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排序方式: 共有308条查询结果,搜索用时 15 毫秒
1.
In quasi-steady operation, convection currents in a Bridgmandevice, used for producing a semi-conductor crystal, createinhomogeneities that may make the crystal unusable. It has oftenbeen suggested that additional forces due to rotation or magnetismmight be efficacious in reducing the segregation of the elementsof the alloy. It has been found that, over a wide range of rotationrates, there is no improvement in performance due to rotationabout the vertical axis. However, numerical results that havebeen obtained previously (Lee & Pearlstein, J. Crys. Growth240, 2002) indicate that, when effects of centrifugal buoyancyare introduced, a substantial reduction in segregation is achieved.In the work reported here, by contrast, in which we extend previouslarge-Rayleigh-number asymptotic analysis to include centrifugalbuoyancy, we find no improvement in radial segregation, butrather increasing segregation with increasing rotation rate. 相似文献
2.
The pseudolactones 6 and 12 were prepared in a straightforward way from methyl α-D -glucopyranoside and methyl α-D -mannopyranoside, respectively. The pseudolactone 6 reacted with tert-butyl lithioacetate to give the protected, trihydroxylated cyclohexenone carboxylate 7 (51 %). The sterically hindered, L-ribo-configurated pseudolactone 12 reacted with diethyl ethylphosphonate and dimethyl methylphosphonate to give the protected trihydroxycyclohexenones 17 (49 %) and 18 (62 %), respectively. The hydroxymethylated cyclohexenone 21 was obtained from 18 by treatment with Me2AlSPh and then formaldehyde, oxidation of the product 19 , and elimination. Deprotection of 21 gave 2 , identical with KD16-Ul. Esterification of 2 gave 1 , identical with the title compound. Alternatively, 1 was obtained in higher yields by esterification of 21 , followed by deprotection of the hydroxy groups. This synthesis gave 1 and 2 from methyl α-D -mannopyranoside in an overall yield of 18 and 20 %, respectively, confirming their absolute configuration. 相似文献
3.
The dependence of the diffusion parameters including slowing down area, neutron diffusion length and migration length on the voided volume fraction in water has been studied experimentally. For this purpose, the PIEAS Neutron Transport Facility (PNTF) comprised of a 10 Ci Am–Be neutron source and a water filled aluminum tank with Perspex voided tubes has been designed and fabricated. A BF3 detector was used for the neutron counting. The slowing down area was determined at the cadmium cutoff level. The diffusion parameters were determined first in the absence of voids. The experimentally measured values of the slowing down area, the diffusion length and the migration length have been found in good agreement with the corresponding values determined by other workers. By varying void volume fraction from 0% to 7.5%, the experimental measurements show a monotonic increase in the slowing down area from 58.71±2.6 to 71.28±3.2 cm2, in the diffusion length from 2.95±0.13 to 3.11±0.13 cm and in the migration length from 8.21±0.165 to 8.99±0.169 cm. Our measurements show that the diffusion parameters exhibit a quadratic dependence on the void volume fraction. 相似文献
4.
Extraction and characterization of adenovirus 总被引:5,自引:0,他引:5
Mirza UA Liu YH Tang JT Porter F Bondoc L Chen G Pramanik BN Nagabhushan TL 《Journal of the American Society for Mass Spectrometry》2000,11(4):356-361
A new methodology for the extraction and characterization of proteins from Coomassie-stained sodium dodecylsulfate polyacrylamide gel electrophoresis using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has been described. The utility of this methodology was demonstrated in the characterization of adenovirus proteins. The key steps in the extraction and destaining process involve washing the excised band with a combination of solvents that include 10% acetic acid, acetonitrile, methanol, and formic acid:water:isopropanol mixture. By using this procedure, we determined adenovirus proteins with molecular weights ranging from 10,000 to 110,000 Da by MALDI-MS, obtaining a detection limit of approximately 6 pmol. Parallel experiments were successfully carried out to analyze adenovirus proteins from Cu-stained gels. It was observed that increase in laser intensity resulted in significant improvements in the quality of MALDI mass spectra for the analysis of inefficiently destained proteins from Cu-stained gels. 相似文献
5.
6.
The extraction of Cu(II), Ga(III), In(III) and Tl(III) with 1-phenyl-3-methyl-4-benzoylpyrazol-5-one (HPMBzP) from aqueous solutions has been investigated. The mechanism of extraction and the composition of the species extracted has been determined. The effect of equilibration time, various organic solvents and salting-out agents on the extraction of copper and gallium has also been investigated. The green Cu(PMBzP)2 chelate has absorption maxima at 298 and 670 nm, and PMBzP has maximum absorbance at 290 nm. A new and sensitive spectrophotometric method for copper has been devised, based on the absorbance at 670 nm. The presence of excess of reagent does not interfere and no special treatment is necessary to destroy it. The proposed method has some advantages and has been applied for the determination of copper in various soil samples. Gallium has been separated from indium, thallium, copper, iron and many other elements. The recovery of gallium and copper was 100 ± 0.2%. 相似文献
7.
M. M. Taqui Khan Shaukat A. Mirza H. C. Bajaj 《Reaction Kinetics and Catalysis Letters》1987,33(1):67-74
The kinetics of Ru(III) catalyzed oxidation of triethylamine by molecular oxygen has been investigated in the pH range 1.5 to 2.5 at 35°C and I=0.1 M KCl. The reaction is first order with respect to substrate, catalyst and molecular oxygen concentrations. The rate of the reaction increases with the increase of pH from 1.5 to 2.5 and then there is a slight decrease in the rate above pH 2.5. Based on the kinetic data, a mechanism for the catalytic oxidation of triethylamine is proposed. The major products in the oxidation of triethylamine are the N-oxide, diethylamine and acetaldehyde.
, Ru(III), pH=1,5+2,5 35°C I=0,1M KCl. , . pH 1,5 2,5, pH 2,5. , . N-, .相似文献
8.
Akbar Ali Mohammad Huq Mirza Aminul Nazimuddin Mohamed Rahman Hafazatur Butcher Raymond J. 《Transition Metal Chemistry》2002,27(3):268-273
New cadmium(II) complexes of empirical formulae, [Cd(dpksme)X] (dpksme = anionic form of the Schiff base; X = NCS–, Cl–, I–) and [Cd(dpksme)2] · 0.5MeOH, respectively have been prepared and characterized. The mono-ligated cadmium(II) complexes, [Cd(dpksme)X] are four-coordinate and tetrahedral but the bis-ligand complex, [Cd(dpksme)2] · 0.5MeOH is six-coordinate and octahedral. The crystal and molecular structure of [Cd(dpksme)2] · 0.5MeOH has been determined by X-ray diffraction. The complex has a distorted mer-octahedral structure in which the ligands are coordinated as uninegatively charged tridentate chelating agents via the pyridine nitrogen atoms, the azomethine nitrogen atoms and the thiolate sulfur atoms. The distortion from regular octahedral geometry is ascribed to the restricted bite angles of the ligands. The Schiff base and its cadmium(II) complexes exhibit mild antibacterial activities against Shigella dysenteriae, Bacillus cereus, Staphylococcus aureus and Escherichia coli. They are also mildly fungitoxic against the phytopathogenic fungi, Alternaria alternata and Macrophomina phaseolina. 相似文献
9.
The effects of gravitomagnetic force
on plasma oscillations are investigated
using the kinetic theory of homogeneous electrically neutral plasma in the
absence of external electric or magnetic field. The random phase assumption is employed neglecting the thermal motion of the electrons with respect to a fixed ion background. It is found that the gravitomagnetic force reduces the characteristic frequency of the plasma thus enhancing the refractive index of the medium. The estimates for the predicted effects are given for a typical white dwarf, pulsar, and neutron star. 相似文献
10.