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.     

Time to cool a cryogenic object by a gaseous cryogenic agent

Dependences to compute the cooling time of a single-channel object are obtained theoretically and confirmed experimentally.Notation D mass of helium in the channel - M mass of metal of the channel wall - G mass flow rate of the cryogenic agent - G_equ equivalent mass flow rate - c_p, c_m mean integrated specific heat of the cryogenic agent and the channel wall material - U perimeter - cooling time - ₁ time of the first cooling period - T₂ time of the second cooling period - channel wall temperature - T flow temperature - T_o initial flow temperature - T_in flow temperature at the channel input - W flow velocity - L channel length - L_in, L_out lengths of the delivery and removal pipelines - F, F_in, F_out cross-sectional areas of the channel being cooled, and of the delivery and removal pipelines - F_s total heat-transfer surface - d channel inner diameter - d_in, d_out inner delivery and removal pipeline diameters - P flow pressure - P flow pressure at the input to the element - P_out flow pressure at the output from the element - G_o, G₁ initial and final flow rates of the cryogenic agent - z a coordinate - ¯z=z/L a dimensionless coordinate - dimensionless channel length - dimensionless cooling time - V₁ dimensionless temperature - k_G,a, k _u , f, m, , g parameters - A, B constants - Re Reynolds number - R gas constant - coefficient of dynamic viscosity - hydraulic drag coefficient - coefficient of heat elimination Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 4, pp. 629–635, October, 1980.     

Tensile fracture characteristics of double convex-faced cylindrical powder compacts

Doubly-convex cylindrical tablets compacted uniaxially from different particle-size fractions of Di-Pac-Sugar powder, have been fractured under diametral loading conditions employing the standard diametral compression test. The ratio of cylinder length to diameter (W/D) ranged from 0.476–1.06; the ratio of cylinder diameter to radius of curvature of the tablet faces (D/R) was varied from 0.0–1.184. An equation based on geometrical volume equivalence conditions, of a doubly-convex cylinder to that of a plane-faced cylinder, relating the tensile strength of the material to the fracture load and dimensions of doubly-convex cylindrical specimens, has been developed. This equation is valid for any compacted cylindrical tablet. Using this equation, it was possible to assess the tensile strength of doubly-convex tablets, and a shape factor has been defined. Also, the predicted fracture loads obtained by this equation are found to compare well with those values determined by utilizing a stress factor based on the photoelastic stress analysis. For higher ratios of W/D and smaller diameter values, the variation in the results calculated is found to be less than 5%. Meanwhile, for higher values of W/D, the geometrical end effect is reduced and the tensile fracture stress tends to become similar to that of a plane-faced specimen.     

Neutron diffraction texture study of deformed uranium plates

The texture of two depleted uranium (DU) samples, labelled DUWR and DUWR2, were studied by neutron diffraction. DUWR was prepared by warm rolling of a cast ingot, and DUWR2 was prepared by adding 20% tensile strain to the warm-rolled DUWR. Complete three-dimensional orientation distribution functions were determined using four neutron pole figures for the DUWR, and using six neutron pole figures for the DUWR2 sample, by the WIMV method of the program popLA. The textures of the two samples were essentially identical to each other. They could be described by a twisted helical density tube spiralling continuously along the -axis of the Euler space. The projection of the backbone of the density tube along the -axis cast a linear shadow running parallel to the diagonal of the - plane, which could be defined by a =+90° (and =+270°) relation. The helical tube was confined within narrow -angle limits, from 14° to 30° with the peak orientation at (103) 0 10. The diffraction patterns of the DUWR2 sample were measured from the normal direction to the rolling surface of the sample, up to the scattering angle of 108° using a 0.15 nm neutron beam. The Rietveld profile refinement using the textured diffraction pattern was quite satisfactory when the texture effect to the entire diffraction profile was corrected for by the corresponding pole density from the inverse pole figure.     

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.     

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.     

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.     

Investigation of the adhesion of polyurethanes at low separation rates

The adhesion of polyurethanes (based on simple polyesters) to metals and glass was investigated. It was found that the work of adhesion increases with the lattice density and decreases in the order steel>brass>duralumin>glass. A method was developed for determining the equilibrium work of adhesion that is independent of the coating thickness, its degree of deformation and separation rate, which makes it possible to obtain more correct data on the interaction of polymer coatings with solid surfaces.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 5, No. 6, pp. 688–691, November–December, 1969.     

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.     

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.     

Kondo Impurity in a Mesoscopic Ring: Charge Persistent Current

We study the influence of a magnetic impurity or ultrasmallquantum dot on the charge persistent current of a mesoscopicring. The system consists of electrons in a one-dimensionalring threaded by spin-dependent Aharonov–Bohm/Casher fluxes,coupled via an antiferromagnetic exchange interaction to alocalized electron. By passing to a basis of electron stateswith definite parities, the problem is mapped onto a Kondomodel for the even-parity channel plus free electrons in theodd-parity channel. The twisted boundary conditionsrepresenting the fluxes couple states of opposite parityunless the twist angles satisfy =f,where f are integers, with spin index=, . For these special values of, the model is solved exactly by a Bethe ansatz.Special cases are investigated in detail. In particular weshow that the charge stiffness in the case= is insensitive to the presenceof the magnetic impurity/quantum dot.     

Analysis of edge stresses in composite laminates under combined thermo-mechanical loading,using a complementary energy approach

An approximate method is presented to investigate the interlaminar stresses near the free edges of composite laminate plates that are subjected to a combined thermo-mechanical loading. The method is based upon admissible function representations of stresses which account for the effects of both the global mismatches and the local mismatches in two of the elastic properties, the Poisson's ratio and the coefficient of mutual influence. For this purpose, new thermo-mechanical mismatch terms are defined to reflect an effective deformation under the combined thermo-mechanical loading. Closed form solutions of all the stress components are sought by minimizing the complementary energy with respect to the unknown functions, in the stress representations, of the width coordinate. These unknown functions are determined by solving five ordinary differential equations along with a set of free edge boundary conditions, which allow complex as well as real roots for their exponential decaying rates. The resulting solutions satisfy the stress equilibrium and all of the boundary conditions exactly, but compatibility is met in a weak form. Numerical examples are given for several typical laminates, and are compared with previous results obtained by finite element and other approximate methods. It is found that the present approximate method yields interlaminar stress results in an efficient, fast and yet reliable way. It is also concluded that unlike some previous approximate methods, the current method is numerically robust and stable.List of symbols A, B, D Laminate stiffness matrices as defined by (27) - b Half laminate width - T ^(k) Temperature difference at the top of the k-th ply - T ^(k)(x ₃) Temperature difference in the k-th ply given as a function of through-thickness coordinate x ₃ - e _0,1,2,3,12 ^(k) Thermal strains of the k-th ply in the laminate axes - h Laminate thickness - M ₁₁ Applied uniform bending load (moment/unit length) - M _ij ^T Applied thermal moments (moment/unit length) - N Total number of plies - N ₁₁ Applied thermal loads (force/unit length) - N _ij ^T Applied thermal loads (force/unit length) - Q _ij ^(k) Ply stiffness for the k-th ply in the laminate axes - S _ij ^(k) Ply compliance for the k-th ply in the laminate axes - t ^(k) Thickness of the k-th ply - (x ₁, x ₂, x ₃) Local coordinate system with the out-of-plane coordinate x ₃ defined at the bottom of each ply - (x ₁, x ₂, z) Global coordinate system with the out-of-plane coordinate z defined at the mid-plane of the laminate - z ^(k) Global out-of-plane coordinate for the top of the k-th ply - ₁₁ ^mech Applied mechanical axial strain - ₁₁ ^tot Applied total (including thermal) axial strain - ^tot Total in-plane strain vector at arbitrary plane as defined by (32) - ⁰ Total in-plane strain vector at the midplane - _12,1 Laminate coefficient of mutual influence - _12,1 ^(k) Coefficient of mutual influence for the k-th ply - _{12, 1E} ^(k) Equivalent coefficient of mutual influence for the k-th ply as defined by (23) - K Total curvature vector - _,,z Coefficients of thermal expansion for a uni-ply in its material principal axes - _11,22,12,33 ^(k) Coefficients of thermal expansion for the k-th ply in the laminate axes - V₁₂ Laminate Poisson's ratio - ₁₂ ^(k) Poisson's ratio for the k-th ply - _12E ^(k) Equivalent Poisson's ratio for the k-th ply as defined by (22) - _{i j} Total stress components in tensor notation - Far-field stress components - _ij ^c Companion stress components This work was supported by a grant from the Federal Aviation Administration, to the Center of Excellence for Computational Modeling of Aircraft Structures at Georgia Institute of Technology.     

Morphological and crystallographic features of γ-γ′ Ni-Al and Ni-Al-Ti two-phase bicrystals

Several- Ni-Al and Ni-Al-Ti two-phase bicrystals were made by the solid-state diffusion couple method. Each couple consisted of a-phase single crystal and a pure-Ni polycrystal, and was annealed at 1473 K in an Ar gas atmosphere. Single crystal layers of-phase with uniform thickness always grow into the parent-phase single crystals. The resultant/ interface has no voids or facets regardless of the orientation of interface and the chemical composition of the-phase. Porosity formation due to the Kirkendall effect is observed in the diffused region. Concentration profiles exhibit nearly constant gradients in-phase. The orientation relationship between both phases is found to be 001//001, that is, the-phase grows epitaxially along the crystal orientation of-phase.     

Estimation of the drawing efficiency of hot spinning of co-polyester fibres in producing high degrees of preferred orientation

A range of liquid crystalline polyester fibres varying in diameter from 65 to 440m were produced by spinning from a hot melt. These were analysed for preferred orientation by flatplate X-ray diffraction to produce equatorial azimuthal densitometry scans/() which were processed to produce the corresponding planar orientation profiles/() corresponding to a Bragg separation of 0.448nm. A further mathematical analysis was applied to these to produce the respective molecular orientation profiles/() which may be more directly related to fibre mechanical properties,/() profiles from this analysis were matched against theoretical/() calculated by assuming an idealized mechanism of affine deformation with no orientation losses due to thermal perturbations. The theoretical draws ratios corresponding to the experimentally observed cos² were matched against experimentally observed draw ratios to produce ratios which indicate drawing efficiencies. Although preferred orientation increased with increasing draw ratios, the drawing efficiency diminished with draw ratio.     

Numerical Calculation of the Flow Regimes of a Fluid Partially Filling a Horizontal Rotating Heat‐Exchange Cylinder

Consideration is given to a numerical determination of a twodimensional unsteady viscous flow with the free surface in a stationarily rotating horizontal cylinder in which heatexchange processes are carried out. The markerandcell method in a polar coordinate system is used. The features of modeling of the walllayer regime and the circulating flow regime that occur in rapid and slow rotation of the cylinder, respectively, are discussed. Based on the given results of numerical calculations, the influence of the Reynolds number on the character of flow is analyzed.     

Growth and structure of TiC coatings chemically vapour deposited on graphite substrates

TiC coatings were grown on graphite substrates by the chemical vapour deposition technique, using gas mixtures of CH₄-TiCl₄-H₂ at a total pressure of 10.7 kPa and at temperatures of 1400 and 1425 K. The growth rate and structure of the TiC coatings were investigated as a function of CH₄ and H₂ concentrations. The deposition rate of TiC increased with increasing CH₄ flow rate, but did not change with H₂ flow rate. This behaviour was explained by a mass transport theory. Thermodynamic analyses based on minimization of Gibbs' free energy predicted carbon codeposition with TiC. X-ray diffraction and Auger electron spectroscopy (AES) studies and microstructural observations, however, suggested that free carbon did not form. Textural analyses indicated that the growth of TiC coatings was initiated as randomly oriented crystallites, and as the thickness of the coatings increased, preferentially oriented columnar grains developed. The textures of TiC coatings with the same thickness changed from the 110 orientation to the 100 orientation with decreasing H₂ flow rate for a constant CH₄ flow rate. The CH₄ concentration also greatly influenced the preferred orientation of the coatings.     

Interface characterization of a β-SiC whisker-Al composite

The nature of the interface, the orientation relationship of -SiC whisker (-SiC_w)-Al combination, and the misfit dislocation structures at the -SiC_w-Al interfaces in a -SiC_w-Al composite have been observed by a high-resolution transmission electron microscopy (HRTEM). It was shown that quite a good bonding between the whisker and the aluminium was achieved due largely to the lattice match between SiC and aluminium at the interfaces. The orientation relationship between the whisker and the aluminium was {002}_SiC{111}_Al; 110_SiC110_Al. The interface was clean, faceted and semicoherent. The misfit dislocation cores were located in the whisker side away from the -SiC_w-Al interfaces.     

In situ X-ray Diffraction Studies of a Multilayered Membrane Fluid under Confinement and Shear

The structure of a fluid membrane system composed of surfactant-co-surfactant-oil-water mixtures has been investigated under confinement and shear conditions. Small angle x-ray scattering (SAXS) was employed with a second generation x-ray surface forces apparatus (XSFA-II) to study the time evolution of the orientational structure of the lamellar fluid under oscillatory shear. In a regime of relatively big confinement gap (800 m) and small shear amplitude (40 m), direct evidence of an orientational phase separation behavior, where a surface boundary layer adopts different orientation and separates from the bulk region, was observed for the first time. Under continuous shearing, the surface boundary layer grows in thickness and aligns towards a shear-favored (low friction) state while the bulk orientation remains unchanged. To further investigate the effects of surface confinement, we spatially mapped, in 1 m sections, the orientation structure of the lamellar fluid sample confined between two glass surfaces using a micro-focused x-ray beam produced by a linear Bragg–Fresnel lens at the Advanced Photon Source. The data confirmed the expected trend that the smectic domains align progressively better with respect to the surface as they approach the surface.     

Electron diffraction study of superlattices and orientation variants in Ca3SrAl6SO16

Samples having the nominal composition of Ca₃SrAl₆SO₁₆ were sintered at 1380 °C and analysed by electron diffraction. The frequent appearances of forbidden and satellite reflections in this compound imply the presence of a number of basal and nonbasal superlattices so that the microstructure of this cement clinker was characterized by various superstructures including one-, two- and even three-dimensional superstructures along the 0 0 1, 1 1 0, 1 1 2, 1 1 4 or 2 2 1, 0 1 3 and 1 2 3 directions with repeat periods of two or three times of that of basic one, respectively, and intergrowth of these. Various domain structures with 90°, 120° and 48.2°, etc., orientation relationships were also detected in these superstructures and the total number of these orientation variants related to the symmetry elements lost in the process of phase transformation, can be predicted according to the conclusions of Van Tendeloo and Amerlinckx, or they are equal to the number of those unique planes in the matrix.