Transposition eventuelle lors de l'action de bromures β-ethyleniques CH2CHCH(R)CH2Br (R = CHCH2, C2H5, C6H5) sur le magnesium

Reaction betweenβ-ethylenic bromides CH₂CHCH(R)CH₂2Br and magnesium in ether has been studied. With R = CHCH₂, it gives rise both to normal and rearranged Grignard reagents. With R = C₂H₅ and C₆H₅, only the normal Grignard reagent is formed.     

Computerized conductometric determination of stability constants of complexes of crown ethers with alkali metal salts and with neutral molecules in polar solvents

A computerized conductometric procedure for the determination of stability constants of the complexes of crown ethers (15-crown-5, benzo-15-crown-5 and 12-crown-4) with alkali metal salts in polar solvents is described, based on a microcomputer-controlled titration system. For the control of the experiments from software, a modular computer program was written in FORTH computer language. The procedure is especially suitable for the study of 1:2 metal ion/ligand complexes, which occur frequently with the compounds used. For the study of the interaction between crown ethers and neutral molecules, an indirect procedure is outlined.     

Junction Line Disclinations: Characterisation and Observations

Experimental observations obtained using high resolution transmission electron microscopy (HREM) of junctions between two or more interfaces are analysed to determine whether they exhibit disclination character. The method of analysis used is circuit mapping, and the advantage of using rotation and mirror symmetry operations in the present context, rather than translation operations as is done conventionally, is demonstrated. This technique is applied to micrographs of junctions selected from published literature, and includes junctions in homophase and heterophase materials. It is concluded that few observations currently provide unequivocal evidence of junction line disclination character. This situation may be due in part to the special crystallographic constraints on the applicability of HREM to studies of junction lines. The examples which have been identified all arise at intersections where favourable interfaces, such as epitaxial and twin boundaries, intersect. Moreover, such juncions occur either in pairs, in the form of disclination dipoles, or in small particles.     

Non-empirical pseudo-potentials for molecular calculations

Our non-empirical pseudo-potential method is tested on the molecules ScH₃, TiH₃F, MnO₄ ^-, Zn(CH₃)₂ and Pd(CO)₄. The calculations are performed with the PSIBMOL algorithm, described in paper I (Molec. Phys., 1977, 33, 159) at the independent particle restricted Hartree-Fock level with minimal and double-zeta basis sets of Slater orbitals expanded in gaussian functions. The agreement between pseudo-potential and all-electron calculations for these molecules is as good as for non-transition element compounds as concerns valence molecular orbital energies and expectation values of various one-electron operators. The general conclusion of this series (papers I, II and III) is that our non-empirical pseudo-potential method can now be used as a routine tool to predict efficiently the ground-state valence electronic properties of molecules containing any atom of the Periodic Table as far as relativistic effects remain unimportant.     

Hessian equations on compact non-negatively curved riemannian manifolds

On a compact connected riemannian manifold, we partly extend to hessian equations an existence result proved for Monge-Ampère equations. Non-negative curvature is required for a priori estimates. Received: 13 July 2001 / Accepted: 25 October 2001 / Published online: 29 April 2002 The author is supported by the CNRS     

Renormalized proton- neutron QRPA and double beta decay of 82Se to excited states in 82Kr

We apply the self-consistent renormalized proton-neutron QRPA (RQRPA) method to calculate the two-neutrino double beta (2νββ) decay matrix elements associated with the ground-state and excited-state transitions of the ⁸²Se → ⁸²Kr decay. The RQRPA method is an extension of the pnQRPA method and promotes the Pauli exclusion principle violated by the pnQRPA ground state and yields more stable nuclear matrix elements with increasing strength of the proton-neutron interaction. In the present work the RQRPA wave functions are also used to evaluate 2νββ-decay rates to excited final states. The resulting theoretical half lives are compared with the new stringent experimental limits obtained by using a HPGe detector and external sources of enriched selenium.     

Failure of particulate reinforced polymers

In this presentation, a review is given on the main effects of mineral particulate fillers (with an aspect ratio of about unity) on the deformation and fracture of amorphous and semicrystalline thermoplastic and thermosetting polymers. Elastomeric modifiers, polymer blends, and filled elastomers are not considered here. Fillers are generally used to reduce cost as well as the thermal sensitivity of mechanical properties of the matrix material and to improve, if possible, the strength and toughness. The addition of particulate fillers influences all stages of the fabrication and use of the resulting composites. We focus on the effects of a stiff second phase on elastic moduli, matrix structure, and on deformation, creep, and failure mechanisms. As the main mechanisms, particle-matrix debonding, void formation, and matrix microshear yielding are identified. Toughness is less sensitive to the quality of adhesion since particle-matrix debonding and formation of voids can be tolerated. If well controlled, debonding contributes to deformation (formation of voids should be well distributed in space and time). Reference is also made to the surprising and positive effect of CaCO₃ particles on the toughness and impact resistance of HDPE, which increases at small interparticle distances due to interfacial effects on lamellar growth in the ligament area. Submitted to the 11th International Conference on Mechanics of Composite Materials (Riga, June 11–15, 2000). Published in Mekhanika Kompozitnykh Materialov, Vol. 36, No. 3, pp. 305–316, March–April, 2000.     

Deposition of inertial particles from turbulent flow in channels at high Reynolds numbers

On the basis of the previously developed asymptotic theory of turbulent particle-laden flow with particle deposition in channels coupled with the transport model for the particle Reynolds stress, an asymptotic solution to the problem on the deposition of particles in the limit of high Reynolds numbers was obtained. The numerical calculations confirmed the presence, in the region of the transition from the diffusion-impaction regime of particle sedimentation to the inertia-moderated regime, bifurcation phenomenon of a solution found previously in earlier studies. Features of particle accumulation in the viscous sublayer are analyzed. On the basis of the numerical solution, correlations for particle deposition velocity were obtained. Boundary conditions of the wall-function type for particle concentration whose use allows widening the applicability limits of the equilibrium Eulerian models in terms of particle inertia are proposed.