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51.
52.
Ee GC Foo CH Jong VY Ismail NH Sukari MA Taufiq Yap YH Awang K 《Natural product research》2012,26(9):830-835
A detailed chemical study on the stem bark of Garcinia nitida has led to the isolation of five xanthones. They are 1,6-dihydroxy-5-methoxy-6,6-dimethylpyrano[2',3':2,3]-xanthone (1), inophyllin B (2), osajaxanthone (3), 3-isomangostin (4) and rubraxanthone (5). The structures of these compounds were established using mainly 1-D and 2-D NMR spectroscopy ((1)H, (13)C, DEPT, COSY, HMBC and HMQC) while molecular masses were determined via MS techniques; 1 is a new compound. 相似文献
53.
A novel approach for ATRP has been developed which enables the polymerization of vinyl monomers including those bearing carboxylic acid groups such as acrylic/methacrylic acid in the free acid form with ppm amounts of copper. The quantity of copper used in the polymerization is comparable to those left in purified polymers obtained by a conventional ATRP process. 相似文献
54.
The observation of superconductivity at 4.3 K in a new crystalline form of Na0.3CoO2·1.3H2O is reported. The new superconductor has three layers of CoO6 octahedral per crystallographic unit cell, in contrast to the previously reported two-layer superconductor. The three-layer cell occurs because the relative orientations of neighboring CoO2 layers are distinctly different from what is seen in the two-layer superconducting phase. This type of structural difference in materials that are otherwise chemically and structurally identical is not possible to attain on the layered copper oxide superconductors. The synthesis and stability of the new phase are described. 相似文献
55.
56.
The synthesis and characterization of [Ba(HBTB)] is reported. This is the first porous framework synthesized with barium using carboxylate ligands. The framework has robust microporous character (Langmuir surface area of 879 m(2) g(-1)) and possesses unsaturated metal sites when fully desolvated. 相似文献
57.
Swee-Boon Chin Ji-Jinn Foo Yin-Ling Lai Terry Kin-Keong Yong 《Heat and Mass Transfer》2013,49(10):1447-1458
Increasing miniaturization of high speed multi-functional electronics demands ever more stringent thermal management. The present work investigates experimentally and numerically the use of staggered perforated pin fins to enhance the rate of heat transfer in these devices. In particular, the effects of the number of perforations and the diameter of perforation on each pin are studied. The results show that the Nusselt number for the perforated pins is 45 % higher than that for the conventional solid pins and it increases with the number of perforation. Pressure drop with perforated pins is also reduced by 18 % when compared with that for solid pins. Perforations produce recirculations in the x–y as well as the x–z planes downstream of the pins which effectively increase convective heat transfer. However, thermal dissipation decreases significantly when the ratio of pin diameter to perforation diameter exceeds 0.375. This is due to both a reduction in the number of perforation per pin and the decrease in the axial heat conduction along the pin. 相似文献
58.
For every real numbers , with , the curve parametrized by valued in with components: has image contained in the CR-umbilical locus: of the ellipsoid of equation , where the CR-umbilical locus of a Levi nondegenerate hypersurface is the set of points at which the Cartan curvature of M vanishes. 相似文献
59.
A series of new calamitic liquid crystals, 2-[4-(4-alkoxybenzoyloxy)benzylidenamino]benzothiazoles comprising a heterocyclic (benzothiazole) and two phenyl rings core system, terminal alkoxy chain, imine and ester linkers were prepared and characterized. This series comprises eight members wherein the members vary by the length of alkoxy chain (CnH2n+1O-, where n?=?4, 6, 8, 10, 12, 14, 16, 18). Spectral analysis results were in conformity with the expected structure. Their thermotropic behaviors were studied by using differential scanning calorimetry, optical polarizing microscopy and powder X-ray diffraction techniques. A single mesophase (nematic) was observed for the first member of the series (n?=?4). As the alkoxy chain increased to n?=?6, 8, 10, 12, 14, the nematic phase appeared together with an additional SmA phase. When moving from n?=?16 until the highest member (n?=?18), the nematic phase disappeared and these compounds only exhibited a single mesophase (SmA). 相似文献
60.
A novel formalism (the effective surface potential method) is developed for calculating surface states. Like the Green function method of Kalkstein and Soven and the transfer matrix method of Falicov and Yndurain, the technique is exact for simple tight binding Hamiltonians. As well as offering an alternative viewpoint, the present method provides a simple analytic expression describing the surface states. At each point ks in the surface Brillouin zone the semi-infinite solid is viewed as an effective linear chain where each element of the chain is a planar layer. The solution to the linear chain problem can be expressed in terms of an effective potential h(ks,E) at each energy E. A number of examples are presented in detail; “spd” Hamiltonians for a linear chain (d = 1), the honeycomb lattice (d = 2), the 111 surface of silicon (d = 3), and a dissected Bethe lattice. Various exact results are given, e.g. the extremities of surface state bands and the surface density of states of p-like (delta function) bands. The results of Kalkstein and Soven for the 100 surface of a simple cubic solid with a perturbation on the surface layer are rederived. 相似文献