Showing papers by "Instituto Superior Técnico published in 1989"
TL;DR: The inhibition of growth by octanoic or decanoic acids, two subproducts of ethanolic fermentation, was evaluated in Saccharomyces cerevisiae and Kluyveromyces marxianus in association with ethanol to indicate that the undissociated form is the toxic molecule.
Abstract: The inhibition of growth by octanoic or decanoic acids, two subproducts of ethanolic fermentation, was evaluated in Saccharomyces cerevisiae and Kluyveromyces marxianus in association with ethanol, the main product of fermentation. In both strains, octanoic and decanoic acids, at concentrations up to 16 and 8 mg/liter, respectively, decreased the maximum specific growth rate and the biomass yield at 30°C as an exponential function of the fatty acid concentration and increased the duration of growth latency. These toxic effects increased with a decrease in pH in the range of 5.4 to 3.0, indicating that the undissociated form is the toxic molecule. Decanoic acid was more toxic than octanoic acid. The concentrations of octanoic and decanoic acids were determined during the ethanolic fermentation (30°C) of two laboratory media (mineral and complex) by S. cerevisiae and of Jerusalem artichoke juice by K. marxianus. Based on the concentrations detected (0.7 to 23 mg/liter) and the kinetics of growth inhibition, the presence of octanoic and decanoic acids cannot be ignored in the evaluation of the overall inhibition of ethanolic fermentation.
158 citations
TL;DR: By an ODE analysis, it is shown that, for an ARMAX plant, the equilibria of a multipredictor based LQ self-tuning regulator, namely, the MUSMAR algorithm, are the extrema of a receding horizon variant of the cost.
72 citations
TL;DR: In this article, the authors describe the application of three-dimensional finite-difference calculation procedures to the problem of a jet impinging on a flat plate through the influence of a confined crossflow.
Abstract: This paper describes the application of three-dimensional finite-difference calculation procedures to the problem of a jet impinging on a flat plate through the influence of a confined crossflow One procedure uses the hybrid central/upwind difference scheme, and the other uses a quadratic upstream weighted difference scheme (QUICK) to calculate the convection terms The standard two-equation "& — c" turbulence model is used to calculate the distribution of the Reynolds stresses The difficulty of assessing turbulence model performance in these complex flows due to the intrusion of numerical diffusion errors is demonstrated by comparing the calculations on both coarse and fine meshes and by improving the accuracy of the convection terms discretization using the higher-order QUICK method The ability of the model calculations to simulate both the mean and the turbulence fields is examined, particularly in the vicinity of the stagnation point The results show the advantages of QUICK differencing scheme over the hybrid treatment, since the same level of numerical accuracy requires far less CPU time and computer memory when the QUICK scheme is used The calculations reveal the existence of large regions of low pressure, associated with an upstream recirculating flow region due to the interaction between the upstream wall jet and the crossflow, which may produce a substantial lift loss for a VSTOL aircraft
70 citations
TL;DR: In this paper, the authors measured the vapour-liquid equilibrium of the systems containing either d-limonene or 1, 8-cineole in the supercritical solvents carbon dioxide and an azeotropic mixture of ethane+carbon dioxide.
68 citations
64 citations
TL;DR: The intrinsic fluorescence of α-tocopherol has been used as a tool to study the location and dynamics of the molecule in phospholipid vesicles made of egg yolk phosphatidylcholine using steady-state and time-resolved techniques.
53 citations
TL;DR: In this paper, a simple kinetic model predicting the concentration of oxygen atoms, metastable singlet molecules O2(a1Δ) and negative ions O − in the positive column of a DC glow discharge is developed.
Abstract: A simple kinetic model predicting the concentration of oxygen atoms, metastable singlet molecules O2(a1Δ) and negative ions O — in the positive column of a DC glow discharge is developed. The calculated O and O2(a1Δ) concentrations are compared to previously reported measurements for pressuresp=0.2–2 Torr and discharge currentsI=10–80 mA. The electron density calculated from the continuity equationj=nee vd agrees well with experiment. The rate coefficients for electron impact processes used in the balance equations of O, O2(a1Δ), and O− were taken from the literature as a function of the reduced electric fieldE/N forE/N=40–80 Td. A reasonable agreement is obtained between the model and the experiment with a set of 10 reactions for the production and destruction of the above-mentioned species
42 citations
01 Jan 1989
TL;DR: The diversity of current work and dynamism in the field of quantitative modelling of disequilibrium and shortage in centrally planned economies are reflected in the contributions made in this volume, which clarify theoretical concepts, resolve disputes between modelling schools, amplify existing disequ equilibrium and shortage models, improve estimation techniques, and uncover sources of data as discussed by the authors.
Abstract: The diversity of current work and dynamism in the field of quantitative modelling of disequilibrium and shortage in centrally planned economies are reflected in the contributions made in this volume, which clarify theoretical concepts, resolve disputes between modelling schools, amplify existing disequilibrium and shortage models, improve estimation techniques, and uncover sources of data. Summaries are presented of the main findings related to shortage models in section 18.1 and disequilibrium models in section 18.2. This is followed by a reassessment of the contrasts and similarities between the disequilibrium and shortage models in light of the new research. Finally, section 18.4 identifies a number of topics that have been inadequately examined in past disequilibrium and shortage model studies but merit further investigation because of their importance. These include the issue of aggregation, cross-section disequilibrium analysis, the role of plans and expectations in models, the second economy in a CPE, data development, and extension of the coverage of disequilibrium and shortage models to include neglected countries and sectors.
40 citations
TL;DR: In this article, the complex [q3-methylallyl)(~4-cycloocta-1,5-diene)nickel hexafluorophosphate (2) was found to be an efficient catalyst for the oligomerization of styrene without using a Lewis acid.
Abstract: SUMMARY: The complex [q3-methylallyl)(~4-cycloocta-1,5-diene)nickel] hexafluorophosphate (2) was found to be an efficient catalyst for the oligomerization of styrene without using a Lewis acid. Oligomers and polymers with low degree of polymerization were obtained and characterized by GPC and NMR spectroscopy. Solvents and ligands have a strong effect on the catalyst activity, the molecular weight distributions and the polymer microstructure. The end groups were characterized in the case of the ligand-free and the tributylphosphine and tricyclohexylphosphinemodified systems. A terminal benzylidene group was observed except for the latter basic and bulky phosphine which led to a methylene terminal group. A mechanism involving a hydridonickel species is proposed.
37 citations
29 May 1989
TL;DR: The main technical result is a normal form theorem saying that any regular implementation, i.e. one composed of any number of extensions and encapsulations, in any order, can be done in just two steps: first an extension, and then an encapsulation.
Abstract: This paper gives semantic foundations of (correct) implementation as a relationship between an "abstract" object and a community of "base" objects. In our aproach, an object is an "observed process". Objects and object morphisms constitute a category OB in which colimits reflect object aggregation and interaction between objects. Our concept of implementation allows for composition, i.e. by composing any number of (correct) implementation steps, a (correct) entire implementation is obtained. We study two specific kinds of implementation, extension and encapsulation, in more detail and investigate their close relationship to object morphisms. Our main technical result is a normal form theorem saying that any regular implementation, i.e. one composed of any number of extensions and encapsulations, in any order, can be done in just two steps: first an extension, and then an encapsulation.
37 citations
TL;DR: In this article, two new cationic complexes [Ni(η3-CH2C6H5)X(PR3)2] (X = Cl, Br) with TIPF6 were synthesized from the corresponding neutral compounds by metathetical halide abstraction.
TL;DR: A non-axenic strain of the microalgaBotryococcus braunii Kützing, isolated from a small lake in Portugal, showed a poor production of hydrocarbons but excreted remarkably high quantities of an exopolysaccharide into the medium.
Abstract: A non-axenic strain of the microalgaBotryococcus braunii Kutzing, isolated from a small lake in Portugal, when cultured at 25°C in mineral medium and under continuous illumination, showed a poor production of hydrocarbons (5% of the dry biomass) but excreted remarkably high quantities of an exopolysaccharide (4–4.5g/l) into the medium. The production of soluble polysaccharide with galactose, fucose and uronic acid residues, follows growth. The role of the mucoid contaminating bacteria in polysaccharide production in the mixed culture was unproven.
TL;DR: In this article, the equilibria in aqueous solution in the systems l -serine and l -threonine +VO2+ have been studied by a combination of pH-potentiometric and spectroscopic methods (EPR, visible absorption and circular dichroism) in the pH range 1.5-13.6.
TL;DR: In this paper, the authors derived a mathematical condition for the energy stored in the field to be finite and showed that this condition is equivalent to specifying the space of solutions to the classical Wiener-Hopf equation of half-plane diffraction (the Sobolev space H − 1 2, 2 + (R )).
TL;DR: When binding an electron-rich group VI (Mo or W) or VII (Re) metal site (M ), such as {M(dppe)2} (M = Mo or W, dppe = Ph2PCH2CH2PPh2) or {ReCl(dpp)2}, isocyanides (M CNR), cyanides (N) or alkyne-derived allene, vinylidene (M ) or alkynyl (M) ligands undergo β-electrophilic
TL;DR: In this paper, the authors reviewed the studies relative to the presence, state and combined form of vanadium in Amanita toadstools and suggested a possible role for the vanadium containing compound "amavadine" is suggeste...
Abstract: The studies relative to the presence, state and combined form of vanadium in Amanita toadstools are reviewed critically. A possible role for the vanadium containing compound “amavadine” is suggeste...
TL;DR: In this paper, the numerical evaluation of double singular integrals arising in the Galerkin BEM for plane problems is presented, and some differences in the type of singularities encountered in the implementation of the collocation and the GBM schemes are pointed out.
TL;DR: In this article, the crystal structure of trans-Mo(NCN) 2 (dppe) 2 ] has been determined by an X-ray diffraction study, and it has been shown that bis(cyanoimido) complexes can be formed by trans-mNCN 2(dppe).
01 Feb 1989-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the authors measured the grain size and hardness of a 2.25 Cr-1Mo steel subframe with different heat inputs in the range 1.1-5.8 MJ m−1.
Abstract: Submerged arc weldings were made on thick plates of a 2.25 Cr-1Mo steel (where the composition is in approximate weight per cent), using different heat inputs in the range 1.1–5.8 MJ m−1. The microstructures in the heat-affected zone (HAZ) were identified, and the austenite grain size and hardness were measured. The microstructure is predominantly bainitic, but some martensite was observed at low heat inputs. The observations in real weldings were compared with those made in welding simulations, using dilatometric tests. In these, the relevant transformation temperatures were determined. The austenite grain size was correlated to the thermal cycle, which was experimentally obtained at one point of the HAZ in each welding experiment. The grain size D, obtained by the linear intercept method, is well described by the kinetic equation Dn−D0n = kI where I is the “kinetic strength” of the thermal cycle which depends on the activation energy Q for grain growth. A method based on the dilatometry results was developed which allows the determination of the grain growth exponent n, independently of Q. With this method, we obtained n = 3.17. This is consistent with the welding data. The best value of Q was found to be 180 kJ mol−1. The grain size in welds was found to be comparable with that measured in the dilatometric specimens, for the same “kinetic strength” of the cycles.
TL;DR: In this article, Fusarium flocciferum was inserted in porous celite beads and the effects of bead size, adsorption time course, washing cycle and spore concentration on spore loading were investigated.
Abstract: Spores of Fusarium flocciferum were inserted in porous celite beads. The effects of bead size, adsorption time course, washing cycle and spore concentration on spore loading were investigated. Cell loadings up to 50% (dry weight/beads) were obtained. The degradation of phenol using adsorbed cells was studied in batch experiments. The immobilized cell system was shown to efficiently degrade high concentrations of the substrate (up to 2.0 g/l) and to remain active for more than 2 motths. The oxygen uptake rate of free and immobilized cells was determined at various concentrations of phenol. The kinetic constants Ks=85 mg/l, Ki=345 mg/l and SMI=170 mg/l were estimated from the experimental data by linearization of the Haldane function for the free cells. The uptake rates exhibited by the confined cells were lower (30%) than those obtained for free cells and no significant differences were found for phenol concentrations between 150 and 1200 mg/l.
TL;DR: In this paper, the problem of diffraction of an electromagnetic wave by a half plane with different face impedances is dealt with, following a rigorous approach based on the [L 2 + R ]2 theory of systems of Wiener-Hopf equations with piecewise continuous presymbols.
TL;DR: In this paper, the authors measured the intensities of C-H and C-D stretching vibrations in films of mixtures of perdeuterated and non-deutated polystyrene in different proportions.
TL;DR: In this paper, the total vapour pressures, the excess Gibbs energy GE (at 90.69 and 103.99 K) and the excess molar volume VE (at 103. 99 K) were reported for liquid mixtures of methane and ethane.
TL;DR: The maximal concentration of ethanol produced during the fermentation of 320 g/l glucose by Saccharomycesbayanus was higher when the yeast cells were immobilized either by adsorption on celite or by entrapment in k-carrageenan beads.
Abstract: The maximal concentration of ethanol produced during the fermentation of 320 g/l glucose bySaccharomycesbayanus was higher when the yeast cells were immobilized either by adsorption on celite or by entrapment in k-carrageenan beads (from 10.5% with free cells up to 14.5% and 13.1% (v/v) respectively). This increase was due to medium supplementation with the compounds present in the immobilization supports.
TL;DR: In this article, a photoacoustic calorimetry of the benzoyl radical has been carried out, and the results show that the radical is resonance stabilized, which does not support a recent suggestion that it is not resonance stabilized.
TL;DR: In this paper, the dissipative Alfven wave equation in a medium stratified in one direction, with a transverse magnetic field, in the presence of dissipation by fluid viscosity and electrical resistance was deduced.
Abstract: We deduce the dissipative Alfven wave equation in a medium stratified in one direction, with a transverse magnetic field, in the presence of dissipation by fluid viscosity and electrical resistance; the dissipative Alfven wave equation generalizes earlier results for homogeneous (Cowling, 1960) and inhomogeneous (Campos, 1983a) media, and corrects an error in the literature (Heyvaerts and Priest, 1983). The wave equation is solved exactly in two cases: a uniform magnetic field, and a magnetic field decreasing with height. In both cases the mean state is assumed to be isothermal, with a constant rate of ionization, so that the magnetic diffusivity is constant, but the dynamic viscosity increases with height. There are therefore two regions, a low- (high-) altitude region where electrical resistance dominates fluid viscosity (or vice versa), and an asymptotic regime relevant to the uppermost (lowermost) layers. The two regions are separated by a transition layer, across which the wave field is cont...
TL;DR: From titration curves of formaldehyde-treated cells of the alga Selenastrum capricornutum with metals, specific adsorption was determined and quantified in terms of average surface complex formation constants and differential equilibrium functions.
TL;DR: A numerical model for predicting the failure of structural steel elements subjected to cyclic loading is presented in this article, where the cyclic response is considered to be inelastic to seismic loading.
TL;DR: In this article, the problem of the factorization in the Wiener algebra of a class of 2×2 matrix functions of Daniele type is considered and sufficient conditions for the existence of a canonical factorization are obtained and provided these conditions are fulfilled, the factors of such factorization can be derived in an explicit form.
Abstract: In this paper the problem of the factorization in the Wiener algebra of a class of 2×2 matrix functions of Daniele type is considered. For these matrix functions necessary and sufficient conditions for the existence of a canonical factorization are obtained and, provided these conditions are fulfilled, the factors of such factorization can be derived in an explicit form.
TL;DR: In this paper, the influence of branching in the binary diffusion coefficients of n-heptane + n-hexane isomers, in the liquid state, was studied using the Taylor dispersion technique.
Abstract: This paper presents a study of the influence of branching in the binary diffusion coefficients of n-heptane + n-hexane isomers, in the liquid state. The measurements have been made with the Taylor dispersion technique, at several compositions, at 283 and 298 K, for the X + n-heptane mixtures, where X= n-hexane, 3-methylpentane, 2, 3-dimethylbutane, and 2, 2-dimethylbutane. The results show a very interesting behavior of the composition dependence of the binary diffusion coefficients, presenting a maximum, for compositions about a molar fraction of n-heptane of 0.5, which increases with the increase in the degree of branching, suggesting the possibility of order-disorder effects caused by stereochemically favored packing in the liquid phase and energetically favored segment interaction in the liquid mixtures. An attempt to apply the van der Waals model to these data could not predict the experimental binary diffusion coefficients of these systems within the experimental accuracy.