Showing papers by "University of Minho published in 1998"

The multi-trip vehicle routing problem

Abstract: The basic vehicle routing problem is concerned with the design of a set of routes to serve a given number of customers, minimising the total distance travelled In that problem, each vehicle is assumed to be used only once during a planning period, which is typically a day, and therefore is unrepresentative of many practical situations, where a vehicle makes several journeys during a day The present authors have previously published an algorithm which outperformed an experienced load planner working on the complex, real-life problems of Burton's Biscuits, where vehicles make more than one trip each day This present paper uses a simplified version of that general algorithm, in order to compare it with a recently published heuristic specially designed for the theoretical multi-trip vehicle routing problem

Designing and implementing combinator languages

Abstract: Ever since the Computer Science community has discovered the concept of a programming language there has been a continuous quest for the ideal, all-encompassing programming language; despite this we have been overwhelmed by an everlasting flow of all kinds of special purpose programming languages. Attempts to bridge this gap between a single language and infinitely many caused research into so-called extensible programming languages.

New starch-based thermoplastic hydrogels for use as bone cements or drug-delivery carriers.

Abstract: The development of new biodegradable hydrogels, based on corn starch/cellulose acetate blends, produced by free-radical polymerization with methyl methacrylate monomer (MMA) and/or an acrylic acid monomer (AA), is reported. The polymerization was initiated by a redox system consisting of a benzoyl peroxide and 4-dimethlyaminobenzyl alcohol at low temperature. These hydrogels may constitute an alternative to the materials currently used as bone cements or drug-delivery carriers. Swelling studies were carried out, as a function of pH and temperature, in buffered solutions. The xerogels were further characterized by Fourier transform-infrared spectroscopy. Tensile and compression tests, and dynamic mechanical thermal analysis were used to assess the mechanical performance of the developed materials. The fracture surfaces were observed by scanning electron microscopy. The developed materials are sensitive to the pH, showing a clear reversible transition in a relatively narrow interval of pH, which is just in the range of physiological conditions. These properties make the materials developed in this study very promising for biomedical applications. Fickian-type diffusion is the mechanism predominant in these systems, except for the composition with a higher concentration of AA, that corresponds to the most desirable kinetical behavior for controlled release (case II-transport mechanism). Furthermore, the results obtained in the mechanical tests are in the range of those reported for typical PMMA bone cements, showing that it is possible to develop partially degradable cements with an adequate mechanical behavior.

Mechanisms underlying the transport and intracellular metabolism of acetic acid in the presence of glucose in the yeast Zygosaccharomyces bailii

Abstract: Zygosaccharomyces bailii ISA 1307 displays biphasic growth in a medium containing a mixture of glucose (0.5%, w/v) and acetic acid (0.5%, w/v), pH 5.0 and 3.0. In cells harvested during the first growth phase, no activity of a mediated acetic acid transport system was found. Incubation of these cells in phosphate buffer with cycloheximide for 1 h restored activity of an acetic acid carrier which behaved as the one present in glucose-grown cells. These results indicated that the acetic acid carrier is probably present in cells from the first growth phase of the mixed medium but its activity was affected by the presence of acetic acid in the culture medium. In glucose-grown cells, after incubation in phosphate buffer with glucose and acetic acid, the activity of the acetic acid carrier decreased significantly with increased acid concentration in the incubation buffer. At acid concentrations above 16.7 mM, no significant carrier activity was detectable. Furthermore, the intracellular acid concentration increased with the extracellular one and was inversely correlated with the activity of the acetic acid carrier, suggesting the involvement of a feedback inhibition mechanism in the regulation of the carrier. During biphasic growth, the first phase corresponded to a simultaneous consumption of glucose and acetic acid, and the second to the utilization of the remaining acid. The enzyme acetyl-CoA synthetase was active in both growth phases, even in the presence of glucose. Activity of isocitrate lyase and phosphoenolpyruvate carboxykinase was found only in acetic-acid-grown cells. Thus it appears that both membrane transport and acetyl-CoA synthetase and their regulation are important for Z. bailii to metabolize acetic acid in the presence of glucose. This fact correlates with the high resistance of this yeast to environments with mixtures of sugars and acetic acid such as those often present during wine fermentation.

Oxidation resistance of (Ti, Al, Si)N coatings in air

Abstract: We prepared TiN-based multicomponent hard coatings by combined d.c. and r.f. magnetron sputtering with different contents of Ti, Al, Zr and Si on high speed steel substrates at 300°C. These coatings, with thicknesses ranging from 1 to 3 μm, were annealed in air at temperatures between 500 and 850°C in order to obtain information on their oxidation behaviour. The composition-depth profiles of heat-treated coatings were then measured by Rutherford backscattering spectrometry (RBS). The results show that the introduction of aluminium improves the oxidation resistance in all cases. During the heat treatment of Ti0.62Al0.38N at 600°C, a mixed oxide of Ti and Al is formed. At temperatures between 700 and 850°C, a protective superficial layer of Al2O3 with traces of Ti is formed, which is followed by an aluminium-depleted zone. However, for Ti0.57Al0.38Zr0.05N coatings, no protective Al2O3 layer was found on the surface after heat treatment. At 600°C, the oxidation resistance of Ti0.57Al0.38Zr0.05N is similar to that of (TiAl)N, but is about 30 times poorer at 700°C due to the absence of the protective Al2O3 layer. The Ti0.62Al0.26Si0.12N system shows a slightly lower oxidation resistance than (TiAl)N (Kp = 9.0 × 10−12 kg2 m−4 s−1 and Kp = 6.4 × 10−12 kg2 m−4 s−1 at 800°C respectively). It also forms a two-phase scale as in (TiAl)N, but the amount of Ti in the Al-rich outer layer is about 10 at.%, instead of 4at.% found in the (TiAl)N system. In the temperature range 700–850°C, oxidation is thermally activated with activation energies of 187 kJ mol−1 and 296 kJ mor−1 for (TiAl)N and (TiAlSi)N coatings respectively.

Carbon formation on nickel and nickel-copper alloy catalysts

Abstract: Equilibrium, kinetic and morphological studies of carbon formation in CH 4 + H 2 , CO, and CO + H 2 gases on silica supported nickel and nickel-copper catalysts are reviewed. The equilibrium deviates in all cases from graphite equilibrium and more so in CO + CO 2 than in CH 4 + H 2 A kinetic model based on information from surface science results with chemisorption of CH 4 and possibly also the first dehydrogenation step as rate controlling describes carbon formation on nickel catalyst in CH 4 + H 2 well. The kinetics of carbon formation in CO and CO + H 2 gases are in agreement with CO disproportionation as rate determining step. The presence of hydrogen influences strongly the chemisorption of CO. Carbon filaments are formed when hydrogen is present in the gas while encapsulating carbon dominates in pure CO. Small amounts of Cu alloying promotes while larger amounts (Cu : Ni > 0.1) inhibits carbon formation and changes the morphology of the filaments (octopus carbon formation). Adsorption induced nickel segregation changes the kinetics of the alloy catalysts at high carbon activities. Modifications suggested in some very recent papers on the basis of new results are also briefly discussed.

Indigo Backstaining During Cellulase Washing

Abstract: We have attempted to understand the mechanisms of indigo backstaining during enzyme stone washing by separately analyzing dye staining levels on different cotton surfaces during the process. The hi...

Effect of Aggregate Gradation on Fatigue Life of Asphalt Concrete Mixes

Abstract: Four-point bending fatigue tests following the Strategic Highway Research Program (SHRP) M009 test protocol were executed to investigate to what extent gradation has an effect on fatigue performance of asphalt aggregate mixes. Gradations and mixes were selected that would satisfy all volumetric Superpave designs passing below the restricted zone. Other mixes were prepared with gradations passing through and above the restricted zone. The measured fatigue lives of 130 actual laboratory tests were compared with predictions by the Shell, Asphalt Institute, and SHRP-A003A fatigue-predictive equations.

Physical, structural and mechanical characterization of Ti1−xSixNy films

Abstract: Within the frame of this work, Ti 1− x Si x N y hard coatings with 0≤ x ≤0.37 and thicknesses ranging from 1.2 to 3.5 μm, were prepared by r.f. reactive magnetron sputtering in an Ar/N 2 gas mixture. X-ray diffraction and Fourier analysis of X-ray profiles were used to investigate the structure and grain size, and its correlation with hardness behaviour, as a function of the Si content, bias voltage and working gas (argon) flow rate. In this respect, the results show that a double cubic phase of NaCl type was developed with lattice parameters of 4.18 and 4.30 A, revealing the (111) orientation for low Si content ( x =0.05), (220) for intermediate Si contents (0.13≤ x ≤0.22) and (200) for the highest Si contents (0.30≤ x ≤0.37). Regarding the results of ultramicrohardness tests, and although all samples with 0.05≤ x ≤0.30 present a hardness value higher than 30 GPa, the Ti 0.85 Si 0.15 N 1.03 revealed the highest hardness value, around 47 GPa, which is more than twice as high as that of common TiN. Furthermore, the study of hardness as a function of the applied bias voltage revealed that best results are achieved between −50 and 0 V. The variation in hardness as a function of the argon flow showed that best results in hardness are obtained when working with flow rates around 110 cm 3 /min.

Individual characteristics and career exploration in adolescence

Abstract: The effects of gender, age and school grade on several career exploration dimensions measured by the Career Exploration Survey were investigated. Subjects were high school students facing an imminent career decision. Regression analyses indicated that sex and grade-level were the most significant and prevailing individual characteristics related to the adolescents' career exploration behaviours, reactions and beliefs. Implications for career exploration interventions are discussed.

Hydrolysis of Cotton Cellulose by Engineered Cellulases from Trichoderma reesei

Abstract: We have characterized the activities of TC, EG-rich, and CBH-rich cellulases from T reesei and have shown that their activities towards cotton fabrics are influenced by ionic strength and adsorbed ionic species as well as by temperature and pH Adsorption and kinetic experiments confirm that increasing mechanical agitation favors EG attack by greatly increasing the availability of sites for EG adsorption It is not clear whether this is a consequence of fiber fibrillation damage or of improved access to fiber surfaces deep within the fabric structure The enhanced rate of cellulolytic hydrolysis of mer cerized cotton and the inhibitory effects on reactive and direct dyed fabrics are ex plained mainly in terms of increased or reduced availability of adsorption sites for CBHS and EGS The implications for textile finishing are far-reaching It is clear that a fabric's processing history (especially mercerizing and dyeing), construction, and level of ap plied mechanical agitation can be as important as the

Experimental behaviour of fibre concrete slabs on soil

Abstract: The cracking control of plain concrete slabs on soil foundation requires the execution of joints with mechanisms of load transfer between adjacent panels. These joints increase the construction costs and, often, are the source of local damage and loss of service performance. Slabs reinforced with steel wire mesh have been used in order to increase the load-carrying capacity and to enhance the cracking control. However, the use of this conventional reinforcement increases the costs, mainly due to labour time spent on the arrangement and positioning of the reinforcement. Fibre-reinforced concrete is a recent material well fitted for applications in industrial floors on soil foundation. The cost of fibres is compensated by a faster construction process and a reduction in the number of expansion joints. The fatigue, impact and flexural strength are significantly improved when steel fibres are added to the concrete mix. The work developed aims to contribute to the on going research effort to clarify the behaviour of fibre-reinforced concrete slabs on soil foundation. For this purpose, an experimental and numerical investigation were carried out. The present article deals basically with the experimental work developed, describing the tests performed and discussing the main results obtained. © 1998 John Wiley & Sons, Ltd.

Hydrodynamic studies in an airlift reactor with an enlarged degassing zone

Abstract: The hydrodynamic behaviour of a 60 l three-phase airlift bioreactor, of the concentric draught tube type, with an enlarged degassing zone has been studied. Ca-alginate beads were used as the solid phase. Airflow rate (from 1.9 to 90.2 l/min), solids loading (0% to 40% (v/v)) and solids density (1016 and 1038 kg/m3) were manipulated and their influence on solids and gas holdup, circulation and mixing times and in the interstitial liquid velocity was determined. Riser and downcomer solids holdup was found to decrease with the increase of airflow rate and to increase with solids loading and density. On the contrary, gas holdup in the riser and in the downcomer increased with airflow rate and decreased with solids loading and density. By increasing airflow rate, a decrease in circulation time was observed while the effects of solids loading and density were negligible. Mixing time decreased with airflow rate, increased with solids density, in the studied range, and presented a maximum for solids loading of approximately 20% (v/v).

Flow cytometric assessment of cell structural and functional changes induced by acetic acid in the yeasts Zygosaccharomyces bailii and Saccharomyces cerevisiae

Abstract: Flow cytometry (FCM) was used with different viability dyes to assess changes in cell structure and function induced by acetic acid (AA) in populations of Zygosaccharomyces bailii (AA resistant) and Saccharomyces cerevisiae (AA sensitive). Kinetic changes in esterase activity, intracellular dye processing, and membrane integrity were monitored, and to detect those changes we used three assays involving fluorescein diacetate hydrolysis, FUN-1 processing, and propidium iodide exclusion, respectively. In S. cerevisiae, the decrease in the ability to process FUN-1 preceded the decrease in esterase activity, and there was loss of cell membrane integrity after incubation with AA. In Z. bailii, with higher AA concentrations, there was a similar decrease in the ability to process FUN-1, which also preceded the loss of cell membrane integrity. Changes in esterase activity in this yeast induced by AA treatment could not be monitored because the changes occurred independently of the presence of the acid. For control samples (untreated cells killed with 10% v/v of AA), the percentages of nonaltered cells as estimated by FCM and percentages of viable cells as estimated by colony forming unit (CFU) counts were identical. However, for cell samples treated for short periods with 3% (v/v) or less of AA, none of the dyes produced FCM results comparable to those produced by CFU counts.

Influence of dissolved oxygen on the nitrification kinetics in a circulating bed biofilm reactor

Abstract: The influence of dissolved oxygen concentration on the nitrification kinetics was studied in the circulating bed reactor (CBR). The study was partly performed at laboratory scale with synthetic water, and partly at pilot scale with secondary effluent as feed water. The nitrifi- cation kinetics of the laboratory CBR as a function of the oxygen concentration can be described according to the half order and zero order rate equations of the diffusion- reaction model applied to porous catalysts. When oxygen was the rate limiting substrate, the nitrification rate was close to a half order function of the oxygen concentration. The average oxygen diffusion coefficient estimated by fit- ting the diffusion-reaction model to the experimental re- sults was around 66% of the respective value in water. The experimental results showed that either the ammonia or the oxygen concentration could be limiting for the nit- rification kinetics. The latter occurred for an oxygen to ammonia concentration ratio below 1.5-2 gO 2 /gN-NH a for both laboratory and pilot scale reactors. The volu- metric oxygen mass transfer coefficient (kLa) determined in the laboratory scale reactor was 0.017 s )1 for a super- ficial air velocity of 0.02 m s )1 , and the one determined in the pilot scale reactor was 0.040 s )1 for a superficial air velocity of 0.031 m s )1 . The kLa for the pilot scale reactor did not change significantly after biofilm development, compared to the value measured without biofilm. List of symbols a m 2 m )3 specific mass transfer surface area of the gas bubbles CL;O2 mgO 2 l ˇ1 actual dissolved oxygen

Regional Incentives and Industrial Location in Puerto Rico

Abstract: This study uses nested logit to estimate the influence of industrial incentives on the location of manufacturing plants in Puerto Rico. Puerto Rican laws grant generous tax exemptions and provide o...