Contribution to the study of structural and elastic properties of wüstite under pressure up to 140 GPa by pseudopotential calculations

Using first-principles calculations based on the density functional theory and the generalized gradient approximations, we have studied the effect of high pressures up to 140 GPa on the structural and elastic properties of wüstite. Our results indicate that FeO undergoes a structural phase transition from NaCl-type (B1) to NiAs-type (B8) almost at the pressure of 77 GPa. The density increases across this transition by about 5%, which is a higher value than that obtained in other researches. We can clearly present the wüstite elastic properties and isotropic wave velocities which are not already studied in this range of pressure, and we could compare these results with the available experiment data, especially with that of PREM model.     

Asymptotic approximation of the solution of Stokes equations in a domain with highly oscillating boundary

We consider a viscous incompressible flow in an infinite horizontal domain bounded at the bottom by a smooth wall and at the top by a rough wall. The latter is assumed to consist in a plane wall covered with periodically distributed asperities which size depends on a small parameter, and with a fixed height. We assume that the flow is governed by the stationary Stokes equations. Using a boundary layer corrector we derive and analyze a first order asymptotic approximation of the flow.      

Dielectric Properties of Calcium,Strontium, or Barium Titanate Sintered with 5 mol.% of Lithium and Calcium Fluorides

Calcium, strontium, and barium titanates were previously synthesized then mixed and wet-ground with 5 mol.% of lithium and calcium fluorides. These mixtures were pressed into pellets and air-fired. The ceramics were investigated by X-ray diffraction, scanning electron microscopy, and dielectric measurements. Each sample is a perovskite single phase. The oxyfluoride deriving from calcium titanate exhibits a phase transition around 283 K. For strontium titanate, no phase transition is detected. On the other hand, the ceramic related to barium titanate displays a ferroelectric phase transition around 300 K and a dielectric relaxation at about 10 MHz. These oxyfluorides could be of interest for capacitor manufacturing.     

Spectral boundary homogenization in domains with oscillating boundaries

We study the asymptotic behavior of the solutions of a spectral problem for the Laplacian in a domain with a rapidly oscillating boundary. We consider both cases where the eigenvalues of the limit problem are simple and multiple. We construct the leading terms of the asymptotic expansions for the eigenelements and verify the asymptotics.     

Organocatalytic asymmetric syntheses of functionalized tetrahydropyridazines

Four tetrahydropyridazines, respectively, substituted at the C-3 position with hydroxymethyl, a silyloxymethyl, a carboxylic acid, and a methyl ester have been prepared in good yields and high enantiomeric purities using organocatalytic α-amination of aldehydes as the key step. These compounds have then been tested as organocatalysts for the same reaction.     

Phase Behavior of Poly(n-butyl acrylate) and Poly(2-ethylhexyl acrylate) in Nematic Liquid Crystal E7

Summary: This paper reports on the phase behavior of photochemically crosslinked poly(n-butyl acrylate) (PABu) and poly(2-ethylhexyl acrylate) (PEHA) networks in a nematic liquid crystal (LC) solvent. The swelling properties of these networks were studied as a function of temperature using a low molecular weight LC (LMWLC), which is an eutectic mixture of cyanoparaphenylenes named E7. To obtain different polymer network densities, the ratio of the reactive monomers ABu (or EHA) to the crosslinking agent hexanedioldiacrylate (HDDA) was varied prior to polymerization/crosslinking reactions. Immersion of these networks in an excess of LC solvent allowed for the measurement of size increase by polarizing optical microscopy in terms of temperature. Diameter ratios were calculated considering swollen to dry network states of the samples. The uptake of LMWLC inside the network preferentially takes place around the nematic to isotropic transition temperature of the solvent. Phase diagrams in the concentration-temperature framework were given and discussed as a function of crosslinking degree of the polymer network and temperature and phase behavior of the solvent.