Synchrotron diffraction studies of TiC/FeTi cermets obtained by SHS

TiC/FeTi composites have been obtained in situ by Self-propagating High-temperature Synthesis (SHS) of an intimate mixture of compacted powders of elemental carbon, titanium and iron. The reaction has been followed in real time by X-ray diffraction at the ESRF. The mechanism of the reaction is discussed in terms of the formation of a liquid phase corresponding to the eutectic of the Fe/Ti system prior to the TiC synthesis. Temperatures of reaction have been estimated by correlating thermal expansion coefficients with diffraction peaks shifts. The microstructures obtained by this method, suitable for cutting tools and wear resistant applications, are presented.     

Supercritical fluid extraction and gas chromatography or electroanalysis of metal chelates from different sample matrices

The supercritical fluid extraction of Pb(DDC)2 and MoO2(acac)2 complexes is performed. The previously formed complexes are used in order to simplify the extraction process. In the extraction cell, 9.0 mg of Pb(DDC)2 or 30.0 mg of MoO2(acac)2 is added. With these two complexes, a study of static and dynamic extraction as a function of pressure (1000-2500 psi), temperature (40-160 degrees C), and presence of modifier (methanol) is performed. Under the best conditions, 5.6 mg of Pb(DDC)2 (2.3 mg of Pb2+) is recovered. The parameters are 2500 psi of pressure, 160 degrees C of temperature, 0.5 mL methanol (placed in a 10-mL extraction cell), 60.0 min of static extraction, and 2.0 min of dynamic extraction. It is necessary to add 3.0 mL of methanol to enhance efficiency on the MoO2(acac)2 complex recovery. Quantitative extractions of MoO2(acac)2 (9.0 mg of MoVI) are obtained when the experiments are carried out under 1000-2500 psi of pressure, 140 degrees C, and times no longer than 10.0 min. Then, the study is carried out forming the in situ complexes. For this purpose, metallic ion and ligand are added. Under these conditions, the Pb2+ recovery decreases from 2.3 to 1.9 mg, and the MoVI recovery decreases from 9.0 to 1.0 mg. When 1.9 mg of Pb2+ and 1.0 mg of MoVI or less is placed in the extraction cell, the recoveries are always 100%. The Pb2+ extracts are directly accomplished using gas chromatography-flame ionization detection (GC-FID), and the MoVI extracts are analyzed using GC-FID and catalytic adsorption voltammetry. The quantitation of pure extracts is carried out by constructing calibration curves with complex solutions and sample solutions using the standard addition method. This method is applied by determination of Pb2+ in sodium alginate extracted from algae and blood, urine, and human milk from patients with diagnosed plumbunemy. MoVI is determined in irrigation water and pasture of animal intake.     

SULPHENE INTERMEDIATES IN THE SYNTHESIS OF POLY(P-BENZENE-SULPHONAMIDES) AND POLY(P-BENZENE SULPHONATES)

Abstract

Various sulfides are easily oxidized selectively to the corresponding sulfoxides in quantitative yields by iodosylarene (ArIO) catalyzed by metalloporphyrin (TPPM(III)Cl (M [dbnd] Fe, Mn)). The oxidation system is demonstrated to be a possible model for monooxygenase in the study of the stereochemistry of these sulfoxides. Metalloporphyrin-iodosylarene can initially equilibrate with the oxometalloporphyrin (TPPM(V)=O·Cl) formed in situ. The initial process may involve one-electron transfer from the sulfide to the intermediate oxometalloporphyrin followed by coupling of two resulting charged products, and/or nucleophilic attack of sulfide on oxometalloporphyrin oxygen. The overall reactions are depicted by paths with different electron demands from the results of Hammett plots.     

Conserved charges for gravity with locally anti-de sitter asymptotics

A new formula for the conserved charges in 3+1 gravity for spacetimes with local anti-de Sitter asymptotic geometry is proposed. It is shown that requiring the action to have an extremum for this class of asymptotia sets the boundary term that must be added to the Lagrangian as the Euler density with a fixed weight factor. The resulting action gives rise to the mass and angular momentum as Noether charges associated to the asymptotic Killing vectors without requiring specification of a reference background in order to have a convergent expression. A consequence of this definition is that any negative constant curvature spacetime has vanishing Noether charges. These results remain valid in the Lambda = 0 limit.     

Constructing a composite indicator with multiplicative aggregation under the objective of ranking alternatives

Composite indicators (CIs), constructed on the basis of the ‘benefit of the doubt’ criterion, are characterized by endogenously determined vectors of weights. In this paper, a new procedure to construct CIs is proposed in an attempt to overcome the main weakness of this family of procedures: the determination of an individual weighting vector for each alternative, which makes comparisons between alternatives difficult and the existence of multiple ties. A new procedure is proposed which, while maintaining the essence of DEA-inspired procedures determines a common weighting vector to evaluate the complete set of alternatives and includes the discrimination between alternatives as an objective of the procedure.