Exponential fitting Direct Quadrature methods for Volterra integral equations

This paper is the first approach to the solution of Volterra integral equation by exponential fitting methods. We have developed a Direct Quadrature method, which uses a class of ef-based quadrature rules adapted to the current problem to solve. We have analyzed the convergence of the method and have found different formulas for the coefficients, which limit rounding errors for small stepsizes. Numerical experiments for comparison with other DQ methods are presented.     

Upper Bounds for the Automorphic Chromatic Index of a Graph

The automorphic H-chromatic index of a graph Γ is the minimum integer m for which Γ has a proper edge-coloring with m colors preserved by a given subgroup H of the full automorphism group of Γ. We determine upper bounds for this index in terms of the chromatic index of Γ for some abelian 2-groups H.     

Protective effects of extracts and flavonoids isolated from Scutia buxifolia Reissek against chromosome damage in human lymphocytes exposed to hydrogen peroxide

Flavonoids are claimed to protect against cardiovascular disease, certain forms of cancer and ageing, possibly by preventing initial DNA damage. Therefore, we investigated the protective effects of crude extract, ethyl acetate fraction and flavonoids (quercetin, quercitrin, isoquercitrin and rutin) isolated from the leaves from Scutia buxifolia against chromosome damage induced by H?O? in human lymphocytes by analyzing cellular growth rate, cell viability, mitotic index and chromosomal instability. We found a differential response among the compounds tested, with the ethyl acetate fraction being more effective than the crude extract, a difference perhaps related to the presence of the antioxidants identified and quantified by HPLC/DAD. In general, quercetin, isoquercitrin and rutin recovered the mitotic index and chromosomal instability more than quercitrin after treatment with hydrogen peroxide.     

Improving catalytic properties of P450 BM3 haem domain electrodes by molecular Lego

In this work the catalytic properties of a cytochrome P450 immobilised onto an electrode surface are improved by means of the molecular Lego approach.     

Coordination chemistry of Ga(C5Me4Ph): novel homoleptic d10 cluster complexes of palladium

The synthesis and characterization of the novel sterically encumbered Ga(I) ligand GaCp(Ph) (1b) (Cp(Ph) = C5Me4Ph) is presented. GaCp(Ph) reacts with the Pd(0) source Pd2(dvds)3 (dvds = tetramethyldivinyldisiloxane) to give the trinuclear cluster [Pd3(GaCp(Ph))(mu2-GaCp(Ph))(mu3-GaCp(Ph))2(dvds)] (2a). 2a is the first example of a Ga(I)-containing cluster with a potentially labile olefinic ligand. It was found that 2a is an intermediate in the formation of the dinuclear cluster [Pd2(GaCp(Ph))2(mu2-GaCp(Ph))3] (2b), which is formed on reaction of 2a with GaCp(Ph). Both clusters were found to be labile toward GaCp, AlCp, or phosphines, giving substitution products in all cases.     

Complex thermal evolution of size-stabilized tetragonal zirconia

Zirconia nanopowder with doping YO_1.5 contents between 0 and 1 mol% were synthesized by the Pechini method. The crystallite dimensions of the powder, around 10 nm, allows for the size stabilization of the tetragonal polymorph over the thermodynamically stable monoclinic one. As the nanopowders are heated to 1200 °C and subsequently cooled back to room temperature, a complex evolution of the phase composition occurs. Upon heating the tetragonal phase transforms slowly into the monoclinic one and the transition cannot be completed before entering the stability range of the tetragonal phase (above 1150 °C). Upon cooling, on the other hand, the reaction is considerably faster and the complete transformation into the monoclinc phase occurs in a narrow temperature range. Rietveld analysis of the high temperature X-ray patterns revealed as, during heating, the transition is mainly controlled by microstructural parameters and in particular it is triggered by the release of RMS microstrain. Upon cooling, on the other hand, the transition is kinetically controlled by the doping content.     

Enhancement of molecular polarizabilities by the push-pull mechanism; a DFT study of substituted benzene, furan, thiophene and related molecules

We report Density Functional Theory (DFT) studies of the dipole polarizabilities of benzene, furan and thiophene together with a number of substituted and related systems. All geometries were optimized (and characterized) at the B3LYP/6-311g(2d,1p) level of theory and polarizabilities then calculated with B3LYP/6-311++G(2d,1p). For the R-ring systems we find group polarizabilities in the order R = NO₂ ∼ OCH₃ ∼ CN ∼ CHO > NH₂ > OH > H = 0. For systems R-ring-R, 〈α〉 differs little from the additivity model, with small positive and negative increments. For systems D-ring-A (where D and A are deactivating and activating groups) we find a positive enhancement to 〈α〉 over and above the value expected on the basis of pure additivity for all pairs A and D studied. This enhancement can be increased greatly by extending the length of the conjugated chain to D-ring-CH=CH-ring-A and D-ring-N=N-ring-A systems. Empirical models of polarizability such as AM1 agree badly with the DFT calculations in an absolute sense but give excellent statistical correlation coefficients. Calculated 〈α〉’s also agree well in a statistical sense with the molecular volumes calculated from molecular mechanics force fields Analysis of the results in terms of the π electrons alone is not satisfactory.     

Effect of support on activity of palladium catalysts in nitrobenzene hydrogenation

The effect of two types of catalysts on the activity of the catalytic hydrogenation of nitrobenzene was studied. Catalysts were prepared by the surface deposition of palladium hydroxide with a simultaneous reduction with formaldehyde in a basic environment and were characterised by X-ray powder diffraction, transmission electron microscopy, adsorption-desorption, and catalytic tests — hydrogenation of nitrobenzene in methanol. The influence of the supports’ (activated carbon and a mixture of activated carbon and multi-walled carbon nanotubes) surface area is discussed. Despite having a size comparable (4–5 nm) to crystallites of metallic palladium, the catalyst prepared on a mixture of activated carbon and nanotubes (Pd/C/CNT) was significantly less active than the catalyst prepared on pure activated carbon (Pd/C); the rate of this reaction was approximately 30 % lower than the initial reaction rate. This feature could be attributed to the lower specific surface area of the Pd/C/CNT (531 m² g^?1) in comparison with the Pd/C (692 m² g^?1).