Showing papers by "University of Coimbra published in 1982"
TL;DR: This paper presents an algorithm for the shortest path problem, where one objective for any Pareto optimal path can not be improved without worsening the other one and a special set of paths is determined.
216 citations
TL;DR: In this article, analytical potential energy functions which are valid at all dissociation limits have been derived for the ground states of SO2 and O3 in terms of a variational procedure.
Abstract: Analytical potential energy functions which are valid at all dissociation limits have been derived for the ground states of SO2 and O3. The procedure involves minimizing the errors between the observed vibrational spectra and spectra calculated by a variational procedure. Good agreement is obtained between the observed and calculated spectra for both molecules. Comparisons are made between anharmonic force fields, previously determined from the spectral data, and the force fields obtained by differentiating the derived analytical functions at the equilibrium configurations.
84 citations
TL;DR: In this paper, a simple potential model for the evaluation of isotropic pairwise interaction energies is proposed and used to predict the lowest triplet state curve of all alkali-alkali interactions.
Abstract: A simple potential model for the evaluation of isotropic pairwise interaction energies is proposed and used here to predict the lowest triplet state curve of all alkali-alkali interactions. The model, which for the alkali dimers contains no adjustable parameters, expresses the interaction potential in terms of the Hartree-Fock interaction energy, V HF(R), and the interatomic correlation energy as approximated semi-empirically from the second order dispersion energy calculated including the effect of charge overlap between the electron clouds of the two interacting species, V inter/disp(R). Lack of repulsive near Hartree-Fock ab initio results for the triplet state of most alkali dimers has been circumvented by proposing a generalized screened Coulomb type repulsion for these systems. The sum of the additional contributions to the interaction energy [V intra(R) + V intra-inter(R)], which arise from intra-atomic correlation effects and intra-inter coupling terms, is also shown to be well approximated by int...
65 citations
TL;DR: In this paper, a quasiclassical trajectory study of the thermoneutral isotopic oxygen exchange reaction was made using a recently reported potential energy surface for the ground state of ozone.
48 citations
TL;DR: The organophosphorus insecticides, parathion and azinphos, significantly stimulate the Ca 2+ -pump activity of sarcoplasmic reticulum, while malathion has a limited effect and the rates of Ca 2- translocation and ATP hydrolysis are both stimulated and, apparently, theCa 2+ ATP ratio is improved.
38 citations
TL;DR: In this article, the upper limits of the Fano factor × mean energy to make an ion-pair for several non metastable Penning gas mixtures were determined using the proportional scintillation process.
30 citations
01 Jan 1982
TL;DR: Ca2+ is now regarded as the triggering agent of many biological reactions and has attained the status of a second messenger and the action of narcotic drugs in the nervous system is mediated by alterations in the Ca2+ content of the nerve cell.
Abstract: During the last decade, the study of Ca2+ -regulated functions has expanded explosively: Ca2+ is now regarded as the triggering agent of many biological reactions and has attained the status of a second messenger.1,2 The functions of Ca2+ in the nervous system are many. At the cell surface, Ca2+ alters the membrane stability and permeability3–5 and is involved in nerve impulse propagation.4,6–8 On stimulation, there is an increased influx of Ca2+ into the nerve cell which couples excitation to neurotransmitter release.4,9–11 The actions of the neurotransmitters on the postsynaptic membrane may also involve Ca2+ in the sequence of events that leads to the response of the postsynaptic cell.12 It is is now recognized that Ca2+ regulates the activity of enzymes such as adenylate cyclase,13–15 phosphodiesterase,14,15 protein kinases,12,16–18 Ca2+ - ATPases,19,20 and tyrosine hydroxylase,21 among others. Furthermore, the action of narcotic drugs in the nervous system is mediated by alterations in the Ca2+ content of the nerve cell,22–26 and the action of local anesthetics occurs through the displacement of Ca2+. 5,27
29 citations
TL;DR: In this article, the Coulomb and exchange integrals in the London equation were used to obtain semi-empirical valence bond surfaces for the homonuclear alkali trimers.
Abstract: Semi-empirical valence bond surfaces for the homonuclear alkali trimers (M 3) have been obtained by evaluating the Coulomb and exchange integrals in the London equation, respectively, as half the sum and difference of new reliable analytical potential energy curves for the 1Σ g + and 3Σ u + states of the dimers (M 2). Calculations were also carried out using an effective 3Σ u + universal diatomic function which was chosen to reproduce the experimentally known binding energy of Li3. The ground state equilibrium structures of those trimers are predicted to be an obtuse triangle (2 B 2 symmetry) bound with respect to M 2(1Σ g + )+M(2 S) and ordered Li3>Na3>K3>Rb3>Cs3 according to their stabilities. The surfaces are found to be extremely flat with two saddle points, an acute isosceles triangle (2 A 1 symmetry) and a linear symmetric structure (2Σ u + ) lying above but very close to the minimum. The force constants of the 2Σ u + , 2 A 1 and 2 B 2 structures, as well as the fundamental frequencies and zero poin...
27 citations
01 Mar 1982
TL;DR: In this article, changes in the C-H stretching region of the Raman spectra of CTAB (hexadecyltrimethylammonium bromide) in aqueous and chloroform solutions with varying concentration, temperature, and electrolyte additives are interpreted in terms of structural and environmental effects.
Abstract: Changes in the C-H stretching region of the Raman spectra of CTAB (hexadecyltrimethylammonium bromide) in aqueous and chloroform solutions with varying concentration, temperature, and electrolyte additives are interpreted in terms of structural and environmental effects. The results are in agreement with the presence of several gauche rotational isomers of CTAB in the aqueous and chloroform solutions, and with CTAB micellar association of the ordinary type in water and “inverted” micellar association in chloroform.
23 citations
TL;DR: In this paper, the NH, CH and CC stretching regions at 3100-3400 cm−1, 2800-3000 cm −1 and 1000-1150 cm− 1, respectively, and the low-frequency accordion-like vibration region, have been investigated by Raman spectroscopy for the octyl-, nonyl-, dodecyl-, tetradecyl- and hexadecyl normal primary amines series, at different temperatures and for different physical states.
Abstract: The NH, CH and CC stretching regions at 3100-3400 cm−1, 2800-3000 cm−1 and 1000-1150 cm−1, respectively, and the low-frequency accordion-like vibration region, have been investigated by Raman spectroscopy for the octyl-, nonyl-, dodecyl-, tetradecyl- and hexadecyl-normal primary amines series, at different temperatures and for different physical states. The spectra were interpreted in terms of structural changes, particularly of the conformations of the paraffin chains, the chain length and the physical state. The changes in the NH region were associated mainly with molecular association, whereas the changes in the other spectral regions studied were associated mainly with the molecular packing of the chains.
18 citations
TL;DR: In this article, generalized diagonal dominant matrices (GDM matrices) were defined and generalized to general matrices, which improved the known results about the intervals of convergence of the AOR method for linear systems.
Abstract: With the definition of generalized diagonal dominant matrices we improve the known results about the intervals of convergence of the (AOR) method for linear systems. We consider this problem for different kinds of matrices and we get some important results forH-matrices.
01 Aug 1982
TL;DR: In this article, cross sections and rate constants for the systems H + H 2 (ν = 0) and H+ H 2(ν = 1) using a recently published H 3 potential energy surface were reported.
Abstract: Quasiclassical cross sections and rate constants are reported for the systems H + H 2 (ν = 0) and H + H 2 (ν = 1) using a recently published H 3 potential energy surface. The inability of quasiclassical trajectory results to predict a strong preference for the vibrational adiabatic channel ν = 1 → ν′ = 1 over its non-adiabatic counterpart ν = 1 → ν′ = 0 is also examined.
TL;DR: In this paper, the reduced secondary light output from the gas proportional scintillation counter is studied as a function of the reduced electric field E / p for several rare gases and a few of their mixtures.
TL;DR: In this article, the Agar and Turner type of cell was used with its ancillary apparatus, built in this laboratory, developed to improve its precision, for thermal diffusion of polyelectrolytes in aqueous solutions.
TL;DR: In this article, the block eigenvalues of block compound matrices and additive block compound matrix matrices were obtained assuming that a certain block Vandermonde matrix is nonsingular.
TL;DR: One of the patients treated in the Intensive Care Unit was 5 months pregnant, and four months later, she gave birth to a normal child, whose follow-up has shown a normal morpho-physiological and psycho-motor development.
Abstract: During the last decade the number of poisonings by pesticides in Portugal has been steadily rising. Out of 140 patients treated in our Intensive Care Unit (I.C.U.), 86 were male and 54 were female, one of whom was 5 months pregnant. Besides all the care and surveillance required by every case of acute poisoning, pregnant females raise particular problems. Four months later, she gave birth to a normal child. Its follow-up has shown a normal morpho-physiological and psycho-motor development.
TL;DR: In this paper, a conductometric cell was used to measure the resistance of a solution inside the capillaries at recorded times, and the results were discussed on the basis of the Onsager-Fuoss theory.
01 Jan 1982
TL;DR: In this article, the energy transfer between excited rare gas atoms and/or molecules was exploited in order to get suitable cheap fillings for the photoionization proportional scintillation chamber (PIPS).
Abstract: Energy transfer between excited rare gas atoms and/ or molecules to rare gas atoms is exploited in order to get suitable cheap fillings for the photoionization proportional scintillation chamber (PIPS). In particular, variation of the emission with the pressure of both donor and acceptor is studied. Xenon doped argon and krypton doped argon are considered and its behaviour compared to pure argon.
TL;DR: In this paper, the diffusion coefficients of atomic and molecular hydrogen have been calculated from the collision integrals using spherically averaged H-H2 interaction potentials which come from the analysis of recent molecular beam experiments and from accurate ab initio calculations, and differ significantly from those previously used in the transport studies.
Abstract: Binary diffusion coefficients of atomic and molecular hydrogen have been calculated from the collision integrals using spherically averaged H-H2 interaction potentials which come from the analysis of recent molecular beam experiments and from accurate ab initio calculations, and differ significantly from those previously used in the transport studies. The new diffusion data from the various potentials are compared and found to lie between the direct measurements of Khouw et al. and those of Sancier and Wise. Estimates of the viscosity coefficient η12 from the potentials used in the present work are also presented and found to agree best with the early experimental values of Browning and Fox.
TL;DR: A small size low cost 128-256 channels multichannel analyser based on an SDK85 microcomputer board using a minimum of external low cost circuitry and carried out fully by software.
Abstract: We describe a small size low cost 128-256 channels multichannel analyser based on an SDK85 microcomputer board using a minimum of external low cost circuitry. This circuitry consists only of a quad comparator, three operational amplifiers and three integrated analog switches and very few discrete components. The pulse amplitude conversion is carried out fully by software. This software as well as that for data acquisition and output functions is described and results are presented.
TL;DR: In this paper, a number of detailed measurements have been made using an automated scanning proton microbeam on an oxidized and traced (18O) Fe-9%Cr sample along a tapered region, of well known tapering angle, to study the oxidation behaviour of iron-chromium alloys.
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01 Dec 1982TL;DR: In this paper, the main features of a new topology based on the Cartesian product of complete graphs applied to multiexchange networks are presented, together with the performance and cost analysis for a particular district.
Abstract: The main features of a new topology based on the Cartesian product of complete graphs applied to multiexchange networks are presented. A method of modelling a multiexchange digital network at district level in a national hierarchical network using the new topology is given, together with the performance and cost analysis for a particular district. A comparison is then made with a least cost network using conventional design techniques applied to the same district.
06 Apr 1982
TL;DR: A new method is proposed to solve the problem of automatic recursion removal using the unfold/fold methodology based on a technique of dynamic completion of a term rewriting system for the property t = _\varepsilon s Rightarrow t\mathop \to \limits^* _R s.
Abstract: We identify the problem of automatic recursion removal using the unfold/fold methodology (2) to the problem of finding a ɛ-pattern-matcher σ for two terms t and s, i.e.so that σt=ɛs. We propose a new method to solve this equation based on a technique of dynamic completion of a term rewriting system for the property \(t = _\varepsilon s \Rightarrow t\mathop \to \limits^* _R s\). This method presentssome advantages because it enables us to work with incomplete theories and limits the number of superpositions we must do during the process of completion.