A correlation between crystal structure and catalytic activity in the solid solutions CdMoxW1−xO4

Two CdMo_xW_1−xO₄ solid solutions with the scheelite and the wolframite structures were synthesised via different techniques and their structures were determined from powder refinements. The limit of the reciprocal solubility of Mo in CdWO₄ has been checked. Several compositions of the solid solutions have been tested in the catalytic mild oxidation of propane or propene and relations between the structures and the catalytic activity are proposed.     

Basic sites on mixed nitrided galloaluminophosphates “AlGaPON”: infrared studies of SO2 and CDCl3 adsorption

The basic properties of nitrided galloaluminophosphate “AlGaPON” are documented by FTIR of sulphur dioxide and deuterated chloroform. To evidence the increase in the number of basic sites with nitrogen enrichment, we compared the spectra recorded after adsorption of CDCl₃ on the phosphate precursor “AlGaPO” and on four oxynitrides with increasing nitrogen contents. On the oxide, adsorption arises from CDCl₃ interacting with surface hydroxyl groups, on the oxynitrides basic sites are shown to be M–NH₂ groups. This interpretation is confirmed by FTIR of adsorbed SO₂. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermodynamic optimization of the Ni-Zn system

Optimization of thermodynamic and phase diagram data has been performed and consistent sets of coefficients for the calculation of the phase equilibria in the system Ni-Zn have been obtained using the program BINGSS. The δ phase has been modeled as a stoichiometric compound (NiZn₈). The binary liquid and the solid Ni-based solutions have been treated as disordered substitutional phases. The intermediate β, β ₁, and γ compounds have been modeled as phases with substitutional defects and vacancies on two sublattices. The calculated phase diagram and thermodynamic quantities are in excellent agreement with the experimental data.     

Quantitative Characterization of Internal Defects in RDX Crystals

Size, shape, internal defects are very important properties of explosives crystals. These parameters play a role on both the explosive formulation processing and the detonic behavior of the explosive formulations. The use of explosive crystals free of solvent inclusions leads to decrease the shock sensitivity of cast explosive formulations. Many efforts for processing such high quality explosive crystals have been done and are still in progress. Qualitative observations of internal crystal defects can be performed by optical microscopy with matching refractive index. The purpose of this paper is to provide two accurate quantitative tools for internal crystal defects measurements. The first method is based on accurate measurements of the crystal apparent density. The second method records the mass of the species entrapped in the crystal internal cavities. Experiments are performed on two RDX batches. The strong correlation recorded between the results of the two complementary methods validates the measurements. Apparent density measurements provide an accurate global characterization of the internal defects population of a crystal batch sorting the crystals in function of their apparent density. The second method is a tool to identify the species entrapped in the crystals.     

Evaluation of the dielectric properties of biodiesel fuels produced from different vegetable oil feedstocks through electrochemical impedance spectroscopy

Biodiesel fuels were prepared from different vegetable oil sources (canola, soybean, sunflower, and corn) and studied through electrochemical impedance spectroscopy. The dielectric constant from these biofuels evidenced no important dependence on feedstock, suggesting basically no change in fuels' polarity from varying the raw materials. In a different way, huge variations of the electrical resistivity and relaxation frequency were found when comparing among the studied biodiesels. Our findings demonstrate that these variations are closely associated with changes in the biodiesel viscosity, which is known to modulate charge mobility and was feedstock dependent. Accordingly, the impedance spectroscopy is here revealed to be a sensitive, alternative and reliable analytical approach for distinguishing among different feedstock-related biodiesels and monitoring certain biofuels' properties, like viscosity and interrelated parameters, usually connected with fatty acid structural profiles in biodiesel fuels.     

Reconnaissance et traitement de cavites naturelles ou artificielles dans le domaine ferroviaire

Bulletin of Engineering Geology and the Environment - L'existence de cavités souterraines et de réseaux karstiques peut poser des problèmes de stabilité des plate-formes,...     

Structural stability of intermetallic phases in the Sn–Ti system

The total energies of intermetallic compounds in the Sn–Ti system are calculated employing electronic density-functional theory (DFT) using pseudopotentials constructed by the projector augmented waves (PAW) method in the generalized gradient (GGA) approximation for the exchange and correlation energy. The calculations are performed for the experimentally observed compounds at their ideal stoichiometry as well as for structures which are stable in systems of early transition metals or rare earth elements with p-elements of columns IIIB, IVB, and VB. The calculated formation enthalpy of the hexagonal Sn₅Ti₆ compound is slightly less exothermic than the value obtained by direct reaction calorimetry. For the stable intermetallic compounds, the calculated zero-temperature lattice parameters agree well with those obtained experimentally at ambient temperature. More, for stable phases with unit cell-internal degree(s) of freedom, the results of ab initio calculations show good agreement when compared with data obtained by structural analysis of X-ray diffraction. The composition dependence of the enthalpies of formation is slightly asymmetric. The electronic densities of state of the D8₈- Sn₃Ti₅ compound have been computed; the curve shows the hybridization of Sn 5p states with Ti 3d states. The stability of the intermetallic compounds in the Ti–Sn system is due to this hybridization.     

Reduction of the correlation sensitivity to the changes of the input illumination by a post processing based on the correlation statistics

Linear-correlation amplitude changes when the intensity level of the input image is modified. As recognition is often based on the correlation-peak level, a change of the input illumination may result in a false recognition. We propose an illumination-change compensation by a post processing of the correlation distribution that is based on statistical measures of the correlation histograms. The theoretical background and simulation results are provided in the frame of an actual application in biology.     

ANTARES: The HTR/VHTR project at Framatome ANP

Framatome ANP is developing a very high temperature reactor (VHTR), relying on its previous experience with high temperature reactor concepts, from its participation in the MODUL and the GT-MHR designs. While being a major actor in the nuclear reactor business with proven light water technology, AREVA wishes to be ready to meet the new challenges calling for small grid requirements, high temperature process heat and cogeneration. The Framatome ANP VHTR design for electricity production is based on an indirect cycle coupled to an “off-the-shelf” combined cycle gas turbine. Although direct cycle HTRs are being promoted for their high efficiency, preliminary evaluations show that the Framatome ANP design efficiency is on par with a direct cycle while avoiding power generation system (PGS) developments and keeping the PGS contamination free. Moreover, the nuclear heat source of the indirect cycle could also be used to meet the heat supplies from a standard design for multiple applications.