Temperature dependence of transport coefficients in liquid and amorphous metals

We apply the muffin-tin effective medium approximation to calculate the temperature dependence of the resistivity and thermopower of amorphous and liquid metals. The results show unambiguously that a large resistivity is accompanied by a negative temperature coefficient, in agreement with the experimental situation. This behavior is shown to result from a pseudo-gap which opens in the one-particle spectrum due to strong scattering at the quasi zone boundary and which tends to close under an increase in temperature. In turn the thermopower is found to have non-trivial density and temperature dependences.     

Molecular dynamics simulation of self-diffusion coefficients for liquid metals

The temperature-dependent coefficients of self-diffusion for liquid metals are simulated by molecular dynamics meth ods based on the embedded-atom-method （EAM） potential function. The simulated results show that a good inverse linear relation exists between the natural logarithm of self-diffusion coefficients and temperature, though the results in the litera ture vary somewhat, due to the employment of different potential functions. The estimated activation energy of liquid metals obtained by fitting the Arrhenius formula is close to the experimental data. The temperature-dependent shear-viscosities obtained from the Stokes-Einstein relation in conjunction with the results of molecular dynamics simulation are generally consistent with other values in the literature.     

Analytic properties of the Ishida-Yonezawa approximation for liquid and amorphous metals

We generally examine the analytic properties of the Ishida-Yonezawa approximation for the tight binding single s-band model. A sufficient condition is derived on which a solution satisfies the physical conditions; (1) sum rule, (2) reality, (3) definiteness, (4) analyticity, (5) boundary condition and (6) uniqueness.     

Number-resolved master equation approach to quantum transport under the self-consistent Born approximation

We construct a particle-number(n)-resolved master equation(ME) approach under the self-consistent Born approximation(SCBA) for quantum transport through mesoscopic systems.The formulation is essentially non-Markovian and incorporates the interplay of the multi-tunneling processes and many-body correlations.The proposed n-SCBA-ME goes beyond the scope of the BornMarkov master equation,being applicable to transport under small bias voltage,in non-Markovian regime and with strong Coulomb correlations.For steady state,it can recover not only the exact result of noninteracting transport under arbitrary voltages,but also the challenging nonequilibrium Kondo efect.Moreover,the n-SCBA-ME approach is efcient for the study of shot noise.We demonstrate the application by a couple of representative examples,including particularly the nonequilibrium Kondo system.     

Laser flash method for measurement of liquid metals heat transfer coefficients

New laser flash technique for the measurement of heat transfer coefficients of liquid metals is presented. The thermal diffusivity of the liquid mercury has been studied experimentally over the room temperature range. The thermal conductivity coefficient has been calculated with the use of the reference data on density and heat capacity. Analysis of systematic errors of the measurements has shown that the data error is about 3%. Comparison of the obtained results with data available in publications has proved their reliability.     

Ward identity and effective medium approximation for conductivity of liquid metals

The self-energy to define the ensemble average of a one-electron Green function for a disordered system is related to the vertex correction for the average of the product of two Green functions by the generalized optical theorem or by the so-called Ward identity. Using this relationship, we evaluate the conductivity of liquid metals both by the Ishida-Yomezawa approximation and by the effective medium approximation from the self-energy forms corresponding to respective approximations. The conductivity formulations thus obtained are shown to be identical with those derived from the diagram method.     

On the unitarization of the Born approximation

A new approximation for the elastic scattering transition matrix is suggested. This approximation satisfies the unitarity condition. A modified Born series is introduced which has this unitarized Born approximation as the leading term. The series is applied to the solvable case of scattering by a separable potential and is found to converge in a wider region of energies than that of the conventional Born series.     

第二玻恩近似理论研究激光辅助e-Ar散射

在电子入射方向平行于激光场的极化方向这种特殊的散射模式下，应用第二玻恩近似(SBA)理论，分别利用含有极化势的静电屏蔽势和单纯的静电屏蔽势这两种原子势模型对激光场中电子-氩原子散射进行了研究，并与低频近似和实验数据进行了比较.结果表明，第二玻恩近似理论给出的结果与实验符合较好.另外，极化势在激光辅助电子-原子散射中起着重要作用. 关键词： 极化势 第二玻恩近似 微分截面 激光场     

The electron transport properties of pure liquid metals

Progress in the theory of the electrical conductivity and other ordinary transport properties of liquid metals since 1961 is reviewed. After a brief account of the basic nearly-free-electron diffraction formula, the quantitative comparison of this formula with experiment is discussed.

For the alkali metals, the agreement is adequate, given the uncertainty of the pseudopotentials, although there is controversy about the calculation of the temperature coefficient of ρ _L. To explain the observed volume dependence of ρ _L, and the thermoelectric power, it also seems necessary to allow for the variation of the pseudopotential with the positions of the Fermi level and the core levels relative to the bottom of the conduction band.

Quantitative results for the noble and polyvalent metals are meagre, and although calculations of ρ _L for Al and Zn are in excellent agreement with experiment there may be other cases where the basic formula is not adequate. The general question of the structure and convergence of the perturbation series for ρ _L is discussed, and it is suggested that corrections for higher order terms can be minimized by making the pseudopotential as near as possible to the t-matrix of an ion.

The anomalous properties of Hg are then discussed, in the light of the work of Mott (1966). In this connection it is shown that Edwards' formula (1962) for ρ _L, in which the Fermi velocity, v _F, is taken to be that of a free electron, ?k _F/m, despite deviations from the free-electron curve for ?(k), can be derived by using the expectation value of the current operator in place of e v _F in the Boltzmann equation. This modification of the elementary theory allows the Hall constant of a liquid metal to deviate from 1/nec, as found experimentally.     

Estimating optical properties in layered tissues by use of the Born approximation of the radiative transport equation

We use the Born approximation of the radiative transport equation to recover simultaneously the absorption and scattering coefficients in a single layer of a two-layer tissue sample from reflectance data. This method reduces the estimation of both optical properties to a single linear, least-squares problem. It is valid over length scales smaller than a transport mean free path and hence is useful for epithelial tissue layers. We demonstrate the accuracy of this method by using spatially resolved reflectance data computed with Monte Carlo simulations.     

Comments on the temperature dependence of the electronic transport coefficients in ferromagnetic f-electron metals

Possibilities of formulation of a theory capable of describing the temperature behaviour of the electronic transport coefficients of f-electron crystal field-free systems on a broad temperature scale are discussed. The approach used by Balberg to study the spin-fluctuation resistivity in the vicinity of T_c is shown to be valid on the broad temperature scale if the scattering cross section is appropriately treated. The results of this approach are compared to that of de Gennes and Friedel and supplementary results for the thermoelectric power are presented.     

Spin treatment-based approach for electronic transport in paramagnetic liquid transition metals

A novel concept is proposed to calculate both the electrical resistivity and thermoelectric power (TEP) of liquid transition metals (Mn, Fe, Co and Ni) characterized by a paramagnetic state in the liquid phase. By contrast to a previous work (PRB64, 094202 (2001)), where the resistivity was calculated by treating separately the interactions between spin up and spin down using the Matthiessen rule, our current approach is based on two types of muffin tin potentials in the t-matrix, namely spin up and spin down. The resistivity is treated as the result of the interference of the two kinds of spin states of electrons including a cross-contribution. The calculated resistivity values agree reasonably well with the available experimental ones for all the metals considered. Moreover, the calculated TEP, as deduced from the slope of resistivity vs. energy, has been found to be positive for Mn and Fe but negative for Co and Ni. Besides that, this formalism for resistivity calculation may be generalized to a system that may exist in different atomic states. It is worth mentioning that this concept is analogous to the one used in the process of neutron scattering on a metal composed of multiple isotopes.     

Comparison of methods for calculating turbulent diffusion coefficients

Different methods for calculating the turbulent diffusion coefficient D _T of a passive scalar impurity in an infinite homogeneous isotropic stationary turbulent medium are examined. The values of D _T calculated by these methods are compared for two limiting types of turbulence, viz., turbulence with a δ-function spectrum and turbulence with a Kolmogorov-type spectrum. The temporal dependence of the velocity correlators is assumed to be exponential. It is shown that the most accurate method is based on the use of the solution of the nonlinear equation for the averaged Green’s function with consideration of the contribution from the four-point turbulent velocity correlators. A comparison with the results of other methods that are simpler from the mathematical standpoint shows that some of them also permit the calculation of D _T with relatively good accuracy. Zh. éksp. Teor. Fiz. 111, 871–881 (March 1997)     

Improving the Born approximation for the scattering of ultrasound in elastic solids

It has recently been demonstrated that the Born approximation for predicting the scattering response of flaws can be improved through the use of simple modifications called the "doubly distorted Born approximation". In this paper the doubly distorted Born approximation itself is modified with phase and amplitude corrections that further improve the Born scattering results for isotropic elastic media. The reliability of this new modification of the Born approximation has been evaluated by comparison with the exact solution for spherical inclusions obtained with the method of separation of variables. Unlike the ordinary Born approximation which works well only for very weak scattering inclusions, our modification of the doubly distorted Born approximation gives improved scattering results for both weak and strong scattering inclusions.     

Revisiting the normalized Born approximation: effects of scattering

The normalized Born approximation has been suggested as a ratiometric method in fluorescence molecular tomography (FMT) applications, to account for heterogeneity variations. The method enabled practical inversions, as it offered fluorescence reconstruction accuracy over a wide range of absorption heterogeneity, while also accounting for unknown experimental factors, such as the various system gains and losses. Yet it was noted that scattering variations affect the robustness and accuracy. Herein we decompose the effects of absorption and scattering and capitalize on the recent development of hybrid FMT/x-ray computed tomography imaging methods to proposed amendments to the method, which improve the overall accuracy of the approach.     

Response function technique for calculating the random-phase approximation correlation energy

We develop a scheme to exactly evaluate the correlation energy in the random-phase approximation, based on linear response theory [Y. R. Shimizu, J. D. Garrett, R. A. Broglia, M. Gallardo, and E. Vigezzi, Rev. Mod. Phys. 61, 131 (1989)]. It is demonstrated that our formula is equivalent to a contour integral representation recently proposed [F. Donau, D. Almehed, and R. G. Nazmitdinov, Phys. Rev. Lett. 83, 280 (1999)] being numerically more efficient for realistic calculations. Examples are presented for pairing correlations in rapidly rotating nuclei.