Ortho-para conversion in hydrogen bubbles in copper

The low-temperature heat release in copper due to ortho-para conversion in hydrogen bubbles is investigated. Deviations from a model of free solid hydrogen are observed: a more intense heat release atT10 K and a rapid (10 h) heat release after cooling to 1.3 K. The experimental results can be explained by the assumption of autocatalytic conversion in the bulk and the catalytic influence of the bubble surface.     

Uncertainty of a measured result and confidence error of measurements

An analysis is made of the known information concerning the concepts of error and uncertainty and it is concluded that they are identical.Translated from Izmeritel'naya Tekhnika, No. 8, pp. 14–17, August, 1994.     

Structure and Magnetism of the Composite Crystal Ca0.824CuO2

We have studied the magnetic state from a viewpoint of crystallographic features of the 1-D chain compound Ca_0.824CuO₂. A possible spin-hole arrangement in the magnetically coexisting state was determined by analyzing the local structural distortion in the CuO₂ chain by means of a modulated-crystal-structure analysis. The essential periodic sequence expected is (: up- and down-spin, : hole), which can be regarded as a kind of spin-1/2 ferromagnetic-antiferromagnetic alternating Heisenberg chain.     

Relations between specific heat discontinuities and Ginzburg-Landau parameters for superfluid 3He

We show that the value of the ratio ₅/₂₄ deduced from specific heat experiments is extremely sensitive to the coefficient of the quadratic term in the Ginzburg-Landau functional. A strong coupling calculation of this coefficient implies that the experimental value of ₅/₂₄ is more than three times larger than previously believed.This work was supported in part by the National Science Foundation through Grant DMR7826530.     

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.     

The Ni3Al-Ni3Cr-Ni3Ru section of the Ni-Cr-Al-Ru system

An investigation is reported of the 75 at% nickel section of the Ni-Cr-Al-Ru system at 1523 and 1273 K. Constitutional data obtained by electron probe microanalysis, X-ray diffraction and microscopical examination are presented as partial isothermal sections. At 1523 K, the major part of the section consists of phase, while the aluminium-rich region contains a and+ region; the extent of the solid solution of chromium and ruthenium in totals ~ 4 at%. The ruthenium-rich corner of the section shows a two-phase region consisting of + ruthenium-rich solid solution. At 1273 K the,+ and + ruthenium regions increase in extent. The/ mismatch values in the equilibrated alloys studied lie in the range ~ –0.08 to –0.39%. Constitutional features of as-cast alloys are also reported.     

Low-temperature synthesis,pyrolysis and crystallization of tantalum oxide gels

Tantalum oxide gels in the form of transparent monoliths and powders have been prepared from hydrolysis of tantalum pentaethoxide under controlled conditions using different mole ratios of Ta(OC₂H₅)₅C₂H₅OHH₂OHCl. Alcohol acts as the mutual solvent and HCl as the deflocculating agent. For a fixed alkoxide water HCl ratio, the time of gel formation increased with the alcohol to alkoxide molar ratio. Thermal evolution of the physical and structural changes in the gel has been monitored by differential thermal analysis, thermogravimetric analysis, X-ray diffraction, and infrared spectroscopy. On heating to 400 °C, the amorphous gel crystallized into the low-temperature orthorhombic phase -Ta₂O₅, which transformed into the high-temperature tetragonal phase -Ta₂O₅ when further heated to 1450 °C. The volume fraction of the crystalline phase increased with the firing temperature. The -Ta₂O₅ converted back into the low-temperature phase, -Ta₂O₅, on slow cooling through the transformation temperature of 1360 °C, indicating a slow but reversible transformation.     

Absorption Spectrum of ZnO Precipitates in ZnSe

The absorption spectrum of ZnO precipitates in ZnSe saturated with oxygen is studied in the spectral range 500–2000 cm^–1 and is shown to correlate with the transmission spectrum of single-crystal ZnO. Saturation of ZnSe with oxygen in the course of growth leads to ZnO precipitation during cooling. The precipitates give rise to narrow absorption bands in the range 5.8–7.1 m, which correlate with the components of the multiphonon absorption spectrum of ZnO, formed by combinations of LO and TO phonons. The 2LO mode defines the long-wavelength transmission edge of ZnO. In addition, the spectrum shows strong absorptions due to the LO + TO(10.2 m) and 2TO (11.3 and 12.7 m) modes. The possible role of SeO₂ is discussed. It is suggested that ZnO with a high carrier concentration may act as a gray filter in the spectral range 2–9 m.     

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     

Grain refinement of a TiAl alloy by heat treatment through near gamma transformation

Casting of TiAl alloys is receiving more and more research because of its relatively low cost. One problem with this technology is that the coarse microstructure developed during solidification is harmful to material properties. Thus it is essential to seek an approach to refining the cast microstructure and this approach may also be applicable to cast components. In this study, a novel heat treatment route is proposed to obtain a fine fully lamellar structure from a cast TiAl alloy with a grain size of 1000 m. This route consists of three steps, namely pretreatment to have a feathery structure, annealing in the + region to have a fine near gamma structure and solution treatment to develop a fully lamellar structure with a grain size of 30 m.     

Diffraction studies of β″-magnesium sialon

The compositions of high magnesium content -magnesium sialon crystals within the 3M/4X plane of the Mg-Si-Al-O-N system indicate some form of metal atom ordering wihtin the structure. Although it is not possible using X-ray diffraction to detect weak additional reflections arising from the ordering between magnesium, aluminium, and silicon atoms, such weak reflections are revealed on electron diffraction photographs for a phase, resulting in a tripling of the hexagonal latticec-dimension. These show to have a structure very similar to rhombohedral willemite (Zn₂SiO₄), with the (Mg, Al) metal atoms ordered with respect to the silicon atoms in a 21 ratio. However, there are some additional weak diffraction spots with indices not obeying the rhombohedral condition of –h+k+l=3n. It is proposed that the structure of this is identical to that of willemite and the extra spots are a result of some form of twinning, which implies the existence of ordered microdomains.     

Dislocations and faults in some alloys containing copper and aluminum

By using the method of variance of the respective X-ray diffraction line profile, the effective particle size (p) and r.m.s.. strain (S ^21/2) of four alloys containing copper and aluminium (Al-0.08, 4 and 10 wt% Cu and Cu-5.87 wt% Al) at different annealing stages (starting from the cold filed stages) have been determined. From the peak shift of these samples, their average stacking fault probability = – where is the intrinsic stacking fault probability and the corresponding extrinsic stacking fault probability, respectively, were determined. Similarly, from the angular distance between the peak and the centroid of the diffraction profiles, the magnitude of + 4.5, where is the twinning fault probability, was measured. From these, the true particle sizeT, the stacking and twinning fault probabilities , and and the minimum stacking fault widthD _min have been determined. The hardness of alloys at different annealing stages was found to be dependent on the dislocation density and the stored energy in the alloys. The relationT S ^21/2 = constant was found to be valid for the alloys and from this a mechanism of grain growth with annealing has been suggested. With annealing the dislocation density and stored energy per unit volume were found to decrease until finally, in the fully annealed stages, they disappeared. The same was found to be valid for stacking and twinning fault probabilities as well as the minimum stacking fault width. A mechanism for the creation and annihilation of the intrinsic and extrinsic stacking faults has been suggested.     

Effect of Intense Self-Irradiation on the Phase Composition of Metallic Plutonium

The crystal structure of film samples of "high-level" (based on ²³⁸Pu) and low-level (based on ²³⁹Pu) metallic plutonium during their prolonged (up to 343 days) storage (self-irradiation) at room temperature was studied by X-ray diffraction. In the samples of high-level plutonium, the -Pu and -Pu lattices coexist. In the period of 40-60 days, the other known crystal modifications of plutonium (-Pu, -Pu, -Pu, and -Pu) are also present. Low-level plutonium had only the -Pu lattice. A possible origin of this phenomenon is discussed.     

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.     

Nonmonotonic Temperature Dependence of the Thermal Hall Angle of a YBa2Cu3O6.95 Single Crystal

We have performed high-resolution measurements of the magnetic field (0 TB9 T) and temperature (10 KT<140 K) dependence of the longitudinal and transverse Hall thermal conductivity of a twinned YBa₂Cu₃O_6.95 single crystal. We have used and compared two recently published methods to extract the thermal Hall angle _H(T, B). Our results indicate that cot(_H) varies quite accurately as T⁴ in the intermediate temperature range 0.3c. It shows a well defined minimum at T_m20 K which resembles that observed in the c-axis microwave conductivity. The electronic part of the longitudinal and the transverse thermal conductivity show the scaling behavior for transport properties predicted for d-wave superconductors in the temperature range 18 KT30 K.     

Further properties of the Falkner-Skan equation

Summary We present some analytical perturbation results from which the skin-friction is accurately predicted over the range 1/2<<, where is the usual Falkner-Skan parameter. The first eigenvalue for various in the range 2<< is also calculated numerically and certain properties noted. We find, analytically, the whole set of eignesolutions for the case when is large.With 1 Figure     

Multi-length scale modeling of CVD of diamond Part II A combined atomic-scale/grain-scale analysis

Chemical vapor deposition of polycrystalline diamond films is studied by combining an atomic-scale kinetic Monte Carlo model with two one three-dimensional and one two-dimensional grain-scale models. The atomic-scale model is used to determine the growth rates of 111- and 100-oriented surface facets, the surface morphology of the facets and the extent of incorporation of the crystal defects. Using the atomic-scale modeling predicted growth rates for the 111- and 100-oriented facets, grain-scale modelling is carried out to determine the evolution of grain structure, surface morphology and crystallographic texture in the polycrystalline diamond films. It is found that depending on the relative growth rates of the 111- and 100-oriented facets, which can be controlled by selecting the CVD processing conditions, one can obtain either 110-textured films with a relatively smooth faceted surface or 100-textured films with a highly pronounced deep facets. In both cases, however, the film surface is composed entirely of the 111 facets. This findings are found to be fully consistent with the available experimental results.     

Dielectric properties of chemically treated wood

Dielectric properties along the grain for absolutely dried untreated and seven kinds of chemically treated Sitka spruce (Picea sitchensis Carr.) woods were measured. Cole-Cole's circular arc law was applied to the results of the relaxation due to the motions of methylol groups. The following changes were caused by chemical treatments. In polyethylene glycol (PEG) impregnation, the distribution of relaxation times became very narrow, the generalized relaxation time (_m) was considerably decreased, and the relaxation magnitude (₀ – ) was slightly increased. In acetylation, the distribution of relaxation times became very broad, _m was considerably increased, and (₀ – ) was remarkably decreased. In propylene oxide treatment, the distribution of relaxation times became slightly narrow and _m was decreased. _m was slightly decreased in formalization, phenol-formaldehyde (PF) resin treatment and wood methyl methacrylate (MMA) composite. (₀ – ) was decreased in formalization and PF-resin treatment and was hardly changed in wood-MMA composite and heat treatment. The distribution of relaxation times was almost unchanged in formalization, PF-resin treatment, wood-MMA composite and heat treatment.     

A novel X-ray technique for inspection of steel pipes

The corrosion-induced material loss in crude oil carrying steel pipelines was originally studied by making use of the backscatter X-ray technique. The steel thickness can be determined by studying the density profile of the backscatter intensity vs. the depth location of a voxel. There are, however, some practical limitations to the above method, and a new method for evaluating steel thickness, namely, the transcatter technique is described. This technique uses the intensity of the beam which is transmitted by the pipe wall and subsequently scattered by the hydrocarbon inside the pipeline. The thickness is evaluated using three techniques, namely, the sequential technique, the dual angle technique, and the reference technique. Of the three techniques, the sequential technique has been studied in detail. The mathematical equations and experimental results related to the transcatter technique show that the thickness can be measured with an accuracy of better than 10% for a nominal steel thickness of 8 mm with a measurement time of several minutes.     

Absence of Phase-Fluctuation Contribution to the Low-Frequency Optical Conductivity in d-Wave Superconductors at Zero Temperature

The behavior of the low-frequency optical conductivity _reg() in superconducting cuprates is, at the present, an open and interesting issue. In particular, since the zero-temperature and zero-frequency limit of _reg() attains a value much larger than the universal value expected within a self-consistent T-matrix calculation, an intriguing possibility is that the collective mode can also contribute to _reg(). By taking into account the effect of dissipation on the collective mode in a d-wave superconductor, we evaluate the phase-fluctuation contribution to _reg(0) within the formalism of the phase-only action. We show that even though the collective mode contributes to _reg() at finite frequencies, approaching the zero-temperature and zero-frequency regime the corrections at _reg() due to phase fluctuations vanish.