Parallel Gaussian elimination on an MIMD computer

This paper introduces a graph-theoretic approach to analyse the performances of several parallel Gaussian-like triangularization algorithms on an MIMD computer. We show that the SAXPY, GAXPY and DOT algorithms of Dongarra, Gustavson and Karp, as well as parallel versions of the LDM^t, LDL^t, Doolittle and Cholesky algorithms, can be classified into four task graph models. We derive new complexity results and compare the asymptotic performances of these parallel versions.     

Polarimetric observation of forest cover in radar remote sensing

In this paper, and from the received waves, we investigate a number of Polarimetric radar techniques to characterize the polarization response of forest cover, using the example of the Landes Forest. Magnitude, as well as phase difference and amplitude ratios between the Polarimetrie channels, which are closely related to the texture of the scene, offer reliable means for data characterization and discrimination purposes. The statistical properties of high resolution Polarimetrie sar are investigated, using the K distribution to model the received amplitude of each area selected. This distribution is derived with a parameter, a, which is closely related to the heterogeneity of the ground cover, and thus provides a good tool for discriminating among different regions. From the Stokes matrix, the co- and crosspola-rized signatures are constructed, for both clear cut and full-grown tree regions, in order to identify the predominant scattering mechanisms contributing to total measured backscatter.     

Numerical simulation of fluid-structure interaction in a stirred vessel equipped with an anchor impeller

A coupling algorithm is used to compute the equilibrium of a flexible anchor impeller in a stirred vessel. This coupling algorithm is based on a partitioned approach, which consists of three relatively independent modules: the computational fluid dynamics (CFD), the computational structure dynamics (CSD) and the interface. In the CFD module, the Euler formulation was used to account for the moving boundary. In the CSD module, the updated Lagrangian formulation for solving the motion of non-linear structure was used and a static study was adopted. In the interface module, an exchange of the forces and displacements was allowed. The numerical results, such as the velocity field, the turbulent kinetic energy, its dissipation rate, the turbulent viscosity and the mechanical deformation, have been presented. Particularly, we are interested in the study of the static behavior of the anchor impeller and the evolution of the displacement field of the arms during various iterations of our coupling algorithm. Accordingly, if the anchor impeller undergoes a deformation due to the flexion of the arms of the anchor impeller, the numerical results changes slightly from iteration to another. At the end of certain iteration, the anchor impeller becomes deformed and the velocity field is preserved. These results confirm that the fluid has a significant effect on the deformation of the arms of the anchor impeller during mixing depending on the velocity of the anchor impeller and the fluid flow. The numerical results were validated by a comparison with literature data.     

Laboratory Study of Successive Soil Saline Leaching and Electrochemical Lead Recovery

This research is related to a laboratory study on the performance of a successive soil saline leaching and electrochemical lead recovery process for soil decontamination. Erlenmeyer leaching assays showed that the addition of 5.5 mol NaCl/L in 25% (w/w) of soil pulp density maintained at pH 3.0 was found the most effective condition for Pb leaching. Under these conditions, 65% of Pb was leached from soil. Electrochemical treatment using an iron–monopolar electrode system operated at a current intensity of 3.0 A was able to reduce Pb content in soil leachate from 650 to 0.15 mg/L and this without production of metallic residue. Then, a leaching tank reactor and electrolytic cell coupled in a closed loop showed that the Pb mass balance of extrants/intrants ratio indicated 99.0±1.6% of Pb was recovered. Likewise, 94.1% of chloride ions were reused in the leaching tank reactor after electrochemical treatment.     

Optimal integrated maintenance/production policy for randomly failing systems with variable failure rate

This article deals with the combined production and maintenance plans for a manufacturing system satisfying a random demand. We first establish an optimal production plan which minimises the average total inventory and production cost. Second, using this optimal production plan, and taking into account the deterioration of the machine according to its production rate, we derive an optimal maintenance schedule which minimises the maintenance cost. A numerical example illustrates the proposed approach, this analytical approach, based on a stochastic optimisation model and using the operational age concept, reveals the significant influence of the production rate on the deterioration of the manufacturing system and consequently on the integrated production/maintenance policy.     

Operational and environmental decisions for a two-stage supply chain under vendor managed consignment inventory partnership

Supply-chain-based organisations are nowadays facing intense pressure to abide to environmental regulatory requirements while they are striving to be responsive to customers’ needs at the least cost possible. As supply chain activities are among the top contributors to carbon emissions, several recent research works have investigated the impact of carbon regulation policies on economic and environmental supply chain performance. This paper presents integrated economic and environmental models for the one-vendor one-buyer supply chain problem under a vendor managed consignment inventory (VMCI) arrangement. Through the developed models, we study the impacts of two carbon reduction policies, namely carbon cap and carbon tax policies, on supply chain wide costs and carbon emissions. We first provide a much simpler and more compact formulation for the basic single-vendor single-buyer supply chain under VMCI agreement. We also present an environmental-based VMCI model where reduction of carbon footprint is considered as the only objective function. We then extend these two basic models to include each of the two carbon emissions reduction policies. We identify structural properties for the optimal solutions of the two hybrid economic and environmental models and propose algorithms to generate optimal solutions. The results of the computational experiments reveal that the implementation of carbon reduction policies, through carbon cap and carbon tax, may call for the adjustment of the vendor’s production and buyer’s delivery quantities to reduce carbon footprint without significantly increasing the operational costs.     

An Investigation on the Recovery of Antioxidant Phenolics from Onion Solid Wastes Employing Water/Ethanol-Based Solvent Systems

Onion solid wastes, composed of the apical trimmings and the outer dry layers of the bulb, were used as raw material for the recovery of antioxidant phenolics by employing acidified water/ethanol-based solvent systems. The extraction efficiency was assessed by measuring the reducing power and the antiradical activity of the extracts, and the total polyphenol yield. Improvement of the extraction yield was based on modifying the solvent composition and the operating conditions (temperature, time). Initial screening of various mixtures showed that significantly higher recoveries (P < 0.001) can be attained by using 60% ethanol containing 0.1% HCl. The assessment of factors affecting yield, including extraction time and temperature, was accomplished using a series of extractions on the basis of a 2 × 3 factorial design model, with time and temperature values varying from 0.5 to 6 h and from 40 to 60°C, respectively. The results obtained showed that improvement of yield is dependent upon increasing extraction time up to 6 hours, whereas increasing the temperature from 40 to 60°C had a negative effect.