Showing papers by "Instituto Superior Técnico published in 1988"
TL;DR: In this paper, the velocity characteristics of the turbulent flow around a square cross-section cylinder mounted in a water channel for Re=14000 were analyzed using spectral analysis and digital filtering of the data obtained behind the cylinder.
Abstract: Laser-Doppler measurements of the velocity characteristics are presented for the turbulent flow around a square cross-section cylinder mounted in a water channel for Re=14000. The study involved spectral analysis and digital filtering of the LDV data obtained behind the cylinder. The purpose of the measurements is to separate and quantify the turbulent and the periodic, non-turbulent, motions of the wake flow, in order to improve knowledge of the nature of the fluctuations in the near-wake region of two-dimensional bodies. The results show, for example, that in the zone of highest velocity oscillations the energy associated with the turbulent fluctuations is about 40% of the total energy.
217 citations
TL;DR: In this article, the conversion of propane into benzenic compounds was studied at 530°C on a series of GaHZSM5 catalysts prepared by impregnation of HZSM 5 with a solution of gallium nitrate.
189 citations
TL;DR: The notion of π-institution is proposed as an alternative to the notion of institution, replacing the notions of model and satisfaction by a primitive consequence operator in the definition of a logic.
Abstract: Building on the work of Goguen and Burstall on institutions and on Tarski's notion of deductive system, a categorial framework for manipulating theories in an arbitrary logic is presented. Its main contribution is the formalisation of the semantics of theory-building operations on top of a consequence relation. For that purpose, the notion of π-institution is proposed as an alternative to the notion of institution, replacing the notions of model and satisfaction by a primitive consequence operator in the definition of a logic. The resulting approach to the semantics of specification languages is intrinsically different from the original one in the sense that the ultimate denotation of a specification is taken herein to be a class of theories (sets of formulae closed for the consequence relation) and not a class of models of that logic. Adopting this point of view, the semantics of Clear-like specification building operations is analysed.
128 citations
TL;DR: In this article, it was shown that the cell model leads to a distribution of cell sizes which is very well described by gamma functions, with α values (Table 2) that depend on the definition of size used.
126 citations
TL;DR: The resistance to ethanol-induced leakage of 260-nm-light-absorbing compounds was found to be closely related with the ethanol tolerance of three strains of yeasts, Kluyveromyces marxianus, Saccharomyces cerevisiae, and SacCharomyces bayanus, indicating the possible adoption of the present method for the rapid screening of ethanol-tolerant strains.
Abstract: Ethanol stimulated the leakage of amino acids and 260-nm-light-absorbing compounds from cells of Saccharomyces cerevisiae. The efflux followed first-order kinetics over an initial period. In the presence of lethal concentrations of ethanol, the efflux rates at 30 and 36°C were an exponential function of ethanol concentration: keX = keXmeE (X-Xm), where keX and keXm are the efflux rate constants, respectively, in the presence of a concentration X of ethanol or the minimal concentration of ethanol, Xm, above which the equation was applicable, coincident with the minimal lethal concentration of ethanol. E is the enhancement constant. At 36°C, as compared with the corresponding values at 30°C, the efflux rates were higher and the minimal concentration of ethanol (Xm) was lower. The exponential constants for the enhancement of the rate of leakage (E) had similar values at 30 or 36°C and were of the same order of magnitude as the corresponding exponential constants for ethanol-induced death. Under isothermic conditions (30°C) and up to 22% (vol/vol) ethanol, the resistance to ethanol-induced leakage of 260-nm-light-absorbing compounds was found to be closely related with the ethanol tolerance of three strains of yeasts, Kluyveromyces marxianus, Saccharomyces cerevisiae, and Saccharomyces bayanus. The resistance to ethanol-induced leakage indicates the possible adoption of the present method for the rapid screening of ethanol-tolerant strains. The addition to a fermentation medium of the intracellular material obtained by ethanol permeabilization of yeast cells led to improvements in alcohol fermentation by S. cerevisiae and S. bayanus. The action of the intracellular material, by improving yeast ethanol tolerance, and the advantages of partially recycling the fermented medium after distillation were discussed.
95 citations
TL;DR: Ritanserin significantly increased Slow Wave Sleep and changed the frequency and distribution of some stage transitions during the night and no other sleep parameters were modified by ritanerin treatment.
Abstract: Ritanserin, a selective and potent serotonin-2 antagonist, is effective in the treatment of a variety of syndromes related to anxiety and depression, including dysthymic disorder. In animals and healthy volunteers, ritanserin specifically increases slow-wave sleep and the hypothesis arises that this effect on sleep may contribute to its therapeutic properties. Therefore, we studied the effects of ritanserin on sleep in a group of dysthymic patients (DSM-III). Polygraphic recording as well as subjective evaluations of the quality of sleep were performed before and at the end of a 4-week period of double-blind medication with either ritanserin (10 mg o.d. in the morning) or placebo. At baseline, patients showed at fragmented and superficial sleep, with low amounts of slow wave sleep. Ritanserin significantly increased Slow Wave Sleep and changed the frequency and distribution of some stage transitions during the night. No other sleep parameters were modified by ritanserin treatment.
74 citations
TL;DR: In this article, the effect of strain rate on the compression behavior of cork was carried out, which takes into account the anisotropy of the material Compression curves at three different rates were obtained for each of the three directions in cork (radial, axial and tangential) Strain-rate sensitivity coefficients,m, were also measured in experiments where the strain rate was suddenly changed during the tests.
Abstract: A study of the effect of strain rate on the compression behaviour of cork was carried out, which takes into account the anisotropy of the material Compression curves at three different rates were obtained for each of the three directions in cork (radial, axial and tangential) Strain-rate sensitivity coefficients,m, were also measured in experiments where the strain rate was suddenly changed during the tests The values ofm are fairly isotropic, around 006 For a given strain rate, the radial direction is stronger (ie larger stresses) than the other two, but these are not equivalent, the axial direction being slightly stronger for most of the strain interval between 0 and 80% The recovery of dimensions following compression in each direction was also studied The change in the three dimensions with time was monitored, following compression to 30% and to 80% strain in a given direction In the first case, recovery is almost total after ∼ 20 days, but for 80% compression the deformation is not completely recovered after unloading The recovery rate decreases appreciably with time and increases with the degree of deformation previously imposed An equation is proposed that describes the recovery behaviour with a reasonable accuracy
71 citations
TL;DR: The effect of Ca on the acidification curve of energized cells in the presence of ethanol was found to be closely associated with its protective effect on growth, fermentation, and viability.
Abstract: The addition of Ca (as CaCl(2)) in optimal concentrations (0.75 to 2.0 mM) to a fermentation medium with a trace contaminating concentration of Ca (0.025 mM) led to the rapid production of higher concentrations of ethanol by Saccharomyces cerevisiae, Saccharomyces bayanus, and Kluyveromyces marxianus. The positive effect of calcium supplementation (0.75 mM) on alcoholic fermentation by S. bayanus was explained by the increase in its ethanol tolerance. The ethanol inhibition of growth and fermentation followed the equation mu(xi) = mu(oi) [1 - (X/X(mi))], where mu(oi) and mu(xi) are, respectively, the specific growth (i = g) and fermentation (i = f) rates in the absence or presence of a concentration (X) of added ethanol, and X(mi) is the maximal concentration of ethanol which allows growth or fermentation. The toxic power is given by n(i). In Ca - supplemented medium (0.75 mM), n(g) = 0.42 for growth and n(f) = 0.43 for fermentation compared with 0.52 and 0.55, respectively, in unsupplemented medium; for both media, X(mg) = 10% (vol/vol) and X(mf) = 13% (vol/vol). For lethal concentrations of ethanol, the specific death rates were minimal for cells that were grown and incubated with ethanol in medium with an optimal concentration of Ca, maximal for cells grown and incubated with ethanol in unsupplemented medium, and intermediate for cells grown in unsupplemented medium and incubated with ethanol in calcium-supplemented medium. The effect of Ca on the acidification curve of energized cells in the presence of ethanol was found to be closely associated with its protective effect on growth, fermentation, and viability.
70 citations
TL;DR: In this article, the equilibria in aqueous solution in the system L -alanine+VO 2+ have been studied by a combination of pH-potentiometric and spectroscopic methods (EPR, visible absorption and circular dichroism) in the pH range 1.5-13.
55 citations
TL;DR: In this article, the acidity and catalytic properties of LaHY zeolites, La3+ or by Ce3+ improved thermal stability, probably owing to the formation of stable oxygen complexes between rare earth cations and lattice oxygen atoms.
50 citations
TL;DR: In this paper, the effects of different Raman data reduction procedures on the so-called "Boson" peak exhibited by most inorganic glasses are investigated. And the problem of extracting the vibrational density of states from spectroscopic data is also addressed.
Abstract: Vibrational spectroscopy is one of the most powerful techniques for studying the structure of non-crystalline materials. It is particularly useful for probing vibrational motions of non-bridging atoms or ions or those of weakly coupled bridging species. Among the different vibrational methods available, infrared absorption and Raman scattering will be considered in detail, along with the specific types of structural information which can be extracted in each case, either directly or through comparison between spectral data and model calculations. Several types of inorganic glasses are examined, including oxide, chalcogenide and halide systems, for which tentative selection rules are presented. The problem of extracting the vibrational density of states from spectroscopic data is also addressed, together with the effects of different Raman data reduction procedures on the so-called “Boson” peak exhibited by most inorganic glasses.
TL;DR: In this paper, a detailed study of the effects of heat treatment on the structure, overall dimensions, mass and compression properties of cork (reproduction and virgin cork) is reported.
TL;DR: In this article, l'equation de reaction-diffusion scalaire avec des conditions aux limites de Neumann is considered, and l'attracteur quand e est petit.
TL;DR: In this article, metal-ligand bond enthalpies are derived for a variety of ligands through a simple method that involves both the experimental standard enthalPies of formation and theoretical calculations, which is suggested that this method may be used to predict the energetics of new complexes with fair accuracy.
TL;DR: In this article, the crystal structure of trans-[ReF( C- CH2Bu5(dppe)2]BF4 is reported. And the treatment of trans[ReCl(CCHR)(dppe)] (R = But or Ph; dppe Ph2PCH2 CH2PPh2) with [Et2OH]BF 4 gives trans
TL;DR: In this article, it was shown that the logarithmic singularity at the critical level (of type I, i.e. singular layer), only occurs for acoustically evanescent waves, of "large" horizontal wavenumber k > Ω/co, whose frequency Ω Ω /co gives way when k <Ω / co to a transition layer (or critical level of type II), i. e. a singularity away from the real axis, which...
Abstract: We consider magnetosonic-gravity waves, in an isothermal atmosphere, under a uniform, horizontal magnetic field, with horizontal wavevector in the plane of gravity and the magnetic field. It is shown (Section 2) that the logarithmic singularity, at the critical level (of type I, i.e. singular layer), only occurs for acoustically evanescent waves, of “large” horizontal wavenumber k >Ω/co , whose frequency Ω Ω/co to the critical level (of type I, or singular layer), gives way when k<Ω/co to a transition layer (or critical level of type II), i.e. a singularity away from the real axis, which ...
TL;DR: In this article, the crystalline structures of (Perylene)2M(mnt)2 for M=Au and Pd (mnt=maleonitriledithiolate or cis-2,3-dimercapto-2-butenedinitrile, S2C2(CN)2).
TL;DR: In this paper, the redox properties of carbyne-, aminocarbyne- and η2-vinyl-(metallacyclopropene) complexes trans-[ReCl(LH)(dppe)2][BF4] (1; LH CCH2R (R But or Ph), CNH2, CH2C(CH2Ph)CH2, dppe ǫ Ph2PCH2CH2PPh2), as well as their parent vinylidene, isoc
TL;DR: The macrocyclic complexone 1-oxa-4,7,10-triazacyclodododecane-N,N',N''-triacetic acid (cODTA) has been synthesized and its protona constants, stability constants of metal complexes and enthalpy changes for the formation of alkaline-earth complexes have been determined.
TL;DR: Based on the integral boundary equation, an a posteriori error estimator is defined, which is used in a comparative study of the accuracy of the solution obtained by the two approaches applied to plane elasticity examples.
TL;DR: In this article, it was shown that the distribution of cell volumes is fairly well fitted by a gamma distribution function with parameter α ≃ 5·56, which is the value of α that gives the exact second moment of the volume distribution, as calculated by Gilbert in 1962.
Abstract: The distribution of cell volumes in a Voronoi partition of three-dimensional Euclidean space was obtained by a computer simulation method in which the volume of a cell is derived from the number of lattice points of a reference cubic lattice which are closer to the centre of that cell than to the centre of any other cell. The cell centres have a Poisson distribution. It has been found that the distribution of cell volumes is fairly well fitted by a gamma distribution function with parameter α ≃ 5·56, which is the value of α that gives the exact second moment of the volume distribution, as calculated by Gilbert in 1962. This is an extension to three-dimensions of the applicability of the gamma function to describe the area distribution in a two-dimensional partition (with α ≃ 3·6) and the length distribution in a one-dimensional partition (with the exact value α = 2).
TL;DR: In this article, the generalized concepts of Doppler factor, local frequency, wave invariant and group velocity were introduced on the basis of the acoustic energy equation, which can be derived from a variational principle.
TL;DR: In this paper, the X-ray structure of [WH2(CCCO2Me)2(dppe)2] is reported, and with HBF4, [MoH4(dpp) 2] reacts with R′CO2CCH (R′ = Me or Et) t give [ MoH 2 {CHCC(O )OR′}(dPP) 2 ]BF4, but with HBr, [ MoBrH2(CHCHR′)(dppe),
TL;DR: In this article, a theoretical model for the emission of low-energy thermalized electrons from hexatriacontane films has been proposed, where negative electron affinity of the order A = -0.5 eV and the electronic anisotropy of the hexatriacoontane are the key elements necessary to describe the emission directionality.
Abstract: Spectra of low-energy electrons inelastically back-scattered from hexatriacontane films contain a component of almost monoenergetic electrons (energy spread ~ kBT) directed preferentially perpendicular to the film surface. This emission is due to electrons having relaxed down to the conduction band edge by multiple scattering. A theoretical model for the emission of such thermalized electrons shows that both, the negative electron affinity of the order A = -0.5 eV and the electronic anisotropy of the hexatriacontane are the key elements necessary to describe the emission directionality.
TL;DR: The complex composition of the medium used for alcoholic fermentation plays a marked role in the ability of the yeast to tolerate and produce ethanol, and Jerusalem artichoke juice proved a very appropriate medium for a productive alcoholic fermentation, namely, in processes based on strains with a low ethanol resistance.
Abstract: Alcoholic fermentation of Jerusalem artichoke juice, a natural complex medium, allowed the production of 13% (v/v) ethanol utilizing an inulin-fermenting strain of Kluyveromyces fragilis, strongly sensitive to ethanol. However, the fermentation of a simple medium with a similar concentration of fermentable sugars (235 g/L) as saccharose stopped prematurely when only 7% (v/v) ethanol had been produced. Differences in the two fermentation profiles were attributed to the significantly lower ethanol tolerance of K. fragilis IGC 2671 in the simple medium with 2% saccharose as compared with diluted J.a. juice with a similar sugar concentration, in fact, (1) in diluted J. a. juice, growth was possible up to 8% (v/v) added ethanol compared with 6% (v/v) in simple medium and (2) ethanol-induced inhibition of the specific growth and fermentation rate as well as ethanol-induced stimulation of the specific death rate were much more drastic in simple medium. Present results show that (1) the complex composition of the medium used for alcoholic fermentation plays a marked role in the ability of the yeast to tolerate and produce ethanol; (2) J. a. juice proved a very appropriate medium for a productive alcoholic fermentation, namely, in processes based on strains with a low ethanol resistance; and (3) to characterize and compare the ethanol tolerance of fermenting yeasts, the standardization of the medium composition must be taken in consideration.
01 Sep 1988
TL;DR: This work combines the object-oriented paradigm with experiences in formal methods in software engineering, especially algebraic data type theory, logical approaches to systems specification and design, and process algebra, and proposes mathematical models for the basic notions of object, object type and abstract object type.
Abstract: There is a need for exploring the theoretical and methodological foundations of database design and development with the intention to achieve provably correct systems and higher levels of reusability. To this end, topics rarely addressed so far in this area must be investigated, among them full incorporation of dynamic aspects, static and dynamic integrity checking, formal methods strongly backed by a sound theory, and design-in-the-large issues like modularization and parameterization. Our approach combines the object-oriented paradigm with experiences in formal methods in software engineering, especially algebraic data type theory, logical approaches to systems specification and design, and process algebra. In analogy to algebraic data type theory, we propose mathematical models for the basic notions of object, object type and abstract object type.
TL;DR: In this article, the standard molar enthalpies of formation, at 298.15 K, of five crystalline bent metallocenes, [M(η-C5H5)2L] (M = Mo, W, Ti) (LH2 = 1,2-benzenediol, C6H4-(OH)2; 2,3-napthalenediol and C10H6(OH) 2; 9,10-phenanthrenediol, 4,14H8(O)2), have been