Nouvelle approche pour la discrétisation de flux diffusifs en volumes finis à forte obliquité

We propose a new approach for the discretization of diffusive flux on a non orthogonal mesh based on the Deferred correction introduced by Peric. This new method is applied successfully to the solution of a Poisson problem in quadrangular domains meshed with very distorted control volumes. The interest of this approach lies in the fact that the precision of the used schemes is conserved despite meshes distortion level. The comparative study of the value of the spectral radius of iteration matrix enables us to explain why our Deferred correction approach is better than that of Peric, which diverges on highly skewed meshes. To cite this article: Y.M. Ahipo, Ph. Traore, C. R. Mecanique 334 (2006).     

Correlation of the volumes and heat capacities of solutions with their solid-liquid phase diagrams

Liquid systems which have strong non-idealities, as seen from their thermodynamic properties, often show evidence of these interactions in the solid-liquid phase diagrams. This suggests that some of the structures present in the solid state can persist in the solution state, on a time average, up to temperatures much higher than the melting point. Volumes and heat capacities of typical systems were either taken from the literature or measured to illustrate this correlation with the phase diagrams. With mixtures of aprotic solvents which show nearly-ideal simple eutectic phase diagrams, the properties of the solutions are also nearly ideal. Examples of systems investigated which show strong non-idealities are ionic surfactant solutions, alcohol-water mixtures, chloroform-triethylamine mixtures and lithium salts in aprotic solvents.Paper written in the honor of Loren Hepler on the occasion of his retirement.     

Cross-correlations in volume space: Differences between buy and sell volumes

We study the cross-correlations of buy and sell volumes on the Korean stock market in high frequency. We observe that the pulling effects of volumes are as small as that of returns. The properties of the correlations of buy and sell volumes differ. They are explained by the degree of synchronization of stock volumes. Further, the pulling effects on the minimal spanning tree are studied. In minimal spanning trees with directed links, the large pulling effects are clustered at the center, not uniformly distributed. The Epps effect of buy and sell volumes are observed. The reversal of the cross-correlations of buy and sell volumes is also detected.     

Adaptive mesh strategy applied to turbulent flows

An adaptive mesh procedure controlled by an error estimate for the Navier–Stokes equations is developed. The mesh can be refined but also coarsened by the mean of an agglomeration algorithm. The error estimation is based on an equation for the discretization error with a source term approximated by the use of a higher order discretized operator. The whole procedure is applied to a turbulent flow around a square-cross section cylinder. The efficiency of the method, evaluated in terms of CPU time and number of cells, shows interesting gains compared to single mesh computations. To cite this article: A. Hay, M. Visonneau, C. R. Mecanique 333 (2005).     

Volumetric and Viscometric Studies on an Aqueous Urea Solution

Of late there has been a renewed inerest in the thermodynamics and other investigations on the behaviour of urea (denaturants) in aqueous solution which induce changes in structure and properties of proteins including their solubility, denaturation, dissociation into subunits and the activity of enzymes. With this in view, density and viscosity of aqueous urea solutions were determined as a function of concentration at 35, 40, 45, 50 and 55C, respectively. The apparent molal volume $(\phi _v )$ of urea was found to be linear function of solute concentration. From the $\phi _v$ versus molality ( m ) plot the apparent molal volume at infinite dilution, $\phi _v^o$ (taken to be equal to partial molal volume, $\bar V_2^o$ ) was determined. Viscosity coefficients B and D were calculated on the basis of the viscosity of the solutions and the solvent concerned using the Jones-Dole equation. The activation parameters for viscous flow $(\Delta G^{\ne} , \,\Delta S^{\ne}\ {\rm and\ }\Delta H^{\ne} )$ were also calculated by means of the Eyring equation. The data were interpreted in terms of the structure making behaviour of urea in water at 35-55C temperature range.     

Volumes of activation for thermal ring-closure reactions of transient W(CO)5 (chelate) complexes

Abstract

The ring-closure reactions of (W(CO)₅L were studied as a function of L (L = en, bpy, dab), temperature and pressure. The corresponding observed rate constants exhibit a marked dependence on the nature of L, and the volumes of activation are throughout significantly negative. These observations imply that the ring-closure reactions proceed via an associative mode of activation.     

Excess Molar Volumes and Partial Molar Volumes of Binary Mixtures Containing Diethylcarbonate with Benzene and Substituted Benzenes at 293.15 K

Densities of the binary mixtures of diethylcarbonate with benzene and substituted benzenes, namely toluene, bromobenzene, chlorobenzene and nitrobenzene have been measured as a function of the composition, at 293.15 K and atmospheric pressure using a bicapillary pycnometer with an accuracy of 4 parts in 10⁴.The calculated excess molar volumes, V ^E were correlated with Redlich-Kister equation. The excess molar volumes are negative over the entire range of composition for the systems diethylcarbonate with benzene, toluene, bromobenzene and nitrobenzene. An inversion of the sign of V ^E is observed over some concentration for mixtures of diethylcarbonate with chlorobenzene. Partial molar volumes, V_i are also evaluated and their values have been extrapolated to zero concentration to obtain the limiting value at infinite dilution, V^o _i . The numerical values of the excess molar volumes for binary mixtures decrease in the order: chlorobenzene > benzene > bromobenzene ≈ toluene > nitrobenzene. The results are explained in terms of dissociation of the self-associated solute molecules and the formation of aggregates between unlike molecules.     

Quantitative magnetic resonance imaging in consecutive patients evaluated for surgical treatment of temporal lobe epilepsy

We present the results of quantitative Magnetic Resonance Imaging (MRI) in 55 consecutively referred patients with clinical evidence of temporal lobe epilepsy (TLE). The Cavalieri method was used in combination with point counting to provide unbiased estimates of the volume of the left and right hippocampus, amygdala, temporal lobe, lateral ventricles and cerebral hemisphere, and pixel by pixel maps of the T2 relaxation time were computed for both central and anterior sections of the hippocampus. The 99th centiles of hippocampal volume, hippocampal volume asymmetry and T2 relaxation times in 20 control subjects provided limits which identified the presence of MTS. The results of the quantitative MRI were compared with the results of conventional diagnostic MRI, foramen ovale (FO) recording and the WADA test. Thirty-one patients were found to have unilateral MTS (17 left and 14 right) and 7 bilateral MTS. No evidence of MTS was detected in 16 patients. Of the 31 patients diagnosed with unilateral MTS on the basis of hippocampal volume and T2 measurement, 74% and 77% would respectively have received the same diagnosis on the basis of hippocampal volume and T2 measurements alone. In comparison to FO recording, quantitative MRI has a sensitivity of 55% and a specificity of 86%, while conventional diagnostic MRI has a sensitivity of 42% and a specificity of 80% for detection of MTS. Unilateral abnormalities were detected by FO recording in 30% cent of patients who appeared normal on quantitative MRI. WADA test results were available for 40 patients. The findings were consistent with quantitative MRI showing reduced memory function ipsilateral to unilateral MTS in 18 patients, but reduced memory function contralateral to unilateral MTS in two patients, and reduced memory function without MR abnormality in seven patients. WADA testing revealed unilateral memory impairments where MRI found bilateral pathology in 4 patients and in 4 patients in whom quantitative MRI detected unilateral MTS there was no evidence of reduced memory during WADA testing of the corresponding cerebral hemisphere. In the patients with unilateral right MTS a highly significant negative correlation (p = 0.0003) was observed between age of onset and the volume of the contralateral temporal lobe.

Quantitative MR imaging of the hippocampus (i.e. volume and T2 measurement) is preferable to conventional radiological reporting for providing objective evidence of the presence of MTS on which to base the referral of patients for surgery, and since it has associated morbidity FO recording is now only being used in selected patients. Furthermore, stereology provides a convenient method for estimating the volume of other brain structures, which is relevant to obtaining a better understanding of the effects of laterality and age of onset of TLE.     

Ultrasonic and viscometric studies of molecular interactions in binary mixtures of tetrahydrofuran with some aromatic hydrocarbons at temperatures from 288.15 to 318.15 K

Densities of the binary systems of 2,2′-oxybis[propane] with ethyl acrylate, butyl acrylate, methyl methacrylate, and styrene have been measured as a function of the composition, at 298.15 K and atmospheric pressure, using an Anton Paar DMA 5000 oscillating U-tube densimeter and used to calculate the partial and excess volumes. The latter were correlated with the Redlich-Kister equation and with a series of Legendre polynomials. The excess volumes are negative for all the systems reported here.     

Solution properties of octyl β-D glucoside. Part 1: Aggregate size. shape and hydration

Aqueous solutions of octyl--D-glucoside have been examined in a wide concentration range. By combining information from density, viscosity and dielectric permittivity, the transition from molecular to micellar state has been evidentiated. Classical equations for the viscosity colloidal dispersions have been reexamined and applied to get information on micelle shape. A combined analysis of dielectric and viscosity findings indicates a slight and continuous dependence of micellar shape on surfactant content. The role of hydration on micellar stability is significant.