Ageing of wet-synthesized oxide powders

Wet chemical synthesis of precursor oxide ceramics is a method to obtain small particulate powders. Such powders are far more prone to ageing in air than more traditional precursors. Thermogravimetric analysis is used to highlight the species responsible for the ageing of ceramic precursors. Indeed water and carbon dioxide are observed to evolve from aged powders. Ceramics obtained from aged precursors can reach a very low final density with respect to the theoretical value. A large degree of the original sintering properties can be recovered after washing the aged powders with ethanol in a basic medium.     

Surface characterization of cellulose fibres by XPS and inverse gas chromatography

Inverse gas chromatography (IGC) was used to determine the dispersive component of the free energy as well as the acid-base properties of cellulose fibre surfaces, before and after modification by corona treatment. It was found that the corona treatment increases both the dispersive contribution to surface energy and its acidic character, whereas only a slight increase in its basicity was observed. It was also found that some chemical degradation of the surface occurs at high corona currents. The extent of modification of the surface properties, as revealed by IGC, was correlated to the surface chemical composition deduced from XPS analysis as well as with the electrical conductance and the pH of the water suspensions of the cellulose fibres.     

Synthese De (1,2a)Benzimidazolo-1,3,5,2-triazaphosphorine-2-oxides

The reaction of hexamethylphosphotriamide or methylphosphonic bis(dimethylamide) compounds with amidines derived from N-Benzimidazoyl imidates 1 leads to (1,2a)benzimidazolo-1,3,5,2-tiazaphosphorine-2-oxides 4 in good yields. If the condensation is realized at room temperature, N-phosphonic amidines 3 can be isolated as intermediates. The isolated compounds 2 , 3 , and 4 are identified by spectroscopic methods: IR, 1 H, 13 C, 31 P, NMR, and M.S.     

About b-weakly compact operators on Banach lattices

We characterize Banach lattices on which each positive operators is b-weakly compact and we derive some characterizations of KB-spaces.     

REACTION DES O,O-DIETHYL OXO-1 ALKANEPHOSPHONATES AVEC LES DERIVES DE L'HYDRAZINE: UNE VOIE DE SYNTHESE DES HYDRAZONES α-PHOSPHONATEES ET DES HYDRAZIDES

Abstract

Under the normal conditions, the reaction of hydrazine and methylhydrazine with OO-diethyl 1 oxoalkane phosphonates 1 proceeds by cleavage of the phosphorus-carbon bond and leads to the formation of diethylphosphite 2 and N-acylhydrazide 3 . A procedure has been developed for the synthesis of new primary hydrazone of OO-diethyl 1-oxoalkane phosphonates 4 . A mechanism is proposed. The structure of those compounds 4 was confirmed by NMR and IR spectroscopy.     

Hydrolysis-Condensation Kinetics of Different Silane Coupling Agents

Abstract

The hydrolysis kinetics of 14 alkoxy silane coupling agents were carried out in an ethanol:water 80:20 (w/w) solution under acidic conditions and were monitored by ¹H, ¹³C, and ²⁹Si NMR spectroscopy. Acidic conditions were selected in order to enhance the silanol formation and to slow down the self-condensation between the resulting hydrolysed silanol groups. In situ ²⁹Si NMR spectroscopy allowed the determination of the intermediate species as a function of the reaction time. Thus, the following silane coupling agents were studied: 3-methacryloxypropyl trimethoxy silane (MPMS), 3-mercaptopropyl trimethoxy silane (MRPMS), 3-cyanopropyl triethoxy silane (CPES), triethoxy vinyl silane (VES), trimethoxy (2-phenylethyl) silane (PEMS), octyl triethoxy silane (OES), trimethoxy (7-octen-1-yl) silane (OEMS), 3-aminopropyl triethoxy silane (APES), 3-aminopropyl trimethoxy silane (APMS), 3-(2-aminoethylamino)propyl trimethoxy silane, (DAMS), 3-[2-(2-aminoethylamino)-ethylamino]propyl trimethoxy silane (TAMS), 4-amino-3,3-dibutyl trimethoxy silane (ADBMS), trimethoxy [3-(phenylamino)propyl] silane (PAPMS), and triethoxy-3-(2-imidazolin-1-yl) propyl silane (IZPES). A parameter quantifying the grafting potentiality of each silane coupling agent towards OH-rich solid substrates (such as cellulose) was established as a function of the nature of the alkoxy groups (methoxy or ethoxy), as well as that of the fourth substituent (vinyl, aminopropyl, etc.) of the silane studied.

GRAPHICAL ABSTRACT     

Metabolic compartmentalization in the human cortex and hippocampus: evidence for a cell- and region-specific localization of lactate dehydrogenase 5 and pyruvate dehydrogenase

Background  

For a long time now, glucose has been thought to be the main, if not the sole substrate for brain energy metabolism. Recent data nevertheless suggest that other molecules, such as monocarboxylates (lactate and pyruvate mainly) could be suitable substrates. Although monocarboxylates poorly cross the blood brain barrier (BBB), such substrates could replace glucose if produced locally.     

Spectral element discretization of the Maxwell equations

We consider a variational problem which is equivalent to the electromagnetism system with absorbing conditions on a part of the boundary, and we prove that it is well-posed. Next we propose a discretization relying on a finite difference scheme for the time variable and on spectral elements for the space variables, and we derive error estimates between the exact and discrete solutions. RESUME. On considère un problème variationnel équivalent aux équations de l'électromagnétisme avec conditions aux limites absorbantes sur une partie de la frontière, qu'on prouve être bien posé. Puis on propose une discrétisation de ce problème par schéma aux différences finies en temps et éléments spectraux en espace, et on établit des estimations d'erreur entre solutions exacte et approchée.