Velocity of second sound and superfluid density near the superfluid transition in3He-4He mixtures

Using superleak condenser transducers, the velocity of second soundU ₂ has been measured near the superfluid transition temperature T in³He-⁴He mixtures with molar concentrationsX of³He of 0.0, 0.038, 0.122, 0.297, and 0.440. We have obtained the superfluid density _s/ fromU ₂ on the basis of linearized two-fluid hydrodynamics. The results for _s/ are consistent with those obtained from the oscillating disk method, as expected from two-fluid hydrodynamics. The value of _s/ at eachX could be expressed by a single power law, _s/=k, where =1-T/R, with the experimental uncertainty. It is found that the exponent is independent of concentration forX0.44 within the experimental uncertainty. This concentration independence of is in agreement with the universality concept. From the conclusion that the values of are universal forX0.44, the concentration dependence of the superfluid component _s is expressed by an empirical equation _s(X, )=²_s(0, ). It is found that corresponds to the volume fraction of⁴He in the superfluid³He-⁴He mixture. The value of is in agreement with that obtained from the measurement of the molar volume by others.This paper is based on a thesis submitted to Tokyo University of Education in partial fulfillment of the requirements for the Ph.D. degree.     

Study of the Temperature Fields in Oil and Gas Strata with Water Injection Based on the Perturbation Method

The problem of the thermal action on oil and gas strata by injection of a heating medium using expansion in a small parameter is reduced to an infinite sequence of boundaryvalue problems that are solved by the method of integral transforms. It is shown that, with an appropriate selection of the small parameter, the zerothorder approximation corresponds to a spaceaveraged (across the stratum thickness) solution of the main problem and leads to a concentratedcapacity scheme that is constructed assuming that the stratum temperature is independent of the vertical coordinate. The first approximation permitted marked refinement of calculations according to the concentratedcapacity scheme and an evaluation of its error. Spacetime temperature distributions are presented that have been calculated using the analytical solutions obtained.     

High-Rate IR Laser Evaporation of Silica Glass

IR (10.6 m) laser irradiation of silica glass preforms ensures rapid evaporation of the surface layer. The resulting deposit consists of amorphous SiO₂ with a particle size of 70 nm.     

The importance of seasonal differences in the cellulose microfibril angle in softwoods in determining acoustic properties

The influence of the micro- and mesoscopic structure of wood cell walls on the acoustic properties of softwood was investigated in a synchrotron X-ray microbeam diffraction experiment with particular attention to the seasonal differences in crystallographic features. A multiple regression analysis was performed for data from 12 different softwood species in order to determine the dependence of longitudinal relative Young's modulus (E/) and loss tangent (tan) on seasonal cellulose microfibril angles (MFAs), crystal width of cellulose microfibrils etc. We conclude that a low MFA in both latewood and earlywood yields high E/ and low tan, which is an attribute of wood used as violin or piano soundboards. Among the softwood species we characterized Sitka spruce best fits this criterion.     

Effect of pH on 980 °C spinel phase-mullite formation of Al2O3-SiO2 gels

Different reaction paths of mullite formation via sol-gel processing techniques are reviewed. These variations are due to differences in hydrolysis/gelation behaviours of the silica and alumina components used. Variations of pH during processing without altering other variables follow three different routes of mullite formation. In the highly acidic region(pH 1), the gel does not exhibit a 980 °C exotherm but forms -Al₂O₃. Mullite forms at high temperature by diminution of -Al₂O₃ and -cristobalite, respectively. In the pH range of 3–4.5, gels exhibit a 980 °C exotherm and develop only mullite. In the highly alkaline region (pH 14), the gel produces a Si-Al spinel phase at the 980 °C exotherm and mullite formation at the 1330 °C exotherm takes place from the intermediate Si-Al spinel phase.     

Nitriding of iron boride to hexagonal boron nitride

A process for preparing hexagonal boron nitride (h-BN) from iron boride (FeB) has been described for the first time. FeB powder was nitrided in ammonia at 700 K for 24 hours yielding non-crystalline BN and -Fe₂N. Subsequent annealing in ammonia for 1 hour at 1273 K resulted in a mixture of crystalline h-BN together with -Fe, -Fe₃N and -Fe₄N. The morphology of the product grains is described. This comprises an iron nitride core loosely encapsulated in a foliated BN layer. The open nature of the product layer may account for the relatively low temperature (700 K) required for the nitriding reaction. These iron containing phases were removed with dilute mineral acid leaving h-BN and trace amounts of FeB₄₉.     

Singular Band Behavior of the Extended Emery Model for the Superconducting Cuprates

Mean field slave-boson approximation is performed on the extended Emery model for the CuO₂ conducting plane. The model is parameterized by Cu–O charge transfer energy _pd , copper–oxygen overlap t ₀, oxygen–oxygen overlap t', and Coulomb interaction U on the copper site taken as infinite. Special emphasis is placed on the role of t in the renormalization trends of the effective band parameters _pf and t, replacing _pd and t ₀, at small doping . It is shown that small, negative t expands the range of stability of the metallic phase, changing, in the second order of the perturbation theory, the nature of the metal–insulator transition point. In the nonperturbative limit, t modifies strongly the renormalization of _pf , making it saturate at the value of 4t. Finite doping suppresses the insulating state approximately symmetrically with respect to its sign. The regime _pf 4t fits very well the ARPES spectra of Y123, Bi2212, and LSCO and also explans, in the latter case, the evolution of the FS with doping accompanied by the spectral weight-transfer from the oxygen to the resonant band.     

Relationships between structure and hardness developed during the high temperature ageing of a smart Cu-based alloy

Smart shape memory alloys are used industrially due to their novel properties. Copperbased shape memory alloys are strongly influenced by ageing treatments which involve microstructural changes. The present work has been carried out on a CuZnAlCo alloy which has been aged at 400, 500 and 600 °C for time durations ranging from 5 min to 12 h. Hardness measurements have been performed and the microstructural evolution has been determined by electron microscopy. The results show that microstructural changes are strongly dependent on the ageing temperature and time. A maximum hardness of 300 Hv _0.2 has been obtained after ageing treatments. Equilibrium and phase and non-equilibrium phases ( or martensite) are present in the alloy depending on the ageing temperature and the ageing time. The maximum hardness has been associated with the presence of the and phases.     

Effect of Rigid Blocks on the Mechanical Characteristics and Abrasive Resistance of Polyurethanes

We study the interrelation of the chemical structure of thermoplastic polyurethanes (TPU) with their deformation-mechanical and tribotechnical characteristics. We have established that the concentration of rigid blocks is the determining parameter of structure that controls the properties of TPU. We discovered three characteristic regions, within the limits of which the shapes of concentration dependences are substantially different: < 24%, 24% < < 42%, and > 42%. These regularities can be useful in obtaining TPU with a given complex of physicomechanical and tribotechnical characteristics.     

Analysis of the complex impedance data for β-PbF2

Previously published complex impedance plots for the ionic conductor -PbF₂ show the familiar depressed circular arcs with an angle 0.7 /2 and an activation energy for the volume conductivity W _v=0.45 eV. A detailed analysis of this behaviour in terms of the recently developed non-Debye model shows the real part of the relative dielectric permittivity to have a frequency dependence ^0.7–1, with a high frequency limit of 50 Hz and with only weak dependence on temperature. The low-frequency spurs on the impedance plots are shown to indicate an interfacial barrier at each electrode having a similar non-Debye frequency characteristic to the bulk but showing a strong temperature dependence with an activation energy equal to W _v/2. This suggests the presence of low Debye-screened barriers of about k T height, resulting from depletion and accumulation of ionic carriers at incompletely transmitting electrodes. There is no visible effect of inter-grain boundaries on the flow of direct current.     

Nuclear specific heat of thallium

We have measured the nuclear specific heat of a 0.79 mole thallium sample of 5 N+ purity in the temperature range 70 µKT20 mK and in magnetic fields from 20 mTB228 mT. The experimental results agree with the theoretical expectation for the specific heat of a nuclear paramagnet with the properties of Tl. Our results for the nuclear specific heat imply that the static properties of bulk Tl seem to differ from the dynamic, surface-sensitive properties of Tl samples investigated in former nuclear magnetic resonance experiments.     

Heat Exchange with Horizontal Cylinders in a Centrifugal‐Bubbling Bed

The authors present results of an analysis of experimental data on heat exchange on horizontal cylinders in rotating gasliquid flow. The hydrodynamic parameters of a thin film in a centrifugalbubbling bed have been determined based on the mathematical modeling of a film flow in the case of a highvelocity gasliquid flow about it. Results of a generalization of the data on heat exchange are given, and the hydrodynamic stability criteria for the film flow on the cylinder surface are evaluated.     

On the dispersion of gases under the action of the medium

Some general regularities of dispersion of a gas emerging from a nozzle submerged in a liquid are considered. A condition for establishment of the so-called maximum dispersion state is formulated.Notation ₀ coefficient of surface tension at the liquidgas boundary - contact angle of wetting of the nozzle material surface by the liquid - p_at atmospheric pressure - p air pressure - density of the liquid - g gravitational acceleration - h height of the liquid column - ₁, and _g dynamic viscosity coefficients of the liquid and gas, respectively - R and r radii of the bubble and nozzle, respectively - Q and F dimensionless criteria - , , , , and undetermined coefficients - ratio of the circumference of a circle to its diameter     

Electron spin resonance spectra of Gd3+ ions in K2SO4-ZnSO4 glasses

Electron spin resonance (ESR) spectra of Gd³⁺ ions doped in K₂SO₄-ZnSO₄ glasses have been studied on an X-band ESR spectrometer at different temperatures (–120 to 150 C). The ESR spectrum at room temperature exhibits three prominent features with effectiveg-values of 5.6, 2.83 and 2.02. The spectra are similar to the U spectra familiar in many oxide and fluoride glasses, indicating very low and disordered site symmetries with a broad distribution of crystal fields. Remarkable changes have been observed in the spectrum with changes in the temperature, concentration and glass composition. The broadening of theg 2.02 line with increasing Gd³⁺ ion content indicates that the dipole-dipole interaction between the resonant centres increases with increase in Gd³⁺ ion content. A weak band at 36350cm^–1 is observed in the optical absorption spectrum of 0.5mol% Gd³⁺ in K₂SO₄-ZnSO₄ glass which has been assigned to the transition⁸S_7/2⁶P_7/2.     

Knudsen molecular flow in a channel with a small temperature difference at its ends

The thermomolecular pressure difference (TPD) of helium, argon, and krypton is measured in a packet of glass capillaries for temperatures 273 and 293 K at their ends in a 10–100 range of Knudsen numbers.Notation exponent of the thermomolecular pressure difference effect - Kn Knudsen number - rarefaction parameter - Q_T reduced thermal creep flux - Q_P reduced Poiseuille flux - C(_t) Cercignani-Lampis scattering kernel - R specular scattering kernel - (1 – ) fraction of specular reflection - _t accommodation coefficient of the tangential momentum - P_c, P_h gas pressure in the cold and hot volumes, respectively - coefficient of dynamic viscosity - m mass of gas molecules - k Boltzmann constant - D, L the capillary diameter and length, respectively Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 54, No. 5, pp. 719–724, May, 1988.     

Interfacial spring model for ultrasonic interactions with imperfect interfaces: Theory of oblique incidence and application to diffusion-bonded butt joints

The quasi-static distributed spring model is used to derive the ultrasonic reflectivity of an imperfectly-bonded interface as a function of frequency and angle of incidence. The results are then incorporated in a model for the corner reflection from a diffusion-bonded joint between two abutting plates, the corner being defined by the bond plane and the common lower surface plane of the plates. An immersion-inspection geometry is assumed, and seven categories of corner reflections are identified and examined in detail. These fall into two classes: those having parallel incident and exiting rays in water (=), and those having nonparallel water rays ( ). The = categories are suitable for single probe (pulse-echo) inspections of the joint. Based on the amplitude of the outgoing corner-reflected signal, two = geometries appear promising. These employ, respectively, a corner reflection involving only longitudinal waves with the interface illuminated at near-grazing incidence (LLL), and a corner reflection involving only transverse waves with the interface illuminated at near 45° incidence (TTT). In addition, two practical geometries are indicated; these both involve mode conversion upon reflection from the interface, with the incident or outgoing longitudinal wave traveling nearly parallel to the interface. Model predictions for LLL and TTT reflections are compared to measurements on diffusion-bonded Inconel specimens, and techniques for applying the model results to more complicated bond geometries are discussed.     

AC electrical conductivity of electron beam evaporated Cu-GeO2 thin cermet films

AC electrical properties of 410 nm think 30 at.wt% Cu-70 at.wt% GeO₂ thin films are reported for the frequency range 10⁴ to 10⁶ Hz and temperature range 150 to 425 K. The loss tangent (tan ) and the dielectric loss (/₀) are found to show striking minima around a cut-off frequency 10⁵ Hz. In the lower frequency range (10⁵ Hz), ₁() ^s T ⁿ is obeyed with s (0 to 0.51) increasing as a function of temperature and n (0.10 to 0.14) showing a very weak temperature dependence. In the higher frequency region (10⁵ Hz), ₁() and /₀ increase sharply leading to the quadratic behavior of ₁() with s equal to 2. These processes are discussed by analyzing an equivalent circuit which shows that at lower frequencies, the effects of series resistance in leads and contacts can be neglected, while at higher frequencies such effect give rise to spurious ² dependance for the conductance. A weakly activated AC conductivity and a frequency exponent s that increases with increasing temperature suggest that the low frequency behavior originates from carrier migration by tunneling process.     

Synthesis of aluminum infiltrated boron suboxide drag cutters and drill bits

Synthesis of boron suboxide (B₆O) was made by reactive sintering of crystalline boron and zinc oxide powders at 1450 °C, in argon, for 12 h. After sintering, Vickers microhardness testing was performed on the material synthesized and an average hardness value of 34 GPa was obtained. Sintered suboxide (in crushed and ground powder form) was then analyzed through optical and scanning electron microscopies and X-ray diffraction. Following the completion of the analyses, consolidation of the powder was performed. Two different routes were carried out: (1) explosive consolidation which was performed in double tube (with a density value of 2.22 g/cm³) and single tube (with a density value of 2.12 g/cm³) canister design arrangements and (2) hot pressing which was performed in a graphite die assembly, at 1600 °C, in vacuum, for 2 and 4 h (with density values of 2.15 and 2.18 g/cm³ respectively). Consolidated samples of both routes showed different levels of mechanical attachment, agglomeration, porosity, fracture toughness and fracture strength values, whereas microhardness values and X-ray diffraction plots (as shown in Table I and Figs 6 and 8 respectively) were determined to be similar. Following characterizations, compacts of both routes were then given a high temperature sintering treatment (pressureless sintering) at 1800 °C, in vacuum, for full densification. Both in the as consolidated and densification sintered stages test results revealed the most desirable and well-established properties for the explosively consolidated double tube design compacts (with densification sintered density, microhardness and fracture toughness values of 2.46 g/cm³, 38 GPa and 7.05 MPa m^1/2 respectively). Consolidation and desification sintering steps were then followed by a pressureless infiltration step. Aluminum was infiltrated into densification sintered double tube design consolidated and 4 h of pressed samples (better-compacted and better-sintered compacts) in the temperature range 1100–1250 °C, in argon, for 10 h. During infiltrations, the optimum temperature of the infiltration process was determined to be 1200 °C. Characterization results revealed the most uniform and well established properties once more for the double tube design explosively consolidated compact (with aluminum infiltrated density, microhardness and fracture toughness values of 2.55 g/cm³, 41 GPa and 8.70 MPa m^1/2 respectively).     

Low temperature heat release,sound velocity and attenuation,specific heat and thermal conductivity in polymers

We have measured the long time (t = 5 to 200 h) heat release of Polymethylmethacrylate (PMMA) and Polystyrene (PS) at 70 mK T 300 mK. After cooling from a charging temperature of 80 K the heat release in PMMA shows a t^–1 dependence in the measured time and temperature ranges in agreement with the tunneling model. In contrast, for PS we observe strong deviations from at ^–1 dependence and a factor of ten smaller heat release than in PMMA in apparent contradiction to specific heat and thermal conductivity data for PS. To compare the heat release with other low temperature properties and to verify the consistency of the tunneling model we have measured also the acoustical properties (sound velocity and attentuation), the specific heat and the thermal conductivity of PMMA and PS in the temperature range 70mKT 100 mK, 70mKT200 mK and 0.3 KT4K, respectively. We show that the anomalous time dependence of the heat release of PS is due to the thermally activated relaxation of energy states with excitation energies above 15 K.     

Ageing characteristics of rapidly solidified Al-Li-Ti alloys at 473 K

The influence of titanium on the precipitate free zones (PFZs) and on the stable phase is investigated in four melt-spun Al-Li-Ti alloys with 2 mass% lithium and 0.10–0.35 mass% titanium. Rapid solidification gives rise to a homogeneous distribution of titanium on the wheel side of the ribbons, and to a cellular distribution of solute atoms in intermediate regions and on the gas side. Heat treatments of up to 1000 h at 473 K do not modify titanium distribution, which remains in solid solution. During ageing, preferential coarsening of particles occurs on cell walls. The growth rate of the PFZs is lower than in other Al-Li alloys and is mainly controlled by the titanium concentration of the alloys. The nucleation and growth of the stable phase is also delayed by the presence of titanium. These results indicate that the effect of titanium in solid solution is to retain vacancies thus reducing lithium diffusion rate.