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961.
Resistance to dislocation glide in slip bands due to the presence of other dislocations may be represented by an additional term in the integral equation formulation of the equilibrium state. As a consequence, the asymptotic behaviour of dislocation density at the edge of interval is modified from the conventional square root singularity. We propose an efficient and fast numerical method that is suitable for solving the resulting singular equations of the second kind based on the Gauss-Jacobi quadrature. The quadrature formulae involve fixed nodal points and provide exact results for polynomials up to degree 2n-1, where n is the number of nodes. A numerical example of the application of the Gauss-Jacobi rule to a slip band problem is provided as a demonstration of the validity of the method. 相似文献
962.
Alexander Pechenik Gasper J. Piermarini Stephen C. Danforth 《Journal of the American Ceramic Society》1992,75(12):3283-3288
Compaction of ultrafine silicon nitride (Si3 N4 ) powder at high pressures and various temperatures followed by pressureless sintering was investigated. The powder, consisting of nearly spherical particles (16 nm in diameter) of amorphous stoichiometric Si3 N4 , was pressed in a diamond anvil cell under pressures up to 5 GPa and temperatures ranging from liquid nitrogen to 500°C. Quality of compaction, evaluated by visual transparency and hardness of the produced compacts, depended on the amount of adsorbed gases on the surface of the particles and on the temperature of compaction. Visually transparent compacts were produced by pressing the starting powder without outgassing in liquid nitrogen under 5 GPa. The transparent compacts exhibited a hardness of 1200 kg/mm2 after pressing in the diamond anvil cell at 500°C for 3 h at 5 GPa. After subsequent pressureless sintering conducted for 1 h at 5 GPa. After subsequent pressureless sintering conducted for 1 h at 1400°C in a tube furnace under nitrogen, the hardness of these samples increased to over 2000 kg/mm2 and the visual transparency was maintained. The results demonstrated that transparency was maintained. The results demonstrated that transparent compacts of nanosize amorphous Si3 N4 particles could be sintered to high hardness at relatively low temperatures without using sintering aids or applying pressure during sintering. 相似文献
963.
Separation of cholesterol,and fatty acylglycerols,acids and amides by thin-layer chromatography 总被引:6,自引:0,他引:6
A rapid unidimensional thin-layer chromatographic (TLC) method for the separation of neutral lipids is described, using two
sequential solvent systems of different polarity. Excellent separations of mono-, di- and triglycerides, fatty acids, fatty
amides, and cholesterol are thereby achieved. Separation is accomplished at room temperature and requires 25 min.
Reference to brand of firm name does not constitute endorsement by the United States Department of Agriculture over others
of a similar nature not mentioned. 相似文献
964.
Shape-factor effect on melting in an elliptic capsule 总被引:1,自引:0,他引:1
Sergei A. Fomin Alexander V. Wilchinsky 《International Journal of Heat and Mass Transfer》2002,45(14):3045-3054
An approximate mathematical model of contact melting of an unfixed material in an elliptical capsule is developed. The main characteristic scales and non-dimensional parameters which describe the principal features of the melting process are found. Choosing a special heat flux distribution on the wall of the capsule allows us to derive a closed-form evolution equation for the motion of the solid accounting for the energy convection in the liquid, expressed through the non-linearity of the temperature distribution across the molten layer. It is shown that the melting rate of the solid depends on the shape of the capsule. Generally, elliptical capsules show higher rate of melting than circular ones. Elongated capsules provide more effective melting than oblate ones, even though they have the same aspect ratios and vertical cross-sectional areas. This phenomenon is caused by the fact, that the pressure necessary to support the solid is larger for the elongated capsules than that for oblate ones, which leads to thinning of the molten layer along with the increase of the heat flux across it. The time required for complete melting can be achieved by the right choice of the shape of the capsule, which is specified by the value of the aspect ratio. The found influence of the capsule shape on the melting rate can be used for design and optimization of practical latent-heat-thermal-energy systems. 相似文献
965.
Shtern Mikhail B. Maidanyuk Alexander P. Cocks A. 《Powder Metallurgy and Metal Ceramics》2002,41(7-8):347-354
The lower and upper boundary approximation for describing the yield condition of porous bodies whose behavior is sensitive to a third strain rate invariant is obtained. Together with porosity the constitutive equations contain a material parameter that is responsible for the change in pore shape. This approach makes it possible to present the macroscopic yield condition in a compact form convenient for analysis and various applications. In particular, generalization of well-known plasticity conditions of Gurson and Green-Shima is presented. The lower estimate generalizes the Gurson model and the upper estimate corresponds to the Green-Shima model. Octahedral contours of the loading surface are constructed that agree with experimental data for loose materials and porous powder bodies. 相似文献
966.
Dale E. Alexander 《Journal of Nuclear Materials》1997,240(3):196-204
Motivated by the recent interest in gamma ray embrittlement of nuclear reactor pressure vessels (RPVs), calculations were performed to evaluate aspects of defect production by gammas in iron and steel. In addition to determining displacement damage cross-sections, the atomic recoil energy dependence of gamma-induced defect production was described by integral recoil damage spectra, W(T), and their associated median recoil damage energies, T1/2. These latter characterizations, should be particularly useful in evaluating the contribution of gamma ray generated defects to microstructural changes causing radiation embrittlement. The results for monoenergetic gammas, as well as for gamma rays with a spectrum of energies characteristic of a RPV, reveal T1/2 values of <100 eV, about three orders of magnitude smaller than for fast-neutrons, the radiation of primary concern in previous embrittlement studies. The relative contributions of various gamma interactions to defect production, as well as the role of light alloy element-induced secondary displacement mechanisms, are also considered. 相似文献
967.
968.
The t-J model is studied including a long-range 1/r repulsive interaction. It is observed that charge-density-wave states become stable as the strength of the 1/r term, Vcoul, is increased. Due to this effect, the domain of stability of the superconducting phase that appears near phase separation at Vcoul=0 is not enlarged by a 1/r interaction as naively expected. Nevertheless, superconductivity exists in a finite region of parameter space, even if phase separation is suppressed. 相似文献
969.
A relation between the Hamming weight enumerator of a linear code and the Tutte polynomial of the corresponding matroid has
been known since long ago. It provides a simple proof of the MacWilliams equation (see D. Welsh, Matroid Theory (1976)). In this paper we prove analogous results for the support weight distributions of a code.
Received March 5, 1996; revised version October 28, 1996 相似文献
970.
Alexander Gelman Eugenia Benjamin 《Journal of the science of food and agriculture》1989,47(2):225-241
The quality of fresh, chilled and frozen mince made from the flesh of pond-bred silvercarp (Hypophthalmichthys molitrix (Val)) was evaluated. Flavour panel scores for all minces were acceptable and this quality did not deteriorate during storage for one week in a domestic refrigerator (5–6°C) or for one year at ?20°C. The levels of oxidative rancidity (2-thiobarbituric acid analysis) in the minces were consistent with this maintenance of quality. Aerobic plate counts at 25°C of fresh mince rose from 7–9 × 104 to 1.1 × 105 after 6 days' storage at 5–6°C. Coliform and psychrotroph counts rose from 1.0 × 101 and 7–8 × 103 to 5–4 × 102 and 1.3 × 104, respectively. The functional and textural properties of pond-bred silvercarp mince in terms of salt-soluble protein content, water binding capacity and penetrometer values were measured on fresh, refrigerated and frozen samples. All-fish sausages and frankfurters developed from pond-bred silvercarp mince were assessed in laboratory and consumer tests against commercial beef sausages and frankfurters. The fish products competed well and achieved levels of acceptance similar to those of the beef-containing products. Texture measurements revealed slight changes in the fish products during storage for 7 days at 5–6°C. No spoilage was detected in any of the products after a week at 5–6°C. The nutritional advantages of the fish sausages and frankfurters are discussed. 相似文献