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981.
Computational investigations are reported on the local flow and heat transfer characteristics from staggered, multiple circular
air jets impinging on a flat surface with effusion holes. The geometrical and flow parameters for the computational study
are chosen as per the experimental arrangement of Cho and Rhee J Turbomachinery 123:601–608, (14) so as to explain salient features observed in these experiments. The two peaks in the Nusselt number observed in the case
of H/D = 6 and three peaks in the case of H/D = 2 are attributed to the flow characteristics such as primary vortices forming
an up-wash region, followed by secondary vortices resulting in a secondary stagnation zone. The magnitude of local peak in
heat transfer increases up to 88% with increasing values of D/d from 0.5 to 1.5 at Re = 10,000. 相似文献
982.
Enantioselective formal synthesis of macrolactone palmerolide A, a polyketide marine natural product, is described. Key strategies in the synthesis include the oxidative furan ring-opening of a chiral furyl carbinol for the installation of the 1,4-dienol core and a Jung nonaldol-aldol reaction for the dienamide core. 相似文献
983.
A highly active catalytic system for the carbonylation of meso- and terminal epoxides to β-lactones is described. The active catalyst, analogous to Coates' catalyst, is generated in situ from commercially available (TPP)CrCl and Co(2)(CO)(8). This practical system circumvents the preparation of air sensitive cobaltate salts, operates at low catalyst loadings, and allows the carbonylation of functionalized, sterically demanding and heterocyclic meso-epoxides. 相似文献
984.
K. Vajravelu K. V. Prasad Robert A. Van Gorder Jinho Lee 《Transport in Porous Media》2011,90(3):977-992
Numerical solutions for the free convection heat transfer in a viscous fluid at a permeable surface embedded in a saturated
porous medium, in the presence of viscous dissipation with temperature-dependent variable fluid properties, are obtained.
The governing equations for the problem are derived using the Darcy model and the Boussinesq approximation (with nonlinear
density temperature variation in the buoyancy force term). The coupled non-linearities arising from the temperature-dependent
density, viscosity, thermal conductivity, and viscous dissipation are included. The partial differential equations of the
model are reduced to ordinary differential equations by a similarity transformation and the resulting coupled, nonlinear ordinary
differential equations are solved numerically by a second order finite difference scheme for several sets of values of the
parameters. Also, asymptotic results are obtained for large values of | f
w|. Moreover, the numerical results for the velocity, the temperature, and the wall-temperature gradient are presented through
graphs and tables, and are discussed. It is observed that by increasing the fluid variable viscosity parameter, one could
reduce the velocity and thermal boundary layer thickness. However, quite the opposite is true with the non-linear density
temperature variation parameter. 相似文献
985.
986.
Amodini MishraS.N. Choudhary K. Prasad R.N.P. Choudhary 《Physica B: Condensed Matter》2011,406(17):3279-3284
The polycrystalline sample of Ba(Pr1/2Ta1/2)O3 was prepared by a high-temperature solid-state reaction technique. The crystal symmetry, space group and unit cell dimensions were derived from the experimental results using FullProf software. XRD analysis of the compound indicated the formation of a single-phase tetragonal structure with the space group P4/mmm (1 2 3). Impedance and electric modulus analysis were used as tools to analyze the electrical behavior of the sample as a function of frequency at different temperatures. The impedance analysis of the compound indicated a typical negative temperature coefficient of resistance behavior, and dielectric relaxation was found to be of non-Debye type. The frequency dependent maximum of the imaginary part of the electric modulus follows the Arrhenius law with activation energy of 0.15 eV. The ac conductivity data obeys double power law. 相似文献
987.
Synthesis and characterization of di- and trivalent pyrazolylborate β-diketonates and cyanometalates
Tang M Li D Mallik UP Zhang YZ Clérac R Yee GT Whangbo MH Mungalimane A Holmes SM 《Inorganic chemistry》2011,50(11):5153-5164
The syntheses, structures, and magnetic properties of a series of di- and trivalent hydridotris(3,5-dimethylpyrazol-1-yl)borate (Tp*) cyanomanganates are described. Treatment of tris(acetylacetonate)manganese(III) [Mn(acac)(3)] with KTp* and tetra(ethyl)ammonium cyanide affords [NEt(4)][(Tp*)Mn(II)(κ(2)-acac)(CN)] (1), as the first monocyanomanganate(II) complex; attempted oxidation of 1 with iodine affords {(Tp*)Mn(II)(κ(2)-acac(3-CN))}(n) (2) as a one-dimensional chain and bimetallic {[NEt(4)][(Tp*)Mn(II)(κ(2)-acac(3-CN))](2)(μ-CN) (3) as the major and minor products, respectively. A fourth complex, [NEt(4)][(Tp*)Mn(II)(η(2)-acac(3-CN))(η(1)-NC-acac)] (4), is obtained via treatment of Mn(acac(3-CN))(3) with KTp* and [NEt(4)]CN, while [NEt(4)](2)[Mn(II)(CN)(4)] (5) was prepared from manganese(II) trifluoromethanesulfonate and excess [NEt(4)]CN. Tricyanomanganate(III) complexes, [cat][(Tp*)Mn(III)(CN)(3)] [cat = NEt(4)(+), 7; PPN(+), 8], are prepared via sequential treatment of Mn(acac(3-CN))(3) with KTp*, followed by [NEt(4)]CN, or [cat](3)[Mn(III)(CN)(6)] with (Tp*)SnBu(2)Cl. Magnetic measurements indicate that 1, 2, and 4 contain isotropic Mn(II) (S = (5)/(2); g = 2.00) centers, and no long-range magnetic ordering is found above 1.8 K. Compounds 7 and 8 contain S = 1 Mn(III) centers that adopt singly degenerate spin ground states without orbital contributions to their magnetic moments. 相似文献
988.
Papia Datta Ambika Prasad Mukhopadhyay César J. Pastor 《Journal of organometallic chemistry》2011,696(2):488-166
Cr, Mo and W tetracarbonyl complexes of 2-(2-pyridyl)benzoxazole (PBO) and 2-(2-pyridyl)benzothiazole (PBT) are spectroscopically characterised. The confirmatory structure of [Mo(CO)4(PBO)] has been determined by X-ray crystallography. The complexes show negative solvatochromic effect, with increasing solvent polarity the MLCT band is shifted to longer wavelength region. Cyclic voltammetry shows M(I)/M(0) redox response and also exhibit fluorescence spectra at room temperature. The electronic structures of the complexes are calculated by density functional theory (DFT) and time dependent-DFT calculated results are used to explain redox property and electronic transitions. 相似文献
989.
A convergent synthesis of the orally active renin inhibitor aliskiren (1) is described. The synthesis was accomplished in 12 steps starting from the known chloride 2. The key step involves the Curtius rearrangement of the advanced intermediate 15, which provides lactone/carbamate 17 containing the correct stereochemistry and all of the functionality required for the preparation of the drug substance. 相似文献
990.
A mild and metal-free access to 1,2,4-tri or 1,2,4,5-tetrasubstituted pyrroles has been developed by the reaction of Morita-Baylis-Hillman acetates of acetylenic aldehydes with amines and sulfonamides. This new protocol is based on K(2)CO(3)-promoted tandem allylic substitution/cycloisomerization reactions. 相似文献