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991.
Grace A. Bennett Patricia A. Swift George B. Mullen Stanley D. Allen Jeffrey T. Mitchell Wendy E. Jones Vassil St. Georgiev 《Journal of heterocyclic chemistry》1989,26(6):1729-1734
The synthesis and antifungal activity of a novel series of 3-aryl-5-[(aryloxy)methyl]-3-[(1H-1,2,4-triazol-1-yl)-methyl]-2-methylisoxazolidines are described. The in vitro activity was evaluated in solid agar cultures against a variety of dermatophytes and yeast fungi, while in vivo activity was measured in an immune-compromised mouse model of systemic candidiasis. The activity of the title series was compared to that of ketoconazole and one derivative, the cis-3-(4-chlorophenyl)-5-(4-chlorophenyloxy)methyl analogue 5f was found to possess a similar potency in the in vivo assay. Structure-activity relationship correlations are also discussed. 相似文献
992.
993.
Cyclization of droxyolefin 3, either with NBS or Hg(OAc)2, gives predominantly the β isomer of a -arabinofuranoside structure. Carbohydrate phosphonate 1 was synthesized from bromide 4a in six steps. 相似文献
994.
Studies of the degradation of organotin stabilizers in poly(vinyl chloride) during gamma irradiation
Organotin stabilizers of the type Bu2SnX2 (X = SCH2CO2C8H17 or O2CCH?CHCO2C8H17) present in poly(vinyl chloride) (PVC) and subjected to varying doses of gamma irradiation in the range 1–200 kGy (0.1–20 Mrad) are shown to suffer degradation with dealkylation to form monobutyltin trichloride and tin(IV) chloride, which have been characterized by a subsequent alkylation procedure followed by gas chromatographic analysis. The extent of degradation of the stabilizers on prolonged gamma irradiation is much more severe than during thermal degradation leading to comparable blackening of the polymer. 相似文献
995.
The thermal antioxidant action of Sanduvor NPU in polypropylene film has been examined at the 0.1% w/w concentration level. Infra-red and second-order derivative u.v.-visible spectroscopic techniques were used to monitor degree of oxidation in the films and stabiliser photodecomposition behaviour respectively. Hydroperoxide analysis was employed to determine the degree of thermal oxidation of films in an air oven. It was found that the behaviour of Sanduvor NPU in polypropylene films as a thermal stabiliser parallels its mode of action when used a melt stabiliser. The metal complex is highly effective in inhibiting hydroperoxide formation during extreme oxidative conditions. Hydroperoxide decomposition appears to play no part in this behaviour due to the inability of the complex to destroy these chromophores in solution, and the effect it has is attributed to the very effective chain breaking acceptor mechanism, i.e. macroalkyl radical scavenging. The relationship between embrittlement time and concentration was studied by varying the stabiliser content of the polymer over a wide range. As in the case of other metal chelates, the relationship is not linear, a limiting concentration behaviour is observed. This effect is attributed to the formation during photooxidation of products which promote the degradation of the polymer. This effect has implications on the efficiency of commercial systems. 相似文献
996.
Allen I. Janis 《General Relativity and Gravitation》1985,17(6):599-612
The electric and magnetic parts of the linearized Weyl tensor, when the stress-energy tensor is that of a perfect fluid and the background is of Robertson-Walker type, are known to satisfy wave equations that differ by the presence of a source term for the electric part. It is shown here that all of the allowed solutions of the inhomogeneous equation can be obtained by applying a differential operator to the solutions of the homogeneous equation; consequently, electric-type and magnetic-type gravitational waves have the same propagation properties. The results of a complete integration of the appropriately linearized Newman-Penrose equations are given. 相似文献
997.
998.
The theery of self-reversal is examined by observing the emission profile of the sodium D2 line excited with light from a scanning tunable dye laser, as a function of vapour pressure. 相似文献
999.
Curtis L. Card Myron B. Allen 《Numerical Methods for Partial Differential Equations》1995,11(2):147-163
Difference-like schemes for the wave equation arise naturally from a Galerkin finite-element formulation, if we adopt certain quadrature rules in evaluating the mass and stiffness matrices. One can extend these schemes to problems involving sharp interfaces by applying the quadrature on a refinement of the finite-element grid that includes the interfaces. We develop error estimates for this modified scheme that corroborate numerical results for acoustic and elastic wave equations, presented in a companion article. © 1995 John Wiley & Sons, Inc. 相似文献
1000.
Optimizing material strength constants numerically extracted from taylor impact data 总被引:2,自引:0,他引:2
Advanced design requirements have dictated a need for the mechanical properties of materials at high strain rates. Mechanical testing for these data poses a significant problem for experimentalists. High-speed testing machines have a limited capability at rates approaching 102/s. The split Hopkinson pressure bar is the most reliable alternative for rates approaching 104/s. Plate impact experiments are capable of generating strain rates of 108/s and higher. The Taylor impact test occupies a place of particular importance by providing data at strain rates on the order of 104/s–105/s. The issue at present is extracting the data. This paper provides a method for obtaining dynamic strength model material constants from a single Taylor impact test. A polynomial response surface is used to describe the volume difference (error) between the deformed specimen from the Taylor test and the results of a computer simulation. The volume difference can be minimized using an optimizer, with the result being an optimum set of material constants. This method was applied to the modified Johnson-Cook model for OFHC copper. Starting from a nominal set of material constants, the iterative process improved the relative volume difference from 23.1 percent to 4.5 percent. Other starting points were used that yielded similar results. The material constants were validated by comparing numerical results with Taylor tests of cylinders having varying aspect ratios, calibers and impact velocities. 相似文献