Showing papers by "Instituto Superior Técnico published in 1999"

Measurements of Omega and Lambda from 42 High-Redshift Supernovae

Abstract: We report measurements of the mass density, Omega_M, and cosmological-constant energy density, Omega_Lambda, of the universe based on the analysis of 42 Type Ia supernovae discovered by the Supernova Cosmology Project. The magnitude-redshift data for these SNe, at redshifts between 0.18 and 0.83, are fit jointly with a set of SNe from the Calan/Tololo Supernova Survey, at redshifts below 0.1, to yield values for the cosmological parameters. All SN peak magnitudes are standardized using a SN Ia lightcurve width-luminosity relation. The measurement yields a joint probability distribution of the cosmological parameters that is approximated by the relation 0.8 Omega_M - 0.6 Omega_Lambda ~= -0.2 +/- 0.1 in the region of interest (Omega_M <~ 1.5). For a flat (Omega_M + Omega_Lambda = 1) cosmology we find Omega_M = 0.28{+0.09,-0.08} (1 sigma statistical) {+0.05,-0.04} (identified systematics). The data are strongly inconsistent with a Lambda = 0 flat cosmology, the simplest inflationary universe model. An open, Lambda = 0 cosmology also does not fit the data well: the data indicate that the cosmological constant is non-zero and positive, with a confidence of P(Lambda > 0) = 99%, including the identified systematic uncertainties. The best-fit age of the universe relative to the Hubble time is t_0 = 14.9{+1.4,-1.1} (0.63/h) Gyr for a flat cosmology. The size of our sample allows us to perform a variety of statistical tests to check for possible systematic errors and biases. We find no significant differences in either the host reddening distribution or Malmquist bias between the low-redshift Calan/Tololo sample and our high-redshift sample. The conclusions are robust whether or not a width-luminosity relation is used to standardize the SN peak magnitudes.

Colour in textile effluents – sources, measurement, discharge consents and simulation: a review

Abstract: This paper aims to review the problem of colour in textile effluents, the different classes of dyes available and their contribution to the problem. Through new regulations, pressure is being placed on water companies all over the world to reduce the amount of colour in sewage effluent. Dyes exhibit low toxicity to mammals and aquatic organisms and therefore colour consents are normally applied for aesthetic and industrial reasons rather than for prevention of toxicity. The absorbance, ADMI values and concentrations of dyes in effluent are examined here with particular reference to reactive azo dyes used in cotton processing. Colour consents, the problem of colour in textile wastewaters and the importance for research in this area are also discussed. Dye concentrations of 0.01 g dm−3 up to 0.25 g dm−3 have been cited as being present in dyehouse effluent, depending on the dyes and processes used. ADMI values ranged from 50 to 3890 units for the dyeing of cotton. It was concluded that 1500 ADMI units was a reasonable value to aim for when simulating coloured effluents. Simulated textile effluents may be used for research purposes. These should resemble real wastes as closely as possible, but it is often difficult to replicate the ADMI values, absorbance and spectra of real effluents. The concentrations of dye used in simulated effluents examined in literature varied from 0.01 g dm−3 to 7 g dm−3. As absorbance and ADMI values change with the types of dye used, it is difficult to relate these values to dye concentrations. A concentration of 0.18 g dm−3 of a Red or Yellow dye or 0.43 g dm−3 of a blue dye would provide an ADMI of approximately 1500 units and fits within the range of dye concentrations presented in literature. A dye mixture simulating colour in a real textile effluent is suggested and some limitations of simulating actual wastewaters discussed. © 1999 Society of Chemical Industry

Content-based hierarchical classification of vacation images

Abstract: Grouping images into (semantically) meaningful categories using low level visual features is a challenging and important problem in content based image retrieval. Using binary Bayesian classifiers, we attempt to capture high level concepts from low level image features under the constraint that the test image does belong to one of the classes of interest. Specifically, we consider the hierarchical classification of vacation images; at the highest level, images are classified into indoor/outdoor classes, outdoor images are further classified into city/landscape classes, and finally, a subset of landscape images is classified into sunset, forest, and mountain classes. We demonstrate that a small codebook (the optimal size of codebook is selected using a modified MDL criterion) extracted from a vector quantizer can be used to estimate the class-conditional densities of the observed features needed for the Bayesian methodology. On a database of 6931 vacation photographs, our system achieved an accuracy of 90.5% for indoor vs. outdoor classification, 95.3% for city vs. landscape classification, 96.6% for sunset vs. forest and mountain classification, and 95.5% for forest vs. mountain classification. We further develop a learning paradigm to incrementally train the classifiers as additional training samples become available and also show preliminary results for feature size reduction using clustering techniques.

Cutinase: from molecular level to bioprocess development.

Abstract: This review analyzes the role of cutinases in nature and their potential biotechnological applications. The cloning and expression of a fungal cutinase, Fusarium solani f. pisi, in Escherichia coli and Saccharomyces cerevisiae hosts are described. The three-dimensional structure of this cutinase is also analyzed and its function as a lipase is discussed and compared with other lipases. The biocatalytic applications of cutinase are described taking into account the preparation of different cutinase forms and the media in which the different types of reactions have been performed, namely hydrolysis, esterification, transesterification, and resolution of racemic mixtures. The stability of cutinase preparations is discussed and, in particular, the cutinase stability in anionic reversed micelles is analyzed considering the role of hexanol as a substrate, a cosurfactant, and a stabilizer. Process development, based on the operation of cutinase reactors, is also reviewed.

Mathematical models for supercritical extraction of olive husk oil

Abstract: Olive husk oil was extracted from olive husk under pressures of 12.0 to 18.0 MPa and temperatures of 308 to 330 K with supercritical carbon dioxide. Olive husk was supplied by an olive oil factory. The effects of pressure, temperature, extractor capacity and superficial velocity on the extraction rate of olive husk oil were studied. Extraction curves were evaluated by an empirical model, a ‘hot sphere’ model and by the extended Lack's plug-flow model and the relative merits of the models are demonstrated. The results are compared with those obtained in the literature. Good agreement between the extended Lack's plug-flow model and our experimental measurements was obtained. The empirical model (in which only one adjustable parameter varied with extraction conditions) also fitted the data well. The ‘hot sphere’ model, as currently applied, gave acceptable results at the higher superficial velocities studied but gave a very poor fit at the lowest velocities. The effects on the parameters in this model of allowing rapid equilibration to occur between the pore fluid and adjacent adsorbed solute are examined and discussed in the light of the experimental findings.

Thermodynamics of Reissner-Nordström-anti-de Sitter black holes in the grand canonical ensemble

Abstract: The thermodynamical properties of the Reissner--Nordstr\"om--anti-de Sitter black hole in the grand canonical ensemble are investigated using York's formalism. The black hole is enclosed in a cavity with a finite radius where the temperature and electrostatic potential are fixed. The boundary conditions allow one to compute the relevant thermodynamical quantities, e.g., thermal energy, entropy, and charge. The stability conditions imply that there are thermodynamically stable black hole solutions, under certain conditions. By taking the boundary to infinity, and leaving the event horizon and charge of the black hole fixed, one rederives the Hawking-Page action and Hawking-Page specific heat. Instantons with negative heat capacity are also found.

Hydrophobicity, surface tension, and zeta potential measurements of glass-reinforced hydroxyapatite composites.

Abstract: Wettability and zeta potential studies were performed to characterize the hydrophobicity, surface tension, and surface charge of P2O5-glass-reinforced hydroxyapatite composites. Quantitative phase analysis was performed by the Rietveld method using GSAS software applied to X-ray diffractograms. Surface charge was assessed by zeta potential measurements. Protein adsorption studies were performed using vitronectin. Contact angles and surface tensions variation with time were determined by the sessile and pendent drop techniques, respectively, using ADSA-P software. The highest (-18.1 mV) and lowest (-28.7 mV) values of zeta potential were found for hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP), respectively, with composite materials presenting values in between. All studied bioceramic materials showed similar solid surface tension. For HA and beta-TCP, solid surface tensions of 46.7 and 45.3 mJ/m2, respectively, were obtained, while composites presented intermediate surface tension values. The dispersive component of surface tension was the predominant one for all materials studied. Adhesion work values between the vitronectin solution and HA and beta-TCP were found to be 79.8 and 88.0 mJ/m2, respectively, while the 4.0 wt % glass composites showed slightly lower values than the 2.5 wt % ones. The presence of beta-TCP influenced surface charge, hydrophobicity, and protein adsorption of the glass-reinforced HA composites, and therefore indirectly affected cell-biomaterial interactions.

Nuclear liquid-gas phase transition

Abstract: The microscopic theory of the nuclear matter equation of state at finite temperature is developed within the Bloch--De Dominicis diagrammatic expansion. The liquid gas phase transition of symmetric nuclear matter is identified, with a critical temperature ${T}_{c}\ensuremath{\approx}20 \mathrm{MeV},$ using the Argonne ${v}_{14}$ as the bare $\mathrm{NN}$ interaction and a phenomenological three-body force adjusted to give the correct saturation point. Pure neutron and asymmetric matter, relevant to supernovae explosions, are also studied. It is found that the liquid-gas phase transition disappears at asymmetries $ag0.9.$ At the bounce-off of the supernova collapse, temperatures of several tens of MeV are reached and we find that the compressibility steeply increases at such temperatures. Finally, we find that the equation of state gives a ``limiting temperature'' of finite nuclei consistent with the experimental observation in compound nucleus reactions. A careful analysis of the diagrammatic expansion reveals that the dominant terms are the ones that correspond to the zero-temperature Bethe-Brueckner-Goldstone diagrams, where the temperature is introduced in the occupation numbers only, represented by Fermi distributions, thus justifying this commonly used procedure of naively introducing the temperature effect.

A Model of Bone Adaptation Using a Global Optimisation Criterion Based on the Trajectorial Theory of Wolff.

Abstract: Julius Wolff originally proposed that trabecular bone was influenced by mechanical stresses during the formative processes of growth and repair such that trabeculae were required to intersect at right angles. In this work, we have developed an analytical parametric microstructural model, which captures this restriction. Using homogenisation theory, a global material model was obtained. An optimal structure constructed of the homogenised material could then be found by optimising a cost function accounting for both the structural stiffness and the biological cost associated with metabolic maintenance of the bone tissue. The formulation was applied to an example problem of the proximal femur. Optimal densities and orientations were obtained for single load cases. The situation of multiple loads was also considered. In this case, we observe that the alignment of principal strains with the material orthotropy direction is, in general, not possible for all load cases. Thus less restrictive microstruct...

Antioxidant synergy of α‐tocopherol and phospholipids

Abstract: The prevention of oxidation of a refined sardine oil by α-tocopherol at 0.04%, by several phospholipids [phosphatidylcholine (PC), phosphatidylethanolamine (PE), and cardiolipin (CL)] at 0.5%, as well as by combinations of α-tocopherol with each phospholipid, was investigated. The evolution of the oxidation process during 1 mon at 40±2°C was followed by a series of methods, measuring peroxide value (PV), diene, triene, and polyene index, and absorbance at 430 nm, while α-tocopherol and phospholipid content were being monitoried. Among these indices, PV was found to be the most adequate to follow the process. PC was the most effective individual antioxidant as shown by the PV values obtained at the end of the storage period, which were 54.0, 83.4, 87.9, and 97.7 meq O2/kg for PC, CL, PE, and α-tocopherol, respectively. The highest synergistic effect was obtained with a mixture of α-tocopherol and PE, and the second and third best by mixtures made with PC and CL, respectively. The corresponding PV values recorded at the end of the period were 27.0, 35.0, and 58.0 meq O2/kg. The high degree of synergy between PE and tocopherol is probably due to the occurrence of a simultaneous antioxidant mechanism involving Maillard compounds.

Structures and Properties of Gellan Polymers Produced by Sphingomonas paucimobilis ATCC 31461 from Lactose Compared with Those Produced from Glucose and from Cheese Whey

Abstract: The dairy industry produces large quantities of whey as a by-product of cheese production and is increasingly looking for new ways to utilize this waste product. Gellan gum is reliably produced by Sphingomonas paucimobilis in growth media containing lactose, a significant component of cheese whey, as a carbon source. We studied and compared polysaccharide biosynthesis by S. paucimobilis ATCC 31461 in media containing glucose, lactose (5 to 30 g/liter), and sweet cheese whey. We found that altering the growth medium can markedly affect the polysaccharide yield, acyl substitution level, polymer rheological properties, and susceptibility to degradation. Depression of gellan production from lactose compared with gellan production from glucose (approximately 30%) did not appear to occur at the level of synthesis of sugar nucleotides, which are the donors of monomers used for biosynthesis of the repetitive tetrasaccharide unit of gellan. The lactose-derived biopolymer had the highest total acyl content; the glucose- and whey-derived gellans had similar total acyl contents but differed markedly in their acetate and glycerate levels. Rheological studies revealed how the functionality of a gellan polysaccharide is affected by changes in the acyl substitution.

Aggregation in Water of Dextran Hydrophobically Modified with Bile Acids

Abstract: The intra- and/or intermolecular aggregation and the structure of the aggregates formed in water by hydrophobically modified dextrans, prepared by covalent attachment of cholic or deoxycholic acid to dextran of Mv = 30 000, were investigated by various fluorescence and light scattering techniques From the variation of the fluorescence quantum yield and fluorescence emission maximum of a hydrophobic fluorescent probe, N-phenyl-1-naphthylamine, with polymer concentration, we conclude about the value of the critical aggregation concentration, cac, and the existence of intermolecular aggregation below cac The values of cac are found to depend on the nature of the hydrophobic moiety and the degree of substitution The hydrodynamic radii of the aggregates are determined using dynamic light scattering, and the apparent weight-average molecular weights, radii of gyration, and second virial coefficients are evaluated by static light scattering over a very large concentration range The results show that below a

Efficient techniques for accurate modeling and simulation of substrate coupling in mixed-signal IC's

Abstract: Industry trends aimed at integrating higher levels of circuit functionality have triggered a proliferation of mixed analog-digital systems. Magnified noise coupling through the common chip substrate has made the design and verification of such systems an increasingly difficult task. In this paper we present a fast eigendecomposition technique that accelerates operator application in BEM methods and avoids the dense-matrix storage while taking all of the substrate boundary effects into account explicitly. This technique can be used for accurate and efficient modeling of substrate coupling effects in mixed-signal integrated circuits.

Neutrino Driven Streaming Instabilities in a Dense Plasma

Abstract: The nonlinear self-consistent propagation of neutrinos in a dense plasma is described using the relativistic kinetic equations for neutrinos and electrons. The general nonlinear dispersion relation for a neutrino fluid coupled with a plasma is derived. For scenarios close to realistic astrophysical conditions, neutrino driven streaming instabilities can develop, with growth rates which scale with the Fermi constant ${G}_{F}$, thus leading to significant energy transfer from the neutrinos to the plasma.

Combinational equivalence checking using satisfiability and recursive learning

Abstract: The problem of checking the equivalence of combinational circuits is of key significance in the verification of digital circuits. Previously, several approaches have been proposed for solving this problem. Still, the hardness of the problem and the ever-growing complexity of logic circuits motivates studying and developing alternative solutions. In this paper we study the application of Boolean satisfiability (SAT) algorithms for solving the combinational equivalence checking (CEC) problem. Although existing SAT algorithms are in general ineffective for solving CEC, in this paper we show how to improve SAT algorithms by extending and applying recursive learning techniques to the analysis of instances of SAT. This in turn provides a new alternative and competitive approach for solving CEC. Preliminary experimental results indicate that the proposed improved SAT algorithm can be useful for a large variety of instances of CEC, in particular when compared with pure BDD-based approaches.