Cristina Matos Silva

Antioxidants in medicinal plant extracts. A research study of the antioxidant capacity of Crataegus, Hamamelis and Hydrastis.

The antioxidant capacity of extracts of Crataegus oxyacantha, Hamamelis virginiana, Hydrastis canadensis, plants native to Europe and North America which have long been used in herbal medicine for the treatment of cardiac and circulatory functions, has been investigated. The total antioxidant potential conferred by all hydrogen donating antioxidants present in these extracts has been assessed by the ABTS assay and the relative order of antioxidant potential has been established. Gas chromatography coupled to mass spectrometry (GC‐MS) has been used for the chemical identification of the antioxidant volatile compounds present in the extracts. The GC‐MS data were related to the results obtained using the ABTS assay. Copyright

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.

Hybrid and Mixed Finite Element Formulations for Softening Materials

The conforming displacement elements are nowadays dominant in standard finite element applications. Nevertheless, they present some known limitations, particulary in what concerns accuracy and safety in stress estimates. With computational development and the motivation to model increasingly more complex structural problems, several alternative numerical techniques have been proposed to substitute or complement the tradicional displacement formulation, e.g. the boundary elements, meshless models and hybrid and mixed formulations. The hybrid and mixed finite element formulations adopted in this work [2] are developed from first-principles of Mechanics, namely, equilibrium, compatibility and constitutive relations. Recently, these formulations have been tested with continuum damage models in order to correctly simulate the behavior of softening materials such as concrete [3], [5], [6], [4]. The most promising formulations are the hybrid-mixed stress formulation, with an independent approximation of the effective stress field instead of an approximation of the stress filed [6], and the hybrid displacement formulation [4].

A Fault-Tolerant Secure CORBA Store using Fragmentation-Redundancy-Scattering

The Fragmentation-Redundancy-Scattering (FRS) is a technique that can be used to achieve security and fault-tolerance [1]. It consists in fragmenting the confidential data and scattering the resulting fragments across several sites. Fragmentation is performed so that any isolated fragment contains no significant information. Scattering is performed in such a way that each archive contains just a subset of (unrelated) fragments and that each fragment is stored in more than one site. The technique provides intrusion-tolerance: if a node is compromised, the intruder has no access to relevant information (and if compromised fragments are deleted or altered, they can be recovered from other nodes).

Damage analysis of concrete structures using polynomial wavelets

This paper presents and discusses a hybrid-mixed stress finite element model based on the use of polynomial wavelets for the physically non-linear analysis of concrete structures. The effective stress and the displacement fields in the domain of each element and the displacements on the static boundary are independently approximated. As none of the fundamental equations is locally enforced a priori, the hybrid-mixed stress formulation enables the use of a wide range of functions. In the numerical model reported here, all approximations are defined using complete sets of polynomial wavelets. These bases present some important features. In one hand, the functions are orthogonal, which is an important issue when implementing hybrid-mixed stress elements as it ensures high levels of sparsity. On the other hand, the polynomial wavelet basis is defined through linear combinations of Legendre polynomials. This fact enables the use of closed-form solutions for the computation of the integrations involved in the definition of all linear structural operators. A simple isotropic damage model is adopted and a non-local integral formulation where the strain energy release rate is taken as the non-local variable is considered. The numerical model is both incremental and iterative and is solved with a modified Newton-Raphson method that uses the secant matrix. Classical benchmark tests are chosen to illustrate the use of the model under discussion and to assess its numerical performance.