Cosmological models in the scalar-tetradic theory B

We present two methods for solving the cosmological equations of the scalar-tetradic theory B [19] when a Friedmann-Robertson-Walker (FRW) geometry is assumed. Among the many solutions found there are several physically meaningful ones including inflationary universe solutions.     

Determination of styrene in olive oil by an automatic purge-and-trap system coupled to gas chromatography-mass spectrometry

Summary A new gas chromatographic method using an automatic purge-and-trap system coupled to a GC with mass selective detection to analyze styrene at the parts-per-trillions (ng kg^–1) level is described. The method shows a good sensitivity and the detection limit is 10 ng kg^–1 with a relative standard deviation (RSD) of 4.7% for 164 ng kg^–1 styrene in olive oil. This analytical method has been successfully applied to the analysis of styrene in extra-virgin olive oil from the European market.     

Synthesis of the insect antifeedant CDE molecular fragment of 12-ketoepoxyazadiradione and related compounds

A diastereoselective synthesis of the model insect antifeedant 29 a CDE molecular fragment of 12-ketoepoxyazadiradione has been achieved in ten steps from indenone 9 in 44% overall yield. Several of the compounds obtained along the synthesis related to model compound 29 show significant antifeedant activity against Spodoptera littoralis and Spodoptera frugiperda.     

Characterization of the behaviour of flavour microcapsules in cotton fabrics

Nanotechnology processes have recently been introduced into the textile field. One of these processes involves encapsulated nanoparticles or nanoproducts, known as microcapsules. They are available with a wide range of products which confer different properties related to the nature of the encapsulated product. The composition of the wall material determines the release of the product into the fabric and is the object of study in the present work. The behaviour of microencapsulated peppermint was analyzed on cotton fabrics.Different application methods have been tested, impregnation versus bath exhaustion. As impregnation turned out to be the most efficient, some recipes were assayed and the effect of microcapsules on maintenance conditions was evaluated in order to determine the most suitable method with the longest lasting effect on fabrics.The effect of microcapsules is usually measured by the presence of a property such as odour measurements when flavours are encapsulated. The aim of this work is to explain the behaviour of the cotton fabrics with microcapsules bound to their fibers, to determine the relationship between their macroscopic properties and microscopic characteristics. A procedure based in FTIR spectroscopy is also proposed to quantify the presence of microcapsules in the fabrics.IR spectra of the textiles were obtained to determine the presence of microcapsules, which was corroborated by SEM techniques.     

Phase transitions in silicon single crystals resulting from directional plastic deformation

The formation of polytypic modifications is observed in dislocation-free silicon single crystals under directional plastic deformation. It is shown that the deformation-stimulated phase appears on the surface of the sample in the form of small grains ranging from several hundred to several thousand angstroms in size. A twin structure in the individual grains is observed. Fiz. Tverd. Tela (St. Petersburg) 40, 746–749 (April 1998)     

On the Cartan–Jacobson Theorem

The well-known Cartan–Jacobson theorem claims that the Lie algebra of derivations of a Cayley algebra is central simple if the characteristic is not 2 or 3. In this paper we have studied these two cases, with the following results: if the characteristic is 2, the theorem is also true, but, if the characteristic is 3, the derivation algebra is not simple. We have also proved that in this last case, there is a unique nonzero proper seven-dimensional ideal, which is a central simple Lie algebra of type A₂, and the quotient of the derivation algebra modulo this ideal turns out to be isomorphic, as a Lie algebra, to the ideal itself. The original motivation of this work was a series of computer-aided calculations which proved the simplicity of derivation algebras of Cayley algebras in the case of characteristic not 3. These computations also proved the existence of a unique nonzero proper ideal (which turns out to be seven-dimensional) in the algebra of derivations of split Cayley algebras in characteristic 3.     

Effect of excess halide on the palladium‐catalyzed insertion‐triggered radical copolymerization of methyl acrylate and 1‐hexene

[Pd₂(μ‐Cl)₂(C₆F₅)₂(tht)₂] ( 1 ) is a very efficient initiator of the radical polymerization of methyl acrylate, but it is not active in the polymerization of methyl methacrylate or in the copolymerization with 1‐hexene. The addition of an excess of NBu₄Cl to solutions of [Pd₂(μ‐Cl)₂(C₆F₅)₂(tht)₂] ( 1 ) provides an initiator system that copolymerizes methyl acrylate and 1‐hexene by an insertion‐triggered radical mechanism. Random copolymers are obtained with 11% incorporation of 1‐hexene in moderate yields (about 35%). Studies of the decomposition products obtained after the first insertion of methyl acrylate in the Pd? C₆F₅ bond of 1 show that the addition of excess halide in the presence of monomer favors the homolytic cleavage of the Pd? C bond, and the generation of the radicals that are active species in the polymerization, versus alternative evolution pathways. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5682–5691, 2006     

Multiscale Finite Element Modeling of Arc Dynamics in a DC Plasma Torch

The dynamics of the electric arc inside a direct current non-transferred arc plasma torch are simulated using a three-dimensional, transient, equilibrium model. The fluid and electromagnetic equations are solved numerically in a fully coupled approach by a multiscale finite element method. Simulations of a torch operating with argon and argon–hydrogen under different operating conditions are presented. The model is able to predict the operation of the torch in steady and takeover modes without any further assumption on the reattachment process except for the use of an artificially high electrical conductivity near the electrodes, needed because of the equilibrium assumption. The results obtained indicate that the reattachment process in these operating modes may be driven by the movement of the arc rather than by a breakdown-like process. It is also found that, for a torch operating in these modes and using straight gas injection, the arc will tend to re-attach to the opposite side of its original attachment. This phenomenon seems to be produced by a net angular momentum on the arc due to the imbalance between magnetic and fluid drag forces.     

Validation of the methods for heavy metal speciation in soils and sediments

The knowledge of the chemical forms of metals is used to assess their availability and uptake by plants, and in sediments the forms of metals determine their transport and mobility in the aquatic media. This information may be obtained by determining chemical forms of metals (speciation) or different phases in which the metals are bound, obtained by applying extraction schemes. The analytical methods used include different steps and all of them must be validated. We report here the recommendations to minimize the errors in this kind of analysis. For validation the use of Certified Reference Materials (CRMs) and the participation in interlaboratory exercises are highly recommended.     

Micellar catalysis in kinetic methods of analysis: improvement of spectrophotometric catalytic determination of copper

The combined effects of micellar and chemical catalysis were studied with a view to improving the features of catalytic kinetic determinations. For this purpose we chose the reaction between N,N-dimethyl-p-phenylenediamine (DPD) and N,N-dimethylaniline (DA) to form Bindschedler's Green leuco base, which is oxidized by hydrogen peroxide in a reaction catalysed by Cu(II). This reaction was found to be accelerated by anionic sodium dodecylsulphate (SDS) and cationic dodecyltrimethylammonium bromide (DTAB) micelles. Several advantages were gained in relation to the analytical features of the kinetic photometric determination of Cu(II) when the reaction was developed in the presence of micelles compared to that occurring in an aqueous medium. Such advantages include a lower detection limit, higher sensitivity, precision and solubility of DPD and DA, and substantially increased selectivity in some cases. A detailed study of the parameters which influence both reactions is reported. Some observations on the effect of SDS and DTAB on the reaction are also commented on.