Some Cyclization Reactions with 1,3-Diphenyl-5-Imino-2-Imidazolidinone-4-Thione

1,3-Diphenyl-5-imino-2-imidazolidinone-4-thione (II) was treated with diazomethanes to give (III-V). Interaction of (II) with amino compounds furnished the corresponding 4-substituted imino derivatives (VIa-m). Imidazoquinoxaline derivatives (VIIIb, c) were obtained through interaction of (II) with o-phenylenediamines. Condensation of (II) with hydrazines afforded the hydrazones (IX, Xa, b). Semicarbazone and thiosemicarbazone derivatives (XIIa-d) were prepared from the reaction of (IX) with isocyanates and isothiocyanates. Again (II) was allowed to react with n-butylmagnesium bromide and HgCl₂ to give (XIII) and (XIV) respectively.     

Theoretical study of laser light generation and color image formation: FA1:Cs+ and FA2:Li+ centers at the low coordination (100) and (110) surfaces of AgCl and AgBr

The F_A1:Cs⁺ and F_A2:Li⁺ color centers at the low coordination (100) and (110) surfaces of AgCl and AgBr play important roles in laser light generation and color image formation. Double‐well potentials at these surfaces are investigated by using ab initio calculations. Quantum clusters were embedded in the simulated Coulomb fields that closely approximate the Madelung fields of the host surfaces, and ions that are the nearest neighbors to the F_A ? defect site are allowed to relax to equilibrium. The calculated Stokes shifts suggest that laser light generation is sensitive to the simultaneous effects of the vibrational coupling mode, the impurity cation, the coordination number of the surface ion, the lattice anion, and the choice of the basis set centered on the anion vacancy. An attempt has been made to explain these effects in terms of Madelung potential, electron affinity, and optical–optical conversion efficiency. All relaxed excited states of the defect‐containing surfaces are deep below the lower edges of the conduction bands of the ground‐state defect‐free surfaces, suggesting that the F_A(I):Cs⁺ and F_A(II):Li⁺ centers are suitable laser defects. The dependence of orientational destruction, recording sensitivity, and exciton (energy) transfer on the empty cation; the coordination number of the surface ion; and the lattice anion is clarified. The Glasner–Tompkins empirical rule was generalized to include the impurity cation and the coordination number of the surface ion. As far as color image formation is concerned, the supersensitizer was found to increase the sensitizing capabilities of two primary dyes in the excited states by increasing the relative yield of quantum efficiency. The (110) surfaces of AgBr and AgCl were more sensitive than the corresponding (100) surfaces, and AgBr thin film was found to be more sensitive than that of AgCl. On the basis of quasi‐Fermi levels, the difference in the sensitizing capabilities between the examined dyes in the excited states is determined. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Polaronic and charge ordering effects in Pr 0.5 Sr 0.5 Mn 1− x Fe x O 3

In this work we report the results of X-ray diffraction and Mössbauer spectroscopy for the systems Pr_0.5Sr_0.5Mn_1???x Fe _x O₃ (with x?=?0.05, 0.10, 0.15, 0.20, 0.25, 0.30). XRD patterns indicated that all samples were single phase with slightly distorted orthorhombic symmetry. Room temperature Mössbauer spectra are all quadrupole split, indicating paramagnetic relaxation of the Fe moment for all values of Fe concentrations. The spectra are fitted with two doublet components associated with Fe^3?+? ions in octahedral sites with different distortions. Mössbauer spectra recorded at liquid nitrogen temperature for this system also indicate paramagnetic relaxation of the Fe moments down to liquid nitrogen temperature (LNT). In these spectra a third quadrupole component with quadrupole splitting close to zero develops. This component is associated with the delocalization of the charge carriers and the consequent disappearance of lattice distortions produced by the polaronic effect at room temperature. The component with the high quadrupole splitting (0.81 to 1.07 mm/s) results from Jahn–Teller distortion as a consequence of charge ordering transition at low temperature.     

Observation and modelling of magnetic vortex core structure in Permalloy nanoparticles

We use an approximate micromagnetic model, based on geometrical simplifications of the problem, to describe the vortex core structure observed in spherical Permalloy nanoparticles using off-axis electron holography. The magnetisation distribution inside the vortex core is directly calculated by minimising the micromagnetic energy functional and is compared with the experimental results. The symmetry constraints underlying the model are discussed envisaging possible generalisation to the case of vortex cores with structure strongly dependent on the coordinate directed along the axis of the vortex. Moreover the many-body effect associated with the presence of two small satellite particles is described by rescaling the size of the particle.     

Numerical Simulation of Highly Viscoelastic Polymer Melts using VF and DEVSS Methods

Viscoelastic polymer melts are usually modeled with a macro approch. This is done using an anisotropic mobility tensor to generalize the Maxwell model. In recent works the use of micro approches is increasing, e.g. the so-called POM-POM model. In this work a frame independent flow type property is introduced in order to help visualizing the elongation and shear regions in a 3D flow. Which in turn helps to choose the right material model, since the model parameters are adjusted with 1D shear flows and the elongation properties are mostly neglected. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

On nonlinear diffusion problems with strong degeneracy

In this Note, we study the ‘triply’ degenerate problem: $b{(v)}_t?\mathrm{\Delta }g(v)+\mathrm{div}\Phi (v)=f$ on $Q:=(0,T)\times \Omega$, $b(v(0,?))=b(v_0)$ on Ω and $g(v)=g(a)$ ‘on some part of the boundary’ $(0,T)\times ?\Omega$, in the case of continuous nonhomogenous and nonstationary boundary data a. The functions $b,g$ are assumed to be continuous nondecreasing and to verify the normalisation condition $b(0)=g(0)=0$ and the range condition $R(b+g)=\mathbb{R}$. Using monotonicity and penalization methods, we prove existence of a weak entropy solution in the spirit of F. Otto (1996). To cite this article: K. Ammar, C. R. Acad. Sci. Paris, Ser. I 343 (2006).