Deformation in spinel

Stoichiometric MgAl₂O₄ spinel was deformed in compression at temperatures from 1790 to 1895 C and the dislocation structures analysed by transmission electron microscopy. {1 1 1}1 1 0 slip was observed on both the primary and cross-slip systems, and there was much secondary slip as well; all six 1 1 0 Burgers vectors were present in electron micrographs. This secondary slip leads to very high work-hardening rates, approximately/70 at 1790 C, where is the shear modulus. Since it is known that deformation in nonstoichiometric (alumina-rich) spinel crystals occurs by {1 1 0}1 1 0 slip, the electrostatic and geometric aspects of 1/4 110 dislocations moving on {1 1 1} and {1 1 0} planes are considered in some detail. It is porposed that the octahedral cation vacancies present in non-stoichiometric spinel diffuse to dislocations during deformation and thus favour {1 1 0} slip.     

X-ray studies of iodine sorption in some silver zeolites

After saturation sorption, in a static system, of molecular iodine onto some silver zeolites at 130° C, powder X-ray diffraction analysis revealed sharp reflections due to crystalline -Agl. However, this -Agl contained only a fraction of the sorbed iodine and it seems likely that this -Agl involves unlocalized ions such that a continuous three-dimensional network of -Agl forms in the zeolite channels. Water in the zeolite channels is probably the underlying cause: heating to 200 to 300° C in air destroyed the sharp -Agl reflections and no such reflections were observed if the sorption was carried out with the zeolites dehydrated beforehand. -Agl formation was enhanced when the zeolite framework was broken down by heating in air at 800° C, heating in water or brine at 200° C, or -irradiation.     

Third Sound and Quartz Crystal Microbalance Measurements of Helium on Rubidium

We present preliminary results from an experiment in progress which seeks to study third sound propagation on clean glass and rubidiated glass for several ⁴ He coverages. The third sound is driven thermally and detected with thin-film zinc bolometers over the temperature range 0.100T0.670 K. Measurements of the frequency of a quartz crystal microbalance which has rubidium deposited onto one side are made through the temperature range 0.100T1.5 K for each helium coverage studied. Results of measurements for pure ⁴ He films, primarily for third sound, are presented for coverages8.52 atomic layers.     

Subcritical growth of fracture (inelastic fatigue)

A local energy criterion of Irwin's type is applied to a problem of a quasi-static extension of a crack embedded in an elastic-plastic or viscoelastic-plastic matrix. The derived nonlinear differential equation (, l, d/dl) + G(, l) = G _c /(/l) governs subcritical growth up to the point of gross instability.The creep rupture under sustained loads and fatigue crack propagation both described by the above equation, are shown to follow almost identical mathematical representations. The essential features such as the resistance curves, the dependence of growth rate on the current K-factor and the amount of growth vs. time relations are shown to be strikingly similar.

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Zusammenfassung Ein Ausdruck für die lokale Energie nach dem Vorschlag von Irwin wurde zur Lösung des Problems der quasistatischen Ausbreitung eines in einer elasto-plastischen oder viskoelastoplastischen Matrize eingebetteten Risses angewandt. Die abgelcitete nicht-lineare Differentialgleichung (, l, d/dl) + G(, l) = Ge/(/l) beschreibt das unterkritische Wachstum bis zum Stadium der allgemeinen Instabilitat.Es wird gezeigt, daB der Bruch unter Dauerbelastung and das Fortschreiten von Alterungsrissen, welche beide durch obige Gleichung beschrieben werden, fast identischen mathematischen Darstellungen folgen. Die wichtigsten Merkmale wie Widerstandskurven, Abhangigkeit der Wachstumsgeschwindigkeit vom K-Wert, Bowie diejenige zwischen Wachstum and Zeit sind auffallend ähnlich.

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Résumé Un critère d'énergie locale, du type proposé par Irwin, et appliqué a l'étude du problème de l'extension quasi-statique d'une fissure sise dans une matrice élasto-plastique ou viscoélastique-plastique.L'équation différentielle non-linéafire (, l, d/dl) + G(, l) = Ge/(/l) régit l'extension subcritique jusqu'au stade de I'instabilité d'ensemble.On démontre que la rupture par fluage sous charges constantes et la propagation des fissures de fatigue qui sont toutes deux recevables de l'équation ci-dessus, peuvent être exprimées en termes mathématiques de maniére sensi blement identique.Des caractéristiques essentielles comme les courbes de résistance, les relations qui lient la vitesse de propagation au facteur K, et le taux de propagation au facteur temps, présentent une similitude remarquable.

     

A four-parameter corresponding-states method for prediction of Newtonian,pure-component viscosity

The extended Lee-Kesler (ELK) method, introduced for calculating thermodynamic properties of polar as well as nonpolar fluids and their mixtures, has been adapted to the calculation of Newtonian, pure-fluid viscosity. The method is a four-parameter, corresponding-states technique requiring as input the critical temperature, critical pressure, a size/shape parameter , and a polar interaction parameter . Because and have been previously tabulated for many fluids (for calculation of thermodynamic properties) and may also be obtained directly from the radius of gyration and a single liquid density, respectively, the method contains no adjustable parameters and is predictive in nature. ELK viscosity predictions were compared to experimental data for nonpolar and polar fluids. For 36 different nonpolar fluids and a total of 5748 different points, the comparison yielded an absolute average deviation (AAD) of 7.88% with a bias of –4.45%. Similarly, the AAD was 10.62% with a bias of –5.34% for a comparison of 15 different polar fluids involving 1500 different points. With this method, viscosities can be calculated within the range 0.55 T _r2.00 and 0<P _r10.     

Radiation of a perforated cylinder

The generalized zonal method is used to find the energy radiated by a perforated cylinder. The existence of a range of geometric optical parameters is established, where in the perforated cylinder radiates more energy than a continuous cylinder.Notation T temperature, °K - net emissivity (degree of blackness) - D cylinder diameter - _ik mean angular coefficient of radiation (ARC) between i-th and k-th elements of finite area surface - R coefficient of reflection - Stefan-Boltzmann constant - dimensionless parameter equal to the ratio of the diameter of coaxial cylinders - ratio of the total area of perforations to the geometric area of the cylinder - _max value at which radiant energy from the surface is maximum - ₀, value below which radiant energy of the perforated cylinder is equal to or greater than the radiant energy of the continuous cylinder - Q_f resultant radiation flux Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 5, pp. 864–867, November, 1978.     

Solution of Mixed Contact Problems in the Theory of Nonstationary Heat Conduction by the Method of Summation‐Integral Equations

The laws governing the development of spatial nonstationary temperature fields in a bounded cylinder and a halfspace where one of the end surfaces of the cylinder touches the surface of the halfspace in a circular region are determined. A solution of a mixed axisymmetric nonstationary problem of heat conduction is obtained in the region of Laplace transforms. In solution of this problem, there appear summationintegral equations with the parameter of the integral Laplace transform (Lparameter) and the parameter of the finite integral Hankel transform (Hparameter).     

Equation of state of3He near its liquid-vapor critical point

We report high-resolution measurements of the pressure coefficient (P/T) for³He in both the one-phase and two-phase regions close to the critical point. These include data on 40 isochores over the intervals–0.1t+0.1 and–0.2+0.2, wheret=(T–T _c )/T _c and =(– _c )/ _c . We have determined the discontinuity (P/T) of (P/T) between the one-phase and the two-phase regions along the coexistence curve as a function of . The asymptotic behavior of (1/) (P/T) versus near the critical point gives a power law with an exponent (+–1)^–1=1.39±0.02 for0.010.2 or–1×10 ^–2t–10 ^–6 , from which we deduce =1.14±0.01, using =0.361 determined from the shape of the coexistence curve. An analysis of the discontinuity (P/T) with a correction-to-scaling term gives =1.17±0.02. The quoted errors are fromstatistics alone. Furthermore, we combine our data with heat capacity results by Brown and Meyer to calculate (/T) _c as a function oft. In the two-phase region the slope (²/T ²)_c is different from that in the one-phase region. These findings are discussed in the light of the predictions from simple scaling and more refined theories and model calculations. For the isochores 0 we form a scaling plot to test whether the data follow simple scaling, which assumes antisymmetry of – ( _c ,t) as a function of on both sides of the critical isochore. We find that indeed this plot shows that the assumption of simple scaling holds reasonably well for our data over the ranget0.1. A fit of our data to the linear model approximation is obtained for0.10 andt0.02, giving a value of =1.16±0.02. Beyond this range, deviations between the fit and the data are greater than the experimental scatter. Finally we discuss the (P/T) data analysis for ⁴ He by Kierstead. A power law plot of (1/) P/T) versus belowT _c leads to =1.13±0.10. An analysis with a correction-to-scaling term gives =1.06±0.02. In contrast to ³ He, the slopes (²/T ²)_c above and belowT _c are only marginally different.Work supported by a grant from the National Science Foundation.     

Editorial gatekeeping patterns in international science journals. A new science indicator

Significant correlations were found between the number of science journal editors from different countries, on the one hand, and the number of scientists, the number of science journals and the number of science papers produced by these countries on the other. We argue for using the extent of participation in the editorial board of international science journals as a new science indicator. The deviations from the regression lines between the new indicator and other publication indicators allow one to assess the open or closed character of the scientific life of a given country.     

Two-particle tunneling current in Josephson junctions

The contribution to the tunneling current of a Josephson junction from the Two-particle tunneling, to the 2nd order approximation in the barrier transparency, is investigated. Expressions for the current onset amplitudes corresponding to eV = _1,2 are given together with the full expressions for the voltage and the temperature dependencies of the two-particles current. The theory has ben developed to take also into account corrections due to depairing mechanisms, which lead to the smearing of the current singularities. Introducing a depairing parameter , which accounts for the probability of these processes, I–V curves in the voltage region of the onset of single and two particle current are obtained. It is shown that, though having the same functional dependence, spreading occurs over a voltage range of different widths. In particular, it is shown that the width of the single-particle structure is twice larger the one for the two-particle. A careful investigation of the I–V curves in the region 2 -eV is presented and some aspects of the interesting voltage region near ¦₁-₂¦ is discussed.     

The propagation and inhibition of an exothermic branched-chain flame with an endothermic reaction and radical scavenging

The effects of the endothermic decomposition of an inhibitory species W to form a radical scavenger on a laminar, pre-mixed flame supported by an exothermic second-order branching reaction are considered. This work extends a previous study, where the effects of the radical scavenger S were ignored. Two cases are identified, dependent on a parameter measuring the relative rate of the decomposition of W. These are described by an high-activation-energy asymptotic analysis and through numerical integration of the propagating-flame equations for representative parameter values. For larger values of the effect of the radical scavenger is to introduce a critical value of the heat-loss parameter for flame propagation. For smaller values of , where there is a critical value of without any S being produced, the effect is to lower this critical value. In both cases the effect of the radical scavenger is to reduce the propagation speed and, if sufficient amounts of S are produced from the decomposition of W, to totally suppress flame propagation, even without any heat loss.     

The Interplay of Electronic and Nuclear Magnetism in PtFe x at Milli-, Micro-, and Nanokelvin Temperatures

We have measured ac susceptibility, nuclear magnetic resonance, and nuclear heat capacity of two PtFe _x samples with concentrations of magnetic impurities x = 11 ppm and 41 ppm at magnetic fields (0 ± 0.05) mTB248 mT. The susceptibility data have been measured at temperatures of 0.3 KT100 mK, no hint for nuclear magnetic ordering could be detected to a temperature of 0.3 K. The nuclear heat capacity data taken at 1.4 KT10 mK show enhanced values which scale with x at low polarization. This effect is described by a model assuming an internal magnetic field caused by the impurities. No indication for nuclear magnetic ordering could be detected to 1.4 K. The nuclear magnetic resonance experiments have been performed on these samples at 0.8 KT0.5 mK and 2.5 mTB22.8 mT as well as on three other samples with x = 5, 10, 31 ppm in a different setup at 40 KT0.5 mK and at 5.4 mTB200 mT. Spin-lattice and effective spin-spin relaxation times ₁and ₂ ^* of ¹⁹⁵ Pt strongly depend on x and on the external magnetic field. No temperature dependence of ₁and ₂ ^* could be detected and the NMR data, too, give no hint for nuclear magnetic ordering to 0.8 K.     

Structure of martensite formed in Cu-Al-Fe single crystals duringin situ HVEM pseudoelastic tensile experiment

Single crystals of the CuAlFe alloy, containing 14.5 wt% Al and 2.2 wt% Fe were subjected toin situ tensile experiment using straining attachment in a 1 MV electron microscope. Loadelongation curves were obtained for three foil plane/tensile direction orientations: (001) [0 1 0], (0 0 1) [1 1 0] and (1 1 0) [¯1 1 2]. Each crystal was subjected to two cycles of pseudoelastic deformation up to maximum 2% strain, showing almost complete shape recovery. Structure observations and electron diffraction pattern indicated that during deformation of samples of (0 0 1) [1 1 0] and (1 1 0) [1 1 2] orientations, formation of ₁ martensite was observed and only at later stages narrow needles of ₁ nucleate in front of ₁. During pseudoelastic deformation in the (0 0 1) [1 0 0] direction, martensite forms as a mixture of narrow plates possessing either 2H or 18R structures. The following crystallographic relationship between the parent phase and both types of martensite was observed: [1 00] ₁ [101] ₁ and (0 0 1) ₁ (0 1 0)₁;(0 0 1) ₁ (0 1 0) ₁ and [1 1 0] ₁ [0 0 1] ₁. From the character of sidebands reflections presence of 1 0 1 1 0¯1 static displacement waves was inferred.     

Tensile fracture of doubly-convex cylindrical discs under diametral loading

Doubly-convex cylindrical gypsum discs have been fractured under the action of two diametrically opposed in-plane forces. The disc diameter was constant throughout the test series. The ratio of cylinder length to diameter ranged from 0.06 to 0.30; the ratio of cylinder diameter to radius of curvature of the disk faces was varied from 0 to 1.43. The fracture loads obtained have been correlated with stress data obtained from the photoelastic analysis of Pitt et al. An empirical equation, valid for any brittle material, relating the tensile strength of the material to the fracture load and dimensions of a doubly-convex disc has also been developed.Nomenclature C, K constants - D diameter of disc - F comparative factor - I _max stress factor - P load - P _s fracture load of convex-faced disc - P ₂ fracture load of plane-faced disc with W/D = 0.2 - R radius of face-curvature - t overall thickness of convex-faced disc - T thickness of plane-faced specimen of convexfaced disc - W cylinder length - _f tensile strength of material - _t maximum tensile stress in convex-faced disc - _x uniform tensile stress in plane-faced disc     

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.     

A Viscosity Equation of State for R123 in the Form of a Multilayer Feedforward Neural Network

A multilayer feedforward neural network (MLFN) technique is adopted for developing a viscosity equation =(T, ) for R123. The results obtained are very promising, with an average absolute deviation (AAD) of 1.02% for the currently available 169 primary data points, and are a significant improvement over those of a corresponding conventional equation in the literature. The method requires a high-accuracy equation of state for the fluid to be known to convert the experimental P, T into the independent variables , T, but such equation may not be available for the target fluid. With a view to overcoming this difficulty, a viscosity implicit equation of state in the form of T=T(P, ), avoiding the density variable, is obtained using the MLFN technique, starting from the same data sets as before. The prediction accuracy achieved is comparable with that of the former equation, =(T, ).     

The age hardening effect in Ti-6 Al-4 V due to ω and α precipitation in the β grains

The structure at room temperature of a quenched TA6V titanium alloy has been investigated. This structure is + or + according to the treatment temperature; it is always metastable. During ageing the grains decomposed by the reaction + + +; this decomposition was accompanied by a large increase of the 0.2% yield stress. No structural modification was observed in. The and phase of TA6V were separately investigated in the form of single-phase alloys. The hardness of was insensitive to ageing, while was considerably hardened by and; we deduced that the strengthening of the minor phase during ageing is mainly responsible for the hardening of TA6V.     

Precipitation hardening in Cu 1.81 wt % Be 0.28 wt % Co

The structure of the precipitation hardening alloy Cu 1.81 wt % Be 0.28 wt % Co has been studied as a function of ageing temperature and time, by transmission electron microscopy. The continuous precipitation sequence found is: supersaturated solid solution G.P. zones .The G.P. zone is an ordered platelet precipitate, which is coherent on {100} matrix planes and is nucleated in very high densities (>10²⁴ m^–3). The coherency stress fields, due to the misfit of the G.P. zone and matrix, overlap to produce a net matrix contrast along {110} 10, and give the characteristic tweed structure, which can be described by the kinematical theory of diffraction. The semi-coherent intermediate precipitate is nucleated by the G.P. zones and the transformation is characterized from the changes in the arrowhead structure produced in the electron diffraction patterns. No transformation of to the equilibrium precipitate is found for the ageing times investigated.     

The mechanism of continuous dissolution of the lamellar structure in aged Al 22 at% Zn alloy

The mechanism of continuous dissolution was studied using transmission electron microscopy, X-ray diffraction and hardness measurements. The metastable phase was identified in the first stage of dissolution nucleating at the - boundaries. Interface dislocations at the - boundaries forming a perpendicular net in the 110 directions were identified as of screw character and of Burgers vector b=1/2a 110. During dissolution a change of shape of precipitates occurs leading to their fragmentation and to a change of the direction of boundaries into 110 directions.     

Characterization of 6FDA-APBP polyimide films through impulsive stimulated thermal scattering

The elastic and thermal properties of 4,4-(hexafluoroisopropylidene)-bis (phthalic anhydride)-4,4-bis (4-aminophenoxy) biphenyl (6FDA-APBP) free-standing polyimide films (2–10 m) were investigated using impulsive stimulated thermal scattering (ISTS), a non-contact optical method for thin film characterization. Shear and longitudinal velocities, Young's modulus, Poisson's ratio and the in-plane thermal diffusivity are reported.