Prolongation of two phases in the model of fluid displacement through a capillaryProlongement de deux phases dans le modèle du déplacement d'un fluide dans un capillaire

The problem of a piston-like displacement of a fluid by another in a capillary is examined. It is suggested that each fluid is prolonged into the domain occupied by the other fluid. This enables the replacement of the two-phase flow problem by a transient single-phase flow problem, with discontinuity in velocity and pressure on a film interface. The problems related to the triple point are solved by introducing a limit fluid near the pore wall. The demonstration of the Washburn equation contributes to the physical justification of our model. To cite this article: Y. Lucas et al., C. R. Mecanique 334 (2006).     

Crystal structure of 4,5-bis(4-dimethylaminophenyl)-2-(4-nitrophenyl)imidazole.

A nonlinear optical chromophore, 4,5-bis(4-dimethylaminophenyl)-2-(4-nitrophenyl)imidazole, was investigated by X-ray crystallography. The study focused on coplanarity among several aromatic rings, including phenyls and imidazole. Two phenyl rings with NMe2 groups are twisted by 46.39(3) degrees from each other. However, they are twisted by 23.05(5) degrees and 46.84(3) degrees from the imidazole, respectively. These unequal twists were elucidated by different conjugation pathways from the donors to the acceptor. The phenyl ring with the NO2 group is twisted by only 6.76(6) degrees from the imidazole.     

A Calorimeter for Measuring the Enthalpy of Solution of Solid Solutes in Supercritical Fluids and Study on CO_2-Naphthlene System

Supercritical fluids (SCFs) have some unique properties1 It has been known that SCFs have very strong ability to dissolve low volatile compounds, which is the basis of SCF technology. However, the mechanism of SCFs to dissolve solutes is not very clear. Enthalpy of solution of solutes in SCFs can provide useful information for studying the mechanism. In this work, we built a calorimeter and ΔH for the dissolution of naphthalene in supercritical CO2 was determined. This kind of work wa…     

TRANSIENT EFFECT OF A BOGER FLUID FLOWING AROUND A CONFINED CYLINDER

This paper is concerned with the numerical simulation of the transient effect of an inertialess Boger flow past aconfined circular cylinder and the comparison of predictions with particle image velocimetry (PIV) measurements given byShiang et al., Dynamic simulation based on the Oldroyd-B constitutive model was carried out using a Lagrangian-Eulerianalgorithm. The evolution of velocity field was obtained for the flow at two Deborah (De) numbers, i.e. De = 1.2 and 3.0. Atlow De, the flow reached steady state rapidly, and showed a symmetric flow regime. However, at high De, the time requiredto reach steady flow behind the cylinder increased significantly, and the distribution of the velocity field appears to beasymmetric with respect to the stagnation line. Fairly good agreement between the numerical results and the experimentalobservations is reported. It can be concluded that both the experimental measurements and the present simulations indicatethat the elasticity of the polymeric flow strongly affect the flow regime of viscoelastic flow around a confined cylinder.     

ON THE EXPONENT SET OF PRIMITIVELOCALLY SEMICOMPLETE DIGRAPHS

A locally semicomplete digraph is a digraph D=(V,A) satisfying the following condi-tion for every vertex x∈V the D[O(x)] and D[I(x)] are semicomplete digraphs. In this paper,we get some properties of cycles and determine the exponent set of primitive locally semicompleted digraphs.     

On upper and lower δ-precontinuous multifunctions

In this paper we introduce and study δ-precontinuous multifunctions as a generalization of precontinuous multifunctions due to Popa [Problemy Mat. 10 (1988) 9]. Some characterizations and several properties concerning upper (lower) δ-precontinuous multifunctions are obtained. The relationships between upper (lower) δ-precontinuous multifunctions and some known concepts are also discussed.     

Determination of the standard Gibbs free energies of formation of barium zirconates in the temperature range (1073 to 1273) K

The standard molar Gibbs free energies of formation of BaZrO₃, and Ba₂ZrO₄ have been determined by solid-state galvanic cells involving a single crystal CaF₂ as a solid-state electrolyte. The e.m.f. measurements were performed in the temperature range (1073 to 1273) K. The average values of the standard molar enthalpy and the standard molar entropy of formation in the temperature range covered by the e.m.f. measurements have been also estimated. The results have been compared with those obtained by other authors.     

Operator-valued Fourier Multipliers on Periodic Triebel Spaces

We establish operator-valued Fourier multiplier theorems on periodic Triebel spaces, where the required smoothness of the multipliers depends on the indices of the Triebel spaces. This is used to give a characterization of the maximal regularity in the sense of Triebel spaces for Cauchy problems with periodic boundary conditions.     

Ca2+ selectivity of the sarcoplasmic reticulum Ca2+-ATPase at the enzyme-water interface and in the Ca2+ entrance channel

The sarcoplasmic reticulum (SR) Ca(2+)-ATPase, a P-type transmembrane protein, can transport Ca(2+) from the cytoplasmic to the luminal side over other cations specifically. The proposed Ca(2+) entrance channel, composed of the main-chain carbonyl oxygen and side-chain carboxyl oxygen atoms of the amino acids, opens on the enzyme surface, just above the biphospholipid layer membrane-water interface, where Trp residues are frequently found. In this work, the physicochemical nature of Ca(2+) selectivity over Mg(2+) on the surface of the SR Ca(2+)-ATPase has been investigated using the density functional theory (DFT) method. The selection process can be regarded as the first step of the specificity of the enzyme to transport Ca(2+). Subsequently, the specificity of the entrance channel to conduct Ca(2+) over other cations has also been explored. As revealed by thermodynamic analyses, either the aromatic or the aliphatic amino acid residues distributed on the surface of Ca(2+)-ATPase have a bigger affinity to Mg(2+) than to Ca(2+), resulting in a concentration decrease of free Mg(2+) in the local region. Thus, Ca(2+) can transport into the Ca(2+)-entrance channel more easily. Whereafter, for a small quantity of Mg(2+) entering this channel accompanying the Ca(2+) current, the strong electrostatic interactions between Mg(2+) and the ligands will limit the activity of this metal ion, which facilitates the weakly bonded Ca(2+) passing through the channel at a relatively high rate, as suggested by the "sticky-pore" hypothesis. Furthermore, the corresponding theoretical investigations have demonstrated that the increase of the ligand electronegativity can enhance their discrimination between these two cations effectively.