Etude des transitions ferroelectrique-paraelectrique des composes du systeme NaNbO3LiNbO3

We consider infinite arrays of dislocations in simple lattice models and show that stress-free uniform motion of an array of screw dislocations in a twist boundary can occur for a range of values of the spacing between dislocations.     

Performance aspects of a mixed s-v LSFEM for the incompressible Navier-Stokes equations with improved mass conservation

In the present contribution we propose an improved mixed least-squares finite element method (LSFEM) and compare it with standard LSFEMs with respect to performance aspects. In detail, we consider an approach for Newtonian fluid flow, which is described by the incompressible Navier-Stokes equations. The basis for the associated symmetric minimization problem is a reduced stress-velocity (s-v) two-field approach, see e.g. CAI ET AL. [1] and SCHWARZ & SCHRÖDER [2]. The main idea for the proposed formulation is to add an additional equation, which yields an overconstrained first-order system. This approach does not introduce additional unknowns, so the advantage of two variables (stresses and velocities) remains. Finally, we present a numerical example in order to show the capability of the proposed formulation. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of polysubstituted imidazo[1,2-a]pyridines via microwave-assisted one-pot cyclization/Suzuki coupling/palladium-catalyzed heteroarylation

A new and efficient method for the synthesis of 2,3,6-trisubstituted imidazo[1,2-a]pyridine derivatives using a microwave-assisted one-pot, two-step Suzuki/heteroarylation or one-pot, three-step cyclization/Suzuki/heteroarylation was developed. Polysubstituted compounds are obtained in good yield from 2-amino-5-halogenopyridines, 2-halogenocarbonyl derivatives, boronic acids, and heteroaryl bromides.     

Optical properties of dibenzo[d,d']thieno[3,2-b;4,5-b']dithiophene monocrystals: the effect of intermolecular interactions

The polarized UV-visible absorption spectra of dibenzo[d,d']thieno[3,2-b;4,5-b']dithiophene single crystals are reported and interpreted to definitively attribute the observed bands and their polarizations. The results provide information on the intermolecular interactions and on the aggregation in the condensed phase, which can be of either herringbone- or H-type, depending on the electronic transition taken into considerations, with consequences on the order and polarization of the absorption bands. A relatively easy method is also discussed to obtain information on the structural/morphological properties of different types of samples, including thin films, which have been recently proposed for high-performance organic film-effect transistors for their high ionization potential and photostability.     

Synthesis, spectroscopic characterization and X-ray structure of [1,2a]benzimidazol-2-yl amidine

[1,2a]Benzimidazol-2-yl amidine was synthesized by adding cyclopentanamine to iminoester in ethanol. The structure of amidine 1 was characterized by IR, 1H NMR, 1H-1H NOESY, 13C NMR, DEPT, XHCOR spectra, thermogravimetric analysis (TGA), differential thermal analysis (DTA), differential scanning calorimetry thermograms (DSC), elementary analysis as well as by X-ray diffraction. The single crystals suitable for X-ray measurement were obtained by recrystallization at room temperature. The amidine group of a model was found to have Z configuration in the crystal. This compound crystallizes in a P2(1)/n monoclinic unit cell with parameters a=12.679(2) ?, b=8.468(3) ?, c=13.108(2) ?, β=96.538(2)°, V=1398.2 ?3 and Z=4.     

A simple dot-blot–Sirius red-based assay for collagen quantification

The assessment of collagen content in tissues is important in biomedical research, since this protein is altered in numerous diseases. Hydroxyproline and Sirius red based assays are the most common methods for collagen quantification. However, these procedures have some pitfalls, such as the requirement of oxygen-free medium or expensive equipment and large sample size or being unsuitable for hydrolyzed collagen, respectively. Our objective was to develop a specific, versatile, and user-friendly quantitative method applicable to small tissue samples and extracts obtained from elastin purification, therefore, suitable for simultaneous quantification of elastin. This method is based on the binding of Sirius red to collagen present in a sample immobilized on a PVDF membrane, as in the dot-blot technique, and quantified by a scanner and image analysis software. Sample loading, Sirius red concentration, temperature and incubation time, type of standard substance, albumin interference, and quantification time are optimized. The method enabled the quantification of (1) intact collagen in several rat tissue homogenates, including small resistance-sized arteries, (2) partially hydrolyzed collagen obtained from NaOH extracts, compatible with elastin purification, and (3) for the detection of differences in collagen content between hypertensive and normotensive rats. We conclude that the developed technique can be widely used since it is versatile (quantifies intact and hydrolyzed collagen), requires small sample volumes, is user-friendly (low-cost, easy to use, minimum toxic materials, and reduced time of test), and is specific (minimal interference with serum albumin).

Nonsmooth Lur’e Dynamical Systems in Hilbert Spaces

In this paper, we study the well-posedness and stability analysis of set-valued Lur’e dynamical systems in infinite-dimensional Hilbert spaces. The existence and uniqueness results are established under the so-called passivity condition. Our approach uses a regularization procedure for the term involving the maximal monotone operator. The Lyapunov stability as well as the invariance properties are considered in detail. In addition, we give some sufficient conditions ensuring the robust stability of the system in finite-dimensional spaces. The theoretical developments are illustrated by means of two examples dealing with nonregular electrical circuits and an other one in partial differential equations. Our methodology is based on tools from set-valued and variational analysis.     

Synthesis, characterization and activity in cyclohexene epoxidation of V2O5–TiO2 anatase xerogel

The system of V₂O₅?CTiO₂ catalysts with V₂O₅ contents from 5 to 20 wt% were prepared by the sol?Cgel route and calcined at 500?°C. The mixed oxide series presented the crystalline structure of TiO₂ anatase phase. BET analysis showed a medium surface area decreasing from 73 to 19?m² g^?1 when V₂O₅ content rose from 5 to 20 wt%. The results of pyridine adsorption followed by FT-IR indicate that the catalysts display identical surface acid densities, independently of the V₂O₅ content, and both Br?nsted and Lewis acid sites are present on their surfaces. The V₂O₅ system presents an activity and selectivity during the cyclohexene oxidation reaction. The presence of V₂O₅ increases the catalyst efficiency and leads to a selectivity change from cyclohexenol (blank test) to epoxide, with a maximum for 15 wt% V₂O₅. The conversion of cyclohexene was 46?% while the selectivity to epoxide was higher (75?%).     

Theoretical determination of the favorable mechanism of the reaction between AlX and HX (X = Br, Cl, and F)

The reaction mechanism between AlX and HX (X = Br, Cl, and F) have been characterized in detail using DFT as well as the ab initio method. The reaction yielding AlX₃ and molecular hydrogen was calculated to be highly exothermic. The present calculations also show that the possible routes to the trihalides species start more favorable with the primary insertion product AlX₂H than with the biadduct AlX(HX)₂ one.