A model for viscosity coefficients of gases with potentials differing in form

A recent theory of non-conformal interactions has been very succesful in providing effective spherical potentials for the pressure of more than 40 real gases and many of their binary mixtures. Here, this theory is applied to deal with low-density viscosity coefficients. In its simplest form, the approximate non-conformal (ANC) theory introduces, besides the usual corresponding states parameters-energy ? and distance r_m-a softness parameter s to account for the form of a particular potential function. We investigate the effects of the potential form on the temperature behaviour of the viscosisty coefficient η. It is shown that the softer potentials, with wider attractive wells, have larger viscosities and an explicit expression for η (T, ?, r_m, s) is obtained. The ANC potentials are tested in their capacity to reproduce the temperature dependence of η for the heavier noble gases (Ar, Kr and Xe), diatomics (H₂, N₂, O₂ and CI₂) and a dozen small polyatomics. It is found that the ANC model η (T, ?, r_m, s), with only three substance-dependent parameters, reproduces experimental 7 data within their estimated error.     

Inverse problems of the nonlinear electrodynamics of high-T c superconductors

A method is developed for reconstructing the dependence of the surface impedance of Z _s (H) of high-T _c superconductors (HTSCs) on the amplitude of an ac magnetic field from measurements of the nonlinear radiophysical characteristics of microwave HTSC resonators. It is shown that the nonuniformity of the structure of the electromagnetic field in a resonator lead to integral equations for Z _s (H). The corresponding integral equations are obtained for certain types of resonators. The errors of the conventional methods employing algebraic relations for Z _s (H) are analyzed. The Tikhonov regularization method, developed in the theory of ill-posed inverse problems, is used to reconstruct the functions Z _s (H) from the integral equations. Numerical experiments on the reconstruction of Z _s (H) were performed, and the requirements for the accuracies and other characteristics of the experimental data were determined from them. Zh. Tekh. Fiz. 68, 78–86 (August 1998)     

From macroscopic to atomic motions in liquid metals

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 ν_s(Q). Information regarding bulk viscosity ν_B(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), ν_s(r) and ν_B(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.     

Strong-coupling constant in coordinate space

The coordinate-space behavior of (vector) strong-coupling constant in the background field α_B(r) is compared with that in standard perturbation theory α_v(r). The numerically calculated two-loop coupling constant α_B(r) is shown to exceed α_v(r) by 1–5% at very small distances, r?0.02 fm, and to be in agreement with lattice measurements of the static potential. At large distances, α_B(r) approaches the freezing value at r?0.5 fm. An analytic form of α_B(r) is proposed that approximates α_B(r) with a precision ?2% in the region r?0.5 fm.     

Probing the field-induced variation of the chemical potential in Bi2Sr2CaCu2Oy via magneto-thermopower measurements

Approximating the shape of the magneto-thermoelectric power (TEP) ΔS(T,H) measured in Bi₂Sr₂CaCu₂O_y by an asymmetric linear triangle of the form ΔS(T,H)≃S _p (H)±B ^±(H)(T _c −T) with positive B ⁻(H) and B ⁺(H) defined below and above T _c , we observe that B ⁺(H) ≃2B ⁻(H). To account for this asymmetry, we explicitly introduce the field-dependent chemical potential μ(H) of holes into the Ginzburg-Landau theory and calculate both an average ΔS _av(T,H) and fluctuation contribution ΔS _fl(T,H) to the total magneto-TEP ΔS(T,H). As a result, we find a rather simple relationship between the field-induced variation of the chemical potential in this material and the above-mentioned magneto-TEP data around T _c , viz. Δ μ(H)∝S _p (H). Zh. éksp. Teor. Fiz. 116, 257–262 (July 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Viscoelastic behaviour of fluids with steeply repulsive potentials

We analyse the shear stress, C _s(t) and pressure or ‘bulk’, C _b(t) time-correlation functions for steeply repulsive inverse power fluids (SRP) in which the particles interact via a pair potential with the analytic form, φ(r) = ε(σ/r) ⁿ , in a new approach to the understanding of their viscoelastic properties. We show analytically, and confirm by molecular dynamics simulations, that close to the hard-sphere limit both these time-correlation functions have the analytic form, C _s(t)/C _s(0) and C _b(t)/C _b(0) = 1 – T*(nt*)²+ O((nt*)⁴), where T* = k _B T/ε, is the reduced temperature, k _B is Boltzmann's constant and t* = (ε/mσ²)^½ t is the reduced time. This leads to an alternative and much simpler derivation of formulae for the shear and bulk viscosities which for the limiting case of hard spheres are numerically very close to the traditional Enskog relations. These simple relations for the finite and continuous SRP interaction are in satisfactory agreement with the essentially exact molecular dynamics simulation results for ca. n ≥ 18.     

Proton conductivity and ferroelectric phase transition in hydrogen-bonded ferroelectric NH4IO3

We report on the ac dielectric permittivity (ε) and the electric conductivity (σ_ω), as function of the temperature 300?K?T4IO₃. The main feature of our measured parameters is that, the compound undergoes a ferroelectric phase transition of an improper character, at (368?±?1)K from a high temperature paraelectric phase I (Pm2₁ b) to a low temperature ferroelectric phase II (Pc21n). The electric conduction seems to be protonic. The frequency dependent conductivity has a linear response following the universal power law (σ_{( ω )}?=?A(T)ω ^{s (T)}). The temperature dependence of the frequency exponent s suggests the existence of two types of conduction mechanisms.     

碰撞能及反应物振动激发对Ar+H_2~+→ArH~++H反应立体动力学性质的影响

基于我们最近所构建的Ar+H+2→ArH++H(12A′)反应的新势能面,采用准经典轨线法研究了碰撞能分别为0.48,0.77,1.24 eV以及能量为0.48 eV时反应物不同振动态下Ar+H+2→ArH++H反应的立体动力学性质.结果显示在给定的碰撞能情况下,以及当反应物振动量子数由0变到2时计算的积分反应截面与实验值符合得较好.通过比较发现,碰撞能对此反应k-j′关联函数P(θr)分布的影响大于其受振动激发的影响,并且关于k-k′-j′三矢量相关的函数P(?r)分布以及极化微分反应截面对碰撞能较敏感,同时发现振动激发对P(?r)分布和极化微分反应截面也有较大的影响.     

Anisotropy effects in the A-15 superconductor Nb3Sn

Experimental B_c2(T) characteristics of two Nb₃Sn samples are analyzed using a full strong coupling theory of B_c2(T) which also includes anisotropy effects. The analysis requires a rather pronounced anisotropy of the electron-phonon interaction and of the Fermi velocity and Pauli paramagnetic limiting in order to reproduce the experimental B_c2(T) data over the whole temperature range. The analysis of the second, dirty sample shows that a pronounced change in the electron density of states at the Fermi energy is required together with reduction of the Fermi velocity anisotropy to reproduce the experimental B_c2(T) data. The analysis does not require any contributions from spin-orbit scattering processes to achieve an excellent match between theory and experiment.     

Magnetostriction and other magnetic properties of Co-Ni based amorphous alloys

The magnetostriction coefficients λ_s of (Co_1−xNi_x)₇₅Si₁₅B₁₀ amorphous alloys have been determined in the range 0 ⩽ x ⩽ 0.41. The dependence of the magnetostriction on temperature T has been related to that of the magnetic polarization J_s in a phenomenological way as λ_s(T) = α[J_s(T)]³ + β[J_s(T)]². The compositional dependence of the coefficients α and β has been obtained.From the studies of the magnetostriction in the region close to the Curie temperature it has been possible to evaluate the magnetostriction critical exponent K.     

Kinetic equation for a weakly nonideal Bose gas

A kinetic equation for a weakly nonideal Bose gas is derived in the range where the thermal wavelength (λ_T) is less than or on the order of the mean interatomic distance (r ₀). The case when λ_T > r ₀ is discussed.     

Pressure dependence of the Grüneisen parameter of sodium and potassium

Temperature changes associated with adiabatic pressure changes (?T/?P)_s have been measured for sodium and potassium at room temperature (297 K) under hydrostatic pressures up to 32 kbar. For both metals a large decrease in the value of (?T/?P)_s is observed as the pressure increases. The Grüneisen parameter γ is related to (?T/?P)_s by γ = B_s(?T/?T)_s/T where B_s is the adiabatic bulk modulus. Available data for the pressure dependence of B_s and the isothermal bulk modulus B_T are used to predict the pressure and volume dependence of γ.     

Magnetic flux distribution in the bulk of the pure type-II superconductor niobium measured with positive muons

The spin precession of positive muons in ultra-pure Nb single crystals of high perfection, cooled down in transverse magnetic fields 0.68B _c2≤B _appl≤0.84B _c2 (B _c2=upper critical field) from temperatures well above the superconducting transition temperatureT _c=9.25 K, has been investigated in the temperature range 2.6 K≤T≤8.0 K. The experiments confirm the periodic fieldB(r) of triangular flux-line lattices as calculated from numerical solutions of the microscopic BCS-Gor'kov theory. The observed broadening of the van Hove singularities in the field distribution is discussed in terms of the combined effects of muon diffusion and random perturbations of the flux-line lattice.     

E.S.R. evidence for the planarity of the t-butyl radical

Monte Carlo calculations are reported for the radial distribution function g ₂(r; λ) of a fluid in which the intermolecular pair potential is [u ^ref(r) + λu ^p(r)], u ^ref(r) being the Weeks-Chandler-Andersen (WCA) reference fluid, and [u ^ref(r) + u ^p(r)] being the Lennard-Jones (6, 12) fluid. The calculations are performed for λ values in the range 0 to 1, at the state condition ρσ³ = 0·80, kT/ε = 0·719. It is shown that at high densities the perturbation expansion of g ₂(r; λ = 1) about g ₂(r; λ = 0) is rapidly convergent, but that the corresponding expansion for y ₂(r; λ) = exp [βu(r; λ)] × g ₂(r; λ) is not. In addition Monte Carlo estimates of the individual terms that contribute to the first-order perturbation term, (?g ₂/?λ)_λ=0, are presented. It is shown that these terms are individually large, but that (?g ₂/?λ)_λ=0 is small because there is strong cancellation between the various terms. Consequently, the calculation of (?g ₂/?λ)_λ=0 is highly sensitive to the approximation used to evaluate the individual terms.     

Analytic Bethe ansatz for fundamental representations of Yangians

We study the analytic Bethe, ansatz in solvable vertex models associated with the YangianY(X _r ) or its quantum affine analogueU _q (X _r ⁽¹⁾ ) forX _r =B _r ,C _r andD _r . Eigenvalue formulas are proposed for the transfer matrices related to all the fundamental representations ofY(X _r ). Under the Bethe ansatz equation, we explicitly prove that they are pole-free, a crucial property in the ansatz. Conjectures are also given on higher representation cases by applying theT-system, the transfer matrix functional relations proposed recently. The eigenvalues are neatly described in terms of Yangian analogues of the semi-standard Young tableaux.     

Thermal physical properties of the La0.825Sr0.175MnO3 single crystals

The heat capacity (C _P), the thermal diffusion (η), the thermal conductivity (κ), and the electrical resistance of the La_0.825Sr_0.175MnO₃ single crystal have been measured in the temperature range 80–350 K in magnetic fields to 40 kOe. Dependences C _P(T), κ(T), and η(T) have anomalies near T _C, which are suppressed in magnetic field. The minima in dependences κ(T) and η(T) near T _C are explained by the phonon scattering on fluctuations of the magnetic order parameter. Dependences κ(T) and η(T) have anomalies near T _S = 200 K related to the structural transition from the rhombohedral (R) to the orthorhombic (O*) phase.

     

Utilization of rotational and vibrational temperatures for plasma diagnostics of high-pressure discharges

In the spectra of high-pressure discharges excited in molecular gases, very intensive molecular spectral bands may usually be observed. We may determine the rotational and vibrational temperatures without difficulty, however, the rotational and vibrational temperatures (T _r, T_v) do not offen equal to the temperature of neutral gas (T ₀) or to that of electrons (T _e). If the collision cross sections of electronic, atomic, and molecular excitation (deexcitation) are known, we may then calculate the dependence of the rotational and vibrational temperatures onT _e,T ₀,N _e and the pressure of the gas. The calculations have been performed for pure N₂ and for an Ar-N₂ mixture at atmospheric pressure. The computed graphs make it possible to determine some of the values 4T _e,T ₀,N _e if the temperaturesT _r andT _v are known.The author wishes to extend his thanks to Prof. V. Truneek for valuable comments and to Mr. A. Struka for the preparation of the diagrams.     

Correlations of Bond and Breakage Parameters of Some Ores with the Corresponding Point Load Index

This paper presents significant correlations of the Bond parameter (work index, W_i and grindability, G) and the breakage parameters (specific rate of breakage, S_i and the fineness value, γ) with the point load index (I_s(50)). The experimental results obtained from calcite, barite, colemanite and bauxite samples have demonstrated that the Bond and breakage parameters were closely correlated with the point load index. That is, the values of G, S_i and a_T parameters decreased with the increase in the values of the point load index; however, the γ parameter of B_i,j increased with increasing I_s(50) values.     

Analogous study in low magnetic field between Cu–Ge and Cu–Si ferrites

Two series of mixed copper ferrites, Cu_1+x Ge_x Fe_2−2x O₄ and Cu_1+x Si_x Fe_2−2x O₄, have been analogously investigated for x=0.0, 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3. The two systems were prepared using the standard ceramic techniques. X-ray diffraction analysis indicates that both systems formed in a single phase cubic spinel structure. The lattice parameter has a constant value (0.838 nm±0.001) for the two series. The grain diameter was estimated from the scanning electron microscope micrographs for the two series. Some magnetic properties were measured at room temperature. The magnetization M was measured in the range of magnetizing field up to 5500 Am⁻¹. The relative permeability (μ_r) was calculated from the B–H relation. The B–H loops were measured at constant magnetizing current (I=2.5 A which is equivalent to 900 Am⁻¹). Also, the hystersis area and the magnetic parameters B_r, B_s, m_R (B_r/B_s) and apparent energy loss (E) were estimated from the B–H loops; μ_r, B_r, B_s and E are composition dependent.     

Lokale Messung von Driftgeschwindigkeit und Temperatur der Ionen einer Argon-Niederdruckentladung mit resonanter Laserstreuung

The radial ion drift velocity and temperature in an argon low-pressure discharge have been measured by a resonant laser scattering method with high spatial resolution. The detection limit for the drift velocities was 2 · 10⁴ cm · s^?1. In the vicinity of the discharge axis the drift velocity grows linear with the distance from the axis. The measurements have shown the existence of a radial dependence of the ion temperature T¹(r). Comparisons of axial ion temperature T_? with T_‖(r = 0) are an experimental demonstration of the anisotropy of the ion velocity distribution in this kind of discharges.