Effect of surface chemistry on the thermodynamics and conductivity of water in silica nanopores

The thermodynamics and conductivity of water confined in nanoporous silicas SBA-15 are studied using differential scanning calorimetry and impedance spectroscopy. The effect of the water/surface interaction is addressed by investigating samples with different surface chemistries.     

Etude des melanges d'antipodes optiques—XII: Mesure de la stabilite des racemiques vrais

The stability of true racemates is defined by the free energy change ΔG^φ of the process D-crystal + L-crystal → DL-crystal. ΔG^φ, varying in the range 0 to ?2 kcal mol^?1, is roughly proportional to the difference in melting points between racemate and antipodes, T_R^f ? T_A^f. In most of the examples studied, the formation of racemates is exothermic. The study of the variation of ΔG^φ with temperature explains the occurrence of crystalline transitions between racemate and conglomerate. Few racemates can give rise to such transitions, particularly when their enthalpies and entropies of formation, ΔH^φ and ΔS^φ, are both positive.     

Cooling of hot electron-hole plasmas in the presence of screened electron-phonon interactions

We have computed for several semiconductors, (GaAs, CdSe, CdS), the energy loss-rate in hot electron-hole plasmas, at high density, when occurs the screening of the electron-phonon interactions. We show that the long range interactions (piezoelectrical and polar) are quickly reduced when the plasma density is raised, and that the energy loss-rate diminishes therefore significantly (one order of magnitude).     

Configuration absolue et dichroïsme circulaire du nitroxyde de la tetramethyl-2,2,5,5 hydroxy-3 pyrrolidine. Etude comparee de la pentamethyl-2,2,3,5,5 cyclopentanone

The absolute configuration of R(+) 3-hydroxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxyl has been determined by Horeau's method. The circular dichroism agrees with the octant rule if the molecule has the half-chair conformation found in the crystal. The synthesis of R(+) 2,2,3,5,5-pentamethyl cyclopentanone is described. The sign of the Cotton effect of this ketone (analog of the studied nitroxide) has been also interpreted considering the predominant conformation in which the substituent responsible for the chirality is in a quasi-equatorial site.     

Binding probability of free electrons and free holes into Wannier-Mott exciton in non-polar semiconductors

A free electron and a free hole in a crystal may be bound together due to the attractive coulomb field: in semiconductors such an electron-hole pair is similar to the Wannier-Mott exciton. The probability of binding into the fundamental state has been calculated by Lipnik[1]. Lipnik's model does not predict our recent low temperature measurements[2]. Actually the binding probabilities of excited states of excitons must be considered. This is the purpose of the present paper: a quantum model, (adequate in the low temperature limit) and a semi-classical model (adequate when the temperature rises) are presented.     

Identification de la relation de dispersion dans les barresIdentification of the dispersion relation in rods

Dispersion and attenuation of longitudinal waves in elastic or weakly viscoelastic rods are measured by analysing the resonant frequencies present in the strain spectrum due to an unknown loading. The method takes the finite measuring time of the test into account. It is applied to an aluminium bar, in which the dispersion relation is identified very accurately at frequencies up to 60 kHz. To cite this article: R. Othman et al., C. R. Mecanique 330 (2002) 849–855.     

An optimisation method for separating and rebuilding one-dimensional dispersive waves from multi-point measurements. Application to elastic or viscoelastic bars

When using a classical SHPB (split Hopkinson pressure bar) set-up, the useful measuring time is limited by the length of the bars, so that the maximum strain which can be measured in material testing applications is also limited. In this paper, a new method with no time limits is presented for measuring the force and displacement at any station on a bar from strain or velocity measurements performed at various places on the bar. The method takes the wave dispersion into account, as must inevitably be done when making long time measurements. It can be applied to one-dimensional and single-mode waves of all kinds propagating through a medium (flexural waves in beams, acoustic waves in wave guides, etc.). With bars of usual sizes, the measuring time can be up to 50 times longer than the time available with classical methods. An analysis of the sensitivity of the results to the accuracy of the experimental data and to the quality of the wave propagation modelling was also carried out. Experimental results are given which show the efficiency of the method.     

The shear modulus of the human vocal fold in a transverse direction

The aim of this study was to measure the shear modulus of the vocal fold in a human hemilarynx, such that the data can be related to direction of applied stress and anatomical context. Dynamic spring rate data were collected using a modified linear skin rheometer using human hemilarynges, and converted to estimated shear modulus via application of a simple shear model. The measurement probe was attached to the epithelial layer of the vocal fold cover using suction. A sinusoidal force of 3g was applied to the epithelium, and the resultant displacement logged at a rate of 1kHz. Force measurement accuracy was 20microg and position measurement accuracy was 4microm. The force was applied in a transverse direction at the midmembranous point between the vocal process and the anterior commissure. The shear modulus of the three female vocal folds ranged from 814 to 1232Pa. The shear modulus of the three male vocal folds ranged from 1021 to 1796Pa. These data demonstrate that it is possible to obtain estimates for the shear modulus of the vocal fold while preserving anatomical context. The modulus values reported here are higher than those reported using parallel plate rheometry. This is to be expected as the tissue is attached to surrounding structures, and is under natural tension.     

Functionalisation of free amino groups of lysine dendrigraft (DGL) polymers

Lysine dendrigraft polymers (DGL) are promising candidates as carriers for targeted drug/gene delivery and bio-imaging, as such deserving extensive chemical functionalisation studies. We describe here examples of complete grafting of DGL amino groups by various substituents: hydrophobic amino acids (Ala, Val, Leu), dicarboxylic acids (succinic, Asp), guanidyl and saccharides (Gal), by means of straightforward coupling reactions, thus opening to versatile tuning of DGL properties (hydrophobicity, nucleophilicity, electric charge…). DGL functionalisation by lactose (when carried out so as to avoid borate ester formation between sugars) however yields partially grafted DGL; besides, partial grafting can be achieved by tuning the reagent/DGL stoichiometric ratio.