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41.
We solve Einstein's field equations in higher-dimensional spherically symmetric spacetime with strange quark matter attached to the string cloud, assuming one parameter group of con formal motions. The solutions match with the higher-dimensional Reissner-Nordstroem metric on the boundary at r=ro. The features of the solutions are also discussed in the framework of higher-dimensional spacetime.  相似文献   
42.
In the present investigation, we obtain a universal stability theorem for a dusty gas model with constant number density of dust particles and as a consequence, we establish a uniqueness criterion for an initial boundary value problem. For a variable number density of dust particles, only a uniqueness theorem is obtained.  相似文献   
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The oxidation of α-benzoyl-o-hydroxyacetophenones (3a-d) using iodobenzene diacetate in methanolic potassium hydroxide provides a new direct method for the synthesis of 2-benzoylcoumaran-3-ones (4a-c) in good yields. The formation of 4a-d is explained by neighb uring group participation.  相似文献   
46.
DBU-CH3I has been poised to be a substitute for diazomethane in the preparation of methyl esters from carboxylic acids. The reactions can be carried out in commercial untreated acetone and acetonitrile, which have been exemplified with several methyl esters, otherwise it is difficult to prepare. Bis-esterification using diiodomethane can also be achieved in a similar fashion. Sufficiently acidic phenols are also conveniently O-methylated by the method.  相似文献   
47.
Microwave absorption studies have been carried out on MgB2 superconductor using a standard X-band EPR spectrometer. The modulated low-field microwave absorption signals recorded for polycrystalline (grain size ∼ 10 μm) samples suggested the absence of weak-link character. The field dependent direct microwave absorption has been found to obey a ✓H dependence with two different slopes, which indicated a transition from strongly pinned lattice to flux flow regime.  相似文献   
48.
Differential pulse polarography is a versatile and sensitive technique which yields both qualitative and quantitative information about N-nitrosamines. The ability of the technique to carry out determinations in-situ permits the study of anchimeric, metabolic, and mechanistic properties in addition to phenomena such as kinetics and transnitrosation.  相似文献   
49.
A simple and efficient protocol has been developed for the synthesis of 3-alkenylated indoles and bis(indol-3-yl) derivatives by sulfonic acid-functionalized ionic liquid-catalyzed reaction of indole with 1,3-diketones/3-ketoesters under solvent-free ultrasound irradiation. Good to excellent yields (68–94%) are obtained in ultrasonication. The product of reaction is dependent on the substituent at C-2 position of indole. The catalyst is reusable and recyclable up to four cycles without significant loss of its catalytic activity. Compared with conventional heating, sound wave activation has the considerable advantages such as shorter reaction time, easy work-up, higher yields, and mild conditions.  相似文献   
50.
A series of Gd(2)Ti(2)O(7)/GdCrO(3) composites are prepared by solid state combustion method using Gd(NO(3))(3), TiO(2), Cr(2)O(3) as metal source and urea as a fuel. The composites are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible diffuse reflectance spectra (DRUV-vis), Brunauer-Emmett-Teller (BET) surface area measurements, photoluminescence spectra (PL), X-ray photoelectron spectroscopic (XPS) studies, photocurrent measurements etc. The photocatalytic activity of the composites is examined towards hydrogen production without using any co-catalyst under visible light illumination. The rate of formation of hydrogen is measured by the photocatalytic activity measurement device and gas chromatography (GC). The highest efficiency is observed over the composite GTC (Cr:Gd:Ti = 1:1:1). On the basis of photocurrent measurements and PL, a mechanism for the enhanced photocatalytic activity has been discussed.  相似文献   
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