Development of a method for the preparation of ruthenium indenylidene-ether olefin metathesis catalysts

The reactions between several derivatives of 1-(3,5-dimethoxyphenyl)-prop-2-yn-1-ol and different ruthenium starting materials [i.e., RuCl?(PPh?)? and RuCl?(p-cymene)(L), where L is tricyclohexylphosphine di-t-butylmethylphosphine, dicyclohexylphenylphosphine, triisobutylphosphine, triisopropylphosphine, or tri-n-propylphosphine] are described. Several of these reactions allow for the easy, in-situ and atom-economic preparation of olefin metathesis catalysts. Organic precursor 1-(3,5-dimethoxyphenyl)-1-phenyl-prop-2-yn-1-ol led to the formation of active ruthenium indenylidene-ether complexes, while 1-(3,5-dimethoxyphenyl)-prop-2-yn-1-ol and 1-(3,5-dimethoxyphenyl)-1-methyl-prop-2-yn-1-ol did not. It was also found that a bulky and strong σ-donor phosphine ligand was required to impart good catalytic activity to the new ruthenium complexes.     

Low Temperature Preparation of High Refractive Index and Mechanically Resistant Sol-gel TiO2 Films for Multilayer Antireflective Coating Applications

TiO₂ sol-gel thin films have attracted a large attention for applications which require high refractive index transparent layers. In this work, sol-gel TiO₂ layers were prepared by Aerosol-gel deposition followed by a thermal treatment procedure in air. Depending on the experimental conditions, abrasion resistant and high refractive index layers could be obtained after post-treatment at only 110°C. In this paper, the experimental parameters which allow the preparation of functional TiO₂ sol-gel layers at such low temperature are discussed. It is concluded that the preparation of high refractive index and mechanically resistant TiO₂ layers can be interpreted in terms of competition between polycondensation and densification mechanisms. This result allows to envisage the sol-gel processing at low temperature of multilayer antireflective coatings.     

Etude de la relaxation dipolaire dans le Ce2(S04)3·9H2O(9D2O) monocristallin

We report in this article the resolution of TSDC (Thermally Stimulated Depolarization Current) spectra and the relaxation parameters of Ce₂(SO₄)₃· 9H₂O(9D₂O) single crystals, for two typical orientations parallel and perpendicular to C₆, symmetry axes The TSDC peaks obtained show a nonDebye type of behavior Calculation of the dipolar relaxation parameters was achieved by fitting the experimental curves to a general order kinetic equation This method allows us to describe the nonDebye-type of behavior of the TSDC peaks on the basis of dipolar interactions during the relaxation process The three different kinds of electric dipoles leading to the three experimentally observed TSDC peaks are ascribed to three different configurations of hydrogen bonds.     

Phase transitions in ferroelectric ceramics of the type Sr0.5Ba0.5Nb2O6

The ferro-paraelectric transition in Sr_0.5Ba_0.5Nb₂O₆ ceramics has been studied by measuring the dielectric pennitivity as a function of temperature at different frequencies. Experimental results in the transition region over ?'_max fit the relation $\text{1}\text{?'}\text{?}\text{1}\text{?'}{}_{\max }\text{= A(T ?}\text{T}{}_0\text{)}{}^{\mathrm{\gamma }}$ with γ > 1, as is typical for dif transitions. In an interval of temperatures of 17°C over T₀ (=Tfor?'_max), γ = 2. Using the relaxors' model of Kirillov-Isupov an equation is inferred in order to compute the activation energy of the relaxors as a function of parameters directly obtained from the experimental results.     

Solution of sparse quasi-square rectangular systems by Gaussian elimination

We present a general method for the linear least-squares solutionof overdetermined and underdetermined systems. The method isparticularly efficient when the coefficient matrix is quasi-square,that is when the number of rows and number of columns is almostthe same. The numerical methods for linear least-squares problemsand minimum-norm solutions do not generally take account ofthis special characteristic. The proposed method is based onLU factorization of the original quasi-square matrix A, assumingthat A has full rank. In the overdetermined case, the LU factorsare used to compute a basis for the null space of A^T. The right-handside vector b is then projected onto this subspace and the least-squaressolution is obtained from the solution of this reduced problem.In the case of underdetermined systems, the desired solutionis again obtained through the solution of a reduced system.The use of this method may lead to important savings in computationaltime for both dense and sparse matrices. It is also shown inthe paper that, even in cases where the matrices are quite small,sparse solvers perform better than dense solvers. Some practicalexamples that illustrate the use of the method are included.     

Excess molar volumes and enthalpies for the binary systems propyl propanoate + o-xylene, m-xylene, and p-xylene at 298.15 K

This paper reports excess molar enthalpies, H_m^E, and excess molar volumes, V_m^E, of the binary systems {propyl propanoate + o-xylene}, {propyl propanoate + m-xylene} and {propyl propanoate + p-xylene} at the temperature 298.15 K and atmospheric pressure, over the whole composition range. V_m^E was calculated from the experimental measurement of the corresponding densities, while H_m^E was measured directly. The excess magnitudes were correlated to a Redlich-Kister type equation. Finally, we will discuss the results of the three mixtures studied here and by comparison with other binary systems containing propyl propanoate and a benzene-based compound previously published.