Regio- and stereoselective alkylation at the 3′-terminal end of ribonucleotides by N-2-methyl-9-hydroxyellipticinium acetate : an antitumor agent

The regio- and stereoselective alkylation at the 3′-terminal end of ribonucleotides by N-2-methyl-9-hydroxyellipticinium acetate under oxidative conditions is reported.     

High temperature crossover in paraconductivity of granular Y1Ba2Cu3O7-y

We have examined the deviation from linearity of the temperature dependence of the electrical resistivity of a YBaCuO ceramics. We have observed at high temprature a crossover behavior toward a logarithmic temperature dependence at lower temperature. It seems relevant to attribute the origin of such a term to a pair breaking mechanism contribution, thus to give a lower bound to the existence of superconductivity fluctuations onset temperature. Our findings also implies that carriers are bosons aboveT _c .     

Transport du cuivre à travers un film mince d'or protecteur

Thin gold films were deposited by “sputtering” onto thick copper substrate. The crystalline structure and topography of the deposits were investigated by scanning and transmission electron microscopy. A scanning Auger microanalysis was performed on the surface and in depth on the gold deposit before and after heating. The observations reveal that the copper arrives at the gold surface especially via holes. The transport rate of the copper via theses holes is very fast compared to the diffusion via grain boundaries. The origin of the holes is discussed: they result of strains due to the gold epitaxial growth on copper grains.     

Position and momentum densities. Complementarity at work: refining a quantum model from different data sets

Although Bragg and Compton scattering are well-established techniques, only very few attempts to simultaneously combine information originating from these two experiments have been made so far. This remark also holds for Bragg neutron magnetic combined with X-ray scattering. We propose a quite general procedure to refine a quantum model from different data sets using basic Bayesian probability theory. As an illustration, a qualitative preliminary study to extract chemical information such as charge transfer in ionic-covalent compounds is reported.     

Superconductivity fluctuations in Bi(Pb) based granular ceramics superconductors: evidence for fractal behavior

We report precise measurements of the electrical resistivity in three different Bi(Pb) based granular ceramics superconductors. We show that a single critical exponent (5/6) describes the superconductivity fluctuations. Such a critical exponent indicates a fractal behavior of the superconducting path. Our results thus indicate a strict two dimensional fluctuation percolation set (below the superconductivity onset temperature 195 K down toT _c), and provide some proof for Tarascon et al. shell conductivity path hypothesis. We estimate the shell thickness to be of the order of 10 Å.     

Comparison between the growth of gold particles onto MgO and amorphous carbon substrates by in situ electrical conductance measurements

The sheet conductance of gold condensates on MgO anda-C is expressed in terms of granulometric quantities. This expression enables us to follow the evolution of metal repartition on its substrate during the gold evaporation. The difference between the growth modes of these gold layers on MgO and ona-C is explained by the predominance of respectively nucleation and coalescence phenomena     

Structure investigation of multiply — twinned Ni particles by electron investigation

Nickel particles are prepared by reducing NiBr₂ in organic solvent. These Ni particles are investigated by electron diffraction. Some of them are icosahedral or decahedral. We have compared the experimental results and the theoretical patterns obtained with models composed of units with a fcc structure or with either rhombohedral or orthorhombic structure for icosahedral or decahedral particles respectively. The results show that the particles are composed of units with fcc structure.     

Analysis of data fusion methods in virtual screening: theoretical model

This paper presents a theoretical model of how data fusion can be used to combine the results of multiple similarity searches of chemical databases. The model is based on frequency distributions of similarity values that are fused using a multiple integration over regions defined by the particular fusion rule that is being applied. For pairwise fusion, the resulting double integrals are straightforward to evaluate for simple model distributions. Similarity values for recovered-active and recovered-nonactive frequency distributions are independently modeled using a constant background, linearly biased terms, and a first-order correlated term. The model shows that two standard fusion rules can give performance enhancements in some cases but that the results of fusion are dependent on many factors that, taken together, can lead to seemingly inconsistent levels of enhancement.