Precipitate strengthening mechanisms in magnesium zinc alloy single crystals

The mechanical behaviour of Mg-5.1 wt % Zn alloy single crystals was studied in the 4.2 to 300° K temperature range. Quenched crystals have activation energies and volumes best associated with the cutting of small clusters of Zn atoms by dislocations. Fully hardened crystals contain fine ₁ and occasional ₂ precipitates with an average ₁ interparticle spacing of 330 to 660 Å. Strengthening in these crystals is mainly ascribed to the cutting of ₁ particles by dislocations. In the overaged condition ₁, ₂ and equilibrium particles are present and lead to a considerable temperature-dependence unusual for an overaged condition. Analysis of this temperature-dependence suggests that below 77° K the relatively easy cutting of ₁ particles by dislocations takes place in addition to the cutting of ₂ and particles. Above 77° K the difficult cutting of ₂ and particles alone controls the deformation, ₁ being more easily cut with the aid of thermal fluctuations.     

Zero Sound Attenuation Near the Quantum Limit in Normal Liquid 3He Close to the Superfluid Transition

The zero sound attenuation of normal liquid ³He has been studied over a range of temperatures from slightly above the superfluid transition temperature, T _c, to approximately 10mK at the constant pressures of 1 and 5bar. Using longitudinal LiNbO₃ transducers, operating both on and off resonance, the experiment was performed at 15 discrete frequencies located in several broadband frequency windows, including 16–25, 60–70, and 105–111MHz. The results are compared to Landau's prediction for the attenuation of zero sound in the quantum limit, (k _B Tk _B T _F), where ₀(P,T, )= (P) T ²{1+(/2k _B T)²}. Calibration of the received zero sound signals was performed by measuring the temperature dependence of the first sound attenuation from 30 to 800mK at those same frequencies and pressures. The data are compared to previous results.     

Magnetic properties of highly dilutedPdFex andPtFex-alloys. Part II. Susceptibility at micro- and milli-kelvin temperatures

We have measured the 16 Hz susceptibility of the giant magnetic moments induced by Fe impurities in highly dilutedPdFe_x andPtFe_x samples with 2.5 ppm x 75 ppm in a wide temperature range, 30 K T 300 mK, and at static magnetic fields 0,01 mT B 25 mT. We find spin glass freezing at Tf(X)/X0,19mK/ppm Fe forPdFe_x and the larger value 0.26 mK/ppm Fe forPtFe_x. This is the first observation of spin glass freezing inPtFe_x. In the low-temperature range T 0.5T_f(x), the susceptibilities follow — ₀ T with small zero-temperature ₀ values forPdFe_X and vanishing ₀ values forPtFe_x. In the paramagnetic high-temperature range, we find (T — )^it-1 at T 10 mK independent of x forPdFe_x, and at T 2Tf(x) dependent of x forPtFe_x with vanishing values for both systems. The data compare well to the predictions of the Thouless-Anderson-Palmer TAP approach of the Sherrington-Kirkpatrick SK model for spin glasses.     

The crystal growth and thermoelectric properties of chromium disilicide

Single crystals of chromium disilicide about 8 mm in diameter and 35 mm long were grown using the floating zone technique. Measurements of electrical resistivity , Hall coefficient R and thermoelectric power were carried out in the temperature range from 85 to 1100 K. The values of and showed the anisotropy over the temperature range studied. The ratios parallel and perpendicular to the c-axis were / =1.9 and /=1.7 respectively, at room temperature. It was found to be a degenerate semiconductor having the hole concentration of 6.3×10²⁰ cm^–3 below 600 K. The effective masses of holes parallel and perpendicular to the c-axis determined from the thermoelectric power and the hole concentration near room temperature were estimated to be five and three times as large as a free electron mass, respectively. The calculation on the values of and was made using those effective masses. These values showed good agreement with the observed values in the temperature range from 150 to 1100 K.     

Investigation of the dominant point defects in tetragonal YBa2Cu3Ox at elevated temperatures

The manner in which oxygen is incorporated into YBa₂Cu₃O _x (YBCO) at 800°C for values ofx close to 6 is shown to be in the form of neutral oxygen interstitials, O _i ^x . The experimental data on which this conclusion is based are obtained from measurements of oxygen partial pressure,P(O₂), as a function of compositionx and temperatureT (5.99x 6.35, 825T1120 K). The data are obtained by a solid-state electrochemical method. Other conclusions of this study include: (a) O _i ^x are noninteracting forx 6. (b) The stoichiometric composition of YBCO isx 6.0. (c) The reaction enthalpy of oxidation is 179 kJ/mol O₂. (d) The Fermi level changes by –0.2 eV asx increases from 6.05 to 6.35.     

Hydrodynamic reaction to accelerated onedimensional motion of gas bubbles of variable volume in an unbounded liquid

A solution is given for the problem of the hydrodynamic reaction of an ellipsoidal gas bubble of variable volume to accelerated motion and the relation between the value of the apparent mass and the eccentricity of the bubble.Notation (,) velocity potential - V velocity of motion of the bubble with respect to the liquid - (, ) velocity potential of the near field - T₂ kinetic energy of the liquid due to the variation in bubble volume - F_r reaction force of the liquid - B₁ momentum of the liquid - _e apparent mass of the ellipsoid - density of the liquid - V_e volume of the ellipsoidal bubble Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 1, pp. 47–50, July, 1980.     

Effect of crack shape,inclination angle,and friction coefficient in crack surface contact problems

In rolling/sliding contact fatigue, it is known that the crack propagates at a characteristic angle =15–30 deg to the surface. To analyze the mechanism, however, the body force method has been widely used assuming 3D crack models for =45–90. In this study, therefore, the unknown body force densities are newly approximated by using fundamental density functions and polynomials. Then, a semi-elliptical crack model is analyzed for =15–90 under compressive residual stresses and Hertzian contact loads. The stress intensity factors K _II, K _III are calculated with varying the crack shape b/a, inclination crack angle , and crack face friction coefficient . The calculations show that the present method is useful for the analysis for =15–30 deg with high accuracy. It is seen that the K _II-values when b/a0 are larger than the ones when b/a=1 by 0–24% for both under compressive residual stress and Hertzian contact load. Regarding the maximum K _II values under Hertzian contact load, the results of =15 deg are smaller than the ones of =45 deg by 23–34%. Regarding the amplitude of (K _{II max}–K _{II min}), the results of =15 deg are smaller than the ones of =45 deg by 4–24%. With increasing the value of friction coefficient for crack faces the value of K _II decreases significantly. When the crack is short and the inclination angle is small, the value of friction coefficient f for Hertzian contact load largely affect the K _II value.     

Group Actions on Binary Resilient Functions

Let G_n,t be the subgroup of GL(n,₂) that stabilizes {x₂ⁿ:|x|t}. We determine G_n,t explicitly: For 1tn–2, G_n,t=S_n when t is odd and G_n,t=S_n, when t is even, where S_n<GL(n,₂) is the symmetric group of degree n and GL(n,₂) is a particular involution. Let _n,t be the set of all binary t-resilient functions defined on ₂ⁿ. We show that the subgroup ₂ⁿ(G_n,tG_n,n–1–t)<AGL(n,₂) acts on _n,t/₂. We determine the representatives and sizes of the conjugacy classes of ₂ⁿS_n and ₂ⁿS_n,. These results allow us to compute the number of orbits of _n,t/₂ under the above group action for (n,t)=(5,1) and (6,2). Keywords:General linear group, Affine linear group, Resilient function.     

Temperature dependence of resistivity for thermally diffused V3Si multilayer films

Results concerning V₃Si films produced by a simple annealed multilayer technique are reported together with X-ray diffraction patterns, Auger spectroscopy, and Rutherford backscattering analysis. Low-temperature electrical resistivity measurements are discussed. It is found that the V₃Si films exhibit aT ² dependence in the temperature rangeT _c T23 K and aT ^2.6 dependence in the rangeT _c T40 K. The normal-state resistivity in the whole temperature range (T _c T600 K) is analyzed in the framework of Cote-Meisel theory. Consistent values of the saturation resistivity _m and of the Debye temperature are obtained by fitting the experimental data with the Cote-Meisel expression for (T).     

Effect of temperature on interfacial shear strengths of SiC-glass interfaces

The in situ temperature dependencies of both the debonding, _d, and frictional, _f, shear stresses of a C-coated 140 m SiC monofilament (Textron SCS-6 SiC fibre) were measured using the single fibre pullout-test. Two matrices, a borosilicate (7740 Corning Glass) and a soda-lime (Thomas Scientific) with different thermal expansion coefficients, were tested. At lower temperatures both _d and _f were found to decrease linearly with increasing temperature as a result of the relaxation of the residual stresses developed during processing, which were compressive in both cases. The stress free debonding shear stress for the borosilicate matrix was found to be 3.5 ± 1 M Pa and the friction coefficient between that matrix and the fibres was calculated to be 0.18. Fibre oxidation are believed to be responsible for enhanced bonding between the fibres and the borosilicate matrix at higher temperatures which results in an increase in both _d and _f. The large thermal expansion mismatch between the soda-lime matrix and the SiC fibres resulted in radial cracking of the former during processing. A technique is described where the whole temperature dependence of the interfacial shear stresses can be measured by a single specimen.     

The Oseen model for internal separated flows

Summary The flow field studied in this paper is the viscous laminar, separated flow downstream of a sudden expansion in a two-dimensional duct. The flow is modelled by the Oseen equations and a solution is sought for the downstream flow given the conditions at the sudden expansion. First, the exact solution to a high-Reynolds-number limit equation suggested by Kumar and Yajnik [6] is obtained. Next, the solution to the full equations is sought in terms of an eigenfunction-expansion procedure which leads to a non-standard eigenvalue problem. A detailed study is made of the latter and a number of expansion procedures are considered for the boundary-value problem. Specific calculations of the separated flow are presented for Reynolds numbers R=10 ⁿ , n=0–5. It is found that as R the solution of the full equation does indeed agree with the solution of the high-Reynolds-number limit equation. In particular it is found that the length of the recirculating region x _r scales with R as R.     

Bone formation induced by calcium phosphate ceramics in soft tissue of dogs: a comparative study between porous α-TCP and β-TCP

Two kinds of tri-calcium phosphate ceramics (Ca/P = 1.50), -TCP and -TCP, which has the same macrostructure and microstructure, but different phase composition, were implanted in dorsal muscles of dogs. The samples were retrieved at 30, 45 and 150 days, respectively, after implantation, and were analyzed histologically. There were critically different tissue responses between -TCP ceramic and -TCP ceramic. Higher cell populations were observed inside the pores of -TCP than those of -TCP, bone tissue was found in -TCP at 45 and 150 days, but no bone formation could be detected in any -TCP implants in this study. On the other hand, the bone tissue in -TCP seemed to degenerate at 150 days. The results indicate that porous -TCP can induce bone formation in soft tissues of dogs; while the rapid dissolution of the ceramic and the higher local Ca²⁺, PO ₄ ^3- concentration due to the rapid dissolution of -TCP may resist bone formation in -TCP and the less rapid dissolution of -TCP may be detrimental to already formed bone in -TCP.     

Development of Spectral Selective Multilayer Film for a Variable Emittance Device and Its Radiation Properties Measurements

A smart radiation device (SRD) that is a variable emittance radiator has been developed as a thermal control material for spacecraft. The SRD has the unique feature of large variation of the total hemispherical emittance _H near room temperature. The _H of the SRD changes depending on its temperature. However, there is a drawback of a large solar absorptance _S. It is too large to use as a thermal control material for spacecraft. In order to reduce the large _S, spectral selective multilayer film was developed. This multilayer film reflects solar radiation and transmits far-infrared radiation to maintain the variation in the _H of the SRD. This paper presents thermal radiative properties of the SRD with spectral selective multilayer film. The multilayer film was designed by using a genetic algorithm (GA). The designed multilayer film was evaporated on the surface of the SRD by the electron beam evaporation method. The experimental results of _S and _H of the SRD with the multilayer film agreed well with calculated results.     

One-dimensional model of heat transfer in cryogenic vacuumshield thermal insulation with radiant heat sources

The heat-transfer problem in an insulation consisting of layers which receive heat from external source through radiation is numerically solved in the one-dimensional approximation.Notation T temperature - x coordinate in the direction normal to the stack - stack thickness - thermal conductivity of the vacuum-shield thermal insulation along the x-coordinate - q_v amount of heat released in a unit volume of vacuum-shield thermal insulation as a result of the incidence of radiation on the face of the shield layers - emissivity - B density of effective radiant flux - Stefan-Boltzmann constant - N number of surfaces - S_ins surface of a vacuum-shield thermal insulation stack - d_di-dj angular coefficient between elementary areas i and j of a surface - Q_o thermal flux through the insulation without a hole - Q_T thermal flux through the insulation with a hole Q_rad thermal flux through the insulation with radiative heat transfer to the bottom base of the hole - Q_s thermal flux reaching the insulation with a hole - Q_rad thermal flux through the insulation with radiative heat transfer to the bottom base of the hole - Q_s thermal flux reaching the stack face by radiative heat transfer through the hole (channel) - x thickness of the i-th insulation layer including one or more shields - _eff effective emissivity of the gap face - q_rad amount of heat reaching a unit area of the bottom base of the hole - T₀ and T₀ boundary temperatures - length of the gap between layers of the insulation stack and the length of the vacuum-shield thermal insulation stack - h width of the gap between layers of the insulation stack - longitudinal thermal conductivity of the vacuum-shield thermal insulation Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 1, pp. 78–85, January, 1982.     

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.     

Paramagnetic resonance in a “dirty” spin-glass

For a spin-glass with nonmagnetic defects (n _m ^1/3l 1, where n _m is the magnetic impurity concentration and l is the mean free path) an absorption function () is derived. Three ranges of temperature and external magnetic field are considered. In the vicinity of the transition the value of () d is estimated as a function of temperature and field.     

Method and apparatus to determine the monochromatic normally hemispherical reflectivity of heat-shield materials

A method and apparatus are described for the determination of the monochromatic normally hemispheric reflectivity _n; results of measuring _n for number of composite materials are presented.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 3, pp. 442–448, March, 1982.     

Cavity growth from crack-like defects in soft materials

We study the growth and failure of small crack-like defects in elastomers under hydrostatic tension. Since the elastic modulus of elastomers are typically very small in comparison with the cohesive strength, crack-like defects can grow into spherical-like cavities before failure. The condition of crack growth or cavity failure is determined using Griffith's fracture criterion, that is, failure of the cavity or crack growth occurs when the energy release rate of the crack-like defect exceeds the surface energy. Three different material behaviors are considered. In the first, we use a power law material model where the strain energy density function w is \displaystylew=\frac2n([1+(I ₁–3)]ⁿ–1), where I ₁ is the sum of squares of the principal stretches, is the infinitesimal shear modulus, and n0 are material constants. In the second case, we consider a Mooney-Rivlin material, which describes the deformation of pressure sensitive adhesives. In the final case, we consider a material model proposed by Gent (1996), which takes into account the condition that a molecular network will fail at some critical stretch ratio. The dependence of the energy release rate on the applied hydrostatic tension is determined using a large strain finite element method. Comparisons are made between our analysis and a previous result of Gent and Wang (GW) (1991), as well as a result of Williams and Schapery or WS (1965). The role of strain hardening in determining the critical applied hydrostatic tension to fail a cavity is examined by comparing the numerical results using the above three constitutive models.     

Thermal stresses in a thin circular disc of orthotropic material due to an instantaneous point heat source

Summary In this paper, we have analysed the transient plane thermal stress problem of a circular disc of orthotropic material with instantaneous point heat source. The variation of with time along different radius vectors is exhibited graphically and compared with that of the isotropic case.

---

Wärmespannungen in einer dünnen Kreisscheibe aus orthotropem Material zufolge einer punktförmigen instantanen Wärmequelle

Zusammenfassung In dieser Arbeit wurde das instationäre ebene Wärmespannungsproblem einer Kreisscheibe aus orthotropem Material zufolge einer punktförmigen instantanen Wärmequelle untersucht. Die Veränderung von über die Zeit für verschiedene Radien ist graphisch dargestellt und wird mit dem isotropen Fall verglichen.

---

Nomenclature r, polar coordinates - T temperature rise - ² ratio of conductivities - ² thermal diffusivity in -direction - J _n Bessel function ofn-th order - t time - p introduced in equation (2) - h heat transfer coefficient - a radius of circular disc - f(r, ) temperature distribution at initial state - r ₀, ₀ a point on the disc - T ₀ strength of point heat source - Dirac delta function - F stress function in two dimensions - ₁, ₂ coefficient of thermal expansion - a ₁₁,a ₁₂,a ₂₂,a ₆₆ elastic constants With 9 Figures     

Stability of the nonequilibrium state of a superconductor irradiated by an electromagnetic field

Irradiation of a superconductor by an electromagnetic field with a frequency ₀ larger than twice the energy gap (order parameter) decreases the order parameter . We obtain the quasiparticle distribution function n and the dependence of the order parameter on the power of the electromagnetic field P by solving numerically the kinetic equations for n and in the steady state. We take ₀/₀ = 2.1, 8, and 20, where ₀ is the equilibrium value of the order parameter at T = 0 K. In the examples considered the dependence of on the pumping power P becomes double-valued above a critical power. We allow phonons also to be out of thermal equilibrium. To discuss the stability of the steady state thus obtained, we derive kinetic equations for small deviations of the quasiparticle distribution function and the order parameter from the steady state n and by means of the nonequilibrium Green's function theory. Assuming n, exp(i kr – t), (k) is computed using n _s/, where n _sis the steadystate quasiparticle distribution function for arbitrary . It is concluded in general that the steady state on the upper branch ( > _{c 2}) is stable with respect to both spatially homogeneous and inhomogeneous fluctuations, and the lower branch ( > _{c 2}) is unstable; _{c 2}is the value where the upper and lower branches of (P) coalesce.This work is partly supported by a Grant-in-Aid for Special Project Research from the Ministry of Education, Science and Culture of Japan.