the interatomic
interactions, phonon dispersion curves (inq and r-space analysis), phonon density of states, mode Grüneisen parameters, dynamical elastic constants (C
11,C
12 andC
44), bulk modulus (B), shear modulus (C′), deviation from Cauchy relation (C
12–C
44), Poisson’s ratio (σ), Young’s modulus (Y), behavior of phonon frequencies in the elastic limit independent of the direction (Y
1), limiting value in the [110] direction (Y
2), degree of elastic anisotropy (A), maximum frequencyω
max, mean frequency 〈ω〉, 〈ω
2〉1/2=(〈ω〉/〈ω
−1〉)1/2, fundamental frequency 〈ω
2〉, and propagation velocities of the elastic constants in Cu, Ag, Au, Ni, Pd, and Pt. The contribution of s-like electrons
is calculated in the second-order perturbation theory for the model potential while that of d-like electrons is taken into
account by introducing repulsive short-range Born-Mayer like term. Very recently proposed screening function due to Sarkar
et al. has been used to obtain the screened form factor. The theoretical results are compared with experimental findings wherever
possible. A good agreement between theoretical investigations and experimental findings has proved the ability of our model
potential for predicting a large number of physical properties of transition metals. 相似文献
9.
Asymptotic behaviors of zero modes of the massless Dirac operator H = α · D + Q(x) are discussed, where α = (α1, α2, α3) is the triple of 4 × 4 Dirac matrices, , and Q(x) = (q
jk
(x)) is a 4 × 4 Hermitian matrix-valued function with | q
jk
(x) | ≤ C 〈x〉−ρ, ρ > 1. We shall show that for every zero mode f, the asymptotic limit of |x|2
f (x) as |x| → + ∞ exists. The limit is expressed in terms of the Dirac matrices and an integral of Q(x) f (x).
相似文献
10.
The branching ratios and photon spectra of the rare processes ρ(ω) → π
0
π
0
γ, ρ(ω) → ηπ
0
γ are calculated in the framework of the standard local quark Nambu-Jona-Lasinio model. Three types of diagrams are considered:
the quark box and the pole diagrams with scalar (σ, α
0(980)) and vector (ρ, ω) mesons. The obtained estimates for the widths of the processes ρ(ω) → π
0
π
0
γ are in satisfactory agreement with existing experimental data. Predictions are made for the widths of the processes ρ(ω) → ηπ
0
γ.
The text was submitted by the authors in English. 相似文献
11.
Measurements have been made of the Hall coefficientR of some alloys of silver in palladium over the temperature range 1°K to 120°K. The alloys contain between ∼1 and ∼10 at.-%
silver. Values ofR were also obtained at room temperature and these were in good agreement with earlier published work. The values ofR are negative in all the alloys, and |R| increases both on reducing the temperature and increasing the silver concentration,c. Below ∼10°K, |R| becomes independent of temperature but shows a linear dependence onc, increasing by a factor of 2.5 over the concentration range measured.
This increase is too great to be accounted for in terms of band structure changes alone, so we have examined the effects of
anisotropic impurity scattering. To a first approximation it can be shown thatR is proportional to an anisotropy parameterA, defined asA=〈τ
2(k)〉/〈τ(k)〉2, whereτ(k) represents the relaxation time of an electron in a statek, and 〈〉 is an average over the Fermi surface. In palladium we assume that the majority of the current is carried by the s-electrons.
In the presence of silver impurities these electrons can be scattered into s-states or d-states with relaxation times given
byτ
ss
α1/c(1−c) andτ
sd
α1/c
2(1−c) respectively. FollowingPlate we have assumed thatτ
ss is isotropic and thatτ
sd is anisotropic, leading to an overall anisotropic relaxation time for impurity scattering. We then find the parameterA increases approximately linearly with silver content, in accordance with our experimental results. 相似文献
12.
Using the appropriate harmonic oscillator states and reasonable approximations, we construct coherent wavepackets corresponding
to the solutions of the Klein-Gordon equation for the attractive potentialV(r)=−k/r, k>0, in two and three space dimensions. We deduce the corresponding classical limit in two dimension by requiring that the
expectation value 〈r〉 of the radial variable is large. In the case of three dimensions, besides the condition of large 〈r〉, we make the uncertainty Δr=[〈r
2〉 − 〈r〉2]1/2 a minimum with respect to certain parameter of the wavepacket. We then investigate the trajectory traversed by the wavepacket
in the classical limit. We find that the classical limit of this relativistic quantal problem gives, in the leading order,
the same expression for the rate of motion of the perihelion as that given by the solution of the corresponding special relativistic
classical dynamical problem. We also briefly discuss some of the subtle aspects of the classical limit of the relativistic
quantal system, in general. 相似文献
13.
Summary In the present review of liquid dynamics studies on liquid metals are reported. Particularly the case of liquid lead is reviewed
because this case was carefully studied by neutron scattering technique,S(Q,ω) being determined at two widely different temperaturesT=623 K andT=1170 K and therefore different densities. In addition extensive supplementary MD simulations were made using a 16 384-particle
system. The simulations ranged from a determination of an effective pair potential for lead to simulation of the density correlation
functionsF(Q,t) andF
s(Q,t), as well as the longitudinal and transversal current correlation functionsJ
1(Q,t) andJ
T(Q,t). The MD simulation ?calibrated? via the experimentalS(Q) andS(Q,ω) was used to prolong the range of neutron data to draw conclusions regarding such quantities as dispersion relations for
the current correlationsJ
1(Q,t) andJ
T(Q,t), the generalized viscosity functions ν1(Q,t), ν1(Q) and νs(Q). Information regarding bulk viscosity νB(Q) is also gained. Conclusions are drawn regarding the relative importance of the derived pair potential form by comparison
to corresponding hard-sphere data. The general framework of linearized hydrodynamic equations for the macroscopic situation
transforming to visco-elastic equations of motion for finite wave-length and high frequency works well also for the case of
a continuous potential. The region of transition from simple visco-elastic to hydrodynamic behaviour is occurring at wavelengths
in the range (12÷20) ? for the cases studied. The spatial properties of the viscosity functions ν1(r), νs(r) and νB(r) are found to correlate well with the range of the radial distribution function for the liquid. The general results for liquid
lead probably have wide range of applicability to other simple liquids with similarS(Q) andg(r) properties.
The authors have agreed not to receive proofs for correction. 相似文献
14.
R. T. Sibatov 《JETP Letters》2011,93(9):503-507
Distributions of the conductance G of a long quantum wire with the fractal distribution of barriers have been obtained in the successive incoherent tunneling
regime. The asymptotic behavior (in the limit L → ∞) of moments 〈G
k
(L)〉, average power of the shot noise 〈S(L)〉, and Fano factor agree with the results of the work [C. W. J. Beenakker et al., Phys. Rev. B 79, 024204 (2009)], and the distributions themselves describe well the Monte Carlo simulation results. The equation that has
been obtained for the distributions of the resistance and conductance agrees with the recent fractional differential generalization
of the Dorokhov-Mello-Pereyra-Kumar equation for the quasi-one-dimensional multichannel disordered semiconductors with a self-similar
distribution of scatterers. 相似文献
15.
Correlations of the topological charge Q, the electric current J
e, and the magnetic current J
m in SU(2) lattice gauge theory in the maximal Abelian projection are investigated. It is found that the correlator 〈〈QJ
eJm〉〉 is nonzero for a wide range of values of the bare charge. It is shown that: (i) the Abelian monopoles in the maximal Abelian projection are dyons which carry fluctuating electric charge; (ii) the sign of the electric charge e(x) coincides with that of the product of the monopole charge m(x) and the topological charge density Q(x).
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 3, 161–165 (10 February 1999)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
16.
I. Kolokolov V. Lebedev M. Stepanov 《Journal of Experimental and Theoretical Physics》1999,88(3):506-516
We consider advection of a passive scalar θ(t,r) by an incompressible large-scale turbulent flow. In the framework of the Kraichnan model all PDF’s (probability distribution
functions) for the single-point statistics of θ and for the passive scalar difference θ(r
1)−θ(r
2) (for separations r
1−r
2 lying in the convective interval) are found.
Zh. éksp. Teor. Fiz. 115, 920–939 (March 1999)
Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor. 相似文献
17.
On the Energy Growth of Some Periodically Driven Quantum Systems with Shrinking Gaps in the Spectrum
We consider quantum Hamiltonians of the form H(t)=H+V(t) where the spectrum of H is semibounded and discrete, and the eigenvalues behave as E
n
∼n
α
, with 0<α<1. In particular, the gaps between successive eigenvalues decay as n
α−1. V(t) is supposed to be periodic, bounded, continuously differentiable in the strong sense and such that the matrix entries with
respect to the spectral decomposition of H obey the estimate ‖V(t)
m,n
‖≤ε|m−n|−p
max {m,n}−2γ
for m≠n, where ε>0, p≥1 and γ=(1−α)/2. We show that the energy diffusion exponent can be arbitrarily small provided p is sufficiently large and ε is small enough. More precisely, for any initial condition Ψ∈Dom(H
1/2), the diffusion of energy is bounded from above as 〈H〉
Ψ
(t)=O(t
σ
), where
. As an application we consider the Hamiltonian H(t)=|p|
α
+ε
v(θ,t) on L
2(S
1,dθ) which was discussed earlier in the literature by Howland. 相似文献
18.
I. K. Kamilov M. I. Daunov A. Yu. Mollaev R. K. Arslanov 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(8):1149-1151
Resistivity ρ and the Hall coefficient R
H at atmospheric pressure in the temperature range of 77–400 K and the dependences of these parameters (ρ(P) and R
H(P)) and magnetic susceptibility (χ(P)) on hydrostatic pressures of up to P ≤ 7 GPa at 300 K in p-InAs〈Mn〉 single crystals was investigated. The baric coefficients of the ionization energy of Mn impurity centers and the
pressure dependence of the dielectric constant ɛ(P) were determined. 相似文献
19.
Peter Reimann 《Journal of statistical physics》2008,132(5):921-935
Consider a mixed quantum mechanical state, describing a statistical ensemble in terms of an arbitrary density operator ρ of low purity, tr ρ
2
≪1, and yielding the ensemble averaged expectation value tr (ρ
A) for any observable A. Assuming that the given statistical ensemble ρ is generated by randomly sampling pure states |ψ〉 according to the corresponding so-called Gaussian adjusted projected measure (Goldstein et al. in J. Stat. Phys. 125:1197,
2006), the expectation value 〈ψ|A|ψ〉 is shown to be extremely close to the ensemble average tr (ρ
A) for the overwhelming majority of pure states |ψ〉 and any experimentally realistic observable A. In particular, such a ‘typicality’ property holds whenever the Hilbert space ℋ of the system contains a high dimensional
subspace ℋ+⊂ℋ with the property that all |ψ〉∈ℋ+ are realized with equal probability and all other |ψ〉∈ℋ are excluded. 相似文献
20.
A pronounced step-like (kink) behavior in the temperature dependence of resistivity ρ(T) is observed in the optimally doped Sm1.85Ce0.15CuO4 thin films around T
sf = 87 K and attributed to the manifestation of strong-spin fluctuations induced by Sm3+ moments with the energy ħωsf = k
B
T
sf ≃ 7 meV. The experimental data are found to be well fitted by the residual (zero-temperature) ρres, electron-phonon ρe-ph(T) = AT, and electron-electron ρe-e(T) = BT
2 contributions in addition to the fluctuation-induced contribution ρsf(T) due to thermal broadening effects (of the width ωsf). According to the best fit, the plasmon frequency, impurity scattering rate, electron-phonon coupling constant, and Fermi
energy are estimated as ωp = 2.1 meV, τ
0
−1
= 9.5 × 10−14 s−1, λ = 1.2, and E
F = 0.2 eV, respectively.
The text was submitted by the authors in English. 相似文献