Showing papers by "University of Coimbra published in 1993"
TL;DR: In this paper, the intrinsic processes and mechanisms of proton transfer in relation to the nature of the intramolecular hydrogen bond ring are reviewed. But the authors focus on the intrinsic process and not the mechanisms of transfer.
Abstract: Excited-state intramolecular proton transfer reactions are reviewed. Special emphasis is given to the intrinsic processes and to the mechanisms of proton transfers in relation to the nature of the intramolecular hydrogen bond ring.
647 citations
TL;DR: Theoretical models that have been proposed and applied to proton transfer reactions are reviewed in this paper, where simple models, like the Eigen model, Marcus theory and the intersecting state model, are applied to excited-state intermolecular proton transfers.
Abstract: Theoretical models that have been proposed and applied to proton transfer reactions are reviewed in this work. Simple models, like the Eigen model, Marcus theory and the intersecting state model, are applied to excited-state intermolecular proton transfers. The kinetics and thermodynamics of proton transfers occuring in the singlet states of aromatic molecules with OH, NH3+, NH2 and CO substituents are reviewed.
507 citations
TL;DR: An efficient computational implementation of a path deletion K shortest paths algorithm and a new algorithm for the same problem that avoids the last K−1 executions of a shortest path algorithm are presented, resulting in a suprising and very substantial reduction in the execution time.
239 citations
TL;DR: The capacity of G. pulex to tolerate reductions in food quality seems to be a consequence of a compensatory system in which respiration rates change to compensate for reductions inFood quality.
Abstract: An important component of the interaction between macroinvertebrates and leaf litter in streams in the extent to which consumers can differentiate between undecomposed and decomposing leaves. The detritivores Gammarus pulex and Asellus aquaticus fed preferentially on conditioned rather on unconditioned leaf material. Growth in A. aquaticus was significantly reduced when unconditioned leaves were provided, but in G. pulex no significant effect of conditioning on growth was observed. The capacity of G. pulex to tolerate reductions in food quality seems to be a consequence of a compensatory system in which respiration rates change to compensate for reductions in food quality. In this way a constant growth rate is maintained. Increases in ingestion rates to compensate for low quality food were not observed.
167 citations
TL;DR: Fungi appear to be an important food source for A. aquaticus and selection of food material was positively correlated with fungal biomass, and for G. pulex, fungi appear toBe more important as modifiers of leaf material, however, no significant correlations were found between food preference and any of the leaf modifications measured.
Abstract: The importance of fungi in the trophic biology of the freshwater detritivores Gammarus pulex and Asellus aquaticus was investigated. Inspection of leaves used in feeding trials indicated that whereas A. aquaticus scrapes at the leaf surface, G. pulex bites through the leaf material. Both species discriminated between fungal mycelia, fungally colonized and uncolonized leaf material but, although A. aquaticus selectively consumed fungal mycelia, G. pulex fed preferentially on leaf material. Fungi appear to be an important food source for A. aquaticus and selection of food material was positively correlated with fungal biomass. In contrast, for G. pulex, fungi appear to be more important as modifiers of leaf material. However, no significant correlations were found between food preference and any of the leaf modifications measured.
153 citations
TL;DR: Results showed that all BCCs were diffusely and intensely labeled, whereas none of the SCCs expressed Ber EP4, irrespective of their histological type or grade of differentiation.
Abstract: Twenty-two cases of basal-cell carcinoma (BCC) and 21 cases of squamous-cell carcinoma of the skin (SCC) were stained for Ber EP4 using indirect immunofluorescence and avidin-biotin-peroxidase techniques. The results showed that all BCCs were diffusely and intensely labeled, whereas none of the SCCs expressed Ber EP4, irrespective of their histological type or grade of differentiation. This difference may prove useful in (a) histologically differentiating between these two neoplasms; and (b) in clarifying the histogenesis of neoplasms considered to be intermediate between BCC and SCC, or derived from BCC. In addition, because significant differences between the staining of hair follicles and BCC were noted, evaluation for Ber EP4 expression could assist in distinguishing between BCC and hair follicles in Mohs micrographic sections.
117 citations
TL;DR: In this article, a reference study on the subtidal macrofauna in the Mondego Estuary was carried out, in order to characterize the community structure in relation to physicochemical environmental factors.
Abstract: The Mondego Estuary consists of two arms, north and south. The north arm is deeper, while the south arm is largely silted up, which causes the freshwater to flow primarily by the north arm. Human impact is significant, due to harbour activities, salt-works, aquaculture farms, and nutrient and chemical discharge from agricultural areas. From December 1989 to September 1990 a reference study on the subtidal macrofauna was carried out, in order to characterize the community structure in relation to physicochemical environmental factors. The subtidal macrofauna in the Mondego Estuary appears to be clearly impoverished compared to a reference Portuguese estuary, the Mira, which has been much less exposed to human impacts. The south arm macrobenthic community consists mainly of infaunal species and appears to be more stable and structured, presenting a higher macrofauna abundance. The north arm community is mainly characterized by sparse mobile epibenthic species populations, exhibiting a lower biodiversity and an impoverished macrofuna, compared to the south arm. The subtidal communities appear to be physically controlled, with emphasis on the type of sediment, salinity and currents. Biologically, due to their distinct physicochemical characteristics, the two arms of the estuary constitute different subsystems. Dredging takes place twice a year along the north arm, and time intervals between dredging operations appear to be inadequate to allow macrofauna recovery. Although structurally more stable, the south arm community, due to the feeble water circulation, may be more exposed to environmental changes. Benthic monitoring of the Mondego Estuary biological communities is clearly necessary in order to assess temporal trends and to establish if the apparent environmental changes are reversible.
102 citations
TL;DR: Findings confirm the hydrophobic nature of tamoxifen and suggest that the localization and effects of TAM are modulated by the order and fluidity of the bilayer.
91 citations
TL;DR: A detailed Monte Carlo simulation model has been developed to study the absorption of soft x rays and the subsequent behavior of the resulting electrons under the influence of an applied electric field in gaseous xenon.
Abstract: A detailed Monte Carlo simulation model has been developed to study the absorption of soft x rays and the subsequent behavior of the resulting electrons under the influence of an applied electric field in gaseous xenon. All relevant physical processes are included from the initial photoionization through the subsequent decay of the residual ion to the scattering and drift of the electrons resulting from the interactions with the background gas. Details are provided for the cross sections and decay rates employed as well as the criteria used to terminate the simulation, depending on the information or results required. Examples of its use in modeling gaseous radiation detectors are included.
90 citations
TL;DR: A strong correlation between fusion and inactivation rate constants is indicated, suggesting that the rate-limiting step in viral hemagglutinin (HA)-mediated fusion, that is, rearrangement of viral glycoproteins at the contact points with the target membrane, is similar to that involved in fusion inactivation.
Abstract: The fusion of influenza virus (A/PR/8/34 strain) with PC-12 cells was monitored by a fluorescence assay, and the results were analyzed with a mass-action model which could explain and predict the kinetics of fusion. The model accounted explicitly for the reduction in the fusion rate constant upon exposure of the virus to low pH, either for the virus alone in suspension or for the virus bound to the cells. When the pH was lowered without previous viral attachment to cells, an optimal fusion activity was detected at pH 5.2. When the virus was prebound to the cells, however, reduction of pH below 5.2 resulted in enhanced fusion activity at the initial stages. These results were explained by the fact that the rate constants of both fusion and inactivation increased severalfold at pH 4.5 or 4, compared to those at pH 5.2. At pH 5.2, lowering the temperature from 37 to 20 or 4 degrees C resulted in a decrease in the fusion rate constant by more than 30- or 1000-fold, respectively. Inactivation of the virus when preincubated in the absence of target membranes at pH 5 was found to be rapid and extensive at 37 degrees C, but was also detected at 0 degrees C. Our results indicate a strong correlation between fusion and inactivation rate constants, suggesting that the rate-limiting step in viral hemagglutinin (HA)-mediated fusion, that is, rearrangement of viral glycoproteins at the contact points with the target membrane, is similar to that involved in fusion inactivation.
69 citations
TL;DR: The enzymatic hydrolysis of olive oil using Chromobacterium viscosum lipase B encapsulated in reversed micelles of dioctyl sodium sulfosuccinate in isooctane was investigated in an ultrafiltration ceramic membrane reactor of tubular type, operating in a batch mode.
Abstract: The enzymatic hydrolysis of olive oil using Chromobacterium viscosum lipase B encapsulated in reversed micelles of dioctyl sodium sulfosuccinate (AOT) in isooctane was investigated in an ultrafiltration ceramic membrane reactor of tubular type, operating in a batch mode. Water concentration was found to be a critical parameter in the enzyme kinetics and hydrolysis yield of the reaction. The size of micelles, recirculation rate, and substrate concentration were found to be the major factors affecting the separation process. A correlation that enables the prediction of final conversion degrees in this bioreactor from the initial reaction conditions was established.
TL;DR: In this paper, a two-dimensional numerical model for surface waves propagation based on the non-linear dispersive wave approach described by Boussinesq-type equations, which provide an attractive theory for predicting the depth-averaged velocity field resulting from that wave-type propagation in shallow water, is presented.
Abstract: SUMMARY A two-dimensional (in-plane) numerical model for surface waves propagation based on the non-linear dispersive wave approach described by Boussinesq-type equations, which provide an attractive theory for predicting the depth-averaged velocity field resulting from that wave-type propagation in shallow water, is presented. The numerical solution of the corresponding partial differential equations by finite-difference methods has been the subject of several scientific works. In the present work we propose a new approach to the problem: the spatial discretization of the system composed by the Boussinesq equations is made by a finite element method, making use of the weighted residual technique for the solution approach within each element. The model is validated by comparing numerical results with theoretical solutions and with results obtained experimentally.
TL;DR: The genus Ampelisca clearly dominated the group of the most frequent and abundant species, which also exhibited a large range of vertical distribution, and may constitute an important food source for many secondary consumers of the shelf sediments, especially for demersal fishes.
Abstract: The biodiversity and distributional ecology of amphipod crustaceans were analysed from benthic surveys in 1985 and 1986 along the coast of Portugal, from the Tagus canyon to the coast of Minho, in order to determine their role in the ecosystem of the Portuguese continental self. In samples obtained from different types of substrate between 18 and 545 m, we identified 113 species belonging to 51 genera of 24 families. Seventeen of these species were new records for the Portuguese coast. The relative frequencies and number of individuals of all species were analysed. The genus Ampelisca clearly dominated the group of the most frequent and abundant species, which also exhibited a large range of vertical distribution. Most of the 113 species were found only down to 150 m depth, corresponding roughly to the lower limit of the continental shelf. Fifteen species exhibited clear bathyal traits, being consistently found deeper than 100 m, especially in the Tagus canyon and the upper zone of the continental slope. The most frequent and abundant species were found predominatly or in large numbers in medium to fine sand bottoms. This type of substrate also contained the highest number of species. The granulometric structure of the habitat could constitute the most important factor controlling both biodiversity and development of large amphipod populations, since oxygen level, water exchange, number of available shelters, and probably the quantity and quality of nutritional resources all vary as a function of substrate texture. Because of their dominance in both frequency and abundance, several Ampelisca species may constitute an important food source for many secondary consumers of the shelf sediments, especially for demersal fishes.
TL;DR: The effects of hydroxytamoxifen (OHTAM) on lipid organization of pure phospholipid liposomes, native sarcoplasmic reticulum (SR) membranes and liposome of SR lipids were evaluated and it was found that OHTAM distributes preferentially in the outer region of the lipid bilayer, without significant effect in the bulk lipid organizations of the bilayer interior.
TL;DR: This paper presents how the user is enabled to grab objects without using any specific and elaborate hand gesture, which is more intuitive and close to the way humans are used to do, and introduces a technique that makes it possible for the user to surround objects without any force-feedback interaction device.
TL;DR: In this article, a simple, inexpensive, high-performance gas proportional scintillation counter for x-ray spectrometry is described, with an energy resolution of less than 9% for 5.9 keV Mn fluorescent x-rays.
Abstract: A simple, inexpensive, high-performance gas proportional scintillation counter for x-ray spectrometry is described. Energy resolutions below 9% are obtained with detector window diameters of less than 22 mm, for 5.9 keV Mn fluorescent x-rays, even for a small window-to-sample distance where beam collimation is not effective. X-ray fluorescence spectra are presented for biotite, pyrite/chalcopyrite and stainless-steel samples.
TL;DR: A new version of the TRIMAP package, developed for this purpose, integrates an efficient basic primal simplex algorithm specialized to solve pure minimum cost flow problems and new interfaces for displaying each solution in graphical network form.
TL;DR: The effect of glutamate on [Ca2+]i and on [3H] gamma-aminobutyric acid (GABA) release was studied on cultured chick embryonic retina cells, suggesting that the pathway for the entry of Ca2+ triggered by glutamate does not lead to exocytosis.
TL;DR: The results suggest a possible relationship between a reduced calcium movement across the membrane, the decrease in neurotransmitters uptake and release and oxidative stress.
TL;DR: In this paper, a two-dimensional numerical model was proposed to solve the generalised Serre equations in the conservative form using an explicit finite-difference method based on the MacCormack time splitting scheme.
Abstract: This paper describes a two-dimensional numerical model to solve the generalised Serre equations. In order to solve the system of equations, written in the conservative form, we use an explicit finite-difference method based on the MacCormack time-splitting scheme. The numerical method and the computational model are validated by comparing one-and two-dimensional numerical solutions with theoretical and experimental results. Finally, the two-dimensional model (in a horizontal plane) is tested in a domain with complicated boundary conditions.
TL;DR: In this article, the authors explore the physics of self-compression for spherical clusters of simple-metal atoms, using the stabilized jellium model, and show that selfcompression also renormalizes the effective curvature-energy coefficient, and contributes to the asymptotic (large-radius) size effect on the ionization energy.
TL;DR: This chapter describes LIS methodologies and their application to study proteins in solution as well as their applications as NMR structural probes in aqueous solutions, particularly for biological systems including peptides and proteins.
Abstract: Publisher Summary The first report by Hinckley more than 20 years ago of the use of lanthanide complexes to simplify unresolved proton resonances in low-field nuclear magnetic resonance (NMR) spectra marked the start of the application of the lanthanide-induced shift (LIS) method to a variety of NMR problems. A year later, Morallee et al. presented that the line broadenings induced by the gadolinium(III)-lysozyme complex in the proton resonances of fl-methyl-N-acetylglucosamine could be analyzed in terms of the absolute distance between the Gd(III) ion and various sugar protons. These observations stimulated much interest and activity in the use oflanthanides as NMR shift and relaxation reagents, in applications ranging from qualitative spectral simplification, proof of molecular stereochemistry, and quantitative analysis of dynamic solution structures to the most recent applications in NMR spectroscopy of perfused cells, organs, and intact animals and magnetic resonance imaging (MRI). This chapter describes LIS methodologies and their application to study proteins in solution. The qualitative uses of lanthanides to simplify complex NMR spectra are not mentioned because highfield magnets and two- and three-dimensional methods have eliminated the need for LIS measurements for this purpose. The use of lanthanides as shift and relaxation reagents in organic solutions has been reviewed extensively, as well as well as their applications as NMR structural probes in aqueous solutions, particularly for biological systems including peptides and proteins.
TL;DR: In general, Legionella spp were isolated in higher numbers from biofilms than from water, although one biofilm with a temperature of 50°C, did not yield isolates of these organisms.
TL;DR: It is proposed that the burst in glucose-stimulated pancreatic β-cells is mediated by a distinct Ca2+-dependent K+ channel and/or by [Ca2+]idependent slow processes of inactivation of Ca1+ currents.
Abstract: In glucose-stimulated pancreatic beta-cells, the membrane potential alternates between a hyperpolarized silent phase and a depolarized phase with Ca2+ action potentials. The molecular and ionic mechanisms underlying these bursts of electrical activity remain unknown. We have observed that 10.2-12.8 mM Ca2+, 1 microM Bay K 8644 and 2 mM tetraethylammonium (TEA) trigger bursts of electrical activity and oscillations of intracellular free Ca2+ concentration ([Ca2+]i) in the presence of 100 microM tolbutamide. The [Ca2+]i was monitored from single islets of Langerhans using fura-2 microfluorescence techniques. Both the high-Ca(2+)- and Bay-K-8644-evoked [Ca2+]i oscillations overshot the [Ca2+]i recorded in tolbutamide. Nifedipine (10-20 microM) caused an immediate membrane hyperpolarization, which was followed by a slow depolarization to a level close to the burst active phase potential. The latter depolarization was accompanied by suppression of spiking activity. Exposure to high Ca2+ in the presence of nifedipine caused a steady depolarization of approximately 8 mV. Ionomycin (10 microM) caused membrane hyperpolarization in the presence of 7.7 mM Ca2+, which was not abolished by nifedipine. Charybdotoxin (CTX, 40-80 nM), TEA (2 mM) and quinine (200 microM) did not suppress the high-Ca(2+)-evoked bursts. It is concluded that: (1) the channel underlying the burst is sensitive to [Ca2+]i rises mediated by Ca2+ influx through L-type Ca2+ channels, (2) both the ATP-dependent K+ channel and the CTX- and TEA-sensitive Ca(2+)-dependent K+ channel are highly unlikely to provide the pacemaker current underlying the burst.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: In this article, the Raman spectra of aqueous vanadium (V) solutions at different pH values, ranging from 13.1 to 7.0, are presented, and the dominant bands in the range 700-1100 cm −1 are assigned to the VO symmetrical stretching of the different oligomers, using additional information from 51 V NMR spectra and empirical models.
Abstract: The Raman spectra of aqueous vanadium(V) solutions at different pH values, ranging from 13.1 to 7.0, are presented. The dominant bands in the range 700-1100 cm −1 are assigned to the VO symmetrical stretching of the different oligomers, using additional information from 51 V NMR spectra and empirical models. The effects of pH, concentration and ionic strength on the oligomerization equilibria are discussed. The ionic strength is found to affect significantly the oligomer composition of vanadate solutions, which is of interest in biochemical and biological studies
TL;DR: In this paper, essential oils were obtained from the dried fruit of Foeniculum vulgare Miller subsp. piperitum (Ucria) Coutinho collected from various locations in central Portugal.
Abstract: Essential oils were obtained from the dried fruit of Foeniculum vulgare Miller subsp. piperitum (Ucria) Coutinho collected from various locations in central Portugal. Gas chromatographic analysis of the oils revealed that the major components, fenchone (6.8–30.8%), methyl chavicol (2.6–36.3%) and (E)-anethole (44.2–74.0%), varied widely. No relationship between component concentrations and fruit ripeness was found. Based on the variation in oil composition between the various taxa, the existence of three chemotypes is proposed.
TL;DR: In this article, the influence of tin on the formation of the σ-phase, caused by an isothermal annealing at 700°C, in FeCr alloys with near equiatomic compositions was studied by means of 57Fe and 119Sn Mossbauer spectroscopy.
Abstract: The influence of tin on the formation of the σ-phase, caused by an isothermal annealing at 700°C, in FeCr alloys with near equiatomic compositions was studied by means of 57Fe and 119Sn Mossbauer spectroscopy. It was shown that the addition of up to 5.5 at% Sn to the FeCr alloys retards the formation of the o-phase significantly. The kinetics of the transformation follows the Johnson-Mehl equation. The evidence was found that tin precipitates on the grain boundaries if its nominal concentration exceeds ≈ 2 at%. For a given nominal concentration of added tin the size of grains was found to be the same in the α and σ-phases, but it was smaller for samples with higher Sn content. The composition of the σ-phase remains constant at a value of 46.7 at% Cr and 1.4 at% Sn, regardless of the nominal tin content.
L'influence de l'etain dans la formation de la phase σ provoquee par un recuit isothermique a 700°C, a ete etudiee pour les alliages FeCr avec des compositions presque equiatomiques par spectroscopie Mossbauer du 57Fe et du 119Sn. On a verife que l'addition d'etain jusqu'a 5,5 at% aux alliages FeCr retarde significativement la formation de la phase σ. La cinetique de la transformation suit l'equation de Johnson-Mehl. On a aussi observe que l'etain precipite sur les joins de grains quand sa composition nominale est superieure a 2 at%. Pour chaque concentration nominale d'etain additional, les grains gardent la taille dans les deux phases: α et σ, cependant leur taille diminue quand la concentration d'etain augmente. On a aussi verifie que la composition de la phase σ est toujours 46,7 at% Cr et 1,4 at% Sn, quel que soit la concentration nominale d'etain.
TL;DR: The results indicate that FTX blocks dihydropyridine‐ and ω‐conotoxin‐insensitive Ca2+ channels that, together with L‐type voltage‐sensitive Ca 2+ channels, are coupled to catecholamine release.
Abstract: In adrenal chromaffin cells, depolarization-evoked Ca2+ influx and catecholamine release are partially blocked by blockers of L-type voltage-sensitive Ca2+ channels We have now evaluated the sensitivity of the dihydropyridine-resistant components of Ca2+ influx and catecholamine release to a toxin fraction (FTX) from the funnel-web spider poison, which is known to block P-type channels in mammalian neurons FTX (1:4,000 dilution, with respect to the original fraction) inhibited K(+)-depolarization-induced Ca2+ influx by 50%, as monitored with fura-2, whereas nitrendipine (01-1 microM) and FTX (3:3), a synthetic FTX analogue (1 mM), blocked the [Ca2+]i transients by 35 and 30%, respectively When tested together, FTX and nitrendipine reduced the [Ca2+]i transients by 70% FTX or nitrendipine reduced adrenaline and noradrenaline release by approximately 80 and 70%, respectively, but both substances together abolished the K(+)-evoked catecholamine release, as measured by HPLC The omega-conotoxin GVIA (05 microM) was without effect on K(+)-stimulated 45Ca2+ uptake Our results indicate that FTX blocks dihydropyridine- and omega-conotoxin-insensitive Ca2+ channels that, together with L-type voltage-sensitive Ca2+ channels, are coupled to catecholamine release
TL;DR: In order to provide a tool for biogeographical comparisons, the available data on the Azores amphipod fauna were compiled and a review of the available literature and the study of several collections from theAzores provided a list of 122 species from 29 families.
Abstract: The Azores archipelago, located in the middle north Atlantic region, is biogeographically very interesting. With regard to the benthic amphipod fauna there are only few studies that concern the Azores, although species inventory and distributional ecology are relatively well known for the Portuguese continental coast (0 to 700 m). Actually, the knowledge of benthic amphipods from the Azores is limited to the results of two oceanographical expeditions, that took place in the first half of this century, and to data provided by some relatively recent papers and several other sporadic references. Moreover, this knowledge is mainly or exclusively taxonomic. Benthic amphipod dispersal capability is small compared to that of molluscs, decapods or fishes. They have direct development and a reduced swimming capability, and their migrations, both nictemeral and horizontal, cannot compensate these features. This limited dispersal capability determines a clear endemic tendency, and a reduced probability of global fauna mixtures. Therefore, amphipods constitute a fine biological material for biogeographic studies. In order to provide a tool for biogeographical comparisons, the available data on the Azores amphipod fauna were compiled. A review of the available literature and the study of several collections from the Azores, sampled during 1988 and 1989 at the islands of S. Miguel and Faial, provided a list of 122 species from 29 families. Thirty species were identified from the study of the S. Miguel and Faial collections, of which 15 (50%) are new records for the Azores, which emphasizes the existing lack of knowledge. One Ampithoe species might be new, and will be further studied, although it will be necessary to collect more specimens. Additionally, some available ecological data for each species arc given in the present paper.
TL;DR: A modem re-assessment is given of the taxonomy and nomenclature of the 8(-9) annual taxa within the mainly Mediterranean/SW Asiatic Bromus L. sect.
Abstract: A modem re-assessment is given of the taxonomy and nomenclature of the 8(-9) annual taxa within the mainly Mediterranean/SW Asiatic Bromus L. sect. Genea Dum. (Poaceae): B. diandrus Roth var. diandrus, B. diandrus var. rigidus Roth, B. fasciculatus Presl, B. madritensis L., B. rubens L., B. sterilis L., B. tectorum L. subsp. tectorum and B. tectorum subsp. lucidus Sales; less emphasis is given to B. madritensis and B. rubens. None of these taxa has previously been investigated throughout their total areas and the taxonomic conclusions expressed here are a result of a multidisciplinary approach. For reasons of convenience the species are considered in three informal groups based on overall similarities: i, B. sterilis, B. diandrus and B. rigidus, so often recognized as independent species in recent Floras but here regarded as varieties of one species; ii, B. madritensis, B. rubens and B. fasciculatus, with particular attention given to B. fasciculatus; and iii, B. tectorum subsp. tectorum and subsp. lucidus, previously regarded as independent species.