Theoretical estimation of the effect of interfacial energy on the mechanical strength of spinodally decomposed alloys

New interfaces are produced on the slip plane when a crystal with continuous composition fluctuation arising from spinodal decomposition is deformed by slip. In this work, the energy of such interfaces is evaluated for both modulated and mottled structures, and their effects on slip behaviour are discussed. It is concluded that the contribution of this interfacial energy is large enough to account for the age-hardening concomitant with spinodal decomposition.     

Two shift theorems leading to lower bounds to eigenvalues

Summary Two theorems are proved by which the other bound can be obtained from the Rayleigh quotient, i.e., the bound which cannot be obtained by the Rayleigh-Ritz method.The method presented here utilizes a shift operation which is the redistribution of weight functions in the Rayleigh quotient.     

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.     

Local Dissipation Phenomena in Crystalline Forms of Boron

A classification is proposed for dissipation (in particular, relaxation) processes in crystalline systems and inorganic materials. The concepts of modifying and aggregation subsystems are defined. Relations are derived for determining the temperature dependences of the local quasi-viscous dissipation parameter r _iand the local quasi-elastic parameter K _ifor each relaxation transition in the tan (T) spectrum.     

Fluctuating collective oscillations and electric field penetration into superconductors

The spectrum of collective oscillations and the penetration of a constant longitudinal electric field into a superconductor are investigated based on microscopic Gor'kov equations integrated over the energy variable of one-particle excitations. The influence of the anharmonicity of collective oscillations upon the attenuation of these oscillations and upon the penetration of the longitudinal electric field into the superconductor has been studied as well. We investigate the problem of the self-attenuation of fluctuating collective oscillations in the vicinity of the critical temperature.     

Three-dimensional interactions of a crack front with arrays of penny-shaped microcracks

Three-dimensional interactions of a crack front with arrays of penny-shaped microcracks are considered. The work extends the earlier analysis of 2-D crack-microcrack interactions to the 3-D configurations.After analysing simple elementary interaction events (involving only one microcrack) we solve the interaction problem for a number of sample arrays (containing up to 50 microcracks)-realizations of certain microcrack statistics.Statistical aspects of the problem are examined. The interaction effects are found to fluctuate, even qualitatively (from shielding to amplification) along the crack front: the intervals of reduced stress intensity factors (SIFs) alternate with local peaks of SIFs that enhance local front advances. Thus, no statistically stable effect of stress shielding is found (at least, for the microcrack statistics considered): the toughening by microcracking, if it exists, may be due to a statistics of the microcrack centers which is biased towards shielding configurations or to expenditure of energy on nucleation of new microcracks, rather than elastic interactions with them. Similarly to the 2-D case, stochastic asymmetries in the microcrack field produce noticeable secondary modes on the main crack (i.e., modes II and III under mode I loading); this may be partially responsible for crack kinking and an irregular crack path.The short range interactions (several microcracks closest to the main crack tip) play a dominant role. Their impact on the main crack is quite sensitive to the individual microcrack locations and cannot be adequately reproduced by modelling the short range microcracking zone by an effective elastic material of reduced stiffness.The interaction effects in 3-D are found to be weaker than in 2-D.     

Equipment for checking dielectric losses in silicon matrices with dielectric insulation

Conclusions The industrial apparatus Omega-2 described above employs an indirect method of measuring the leakage current in the pockets of a silicon matrix with dielectric insulation. The basic error of the apparatus does not exceed 5%.By regulating the voltage applied to the pocket, we would be able to select the structure needed for creating devices with high breakdown voltages and low reverse currents.Translated from Izmeritel'naya Tekhnika, No. 1, pp. 61–62, January, 1979.     

Critical and Flash Points for Metastable Systems in a Mean-Field Approach

By using, as a model, an analytical equation of state which describes a system that can exist in a liquid or vapor phase, scaling properties regarding the critical temperature and the flash temperature were found. The flash temperature is defined as the highest temperature at which a self-bound system can exist in hydrostatic equilibrium. The flash temperature can provide an alternate natural dimension-dependent scale of temperature, other than the critical temperature.     

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.     

Some simple flows of a Johnson-Segalman fluid

Summary Unlike most other fluid models, the Johnson-Segalman fluid allows for a non-monotonic relationship between the shear stress and rate of shear in a simple shear flow for certain values of the material parameter. This has been used for explaining a phenomenon such as spurt. Here, we study three simple flows of a Johnson-Segalman fluid with a view towards understanding its response characteristics. We find that boundary conditions can have a very interesting effect on the regularity of the solution; changing them continuously leads to solutions that change their regularity. First, we consider the flow through a circular pipe and find solutions that have discontinuous velocity profiles which have been used to explain the phenomenon of spurt (cf. [10], [11]). Second, we consider the flow past an infinite porous plate and show that it will not admit solutions which have discontinuous velocity gradients, the solutions being necessarity smooth. Lastly, we study Poiseuille flow in a concentric annulus with porous boundaries. While spurt could be explained alternatively by allowing for stick-slip at the wall, the Johnson-Segalman model seems particularly suited in describing the appearance of shear-layers (cf. [13]).     

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.     

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.     

A non-local rate-type viscoplastic approach to patterning of deformation

Summary We propose here a new model to the problem of phase transformations which account for micro-structural effects and non-equilibrium phenomena. The model is obtained by incorporating higher-order strain gradients in the relaxation function of a Maxwell's rate-type constitutive equation. This approach can be included in ilhavý's thermodynamical theory of non-simple bodies with internal variables. Explicit necessary and sufficient conditions are given such that the model be fully compatible with the unmodified Clausius-Duhem inequality and balance equations. We show that its elastic set has to be the closure of an open set in the strain-stress-higher strain gradients space, i.e., the model is a viscoplastic one in the sense of Sokolovskii-Malvern. Energy estimates for smooth solutions of strain controlled problems are given. The influence of the viscous mechanism, softening mechanism and of the strain gradients effects on the local behaviour of solutions is investigated. Critical wave lengths for the onset of instability and pattern formation are determined.     

Ordinary size effects and deviations from Matthiessen's rule in the resistance of fine wires

Contrary to previous statements in the literature, large deviations from Matthiessen's rule in fine wiresare to be expected on the basis of a straight-forward solution of the ordinary transport equation, assuming the relaxation-time approximation and imposing the idealized condition of diffuse scattering of electrons at the boundaries. Using Chambers' path-integral method to evaluate the current density in a wire of arbitrary cross-sectional shape, the effects of boundary scattering on the resistivity in the regimed 0.1 have been calculated for two model Fermi surface geometries. For the temperature-dependent part of the resistivity, _d (T) _d (T)– _d (0), two distinct types of behavior are found in the alternative cases: (1) for a spherical Fermi surface, _d(T) increases logarithmically with _d(0); (2) for a cylindrical Fermi surface, _d (T) increases essentially linearly with _d (0). [In each case the qualitative dependence of _d(0) on /d is, for practical purposes, linear. However, the correct value of the product in the cylindrical case is not simply given in the ordinary way by the slope of an empirical plot of _d (0) vs.d ^–1.] A comparison of theoretical results for the two simple models with the published data for indium and gallium shows that the actual temperature-dependent size effects are consistent, both qualitatively and, by a rough estimation, quantitatively, with the expected behavior.     

The formation of moisture and temperature fields in the process of heat- and mass-transfer in hydrothermal solutions with enclosing rocks

We consider the mathematical model of the heat- and mass-transfer process in the hydrothermal solution-enclosing rocks system and we present a method for the construction of the mathematical model.     

Thermodynamic and structural factors determining the wear resistance of aluminum cast irons

When the carbon content in aluminum cast iron containing about 2.5% Al is reduced (to about 2.5%),. carbon is concentrated near the dendritic branches where a specific variety of pearlite (containing a finely dispersed carbon-rich -phase) is formed, the interdendritic regions remaining ferritic. Modifying cast irons of this kind with cerium leads not only to spherodization of graphite but also to the formation of -phase dendrites with a corresponding reduction in the carbon content in the ferritic matrix surrounding -phase dendrites and pearlite. This has a beneficial effect on the wear resistance of cast iron.     

Formation of Friction Layers and Wear Resistance of Steels under Conditions of Boundary Friction

We studied the influence of the lubricant compositions Grafitol with 10% graphite (1), Aerol containing 17% MoS₂ (2), Limol containing 60% MoS₂ (3), Limol + 10% chlorine-paraffin (4), and Limol + 10% copper powder (5) on the wear rate and formation of the fine structure of surface friction layers of structural steels. We established a correlation between the tribological characteristics of steels and lubricants. The abrasive wear of 40KhFA steel was minimum if it was lubricated with Limol + 10% copper powder. In this case, its wear was smaller by a factor of 10, 2, 1.25, and 7.25 as compared with lubricant compositions 1–4, respectively. In the course of minimum wear of 40KhFA steel, in the surface friction layers, we observed the minimum values of second-kind distortions (a/a) and of the true size of domains of X-ray coherent scattering (D) as well as the minimum difference between the crystal lattice constants (a) of steel before and after friction.     

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.     

An electron microscopic study of nickel sulfide inclusions in toughened glass

It has been known since the early sixties that nickel sulfide inclusions cause spontaneous fracture of toughened (thermally tempered) glass, but despite the considerable amount of work done on this problem in the last four decades, failures still occur in the field with regularity. In this study we have classified (by viewing through a 60× optical microscope) inclusions into two groups, which are classic and atypical nickel sulfides. The classics look like the nickel sulfide inclusions found at the initiation-of-fracture of windows that have broken spontaneously. We have compared the structure and composition of the atypical inclusions with the structure and composition of the classics. All of the classic and atypical nickel sulfide inclusions studied in this work were found to have a composition in the range of Ni₅₂S₄₈to Ni₄₈S₅₂. Inclusions on the nickel rich side of stoichiometric NiS were found to be two-phase assemblies, and inclusions on the sulphur rich side of NiS were single phase. It had been proposed that the atypicals were passive, and of a different composition to the classics. However, we found that the difference between passive and dangerous nickel sulfide inclusions was not a difference in composition but rather a difference in the type of material in the internal pore space. The passive's had carbon char in their internal pore space, whereas the pore space of dangerous inclusions contained Na₂O. The presence of Na₂O and carbon char with the inclusions indicates that the formation of the inclusions results from a reaction of a nickel-rich phase with sodium sulphate and carbon.     

The effect of Si,Zr, Al and Mo on the structure and strength of Ti martensite

The structure and strength of martensite in near titanium alloys have been studied in the composition range (wt %) up to 10% Zr, 6%, Al, 1/2% Mo, 2.4% Si. [0001], 1/3 11¯20 dislocations, 1/3 10¯10 stacking faults and approximately {10¯11} twin related martensite plates are found to be common features of the martensite. Martensite midribs consist either of finely transformed material between martensite plates, or regions of low dislocation density within martensite plates.The martensite morphology is related to the alloy composition, changing from massive to plate-like with increasing solute content. The strength of the martensite is controlled largely by solid solution strengthening.