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161.
C. Menéndez P.J.G. Nieto F.A. Ortega A. Bello 《Mathematical and Computer Modelling》2009,49(9-10):2002-2018
The main aim of this paper is to validate and to solve a model for consolidation of an elastic saturated soil with incompressible fluid. Firstly, we prove the existence and uniqueness of the solution of the variational problem corresponding to an initial and boundary value problem (IBVP): a special case of the Biot’s ‘consolidation of clay’ model (where the applied forces depend on time). Secondly, we prove the stability of the method as well as the estimation of the error by using semi-discretization in time. Finally, we then solved this one by the finite element method (FEM) employing repeated fixed point techniques in order to obtain the results for displacement and pore water pressure. The pore fluid is considered incompressible. The results of the numerical experiments are compared with analytical solutions and, in cases where such solutions do not exist, with experimental data. 相似文献
162.
Anélia N. Gurova Ana P.C. Ribeiro Carlos A. Nieto de Castro Umesh V. Mardolcar 《Fluid Phase Equilibria》2009
The relative permittivity (?r) data of 1,1,1-trifluoroethane (HFC-143a), (CAS N# 420-46-2), a hydrofluorocarbon (HFC) developed as a refrigerant that has zero ozone depletion potential, is reported. The relative permittivity of HFC-143a in the liquid phase was measured using a direct capacitance method at temperatures from T = 218 to 294 K and at pressures up to P = 15 MPa, for a frequency of 10 kHz. The uncertainty of the ?r measurements is estimated to be better than ±1.2 × 10−2. A complete set of tables of experimental data as a function of temperature, pressure and density, is presented that covers the dielectric property needs for most engineering applications. To study the dependence of ?r on density and temperature on a molecular basis, the theory developed by Vedam et al. and adapted by Diguet was applied to analyse the data. The Kirkwood modification of the Onsager equation was used to obtain the value of its dipole moment in the liquid phase (μ*). The apparent dipole moment obtained was μ* = 3.293 D. The effective dipole in the liquid state predicted by the Kirkwood–Frölich theory is 2.530 D. The measured values are compared with density functional and density functional self-consistent calculations (SCIPCM) of the electronic distribution and of the dipole moment of HFC-143a. Finally, the values of the isobaric thermal expansion and isothermal compressibility were estimated from the reported measurements. 相似文献
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164.
165.
The polymer matrix, divided in a number of cells in which the penetrant molecules can be sorbed and migrate, is considered. Each cell has been assigned an effective energy value that obeys a particular distribution. The effective diffusion coefficient and its concentration and temperature dependence are determined. The origin of sorbed penetrant mobility is studied. Using a delta-Dirac distribution for the site's energetic values, the model is reduced in the appropriate limit (low pressure) to other formulations of the dual transport model. More general results, allowing the site's energetic values to be drawn from a Gaussian distribution, are also given. © 1994 John Wiley & Sons, Inc. 相似文献
166.
A complete analysis of the temperature dependence (?30 to 52°C) of the 1H NMR spectra in d-chloroform of the ternary complexes, bis-(8-quinolinato)tin(IV) dichloride and bis-(5,7-dichloro-8-quinolinato)tin(IV) dichloride has been performed. The intramolecular character of the exchange process has been established, and the spectra have been analyzed by the total lineshape method in terms of the interconversion of two isomers, the cis-cis-trans and the cis-trans-cis (with respect to Cl, N and O atoms), including the tin-proton couplings in the simulations. Arrhenius parameters of the process were Ea = 54 ± 1 and 52 + 1 kJ mol?1, and log A = 11.8 ± 0.2 and 11.7 ± 0.3, respectively, for the two complexes. The similarity of the activation parameters obtained for both complexes indicates that the presence of bulky Cl atoms in the 8-quinolinol ring had no appreciable energetic influence on the isomerization process. Data were compared with those reported for other chlorinated hexacoordinated complexes, involving ligands other than the 8-quinolinol ring. 相似文献
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168.
[2+2] photocycloadditions involving chiral 3-acryloyl-2-vinylperhydro-1,3-benzoxazines derived from (-)-8-aminomenthol are highly diastereoselective reactions. The facial selectivity depends on the type of substitution at the vinyl double bond, and always leads to cis-fused bicyclic derivatives. The de is good for compounds with one substituent at the outer carbon of the double bond at C-2, but only one diastereomer is formed in cyclizations of compounds with two substituents at that position. The elimination of the menthol appendage gives enantiopure 3-azabicyclo[3.2.0]heptanes. 相似文献
169.
Toribio L Bernal JL del Nozal MJ Jiménez JJ Nieto EM 《Journal of chromatography. A》2001,921(2):305-313
Two chiral columns based on polysaccharide derivatives (Chiralpak AD and Chiralcel OD) have been tested for the chiral separation of several dioxolane compounds, using supercritical fluid chromatography. The compounds studied included ketoconazole and some of its precursors. The effect of the different modifiers and the pressure, on the chromatographic parameters was also evaluated. In general, the alcohol modifiers provided better results than acetonitrile, and all the compounds could be separated with these two columns, but the selection of the column depends on the kind of compound. 相似文献
170.
IMDA reactions on chiral perhydro-1,3-benzoxazines, derived from (-)-8-amino menthol, bearing a styrene substituent at C-2 acting as diene and an acryl amide acting as dienophile occur with high stereoselection and excellent chemical yields. After elimination of the chiral appendage, enantiopure 3a,4,9,9a-tetrahydrobenz[f]isoindolines are prepared in this way. The effect of the substituents at both diene and dienophile are studied, showing that a methyl group at C-1 in the diene inhibited the reaction, while the ene adduct, instead of the IMDA product, was obtained when a methyl group was at C-2. 相似文献