Exact Solutions of Extended Boussinesq Equations

The problem addressed in this paper is the verification of numerical solutions of nonlinear dispersive wave equations such as Boussinesq-like system of equations. A practical verification tool for numerical results is to compare the numerical solution to an exact solution if available. In this work, we derive some exact solitary wave solutions and several invariants of motion for a wide range of Boussinesq-like equations using Maple software. The exact solitary wave solutions can be used to specify initial data for the incident waves in the Boussinesq numerical model and for the verification of the associated computed solution. The invariants of motions can be used as verification tools for the conservation properties of the numerical model.     

Influence of Relative Permeability on the Stability Characteristics of Immiscible Flow in Porous Media

Relative permeability functions for immiscible displacements in porous media show a wide range of profiles. Although, this behavior is well known, its impact on the stability of the displacement process is unexplored. Our analysis clearly demonstrates for the first time that the viscous instability characteristics of two-phase flows are governed not only by their end point values, but are strongly dependent on the actual profile of relative permeability functions. Linear stability analysis predicts the capacity of the flow to develop large scale fingers which can result in substantial bypassing of the resident fluid. It is observed that relative permeability functions attributed to drainage processes yield a more unstable displacement as compared to functions related to imbibition processes. Moreover, instability is observed to increase for those relative permeability functions which result from increased wettability of the wetting fluid. High accuracy numerical simulations show agreement with these predictions and demonstrate how large amplitude viscous fingers result in significant bypassing for certain relative permeability functions. In the nonlinear regime, the finger amplitude grows at a rate ∝ t^1/2 initially, drops to t^1/4 at a later time and finally grows ∝ t. The basic mechanisms of finger interaction, however, are not substantially influenced by relative permeability functions.     

A study of superficial associations at a mercury electrode in the case of tetrabutylammonium halide solutions

The influence of the nature of the anion on the adsorption of the tetrabutylammonium cation from halide solutions at a mercury—solution interface has been studied. A series of measurements of the interfacial tension for such solutions also containing a non-adsorbable cation, have led to the evaluation of the adsorption of both the tetraalkylammonium cation and of the halide anion. The variation of global surface excesses of entropy and concentration with temperature have also been determined. The results obtained can be explained by the formation, at the surface of the electrode, of both paired and non-paired ions, the latter neutralizing the charge on the electrode. The role of hydrophobic forces whose importance has been recognized in the adsorption of neutral substances is stressed in the case of surfaceactive cations.     

Solvates of Indomethacin

Indomethacin is known to exhibit polymorphism and solvates, the different forms obtained do not exhibit the same solubility and their bioavailabilities are different. It is of a prime importance to identify the various polymorphic and solvated forms. This study was carried out by: DSC (different scanning calorimetry), TG (thermogravimetric analysis), X-ray diffraction and thermomicroscopy. Seven solvates, with acetone, benzene, dichloromethane, tetrahydrofurane, propanol, chloroform and diethylether, were isolated and studied. Their formulae have been determined by thermogravimetric analysis and their X-ray patterns on powder are presented, by DSC their behaviour after desolvation is recorded, the temperature and the enthalpy of fusion are measured and by this way the form obtained is deduced. This revised version was published online in July 2006 with corrections to the Cover Date.     

Temperature dependent preferential sputtering in CoSi2 and NbSi2

Sputtering of CoSi₂ and NbSi₂ has been carried out by Xe ion bombardment at room temperature, as well as at elevated temperatures putting these systems in their radiation-enhanced diffusion regimes. The range of the Xe ions (at 200–260 keV) was appreciably less than the thickness of the silicides. The samples were analyzed by 2 MeV He⁺ backscattering spectrometry, x-ray diffraction and optical microscopy. The ratio of the sputtering yield of Si to that of the metal (i.e., Co or Nb) always exceeds the stoichiometric ratio 21, leading to Si depleted surface layers. The amount of the sputtered species increases almost linearly with dose until intermixing of the silicide with the underlying Si becomes appreciable. This happens at lower doses in the radiation-enhanced diffusion regime than at room temperature. Irradiation of CoSi₂ samples at high temperature leads to a broadening of the implanted Xe profile compared to the room temperature profile. No such phenomenon has been found in NbSi₂. The effect of Xe broadening on the sputtering yields is discussed.     

Solute-solvent interactions in surfactant adsorption: Part I. The influence of the polar head

This study deals with the variation of the interfacial tension of mercury aqueous solutions with potential and concentrations for solutions of butanol. butyric acid, butyramide and butyl monoether glycol. The results obtained have been analysed using an isotherm proposed by Bennes leading to values for the energy of adsorption corrected for the influence of the solute-solvent interactions in solution.A correlation has been revealed been to exist between the corrected energy of adsorption, the hydrophobicity coefficient and the dipole moment of the molecule which are all parameters related to the nature of the hydrophilic grouping.These result serve to show how the adsorption on mercury can be used to approach the problem of interactions between molecules in surfactant solutions.     

Synthesis, crystal structure, magnetic properties, and electronic structure of the new ternary vanadate CuMnVO4

A new magnetic oxide, CuMnVO4, was prepared, and its crystal structure was determined by single-crystal X-ray diffraction. The magnetic properties of CuMnVO4 were characterized by magnetic susceptibility and specific heat measurements, and the spin exchange interactions of CuMnVO4 were analyzed on the basis of spin-polarized electronic band structure calculations. CuMnVO4 contains MnO4 chains made up of edge-sharing MnO6 octahedra containing high-spin Mn2+ cations. Our work shows that CuMnVO4 undergoes a three-dimensional antiferromagnetic transition at approximately 20 K. Both the intrachain and interchain spin exchanges are antiferromagnetic, and the interchain spin exchange is not negligible compared to the intrachain spin exchange.     

The photogalvanic effect of Fe(II)-β-diketonate/thionine systems in aqueous acetonitrile

Summary The photogalvanic effect of ferrousbis-(acetylacetonate) (Fe(II)(acac)₂) and ferrousbis-(trifluoroacetylacetonate) (Fe(II)(tfac)₂) complexes in aqueous acetonitrile thionine dye solutions has been studied in a photogalvanic cell of 70 cm³ capacity with identical platinum electrodes (area: 0.25 cm²) using visible light (80 mW/cm²) at 25°C. The theoretical Sunlight Engineering Efficiency (SEE) was determined for both complexes and it was found that the best SEE was obtained when Fe(II)(tfac)₂ was used at a concentration of 1.5×10^–4 mol/dm³ with a thionine concentration of 1×10^–4 mol/dm³ atpH=4 in 40% aqueous acetonitrile. Effects of incident light intensity and temperature on the photogalvanic performance and the action spectrum of the present system were also investigated. A mechanism of the photoredox reaction between the Fe(II)-complex and the dye molecule is proposed.

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Der photogalvanische Effekt von Fe(II)--Diketonat/Thionin-Systemen in wäßrigem Acetonitril

Zusammenfassung Der photogalvanische Effekt von Eisen(II)-bis-(acetonylacetonat) (Fe(II)(acac)₂) und Eisen(II)-bis-(trifluoracetylacetonat) (Fe(II)(tfac)₂ in wäßriger acetonitrilischer Thioninlösung wurde in einer photogalvanischen Zelle (70 cm³) mit identischen Platinelektroden (Fläche: 0.25 cm²) mit sichtbarem Licht (80 mW/cm²) bei 25°C untersucht. Für beide Komplexe wurde die theoretische Sunlight Engineering Efficiency (SEE) bestimmt; der beste SEE-Wert wurde für Fe(II)(tfac)₂ bei einer Konzentration von 1.5×10^–4 mol/dm³ beipH=4 in 40%igem Acetonitril gefunden (Thioninkonzentration: 1.0×10^–4 mol/dm³). Effekte, die durch Änderung der Lichtintensität und der Temperatur hervorgerufen werden, werden diskutiert. Ein Mechanismus für die Photoredoxreaktion zwischen dem Fe(II)-Komplex und dem Farbstoffmolekül wird vorgeschlagen.

     

Synthesis, structural characterization and electrochemical studies of new macrocyclic Schiff base containing pyridine head and its metal complexes

A new macrocyclic ligand, 1,3,5-triaza-2,4:7,8:13,14-tribenzo-9,12-dioksa-cyclopentadeca-1,5-diene was synthesized by reaction of 2,6-diaminopyridine and 1,2-bis(2-carboxyaldehyde phenoxy)ethane. Then, its Cu(II), Ni(II), Pb(II), Co(III) and La(III) complexes were synthesized by the template effect by the reaction of 2,6-diaminopyridine and 1,2-bis(2-carboxyaldehyde phenoxy)ethane and Cu(NO₃)₂ · 3H₂O, Ni(NO₃)₂ · 6H₂O, Pb(NO₃)₂, Co(NO₃)₂ · 6H₂O, La(NO₃)₃ · 6H₂O, respectively. The ligand and its metal complexes have been characterized by elemental analysis, IR, ¹H and ¹³C NMR, UV-Vis spectra, magnetic susceptibility, thermal gravimetric analysis, conductivity measurements, mass spectra, and cyclic voltammetry. All complexes are diamagnetic and Cu(II) complex is binuclear. The Co(II) was oxidized to Co(III). The comparative electrochemical studies show that the nickel complex exhibited a quasi-reversible one-electron reduction process, while copper and cobalt complexes gave irreversible reduction processes in DMSO solution.