On the theory of the Kondo effect

The Kondo effect is investigated by methods developed in the theory of fields with strong coupling. Renormalizability relations analogous to the scaling laws in the theory of second-order phase transitions are found. The behavior of the scattering amplitude of an electron by an impurity is analyzed as a function of the electron energy. Formulas are derived for the resistance as a function of the temperature and for the magnetic moment as a function of the magnetic field and temperature. For the antiferromagnetic interaction sign the resistance tends to a constant and the magnetic moment to zero asT 0 according to power laws with universal exponents that depend only on the spin of the impurity. For sufficiently large spin the susceptibility tends to infinity asT 0.     

Empirical heat-exchange equation for a hydroresistor thermoanemometer

An empirical equation is obtained which well describes the heat-exchange process at the sensor of a hydroresistor thermoanemometer in the range of Reynolds numbers from 3 · 10³ to 10⁵ and with a Prandtl number of 7.5.Notation effective electrical conductivity of water in the averaging volume of the sensor, (·cm)^–1 - ₀ electrical conductivity of the surrounding medium - t effective temperature of water heating at sensor, deg - t₀ temperature of surrounding medium - R active resistance of sensor at the temperature t, - R₀ resistance at the temperature t₀ - I effective value of current through the sensor, A - F area of heating layer on sensor head, cm² - heat-transfer coefficient - D diameter of the sensor head - Nu Nusselt number - Pr Prandtl number - Re Reynolds number - circular frequency of voltage supplied to sensor, sec^–1 - magnetic permeability of the medium - v local stream velocity beyond the limits of the boundary layer at the surface of the sensor head, cm/sec - V velocity of the undisturbed stream, cm/sec - x distance from center of the microelectrode along the surface of the head, cm - f designation of functional dependence - coefficient of thermal conductivity of water - kinematic viscosity - _* electrical conductivity of water at the base temperature t_* - b temperature coefficient of electrical conductivity Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 5, pp. 827–833, November, 1978.     

Plastic behaviour of Cd x Hg1−x Te (0⩽ x⩽1) crystals

Cd _x Hg_1–x Te (0x1) single crystals were strained by microhardness and by constant strain rate uniaxial compression tests, in the temperature range 300 to 600 K. Hardness curves as function of temperature can be described by empirical relations. Stress-strain curves, relaxation tests and dislocation observations using transmission electron microscopy show that the deformation is controlled by a thermally activated Peierls mechanism. Moreover, dislocations are dissociated with a stacking fault energy which does not depend on thex composition.     

Some transport properties of palladium films

The effect of deposition rate and substrate temperature on the electrical resistivity (), temperature coefficient of resistance (TCR) and thermolelectric power (TEP) of palladium films, in the thickness range 2 to 25 nm, is found to be marked. Higher rates of deposition and substrate temperatures are found to result in larger grains and hence changes in transport properties. The Fuchs-Sondheimer theory is used to explain the size effect in palladium films while the Mayadas-Shatzkes and Meyer relations are employed to study these effects on, TCR and TEP.     

Simulation of temperature distributions in vacuum

A method is presented for simulating the temperature distribution in an object when there is no convective heat transfer. Similarity of boundary conditions is ensured by a heat shield with a controlled temperature serving as a free parameter.Notation surface emissivity - thermal conductivity - radiative heat-transfer coefficient - l characteristic linear dimension - c length scale for the model - P power - T_iob T_ia, T_is, T₀ temperatures of the object, the model, the shield, and the environment - Stefan-Boltzmann constant Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 20, No. 5, pp. 925–927, May, 1971.     

Contact Angle of Liquid 4He on Cs: Evidence for Ripplons at the He-Cs Interface

Two independent methods to measure the contact angle, , of isotopically pure ⁴ He on Cs are described, and applied to the same Cs sample. The two methods agree well. The contact angle as a function of temperature is measured and clearly shows a first order surface phase transition with a wetting temperature T _w = 2 K. From (T) the difference in surface free energy of the Cs-vapour interface and the Cs-liquid interface is calculated. Its large temperature dependence suggests the existence of ripplons at the liquid He-Cs interface. This surprising possibility is discussed.     

Review on zirconia air-fuel ratio sensors for automotive applications

During the operation of a gasoline engine, the air-fuel ratio (A/F) is a key parameter in controlling fuel consumption and pollutant emissions. In this article, the various zirconia A/F sensors for automotive applications such as the stoichiometric sensor, the limiting current-type sensor, and the wide range A/F sensor were reviewed in the viewpoint of the necessity, structure, operation principle, long-term stability, and the algorithm for catalyst monitoring. The miniaturization and simplification of a sensor design using co-firing and planar processing technology will be an effective approach to improve the performance and cost-effectiveness of the sensor.     

Green's functions for superfluid3He-A in the case of spin hydrodynamics: Influence of the spin-orbit coupling

The spin hydrodynamic equations for superfluid³He-A for the case of external, time-dependent fields are considered. The terms in equations containing these fields are found on the basis of a microscopic approach. Considering the linear response of the system to the switching on of external fields, formulas are found for suitable Green's functions constructed from operators entering the spin hydrodynamics. The Green's function connected with the order parameter operator has a 1/q ² singularity. Suitable connections between Green's functions lead to relations among kinetic coefficients (Onsager relations). A more detailed consideration of the spin-orbit coupling when the spin waves are not true Goldstone modes removes the mentioned singularity and the Onsager relations remain valid.     

Simultaneous Measurement of the Density and Viscosity of Compressed Liquid Toluene

A vibrating-wire densimeter described previously has been used to perform simultaneous measurements of the density and viscosity of toluene at temperatures from 222 to 348 K and pressures up to 80 MPa. The density measurements are essentially based on the hydrostatic weighing principle, using a vibrating-wire device operated in forced mode of oscillation, as a sensor of the apparent weight of a cylindrical sinker immersed in the test fluid. The resonance characteristics for the transverse oscillations of the wire, which is also immersed in the fluid, are described by a rigorous theoretical model, which includes both the buoyancy and the hydrodynamic effects, owing to the presence of the fluid, on the wire motion. It is thus possible, from the working equations, to determine simultaneously, both the density and the viscosity of the fluid from the analysis of the resonance curve of the wire oscillation, the density being related essentially to the position of the maximum and the viscosity to its width. New results of measurements of the density and viscosity of toluene in the compressed liquid region are presented, and compared with literature data. The density results extend over a temperature range 222 KT348 K, and pressures up to 80 MPa. The viscosity results cover a temperature range of 248 KT348 K and pressures up to 80 MPa. The uncertainty of the present density data is estimated to be within ±0.1% at temperatures 298 KT350 K, and ±0.15% at 222 KT273 K. The corresponding overall uncertainty of the viscosity measurements is estimated to be ±2% for temperatures 298 KT350 K, and ±3% for 248 KT273 K.     

Thermally activated flow parameters in the deformation of MgO single crystals

Strain-rate cycling methods have been used to determine the thermally activated flow parameters in the compressive deformation of MgO single crystals. Activation volumes of the order of 100b ³ have been measured for deformation below room temperature, indicating dislocation-point defect interactions as the rate controlling mechanism for hardening at these temperatures, whileV ^* values of the order of 1000b ³ have been measured at and above room temperature. This, together with the fact that the effective stress remains constant with strain at these temperatures identifies the interaction of dislocations with dislocation dipoles as the rate controlling mechanism in this temperature range. The Gibbs free energy for deformation,G, equals the activation enthalpy,H, at low temperatures and the deviation ofG fromH above room temperature may be attributed to entropy effects.     

Magnetic collective excitations in the B phase of superfluid He-3

The dynamical susceptibility of the B phase of superfluid He-3 in the presence of dipolar coupling is calculated in the collisionless regime. Two poles of the susceptibility that correspond to the spin wave and the mode with energy gap (2/5)^1/2 2 are found. The result agrees with that of Tewordt and Einzel qualitatively and contradicts the recent work by Maki. The residue of the high-frequency mode becomes remarkable near the transition temperature. The dispersion relations of these modes atT=0 K and near the transition temperature are given in the most general form.     

High Critical Current Density of c-Axis-Oriented MgB2 Thin Films

From the magnetic hysteresis loops (M-H) and the current-voltage (I-V) relations, we obtained the critical current density (J _c) for c-axis-oriented MgB₂ thin films with a transition temperature of 39 K. The temperature dependence of J _c obtained from the M-H and the I-V curves coincide, which indicates the strongly linked nature of the intergrains in these thin films. And, the high value of J _c was estimated to be 4×10⁷ A/cm² at 5 K and 1×10⁵ A/cm² at 37 K under a self field, indicating a promising candidate for technological applications.     

Thermal diffusivity of fluids in a broad region around the critical point

Dynamic light scattering is a suitable method for the investigation of transport properties such as the thermal diffusivity of optically transparent fluids. The main advantages of the method are its quickness, the fact of the thermodynamic state of equilibrium of the sample (gradients are not required), and the relatively simple evaluation of data without the necessity of calibration. However, an insufficient production of intensity of scattered light may be a limiting effect. For that reason the vicinity of the gas-liquid critical point represents the classical range of application. In this paper, it is shown that by means of an appropriate choice of experimental apparatus, measurements are also feasible in an extended range of states. Broad regions around critical points of three pure fluids (sulfur hexafluoride, SF₆; ethane, C₂H₆; nitrous oxide, N₂O) over temperature ranges ¦T-T _c¦ of 0.02 to 50 K and density ranges (/_c) of 0.2 to 2 were investigated. In this region the thermal diffusivity shows great variations with temperature and density and cannot be described by means of ideal-gas behavior or relations for liquids. The measurements were carried out along the coexistence curve for both phases, along the critical isochore and along some isotherms with TT _c. The measured or calculated density, pressure, and thermal diffusivity data as well as some correlations are presented.     

Chemical techniques for measuring and controlling the thermodynamic properties of aqueous fluids at high pressures and temperatures

Several chemical techniques have recently been developed for measuring and controlling the fugacitiesf _{O 2},f _{H 2},f _{H 2 O}, andf _HCl in supercritical aqueous fluids. Experimental samples consisting of fluid components and solid chemical sensors or buffers are sealed in H₂-permeable noble metal (Pt or Ag Pd alloy) capsules and reacted at high pressure and temperature, Hydrogen diffusion through the walls of the capsule(s) allowsf _{H 2} to be controlled or measured. After quenching, the fluids and solids are analyzed to quantify one or more thermodynamic properties of interest. Methods for determining the activity Composition relations of H₂O in aqueous fluid mixtures are discussed.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder. Colorado. U.S.A.     

Analysis of multiwavelength pyrometry using nonlinear chi-square fits and Monte Carlo methods

An analysis of multiwavelength pyrometry is made using Monte Carlo methods to evaluate the measurement error as a function of temperature for three, four, five, and six channels. Both a graybody and an emissivity with linear wavelength dependence are considered. ² is calculated using the observed intensity in each channel and is minimized with respect to the temperature and the emissivity coefficients, using the Levenberg-Marquardt method. The influence of spectral span of the channels and the weight function used in the ² fit are exmained. For the case of linear wavelength dependence, the solutions are found to be nonunique, even with six channels. The results show little improvement of precision with increasing number of channels beyond four channels when the nonlinear variable T is free. Both the spectral span and the weight function are shown to be important variables.     

Density Response and Equilibration in a Pure Fluid Near the Liquid-Vapor Critical Point: 3He

We report measurements of the local density response inside a quasi 1-D horizontal ³ He fluid layer to a step-like change T of the boundary temperature, where |T| 80 K and much smaller than |T – T_c| where T_c is the critical temperature. These experiments used a new cell design, described in the text, and were carried out along the critical isochore both above and below T_c. The observed temporal and spatial density response (t, z) and its equilibration time are described adequately by the relations developed from the thermodynamic theory of Onuki and Ferrell. We verify that over the temperature range of low stratification, where computer simulations and closed-form calculations can be compared, they are in exact agreement. The systematic differences of experimental results from predictions can be accounted for by the departure of the cell from the ideal 1-D geometry. The much larger disagreement between the experimental and predicted equilibration time scale in earlier experiments is also explained. Finally, deviations from linearity observed in the density response for steps |T| larger than 90 K are reported and the implications of such nonlinearity for the (t, z) profile and especially the effective relaxation time _eff are analyzed. We also discuss the predicted onset of convection near T_c for the conditions in our experiment. In the Appendix, the likely sources for systematic deviations in the density response function for the experimental cell from calculations in the ideal 1-D geometry are presented and their effects calculated. The so-obtained response function Z_F(, z) is compared with previously published data.     

Design and operation of a thermal sensor with micrometer-spatial resolution

We have developed a simple superconducting thin film device that can be used as either a thermometer or a thermal conductivity sensor. Over a narrow range the device has somewhat better temperature resolution than a conventional germanium thermometer, but its main advantage is that it has very high spatial resolution. The fabrication and operation of the device are described, together with preliminary results of experiments in which it is used to study liquid⁴He very nearT . Potential improvements are also discussed.     

Thermodynamic stability of the superconducting phase diagram of UPt3

The superconducting phase diagram ofUPt ₃, as determined by accurate dilatometry as function of temperature and magnetic field (Bc andBc), exhibits three superconducting phases which meet in a tetracritical point. We show that the measured phase diagrams are thermodynamically stable and that all four phase lines are of second order. Via Ehrenfest relations the pressure dependence of the various phases has been determined. The so-calledC phase is the most stable phase under uniaxial pressure along the c-axis (p _c>2.5 kbar). The resulting phase diagram in thep _c -T plane yields stringent constraints on the fourth order coupling constants in the Ginzburg-Landau scenario of a vector superconducting order parameter coupled to a symmetry breaking field.     

Low temperature deformation behaviour of ASTM A-203D nuclear structural steel

The steel A-203D in martensitic, tempered martensitic and ferritic-pearlitic microstructural conditions, was deformed in tension at temperatures between 77 to 300 K and at a strain rate of 6.67×10^–5 sec^–1. The thermal component of the flow stress and the activation parameters were measured as a function of temperature. It was observed that the microstructure did not affect either the thermal part of the flow stress (*) or the activation parameters (V* and H) and that its effect was felt only on the athermal component ( ) of the flow stress. Further the relations of the activation parameters with stress, strain and temperature were found to be consistent with Dorn-Rajnak theory of Peierls mechanism of plastic deformation. In addition measurements of slow-bend and impact transition were also carried out for ferritic-pearlitic structure. Based on these observations, it is shown that the impact transition temperature of this structure can be emperically correlated with the thermal activation parameters.     

Laser-target technique for determination of elastic constants of glass over a wide temperature range

Optical methods have been developed for high temperature application in the determination of the basic quantities, E, Young's modulus and , Poisson's ratio. The methods are simple and the techniques are inexpensive. The methods presented have been tried on commercially available soda-lime-silica glass and consistent results were obtained.