Knizhnik-Zamolodchikov-Bernard equations connected with the eight-vertex model

Using quasiclassical limit of Baxter's 8 - vertex R - matrix, an elliptic generalization of the Knizhnik-Zamolodchikov equation is constructed. Via Off-Shell Bethe ansatz an integrable representation for this equation is obtained. It is shown that there exists a gauge transformation connecting this equation with Knizhnik-Zamolodchikov-Bernard equation for SU(2)-WZNW model on torus.Comment: 20 pages latex, macro: tcilate

Chemical Potential and the Nature of the Dark Energy: The case of phantom

The influence of a possible non zero chemical potential $\mu$ on the nature of dark energy is investigated by assuming that the dark energy is a relativistic perfect simple fluid obeying the equation of state (EoS), $p=\omega \rho$ ($\omega <0, constant$). The entropy condition, $S \geq 0$, implies that the possible values of $\omega$ are heavily dependent on the magnitude, as well as on the sign of the chemical potential. For $\mu >0$, the $\omega$-parameter must be greater than -1 (vacuum is forbidden) while for $\mu < 0$ not only the vacuum but even a phantomlike behavior ($\omega <-1$) is allowed. In any case, the ratio between the chemical potential and temperature remains constant, that is, $\mu/T=\mu_0/T_0$. Assuming that the dark energy constituents have either a bosonic or fermionic nature, the general form of the spectrum is also proposed. For bosons $\mu$ is always negative and the extended Wien's law allows only a dark component with $\omega < -1/2$ which includes vacuum and the phantomlike cases. The same happens in the fermionic branch for $\mu 0$ are permmited only if $-1 < \omega < -1/2$. The thermodynamics and statistical arguments constrain the EoS parameter to be $\omega < -1/2$, a result surprisingly close to the maximal value required to accelerate a FRW type universe dominated by matter and dark energy ($\omega \lesssim -10/21$).Comment: 7 pages, 5 figure

Reliability analysis of shear strengthening EBR FRP models

This work presents a statistically oriented study aiming to assess the reliability of some of the most well known design models available for the prediction of the contribution of fiber reinforced polymer (FRP) systems applied according to the externally bonded reinforcing (EBR) technique for the shear strengthening of reinforced concrete (RC) beams. Relevant data was collected from experimental programs carried out in recent years in the context of the shear strengthening with FRP, and an extended database was obtained. Using this data, the performance of fib, ACI, Italian and Australian design guidelines was appraised by means of comparing the contribution of the FRP shear systems predicted by the analytical formulations with those registered experimentally. In general, the obtained results were not very promising, since a large scatter of the design safety factor was observed and, for some cases, the contribution of the FRP systems predicted by the design models was highly unconservative, which may be a serious concern as these formulations may be currently being used in design practice.The study reported in this paper forms a part of the research programme Cutinemo, supported by FCT, PTDC/ECM/73099/2006

Otimização e validação de método para determinação de ácidos orgânicos em vinhos por cromatografia líquida de alta eficiência.

Reagentes e soluções analíticas; Instrumentação e condição cromatográfica; Estabilidade dos padrões analíticos e da fase móvel; Validação do método; Preparação das amostras de vinho

Desempenho de modelos analíticos de previsão da contribuição de materiais compósitos no reforço ao corte de vigas de betão armado

Na presente comunicação são apresentados alguns modelos analíticos para previsão da contribuição de materiais compósitos no reforço ao corte de vigas de betão armado recentemente introduzidos nos códigos de dimensionamento, sendo o seu desempenho aferido por comparação entre os valores estimados pelas formulações analíticas com os registados numa base de dados contendo informação referente a mais de 200 programas experimentais.Os autores manifestam os seus agradecimentos ao apoio prestado pela Fundação para a Ciência e Tecnologia (FCT) no projecto POCI/ECM/59033/2004. O primeiro autor agradece a bolsa UMINHO/POCI-59033/BI/05 concedida ao abrigo deste projecto

Novas perspectivas para o desenvolvimento de modelos de dimensionamento ao corte de vigas de betão armado reforçadas com FRP colado externamente

Com o presente artigo pretende-se apresentar uma base de dados (BD) contendo os registos relativos a mais de 250 vigas reforçadas ao corte com materiais poliméricos reforçados com fibras (FRP) e ensaiadas em diversos programas experimentais conduzidos por diferentes autores. O desempenho dos modelos de dimensionamento propostos pelo fib, ACI, e pelas Norma Italiana CNR-DT200 e Norma Australiana CIDAR é aferido comparando o comportamento observado experimentalmente com as previsões obtidas por via analítica. Tendo por base os resultados registados na BD, foi efectuado um estudo paramétrico com o objectivo de avaliar a influência no desempenho dos modelos de dimensionamento de diversos factores não explicitamente considerados nas formulações analíticas que os suportam. Os resultados são analisados, interpretados e apontadas as limitações encontradas nos modelos de dimensionamento em estud

Design models for shear strengthening of reinforced concrete beams with externally bonded FRP composites : a statistical vs reliability approach

Fundação para a Ciência e a Tecnologia (FCT) - POCTI/ECM/59033/200

On Matrix Superpotential and Three-Component Normal Modes

We consider the supersymmetric quantum mechanics (SUSY QM) with three- component normal modes for the Bogomol'nyi-Prasad-Sommerfield (BPS) states. An explicit form of the SUSY QM matrix superpotential is presented and the corresponding three-component bosonic zero-mode eigenfunction is investigated.Comment: 17 pages, no figure. Paper accepted for publication in Journal of Physics A: Mathematical and Theoretica

Clustering, Angular Size and Dark Energy

The influence of dark matter inhomogeneities on the angular size-redshift test is investigated for a large class of flat cosmological models driven by dark energy plus a cold dark matter component (XCDM model). The results are presented in two steps. First, the mass inhomogeneities are modeled by a generalized Zeldovich-Kantowski-Dyer-Roeder (ZKDR) distance which is characterized by a smoothness parameter $\alpha(z)$ and a power index $\gamma$, and, second, we provide a statistical analysis to angular size data for a large sample of milliarcsecond compact radio sources. As a general result, we have found that the $\alpha$ parameter is totally unconstrained by this sample of angular diameter data.Comment: 9 pages, 7 figures, accepted in Physical Review

Otimização e validação de método para determinação de ácidos orgânicos em vinhos por cromatografia líquida de alta eficiência.

The organic acids (tartaric, malic, citric, lactic and succinic) are de main components responsible for the acidity in the wine. This method for simultaneous determination of organic acids and interfering peaks in wines can be achieved in 16 min. The sample preceded by a dilution and filtration step. The chromatographic separation required one reversed phase column, isocratic mobile phase (acetonitrila, formic acid in water) and detection wavelength was set at 212 nm. The validation confirmed good repeatability, recovery and application in red and white wines.Nota técnica