Simultaneous spectrophotometric determination of diuretics by using multivariate calibration methods

The wavelength range and number of factors used in partial least-squares (PLS) calibration for the resolution of the dihydralazine (DHZ)-hydrochlorothiazide (HCT) binary mixture and the dihydralazine-hydrochlorothiazide-reserpine ternary mixture were optimized in terms of the relative standard error (R.S.E.) and relative mean standard error (R.M.S.E.). Under the optimum conditions thus established, synthetic mixtures of the analytes can be resolved with errors and relative standard deviations (R.S.D) less than 4.5 and 1.0%, respectively. The ensuing method, which was validated by comparison with high performance liquid chromatography (HPLC), also gives good results with real samples (pharmaceutical preparations).     

Kinetic study of an epoxy system badge (n=0)/1, 2 dch modified with an epoxy reactive diluent

The curing reaction of an epoxy system consisting of a diglycidyl ether of bisphenol A (n=0) and 1, 2 diaminecyclohexane (DCH) with an epoxy reactive diluent vinylcyclohexane dioxide was studied by temperature modulated differential scanning calorimetry (TMDSC). The models proposed by Kamal and by Horie et al. were employed in the kinetic study. From these studies reaction orders, rate constants, and activation energies were determined. The technique of TMDSC allows to include in the kinetic study the effect of diffusion by means of the mobility factor, calculated from the curves of the complex heat capacity registered during the curing isothermal experiments. The results were compared to those obtained for the same system employing the reaction rate data. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydrodynamic models for heavy-ion collisions and beyond

A generic property of a first-order phase transition in equilibrium, and in the limit of large entropy per unit of conserved charge, is the smallness of the isentropic speed of sound in the “mixed phase”. A specific prediction is that this should lead to a non-isotropic momentum distribution of nucleons in the reaction plane (for energies ≈ 40 A GeV in our model calculation). On the other hand, we show that from present effective theories for low-energy QCD one does not expect the thermal transition rate between various states of the effective potential to be much larger than the expansion rate, questioning the applicability of the idealized Maxwell/Gibbs construction. Experimental data could soon provide essential information on the dynamics of the phase transition.     

Cosmic acceleration from interaction of ordinary fluids

Cosmological models with two interacting fluids, each satisfying the strong energy condition, are studied in the framework of classical General Relativity. If the interactions are phenomenologically described by a power law in the scale factor, the two initial interacting fluids can be equivalently substituted by two non interacting effective fluids, where one of them may violate the strong energy condition and/or have negative energy density. Analytical solutions of the Friedmann equations of this general setting are obtained and studied. One may have, depending on the scale where the interaction becomes important, non singular universes with early accelerated phase, or singular models with transition from decelerated to accelerated expansion at large scales. Among the first, there are bouncing models where contraction is stopped by the interaction. In the second case, one obtains dark energy expansion rates without dark energy, like ΛCDM or phantomic accelerated expansions without cosmological constant or phantoms, respectively. We would like to thank CNPq of Brazil for financial support. One of us (NPN) would like to thank the French/Brazillian cooperation CAPES/COFECUB for partial financial support. We would also like to thank ‘Pequeno Seminario’ of CBPF’s Cosmology Group for useful discussions.     

Study of the influence of a reactive diluent on the rheological properties of an epoxy-diamine system

The generalized temperature integral I(m, x) appears in non-isothermal kinetic analysis when the frequency factor depends on the temperature. A procedure based on Gaussian quadrature to obtain analytical approximations for the integral I(m, x) was proposed. The results showed good agreement between the obtained approximation values and those obtained by numerical integration. Unless other approximations found in literature, the methodology presented in this paper can be easily generalized in order to obtain approximations with the maximum of accurate.     

Mixed moment estimator and location invariant alternatives

A new class of estimators of the extreme value index is developed. It has a simple form and is asymptotically very close to the maximum likelihood estimator for a wide class of heavy-tailed models. We also propose an alternative class of estimators, dependent on a tuning parameter p ∈ (0,1) and invariant for changes in both scale and/or location. Such a tuning parameter can help us to choose the number of top order statistics to be used in the estimation of extreme parameters. Research partially supported by FCT / POCTI, POCI, PCDT and PPCDT / FEDER.     

Natural sesquiterpenoids

This review covers the isolation, structural determination, synthesis and chemical and microbiological transformations of natural sesquiterpenoids. The literature from January to December 2005 is reviewed,and 386 references are cited.