Effect of anharmonicity on Kapitza resistance

To understand the effect of anharmonicity on the Kapitza resistance, a one-dimensional model is used to simulate the system of heavy element-light element solids. The system is coupled to high- and low-temperature sources, respectively, at its end points. The Lennard-Jones potential is used as the interaction potential in the light solid. For various parameters in the potential, the Kapitza resistance is calculated. It is found that the stronger the anharmonicity in the light side, the smaller is the Kapitza resistance. Also, the cases that only one to four pairs of light atoms with anharmonic interaction across the boundary is considered. With the number of anharmonic pairs across the interface increasing, the Kapitza resistance is found to be decreasing.     

Investigation of Thermal Resonance in Solution of a Two-Dimensional Singularly Perturbed Boundary-Value Problem of Nonstationary Heat Conduction with Nonlinear Boundary Conditions of the Stefan–Boltzmann Type

Data of the analytical-numerical parametric investigation of a singularly perturbed temperature field in the boundary layer of the side of a rectangle on which nonlinear boundary conditions of the Stefan–Boltzmann type are specified have been given. It has been established that a nonuniform initial temperature distribution of the Gaussian type causes the appearance of discontinuous traveling thermal waves in the corresponding boundary layer. A set of parameters for which the discontinuous traveling thermal waves, being superimposed, lead to a local nonlinear enhancement of the thermal field has been found. This effect can be considered as thermal resonance.     

Irreversibilites in science and technology networks: An empirical and analytical approach

The theory of autopoiesis, i.e., self-referentiality in the operation of the system, provides us with a production rule for change in the structure of the network. Using information theory, a model system is developed to study the relative likelihood of dynamic transitions: various senses of irreversibility (emergence, and path dependency) are disinguished. A test for path dependency is applied to two sets of empirical data which supposedly reflect historical discontinuities: the budget of theFraunhofer Gesellschaft, and the citation network among AIDS research related journals. The model for the interaction between self-referential developments and goal-referential boundary conditions is further specified, using the example of technological trajectories and selection environments.     

Superconductivity in a multi-layered non-fermi liquid

A model of high-T_c superconductivity based on an inter-layer tunneling mechanism is solved in mean-field theory with an arbitrary number of identical layers per unit cell. The nodal structure of the gap function is determined by the nodal structure of the intra-layer contribution to the pairing kernel. The gap-anisotropy in internal layers of each unit cell is enhanced compared to the gap-anisotropy of edge layers. The critical temperature T_c is calculated as a function of number of layers per unit cell, and is found to increase monotonically with increasing number of layers. A possible extension of the model to compounds that nominally have a single CuO₂ layer per unit cell, but where the bare interlayer tunneling matrix element may nevertheless be appreciable is discussed. Such compounds are suggested to have a T_c reminiscent of -layered compounds.     

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.     

A scientometric assessment of agricultural research in South Africa

This article reports the results of a scientometric assessment of agricultural research in South Africa over the period 1974–1984. The Science Literature Indicators Database of CHI is used and South Africa is compared with 7 other countries spread in America, Asia, Oceania, and Africa. The criteria used for the assessment are the contribution of each country to international agricultural literature (in terms of publications) and their impact in the Schubert-Glänzel-Braun Impact Scale. It was found that, although the South African contribution has improved in that period, it is comparable to that of Brazil and Argentina; that Nigeria and Israel produce 3 times more, and: that Australia and Canada contribute more than one order of magnitude of publications more than South Africa. As far as research impact is concerned Plant Science research in South Africa is rated fair in the Schubert-Glänzel-Braun scale, whilst Dairy and Animal Science and Veterinary research are rated poor.     

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.     

Checking contact angles of radial-thrust bearings

Summary On the basis of the above method of measurement, using expression (4), highly productive semiautomatic devices were made for sorting out bearings by their contact angles into three groups: small, good and large.The adoption by our industry of these measuring devices for checking the contact angles will raise considerably the quality and life of radial-thrust bearings.     

Critical size and shape of CdO ex-Cd(OH)2 crystallites

The present paper reports the extent to which the size and shape of oxide crystallites resulting from a decomposition reaction depend on the crystallite size of the initial material. If those sizes are sufficiently large i.e. higher than critical sizes, the resulting oxide crystallites assume exactly these critical sizes. They are the maximum size that can be reached by oxide crystallites in the absence of any evolution process such as ageing or sintering and are specific to a particular shape of these crystals, which is independent of initial crystallite size. Alternatively, if the initial material crystals are below these critical sizes, at least in one direction, then the dimensions and shape of the oxide crystallites depend on the size of the initial crystallites. These results were interpreted within the framework of the structural conversion mechanism related to the decomposition reaction and showing great similarities with a shear transformation.     

Thermal shock resistance of miniaturized multilayer ceramic capacitors

The thermal shock resistance of miniaturized multilayer ceramic capacitors (MLCs), of sizes 0402, 0603, 0805 and 1206, was investigated by comparing the leakage currents before and after thermal shock. It was generally found that smaller capacitors have a higher thermal shock resistance than larger ones. The 0402 MLC possesses a thermal shock resistance in excess of 420 C. The linear interdependence of thermal shock resistance and reciprocal of half thickness, as predicted by conventional thermal shock analysis, was not observed. Instead, the thermal shock resistance of an MLC was found to be inversely proportional to the total area of its ceramic surface. This confirms that pre-existing flaws on the ceramic surface dominate the crack initiation process and are therefore primarily responsible for determining the thermal shock resistance of an MLC.     

Comments on the article of G. S. Ioffee on the “rationalization of equations in the theory of electricity and magnetism”

Conclusion The arguments of the author of the above article in defense of the thesis on the existence of assumed internal contractions in the SI system are not convincing. Nevertheless, in our opinion it is advisable to change in GOST9867-61 the term measurement unit size to the term measurement unit dimension.Translated from Izmeritel'naya Tekhnika, No. 2, pp. 63–64, February, 1967.     

Distribution of local stresses across the thickness of cracked plates under bending fields

A series of three-dimensional photoelastic experiments were conducted on plates containing through cracks which were loaded in bending with sufficient extension to prevent closure on the compressive side of the plate. Cracked plate geometries were selected so as to span the transitional thin to thick range. Slices were made parallel to the plate surfaces in the stress frozen material so as to remove the region around the crack tips. These slices were analyzed photoelastically and functions were evaluated experimentally corresponding to stress intensity factor distributions through the plate thickness. Results were compared with the theory of G. C. Sih. Agreement was excellent with theory for thin cracked plate geometries. For thicker cracked plate geometries results diverged progressively. For all cases studied, the use of a linear distribution of the stress intensity factor function through the plate thickness appeared to be satisfactory.

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Zusammenfassung Eine Reihe von dreidimensionalen photoelastischen Versuchen wurden auf Platten, die durchgehende Risse enthalten, unter Biegebelastung und genügendem Zug um das Schließen auf der Druckseite der Platte zu verhindern, ausgeführt. Die Dimensionen der gerissenen Platten wurden so gewählt daß sie das Übergangsgebiet dünn auf dick enthalten. Man machte Streifen paralell zu den Plattenoberflächen im spannungsgefrohrenen Material um die Teile um die Rißspitze zu entfernen. Die Streifen wurden photoelastisch untersucht und man stellte experimentelle Funktionen auf, die der Verteilung der Spannungsintensitätsfaktoren über die Plattendicke entsprechen. Die Ergebnisse wurden mit der Theorie von G. C. Sih verglichen. Die Übereinstimmung war ausgezeichnet für dünne Platten mit Rissen. Für dickere Platten mit Rissen gehen die Ergebnisse progressiv auseinander. Für alle untersuchten Fälle erwies sich die Anwendung einer linearen Verteilung der Spannungsintensitätsfaktorenfunktion über die dicke der Platte als zufriedenstellend.

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Résumé Une série d'essais de photo-élasticité à trois dimensions a été conduite sur des plaques comportant des fissures traversantes, sollicitées en flexion avec une composante de traction suffisante pour éviter que les fissures ne se referment du côté comprimé de la plaque.Les géométries des plaques fissurées ont été choisies de sorte à couvrir la gamme de la transition mince à épais. Des tranches ont été découpées parallèlement aux surfaces de la plaque, après que l'on eût figé les contraintes dans le matériau. Ces tranches ont été analysées par photo-élasticité, et des fonctions correspondant aux distributions des facteurs d'intensité des contraintes ont été évaluées expérimentalement.Les résultats ont été comparés avec la théorie de G. C. Sih. L'accord est excellent pour les tôles fissurées correspondant aux géométries minces. Ils divergent progressivement au fur et à mesure que l'on passe à des géométries épaisses.Pour tous les cas étudiés, l'emploi d'une distribution linéaire de la fonction représentant le facteur d'intensité des contraintes au travers de l'épaisseur de la plaque apparaît satisfaisant.

     

New high-pressure Sr-Ca-Cu-O compounds and their superconducting properties

It is shown for (Sr, Ca)_1–y CuO_2.00+z (nominal composition) superconductors fabricated under a high pressure of 5 GPa and at 930°C that, as z increases, the Meissner fraction increases from a few percent to 20% and then starts to decrease. In the X-ray powder diffraction pattern for the sample with the maximum Meissner fraction, it is obvious that the infinite-layer structure has been decomposed and a new structure becomes the major phase. It appears that the new structure is the 0223 structure which consists of rock-salt and the infinite-layer type blocks. This material is likely to be a new superconducting cuprate.     

The analysis of scientometric matrices for policy implications

A method is explained for analysing matrices of statistics where each element should be approximately proportional to some column coefficient and also to some row coefficient. Using U. S. patent data as an example it is shown that entries are usually proportional to country size and patent category size. Deviations from proportionality expectations when tabulated often suggest policy implications.     

Experimental status of the ac Josephson effect in liquid helium

The presence of an ac sound field causes several distinct effects in a system of two baths of superfluid liquid helium which are coupled by a small orifice. The primary effects of the sound field can be classified as a Z-T structure, steps, and anomalies. Each of these three effects has been subjected to various criteria which are necessary for an interpretation in terms of the ac Josephson effect. These three effects failed the criteria which were applied, and therefore they are not due to the Josephson effect. However, it is shown that the properties of these three effects correlate quite well with the expected properties of first-sound resonances within one of the two liquid baths.Financial support was provided in part by the National Science Foundation.     

Spin hydrodynamic equations with external disturbances and suitable Green's functions for superfluid3He-B. New onsager relations

The spin hydrodynamic equations for superfluid³He-B have been obtained for the case of external, time-dependent fields. On the basis of a microscopic approach, expressions are found for additional terms in equations containing these fields. Considering the linear response of the system to the switching on of external fields, formulas are found for suitable Green's functions (magnetization-magnetization, rotation-rotation, magnetization-rotation, rotation-magnetization). The rotation-rotation Green's function has the 1/q ² singularity characteristic of superfluid systems. Connections between Green's functions lead to relations among kinetic coefficients v, ₁, and ₂. It is also shown that there is a conserved quantityQ ^(B) = div v _s ^(B) that describes sources or magnetic type charges (monopoles) of the superfluid velocity v _s ^(B) . Comparison with the phenomenological approach suggests thatQ ^(B) is proportional to a pseudoscalar giving the projection of the spin density onto the vector describing the axis of rotation.     

Effects of dimensionality and crystal structure on bound states of point defects in quantum solids

The effects of dimensionality and crystal structure on the bound states of point defects in quantum crystals are investigated. It is shown that tightly bound states tunnel slowly in some lattices (e.g., bcc) while they tunnel quickly through other lattices (e.g., hcp). Explicit band calculations are made for ( ³ He) ₂ impurity molecules in solid host ⁴ He crystals. These illustrate the qualitative differences present in various molecular tunneling modes.     

The stacked lamellar texture on the fracture surfaces of fibre composites

A fracture surface texture, which has been variously termed as lacerations, hackles or serrations, is often observed on the matrix surface of fibre composites, most often in resin-rich regions. This texture, referred to here as a stacked lamellar texture to emphasize its plate-like nature, was studied in an E-glass/epoxy composite. Scanning electron fractographs of these materials suggest that the stacked lamellar texture arises from crack fingers due to a meniscus instability mechanism interacting with a reorienting stress field.     

Observation of hydrogen distribution in high-strength steel

The diffusible hydrogen in Cr-Mo steels are observed with autoradiography technique. Specimens with the diffusible hydrogen are prepared by an electrochemical cathodic charging method and those without the diffusible hydrogen by annealing at 373 K after charging hydrogen. TEM autoradiographs suggests, by the developed silver grains, that the hydrogen trapping sites are the grain boundary and internal interface of ferrite-cementite and ferrite-lath structure. After keeping the sample at 373 K, the silver grains disappeared. Most of hydrogen trapping sites release almost all the hydrogen at 373 K. It is clear that these sites of high-strength steels supplies the diffusible hydrogen. Hydrogen absorption characteristics of quench hardening tempering Cr-Mo steels have been evaluated by thermal desorption spectrometry (TDS). From tritium electron microscopic autoradiography and TDS analysis, the lower temperature (360 K–370 K) peaks show the diffusing hydrogen which is released a few days. The diffusible hydrogen from trapping sites such as the internal interface of ferrite-cementite or ferrite-lath structure are distinguished to the diffusing hydrogen.     

On the “inertial” time in instability of materials with non-monotone yield stress

Summary We consider the shear instability problem of a ductile material which exhibits strain softening response after a critical value of the plastic strain, as well as strain-rate sensitivity. We first show that the time which corresponds to the maximum stress cannot be considered as the exact critical time at which instability occurs, by establishing the existence of an inertial time, which extends the stability regime into the softening region. We study the parameters that influence the value of this inertial time and show the importance of the strain-rate sensitivity. More precisely, we show that its presence, independent of its value, is sufficient to ensure the prolongation of the stability regime after the maximum value of the yield function. Finally, we present the numerical simulation of the non-linear problem to show that there exists a transition regime after the maximum stress, in which the strain-rate non-uniformities evolve very slowly. This regime is followed by an unstable situation, in the sense that the strain-rate localizes in the softer regions. The localization is due to a feed-back mechanism, which favors the strain increase much more at the softer regions, forcing the stress to decrease much more there, which, in turn, allows for the development of larger strain-rate values.