LocalSolver 1.x: a black-box local-search solver for 0-1 programming

This paper introduces LocalSolver 1.x, a black-box local-search solver for general 0-1 programming. This software allows OR practitioners to focus on the modeling of the problem using a simple formalism, and then to defer its actual resolution to a solver based on efficient and reliable local-search techniques. Started in 2007, the goal of the LocalSolver project is to offer a model-and-run approach to combinatorial optimization problems which are out of reach of existing black-box tree-search solvers (integer or constraint programming). Having outlined the modeling formalism and the main technical features behind LocalSolver, its effectiveness is demonstrated through an extensive computational study. The version 1.1 of LocalSolver can be freely downloaded at and used for educational, research, or commercial purposes.     

Measurement of Lamb wave polarization using a one-dimensional scanning laser vibrometer (L)

A single head scanning laser Doppler vibrometer is used for the estimation of the polarization of the first symmetric (S(0)) and antisymmetric (A(0)) Lamb wave modes. The measurements at two known incidence angles are performed in order to resolve the two components of motion. Filtering in the frequency/wavenumber domain of the response recorded along a scan line separates the contributions from each mode and allows the evaluation of the corresponding elliptical trajectories of particle motion. Comparison between measured and analytically estimated trajectories validates the measurement technique and suggests its application for the development of material characterization and diagnostics tools.     

Averaging on slow and fast cycles of a three time scale system

Pontryagin–Rodygin?s Theorem for slow and fast systems describes the slow drift during the rolling up of the trajectories around the cycles of the fast dynamics. This drift is approximated by the averaging on the cycles. The calculation of this average is generally a difficult task since it requires the knowledge of the closed orbits and their periods. We present two paradigms of three time scale systems where we can overcome this limitation. It is the case of systems the fast dynamics of which have cycles with relaxation presenting or not a canard phenomenon. We can not apply Pontryagin–Rodygin?s Theorem to these systems because their fast equation is itself singularly perturbed. We also investigate the extension of the results to unbounded time intervals. The results are stated classically and proved within the framework of nonstandard analysis.     

On the solvability of initial boundary value problems for nonlinear time-dependent Schrödinger equations

In this paper, we study the initial boundary value problems for a nonlinear time-dependent Schrödinger equation with Dirichlet and Neumann boundary conditions, respectively. We prove the existence and uniqueness of solutions of the initial boundary value problems by using Galerkin’s method.     

Predicted Influence of N-Acetyl Group Content on the Conformational Extension of Chitin and Chitosan Chains

ABSTRACT

Conformational analysis of chitosan molecules has been performed using the MM3(92) force field to investigate the role played by the acetamido groups on the stiffness of these chains. A high dielectric constant value was needed to model an aqueous environment and to reproduce the distribution of the N-acetyl glucosamine group orientation that is observed by NMR. Disaccharidic fragments, differently substituted at C2, were selected as models for chitin and chitosan chains. Their conformational space has been explored by means of adiabatic mapping of the glycosidic Φ,Ψ torsion angles. Although the overall features of all the potential energy surfaces created appear similar, the accessible conformational space of a glycosidic bond is affected by the nature of the substituent at C2 on the non-reducing residue of the disaccharide unit. This is illustrated by the differences in the calculated partition functions together with the predicted average homonuclear and heteronuclear coupling constants. Computed maps were used to predict polymeric unperturbed dimensions, characteristic ratio and persistence length of idealized chitin and chitosan chains, by Monte Carlo methods. Pure chitosan is predicted to be more coiled than pure chitin chains. At low N-acetyl group contents, chain extension appears to be dependent on the degree of substitution. Average chain dimensions increase monotonically for increases in content up to 60% of N-acetyl groups, but show no significant variation at higher contents. For molecules consisting of 50% amino and 50% N-acetylated residues, random, alternate and block patterns of substitution have been investigated. It has also been shown that the spatial extension of the polymer chains is dependent on the primary structure. Comparison with the literature experimental data is difficult because of the extreme diversity of the reported conformationally dependent values. However, such study provides a unique insight into the dependence of these two factors (degree of acetylation and distribution of acetyl groups) on the stiffness and flexibility of different chitin and chitosan chains.     

Instant controlled pressure drop extraction of lavandin essential oils: Fundamentals and experimental studies

Détente Instantanée contrôlée (DIC), French for Instant Controlled Pressure Drop, was performed on laboratory apparatus as well as on a pilot plant for proving its feasibility, and identifying the optimized processing conditions and recognizing the energy consumption and the quantity of water used for such an operation. GC–MS and SPME analysis of the extracts and residue material were carried out to assess the extracts and solid residues. The lavandin essential oils obtained by using the new DIC extraction process was studied, modeled and quantitatively and qualitatively compared to the conventional hydrodistillation method. The most important differences between the two essential oils were reflected in the yields, with 4.25 as against 2.3 g EO/100 g of raw matter, and in the extraction time, with 480 s as against some hours for respectively the DIC and the hydrodistillation operations. These differences have been previewed through the fundamental analysis. They can normally explain the great decreasing of energy consumption to be 662 kWh/t of raw material. The amount of water to be added was about 42 kg water/t of raw material.     

Multigrid convergence acceleration for implicit and explicit solution of Euler equations on unstructured grids

The multigrid method is one of the most efficient techniques for convergence acceleration of iterative methods. In this method, a grid coarsening algorithm is required. Here, an agglomeration scheme is introduced, which is applicable in both cell‐center and cell‐vertex 2 and 3D discretizations. A new implicit formulation is presented, which results in better computation efficiency, when added to the multigrid scheme. A few simple procedures are also proposed and applied to provide even higher convergence acceleration. The Euler equations are solved on an unstructured grid around standard transonic configurations to validate the algorithm and to assess its superiority to conventional explicit agglomeration schemes. The scheme is applied to 2 and 3D test cases using both cell‐center and cell‐vertex discretizations. Copyright © 2009 John Wiley & Sons, Ltd.     

Totally positive extensions and weakly isotropic forms

The aim of this article is to analyse a new field invariant, relevant to (formally) real fields, defined as the supremum of the dimensions of all anisotropic, weakly isotropic quadratic forms over the field. This invariant is compared with the classical u-invariant and with the Hasse number. Furthermore, in order to be able to obtain examples of fields where these invariants take certain prescribed values, totally positive field extensions are studied.