Eventual Right Disfocality on Time Scales

Eventual right disfocality of a dynamic equation y j j ( t )+ p 1 ( t ) y j ( t )+ p 2 ( t ) y ( t )=0, t ] T is established where T is a time scale. The results are obtained by imposing integrability conditions on p 1 and p 2 .     

Dissociation enthalpies and phase equilibrium for TBAB semi-clathrate hydrates of N<Subscript>2</Subscript>, CO<Subscript>2</Subscript>, N<Subscript>2</Subscript> + CO<Subscript>2</Subscript> and CH<Subscript>4</Subscript> + CO<Subscript>2</Subscript>

Tetra-n-butyl ammonium bromide (TBAB) semi-clathrate (sc) hydrates of gas are of prime importance in the secondary refrigeration domain and in the separation of gas molecules by molecular size. However, there is a scarcity of dissociation enthalpies under pressure of pure gases and gases mixtures for such systems. In addition, the phase equilibrium of TBAB sc hydrates of several pure gases is not well defined yet as a function of the TBAB concentration and as a function of the pressure. In this paper, dissociation enthalpies and the phase equilibrium of TBAB sc hydrates of gas have been investigated by differential scanning calorimetry (DSC) under pressure. Pure gases such as N₂ and CO₂ and gases mixtures such as N₂ +  CO₂ and CH₄ +  CO₂ were studied. To our knowledge, we present the first phase diagram of TBAB sc hydrates of N₂ for different pressures of gas in the TBAB concentration range from 0.170 to 0.350 wt. Enthalpies of dissociation of TBAB sc hydrates of pure gases and gases mixtures were determined as a function of the presssure for a compound with a congruent melting point whose hydration number corresponds to 26.     

On multiple fixed-sign solutions of a discrete system with Hermite boundary conditions

We consider the discrete system

     

Preliminary study on the recuperation of exhausted graphite tubes for the analysis of Cu and Cr by ETAAS

Preliminary investigations concerning the surface and lifetime of rejuvenated graphite tubes were carried out in order to recuperate exhausted graphite tubes considered unusable for flameless atomic absorption spectroscopy. The effect of a tungsten carbide surface on the sensitivity and precision of Cu and Cr and the lifetime of the new surface in oxidant media are reported.     

Effect of bromine substitution on the solubility of gases in hydrocarbons and fluorocarbons

The interactions of oxygen and of carbon dioxide with normal and brominated octane are studied by analysing original experimental gas solubility data as a function of temperature in the range between 288 and 313 K. The temperature dependence of the solubility yields the thermodynamic properties of solvation. The influence of bromine substitution was studied by comparing the present data with that for perfluorooctane and 1-bromoperfluorooctane. A molecular interpretation of the effects observed was done using atomistic simulation. In order to simulate 1-bromooctane, parameters of the molecular force field were developped for bromoalkanes within the OPLS-AA framework. In general, simulation provides correct predictions of the solubility and of its temperature dependence, except in cases where values are too close (within the error bars of the simulation). Structural aspects of the solvation of the two gases were analysed in light of the site–site solute–solvant radial distribution functions. The relative importance of electrostatic interactions is assessed by modifying the intermolecular potential models for the gases.     

Demethylation of crown ethers,aza crown ethers,and cryptands which have inward-facing anisole units by lithium aluminum hydride in tetrahydrofuran

Lithium aluminum hydride in tetrahydrofuran is an efficient demethylating reagent combination for mono- and bicyclic polyether compounds which bear intra-annular methoxyaryl groups.     

The adsorption structure of NO on Pd(111) at high pressures studied by STM and DFT

Using a combination of scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we study the adsorption structure of NO on Pd(111) at pressures of up to 720 Torr. From atomically resolved STM images, we identify, at high pressures, only the (2 x 2)-3NO structure, which is identical with the highest NO-coverage structure found at low pressure and low temperature. DFT calculations confirm that the (2 x 2)-3NO structure is indeed the most stable adsorption structure at high pressures. Contrary to recent suggestions in the literature, we therefore conclude that we find no evidence for a (3 x 3)-7NO structure on Pd(111) at high NO pressure.