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91.
Sheha R. R. Moussa S. I. Attia M. A. Sadeek S. A. Someda H. H. 《Russian Journal of Applied Chemistry》2018,91(3):483-498
Russian Journal of Applied Chemistry - Magnesium-cadmium hydroxyapatite [(Mg-Cd)HAP] and novel multi-wall carbon nanotubes Mg-Cd hydroxyapatite (CNTs/(Mg-Cd)HAP) composites were synthesized by a... 相似文献
92.
93.
94.
The steady and dynamic shear properties of two non-aqueous drag-reducers (a medium molecular weight polyisobutylene and a commercial organic drag-reducer) in kerosene solutions over a wide range of temperature and concentration were presented. The intrinsic and zero-shear viscosity results were used to identify the concentrate regimes of these solutions. A characteristic time constant λ0, which was based on the spring-bead model for dilute solutions, was employed as the scaling parameter for both steady-shear and dynamic data over a wide range of concentration and temperature. The inadequacy of the Graessley reduced-variable method in the dilute region was illustrated. The shear-thinning behaviour of these polymer solutions could be described by the Carreau model. The dynamic data followed the Zimm and Rouse-like behaviour in the low and high frequency limits. The Cox-Merz rule was obeyed in the low shear rate and frequency regions. The Carreau and the zero-frequency Maxwell time constants appeared to be related to λ0 by a constant factor over a wide range of polymer concentrations. The finding provides a method for extrapolating viscoelastic information into the drag reduction regime, and could be useful for interpretation of drag reduction results. 相似文献
95.
Four constant viscosity, highly elastic fluids of different viscosity and elasticity levels are presented. The viscosity ranges from 4 × 10?3 to 5.0 Pa s and the Maxwell relaxation time varies from 0.09 to 4.5 s. The steady and dynamic shear properties are determined. These fluids comply with the requirements of the simple fluid theory except for theG′ andN 1/2 data where a slight deviation is observed. The results suggest the possibility of preparing a wide range of constant viscosity elastic fluids with specific values of viscosity and relaxation time by manipulating polymer molecular parameters as well as polymer concentration, solvent viscosity and salt addition. The effects of each of these parameters on the rheological behaviour are examined. 相似文献
96.
Moussa Kfoury Rachid Ababou Benoit Nœtinger Michel Quintard 《Comptes Rendus Mecanique》2004,332(8):679-686
We present in this Note a stochastic approach to the matrix-fracture exchange in a heterogeneous fractured porous medium. We introduce an intermediate scale, called the unit-scale, between the local-scale (fracture-scale) and the large-scale characteristic of the reservoir mesh (reservoir block). This paper focuses on the problem of upscaling fluid exchange phenomena from the unit scale to the reservoir mesh or block scale. Simplifying the Darcian flow terms enables us to obtain a probabilistic solution of the dual continuum problem, in continuous time, in the case of a purely random exchange coefficient. This is then used to develop several upscaling approaches to the fluid exchange problem, and to analyze the so-called ‘effective’ exchange coefficient. The results are a first contribution to the more general problem of upscaling multidimensional flow-exchange processes in space and time, in randomly heterogeneous dual continua. To cite this article: M. Kfoury et al., C. R. Mecanique 332 (2004). 相似文献
97.
Thomas G. Back Ziad Moussa 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):767-776
Glutathione peroxidase (GPx) mimetics comprise an important class of selenium-containing antioxidants that catalyze the destruction of biologically harmful peroxides in the presence of stoichiometric thiol reductants. The synthesis of two novel cyclic selenium compounds and their evaluation as GPx mimetics was achieved. The first is a cyclic seleninate ester that is formed in situ from the oxidation of allyl 3-hydroxypropyl selenide. The second is a spirodioxyselenurane that is similarly formed from di(3-hydroxypropyl) selenide. Both compounds were shown to be remarkably active catalysts in an assay based on the reduction of t-butyl hydroperoxide with benzyl thiol. The mechanisms of the catalytic cycles of the two novel selenium compounds were elucidated and were found to be distinct from each other and from that of GPx. 相似文献
98.
Thomas G. Back Ziad Moussa Masood Parvez 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2569-2579
(1R)-2-endo-(Dimethylamino)methyl-2-exo-methoxy-3-endo-camphor- ylselenenyl bromide and its 2-endo-(pyrrolidenyl)methyl analogue were prepared from (1R)-2-endo-acetamidomethyl-2-exo-hydroxy-3-endo-camphoryl diselenide. Both compounds showed an unusual lack of reactivity in electrophilic oxyselenenylation and cyclization reactions that are typical of other selenenyl bromides. X-ray crystallography indicated that both compounds have strong N─Se interactions, with N─Se interatomic distances of ca. 2.1 Å, which diminish the electrophilic character of the selenium atom. 相似文献
99.
Reactions of monooxidized thioyl and selenoyl bis(phosphanyl)amine ligands C10H7‐1‐N(P(E)Ph2)(PPh2) [E = S ( 1 ), Se ( 2 )] with Mo(CO)4(pip)2 and W(CO)4(cod) afforded the complexes [M(CO)4{ 1 ‐κ2P,S}] [M = Mo ( 3 ), W ( 4 )] and [M(CO)4{ 2 ‐κ2P,Se}] [M = Mo ( 5 ), W ( 6 )]. Complexes 3 – 6 were characterized by multinuclear NMR (1H, 13C, 31P, and 77Se NMR) and IR spectroscopy. Crystal‐structure determinations were carried out on 3 , 5 , and 6 , which represent the first examples of structurally characterized complexes of such ligands with group‐6 metal carbonyls. 相似文献
100.
Two stability-indicating spectrofluorimetric methods have been developed for the determination of ezetimibe and olmesartan
medoxomil, drugs affecting the cardiovascular system, and validated in the presence of their degradation products. The first
method, for ezetimibe, is based on an oxidative coupling reaction of ezetimibe with 3-methylbenzothiazolin-2-one hydrazone
hydrochloride in the presence of cerium (IV) ammonium sulfate in an acidic medium. The quenching effect of ezetimibe on the
fluorescence of excess cerous ions is measured at the emission wavelength, λem, of 345 nm with the excitation wavelength, λex, of 296 nm. Factors affecting the reaction were carefully studied and optimized. The second method, for olmesartan medoxomil,
is based on measuring the native fluorescence intensity of olmesartan medoxomil in methanol at λem = 360 nm with λex = 286 nm. Regression plots revealed good linear relationships in the assay limits of 10–120 and 8–112 g/ml for ezetimibe
and olmesartan medoxomil, respectively. The validity of the methods was assessed according to the United States Pharmacopeya
guidelines. Statistical analysis of the results exposed good Student’s t-test and F-ratio values. The introduced methods were
successfully applied to the analysis of ezetimibe and olmesartan medoxomil in drug substances and drug products as well as
in the presence of their degradation products. 相似文献