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171.
Daoubi M Benharref A Hernandez-Galán R Macías-Sánchez AJ Collado IG 《Natural product research》2004,18(2):177-181
Two novel steroids, 3beta,7alpha-dihydroxy-4alpha,14alpha-dimethyl-5alpha-cholest-8-en-11-one (2) and 3beta,7beta-dihydroxy-4alpha,14alpha-dimethyl-5alpha-cholest-8-en-11-one (3) were isolated from the latex of Euphorbia officinarum. Their structures were established on the basis of NMR and MS studies. 相似文献
172.
K.D. Belfield M.V. BondarO.V. Przhonska K.J. SchaferW. Mourad 《Journal of luminescence》2002,97(2):141-146
Investigations of the absorption, steady-state fluorescence, excitation and excitation anisotropy properties of several fluorene derivatives, (7-benzothiazol-2-yl-9,9-didecylfluoren-2-yl)-diphenylamine, 9,9-didecyl-2,7-bis-(N,N-diphenylamino)fluorene and {4-[2-(7-diphenylamino-9,9-diethylfluoren-2-yl)vinyl]phenyl}phosphoric acid diethyl ester, in liquid solutions have been conducted. Spectral characteristics of these compounds, including fluorescence quantum yields, were measured in acetonitrile, methylene chloride, tetrahydrofuran and hexane at room temperature. Excitation anisotropy spectra provided a means to determine the nature of the short wavelength absorption bands as an electronic transition into a higher excited singlet state. It was found that excitation spectra in the short wavelength region do not correspond to the absorption bands that are correlated with the wavelength dependence of the fluorescence quantum yields. Major reasons of such spectral behavior are discussed. 相似文献
173.
Zouhaier Mehrez Mourad Bouterra Afif El Cafsi Ali Belghith Patrick Le Quere 《Heat and Mass Transfer》2009,46(1):107-112
A numerical study based on the large eddy simulation methodology was made of heat transfer in locally disturbed turbulent
separated and reattached flow over a backward facing step. The local disturbance was given to the flow by a sinusoidally blowing/suction
of the fluid into a separated shear layer. The Reynolds number was fixed at 33,000 and Richardson number at 0.5. The disturbance
frequency was varied in the range 0 ≤ St ≤ 2, where St is the Strouhal number of disturbance. The obtained results revealed the existence of an optimum perturbation frequency value,
St = 0.25, in terms of the reduced reattachment length. At this frequency the heat transfer is significantly enhanced in the
recirculation zone. The influence of the frequency and the amplitude of disturbance, in the maximum heat transfer positions
and the maximum local Nusselt number, is analysed. 相似文献
174.
We characterize pointwise directional regularity by highly oriented multi-scaled wavelet coefficients. 相似文献
175.
Many natural mathematical objects, as well as many multi-dimensional signals and images from real physical problems, need to distinguish local directional behaviors (for tracking contours in image processing for example). Using some results of Jaffard and Triebel, we obtain criteria of directional and anisotropic regularities by decay conditions on Triebel anisotropic wavelet coefficients (resp. wavelet leaders). 相似文献
176.
Abdelhak Ayadi Sana Elgasri Abderrazek Mezghani Mickaël Castro Foued Elhaouani 《ournal of non Newtonian Fluid Mechanics》2011,166(12-13):661-666
The gross melt fracture defect is related to the flow instabilities developed in the contraction region. To mitigate these upstream instabilities, a convergent radial flow in the die entrance has been created. In fact, the ultimate objective of the present work is to examine the effect of the clearance width of radial flow on the appearance and development of gross melt fracture defect. So, capillary rheometer experiments were performed with linear polydimethylsiloxane (PDMS) oil.As for the influence of radial flow width on the morphology of gross melt fracture defect, extrudate photographs show that this imperfection can be mitigated since its frequency is higher and amplitude smaller when the gap of radial flow decreases. Such results may be related both to shear and elongational components of radial flow. Actually, when gap width is very small compared to the external diameter of radial flow, shear deformations become more enhanced with respect to the elongational deformations and thus the helical gross melt fracture becomes more like a surface defect than volume defect. 相似文献
177.
We provide a complete spectral analysis of all self-adjoint operators acting on which are associated with two doubly infinite Jacobi matrices with entries given by and respectively, where and . As an application, we derive orthogonality relations for the Ramanujan entire function and the third Jackson q-Bessel function. 相似文献
178.
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