Analysis of the parameters of discrete particle motion in axisymmetric turbulent impinging jets

The parameters of discrete particle motion in axisymmetric turbulent impinging air jets are determined.Notation x, y coordinates (Fig. 1) - v_x jet velocity - V_o maximum jet velocity - r_o nozzle radius - l _i length of the initial jet section - L spacing between the nozzle and the collision plane - ¯x dimensionless coordinate referred to the nozzle radius - ¯x_i dimensionless length of the initial section referred to the nozzle radius - d particle diameter - ₁ jet density - particle density - c_x particle drag coefficient - v particle velocity - v₁ axial jet velocity - kinematic coefficient of the flow viscosity - ¯x_o dimensionless coordinate referred to the distance L - d_c cement particle diameter - d_s sand particle diameter - ¯v_i dimensionless velocity of particle insertion into the jet, referred to V_o Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 5, pp. 813–817, November, 1979.     

Graphicoanalytical method for calculation of heat transfer through the piston of an internal combustion engine

Using a quantitative estimate of deposit formation on the pistons of a diesel engine and results of engine thermometry, a graphicoanalytical method is developed for calculation of heat transfer through an oil-cooled piston.Notation T_m mean resultant gas temperature in engine cylinder - t_h temperature of heated side of piston - t_c temperature of cooled piston surface - t_o temperature of cooling oil - q specific thermal flux through piston - P_e mean effective engine pressure - C_m mean piston speed - T_i injected air temperature, °K - P_i injected air pressure - g_e effective fuel flow rate - mean thickness of piston bottom - thermal-conductivity coefficient of piston bottom - Z number of strokes in engine cycle - _w gas-to-wall heat-transfer coefficient - _o wall-to-oil heat-transfer coefficient - R total thermal resistance Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 5, pp. 918–925, November, 1979.     

A method of joint determination of the effective coefficients of horizontal mixing of large particles and of external heat exchange in an organized fluidized bed

A method is proposed for the joint determination of the coefficients of horizontal particle diffusion and external heat exchange in a stagnant fluidized bed.Notation c_f, c_s, c_n specific heat capacities of gas, particles, and nozzle material, respectively, at constant pressure - D effective coefficient of particle diffusion horizontally (coefficient of horizontal thermal diffusivity of the bed) - d equivalent particle diameter - d_t tube diameter - H₀, H heights of bed at gas filtration velocities u₀ and u, respectively - H_a height of active section - l width of bed - L tube length - l _o width of heating chamber - N number of partition intervals - p=H/H₀ expansion of bed - s_n surface area of nozzle per unit volume of bed - S_h, S_v horizontal and vertical spacings between tubes - t_c, t₀, t_s, t_n, t_w initial temperature of heating chamber, entrance temperature of gas, particle temperature, nozzle temperature, and temperature of apparatus walls, respectively - u₀, u velocity of start of fluidization and gas filtration velocity - y horizontal coordinate - ^*, coefficient of external heat exchange between bed and walls of apparatus and nozzle - ₁, ₁, ₂, ... coefficients in (4) - thickness of tube wall - _b bubble concentration in bed - ₀ porosity of emulsion phase of bed - _n porosity of nozzle - =(t_s – t₀)/(t_c – t₀) dimensionless relative temperature of particles - _n coefficient of thermal conductivity of nozzle material - f, _s, _n densities of gas, particles, and nozzle material, respectively - _be=_s(1 – ₀) (1 – _b) average density of bed - time - _max time of onset of temperature maximum at a selected point of the bed - R =l _o/l Fourier number - Pe = ₁ l ²/D Péclet number - Bi = /_n Biot number Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 41, No. 3, pp. 457–464, September, 1981.     

Tests on a flow cryostat with series cooling

Measurements and calculations on a flow cryostat with serial cooling have given equivalent thermal schemes that have been tested for adequacy and consequent simple working formulas.Notation T_c, T_i, T_w, T_f temperatures of case, body i, tube wall, and flowing coolant in K - T₀ and T_e coolant temperatures at inlet and exit for heat exchanger and pipes in K - T_wi mean pipe wall temperature at points of attachment of bundles from body i in K - T_wn pipe wall temperature at point of attachment for bundle n in K - (_i)_n and _i thermal conductivities of bundle n and all bundles from body i in W/K - _ij thermal conductivity between bodies i and j in W/K - _ci, , _cw thermal conductivities from case to body i and total and radiative conductivities from case to pipe in W/K - _c convective heat-transfer coefficient between pipe and coolant in W/m²·K - _r radiative heat-transfer coefficient between case and pipe in W/m²·K - pipe material thermal conductivity in W/m·K - c specific heat of helium at constant pressure in J/kg·K - q and q_r correspondingly densities of the total heat flux and radiative flux to the pipe in W/m² - P_r heat flux along bundle r in W - M coolant mass flow rate in kg/sec - F tube cross section area in m² - S_i and S_o inside and outside surface areas of pipe in m² - L pipe length in m - ¯x=x/L relative coordinate along pipe axis - ¯x_r relative coordinate for bundle r attachment - R total number of bundles - N_i number of bundles cooling body i - J_i number of bodies linked by heat bridges to body i - _i relative error in calculating the temperature of body i by comparison with numerical result in % - _w mean relative error in heat exchanger temperature calculated numerically by comparison with temperature from (4) taken at ten equally separated points in % - (¯x-¯x_r) Dirac function Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 56, No. 5, pp. 760–767, May, 1989.     

Recovery of a creep-deformed Type 316 stainless steel

The recovery of the dislocation structures produced in a Type 316 steel during creep has been examined by annealing over a range of temperatures and times, both in the presence and in the absence of stress. The influence of dislocation recovery on subsequent reloading behaviour has also been examined.Initial dislocation recovery occurs rapidly but the rate of recovery subsequently decreases as precipitate effects become more important. Dislocation recovery in the early, rapid stage appears to be controlled by vacancy diffusion between the dislocation links. The application of stress during recovery leads to an enhancement of the recovery rate in agreement with the network coarsening model whilst the incremental strains observed on reloading after recovery correlate well with the changes in dislocation structure produced during the recovery periods.List of symbols and appropriate values l dislocation link length - D _s self diffusion coefficient - b Burgers vector (2.5×10^–1 m) - C _j equilibrium jog concentration - dislocation link tension - k Boltzman's constant (1.38×10^–23 J atom^–1 K^–1) - T absolute temperature - t recovery time - M mobility term - Z frictional term associated with particles - _d dislocation density determined from micrographs - N _d number of dislocation intersections on test line - p length of test line - S foil thickness - ¯l mean dislocation link length - _c mean intragranular particle (carbide) spacing - r ₀ mean intragranular particle radius at timet=0 - r _t mean intragranular particle radius at timet - D solute diffusion coefficient - B solubility of M₂₃C₆ in austenite - particle-matrix interface energy - atomic volume (10^–29m³) - change in dislocation density during recovery period - incremental strain associated with reloading after recovery period - K constant - dislocation density - ₀ dislocation density at timet=0 - _t dislocation density at timet - ₀ friction stress associated with particles - constant (1) - shear modulus - angle between dislocation segments as dislocation breaks through a particle - A 1 cos (/2) - E constant - creep rate - F Taylor factor - L mean slip distance of dislocations - rate of dislocation recovery - stress - _y yield stress - J strength coefficient - _p plastic strain     

Dependence of the contact heat conductivity of granular systems on the external load

An examination has been made of the dependence of the contact heat conductivity of granular systems on the external load. The calculation formulas proposed for contact heat conduction are applicable over a wide range of materials.Notation s_a area of actual contact of two particles in a granular material - _c conductivity of the contact between two particles - h_r height of a micro-roughness - _s thermal conductivity of the material of the particles - d=2r particle diameter - _c contact thermal conductivity of the granular material - p porosity of the system - S_a1, S_a2 area of contact of two particles in the freely poured state and under the action of a load - f thermal conductivity of the granular system in the freely poured state - () portion of the thermal conductivity of a granular material that depends on the external load - relative area of contact - s_n nominal area of contact of the two particles - external specific load - E modulus of elasticity of the particle material - E₀ effective modulus of elasticity of the granular material - k₁, k₂, k₃, k_m, k_b empirical coefficients     

Synthesis of silicon nitride powder through nitrogen gas atomization

The feasibility of synthesizing silicon nitride powder utilizing reactive atomization processing was analysed. The range of times required for the flight time of particles, the cooling rate of the silicon melt, the reaction time of silicon and nitrogen, and the diffusion of nitrogen through silicon nitride layers were obtained and compared. The results of this study indicated that the production of silicon nitride powder through the reactive atomization process would be limited by diffusion of nitrogen through the nitride (ash) layer, assuming the nitride layer was coherent and the unreacted core model was a valid representation of the liquid silicon-silicon nitride system.Nomenclature k(T) reaction rate constant at temperature, T(s^–1) - k ₀ Arrhenius coefficient - E activation energy (kJ mol^–1) - R gas constant - T temperature (K) - fraction of normalized conversion of -phase in time t - fraction of normalized conversion of -phase in time t - k reaction rate constant for -phase (s^–1) - k reaction rate constant for -phase (s^–1) - k ⁱ intrinsic first-order rate constant for -phase (s^–1) - x conversion fraction of -phase in time t - x conversion fraction of -phase in time t - n reaction order for -phase = 1 - n reaction order for -phase = 0.5 - J diffusion flux (mol m^–2 s^–1) - D diffusivity, or diffusion coefficient (m² s^–1 or cm² s^–1) - dC change in concentration (mol m^–3) - dl change in distance, l (m) - A(_g) gaseous reactant A - B reactant B (may be solid or liquid) - P solid product P - b stoichiometric coefficient of reactant B - p stoichiometric coefficient of product P - t time of reaction passed (s) - time for complete reaction of a particle (s) - X _B conversion fraction - r _c core radius (m) - R _p particle radius (m) - _B molar density of reactant B (mol m^–3) - k _g mass transfer coefficient between fluid and particle (m s^–1) - C _Ag concentration of gaseous reactant A (mol m^–3) - D _e effective diffusion coefficient of gaseous reactant in ash layer (m² s^–1)     

Breakup of an anomolously viscous liquid film in a centrifugal force field

An equation is obtained for the breakup radius with consideration of tipping moments and Laplacian pressure forces acting on the liquid ridge at the critical point.Notation K, n rhenological constants - density - surface tension - r current cup radius - R maximum cup radius - r_c critical radius for film breakup - ¯r=¯r=r/R dimensionless current radius - ¯r_c=r_c/R dimensionless critical radius - ₀, _c actual and critical film thicknesses - current thickness - R_r ridge radius - h₀ ridge height - h current ridge height - ₀ limiting wetting angle - current angle of tangent to ridge surface - angle between axis of rotation and tangent to cup surface - angular velocity of rotation - q volume liquid flow rate - v₁ and v meridional and tangential velocities - =4vv _lm/r,=4v_m/r dimensionless velocities - M moments of surface and centrifugal forces - M_v moment from velocity head - p_r pressure within ridge - P_vm pressure from velocity head - p_m, p_pm pressures from centrifugal force components tangent and normal to cup surface - deviation range of breakup radius from calculated value - ¯r_max, ¯r_min limiting deviations of breakup radius - _c angle of tangent to curve _c/°₀=f(¯r) at critical point - t random oscillation of ratio _c/_c Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 1, pp. 51–56, July, 1980.     

Recent advances in the numerical analysis of heat pipes

Numerical simulation of heat pipes has progressed significantly in recent years. The state-of-the-art has been advanced in steady state, continuum transient, and frozen startup simulation for high, moderate, and low temperature heat pipes of conventional cylindrical and nonconventional geometries such as wing leading edges and spacecraft nosecaps. This review summarizes these advancements and discusses the important results.List of symbols A cross-sectional area of the vapor channel, m² - c specific heat, J/(kg-K) - C _p specific heat at constant pressure, J/(kg-K) - C _v specific heat at constant volume, J/(kg-K) - D vapor space diameter, m - D _v coefficient of self-diffusion, m²/s - G vapor mass flux, kg/(m²-s) - h convective heat transfer coefficient, W/(m²-K) - h _fg latent heat of evaporation, J/kg - H latent heat due to melting or freezing, J/kg - k thermal conductivity, W/(m-K) - Kn Knudsen number, /D - L total length of the heat pipe, m - L _a length of the adiabatic section, m - L _c length of the condenser, m - M molecular weight, kg/kmol - Ma Mach number, - m _i mass flux at the liquid-vapor interface, kg/(m²-s) - P pressure, N/m² - q heat flux, W/m² - Q heat input at the active evaporator, W - Q _o heat output at the condenser, W - r radial coordinate, m - R gas constant, J/(kg-K) - R _o outer pipe wall radius, m - R _u universal gas constant, J/(kmol-K) - R _v vapor space radius, m - t time, s - T temperature, K - T _i,c interfacial temperature on the continuum vapor flow side, K - T _i,r interfacial temperature on the rarefied vapor flow side, K - T _rf reference (saturation) temperature, K - T _tr transition vapor temperature, K - v radial velocity, m/s Funding for this work was provided by a joint effort of the NASA Lewis Research Center and the Thermal Technology Center of Wright Laboratory under contract No. F33615-88-C-2820     

Investigation of the evaporation process and sonic limits in sodium heat pipes

The maximum heat fluxes in the heating zone and the sonic limits of power transfer in sodium heat pipes and vapor chambers with composite (channel) wicks are investigated experimentally.Notation P vapor pressure - T temperature - density - molecular weight - L latent heat of vaporization - q specific heat flux in heating zone - Q specific heat transfer along heat pipe - G mass flow of vapor in pipe cross section - W average vapor flow velocity in pipe - surface porosity of wick - R universal gas constant - f coefficient of evaporation - momentum-flux coefficient - coefficient of friction - d_v diameter of heat pipe vapor channel Indices 0 liquid surface - v vapor at liquid surface - w wall surface - in entrance to heating zone - so critical cross section Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 5, pp. 832–837, November, 1977.     

Study of flow on the surface of fins on cross-finned tubes

The visualization method was used to study the washing of a flow of air over the surface of fins on tubes with external fins in an annular arrangement.Notation S₁ transverse spacing of tubes in bundle - S₂ lengthwise spacing of tubes in bundle - d diameter of tube bearing the fins - h fin height - t fin spacing - fin thickness - finning coefficient - Re Reynolds number calculated from the velocity of the incoming flow U and the diameter d - x_os size of the separation zone A on the OX axis - heat-transfer coefficient Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 1, pp. 28–34, July, 1984.     

Evolution of transient thermal processes in layer counterflow apparatuses and heat exchangers

Results are given of an analytic investigation of transient processes inside counterflow apparatuses and heat exchangers with temperature disturbance in one of the heat carriers at the entry to the apparatus.Notation =(t–t₀)/(T₀–t₀),=(T–t₀)/(T₀ s-t₀) relative temperatures - t, T temperatures of material and gas respectively - t₀, T₀ same for the initial state - Z=[ _Vm₁/c(1–w/w_g)] [–(y₀–y)/w_g] dimensionless time - m₁=1/(1+Bi/) solidity coefficient - B₁=( _FR/) Biot number - _{F V} heat-exchange coefficients referred to 1 m² surface and 1 m³ layer - R depth of heat penetration in a portion - portion heat conductivity coefficient - shape coefficient (=0 for a plate,=1 for a cylinder,=2 for a sphere) - c, C_g heat capacities of material and gas respectively - , _g volumetric masses - w, W_g flow velocities of material and gas - y distance from the point of entry to the heating heat carrier - y₀ heat-exchanger length - Y= _Vm₁y/W_gC_{g g} dimensionless coordinate - m=cw/C_g– _gW_g water equivalent ratio Deceased.Translated from Inzhenerno-Fizicheskii Zhurnal, vol. 20, No. 5, pp. 832–840, May, 1971.     

A heat meter of finite thickness

The two-dimensional steady-state problem is solved for a heat meter of finite thickness. Corrections to the heat meter readings are estimated.Notation q_o unperturbed heat flux - q_H heat flux recorded by heat meter - heat-transfer coefficient - thermal conductivity - thickness of heat meter - R radius of heat meter - J_o, J₁ zero- and first-order Besael functions - T₁, T₂ temperature distributions of semi-infinite wall and heat meter - T_o temperature distribution of wall in the absence of heat meter Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 5, pp. 835–842, November, 1979.     

Measurement of the effective thermal conductivity of agricultural products

This paper reports new measurements of the effective thermal conductivity of agricultural materials such as grains by means of the transient heat flow method using a line heat source. The effect of a probe diameter used for the transient heat flow method on the effective thermal conductivity was studied using standard spherical particles and some grains. It was concluded that the transient heat flow method can be applied to the measurement of the effective thermal conductivity of agricultural materials such as grains provided that the ratio of the probe diameter to the diameter of the particles of the specimen is greater than unity.Nomenclature A Area of heating surface - d Diameter of particles of the specimen - d _e Hydrodynamic diameter of particles of the specimen - E Error - H Distance between hot and cold walls - L Probe length - M Moisture content - N Number of contact points of particles of the speciment to the probe surface - Q Net heat flux - q Heat flux per probe length added to probe - R Probe radius - r Radial distance - T Temperature - T _h Surface temperature of the hot wall - T _c Surface temperature of the cold wall - t Time - _a Thermal conductivity of air - _eff Effective thermal conductivity - _s Thermal conductivity of a single kernel - Thermal diffusivity - _s Thermal diffusivity of a single kernel - Porosity - Euler constant (=0.5775...) - Angle Invited paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Mass transfer of a single bubble in a minimally fluidized granular bed

The transfer of a gas admixture through the boundary of a cloud of closed circulation of gas is examined with a view to both molecular and convective dispersion.Notation a particle radius - c concentration of the admixture - D, D _c tensors of effective diffusion coefficients and of coefficients of convective dispersion, respectively - D parameter in (14) - D₀, D_m coefficients of molecular diffusion, respectively not taking and taking compressibility into account - F, f functions in (17) and (18), respectively - f fraction of the volume of the sphere with radius R_B occupied by the wake of the bubble - g acceleration of gravity - K mass-transfer coefficient determined in (22) - k coefficient in (7) - L coefficient in (22) - p, s functions determined in (13) - Q, q flow of admixture for the entire bubble and local flow, respectively - r_B, R_c radii of bubble and of cloud of closed circulation, respectively - r radial coordinate - U lift velocity of the bubble - u=v-w; u₀=u_*/u_* minimum velocity of fluidization - V volume of bubble - v, w mean gas velocities in the gaps between particles and of the particles, respectively - parameter determined in (8) - , parameters from (14) - porosity of the dense phase and of the cloud - polar angle - independent variable introduced in (12) - p = 1 - flow function Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 2, pp. 323–333, August, 1980.     

Measurement of temperature in a non-steady-state gas flow

A method is described for measuring the temperature of a non-steady-state gas flow with a thermocouple which is an inertial component of the first order.Notation T*_f non-steady-state gas flow temperature - T_t thermosensor temperature - thermal inertia factor of thermosensor - time - C total heat capacity of thermosensor sensitive element - S total heat-exchange surface between sensitive element and flow - heat-liberation coefficient - temperature distribution nonuniformity coefficient in sensitive element - Re, Nu, Pr, Bi, Pd hydromechanical and thermophysical similarity numbers - P^* total flow pressure - P static flow pressure - T^* total flow temperature - d_t sensitive element diameter - w gas flow velocity - flow density - flow viscosity - _f flow thermal conductivity - k gas adiabatic constant - R universal gas constant - M Mach number - T thermodynamic flow temperature - _o, _o and values at T=288°K - A, m, n, p, r coefficients - _c heat-liberation coefficient due to colvection - _r heat-liberation coefficient due to radiation - _b emissivity of sensitive element material - Stefan-Boltzmann constant - T_e temperature of walls of environment - _c, _r, _tc thermosensor thermal inertia factors due to convective, radiant, and conductive heat exchange - L length of sensitive element within flow - a thermal diffusivity of sensitive element material - _t thermal conductivity of sensitive element material Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 1, pp. 59–64, July, 1984.     

Channel cross-mixing in a finned-rod bundle

A method is given for processing data on channel cross-mixing in bundles of finned rods, which allows one to analyze various sources of data and to derive general relationships for the mixing coefficients.Notation G_ij transverse flow from cell i into cell j per unit length - G_i axial flow rate - T temperature - u velocity - density - P pressure - x, r coordinates - hydraulic-resistance coefficient - Pr_T turbulent Prandtl number - c_p specific heat - q_V volumetric heat-production rate - thermal conductivity - R_o bundle radius - F_u useful cross section - _w wetted perimeter - viscosity - Re Reynolds number - Fr_m centrifugal flow factor Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 5, pp. 777–783, November, 1979.     

Influence of stefan flow on heat and mass transfer and kinetics of chemical reactions of a carbon particle in air

With account taken of Stefan flow, an analysis of the interrelated heat and mass transfer of a carbon particle in parallel reactions on its surface is performed.Notation T temperature, K - t time, sec - density, kg/m³ - c specific heat, J/(kg·K) - d diameter - R particle radius, m - thermal conductivity coefficient, W/(m·K) - particle emissivity - v Stefan flow velocity, m/sec - r radial coordinate - C _j relative mass concentration of the jth component - µ _j molar weight, kg/mole - k ₁,k ₂ constants of the first and the second reaction rates, m/sec - k ₀₁ andk ₀₂ preexponents - E ₁,E ₂ activation energies, J/mole - D diffusion coefficient, m²/sec - =v _RR/D dimensionless value of the Stefan flow velocity - Q _x surface power of heat release, W/m² - Q _st density of the heat flux via heat conduction and Stefan flow, W/m² - Q _r density of the heat flux via radiation - j _j mass flux density - W rate of the heterogeneous chemical reaction in O₂, kg/(m²·sec). Indexes - 1 particle - 2 gas - w wall - st Stefan - infinitely distant - in initial - R on the particle surface - by heat conduction - r by radiation - j 1, O₂ - j 2, CO₂ - j 3, CO - j 4, N₂ Odessa State University. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 4, pp. 576–582, July–August 1995.     

Non-Newtonian properties of emulsions in solutions of surface-active agents

The adsorption of surface-active agents (surfactants) on channels changes the effective viscosity of an emulsion and gives it non-Newtonian properties.Notation a drop radius - C and C° concentration of surfactant near a drop and averaged over the medium - D diffusion coefficient of the surfactant - I second-rank unit tensor - n_i components of the unit normal vector to the drop surface - r radius vector directed from the center of the drop - s surface area of the drop occupied by one molecule of surfactant - t_j and T characteristic times - and sorption and desorption constants - gG and ° true and equilibrium surface concentrations of surfactant - , , and gh₁ effective viscosity and the viscosities of the disperse phase and dispersion medium - volume concentration of the disperse phase - surface tension of the drop - T_j, and characteristic times Indices + and * quantities near and inside the drop - t tangential components of vectors and tensors. The operators div_s and grad_s have the same meaning as the ordinary divergence and gradient operators, but with fixed values of the radius vector ra Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 56, No. 5, pp. 787–793, May, 1989.     

Heating of a bulky body by a circular heat source with heat elimination from the surface taken into account

Results of an analytical and numerical solution of the problem, in a form suitable for the determination of material properties, are given.Notation =(t–t_c)/(q₀R) and T= Bi= (t–t_c)/q₀ dimensionless temperature - q₀ heat flux, W/m² - Bi=R/ Blot criterion - R radius of the heating spot, the characteristic dimension, m - ¯r, ¯z radius and depth, m - r=¯r/R, z=¯z/R dimensionless radius and depth - time, sec - Fourier number - criterion - coefficient of heat elimination, W/m²·deg - heat conductivity, W/m·deg - c specific heat, J/kg·deg - density, kg/m³ - a thermal diffusivity, m²/sec - t _c temperature of the external medium Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 3, pp. 524–526, March, 1981.