Interaction between a dislocation and an impurity in KCl: Mg2+ single crystals

The interaction between a dislocation and the impurity in KCl: Mg²⁺ (0.035 mol% in the melt) was investigated at 77–178 K with respect to the two models: one is the Fleischer's model and the other the Fleischer's model taking account of the Friedel relation. The latter is termed the F-F. The dependence of strain-rate sensitivity due to the impurities on temperature for the specimen was appropriate to the Fleischer's model than the F-F. Furthermore, the activation enthalpy, H, for the Fleischer's model appeared to be nearly proportional to the temperature in comparison with the F-F. The Friedel relation between effective stress and average length of the dislocation segments is exact for most weak obstacles to dislocation motion. However, above-mentioned results mean that the Friedel relation is not suitable for the interaction between a dislocation and the impurity in the specimen. Then, the value of H(T _c) at the Fleischer's model was found to be 0.61 eV. H(T _c) corresponds to the activation enthalpy for overcoming of the strain field around the impurity by a dislocation at 0 K. In addition, the Gibbs free energy, G ₀, concerning the dislocation motion was determined to be between 0.42 and 0.48 eV on the basis of the following equation ln / = G ₀/(kT_p0)1 – (T/T _c)^{1/2 –1}(T/T _c)^1/2 + ln ₀/where k is the Boltzmann's constant, T the temperature, T _c the critical temperature at which the effective stress due to the impurities is zero, _p0 the effective shear stress without thermal activation, and ₀ the frequency factor.     

The athermal α → ω transformation in Zr-2 at% Nb alloy

The athermal transformation in Zr-2 at.% Nb alloy has been investigated by transmission electron microscopy. Analysis of the selected-area diffraction pattern has shown that the orientation relationships between the omega and the parent-phase in quenched Zr-2 at.% Nb alloy are the same as have been previously observed for the reaction in pure zirconium. Thus it was deduced that the direct transition has taken place in the alloy during cooling. The-originated -particles were visualized using the dark-field technique. The formation of the athermal omega in the-region of-stabilized Zr-Nb alloy is discussed in terms of the relative positions of the free energy equilibrium curvesT ₀ ,T ₀ ,T ₀ and the correspondingM _s ,M _s andT _s start curves. It is concluded that the omega phase can occur over a much wider range of alloy compositions than is usually recognized on the basis of transformation data.     

Magnetic field dependence of zero-sound attenuation close to the pair-breaking edge in3He-B due toJ=1−,J z =±1 collective modes

Our previous theory yielded for the Zeeman splitting of the imaginaryJ=1 collective mode in³He-B the result =2+0.25J _z ( is the effective Larmor frequency). In this paper we take into account the downward shift of the pair-breaking edge from 2 to 2₂– (₂ and ₁ are the longitudinal and transverse gap parameters). This leads to a complex Landé factor: the frequencies of theJ _z =±1 components become =2+0.39J _z , and the linewidths of these resonances become finite: =0.18. The coupling amplitudes of theJ _z =±1 components to density are found to be proportional to gap distortion, (₁–₂/(/)². Our results for the ultrasonic attenuation due to theJ _z =±1,J=1 modes are capable of explaining the field dependence of the attenuation close to the pair-breaking edge as observed by Dobbs, Saunders, et al. The observed peak is caused by theJ _z =–1 component: its height increases due to gap distortion as the field is increased, and the peak shifts downward in temperature and its width increases with the field due to the complex Landé factor. TheJ _z =+1 component gives rise to a corresponding dip relative to the continuum attenuation.     

Critical scattering in the electrical resistance of GdB6 and DyB6

Detailed investigations of the electrical resistance of GdB₆ and DyB₆ near T _N, their antiferromagnetic transition temperatures, and of nonmagnetic LaB₆ are reported. In GdB₆ a recently reported magnetic phase transition around 6 K has been found to be sample dependent. The resistance of this compound shows a very rapid increase at about T _N = 15.15 K and a small maximum near 15.5 K. Analysis of the data using r = r₀ + Bt + A_±t^1–, where t = (T–T _N )/T _N , for –4 × 10^–3 t –7 × 10^–2, yields 0.36. This is in agreement with a renormalization group theory prediction for a system with a three-dimensional lattice (d = 3) that is magnetically isotropic and has six spin degrees of freedom (n = 6). The resistance of DyB₆ shows features of a typical antiferromagnetic transition with electron scattering mainly dominated by fluctuations in short-range spin correlations.Using the above expression for –1.8 × 10^–2 t 4.8 × 10^–2 with the A ₊term when t is positive and A _–when t is negative, we obtain T _N = 20.32 K and = –0.16, which is close to the theoretical value ( = –0.17) for d = 3 and n = 4. The results are discussed in terms of the present theories for critical scattering.This research was supported in part by a grant from the Natural Sciences and Engineering Research Council of Canada.     

Free convection effects on the oscillatory flow of a couple stress fluid through a porous medium

Summary Effects of free convection currents on the oscillatory flow of a polar fluid through a porous medium, which is bounded by a vertical plane surface of constant temperature, have been studied. The surface absorbs the fluid with a constant suction and the free stream velocity oscillates about a constant mean value. Analytical expressions for the velocity and the angular velocity fields have been obtained, using the regular perturbation technique. The effects of Grashof numberG; material parameters and ; Prandtl numberP; permeability parameterK and frequency parametern on the velocity and the angular velocity are discussed. The effects of cooling and heating of a polar fluid compared to a Newtonian fluid have also been discussed. The velocity of a polar fluid is found to decrease as compared to the Newtonian fluid.List of symbols C _p specific heat at constant pressure - g acceleration due to gravity - G Grashof number - K ⁺ permeability of the porous medium - K dimensionless permeability - P Prandtl number - t ⁺ time - t dimensionless time - T _w ⁺ mean temperature of the surface - T ⁺ temperature of the fluid - T ⁺ temperature of the fluid away from the surface - density of the fluid - viscosity - _r rotational viscosity - C _a ,C _d coefficients of couple stress viscosities - I a scalar constant of dimension equal to that of the moment of inertia of unit mass - x ⁺,y ⁺ coordinate system - u ⁺,v ⁺ velocity components in thex ⁺ andy ⁺ directions - u dimensionless velocity in thex ⁺-direction - ⁺ angular velocity component - dimensionless angular velocity - n ⁺ frequency of oscillations - n dimensionless frequency - perturbation parameter - U a constant velocity - u ₀ mean velocity - u ₁ fluctuating part of the velocity - ⁰ mean angular velocity - ¹ fluctuating part of the angular velocity - T ₀ mean temperature - T ₁ fluctuating part of the temperature - ⁰ coefficient of the volume expansion - kinematic viscosity - ^r rotational kinematic viscosity - , material parameters characterizing the polarity of the fluid - v ₀ suction velocity - density of the fluid far from the surface - y dimensionless coordinate normal to the surface     

Second-order wave force on a large cylinder

Summary A new technique has been developed for estimating the wave loadings on large circular cylinders. The theory, mainly due to Lighthill, has been applied to the case of large cylinders. Comparison with the previously reported experimental results shows favourable agreement for the range of parameters indicated in the graphs.Notations The following symbols are used in this paper a Wave amplitude - b Radius of the cylinder - D Diameter of the cylinder - F _l Linear force - F _d Dynamic force - F _q Quadratic force - F _w Water line force - g Acceleration due to gravity - h Depth of water - H=2a Total wave height - k Wave number,k=2/L - L Wave length - n Outward normal to body surface - n _x Direction cosine between the normaln and the given force - S Body surface - t Time - T Wave period - x, y, z Cartesian coordinates - r, ,z Cylindrical coordinates - W Vertical velocity of fluid - Density of fluid - Wave frequency, =2/T - Total velocity potential - _r , _z Partial derivatives with respect tor andz, respectively - ⁽¹⁾, _l Linear theory velocity potential - ⁽²⁾, _q Second-order velocity potential - Water surface elevation or wave height - _i Linear theory wave height - _q Quadratic theory wave height With 3 Figures     

Angular Dependence of the Activation Energy in YBCO/PBCO Multilayers

The activation energy in several (YBCO) _m /(PBCO) _n superconducting multilayers was deduced from resistivity measurements in magnetic fields up to 16 T, as a function of the angle between the magnetic field and the ab planes. The activation energy U ₀ (B,) scales with a reduced field B _red =B(sin ² +cos ² / ² ) ^1/2 , with an angle dependent anisotropy parameter . A crossover from U ₀ log B _red , at low B _red , to U ₀ (B _red ) at high B _red , is also observed. The implications of these results on vortex dynamics and on the coupling between the superconducting layers will be discussed.     

The influence of antimony-additions on the creep behaviour of a 25wt% Cr-20wt% Ni austenitic stainless steel

The effect of antimony on the creep behaviour (dislocation creep) of a 25 wt% Cr-20 wt% Ni stainless steel with ~ 0.005 wt% C was studied with a view to assessing the segregation effect. The antimony content of the steel was varied up to 4000 ppm. The test temperature range was 1153 to 1193 K, the stress range, 9.8 to 49.0 MPa, and the grain-size range, 40 to 600m. The steady state creep rate, , decreases with increasing antimony content, especially in the range of intermediate grain sizes (100 to 300m). Stress drop tests were performed in the secondary creep stages and the results indicate that antimony causes dislocations in the substructure to be immobile, probably by segregating to them, reducing the driving stress for creep.Nomenclature _a Creep stress in a constant load creep test without stress-drop - _A Initial applied stress in stress-drop tests - Stress decrement - ( _A-) Applied stress after a stress decrement, - t _i Incubation time after stress drop (by the positive creep) - _C Strain-arrest stress - _i Internal stress - _{s s}-component (= _i- _c) - Steady state creep rate (average value) in a constant load creep test - Strain rate at time,t, in a constant load creep test - New steady state creep rate (average value) after stress drop from _A to ( _A-) - Strain rate at time,t, after stress drop.     

Natural damped frequencies and axial response of a rotating finite viscous liquid column

Summary For a finite solidly rotating cylindrical liquid column the damped natural axisymmetric frequencies have been determined. The liquid was considered incompressible and viscous. The cases of freely slipping edges and that of anchored edges have been treated. It was found that instability appears in a purely aperiodic root for the spinning liquid bridge. This is in contrast to the instability appearing in the damped oscillatory natural frequency of a nonspinning liquid column at . The spinning viscous liquid column exhibits the same instability as the frictionless liquid. It appears at for axisymmetric oscillations.List of symbols a radius of liquid column - I _m modified Bessel function of first kind and orderm - s complex frequency ( ) - r, ,z polar cylindrical coordinates - p pressure - t time - u, v, w radial-, azimuthal- and axial velocities of liquid, respectively - Weber number - h height of liquid column - dynamic viscosity of liquid - v kinematic viscosity of liquid (v=/) - density of liquid - surface tension of liquid - _r , _rz shear stress - (r, z, t) circulation - (r, z, t) streamfunction - ₀ angular velocity of liquid column about the axis of symmetry - (,t) free surface displacement     

Gas absorptivity in a complete spectrum

Necessary conditions are established for the validity of the Hottel formulas for the absorptivity relative to black radiation. The formulas are used in describing the absorption of a badly mixed medium and for nonblack incident radiation.Notation x ray path in mat - p, P partial and total pressure - P_eff effective broadening pressure - T, T₀ gas and wall temperatures, °K - T_*, T_i selected temperature values - T_c weighted-mean temperature - a₀ absorptivity of the gas for black radiation - a same for a flux with nonblack spectrum - emissivity - m, u, n, , power exponents - i _0j Planck function for the center of the band, cm · W/m² · sr - I_j incident flux intensity at the center of the band j, cm · W/m² · sr - I integrated incident flux intensity, W/m² · sr - A_j integral absorption (equivalent width) of band f, cm^–1 - _j mean absorption in the band - wave number, cm_–1 - ₀ position of the band center - _j width parameter - _effj effective width - _j total width of the band j, cm^–1 - D_j mean transmissivity in the band j - S integrated line intensity, cm–1/mat - d, b spacing between lines and their half-width, cm–1 - S_j integrated intensity of the band j - L Landenburg and Reiche functions - spectral absorption coefficient, mat_–1 - (T) dimensionless function - c_i dimensionless number - R_*, R_c general notation for parameters averaged over the band and for T_c - E Elsasser function Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 20, No. 5, pp. 802–808, May, 1971.     

Microstructure and mechanical properties of rapidly quenched L20 and L20+L12 alloys in Ni-Al-Fe and Ni-Al-Co systems

Ductile L2₀-type wires and+L1₂-type duplex wires with high strengths and large elongation in the Ni-Al-Fe and Ni-Al-Co ternary systems have been manufactured directly from the liquid state by an in-rotating-water spinning method. The wire diameter was in the range 80 to 180m and the average grain size was 2 to 4m for the wires and 0.2 to 1.0m for the+ wires. _y, _f and _p of the wires were found to be about 360 to 760 MPa, 560 to 960 MPa, and 0.2 to 5.5%, respectively, for the Ni-Al-Fe system, those of the+ wires were about 395 to 660 MPa, 670 to 1285 MPa, and 3.5 to 17%, respectively, for the Ni-Al-Fe system, and about 260 to 365 MPa, 600 to 870 MPa, and 4.0 to 7.0%, respectively, for the Ni-Al-Co system. Cold-drawing caused a significant increase in _y and _f and the values attained were about 1850 and 2500 MPa, respectively, for Ni-20Al-30Fe and Ni-25Al-30Co wires drawn to about 90% reduction in area. The high strengths, large elongation and good cold-workability of the melt-quenched and+ compound wires have been inferred to be due to the structural change into a low-degree ordered state containing a high density of phase boundaries, suppression of grain-boundary segregation and refinement of grain size.     

Correlation of burst pressure of GRP cylinders with the stress wave factor

Glass fibre-reinforced plastic (GRP) cylinders are increasingly used for highly stressed structural elements. The higher the demands on the materials, the higher are the fault detection requirements to be met by non-destructive materials testing methods. Acousto-ultrasonics is a valuable aid for the non-destructive evaluation of GRP composite materials, because it may be the answer to evaluating effects of subtle defects in composites. The aim of the research is to evaluate the burst pressure of GRP cylinders by acousto-ultrasonics techniques. The theoretical results have been found to be in good agreement with the experimental values. Hence the results strongly suggest that stress wave factor measurements can be exploited successfully to predict burst pressure of GRP cylinders.Nomenclature P Internal pressure, kgf cm^–2 - d Internal diameter, cm - t Thickness of cylinder, cm - (N ,N ,N ) Resultant forces, kgf - (M ,M ,M ) Moments, kg cm - [A] Extensional stiffness matrix - [B] Bending stretching coupling matrix - [D] Flexural stiffness matrix - ( ⁰ , ⁰ , ⁰ ) Midplane strains - (k ,k ,k ) Curvatures - n Number of laminae - Z Distance from midplane, cm - _u Ultimate tensile strength of GRP composite, kg cm^–2 - S _W Stress wave factor - m Material parameter - Filament winding angle     

Thermal Expansion and Isothermal Compressibility of TlIn1 – xNdxSe2 (0 ≤ x≤ 0.08) Crystals

The thermal expansion coefficient () and isothermal compressibility ( _T ) of TlIn_{1 – x} Nd _x Se₂(0 x 0.08) crystals were measured between 77 and 400 K. In the range 77–160 K, both and _T increase with temperature, the increase in being much steeper. At higher temperatures, and _T change very little. The observed composition dependences of and _T are interpreted in terms of energy-band structure.     

The behavior of the4He viscosity near the superfluid transition

Measurements of the shear viscosity at saturated vapor pressure through the lambda transition indicate a singular behavior of the form |1 – (/)|=A ^x , (where =|1–(T/T )|, with equal values for the critical exponent on both sides of the transition.Work sponsored by Consiglio Nazionale delle Ricerche, Rome (Italy).     

Some expectation on the mechanism of cross-flow instability in a swept wing flow

Summary Three-dimensional boundary layer transition on axisymmetric rotating bodies is the subject of a comprehensive experimental study. Based on this study, hypotheses are made on the mechanism of cross-flow instability for swept wing flow. These new results are combined with past explanations to provide a rough sketch for the entire flow field over the swept wing. From this new viewpoint there appears the mechanism of traveling waves, being induced by a stationary disturbance. Some uncertainties appearing in recent papers concerning this flow field are discussed. Among these uncertainties for which an explanation is provided, is the discrepancy of frequencies between the hot wire signal and the visualized flow pattern.Nomenclature x direction along a potential flow stream line - y direction normal to a potential flow stream line - z direction normal to bothx andy directions - U mean velocity inx-direction - V mean velocity iny-direction - x direction along a disturbance - y direction normal tox direction - u, v, w fluctuating velocity components inx, y, z directions - U velocity inx-direction with wall fixed coordinate - U _e velocity of outer edge of boundary-layer - U uniform flow velocity normal to leading edge - V uniform flow velocity parallel to leading edge - Q upstream velocity - N rotation speed of an axisymmetric body - P arbitrary point on a disk surface - r radius to a pointP - R ₀ radius of a disk or a cylinder - U _p phase velocity of ring like vortices - T position where wall streaks appear in the case of oil flow visualization - Re _c,t critical and transitional Reynolds numbers - angle of the spiral disturbance - boundary-layer thickness - angular velocity - sweep angle of a body - wave length of disturbance - kinematic viscosity of a fluid With 11 Figures     

Dependence of the flux flow viscosity coefficient on the Ginzburg-Landau parameter κ in superconducting indium films

The flux flow viscosity coefficient b ^–1 (in units of ₀ H _{c n} ^–1 c ^–2) of vacuum-deposited indium thin films with low values (1.0–2.8) is measured at temperatures between 0.5T _cand 0.98T _cin the weak magnetic field region. At each temperature, b ^–1 decreases as increases for larger than 1.7. The decrease of b ^–1 with increasing is more rapid as the temperature increases. From an analysis of the present results as well as the existing data on intermediate- and high- superconducting alloys, the relation between b ^–1 and is established over a wide range of . The dependence of b ^–1 on is qualitatively explained by taking into account the contribution of the normal electron dissipation to the viscosity coefficient in the Bardeen-Stephen model.Financial support provided by the Fonds National Suisse de la Recherche Scientifique.On leave from the Department of Electronic Engineering, Faculty of Engineering, Kyushu Industrial University, Fukuoka, Japan.     

Precipitation phenomena in the Mg-31 at% Li-1 at% Al alloy

Precipitation phenomena produced in the -phase (b c c) of the Mg-31 at% Li-1 at%Al alloy subjected to different heat treatments have been studied by sensitive single-crystal X-ray diffraction techniques. The variation of the hardness values of specimens quenched and then aged was also examined. It was confirmed that AlLi is a stable phase at room temperature for the examined Al content; AlLi precipitation is only produced for very slow cooling rates from the -field. Phase reactions for specimens quenched and then aged can be summarized as follows: ++ after ageing at room temperature; + ++ AlLi after ageing at 473 K. A considerable increase of the hardness, which attains its maximum value after about 30 h ageing at room temperature, was observed. Neither the -phase nor the AlLi-phase precipitation can account for the observed hardening process. The presence of the -metastable phase when the hardness reaches its maximum value is verified.     

A Monte Carlo Study of Disorder in the High Pressure Mixed Crystal N2-Ar

In order to obtain a better notion of the experimental results in our laboratory, Monte Carlo calculations have been performed of the N ₂-Ar crystal on the N ₂-rich side, in the p-T region where the and phases exist in pure N ₂. Considering the enthalpy, the system prefers the Ar atoms to be located on the sphere positions. The * phase is present for mixtures down to but is most likely metastable. The *-* transition shifts to lower temperatures with decreasing . The 2 ^nd order transition within the phase continues to exist to even smaller . In contrast to the * -* transition, the transition temperature for the 2 ^nd order transition does not shift to lower temperatures. For a mixture of it is within 5 K from the pure 2 ^nd order transition at a pressure of 7.0 GPa.     

Universality and the scaling laws in the superfluid phase transition of3He-4He mixtures

From the second-sound velocityU ₂ near the superfluid transition point, the superfluid densities in³He-⁴He mixtures, _s (X) and _s (), were deduced along the paths of constant³He concentrationX and of constant chemical potential difference of³He and⁴He. The following critical exponents of _s are determined: (a) =XX for _s (X) in the(X, T) plane,(b) X for _s (X) in the(, T) plane, and(c) for _s () in the(, T) plane. It is found that and _X change by about 4–6% relative to with increasing³He concentration up toX=0.4 and by 8–10% up toX=0.53. It seems that, belowX=0.53, universality hold for . Values of have been found to be in good agreement with the critical exponent of _s in pure⁴He under constant pressure. The values of and _X forX0.53 are also found to be consistent with the scaling relations in the (,T) plane of³He-⁴He mixture.Work performed in part while at the Electrotechnical Laboratory.     

Optical thermophysical characteristics of the condensed phase of combustion products and heatproof materials

An unconventional unit for experimentally studying the optical thermophysical properties of materials over a wide temperature range is described. Results are presented of studying the temperature function and dispersion of the absorption index for the condensed phase of the combustion products of a metalbearing fuel and of the emittance of fiber fireproof materials.Notation K spectral absorption coefficient - D spectral transmission coefficient - spectral absorption index - wavelength - d sample thickness - d_s surface layer thickness - I spectral intensity of radiation - , spectral and total emittances Kirov Polytechnical Institute. Kazan Chemical Engineering Institute, Russia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 64, No. 3, pp. 330–336. March, 1993