Showing papers by "University of Coimbra published in 1996"
TL;DR: The results indicated that the in vivo AChE inhibition test is selective, being very sensitive to detect toxicity of the organophosphates tested, and less time consuming, requires less human effort and produces less toxic waste than conventional acute bioassays and the in vitro A cholinesterase inhibition test.
275 citations
TL;DR: The results obtained suggest that similar concentrations of phosphoric acid etchants containing distinct thickeners result in different demineralization depths as well as different morphology of etched dentin.
182 citations
TL;DR: Intrinsic factors such as nitrogen and polyphenolic content may explain differences in leaf decomposition and the possible incorporation of eucalyptus litter into secondary production in a reasonable time span is suggested, although community balance and structure might be affected by differences in allochthonous patterns determined by eucallyptus monocultures.
Abstract: Leaf decomposition of the exotic evergreen Eucalyptus globulus (eucalyptus), and three native deciduous tree species, Alnus glutinosa (alder), Castanea sativa (chestnut) and Quercus faginea (oak), was compared in a second order stream in Central Portugal. Changes in dry weight, nitrogen and polyphenolic compounds and microbial colonization were periodically assessed for three months. Negative exponential curves fit the leaf weight loss with time for all leaf species. Mass loss rate was in the order alder (K = 0.0161) > chestnut (K = 0.0079) > eucalyptus (K = 0.0068) > oak (K = 0.0037). Microbial colonization followed the same pattern as breakdown rates. Evidence of fungal colonization was observed in alder after 3 days in the stream, whereas it took 21 days in oak leaves to have fungal colonization. Fungal diversity was leaf species-dependent and increased with time. In all cases, percent nitrogen per unit leaf weight increased, at least, at the initial stages of decay while soluble polyphenolics (expressed as percentage per unit leaf weight) decreased rapidly in the first month of leaves immersion. Intrinsic factors such as nitrogen and polyphenolic content may explain differences in leaf decomposition. The possible incorporation of eucalyptus litter into secondary production in a reasonable time span is suggested, although community balance and structure might be affected by differences in allochthonous patterns determined by eucalyptus monocultures.
159 citations
TL;DR: In this article, the authors compared streams flowing through eucalyptus and deciduous forests, paying attention to: (i) litterfall dynamics, (ii) accumulation of organic matter, (iii) processing rates of two dominant leaf species: (e.g., chestnut leaf litter and tree species), and (iv) macroinvertebrate community structure.
Abstract: To test the hypothesis whether afforestation with Eucalyptus globulus affects litter dynamics in streams and the structure of macroinvertebrate aquatic communities, we compared streams flowing through eucalyptus and deciduous forests, paying attention to: (i) litterfall dynamics, (ii) accumulation of organic matter, (iii) processing rates of two dominant leaf species: eucalyptus and chestnut, and (iv) macroinvertebrate community structure. The amount of allochthonous inputs was similar in both vegetation types, but the seasonality of litter inputs differed between eucalyptus and natural deciduous forests. Eucalyptus forest streams accumulated more organic matter than deciduous forest streams. Decomposition of both eucalyptus and chestnut leaf litter was higher in streams flowing through deciduous forests. The eucalyptus forest soils were highly hydrophobic resulting in strong seasonal fluctuations in discharge. In autumn the communities of benthic macroinvertebrates of the two stream types were significantly different. Deciduous forest streams contained higher numbers of invertebrates and more taxa than eucalyptus forest streams. Mixed forest streams (streams flowing through eucalyptus forests but bordered by deciduous vegetation) were intermediate between the two other vegetation types in all studied characteristics (accumulation of benthic organic matter, density and diversity of aquatic invertebrates). These results suggest that monocultures of eucalyptus affect low order stream communities. However, the impact may be attenuated if riparian corridors of original vegetation are kept in plantation forestry.
157 citations
TL;DR: The results herein described on the structural and kinetic properties of the cardosins indicate that they are the products of distinct genes which have probably arisen by gene duplication.
Abstract: Two new aspartic proteinases have been isolated from stigmas of the cardoon Cynara cardunculus L. by a two-step purification procedure including extraction at low pH, gel filtration on Superdex 200, and ion-exchange chromatography on Mono Q. To follow the conventional nomenclature for aspartic proteinases, we have named these proteinases cardosin A and cardosin B. On SDS/PAGE, cardosin A migrated as two bands with apparent molecular masses of 31 000 Da and 15000 Da where as the chains of cardosin B migrated as bands of 34000 Da and 14000 Da. The partial amino acid sequences of the two cardosins revealed that they are similar but not identical, and that they differ horn the previously reported cardoon proteinases named cynarases, which were assumed to be derived from a common precursor. Although the cardosins show some degree of similarity to each other, we could detect no immunological cross-reactivity between them. Both cardosins were active at low pH and were inhibited by pepstatin, with Ki values of 3 nM for cardosin A and 1 nM for cardosin B, indicating that they belong to the class of aspartic proteinases. Significant differences between the two enzymes were also found for the Kcat/Km values for the hydrolysis of two chromophoric synthetic peptides. The active-site ionization constants, pKe1 and pKe2, for cardosin A are 2.5±0.2 and 5.3±20.2, whereas for cardosin R they are 3.73±10.09 and 6.7±50.1. The results herein described on the structural and kinetic properties of the cardosins indicate that they are the products of distinct genes which have probably arisen by gene duplication. A scheme for the proteolytic processing of the two enzymes is also proposed.
156 citations
145 citations
TL;DR: In this article, different steric stabilizers were used in the preparation of poly-isobutylcyanoacrylate (PIBCA), poly-lactic acid (PLA), polylactic-co-glycolic copolymer (PLAGA) and poly-ϵ-caprolactone (poly-κϵ) nanoparticles to characterize their electrophoretic mobility, zeta potential and particle size.
138 citations
TL;DR: In this article, the authors analyze some properties of the discrete linear bilevel program for different discretizations of the set of variables and study the geometry of the feasible set and discuss the existence of an optimal solution.
Abstract: In this paper, we analyze some properties of the discrete linear bilevel program for different discretizations of the set of variables We study the geometry of the feasible set and discuss the existence of an optimal solution We also establish equivalences between different classes of discrete linear bilevel programs and particular linear multilevel programming problems These equivalences are based on concave penalty functions and can be used to design penalty function methods for the solution of discrete linear bilevel programs
124 citations
TL;DR: The correlation observed between glutamate levels and the release of dopamine and 5-hydroxytryptamine in ischemic conditions suggests a functional linkage between the two transmitter systems.
Abstract: Background and Purpose It is known that the extracellular accumulation of glutamate during anoxia/ischemia is responsible for initiating neuronal injury. However, little information is available on the release of monoamines and whether the mechanism of its release resembles that of glutamate, which may itself influence the release of monoamines by activating presynaptic receptors. This study was designed to characterize the release of both amino acids and monoamines under chemical conditions that mimic anoxia, hypoglycemia, and ischemia. Methods The contents of synaptosomes in adenine nucleotides (ATP, ADP, and AMP), amino acids (aspartate, glutamate, taurine, and γ-aminobutyric acid), and monoamines (dopamine, noradrenaline, and 5-hydroxytryptamine) were measured by high-performance liquid chromatography, after the synaptosomes were subjected to anoxia (KCN+oligomycin), hypoglycemia (2 mmol/L 2-deoxyglucose in glucose-free medium), and ischemia (anoxia plus hypoglycemia). Results The anoxia- and ischemia...
115 citations
TL;DR: Several solution properties of complexes formed between the trivalent lanthanide ions (LnIII) and the macrocyclic ligand DOTP8-, including stability constants, protonation equilibria, and interactions of the LnDOTP5- complexes with alkali metal ions, have been examined by spectrophotometry, potentiometry, osmometry, and 1H, 31P, and 23Na NMR spectroscopy as mentioned in this paper.
Abstract: Several solution properties of complexes formed between the trivalent lanthanide ions (LnIII) and the macrocyclic ligand DOTP8-, including stability constants, protonation equilibria, and interactions of the LnDOTP5- complexes with alkali metal ions, have been examined by spectrophotometry, potentiometry, osmometry, and 1H, 31P, and 23Na NMR spectroscopy. Spectrophotometric competition experiments between DOTP and arsenazo III for complexation with the LnIII ions at pH 4 indicate that the thermodynamic stability constants (log KML) of LnDOTP5- range from 27.6 to 29.6 from LaIII to LuIII. The value for LaDOTP5- obtained by colorimetry (27.6) was supported by a competition experiment between DOTP and EDTA monitored by 1H NMR (27.1) and by a potentiometric competition titration between DTPA and DOTP (27.4). Potentiometric titrations of several LnDOTP5- complexes indicated that four protonation steps occur between pH 10 and 2; the protonation constants determined by potentiometry were consistent with 31P shif...
114 citations
TL;DR: Ellagic acid and myricetin 3′-methyl ether, which have not been detected in any of the monofloral honey samples investigated so far, with the only exception being a French honey sample of the botanically relatedCalluna (Ericaceae), seem to be the most useful potential markers for the floral origin of heather honey.
Abstract: In order to find out biochemical markers for the botanical origin of heather (Erica) honey, the phenolic metabolites present in heather floral nectar, collected from the honey-stomach of bees gathering nectar from these flowers, were analysed. The flavonoid fraction of nectar contained four main flavonoids. Two of them were quercetin and kaempferol 3-rhamnosides, and the other two were tentatively identified as myricetin 3′-methyl ether and isorhamnetin 3-rhamnosides. Since the natural glycosides are hydrolysed by bee enzymes to render the corresponding aglycones, which are the metabolites detected in honey, acid hydrolysis of the nectar glycosides was achieved. The aglycones quercetin, myricetin 3′-methyl ether, kaempferol and isorhamnetin were identified, as well as the gallic acid derivative ellagic acid. The analysis of Portuguese heather honey samples showed that ellagic acid was present in all the samples in significant amounts ranging between 100 μg and 600 μg per 100 g honey. The other nectar-derived flavonoids were also present, although some of them in very variable amounts. Ellagic acid and myricetin 3′-methyl ether, which have not been detected in any of the monofloral honey samples investigated so far, with the only exception being a French honey sample of the botanically relatedCalluna (Ericaceae) which also contained ellagic acid, seem to be the most useful potential markers for the floral origin of heather honey. However, more detailed and extensive investigations are needed to prove the utility of these markers.
TL;DR: In this article, the dissolution rate of tolbutamide/cyclodextrin complexes was investigated and compared with those of the physical mixtures and pure drug, and it was shown that dissolution of the inclusion complexes was much more rapid than the pure drug.
TL;DR: The results indicate that the naturally occurring phenolic acids prevent ferrylmyoglobin-dependent LDL oxidation in a way strongly dependent on the substitution pattern on the phenol ring, and the protection of LDL against oxidation is assigned to the reduction of the oxoferryl moiety of the hemoprotein to the ferric form.
TL;DR: In this paper, a computer-based method for the optimum design of steel frameworks accounting for the behaviour of semi-rigid connections is described, which explicitly accounts for both connections and members by taking connection stiffnesses and member sizes as continuous-valued and discrete-valued design variables, respectively.
TL;DR: In this article, the problem of a relativistic spin 1/2 particle confined to a one-dimensional box is solved in a way that resembles closely the solution of the well known quantum-mechanical textbook problem of non-relativistic particle in a box.
Abstract: The problem of a relativistic spin 1/2 particle confined to a one-dimensional box is solved in a way that resembles closely the solution of the well known quantum-mechanical textbook problem of a non-relativistic particle in a box. The energy levels and probability density are computed and compared with the non-relativistic case. Resumo. O problema de uma particula de spin 1/2 confinada por uma caixa a uma dimensao e resolvido de uma maneira muito semelhante a da resolucao do problema de uma particula no-relativista numa caixa referido em muitos livros introdutorios de Mecânica Quntâica. Os niveis de energia e a densidade de probabilidade sao calculados e comparados com os valores nao-relativistas.
TL;DR: The first biomimetic oxidations were achieved using the special oxygen donor iodosylbenzene, but cheaper and generally available oxidants such as sodium hypochlorite or hydrogen peroxide are presently used as the oxidants.
Abstract: Work during the last decade laid down the basis for biomimetic oxidation catalysis, which has become an established technique. Preliminary work relied on the use of metal complexes of 5,10,15,20-tetrakisphenylporphyrin (TPP), but these proved to be inadequate to perform the catalytic function. Further, derivatives of TPP with suitable and adequately positioned substituents, allowed the preparation of high performance catalysts, in terms of catalytic efficiency and stability, for some selected oxidations under specific reaction conditions and for a diversity of oxygen donors. The first oxidations were achieved using the ‘special’ oxygen donor iodosylbenzene, but cheaper and generally available oxidants such as sodium hypochlorite or hydrogen peroxide are presently used as the oxidants. Catalysts capable of promoting stereoselective catalysis are reported. Conditions for the efficient use of the catalysts so far reported require particular specificities and the catalytic activity is only shown, in the majority of the reported works, in the presence of selected species to act as axial ligands to the metal ion of the catalyst. Specific porphyrin structures were reported where the addition of a specific axial ligand can be avoided.
TL;DR: In this article, an electrochemical method for the determination of the anticancer platinum drug carboplatin using a DNA-modified electrode was developed, and the electrode was successfully used for the electrochemical determination of carbplatin in serum samples of patients with ovarian cancer undergoing treatment.
Abstract: An electrochemical method for the determination of the anticancer platinum drug carboplatin using a DNA-modified electrode was developed. This electrode was successfully used for the electrochemical determination of carboplatin in serum samples of patients with ovarian cancer undergoing treatment. The electrochemical results clearly demonstrated that, for low concentrations, carboplatin interacts preferentially with adenine rather than guanine groups in the DNA and they can contribute to clarifying the mechanisms of interaction of platinum anticancer drugs with DNA. The pharmacokinetics corm ondIng to the administration of the drug was followed electrochemically and the detection limit in serum samples was 5.7 x 10 M. Due to a similar mechanism of reaction with DNA other platinum anticancer drugs can be determined by this method.
TL;DR: In this paper, a two-dimensional numerical model of coupled fluid flow, heat transfer and rock mechanics in naturally fractured rock is developed, which is applicable to assessments of hot dry rock (HDR) geothermal reservoir characterisation experiments.
TL;DR: Macroinvertebrate communities and environmental variables were assessed seasonally for 1 year in a temporary river in South Portugal receiving an effluent with high conductivity, pH, sulphates, nitrates and low oxygen content to suggest the usefulness of ordination methods in detecting pollution during low flows.
TL;DR: The diffractive bifocal IOL performed well at distance and near, and patients who no longer require spectacles will benefit significantly from a bifOC IOL, but many with an IOL in one eye will need spectacles for the fellow eye.
Abstract: Purpose: To compare a Pharmacia diffractive bifocal intraocular lens (IOL) with a monofocal lens of the same design without the diffractive grating. Setting:. Multicenter study. Methods: This randomized, prospective study comprised 70 patients with a monofocal IOL and 79 with a diffractive bifocal IOL. Follow-up was 5 to 6 months. Near and distance visual acuities, contrast sensitivity, patient satisfaction, and spectacle use were evaluated. Results: All patients achieved a best corrected visual acuity of 0.5 or better; 80% in the monofocal and 71 % in the bifocal group had a best corrected visual acuity of 1.0 or better. Without correction, 93% of the bifocal and 9% of the monofocal group could read J3 or better. With distance correction, 99% and 4%, respectively, could read J3 or better. Contrast sensitivity was slightly lower in the bifocal group at distance and near for all spatial frequencies. In the bifocal group, 46% never used spectacles for near tasks. Overall satisfaction was rated good by 86% of the monofocal and 85% of the bifocal group. Conclusions: The diffractive bifocal IOL performed well at distance and near. Patients who no longer require spectacles will benefit significantly from a bifocal IOL, but many with a bifocal IOL in one eye will require spectacles for the fellow eye.
TL;DR: The results show that the activation of NMDA or AMPA/kainate receptors can cause excitotoxicity in retinal neurons by mechanisms not involving Na+ influx, but rather depending on the permeation of Ca2+ through glutamate receptor-associated channels.
TL;DR: No determinant role for Ca2+ in triggering the process of endonucleolytic cleavage of genomic DNA in these leukemic T-lymphocytes is suggested and a causal relationship between increasedCa2+i and induction of apoptosis could not be clearly established.
25 Jun 1996
TL;DR: The results of injecting physical pin-level faults show that these tests can prevent about 40% of the fail-silent model violations that escape the simple hardware-based error detection techniques.
Abstract: An important research topic deals with the investigation of whether a non-duplicated computer can be made fail-silent, since that behaviour is a-priori assumed in many algorithms. However, previous research has shown that in systems using a simple behaviour based error detection mechanism invisible to the programmer (e.g. memory protection), the percentage of fail-silent violations could be higher than 10%. Since the study of these errors has shown that they were mostly caused by pure data errors, we evaluate the effectiveness of software techniques capable of checking the semantics of the data, such as assertions, to detect these remaining errors. The results of injecting physical pin-level faults show that these tests can prevent about 40% of the fail-silent model violations that escape the simple hardware-based error detection techniques. In order to decouple the intrinsic limitations of the tests used from other factors that might affect its error detection capabilities, we evaluated a special class of software checks known for its high theoretical coverage: algorithm based fault tolerance (ABFT). The analysis of the remaining errors showed that most of them remained undetected due to short range control flow errors. When very simple software-based control flow checking was associated to the semantic tests, the target system, without any dedicated error detection hardware, behaved according to the fail-silent model for about 98% of all the faults injected.
TL;DR: In this paper, a two-dimensional Gaussian distribution of isomer shift and quadrupole splitting was proposed to evaluate the hyperfine parameter distribution in Mossbauer spectra of silicate glasses.
Abstract: A new method is proposed to evaluate the hyperfine parameter distribution in Mossbauer spectra of silicate glasses. The method assumes a distribution of isomer shift and quadrupole splitting with a two-dimensional Gaussian shape. Application of the method to Mossbauer spectra of CaOSiO2FeO glasses containing different redox ratios, Fe3+/Fe2+, is discussed. It is shown that the two-dimensional Gaussian distribution method leads to a very good description of the data with a relatively small number of free parameters.
TL;DR: In this article, the effect of rainfall on the process of wind erosion of beach sands and presents results from both field and wind tunnel experiments, showing that rain significantly increased threshold wind velocities for the initiation of sediment transport and modified vertical sediment profiles.
Abstract: This paper deals with the effect of rainfall on the process of wind erosion of beach sands and presents results from both field and wind tunnel experiments. Although sediment transport by splash is of secondary importance on coastal dunes, splash-saltation processes can move sediments in conditions where no motion is predicted by aeolian processes. The effect of raindrop impact on the movement of soil particles by wind was measured on a sand beach plain using an acoustic sediment sampler. In general, an increase of particle movement by wind at the sensor heights was observed during rainfall. Rainfall also affected the wind erosion process during and after rain by changing the cohesive conditions of the surface. The influence of the surface moisture content on the initiation of wind erosion and on the vertical distribution of transported sand particles was studied in a wind tunnel. Moisture significantly increased threshold wind velocities for the initiation of sediment transport and modified vertical sediment profiles.
TL;DR: In this article, an amperometric detector for end-column detection in capillary electrophoresis is described and the influence of the high voltage on the detection performance is studied.
Abstract: It is well established that particle size and shape substantially influence the bulk properties of powdered materials. Although these characteristics are closely interrelated, the tendency has been to analyse the particle size independently from particle shape. The aim of this work was the assessment of particle shape through particle sizing data. For this purpose, three different particle shape materials - glass beads (spherical), crushed glass (moderately irregular) and mica (lamellar) - were tested, employing four particle sizers. The shape factor selected was the Wadell's sphericity, which was evaluated utilizing distinct equations. The comparison of the results reveals problems arising from the use of approximations rather than more fundamental equations.
TL;DR: The action of cardosin on bovine αs- and β-casein at 30 °C in 50 mM citrate buffer (pH 6.2) was studied in this article.
Abstract: The action of cardosin on bovine αs- and β-casein at 30 °C in 50 mM citrate buffer (pH 6.2) was studied. Peptides were isolated by reversed-phase HPLC on C18 columns and identified from their amino acid composition and N-terminal amino acid sequence. The relative susceptibility of peptide bonds cleaved was Phe23-Phe24 > Trp164-Tyr165 > Tyr166-Val167 > Tyr165-Tyr166 > Phe153-Tyr154 > Phe145-Tyr146 ≈ Leu149-Phe150 ≈ Leu156-Asp157 ≈ Ala163-Trp164 for αs1-casein and Leu192-Tyr193 > Leu191-Leu192 ≈ Leu165-Ser166 > Phe190-Leu191 ≥ Ala189-Phe190 ≈ Leu127-Thr128 for β-casein. In αs2-casein, cardosin cleaved the bonds Phe88-Tyr89 and Tyr95-Leu96. The enzyme shows a clear preference for bonds between hydrophobic, bulky amino acids, cleaving four consecutive peptide bonds in extremely bulky, hydrophobic regions of both αs1-CN (Ala163-Val167) and β-CN (Ala189-Tyr193), which was less attacked by chymosin in various experimental conditions. The active site cleft of cardosin accommodates sequences as bulky as Trp-Tyr-Ty...