Homogenization of a model for water–gas flow through double‐porosity media

This paper presents a study of immiscible compressible two‐phase, such as water and gas, flow through double porosity media. The microscopic model consists of the usual equations derived from the mass conservation laws of both fluids, along with the standard Darcy–Muskat law relating the velocities to the pressure gradients and gravitational effects. The problem is written in terms of the phase formulation, that is, where the phase pressures and the phase saturations are primary unknowns. The fractured medium consists of periodically repeating homogeneous blocks and fractures, where the absolute permeability of the medium becomes discontinuous. Consequently, the model involves highly oscillatory characteristics. The major difficulties related to this model are in the nonlinear degenerate structure of the equations, as well as in the coupling in the system. We obtain the convergence of the solutions, and a macroscopic model of the problem is constructed using the notion of two‐scale convergence combined with the dilatation technique. Copyright © 2015 John Wiley & Sons, Ltd.     

Crystal structure,vibrational studies,optical properties,and Hirshfeld surface analysis of (C5H6N5)2[Cr2O7]

Single crystals of a new organic–inorganic compound, (C₅H₆N₅)₂Cr₂O₇ (1), adeninium dichromate, were grown by the slow evaporation technique and characterized by X-ray diffraction, infrared absorption, and the optical properties were also investigated by UV-vis absorption spectroscopy. The compound crystallizes in the triclinic system and P-1 space group with a = 11.6850(2) Å, b = 11.7531(5) Å, c = 14.5603(7) Å, α = 83.956(3)°, β = 70.481(4)°, γ = 61.863(2)°, V = 1658.70(12) Å³. The structure of the compound consists of four adeninium, (C₅H₅N₂)⁺, cations, and two dichromate dianions with all the atoms situated in general positions. Each dichromate anion is formed by two tetrahedral CrO₄ joined through shared O atoms and are linked to the cations with several weak hydrogen bonding interactions resulting in an extended network. 3-D Hirshfeld surface analysis and 2-D fingerprint plots indicate that the packing is dominated by H?O/O?H and H?N/N?H contacts.     

A mechanistic MEDT study of the competitive catalysed [4+2] and [2+2] cycloaddition reactions between 1-methyl-1-phenylallene and methyl acrylate: the role of Lewis acid on the mechanism and selectivity

The selectivity and the nature of the mechanism of the competitive Lewis acid catalysed [4+2]/[2+2] cycloaddition reactions of 1-methyl-1-phenylallene (MPA) with methylacrylate (MA) have been theoretically studied within the Molecular Electron Density Theory using DFT methods at the B3LYP/6-31G(d) theoretical level. DFT reactivity indices indicate that MPA is a strong nucleophile and the LA-MA complex is a strong electrophile. The coordination of LA to MA enhances the reaction rate and increases the asynchronicity of the [4+2] CA reaction, changes the nature of the mechanism from one step to stepwise for the [2+2] CA reaction and increases the polar character of these cycloaddition reactions, which become demands a relatively low activation energy. Analysis of different energy profiles indicates that these competitive LA-catalysed CA reactions favour the formation of a mixture of meta regioisomers in both types of cycloaddition, in which the [4+2] cycloadducts were obtained in majority amount, in agreement with the experiment. Analysis based on Electron Localisation Function topological shows that the favoured [4+2] CA reaction takes place through a non-concerted two-stage one-step mechanism.     

Chemical and Biological Sensors Based on Electrochemical Detection Using Conducting Electroactive Polymers

The electrochemical behavior of composites of conducting electroactive polyaniline (PAn) and polypyrrole (PPy) formulated within cross-linked hydrogel networks was investigated by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Composite PAn gels displayed similar anodic charge density compared to the pristine conducting polymer (80mC/cm² and 84mC/cm², respectively), suggesting a similar degree of electroactivity between the two systems. Composite gels of PAn displayed fast cation transport with K⁺ diffusivity (D_appt= 5.31×10^–7cm²s^–1) that were three orders of magnitude larger than that of pristine PAn (D_appt=3.12×10^–10cm²s^–1), while PPy composite gels showed similar ferrocene anion diffusivity (D_appt=7.05×10^–5cm²s^–1) compared to electropolymerized PPy (D_appt=6.54×10^–5cm²s^–1). The electrochemical interactions between CYP2D6, a cytochrome P450 isoenzyme, and fluoxetine mediated by electroactive polyaniline films on glassy carbon electrodes (GCEs) were investigated. Cyclic voltammograms indicate that PAn is an effective mediator of CYP2D6 activity under anaerobic conditions. An analytical interrogation methodology based on small-amplitude, pulsed DC was developed and incorporated into the Electroconductive Polymer Sensor Interrogation System (EPSIS). Polypyrrole membranes were rendered biospecific by either copolymerization of pyrrole (Py) with 4-(1-pyrrolyl) butyric acid (4PyBA), followed by direct conjugation with 5-(biotinamido)pentyl amine (5BPA), or by reacting 4PyBA with 5BPA to form pyrrolyl-biotin conjugates. The biotinylated PPy was made responsive to glucose or urea by exploiting strong biotin-streptavidin binding to either streptavidin-glucose oxidase or biotin-urease conjugates. These bioactive conducting polymer membranes were demonstrated as conductimetric glucose and urea biosensing layers using the EPSIS. The rate of conductivity of the bioactive PPy membranes was observed to double upon increasing glucose concentration from 100µM (4×10^–6Scm^–1s^–1) to 600µM (9×10^–6Scm^–1s^–1).     

An efficient hybrid, nanostructured, epoxidation catalyst: titanium silsesquioxane-polystyrene copolymer supported on SBA-15

A novel interfacial hybrid epoxidation catalyst was designed with a new immobilization method for homogeneous catalysts by coating an inorganic support with an organic polymer film containing active sites. The titanium silsesquioxane (TiPOSS) complex, which contains a single-site titanium active center, was immobilized successfully by in-situ copolymerization on a mesoporous SBA-15-supported polystyrene polymer. The resulting hybrid materials exhibit attractive textural properties (highly ordered mesostructure, large specific surface area (>380 m2 g-1) and pore volume (>or==0.46 cm3 g-1)), and high activity in the epoxidation of alkenes. In the epoxidation of cyclooctene with tert-butyl hydrogen peroxide (TBHP), the hybrid catalysts have rate constants comparable with that of their homogeneous counterpart, and can be recycled at least seven times. They can also catalyze the epoxidation of cyclooctene with aqueous H2O2 as the oxidant. In two-phase reaction media, the catalysts show much higher activity than their homogeneous counterpart due to the hydrophobic environment around the active centers. They behave as interfacial catalysts due to their multifunctionality, that is, the hydrophobicity of polystyrene and the polyhedral oligomeric silsesquioxanes (POSS), and the hydrophilicity of the silica and the mesoporous structure. Combination of the immobilization of homogeneous catalysts on two conventional supports, inorganic solid and organic polymer, is demonstrated to achieve novel heterogeneous catalytic ensembles with the merits of attractive textural properties, tunable surface properties, and optimized environments around the active sites.     

Synthesis of new spiro‐[isothiochromene‐3,5′‐isoxazolidin]‐4(1H)‐ones

A series of seven new 2′,3′,4′‐substituted spiro[isothiochromene‐3,5′‐isoxazolidin]‐4(1H)‐ones ( 7‐13 ) has been prepared in the reaction of benzylidene(phenyl)azane oxide ( 5 ) or benzylidene(methyl)azane oxide ( 6 ) with (3Z)‐3‐(4‐substituted‐benzylidene)‐1H‐isothio‐ chromen‐4(3H)‐one ( 1‐4 ). The reaction occurs by a 1,3‐dipolar cycloaddition mechanism that leads to the regiospecific formation of various spiroisoxazolidines ( 7‐13 ).     

Functionalized tellurols: synthesis, spectroscopic characterization by photoelectron spectroscopy, and quantum chemical study

Ethene-, cyclopropane-, 3-butene-, and cyclopropanemethanetellurol have been synthesized by reaction of tributyltin hydride with the corresponding ditellurides and characterized by 1H, 13C, and 125Te NMR spectroscopy and high-resolution mass spectrometry. The tellurols of this series, with a gradually increasing distance between the tellurium atom and the unsaturated group, have been studied by photoelectron spectroscopy and quantum chemical calculations. Two stable conformations of ethenetellurol and cyclopropanetellurol, five of allyltellurol, and four of cyclopropanemethanetellurol were found. In the photoelectron spectrum of vinyltellurol, the huge split between the first two bands indicates a direct interaction between the tellurium lone electron pair and the double bond. In the allyl derivative, a hyperconjugation effect was found for the most stable conformers. In contrast to the vinyl compounds, no direct interaction between the lone electron pair of X (X = O, S, Se, and Te) and the three-membered ring could be observed in the cyclopropyl derivatives. A hyperconjugation-like effect, which is independent of the relative orientation of the X-H group, is found to increase from S to Te. Thus, the type and extent of the interaction between the TeH group and an unsaturated or cyclopropyl moiety are clarified while the first comparison of interactions between the nonradioactive unsaturated chalcogen derivatives is performed.     

Global behavior of compressible three-phase flow in heterogeneous porous media

The homogenization method is used to analyze the equivalent behavior of a compressible three-phase flow model in heterogeneous porous media with periodic microstructure, including capillary effects. Asymptotic expansions lead to the definition of a global or effective model of an equivalent homogeneous reservoir. The resulting equations are of the same type as the points equations, with effective coefficients. The method allows the determination of these effective coefficients from a knowledge of the geometrical structure of the basic cell and its heterogeneities. Numerical computations to obtain the homogenized coefficients of the entire reservoir have been carried out via a finite element method.     

An Attempt to Realize Experimental Isotropic Turbulence at Low Reynolds Number

This paper presents an attempt to realize experimental isotropicturbulence at low Reynolds number. For this aim an experimentalapparatus, a turbulence chamber “Box”, was designed and built togenerate a turbulent flow field in the center of the chamber. Theturbulent airflow field was generated by eight electrical fans placedsymmetrically at the eight internal corners of the externally cubicchamber. The turbulence intensity was controlled by the fans speed.Laser Doppler velocimeter (LDV) in single and two-point velocitymeasurements was used to fully characterize the turbulent field insidethe chamber. The main results indicate that the turbulence ishomogeneous and isotropic with a quasi-zero mean velocity within aspherical region of 20 mm radius from the center of the chamber. Themeasured turbulent integral length scale was found to be constant andindependent of the turbulence intensity (or fans speed). Furthermore, anoticeable spectral inertial subrange as prescribed by the Kolmogorovtheory has not been observed at the range of Reynolds number exploredhere, where Re_λ < 100. But rather a scaling region characterized by anexponent that is lower than the Kolmogorov value, ?5/3, has beenidentified. Moreover, the value of this exponent showed no definedtrend, while the width of the inertial scaling region expands as themicroscale Reynolds number increases.     

Generalized Invexity and Duality in Multiobjective Programming Problems

In this paper, we are concerned with the multiobjective programming problem with inequality constraints. We introduce new classes of generalized type I vector-valued functions. Duality theorems are proved for Mond–Weir and general Mond–Weir type duality under the above generalized type I assumptions.