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991.
[reaction: see text] A synthetic approach to malibatol A featuring a novel benzofuran synthesis is described. 相似文献
992.
Facile synthesis of cis and trans olefinic analogues of oxytocin 1 that have carbon in place of sulfur is achieved via ring-closing metathesis (RCM) on a resin-bound linear precursor peptide. Hydrogenation of the cis olefin, 3, proceeds selectively to generate the previously reported saturated derivative 5. Biological testing on rat uterus strips shows that cis compound 3 has an EC50 value of 38 ng/mL (EC50 for oxytocin is 2.7 ng/mL) whereas 5 and trans olefin 4 are less active. [reaction--see text] 相似文献
993.
Preparation of hydroxyapatite via microemulsion route 总被引:7,自引:0,他引:7
Koumoulidis GC Katsoulidis AP Ladavos AK Pomonis PJ Trapalis CC Sdoukos AT Vaimakis TC 《Journal of colloid and interface science》2003,259(2):254-260
Hydroxyapatite (HAp) was prepared using a microemulsion route in combination with the pH-shock wave method. The samples as received consisted of amorphous aggregated particles, which had remarkable mesoporosity with a narrow pore size distribution. After being heated at 650 degrees C, the A-type carbonate hydroxyapatite was crystallized at 635 degrees C in particles of similar size (40--120 nm) with no internal porosity. At a higher temperature (900 degrees C) a sintering process took place, resulting in network of a larger particles, consisting of HAp and beta-tricalcium phosphate (beta-TCP). The crystallization of HAp occurs at 635 degrees C with an activation energy of 62.7--72.2 kcalmol(-1). 相似文献
994.
995.
996.
The hydrazino complex {methoxo[4-phenylbutane-2,4-dione(p-nitrobenzoyl)hydrazonato(2-)]oxovanadium(V)}, VO(p-NO2bhbzac)OCH3, (1), has been prepared by the direct reaction of bis(benzoylacetonato) oxovanadium(IV), VO(bza)2, with p-NO2-C6H4C(O)NHNH2, p-NO2bh, in CH3OH. The resulting compound contains benzoylacetone-(p-NO2)benzoyl hydrazone as tridentate Schiff base-type ligand and OCH3 group as Lewis base, both ligated to vanadium. The crystals are orthorhombic, with Z = 8, space group Pbca, a = 11.699(5) Å, b = 14.035(5) Å, c = 22.564(5) Å, R1 = 0.0756 and wR2 = 0.1302. The crystal structure demonstrated the square-pyramidal geometry of the VOoxo(ONO)O coordination sphere with the oxo ligand at the apical position. The electronic absorption spectra revealed a ligand-to-metal charge-transfer (LMCT) band in the near UV region at max = 23,700 cm–1 (B = 5640 dm3 mol–1 cm–1) in CH3CN, max = 23,420 cm–1 (B = 5550 dm3 mol–1 cm–1) in DMSO, and max near 26,950 (sh) cm–1 (B = 10,550 dm3 mol–1 cm–1) in CH2Cl2. The FT-IR spectra of (1) show the characteristic strong (V = O) stretching vibration at 993 cm–1 and support the view that the oxovanadium complex is pentacoordinated and monomeric. 相似文献
997.
George B. Seligman 《Transactions of the American Mathematical Society》2003,355(8):3291-3300
Explicit constructions are given for idempotents that generate all projective indecomposable modules for certain finite-dimensional quotients of the universal enveloping algebra of the Lie algebra in odd prime characteristic. The program is put in a general context, although constructions are only carried through in the case of .
998.
K. L. Boey Patricia J. Y. Wong Y. C. Soh 《Nonlinear Analysis: Real World Applications》2003,4(5):787-804
The modelling of the spread of infectious disease is carried out for time t on a measure chain T. Our approach unifies the continuous case
and the discrete case
. The model is described by the integral equationwhere x(t) represents the proportion of the population infected at time t, f(t,x(t)) denotes the proportion of the population newly infected per unit time, and τ is the length of time an individual remains infectious. Using the measure chain calculus, we shall develop criteria for the existence of a nontrivial and nonnegative periodic solution for the modelling equation. The criteria can be implemented numerically, for this we shall give an algorithm as well as illustrative examples. 相似文献
999.
Transmission functions are derived that are valid in the nonparaxial case for a class of lenses that will image a continuum of points along an optical axis to a single image point. This lens, which we call a logarithmic asphere, is then used in a digital camera. The resolution of the camera is limited by the pixel size of the CCD; i.e., it is not diffraction limited. Digital processing is used to recover the image, and image-plane processing is used for speed. We find a tenfold increase in the depth of field over that for the diffraction-limited case. 相似文献
1000.
George Iliopoulos 《Annals of the Institute of Statistical Mathematics》2001,53(3):436-446
In this paper the problem of estimating the ratio of variances, , in a bivariate normal distribution with unknown mean is considered from a decision-theoretic point of view. First, the UMVU estimator of is derived, and then it is shown to be inadmissible under two specific loss functions, namely, the squared error loss and the entropy loss. The derivation of the results is done by conditioning on an auxiliary negative binomial random variable. 相似文献