Oxidation of some catecholamines by sodium N-chloro-p-toluenesulfonamide in acid medium: A kinetic and mechanistic approach

The kinetics of the oxidation of five catecholamines viz., dopamine (A), L-dopa (B), methyldopa (C), epinephrine (D) and norepinephrine (E) by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) in presence of HClO 4 was studied at 30 ± 0.1 °C. The five reactions followed identical kinetics with a first-order dependence on CAT o, fractional-order in substrate o, and inverse fractional-order in H +. Under comparable experimental conditions, the rate of oxidation of catecholamines increases in the order D > E > A > B > C. The variation of ionic strength of the medium and the addition of p-toluenesulfonamide or halide ions had no significant effect on the reaction rate. The rate increased with decreasing dielectric constant of the medium. The solvent isotope effect was studied using D 2O. A Michaelis-Menten type mechanism has been suggested to explain the results. Equilibrium and decomposition constants for CAT-catecholamine complexes have been evaluated. CH 3C 6H 4SO 2NHCl of the oxidant has been postulated as the reactive oxidizing species and oxidation products were identified. An isokinetic relationship is observed with β = 361 K, indicating that enthalpy factors control the reaction rate. The mechanism proposed and the derived rate law are consistent with the observed kinetics. © Central European Science Journals. All rights reserved

Resonance induced by repulsive interactions in a model of globally-coupled bistable systems

We show the existence of a competition-induced resonance effect for a generic globally coupled bistable system. In particular, we demonstrate that the response of the macroscopic variable to an external signal is optimal for a particular proportion of repulsive links. Furthermore, we show that a resonance also occurs for other system parameters, like the coupling strength and the number of elements. We relate this resonance to the appearance of a multistable region, and we predict the location of the resonance peaks, by a simple spectral analysis of the Laplacian matrix

Fitness profiles of elite Portuguese rugby union players

The aim of this study was to describe the fitness profiles of senior elite Portuguese rugby players. Forty-six senior Portuguese rugby players, classified as backs (n=22; age 26.2±2.8) and forwards (n=24; age 26.7±2.9) were assessed during physical testing sessions carried out for the Portuguese National rugby team. The body composition, maximum strength and anaerobic capacity of players are hypothesized to be important physical characteristics as successful performance in rugby is predicated on the ability to undertake skilled behaviours both quickly and whilst withstanding large forces when in contact situations. No absolute differences were found between the backs and forwards for the speed performance variables although positional differences were found across all speeds when assessed relative to body mass since the forwards were significantly heavier. Coaches and the management team can use this information for monitoring progressive improvements in the physiological capacities of rugby players. These physical characteristics of elite rugby players provide normative profiles for specific positions and should form the basis of developmental programmes for adolescents

The Quantum Stress-Tensor in Self-Similar Spherical Dust Collapse

We calculate the quantum stress tensor for a massless scalar field in the 2-d self-similar spherical dust collapse model which admits a naked singularity. We find that the outgoing radiation flux diverges on the Cauchy horizon. This may have two consequences. The resultant back reaction may prevent the naked singularity from forming, thus preserving cosmic censorship through quantum effects. The divergent flux may lead to an observable signature differentiating naked singularities from black holes in astrophysical observations.Comment: Latex File, 19 page

Ruthenium catalyzed oxidative conversion of isatins to anthranilic acids: Mechanistic study

Oxidation of isatins (isatin, 5-methylisatin, 5-bromoisatin, and 5-nitroisatin) to their corresponding anthranilic acids was performed with sodium N-bromo-p-toluenesulfonamide or bromamine-T (BAT) as an oxidant and ruthenium trichloride (Ru(III)) as a catalyst in HCl medium at 30 +/- 0.1 degrees C. The four reactions follow identical kinetics with a first-order dependence each on [BAT](o) and [Ru(III)], zero-order on [Isatin], and inverse fractional-order on [H(+)]. Activation parameters have been deduced for the composite reaction. The rates satisfactorily correlate with the Hammett U relationship and the reaction constant p is -0.36 signifies that the electron donating groups accelerate the reaction while the electron withdrawing groups retard the rate. An isokinetic relationship is observed with beta = 360 K, indicating that enthalpy factors control the reaction rate. Oxidation products of isatins were identified as their corresponding anthranilic acids by GC-MS analysis and the yields were found to be > 90%. Under similar experimental conditions, the kinetics of Ru(III)-catalyzed oxidation of isatins with BAT has been compared with that of uncatalyzed reactions, revealing that the catalyzed reactions are three to fourfold faster. The observed results have been explained by a plausible mechanism and the related rate law has been deduced. The method adopted for the oxidation of isatins to anthranilic acids in the present work offers several advantages and can be scaled up to industrial operation. (c) 2008 American Institute of Chemical Engineers

Controlo por fase única de conversores A/D de baixa tensão

Este trabalho apresenta a aplicação de um controlo de fase única a um conversor concorrencial de baixa tensão. Com vista à validação da análise e conclusão teóricas, um conversor concorrencial de 10-bit 4 MS/s foi projectado e simulado. Foi primeiramente simulado com um controlo clássico de 6 fases, e posteriormente com um esquema de fase única. Os resultados de simulação mostram que as características globais são mantidas, apontando para que o uso de esquemas de fase única em conversores de baixa tensão seja uma solução que reduz a complexidade dos sistemas clássicos não sobrepostos.info:eu-repo/semantics/publishedVersio

Revestimentos decorativos pelo efeito SPR obtido pela adição de Au a matrizes dieléctricas

A SPR (ressonância dos plasmões de superfície) originada pela introdução de nanopartículas metálicas em matrizes dieléctricas possui um elevado leque de aplicações, sendo alvo de uma actividade intensa de investigação. De modo a tirar partido da forte extinção da luz em certas gamas do visível que estes sistemas proporcionam, foi objectivo deste trabalho desenvolver revestimentos nanocompósitos com efeito SPR para aplicações decorativas. Para tal, recorreu-se à técnica de pulverização catódica reactiva para depositar os revestimentos nanocompósitos consistindo em nanopartículas de Au dispersas em matrizes de WO3 e Al2O3. Por outro lado, pela aplicação de tratamentos térmicos pós-deposição foi promovido o crescimento das nanopartículas de Au. A incorporação crescente de diferentes teores em Au na matriz permitiu a presença de nanopartículas com tamanhos maiores. Além disso, os tratamentos térmicos influenciaram com sucesso o crescimento das nanopartículas de Au na matriz, permitindo alterar a posição, forma e intensidade dos picos de SPR e, onsequentemente, a coloração obtida para as amostras. Contudo, também as propriedades estruturais e dieléctricas da matriz foram afectadas pela temperatura de recozimento, como por exemplo um aumento do índice de refracção que promoveu um deslocamento da posição dos picos de SPR para o “vermelho” (sistema W-O+Au). Nos resultados alcançados houve por isso um efeito combinado entre o crescimento das nanopartículas e a variação do índice de refracção da matriz. Através da variação de três parâmetros, matriz, composição química e temperatura de recozimento, foi possível depositar revestimentos nanocompósitos de WO3+Au e AlO+Au com diferentes cores pelo ajuste dos picos de SPR das nanopartículas de Au.The deposition of thin films consisting of metallic clusters embedded in dielectric matrixes can originate a strong SPR (Surface Plasmon Resonance) signal that has a wide range of applications, being the subject of an intense research nowadays. The main idea of this research work was to utilize the strong extinction of light that arises in these systems in certain zones of the visible spectrum for decorative coatings. Nanocomposite coatings consisting of Au clusters embedded in a WO3 or Al2O3 matrix were prepared by reactive sputtering with different Au contents. The higher the Au contents in the coatings the larger the nanoparticles were. By further annealing these samples at increasing temperatures, the Au segregation in the matrix was promoted. Both events permit to determine the SPR peak position along with its shape and intensity and, consequently, the optical properties of the coatings. Moreover, the thermal treatments also influenced the optical characteristics of the matrix, e.g. the refractive index was increased, leading to the redishing of the SPR position. Thus, the final results attained in the SPR peak shape, intensity and position for each case were mainly due to a combined effect between the Au cluster size and the refractive index of the oxide matrix. By varying the three major experimental parameters, the oxide matrix, the Au composition and the annealing temperature, it was possible to achieve nanocomposite coatings of WO3+Au and AlO+Au with different colours by tailoring the SPR peak shape and position.FCT - DECOMAT (PTDC/CTM/70037/2006), FEDER, através do programa COMPETE - Programa Operacional Factores de Competitividade

Process monitoring during AlNxOy deposition by reactive magnetron sputtering and correlation with the film’s properties

In this work, AlNxOy thin films were deposited by reactive magnetron sputtering, using an aluminum target and an Ar/(N2+O2) atmosphere. The DC magnetron discharge parameters during the deposition process were investigated by optical emission spectroscopy and a plasma floating probe was used. The discharge voltage, the electron temperature, the ion flux and the optical emission lines were recorded for different reactive gas flows, near the target and close to the substrate. This information was correlated with the structural features of the deposits as a first step in the development of a system to control the structure and properties of the films during reactive magnetron sputtering. As the target becomes poisoned, the discharge voltage suffers an important variation, due to the modification of the secondary electron emission coefficient of the target, which is also supported by the evolution of the electron temperature and ion flux to the target. The sputtering yield of the target was also affected, leading to a reduction of the amount of Al atoms arriving to the substrate, according to optical emission spectroscopy results for Al emission line intensity. This behavior, together with the increase of non-metallic elements in the films, allowed obtaining different microstructures, over a wide range of compositions, which induced different electrical and optical responses of films.This research was supported by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PEST-C/FIS/UI607/2011. J. Borges also acknowledges FCT financial support under PhD grant Nº SFRH/BD/47118/2008 (financiado por POPH – QREN – Tipologia 4.1 – Formação Avançada, comparticipado pelo Fundo Social Europeu e por fundos nacionais do MCTES)