The issues of the uniqueness and the stability of the homogeneous response in uniaxial tests with gradient damage models

We consider a wide class of gradient damage models which are characterized by two constitutive functions after a normalization of the scalar damage parameter. The evolution problem is formulated following a variational approach based on the principles of irreversibility, stability and energy balance. Applied to a monotonically increasing traction test of a one-dimensional bar, we consider the homogeneous response where both the strain and the damage fields are uniform in space. In the case of a softening behavior, we show that the homogeneous state of the bar at a given time is stable provided that the length of the bar is less than a state dependent critical value and unstable otherwise. However, we also show that bifurcations can appear even if the homogeneous state is stable. All these results are obtained in a closed form. Finally, we propose a practical method to identify the two constitutive functions. This method is based on the measure of the homogeneous response in a situation where this response is stable without possibility of bifurcation, and on a procedure which gives the opportunity to detect its loss of stability. All the theoretical analyses are illustrated by examples.     

The strange-quark distribution

We discuss the latest CCFR determination of the strange sea density of the proton. We comment on the differences with a previous, leading-order, result and point out the relevance of quark mass effects and current non-conservation effects. By taking them into account it is possible to solve the residual discrepancy with another determination of the strange-quark distribution. Two important sources of uncertainties are also analysed.     

Lattice and ion dynamics in gel electrolytes based on poly(acrylonitrile) by6Li-7Li NMR

Two composite gel electrolytes prepared from mixtures of poly(acrylonitrile) (PAN), propylene carbonate (PC), ethylene carbonate (EC) and LiClO₄ have been studied with differential scanning calorimetry (DSC) and⁷Li-⁶Li NMR. The data allow estimation of ionic conductivities, local (short range) diffusivities, and lattice dynamics. Furthermore, they point to an unexpected behavior of the Li-rich sample that hints to a complex LiClO₄-PAN phase diagram. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, September 11–18,1994     

Tin–DNA complexes investigated by nuclear inelastic scattering of synchrotron radiation

Nuclear inelastic scattering (NIS) of synchrotron radiation has been used to investigate the dynamics of tin ions chelated by DNA. Theoretical NIS spectra have been simulated with the help of density functional theory (DFT) calculations using 12 models for different binding sites of the tin ion in (CH₃)Sn(DNA_Phosphate)₂. The simulated spectra are compared with the measured spectrum of the tin–DNA complex.     

Ion-pair reversed-phase high-performance liquid chromatography for trace metal preconcentration followed by ion-interaction chromatography

Ion-interaction chromatography of Plasmocorinth B (a disulphonated azo dye) complexes of Co(III), Cu(II), Fe(III), Ga(III), In(III), Ni(II), V(V) and Zr(IV) was studied. The behaviour of two different reversed-phase C₁₈ columns (5 and 10 μm) was compared and an on-line enrichment procedure was developed following the optimization of eluent (pH, ligand concentration, ionic strength and organic modifier). The described technique, applied to the analysis of metal ions at μg/1 levels in natural waters, gave satisfactory precision and accuracy in comparison with inductively coupled plasma atomic emission spectroscopic results.     

Pyrazolo[3,4-d][1,2,3]triazolo[1,5-a]pyrimidine: a new ring system through Dimroth rearrangement

Derivatives of the new ring system pyrazolo[3,4-d][1,2,3]triazolo[1,5-a]pyrimidine were synthesized from the corresponding angular isomers, through a Dimroth rearrangement, in quantitative yields. Preliminary computational studies demonstrated that this class of compounds could be a good candidate as DNA intercalating agents.     

A search for neutrino oscillations

We present here the final results of experiments searching for neutrino oscillations, carried out by the CHARM Collaboration. The data — taking took place in 1983. The first experiment was performed by exposing two detectors simultaneously to the CERN PS low energyv _µ beam. In the second experiment the full CHARM detector was exposed to the wide-band horn-focusedv _µ beam of the CERN SPS. Complete details of the experiments and data reduction are presented. No statistically significant signals for neutrino oscillations were observed. Our 90% CL limits in the appearance experiment (v _µ→v _e ) exclude Δm ²≧0.19 eV² for complete mixing (sin²2θ=1), and sin²2θ≧0.008 for the region Δm ²≧30 eV². These results, and the limits observed for (v _µ→v _x ) (disappearance of (v _µ), are in agreement with those of most other experiments but exclude part of the region previously reported as a possible indication ofv _µ→v _e oscillations.     

A theoretical characterization of the structure formation enthalpy,and fluzional behaviour of B2H6 and AlBH6

Summary A comprehensive study of the binary association complexes B₂H₆ and AlBH₆ has been performed by ab initio molecular orbital theory. Reliable formation enthalpies can be computed only be extended basis sets and a reasonably complete account of correlation. The greater stability towards neutral dissociation of AlBH₆ with respect to B₂H₆ obtained at the Hartree-Fock level employing the 6-21G^* basis set ( 10 kcal/mol) is reduced to only 2 kcal/mol when the basis set is sufficiently saturated and correlation energy properly included. The value of the activation energy for hydrogen scrambling in AlBH₆ is much less sensitive to the method used, although correlation still plays a significant rôle reducing the potential energy barrier from 11.4 to 7.7 kcal/mol.