Application of an alternative contractor selection model

The results described confirm the thorough assessment implemented by the model and an output mechanism able to highlight key contractor characteristics. The exercise also supports the contention, that examination of contractors should aim to establish project performance potential and rely less on estimated project cost (tender sum).     

DEFECT CORRECTION WITH A FULLY COUPLED INEXACT NEWTON METHOD

Abstract

We examine the characteristics of a fully coupled inexact Newton method using defect correction to obtain high-order solutions for two problems: natural convection in a square cavity and mixed-convection flow over a backward step. Newton's method produces a linearized system with a Jacobian matrix and a residual vector, each of which can be formed using different discrete operators. Solution accuracy depends on the discretization used for the residuals. Defect correction employs low-order operators for the Jacobian but high-order operators for the residuals. We employ an O(h³) convection operator in the residual vector and upwinding in the Jacobian. We find that defect correction is an efficient and effective way to achieve high-order solutions.     

The limits of testing particle-mediated oxidative stress in vitro in predicting diverse pathologies; relevance for testing of nanoparticles

In vitro studies with particles are a major staple of particle toxicology, generally used to investigate mechanisms and better understand the molecular events underlying cellular effects. However, there is ethical and financial pressure in nanotoxicology, the new sub-specialty of particle toxicology, to avoid using animals. Therefore an increasing amount of studies are being published using in vitro approaches and such studies require careful interpretation. We point out here that 3 different conventional pathogenic particle types, PM₁₀, asbestos and quartz, which cause diverse pathological effects, have been reported to cause very similar oxidative stress effects in cells in culture. We discuss the likely explanation and implications of this apparent paradox, and its relevance for testing in nanotoxicology.     

Influence of H2/NH3 mixtures on the composition of SiCNYO and SiCNAl(O) nanopowders

We performed pyrolysis of SiCNAlH and SiCNYOH nanopowder precursors under a reactive atmosphere (Ar/NH₃/H₂) with various compositions of ammonia (NH₃) and dihydrogen (H₂) to diminish C content, which is deleterious for thermal stability and sintering of the powders. This paper continues a previous work on the fabrication of an Si₃N₄/SiC composite without free C by studying the effect of H₂ on the C/N atomic ratio of the powder. We studied the influence of the nature of the gaseous mixture (Ar/NH₃/H₂) on the powder composition. Elemental analysis showed that the introduction of H₂ in the pyrolysis atmosphere limited the decomposition of NH₃ and allowed for control of the C/N ratio. This behaviour can be explained by the structural evolution observed by ²⁹Si NMR spectrometry but also by Fourier transform infrared and Raman spectroscopy. An Si₃N₄/SiC composite, with traces of free C, was obtained after post-pyrolysis heat treatment of the powders synthesized with 10 wt.% of H₂ and 25 wt.% NH₃.     

Secondary population implementation in multi-objective evolutionary algorithm for scheduling of FMS

Any practical implementation of any multi-objective evolutionary algorithm (MOEA) must include a secondary population composed of all Pareto-optimal solutions found during its search process. Such an implementation with an active participation of solutions from the secondary population into the generational population of the genetic cycle is expected to improve the effectiveness of the MOEA. In this work, two kinds of secondary population, one with set of non-dominated solutions and another with a set of inferior solutions, accrued out of the generation cycles are constructed, and with different combinations of feeding of solutions from these two secondary populations, seven different implementation schemes are designed with an aim of intensifying the convergence and diversification capabilities of the genetic process of MOEA. All the schemes were implemented in a genetic algorithm-based MOEA designed to solve the scheduling problem with dual objectives for a flexible manufacturing system and tested with common experimental data. The performances of the schemes are compared, and the most appropriate implementation scheme is proposed.     

Coplanar QCA crossovers

Quantum-dot cellular automata (QCA) is one of the promising nextgeneration fabrics for circuits. Coplanar wire crossings are one of the more elegant features of this new low-power computing paradigm. Proposed are coplanar wire crossovers using a single type of QCA cells, which has significant implications in fabrication and fault tolerance.     

Implications of sensor location in steam reformer temperature control

Hydrogen can be produced via steam reformation of many feedstocks. External heat sources provide the thermal energy required by the endothermic steam reformation reactions. Temperature control of the steam reformation reactor is critical to reactor performance and catalyst life. Closed-loop control systems are typically used to modulate the heat input rate based on a comparison between a set point temperature and a temperature measurement. The location of the temperature sensor relative to the heat input location is a choice made during reactor design that can have significant impact on reactor temperature control.     

Tert-butyl acetate: Non-HAP solvent for high-solids epoxy formulations

Xylene is the traditional diluent solvent for formulating epoxy/amine paints used in protective coatings and linings. Currently, it is under regulatory pressure because it is on the hazardous air pollutant (HAP) list and it is also a volatile organic compound (VOC). Ketones and acetate esters are powerful solvents, but their use is limited by their reaction with the amine curatives before paint application. Tert-butyl acetate (t-BAc) proposed as a VOC-exempt solvent, is a nonreactive, non-HAP solvent suitable for both the epoxy resin and amine curative sides of a two-component epoxy system. Molecular modeling predicts very low reactivity of the t-BAc ester functionality with amine nucleophiles as a result of steric hindrance. Long-term aging studies with amine curatives in t-BAc solutions confirm these theoretical results. Kinetics of the reaction of amines with t-BAc and its n-butyl acetate isomer support the view that steric hindrance plays a major role in amine solution stability. Presented at the International Waterborne, High-Solids, and Powder Coatings Symposium, February 21–23, 2001, New Orleans, LA. 3801 West Chester Pike, Newtown Square, PA 19073.