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排序方式: 共有215条查询结果,搜索用时 31 毫秒
1.
Ahmed Waqar Chowdhury Z. Z. Kazi S. N. Johan MR. Akram Naveed Oon C. S. Abdelrazek Ali H. 《Journal of Thermal Analysis and Calorimetry》2021,144(4):1517-1534
Journal of Thermal Analysis and Calorimetry - In recent decades, the growth of heat transfer using nanomaterials in the conventional base fluid has caught the attention of researchers... 相似文献
2.
If M is an isoparametric hypersurface in a sphere S
n
with four distinct principal curvatures, then the principal curvatures κ1, . . . , κ4 can be ordered so that their multiplicities satisfy m
1 = m
2 and m
3 = m
4, and the cross-ratio r of the principal curvatures (the Lie curvature) equals −1. In this paper, we prove that if M is an irreducible connected proper Dupin hypersurface in R
n
(or S
n
) with four distinct principal curvatures with multiplicities m
1 = m
2 ≥ 1 and m
3 = m
4 = 1, and constant Lie curvature r = −1, then M is equivalent by Lie sphere transformation to an isoparametric hypersurface in a sphere. This result remains true if the
assumption of irreducibility is replaced by compactness and r is merely assumed to be constant.
相似文献
3.
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
4.
Thomas E. Cecil 《Geometriae Dedicata》1989,32(3):281-300
Pinkall's standard constructions for obtaining a Dupin hypersurface W in
N
from a Dupin hypersurface M in
n
, N>n, are studied in the context of Lie sphere geometry. It is shown that a compact Dupin hypersurface W in
N
with g distinct principal curvatures at each point is reducible to a compact Dupin hypersurface M in
n
if and only if g=2.This research was supported by NSF Grant No. DMS 87-06015. 相似文献
5.
6.
Gehan M. El-Subruiti Kamal H. Halawani Cecil F. Wells Ibrahim M. Sidahmed 《Transition Metal Chemistry》1993,18(3):323-328
Summary The kinetics of the solvolysis of complex ions trans-[Co(Rpy)4Cl2]+, with R = 4-t-Bu, 3-Me and 3-Et, have been investigated in mixtures formed by adding urea to water, which enhances the dielectric constant and decreases solvent structure. Differential effects of the changes in solvent structure on the initial and transition states are found to be important factors controlling changes in the rate constant with solvent composition. The variation of the enthalpy and the entropy of activation with solvent composition are contrasted with their variations found for the solvolysis of [Co(Rpy)4Cl2]+ in mixtures where solvent structure is enhanced by additions of a co-solvent to water. The application of a free energy cycle to the process of the initial state going to the transition state suggests that the Co3+ cation in the transition state is more stable than the Co3+ cation in the initial state in the water + urea mixtures. 相似文献
7.
Summary The kinetics of the solvolysis of thetrans-[Coen2Cl2]+ cation (en = 1,2-diaminoethane) have been investigated over a range of temperatures in water with added ethanonitrile which has much less effect on the solvent structure than the acohols already used as co-solvents with water for this solvolysis. However, the non-linear relationship obtained for the variation of log (rate constant) with the reciprocal of the dielectric constant at constant temperature shows that the effect of changing solvent structure is still important, although, as expected from the absence of pronounced extrema in the variation with composition in water + ethanonitrile of physical properties which are influenced by such changes in solvent structure, the enthalpy and entropy of activation for the solvolysis vary smoothly with composition. The application of a free energy cycle shows that changes in solvent structure affect the pentacoordinated cobalt(III) ion in the transition state more than the hexacoordinated cobalt(III) ion in the initial state. 相似文献
8.
Peter Brown Cecil L. Hornbeck John R. Cronin 《Journal of mass spectrometry : JMS》1972,6(12):1383-1399
The positive ion electron-impact mass spectra of a series of alloxazines, iso-alloxazines and some derivatives have been examined. The compounds employed were lumichrome (7,8-dimethylalloxazine), 1,3-dimethyllumichrome, lumiflavin (7,8,10-trimethyl-iso-alloxazine), 3-methyllumiflavin, riboflavin [7,8-dimethyl-10-(D-1′-ribityl)-iso-alloxazine], riboflavin tetraacetate, 3-methylriboflavin tetraacetate and riboflavin tetrapropionate. By using exact mass measurements, metastable ion defocusing and the mass/composition shifts occurring with derivatives, it has been possible to arrive at detailed interpretations of the mass spectra of all compounds. With lumichrome and lumiflavin, fragmentation commences by elimination of HNCO from the pyrimidine ring. With riboflavin and its derivatives the ribityl chain cleaves off first, followed by decomposition of the iso-alloxazine ring. Application of these methods and findings to the structural analysis of chemically interesting modified flavins is predicted to be rewarding. 相似文献
9.
Cecil D. Bailey 《Foundations of Physics》1981,11(3-4):279-296
It has been recognized in the literature of the calculus of variations that the classical statement of the principle of least action (Hamilton's principle for conservative systems) is not strictly correct. Recently, mathematical proofs have been offered for what is claimed to be a more precise statement of Hamilton's principle for conservative systems. According to a widely publicized version of this more precise statement, the action integral for conservative systems is a minimum for discrete systems for small time intervals only and is never minimum for continuous systems. In this paper, two contradictions to this more precise statement are demonstrated, one for a discrete system and one for a continuous system. 相似文献
10.
Ryan Gianatassio Shuhei Kawamura Cecil L Eprile Klement Foo Jason Ge Aaron C. Burns Michael R. Collins Phil S. Baran 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(37):10009-10013
A simple method to convert readily available carboxylic acids into sulfinate salts by employing an interrupted Barton decarboxylation reaction is reported. A medicinally oriented panel of ten new sulfinate reagents was created using this method, including a key trifluoromethylcyclopropanation reagent, TFCS‐Na. The reactivity of six of these salts towards C H functionalization was field‐tested using several different classes of heterocycles. 相似文献