Special issue on information systems quality management in practice

Software Quality Journal -     

Dynamics of deviations from the Gaussian state in a freely cooling homogeneous system of smooth inelastic particles

The time dependence of deviations from the Gaussian state in a freely cooling homogeneous system of smooth inelastically colliding spheres is investigated by kinetic theory. We determine the full time dependence of the coefficients of an expansion around the Gaussian state in Generalized Laguerre polynomials. Approximating this system of equations to sixth order, we find that the asymptotic state, where the mean energy T follows Haff's law with time independent cooling rate, is reached within a few collisions per particle. Two-dimensional molecular dynamics simulations confirm our results and show exponential behavior in the high-energy tails. Received: 10 January 2000     

NUMERICAL MODEL FOR WAX DEPOSITION IN OIL WELLS

A liquid-solid compositional model that uses an equation of state has been developed to predict the phenomenon of wax deposition in model oil wells. Numerical solutions to the conservation equations for Newtonian-to-non-Newtonian flow regimes show temperature, radial mass flux and wax deposition profiles as a function of time and position in the pipe, using realistic pressure and temperature profiles of a model well. Such rheologic regime changes are dictated by thermodynamic arguments.     

One-step, PCR-mediated, gene disruption in the yeast Hansenula polymorpha.

Previous evidence based on the experience of our laboratory showed that one-step gene disruption in the yeast Hansenula polymorpha is not straightforward. A systematic study of several factors which could affect gene disruption frequency was carried out. We found that the more critical factor affecting one-step gene disruption in H. polymorpha is the length of the target gene region flanking the marker gene. Target gene regions of about 1 kb flanking the marker gene were necessary to obtain a disruption frequency of about 50%. However, the gene marker, either homologous or heterologous, the locus and the strain examined did not significantly affect the frequency of disruption; the highest disruption frequency obtained for the YNR1 gene was in the strain HMI39, using the Saccharomyces cerevisiae URA3 gene as a marker. Since long regions flanking the gene marker do not allow the easy PCR-mediated strategies, developed for S. cerevisiae, to obtain constructs to disrupt a given gene in H. polymorpha, an alternative PCR strategy was developed.     

Expected render performance assessment based on impact resistance in situ determination

External renders must fulfil certain functions to ensure a good in-service performance of façades such as: waterproofing and protection of the walls, finishing of the surfaces, durability in face of the external degradation agents, and adequacy to use. Defective surface resistance of the renders (significant deterioration under impact and friction actions inherent to the normal use of the building) accelerates the degradation process, leading to a significant loss of physical and aesthetical performance. Based on laboratory experimental testing and on-site investigation, with various types of renders and using the Martinet-Baronnie device, the parameters of surface resistance are discussed, in terms of resistance to the impact of hard objects (with and without cutting edges). The results allowed criteria to be proposed for the in situ assessment of external renders in buildings with brick masonry walls (characterization of predicted surface impact resistance in-service conditions).     

New approach for the prediction of azeotropy in binary systems

A new approach for the prediction of azeotrope formation between components in a mixture, that does not require vapor–liquid equilibrium calculations, is presented. The method employs neural networks to correlate azeotropic data for binary mixtures with a series of macroscopic and microscopic properties of the pure components, without explicit consideration of non-ideality of mixture. The model fails to make a clear prediction regarding azeotropy in only a relatively small number of situations in which structurally homologous molecules are known to exhibit quite distinct azeotropic behavior.     

High-Strength Porous Alumina Ceramics by the Pulse Electric Current Sintering Technique

High-strength porous alumina has been fabricated with a microstructure control using the pulse electric current sintering (PECS) technique. During sintering the discharge, which is assumed to take place in the voids between the particles, is thought to promote the bridging of particles by neck growth in the initial stages of sintering, leaving high porosity. The effect of dopants (MgO, 200 ppm; TiO₂, 1000 ppm) and of secondary inclusions (3 vol% 3Y-TZP) on the constrained densification and the improvement in the mechanical behavior of porous alumina ceramics has been reported. The porosity of the fabricated porous alumina was controllable between 30% and 50% depending on the sintering temperature. The flexural strength of alumina having 30% and 42% porosity showed impressive values of 250 and 177 MPa, respectively. The dominance of the preferential neck growth of grains over densification significantly improved the mechanical properties of porous alumina, besides leaving high porosity.