Showing papers by "Instituto Superior Técnico published in 1986"

Standard Reference Data for the Thermal Conductivity of Liquids

Abstract: The available experimental liquid‐phase thermal conductivity data for water, toluene, and n‐heptane have been examined with the intention of establishing standard reference values along the saturation line. The quality of available data is such that for toluene and water new standard reference values can be proposed with confidence limits better than ±1.0% for most of the normal liquid range. For n‐heptane there are insufficient reliable experimental data for the system to be treated as a primary reference standard, so a lower quality correlation has been developed which yields a set of secondary reference data with confidence limits of ±1.5% for most of the normal liquid range.

Digital pulse position modulation over optical fibres with avalanche photodiode receivers

Abstract: The question of performance evaluation in digital pulse position modulation (PPM) transmitted over slightly dispersive optical fibres and detected by avalanche photodiodes (APD) is considered. In view of numerical complexity implicit in exact average error probability evaluation, a bound on this probability is derived. Making use of this bound we conclude that optical fibre PPM receivers based on APDs offer some improvement over optical fibre PPM receivers based on PINFETs and a big improvement when compared with PCM receivers.

Thermal conductivity of argon in the temperature range 107 to 423 K

Abstract: The thermal conductivity of argon between 107 and 425 K has been measured in a transient hot-wire instrument. The results in the limit zero density have been employed to assess the accuracy of the instrument using exact kinetic theory expressions and has been found to be better than ±0.5%. The data at elevated densities are employed to examine the applicability of the modified Enskog theory in the gaseous phase and the hard-sphere theory in the liquid phase.

Wave Propagation in Polyphase Transmission Lines a General Solution to Include Cases Where Ordinary Modal Theory Fails

Abstract: The solution of transmission line equations is usually written as a superposition of so called natural modes of exponential type. These are obtained through the use of a suitable transformation that decouples the original sets or N simultaneous 2nd order wave equations for voltages and currents into N independent equations. For such a transformation to exist the fundamental product matrix ZY must be diagonalizable. In a previous paper it has been shown that physically realizable transmission lines are possible for which ZY is not diagonalizable and to which ordinary modal theory does not apply. In the present paper a new generalized modal theory is developed for the purpose of including non-diagonalizing cases.

Callus and suspension culture ofSilybum marianum. Biosynthesis of proteins with clotting activity

Abstract: Silybum marianum plants contain a proteinase with clotting activity which is used for the production of soft cheese. The influence of the concentrations of phytohormones (2,4-D and kinetin), of aminoacids and sucrose on the growth rate and intracellular protein content of calli and suspension cultures was studied. The clotting: proteolytic activity ratio was compared with that of a microbial rennet.

Flash photolysis and pulse radiolysis of the Co(sep)3+-X- (sep = sepulchrate; X = I, Br) systems in aqueous solution

Abstract: The Co(sep)/sup 3 +/ complex (sep = sepulchrate = 1,3,6,8,10,13,16,19-octaazabicyclo(6.6.6)eicosane) in aqueous solution forms ion pairs with the I/sup -/ and Br/sup -/ anions, which exhibit a relatively intense charge-transfer absorption. In deoxygenated aqueous solution no net reaction is obtained upon continuous light excitation in the ion-pair charge-transfer bands, but formation of transient species is observed in flash photolysis experiments. For the Co(sep)/sup 3 +/-I/sup -/ system, I/sub 2//sup -/ ions are formed that decay in the 50-..mu..s time scale to give I/sub 3//sup -/. The latter species disappears in a time scale of seconds, leading the system back to the preexcitation conditions. For the Co(sep)/sup 3 +/-Br/sup -/ system, only formation of the Br/sub 2//sup -/ transient is observed, followed by regeneration of the preexcitation conditions in the 20-..mu..s time scale. In order to elucidate the kinetic aspects of the transient formation and disappearance, pulse radiolysis experiments on the Co(sep)/sup 3 +/-I/sup -/ and Co(sep)/sup 3 +/-Br/sup -/ systems have been carried out. The rate constants of the reactions of Co(sep)/sup 2 +/ with I/sub 2//sup -/, I/sub 3//sup -/, and Br/sub 2//sup -/ have been measured, and a complete picture of the redox processes that follow flash photolysismore » and pulse radiolysis excitations has been obtained. 5 figures.« less

On a Systematic Approach to some Properties of Special Functions

Abstract: On peut montrer que plusieurs fonctions speciales importantes peuvent s'exprimer comme des derivees d'ordre complexe de fonctions elementaires

Purification and characterization of three proteins from a halophilic sulfate-reducing bacterium, Desulfovibrio salexigens

Abstract: Hydrogenase, desulfoviridin and molybdenum proteins have been isolated from a halophilic sulfate-reducing bacteria,Desulfovibrio salexigens strain British Guiana. At least 50% of the hydrogenase was found to be located in the periplasm. The hydrogenase has a typical absorption spectrum, a 400/280 nm ratio of 0.28, a molecular weight by sedimentation equilibrium of 81 000 and is composed of two subunits. It has one nickel, one selenium and 12 iron atoms per molecule. The sulfite reductase has a typical desulfoviridin absorption spectrum, a molecular weight of 191 000 and iron and zinc associated with it. The molybdenum-iron protein is gray-green in color and exhibits an absorbtion spectrum with peaks around 612, 410, 275 nm and a shoulder at 319 nm. It is composed of subunits of approximately 13 250 and has an approximate molecular weight of 110 000. Three molybdenum and 20 iron atoms are found associated with it. An extensive study of these three proteins will allow a better understanding of the function of these enzymes and also of their possible role in microbially caused corrosion.

The structure of an abietic acid dimer

Abstract: The first X-ray structural determination of an acid-catalysed dimer of abietic acid is reported.

Liquid mutual diffusivities of the H2O/D2O system

Abstract: The liquid-phase mutual diffusivities of the water (H2O) and deuterium oxide (D2O) system at 298.2 K were measured using an instrument based on the Taylor dispersion technique. The instrument has been designed to match, as closely as possible, the mathematical model of ideal Taylor dispersion, minimizing all the departures from the ideal model. The diffusivities were measured over the entire concentration range and the results follow a linear dependence on molar fraction given by 109D12 =\(2.24 - 0.36x_{D_2 O} \), where D12 is in m2·s−1. Comparison with highly accurate data obtained by a Rayleigh interferometer seems to indicate that the accuracy of the present instrument is 1%. The hard-sphere model was applied to the estimation of the mutual diffusivities of this system and good agreement was found with experiment, deviations being ±3.5%.

On aircraft flight performance in a perturbed atmosphere

Abstract: Summary We consider the effect of atmospheric disturbances, such as wind, shears, turbulence, wakes and downflows, on aircraft performance (section 1), recalling the minimum of aerodynamics (section 2) necessary for the calculation of the effects on flight mechanics. For example, it is shown (section 3) that the relative lift change, due to wind, shear or both, coincides with the disturbance intensity G, defined as the instantaneous vertical acceleration, measured in g's, that an aircraft will experience as a consequence of atmospheric disturbances, assuming constant velocity and attitude. The disturbance intensity is a measure of the total force that the atmospheric disturbance can exert on the aircraft; this force may cause changes in normal acceleration, flight velocity and angle-of-attack, either isolated (section 5) or combined (section 6), in straight and level flight; in the case of a horizontal turn (section 7), the disturbance intensity specifies the changes in instantaneous turn rate, velocity, radius (section 8), acceleration and bank angle (section 9) due to atmospheric perturbations, and their cumulative effect over time in (section 10) deforming and displacing trajectories. These effects (section 11) are quantified by formulas and illustrated in graphics, and we indicate throughout the flight mechanical consequences of disturbances with the critical intensities G 1 = — 0·17 and G 2 = — 0·42; these are the disturbance intensities which, if uncompensated, would be just enough to cause an aircraft to stall (section 4) respectively at unstick on take-off and on approach to land. We conclude (section 12) with a discussion of the use of the disturbance intensity as a parameter in the reduction and analysis of flight data.

On Umbral Oscillations as a Sunspot Diagnostic

Abstract: The observation that p-modes are attenuated in sunspots1, i.e. sunspots act as ‘sinks’ of acoustic wave energy, is explained by the transfer of energy to motions along the magnetic field lines. The latter appear as Alfven waves (Figures 1–2), reflected between the atmosphere, and anchoring points in the convection zone, and have periods (Table I) and amplitudes (Table II) consistent with observations 2–10 of umbral oscillations. The depth of generation of these waves, as inferred from a crude inversion of periods, is about 10 Mm, i.e., consistent with the depth of origin11 of ephemeral magnetic regions in the solar surface. The oscillation model is used to calibrate a general dimensional law, for the intensity of radiation of MHD waves, which gives reasonable results for the sun, and may apply to other stars.

Exact solution of a nonlinear eigenvalue problem.

Abstract: We show that Shastry's exact solution of a nonlinear eigenvalue problem in one dimension can be recovered by a method which is familiar in the theory of nonlinear ordinary differential equations.

The average rate of growth of individual cells in a cellular structure: Effect of the number of topological elements

Abstract: Equations are derived for the average rate of growth or shrinkage of individual cells in two-and three-dimensional cellular structures, when the driving forces for displacement are the excess free energies associated with faces and edges. Curvature effects are neglected. It is shown that in three-dimensional structures, such as polycrystals, cells (grains) with fourteen or more faces tend to grow while those with thirteen or less faces tend to shrink, the rate of growth/shrinkage increasing as the number of faces increases/decreases. In two-dimensional structures, the threshold between growth and shrinkage is for cells with six sides. The specific behaviour of particular cells can be predicted from a simple geometrical construction and can be quite different from the behaviour of the average cell with the same number of edges.

Modelling of the Hydrolysis of Benzylpenicillin to 6‐Aminopenicillanic Acid and Phenyl Acetic Acid by an Immobilised Penicillin Amidase in a Small Pilot Plant Batch Recirculated Reactor

Abstract: This paper deals with the modelling of the hydrolysis of benzylpenicillin to 6-aminopenicillanic acid (6-APA) and phenyl acetic acid (PAA) in a small pilot plant batch recirculated reactor by an immobilised penicillin amidase preparation. By using the following linearised form for an integrated Michaelis-Menten equation Et/V0X=α+β| In (1-X)/X| where α and β are reaction kinetic parameters, good correlations are obtained of α and β with linear velocity across the reactor, substrate concentration and temperature of operation. A process to determine α and β from initial velocity measurements is outlined. The applicability of the above equation to published data is also analysed.

A numerical method for the Hartree equation of the Helium atom

Abstract: We describe in this paper a numerical method for computing the normalized pointwise positive solution of the Hartree equation for the Helium atom. The method consists of minimizing the Hartree energy by a decomposition coordination method via an augmented Lagrangian. Some numerical results are presented.

A Comparative Study of Copper Cycles in Two Freshwater Environments

Abstract: A comparison of copper distribution in two freshwater environments is presented. Based on field results, it is discussed the role of the sediments as an internal source the particulate/dissolved interaction at different chemical and biological conditions, the changes of copper speciation and its ecological significance.