Showing papers by "University of Coimbra published in 1988"
01 Aug 1988
TL;DR: A doze anos do final decade of the século XX as mentioned in this paper, a primeira imagem is that the progressos científicos dos últimos trinta anos são de tal ordem dramáticos.
Abstract: Estamos a doze anos do final do século XX. Vivemos num tempo atônito que ao debruçar-se sobre si próprio descobre que os seus pés são um cruzamento de sombras, sombras que vêm do passado que ora pensamos já não sermos, ora pensamos não termos ainda deixado de ser, sombras que vêm do futuro que ora pensamos já sermos, ora pensamos nunca virmos a ser. Quando, ao procurarmos analisar a situação presente das ciências no seu conjunto, olhamos para o passado a primeira imagem é talvez a de que os progressos científicos dos últimos trinta anos são de tal ordem dramáticos que os séculos que nos precederam — desde o século XVI, onde todos nós, cientistas modernos, nascemos, até ao próprio século XIX — não são mais que uma pré-história longínqua. Mas se fecharmos os olhos e os voltarmos a abrir, verificamos com surpresa que os grandes cientistas que estabeleceram e mapearam o campo teórico em que ainda hoje nos movemos viveram ou trabalharam entre o século XVIII e os primeiros vinte anos do século XX, de Adam Smith e Ricardo a Lavoisier e Darwin, de Marx e Durkheim a Max Weber e Pareto, de Humboldt e Planck a Poincaré e Einstein. E de tal modo é assim que é possível dizer que em termos científicos vivemos ainda no século XIX e que o século XX ainda não começou, nem talvez comece antes de terminar. E se, em vez de no passado, centrarmos o nosso olhar no futuro, do mesmo modo duas imagens contraditórias nos ocorrem alternadamente. Por um lado, as potencialidades da tradução tecnológica dos conhecimentos acumulados fazem-nos crer no limiar de uma sociedade de comunicação e interativa libertada das carências e inseguranças que ainda hoje compõem os dias de muitos de nós: o século XXI a começar antes de começar. Por outro lado, uma reflexão cada vez mais aprofundada sobre os limites do rigor científico combinada com os perigos cada vez mais verossímeis da catástrofe ecológica ou da guerra nuclear fazem-nos temer que o século XXI termine antes de começar.
155 citations
TL;DR: In this article, a generalized hedgehog baryon is projected onto states with good spin and isospin and noticeable deviations from the simple hedgehog form occur (η ≅ 20°), if the relevant degrees of freedom of the wave functions are varied after the projection.
44 citations
TL;DR: The problem of accessibility and controllability of certain bilinear systems is considered, and the root structure of elements in a Lie algebra is related to the nodal connection graphs obtained from their standard matrix representations to weaken the requirement that the controlled vector field is strongly regular.
Abstract: We consider the problem of accessibility and controllability of certain bilinear systems. These evolve on Lie groups whose Lie algebras are the normal real forms of complex simple Lie algebras. Previous results by other authors were obtained under the assumption that the controlled vector field is strongly regular. Our paper is aimed at weakening this requirement, and involves relating the root structure of elements in a Lie algebra as above to the nodal connection graphs obtained from their standard matrix representations. This is in turn related to a standard irreducibility assumption on the uncontrolled vector field. The abstract results on generation of Lie algebras are of some independent interest.
39 citations
TL;DR: In this article, the energy and yields of K-series X-rays from pd atoms were measured with two gas scintillation proportional detectors at target gas densities of 0.25 and 0.92 ρ STP.
38 citations
TL;DR: In this article, the effect of porous wind breakers over a row of coal piles is studied in a wind tunnel. But the results of these experiments were limited to two dimensional configurations and were not extended to tridimensional models.
37 citations
TL;DR: A review of the double many-body expansion of molecular potential energy functions and the role of long-range forces in the rates of chemical reactions is given in this paper, where the O+OH→O2+H and H+H2→H 2+H reactions are discussed.
Abstract: A review is given of the double many-body expansion (DMBE) of molecular potential energy functions and of the role of long-range forces - these being properly described in the DMBE - in the rates of chemical reactions. The O+OH→O2+H and H+H2→H2+H reactions are discussed. New thermal rate coefficients for the former reaction are also reported from the assumption of loose transition states.
37 citations
TL;DR: In this article, the angular momentum and isospin projected mean field solutions are determined variationally assuming valence quarks and pions in generalized hedgehog configurations, with the proper pion decay constant and after fitting the quark-meson coupling constant to the nucleon energy both proton and neutron charge form factors are reproduced as well as the slope of the magnetic ones.
33 citations
TL;DR: Comparison of the behavior of the free with the immobilized enzyme showed that satisfactory yields were obtained and the immobilization system has an extended pH profile and good stability and thus would have broad applicability.
Abstract: A study of the immobilization of trypsin and other enzymes onto hydrolyzed poly(2-hydroxyethyl methacrylate)-g-co-polyethylene using hydroxyl and carboxyl activating agents has been undertaken. Some emphasis was placed on the immobilized trypsin system which involved examination of the variation of (i) the extent of hydrolysis of the graft copolymer, (ii) the concentration of activating agent, and (iii) the temperature of coupling. With the trypsin system, an increase in carbodi-imide concentration gave an increase in the amount of protein immobilized but a marked decrease in the retention of enzymic activity. Comparison of the behavior of the free with the immobilized enzyme showed that satisfactory yields were obtained and the immobilized system has an extended pH profile and good stability and thus would have broad applicability. The kinetic factors were examined further, and the role of the graft copolymer chains in the immobilized system is discussed.
29 citations
TL;DR: In this paper, a necessary and sufficient condition on the vectors x1,…,xm is given for x1∗∗xm to be zero, where x1 is a decomposable symmetrized tensor corresponding to the symmetric group Sm.
26 citations
TL;DR: In this paper, an asymptotic behavior and a control of deposition by adhesion and growth phenomena were studied at two different velocities and pH values of 7 and 9.
Abstract: Biofilm adhesion to metals (copper, aluminium and brass) was studied at two different velocities and pH values of 7 and 9. Both bacteria and metals showed negative surface charges at those values of pH, which tends to slow down adhesion. Film densities increased with the fluid velocity and were also affected by the pH and by the growth rate of the bacteria. Long duration tests based on heat transfer measurements were run at five different fluid velocities and at pH = 7, showing in general an asymptotic behaviour and a control of deposition by adhesion and growth phenomena.
On a etudie l'adhesion de films biologiques sur des metaux (cuivre, aluminium et laiton) a differentes vitesses et pour des pH de 7 et 9. Les charges de surface negatives des metaux et des bacteries, obtenues pour ces valeurs de pH, tendent a ralentir l'adhesion. La densite des films augmente avec la vitesse du fluide et est modifiee par le pH ainsi que par la vitesse de croissance des bacteries. Des tests de longue duree utilisant des mesures de transfert de chaleur ont ete effectues pour cinq vitesses de fluide differentes a un pH de 7, montrant un comportement asymptotique ainsi qu'un controle du depot par la croissance et l'adhesion; en outre, la deposition est contro1ee par l'adheion.
26 citations
TL;DR: In this article, a number of even chain length lead(II) carboxylates (soaps) at various temperatures are reported, and they all form a highly ordered smectic phase, which gives a very broad 207Pb signal of linewidth comparable to that of the solid phase.
Abstract: 207Pb N.M.R. data are reported for a number of even chain length lead(II) carboxylates (soaps) at various temperatures. At room temperature, the solid lead(II) decanoate and tetradecanoate show similar spectra, with a single metal ion site, and modest shielding anisotropy. As the temperature is increased, the soaps (hexanoate to octadecanoate) all form a highly ordered smectic phase, which gives a very broad 207Pb signal of linewidth comparable to that of the solid phase. At higher temperatures, the hexanoate to dodecanoate soaps form a lamellar L α (smectic A) phase, whilst the longer chain length carboxylates melt directly to the liquid phase. Both the lamellar L α and liquid phase give fairly sharp, isotropic signals, whose chemical shifts and linewidths are strongly temperature dependent. Possible explanations for this effect include paramagnetic contributions to the shielding tensor from low-lying electronic states of Pb(II), and contributions to the observed signal from different coordinati...
TL;DR: The linear chiral sigma model with quark fields and elementary pion and sigma fields is used to describe static properties of the nucleon and the ..delta.. resonance and baryon Fock states with good spin and isospin are constructed.
Abstract: The linear chiral \ensuremath{\sigma} model with quark fields and elementary pion and \ensuremath{\sigma} fields is used to describe static properties of the nucleon and the \ensuremath{\Delta} resonance. To this end baryon Fock states with good spin and isospin are constructed from summations of components in which three quarks in s states with the SU(2)\ifmmode\times\else\texttimes\fi{}SU(2) quantum numbers of the nucleon and \ensuremath{\Delta} are coupled to multipion states and a scalar-isoscalar coherent state of the \ensuremath{\sigma} fields. The multipion states are constructed to have coherent properties as well as definite spin-isospin quantum numbers. Ignoring the effects of vacuum polarization the baryon energy is made stationary, resulting in a set of four coupled nonlinear eigenvalue equations and a diagonalization procedure between frozen fields. The corresponding solitonic solutions are used to evaluate the relevant nucleon properties. A comparison is made with the results from the cloudy-bag model, the projected mean-field chiral-soliton model, and the Skyrme approach.
TL;DR: The results suggest that the interaction of the receptor with the G-proteins, induced or stabilized by the binding of agonist, leads to an increase in entropy and to negative heat capacity changes in the system.
TL;DR: The shift in charge microheterogeneity of basic protein to the less cationic isomers in the less compact myelin fractions correlated with an increase in protein kinase activity and a greater specific activity of phosphorylated basic protein.
Abstract: Fractions containing myelin of varying degrees of compaction were prepared from human white matter. Protein kinase activity in these fractions was measured by using both endogenous and exogenous myelin basic protein (MBP) as substrates. In both cases, less compact myelin fractions possessed higher levels of protein kinase activity than the compact myelin fraction. In addition, the specific activity of phosphorylated basic protein was greater in the loosely compacted fractions than in compact multilamellar myelin. When basic protein in compact myelin or the myelin fractions was phosphorylated by the endogenous kinase, approximately 70% of the ({sup 32}P)phosphate was incorporated at a single site, identified as Ser-102. The remaining 30% was found in three other minor sites. Electron microscopy of less compact myelin showed it was composed of fewer lamellae which correlated with a relative decrease in the proportion of cationic charge isomers (microheteromers) when MBP was subjected to gel electrophoresis at alkaline pH. The shift in charge microheterogeneity of basic protein to the less cationic isomers in the less compact myelin fractions correlated with an increase in protein kinase activity and a greater specific activity of phosphorylated basic protein.
TL;DR: A number of well-known mathematical programming problems are reformulated as members of this family of four complementarity problems, including quadratic programming, linear variational inequalities, bilinear programming, game theory, and zero-one integer programming.
Abstract: A family of complementarity problems is defined as extensions of the well-known linear complementarity problem (LCP). These are:
A number of well-known mathematical programming problems [namely, quadratic programming (convex, nonconvex, pseudoconvex, nonconvex), linear variational inequalities, bilinear programming, game theory, zero-one integer programming, fixed-charge problem, absolute value programming, variable separable programming] are reformulated as members of this family of four complementarity problems. A brief discussion of the main algorithms for these four problems is presented, together with some computational experience.
TL;DR: The histological examination of these proembryogenic structures suggested that somatic embryos arise from single cells, and the potential for plantlet regeneration has been maintained for over a year.
Abstract: Callus cultures with globular proembryogenic structures were induced from zygotic embryos and hypocotyl segments of Cyphomandra betacea on MS medium supplemented with 2,4-D. Proembryogenic structures produced somatic embryos and plantlets on regulator-free basal medium. Pieces of embryogenic callus subcultured on medium with the same original composition gave rise to new globular structures and the potential for plantlet regeneration has been maintained for over a year. The histological examination of these proembryogenic structures suggested that somatic embryos arise from single cells. Regenerated plants are phenotypically normal, having diploid chromosome numbers (2n = 24).
TL;DR: The applicability of enumerative tree-search methods for general LCPs (without any assumption on the class of the matrix) and the numerical results presented in this paper show that it is worthwhile to use them for general medium scale sparse L CPs.
TL;DR: This algorithm either finds all the solutions of any general LCP (that is, no assumption is made concerning the class of the matrix), or it establishes that no such solution exists.
TL;DR: In this article, the Bueckner weight function was used for computing the stress intensity factor using a 2D finite element program, and the results showed that plate length has little or negligible influence on fatigue strength provided that the plate length to thickness ratio is below 20 to 50 depending on the plate thickness.
TL;DR: In this article, a proton, carbon-13 and vanadium51 NMR study has shown that vanadium(V) forms one complex with (D)-tartaric acid, in aqueous solution (pH range 3.0-7.5), having composition 2:1 (presumably a 4:2 species) and involving the ligand in a tetradentate symmetrical fashion.
TL;DR: In this article, the aldoses D-mannose, D-lyxose and D-ribose from tridentate complexes with Mo(VI) and W(VI), at pH ≃ 5, via the 1,2,3-hydroxyl groups, which are cis to each other in these sugars.
Abstract: Proton, 13C and 31P nuclear magnetic resonance spectroscopy has been used to study the complexation of M(VI), W(VI) and U(VI) oxocations with various aldoses, cyclic polyols and ribose-5-phosphate in aqueous solution. The aldoses D-mannose, D-lyxose and D-ribose from tridentate complexes with Mo(VI) and W(VI) at pH ≃ 5, via the 1,2,3-hydroxyl groups, which are cis to each other in these sugars. Other aldoe, like D-arabinose, D-glucos, D-xylose and D-galactose from weaker bidentate complexs with those ions because they can onl use the 1 and 3-cis hydroxyl groups in metal binding. These bidentate interactions also take place in the binding of U(VI) to D-ribose, at pH ≃ 110. However, sugars having 1,3,5-hydroxyl groups in the cis position do not from stable chelates with these oxocations, possibly due to steric crowding. In the case of ribose-5-phosphate, the phosphate group is the exclusive binding site for the three oxocations. except for U(VI) at ver basic pH(pH > 10), where the hdroxyl groups al...
TL;DR: In this paper, a detailed investigation of the electrochemical kinetics of dioxygen reduction on thin films of platinum phthalocyanine is reported, and it has been found that the initial behaviour of the films is affected profoundly by the method of preparation, but that after potential cycling and/or lengthy exposure to air all the films investigated become highly active.
01 Oct 1988
TL;DR: In this article, a transicação de modernidade, e desintegracao da ideia moderna de uma racionalidade abrangente em inumeras mini-racionalidades, is examined.
Abstract: O paradigma cultural da modernidade esta em vias de extinguir-se, sustenta o autor, para em seguida examinar esse processo de transicao, denominado "pos-modernidade" a falta de melhor termo. Um aspecto central dessa transicao, que o autor examina, e o da desintegracao da ideia moderna de uma racionalidade abrangente em inumeras mini-racionalidades. Conclui-se que so no plano "local" pode-se fazer frente a irracionalidade "global".
TL;DR: In this article, it was shown that the thin films of platinum phthalocyanine evaporated onto gold-coated pyrolytic graphite have been remarkably active as four-electron reductants for oxygen.
TL;DR: In this article, the influence of the presence of a plane boundary on drag and lift coefficients, and on both local and global Nusselt numbers, was examined, and it was found that the formation of closed recirculation regions upstream and downstream of the cylinder is responsible for the occurrence of small values of the local heat transfer coefficient.
TL;DR: In this paper, a class of normal matrices satisfying the inclusion { det (A+UBU ∗ ):U∈μ n } ⊆ Co { ∏n i=1 (α i +β σ(i) :σ∈ S n }, where Co{} is the convex hull of {} and S n is the symmetric group of degree n, is obtained.
TL;DR: In this article, the emission spectrum of lead(II) decanoate at 77 K is reported, and shows a maximum at 420 nm. And the maximum in the excitation spectrum of this at 258 nm corresponds fairly closely to the lowest-energy band in the absorption spectrum of a lead (II)decanoate film, and is assigned to the 6 s 6 p ← 6 s 2 transition.
01 Jan 1988
TL;DR: Synaptosomes, the subcellular fraction of brain homogenates rich in presynaptic nerve terminals, possess the principal functional features of intact neurons.
Abstract: Synaptosomes, the subcellular fraction of brain homogenates rich in presynaptic nerve terminals (Gray and Whittaker 1962; De Robertis 1962; Whittaker et al 1964; Whittaker 1965; Bradford 1969), possess the principal functional features of intact neurons: maintenance of membrane potential (Bradford 1971; Blaustein and Goldring 1975; Coutinho et al 1984), neurotransmitter uptake and release (Blaustein 1975; Raiteri and Levi 1978), depolarization dependent Ca2+ entry (Nachshen and Blaustein 1980; Blaustein 1975) and Na+/Ca2+ exchange (Blaustein 1974; Blaustein and Osborn 1975; Blaustein and Ector 1976; Carvalho 1982; Coutinho et al 1983, 1984).
TL;DR: In this paper, the convergence conditions for the AOR method with strictly diagonally dominant matrices were given. But the convergence region was not extended to the case where the matrix A is a nonsingular H-matrix.