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991.
Pseudo-first-order rate constants (kobs) for alkaline hydrolysis of 4-nitrophthalimide show a monotonic decrease with increase in [C12E23]T (total concentration of Brij 35) at constant [CH3CN] and [NaOH]. This micellar effect is explained in terms of a pseudophase micelle model. The rate of hydrolysis becomes too slow to monitor at [C12E23]T≥0.03 M in the absence of cetyltrimethylammonium bromide (CTABr) and at [C12E23]T≥0.04 M in the presence of 0.006–0.02 M CTABr at 0.01 M NaOH. The plots of kobs versus [C12E23]T show minima at 0.006 and 0.01 M CTABr, while such a minimum is not visible at 0.02 M CTABr. 相似文献
992.
The deformation, drainage, and rupture of an axisymmetrical film between colliding drops in the presence of insoluble surfactants under the influence of van der Waals forces is studied numerically at small capillary and Reynolds numbers and small surfactant concentrations. Constant-force collisions of Newtonian drops in another Newtonian fluid are considered. The mathematical model is based on the lubrication equations in the gap between drops and the creeping flow approximation of Navier–Stokes equations in the drops, coupled with velocity and stress boundary conditions at the interfaces. A nonuniform surfactant concentration on the interfaces, governed by a convection–diffusion equation, leads to a gradient of the interfacial tension which in turn leads to additional tangential stress on the interfaces (Marangoni effects). The mathematical problem is solved by a finite-difference method on a nonuniform mesh at the interfaces and a boundary-integral method in the drops. The whole range of the dispersed to continuous-phase viscosity ratios is investigated for a range of values of the dimensionless surfactant concentration, Peclét number, and dimensionless Hamaker constant (covering both “nose” and “rim” rupture). In the limit of the large Peclét number and the small dimensionless Hamaker constant (characteristic of drops in the millimeter size range) a fair approximation to the results is provided by a simple expression for the critical surfactant concentration, drainage being virtually uninfluenced by the surfactant for concentrations below the critical surfactant concentration and corresponding to that for immobile interfaces for concentrations above it. 相似文献
993.
《Arabian Journal of Chemistry》2020,13(2):4082-4091
In present study, an investigation was carried out to develop and validate an analytical method for the selective extraction and determination of griseofulvin (GSF) from plasma samples. For this purpose, a rational approach was made to synthesize and characterize the surface molecularly imprinted polymers (SMIPs). The SMIPs were utilized as solid phase extraction (SPE) sorbents. The SMIPs were prepared by using GSF as template molecule on the surface of modified silica particles through a non-covalent technique. The particles demonstrated high adsorption capacity (119.1 µg/mL), fast adsorption equilibrium time (30 min) and good recognition selectivity for the template drug. The scanning electron microscopy and infrared spectroscopy were used to explain the structural and morphological characteristics of the SMIPs and surface non-imprinted polymers. The SPE method was combined with HPLC for plasma analysis. The method validation results demonstrated that the established method possessed good linearity for GSF ranging from 0.1 to 50 µg/mL (R2 = 0.997). The limit of detection for this method was 0.02 µg/mL for rat plasma samples. The recoveries of GSF from spiked plasma samples were (90.7–97.7%) and relative standard deviations were (0.9–4.5%). Moreover, the SMIPs as selective SPE sorbent can be reused more than 8 times which is a clear advantage over commercial SPE sorbents. Finally, the usefulness of the proposed strategy was assessed by extraction and detection of GSF in real rat plasma samples. 相似文献
994.
《Arabian Journal of Chemistry》2022,15(12):104330
The present study was carried out to design and synthesize a number of novel aromatic carboxamide derivatives of dehydroabietylamine. The preliminary antifungal assay indicated that most of title compounds displayed moderate to good antifungal activity toward the six fungal strains in vitro. Compounds 3i, 3q, 4b and 4d showed significant antifungal activity against Sclerotinia sclerotiorum, with EC50 values ranging from 0.067 ~ 0.393 mg/L. Compounds 3i, 4b and 4d also showed pronounced mycelial growth inhibition activities against B. cinerea and A. solani. Furthermore, in the in vivo assay, compound 4b exhibited brilliant protective activity against S. sclerotiorum-infected rape leaves. Meanwhile, the in vivo bioassay on tomato plants infected by B. cinerea showed that compound 3i and 4d displayed excellent protective activity at 200 mg/L, which were near to boscalid. Primary mechanistic study revealed that 4b could inhibit sclerotia formation as well as reduce the exopolysaccharide level. SEM and TEM analysis indicated that 4b possessed a strong ability to destroy the surface morphology of mycelia, cell structure and seriously interfere with the growth of the fungal pathogen. In addition, 4b exhibited good inhibitory activity (IC50 = 23.3 ± 1.6 μM) toward succinate dehydrogenase (SDH). Molecular modeling study confirmed the binding modes between compound 4b and SDH. The above antifungal results and fungicidal mechanism study revealed that this class of dehydroabietylamine derivatives could be potential SDH inhibitors and lead compounds for novel fungicides development. 相似文献
995.
C.N.R. Rao D.D. Sarma P.R. Sarode E.V. Sampathkumaran L.C. Gupta R. Vijayaraghavan 《Chemical physics letters》1980,76(3):413-415
The valence state of Yb in some of its intermetallics, YbNi2Ge2, YbCu2Si2 and YbPd2Si2 has been investigated by LIII(Yb) absorption edges and X-ray pnotoelectron spectra in the 4f and 4d regions. These studies establish the presence of mixed valence in all three systems and illustrate the utility of 4f and 4d spectra in the study of mixed valence in Yb compounds. 相似文献
996.
S. Kesavan 《Numerische Mathematik》1979,32(2):209-232
Resumé Le but de cet article est l'étude de l'approximation numérique des solutions non-triviales des équations de Von Karman pour le flambage d'une plaque mince encastrée. S'inspirant de la méthode de Kikuchi pour des problèmes quasi-linéaires du second ordre, on propose une méthode itérative d'éléments finis qui donne des approximations des solutions de norme «petite» qui bifurquent de la solution triviale au voisinage d'une valeur propre simple du problème linéarisé. On démontre la convergence et on obtient des estimations de l'erreur.
Application of Kikuchi's method to the von Karman equations
Summary The aim of this article is to study the numerical approximation of non-trivial solutions of the Von Karman equations for the buckling of a thin elastic clamped plate. Following Kikuchi's method for second order quasilinear problems, we propose an iterative finite element method which produces approximations of non-trivial solutions of small norm which bifurcate from the trivial solution near simple eigenvalues of the linearised problem. The convergence is proved and error estimates are obtained.相似文献
997.
Zdzislaw Jackiewicz 《Numerische Mathematik》1979,32(3):307-332
Summary This paper deals with the convergence of nonstationary quasilinear multistep methods with varying step, used for the numerical integration of Volterra functional differential equations. A Perron type condition (appearing in the differential equations theory) is imposed on the increment function. This gives a generalization of some results of Tavernini ([19–21]). 相似文献
998.
Summary GeneralizedA()-stable Runge-Kutta methods of order four with stepsize control are studied. The equations of condition for this class of semiimplicit methods are solved taking the truncation error into consideration. For application anA-stable and anA(89.3°)-stable method with small truncation error are proposed and test results for 25 stiff initial value problems for different tolerances are discussed. 相似文献
999.
Summary A new method is proposed for the inclusion of the critical parameter * of some convex operator equationu=Tu (appearing e.g. in thermal explosion theory). It is based on the fact that for a fixed Newton's method starting with a suitable subsolution is not monotonically if and only if >*. Several numerical examples arising from nonlinear boundary value problems illustrate the efficiency of the method. 相似文献
1000.