Anti-Dissipative Schemes for Advection and Application to Hamilton–Jacobi–Bellmann Equations

We propose two new antidiffusive schemes for advection (or linear transport), one of them being a mixture of Roe’s Super-Bee scheme and of the “Ultra-Bee” scheme. We show how to apply these schemes to treat time-dependent first order Hamilton–Jacobi–Bellman equations with discontinuous initial data, possibly infinitely-valued. Numerical tests are proposed, in one and two space dimensions, in order to validate the methods AMS subject classifications. Primary 65M12, Secondary 58J47     

Mathematical modeling of gas‐phase biofilter performance

In the present paper, a new mathematical model describing the physical, chemical and biological phenomena involved in the process of contaminant removal in biofilters is developed. In addition to the contaminant, the key components of the present theoretical model are carbon dioxide and oxygen. The model predicts the concentration profile of the key components in the gas phase, the biofilm and the sorption liquid retained in the solid particles composing the filter bed at both steady and transient regimes. The model equations were solved numerically and comparison between theory and experiment showed that the model results for styrene and carbon dioxide concentration profiles were in very good agreement with experimental data for the biofiltration of styrene vapors at steady state. The analysis of oxygen concentration profile in the biofilm predicted by the theoretical model revealed that oxygen limitation does not occur under the operating styrene biodegradation rate in the biofilter. Copyright © 2003 Society of Chemical Industry     

Evaluation of the two‐parameter fracture criterion for various crack configurations made of 7075‐T6 aluminium alloy using finite‐element fracture simulations

For many years, a two‐parameter fracture criterion (TPFC) has been used to correlate and predict failure loads on cracked metallic fracture specimens. The current study was conducted to evaluate the use of the TPFC on a high‐strength aluminium alloy, using elastic‐plastic finite‐element (FE) analyses with the critical crack‐tip‐opening angle (CTOA) fracture criterion. In 1966, Forman generated fracture data on middle‐crack tension, M(T), specimens made of thin‐sheet 7075‐T6 aluminium alloy, which is a quasi‐brittle material. The fracture data included a wide range of specimen half‐widths (w) ranging from 38 to 305 mm. A two‐dimensional FE analysis code (ZIP2D) with a “plane‐strain core” option was used to model the fracture process with a critical CTOA chosen to fit the M(T) test data. Fracture simulations were then conducted on other M(T), single‐edge‐crack tension, SE(T), and bend, SE(B), specimens over a wide range in widths (w = 19‐610 mm). No test data were available on the SE‐type specimens. The results supported the TPFC equation for net‐section stresses less than the material proportional limit. However, some discrepancies in the FE fracture simulations results were observed among the numerical analyses made on the three specimen types. Thus, more research is needed to improve the transferability of the TPFC from the M(T) specimen to both the SE(T) and SE(B) specimens for quasi‐brittle materials.     

A novel procedure for the measurement of the kinetics of styrene biodegradation in a biofilter

A novel procedure for the study of the biodegradation kinetics of styrene is proposed in this paper. Microbial growth tests in the presence of styrene were performed using suspensions of microorganisms prepared from samples of filter bed material. This material had been directly withdrawn previously from an operating biofilter employed for the removal of styrene vapours from air. The kinetics tests were initiated immediately after transfer of filter bed samples from the active styrene filter bed to sealed flasks containing a mineral‐based medium, and were performed in such a manner that no enrichment technique or lag phase treatment was necessary to activate the desired biodegradation of styrene. The complete biodegradation of freshly introduced styrene was observed within a few hours of the filter bed's initial contact with the active microbial suspension. A novel theoretical development, as proposed in this study, has provided us with the means for estimating the yield coefficient of the biomass with respect to the styrene consumed and the kinetic coefficients of the growth rate without having to perform any analyses of the liquid phase after start‐up of the growth tests. Only monitoring of the styrene and carbon dioxide concentrations in the liquid and gas phases in the test flasks was necessary. The Haldane model, with inhibition expected at high styrene concentrations, was found to be the best to represent the biodegradation kinetics of styrene in this environment. Copyright © 2005 Society of Chemical Industry     

Multicast Routing in Mobile Ad Hoc Networks

We focus on one critical issue in mobile ad hoc networks that is multicast routing. Advantages and limitations of existing routing protocols are illustrated. Optimal routes, stable links, power conservation, loop freedom, and reduced channel overhead are the main features to be addressed in a more efficient mechanism. In this paper, we propose a new on-demand multicast routing protocol, named Source Routing-based Multicast Protocol (SRMP). Our proposition addresses two important issues in solving routing problems: (i) path availability concept, and (ii) higher battery life paths. SRMP applies a source routing mechanism, and constructs a mesh to connect group members. It provides stable paths based on links' availability according to future prediction of links' states, and higher battery life paths. This protocol succeeded to minimize network load via designing optimal routes that guarantee reliable transmission and active adaptability. A performance comparison study with On-demand Multicast Routing Protocol (ODMRP) and Adaptive Demand-driven Multicast Routing (ADMR) protocol is undertaken. Analysis results show the strength of the SRMP nodes' selection criteria and its efficient energy consumption compared to the other two protocols.     

LBIC measurement optimization to detect laser annealing induced defects in Si

Because of the short penetration depth of ultraviolet (UV) in semiconductor, the realization of UV sensors requires the reduction of the junction thickness. Excimer laser annealing (ELA) is a new annealing technical allowing to achieve a thin layer (<30 nm) heavily boron doped (R_sq < 350 Ω/sq) on n-type silicon substrate together with a good profile abruptness (<3 nm/dec).     

Understanding improvisation in construction through antecedents,behaviours and consequences

Improvisation is a deliberate, spontaneous and rational decision-making process that helps address emerging issues or unplanned work. Traditional management avoids relying on improvisation as it indicates deviation from the pre-planned procedures and standards. However, improvisational practices continue to exist within numerous uncertain environments such as construction where improvised actions emerge even though they are not encouraged. The purpose of this study is to develop a better understanding of the improvisational practices occurring in construction and recognize the factors contributing to successful improvisation. This study elucidates antecedents, behaviours and consequences of improvisation in various construction operations. Surveys were conducted among different construction professionals to understand improvisation on real-life construction projects. Statistical analyses show that personal experience and the type of organization a person works for have a significant effect on the outcomes of improvisation. In addition, results highlight the most frequent antecedents that trigger the need for improvisation to complete a certain task. The outcomes of this study can help managers and decision makers in the construction industry identify personal, organizational and other specific characteristics that may improve the practice of improvisation for complementing planning processes rather than undermining them.     

Treatment of air polluted with high concentrations of toluene and xylene in a pilot-scale biofilter

Air biofiltration is now under active consideration for the removal of the volatile organic compounds from air polluted streams. In order to investigate the performance of this newly developed technology, a biofiltration pilot unit was operated for a continuous period of 8 months. The biofilter column was packed with commercially conditioned peat. At start-up, the filter bed was inoculated with four species of microorganisms. The resulting biofilter was fed with air contaminated with toluene, xylene or a mixture of toluene and xylene. The maximum elimination capacities attained were 165 g m⁻³ h⁻¹ for toluene, 66 g m⁻³ h⁻¹ for xylene and 115 g m⁻³ h⁻¹ for the mixture of toluene and xylene. These specific performances exceed the values published in the technical and commercial literature for similar processes. Xylene isomers were degraded in decreasing order of reactivity, m-xylene, p-xylene, o-xylene. In the case of air polluted with a toluene and xylene mixture, it was noticed that the metabolism of toluene biodegradation was inhibited by the presence of xylene. Characterization of the biofilm microbial populations after several weeks of operation showed that the dominant strains among the isolated culturable strains from the biofilm, even if different from the initially inoculated strains, had at least one physiological property favoring degradation of aromatic organic rings. The performance of the biofilter was found to be dependent on the temperature of the filter media and the pressure drop through the bed. Finally, a steady state mathematical model was tested in order to theoretically describe the experimental results. This model is used to illustrate the operating diffusion and reaction regimes at steady state for the case of each pollutant. © 1998 Society of Chemical Industry