Showing papers by "University of Minho published in 2000"

Decolorization and detoxification of textile dyes with a laccase from Trametes hirsuta.

Abstract: Trametes hirsuta and a purified laccase from this organism were able to degrade triarylmethane, indigoid, azo, and anthraquinonic dyes. Initial decolorization velocities depended on the substituents on the phenolic rings of the dyes. Immobilization of the T. hirsuta laccase on alumina enhanced the thermal stabilities of the enzyme and its tolerance against some enzyme inhibitors, such as halides, copper chelators, and dyeing additives. The laccase lost 50% of its activity at 50 mM NaCl while the 50% inhibitory concentration (IC(50)) of the immobilized enzyme was 85 mM. Treatment of dyes with the immobilized laccase reduced their toxicities (based on the oxygen consumption rate of Pseudomonas putida) by up to 80% (anthraquinonic dyes). Textile effluents decolorized with T. hirsuta or the laccase were used for dyeing. Metabolites and/or enzyme protein strongly interacted with the dyeing process indicated by lower staining levels (K/S) values than obtained with a blank using water. However, when the effluents were decolorized with immobilized laccase, they could be used for dyeing and acceptable color differences (DeltaE*) below 1.1 were measured for most dyes.

Characterisation of Ti1−xSixNy nanocomposite films

Abstract: Ti 1− x Si x N y films were synthesised by RF reactive sputtering from Ti and Si elemental targets, in an Ar/N 2 gas mixture. XRD results revealed the development of a two-phase system, composed of a nanocrystalline f.c.c. TiN (phase 1: B1 NaCl type) and a second one (phase 2), where Si atoms replaced some of the Ti ones, inducing a structure that we may call a solid solution. An amorphous phase, supposed to be of silicon nitride, within grain boundaries seems to be also present, especially for high Si contents. TEM experiments confirmed the f.c.c.-type structure for phase 2, which is the only phase that develops without ion bombardment. The higher lattice parameter of phase 1 (∼0.429 nm compared to 0.424 nm for bulk TiN) may be explained by the residual stress effect on peak position. The Ti replacement by Si would explain the low value of the lattice parameter for phase 2 (∼0.418 nm). All samples showed good results for hardness (Hv≥30 GPa), and Ti 0.85 Si 0.15 N 1.03 at a deposition temperature of 300°C showed a value of approximately 47 Gpa, which is approximately double that of pure TiN. For higher deposition temperatures, an increase in hardness is observed, as demonstrated by this same sample, which at 400°C reveals a value of approximately 54 GPa. Similar behaviour was observed in adhesion, where this same sample revealed a critical load for adhesive failure of approximately 90 N. In terms of oxidation resistance, a significant increase has also been observed in comparison with TiN. At 600°C, the oxidation resistance of Ti 0.70 Si 0.30 N 1.10 is already 100 times higher than that of TiN. For higher temperatures this behaviour tends to be even better when compared with other nitrides.

Target Representation on an Autonomous Vehicle with Low-Level Sensors

Abstract: How can low-level autonomous robots with only very simple sensor systems be endowed with cognitive capabilities? Specifically, we consider a system that uses seven infrared sensors and five microphones to avoid obstacles and acquire sound targets. The cognitive abilities of the vehicle consist of representing the direction in which a sound source lies. This representation supports target detection, estimation of target direction, selection of one out of multiple-detected targets, storage of target direction in short-term memory, continuous updating of memory, and deletion of memorized target information after a characteristic delay. We show that the dynamic approach (attractor dynamics) employed to control the motion of the robot can be extended to the level of representation by using dynamic neural fields to interpolate sensory information. We show how the system stabilizes decisions in the presence of multivalue sensorial information and activates and deactivates memory. Smooth integration of this targe...

Anisotropic Softening Model for Masonry Plates and Shells

Abstract: A model for the numerical analysis of masonry subjected to out-of-plane loading is proposed. The proposed composite plasticity model is able to reproduce elastic and inelastic behavior in two orthogonal directions coinciding with the orientation of the bed and head joints of masonry. The implementation of the model is described, and a comparison with experimental data on masonry strength is provided. Good agreement is found for different masonry types. Further validation of the model with experimental results on masonry panels subjected to out-of-plane loading demonstrates the accuracy of the proposed approach and the possibilities offered by numerical analysis for the understanding of the complex nonlinear phenomena involved in the failure of masonry plates and shells. In particular, this paper addresses issues such as the adequacy of yield-line analysis for the design of masonry structures subjected to out-of-plane loading, the influence of the aspect ratio of the panels, and the influence of in-plane n...

Hard nanocomposite Ti–Si–N coatings prepared by DC reactive magnetron sputtering

Abstract: Films resulting from Si additions to TiN matrix were prepared with Si contents in the range 0–19 at.%, using a closed field unbalanced DC magnetron sputtering system. Transmission Electron Microscopy (TEM) analyses revealed the nanocrystalline nature of these coatings, confirming the results of grain size evaluation from X-ray diffraction (XRD) patterns. Nanoindentation tests and scratch tests were carried out for the mechanical characterisation. Regarding the results, the samples show hardness values as high as 45 GPa. Best hardness values were found for Si content in the range 4–10 at.%. Almost all samples showed high critical loads for total adhesion failure, generally higher than 80 N, although the critical load for the first adhesion failure was found to be lower than 20 N for several samples. XRD patterns revealed the presence of only one phase that can be assigned to a cubic B1 NaCl structure, typical for TiN, with a lattice parameter of approximately 0.430 nm. The preferential growth, as a function of Si content, changes from a strong (111) orientation at the lowest Si additions to a weak (200) orientation at the highest Si content. Density values in the range 3.0–3.7 g/cm3 were obtained for most of the samples prepared with deposition rates between 0.5 and 1.1 μm/h, although higher density values were obtained for higher Ti deposition rates, with maximum of approximately 4.7 g/cm3 for the case of samples with low Si content.

Biomass conversion: attempted electrooxidation of lignin for vanillin production

Abstract: Electrochemical oxidative degradation of Kraft lignin was investigated in batch and flow cells on Pt, Au, Ni, Cu, DSA–O2 and PbO2 anodes. Production of vanillin was evaluated by means of formal kinetic analyses. Conversion and chemical yields were found to be dependent mainly on the applied current density, that is on the partial pressure of oxygen at the interface, while the nature of the electrode influenced the reaction rates.

Selective Enzyme-Mediated Extraction of Capsaicinoids and Carotenoids from Chili Guajillo Puya (Capsicum annuum L.) Using Ethanol as Solvent

Abstract: The selective extraction of capsaicinoids and carotenoids from chili guajillo "puya" flour was studied. When ethanol was used as solvent, 80% of capsaicinoids and 73% of carotenoids were extracted, representing an interesting alternative for the substitution of hexane in industrial processes. Additionally, when the flour was pretreated with enzymes that break the cell wall and then dried, extraction in ethanol increased to 11 and 7% for carotenoid and capsaicinoid, respectively. A selective two-stage extraction process after the treatment with enzymes is proposed. The first step uses 30% (v/v) ethanol and releases up to 60% of the initial capsaicinoids, and the second extraction step with industrial ethanol permits the recovery of 83% of carotenoids present in the flour.

Transport properties of polymer-vapour grown carbon fibre composites

Abstract: DC electrical resistivity and thermal conductivity of polypropylene (PP) filled with vapour grown carbon fibre (VGCF) was studied. This was done for a wide range of fibre content and compared to systems produced under the same conditions in which a conventional carbon fibre was used as filler. The composites studied exhibit characteristic percolating behaviour. Because of the low degree of graphite perfection in the VGCF used in this work, the fraction of VGCF required to achieve percolation was higher than expected. Non-linear I – V characteristics and time dependent electrical resistivity effects are only observed in PP filled with VGCF. Several mechanisms must be called upon to explain the observed electrical behaviour of the PP/VGCF composite. The thermal conductivity of the composites is in agreement with the effective medium theories.

GUP1 and its close homologue GUP2, encoding multimembrane-spanning proteins involved in active glycerol uptake in Saccharomyces cerevisiae.

Abstract: Many yeast species can utilize glycerol, both as a sole carbon source and as an osmolyte. In Saccharomyces cerevisiae, physiological studies have previously shown the presence of an active uptake system driven by electrogenic proton symport. We have used transposon mutagenesis to isolate mutants affected in the transport of glycerol into the cell. Here we present the identification of YGL084c, encoding a multimembrane-spanning protein, as being essential for proton symport of glycerol into S. cerevisiae. The gene is named GUP1 (glycerol uptake) and, for growth on glycerol, is important as a carbon and energy source. In addition, in strains deficient in glycerol production it also provides osmotic protection by the addition of glycerol. Another open reading frame (ORF), YPL189w, presenting a high degree of homology to YGL084c, similarly appears to be involved in active glycerol uptake in salt-containing glucose-based media in strains deficient in glycerol production. Analogously, this gene is named GUP2. To our knowledge, this is the first report on a gene product involved in active transport of glycerol in yeasts. Mutations with the same phenotypes occurred in two other ORFs of previously unknown function, YDL074c and YPL180w.

Enzymatic Decolorization of Textile Dyeing Effluents

Abstract: Commercial azo, triarylmethane, antraquinonic, and indigoid textile dyes are efficiently decolorized with enzyme preparations from Pleurotus ostreatus, Schizophyllum commune, Neurospora crassa, Polyporus sp., Sclerotium rolfsii, Trametes villosa, and Mycelioph tora thermophila. The nature of substituents on the dyes' benzene rings influences enzyme activity, and hydroxyl and amino groups enhance decolorization. The presence of lignin peroxidase and/or manganese peroxidase in addition to laccase (P. ostreatus, S. commune, S. rolfsii, N. crassa) increases decolorization by up to 25%. The effect of textile dyeing auxiliaries depends on the individual enzymes. Polyporus sp. and T. villosa are inhibited up to 20% by copper and iron chelating agents and anionic detergents, while the S. commune enzymes lose up to 70% of their activity.

Biological treatment of effluent containing textile dyes

Abstract: Colour removal of textile dyes from effluent was evaluated using a laboratory ‘upflow anaerobic sludge blanket’ reactor. Several commercial dyes were selected to study the effect of dye structure on colour removal. The anaerobic reactor was fed with glucose, an easily biodegradable organic matter and selected individual dyes. Results show that some of the dyes are readily reduced under anaerobic conditions even at a high concentration of 700 mg/l. The average removal efficiency for acid dyes using this method was between 80 and 90% and that observed for the direct dye used was 81%. Laboratory experiments using the anaerobic reactor with disperse dyes, such as an anthraquinonebased dye, were unsuccessful even at low concentrations of 35 mg/l. Additional experiments were conducted to evaluate the toxicity of a selected disperse dye to an anaerobic environment. Results indicate that the purified dye is more toxic to the biomass than the commercial one.

Estudo de validação da bateria de provas de raciocínio (BPR-5)

Abstract: This research investigates reliability and validity of the Reasoning Battery Tests (BPR-5), a reduced version of the Battery of Differential Reasoning Tests (BPRD; Almeida, 1988). It is comprised by five subtests: Abstract Reasoning, Verbal Reasoning, Numerical Reasoning, Spatial Reasoning and Mechanical Reasoning. The participants were 1243 sixth grade to high school students from Brazil (N=771) and Portugal (N=472). The internal consistency coefficients varied from 0,62 to 0,84 and split-half coefficients 0,65 to 0,87. The factor analysis indicated an unidimensional solution accounting for approximately 55% of the total variance representing a composite score based on fluid intelligence, crystallized intelligence, visual processing ability, quantitative ability and practical-mechanical knowledge. The criterion validity coefficients based on the correlation with school success were around 0,54 (p < 0,01). It was concluded that the BPR-5 constitutes an efficient and fast way to assess general and specific abilities and could be a valuable instrument for professionals in their assessment needs.

Nitrile hydratase and amidase from Rhodococcus rhodochrous hydrolyze acrylic fibers and granular polyacrylonitriles.

Abstract: Rhodococcus rhodochrous NCIMB 11216 produced nitrile hydratase (320 nkat mg of protein−1) and amidase activity (38.4 nkat mg of protein−1) when grown on a medium containing propionitrile. These enzymes were able to hydrolyze nitrile groups of both granular polyacrylonitriles (PAN) and acrylic fibers. Nitrile groups of PAN40 (molecular mass, 40 kDa) and PAN190 (molecular mass, 190 kDa) were converted into the corresponding carbonic acids to 1.8 and 1.0%, respectively. In contrast, surfacial nitrile groups of acrylic fibers were only converted to the corresponding amides. X-ray photoelectron spectroscopy analysis showed that 16% of the surfacial nitrile groups were hydrolyzed by the R. rhodochrous enzymes. Due to the enzymatic modification, the acrylic fibers became more hydrophilic and thus, adsorption of dyes was enhanced. This was indicated by a 15% increase in the staining level (K/S value) for C.I. Basic Blue 9.

Rheological Behavior of (Short) Carbon Fiber/ Thermoplastic Composites. Part I: The Influence of Fiber Type, Processing Conditions and Level of Incorporation

Abstract: The aim of this work is to understand the influence of type of (short) carbon fibers, processing conditions and fiber incorporation level on the rheological behavior of carbon fiber/polypropylene (PP) composites. For this purpose, two types of fibers (sub-micron Vapor Grown Carbon Fibers, VGCF, and ex-PAN, PAN), three different extruder screw geometries and three different fiber incorporation contents were studied. The rheological characterization was performed by means of capillary and rotational rheometry, results being presented and discussed in terms of reinforcing capability in both shear (steady and oscillatory) and extensional flows. The results show that VGCF have a generally higher influence on the rheological behavior of the composites than the PAN fibers. However, because of their higher intrinsic rigidity, PAN fibers give rise to composites with better mechanical properties than the VGCF ones. It is also shown that the influence of the screw geometry on fiber damage and, consequently, on the behavior of the composites, is weak, fiber degradation occurring mainly in the compounding stage. The incorporation level has the expected influence, i.e., it produces gradual changes in all the properties considered in this study.

Experimental and theoretical study of twin‐screw extrusion of polypropylene

Abstract: The flow of a polypropylene in a self-wiping corotating twin-screw extruder was characterized by measuring the pressure, temperature, and residence time along the screw profile. The influence of the operating conditions (feed rate, screw speed, barrel temperature) and screw profile was studied. Flow modeling was performed using the Ludovic© software and measured and calculated pressure, temperature, residence time, and energy consumption were compared. The values of the temperature close to the melting zone were overestimated by the model, which considers instantaneous melting upon the first restrictive screw element. If the program assumes that melting occurs at the screw location identified experimentally, a correct description of the temperatures along the screw profile is produced. The influence of the processing conditions (feed rate, screw speed, barrel temperature, screw profile) is well described by the model. These results put in evidence the importance of including an adequate melting model in the modeling of the twin-screw extrusion process. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1419–1430, 2000

Applications of yeast flocculation in biotechnological processes

Abstract: A review on the main aspects associated with yeast flocculation and its application in biotechnological processes is presented. This subject is addressed following three main aspects—the basics of yeast flocculation, the development of “new” flocculating yeast strains and bioreactor development. In what concerns the basics of yeast flocculation, the state of the art on the most relevant aspects of mechanism, physiology and genetics of yeast flocculation is reported. The construction of flocculating yeast strains includes not only the recombinant constitutive flocculent brewer's yeast, but also recombinant flocculent yeast for lactose metabolisation and ethanol production. Furthermore, recent work on the heterologous β-galactosidase production using a recombinant flocculentSaccharomyces cerevisiae is considered. As bioreactors using flocculating yeast cells have particular properties, mainly associated with a high solid phase hold-up, a section dedicated to its operation is presented. Aspects such as bioreactor productivity and culture stability as well as bioreactor hydrodynamics and mass transfer properties of flocculating cell cultures are considered. Finally, the paper concludes describing some of the applications of high cell density flocculation bioreactors and discussing potential new uses of these systems.

Monitoring polyolefin modification along the axis of a twin‐screw extruder. II. Maleic anhydride grafting

Abstract: The physico-chemical phenomena developing along the screw axis of a twin-screw extruder during the grafting of maleic anhydride (MA) onto polyolefins [polyethylene (PE), ethylene–propylene rubber (EPM), and polypropylene (PP)] were investigated. For this purpose, sampling devices located along the extruder barrel were used to collect polymer samples that were subsequently characterized to follow the degrees of grafting and crosslinking or degradation. A similar evolution of MA grafting was observed regardless of the polyolefin type or MA and peroxide concentration when grafting was performed under identical conditions, that is, the same peroxide type and set temperature. A correlation between the MA grafting and the calculated peroxide decomposition was established. Chemical reactions occurred along the extruder axis until the peroxide was fully converted. More detailed quantitative measurements of the peroxide decomposition and MA grafting would allow the development of accurate process models. The final MA content depended on the polyolefin composition (PE > EPM ≫ PP). As expected for PE, crosslinking occurred in addition to grafting, but after a certain residence time, the PE network degraded. The PP viscosity reduction after MA grafting was due to the conversion of tertiary PP radicals into primary PP radicals after grafting. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3919–3932, 2000

An Experimental Investigation of the Effect of Groove Location and Supply Pressure on the THD Performance of a Steadily Loaded Journal Bearing

Abstract: This paper aims to present the results of parametric experiments carried out in order to study the influence of groove location and supply pressure on the performance of a steadily loaded journal bearing with a single-axial groove, Hydrodynamic pressure and temperature distributions on the bush surface, shaft temperature, flow rate and bush torque were measured at variable supply pressure, using bushes with a single groove located at three different positions. A series of tests were carried out for variable applied load and rotational speed. The experimental evidence shows that some bearing characteristics are significantly sensitive to changes in groove location and supply pressure. One groove located at 30 degrees in relation to the load line, in the direction of shaft rotation, can conduct to reductions in maximum temperature, maximum hydrodynamic pressure and bush torque, with a moderate increase in oil flow rate.

The role of exopolymers in the attachment of sphingomonas paucimobilis

Abstract: The importance of exopolymers in the adhesion of Sphingomonas paucimobilis was established by studying the attachment to glass of three mutants with defective gellan production. The attachment assays were performed in either phosphate buffered saline (controls) or in the exopolymeric solutions produced by the mutants. The exopolymer was found to have surface active properties, changing the glass surface from hydrophilic to hydrophobic, making adhesion thermodynamically favourable. Only the cells that had a substantial polymeric layer surrounding their walls were able to significantly colonise glass coated with the exopolymer. It is hypothesised that the exopolymer bound to the glass and the exopolymer present at the surface of the bacteria bound together, overcoming the energy barrier created by the negative charge of both surfaces. It is concluded that the exopolymer from S. paucimobilis has a dual role in the process of adhesion by both coating the surface thereby strengthening adhesion and by enhancing...