Determination of silicon in fats and oils by electrothermal atomic absorption spectrometry with in-furnace air oxidation

A graphite-furnace atomic absorption spectrometric emthod is reported for determination of dimethylpolysiloxane (silicone) in edible fats and oils. It incorporates an air-oxidation step in the furnace program to reduce matrix interferences. The detection limit is 0.3 mg kg^?1 in soils, and short-term precision is about 6% at silicon concentrations of 1.7–2.0 mg kg^?1. The procedure was successfully applied to a variety of commercial frying fats and oils, to quantify silicone loss during polish filtration during oil manufacture, to quantify sorption of antifoam onto fried food, and to detect fugitive sources of silicone encountered in deep-fat frying operations.     

Stabilization of the Gurtin–MacCamy population system

We consider the classical Gurtin–MacCamy system describing the growth and spread of an age structured population and show that the steady states are actually stabilizable by a controller v = v(a, t) acting on an age interval [a ₁, a ₂].     

Nitrogen,phosphorus and organics removal in two vertical flow experimental wetlands receiving pretreated municipal wastewater

Pollutants removal in two vertical flow experimental wetlands receiving pre-treated municipal wastewater was investigated. Laboratory investigations using microcosms were also carried out in order to identify key processes regulating pollutants removal. Results obtained from experimental wetlands seem to confirm the ability of a single stage installation, where nitrification and denitrification processes are jointly optimised using a gravel medium, always wet but not saturated with water. Results obtained from microcosm investigations show the prominent role of O2 supply, of microbial activity and of bio-available C from vegetal metabolism in the nitrogen removal.     

Decomposition of formamide assisted by microwaves, a tool for synthesis of nitrogen-containing heterocycles

Generation of ammonia via thermal decomposition of formamide was studied under microwave conditions to provide an efficient tool for the synthesis of nitrogen-containing heterocycles. Quinazolin-4-ones, which are known as building blocks for molecules with pharmaceutical interest, were chosen as examples. Our work confirms that reactants may have different behaviours under microwaves, depending on power input, reached temperature and pressure in the vials. Full control and fine tuning of these parameters are achievable using modern microwave technology.     

Molecular orientation in liquid fibers of nematic polymers

The degree of macroscopic orientation of molten fibrous samples of nematic semiflexible polymers has been investigated by x-ray diffraction. Melting of highly oriented fibers is followed by a partial loss of macroscopic orientation but does not produce collapse of the fiber. The residual orientational order remains unaltered for a considerable time. The degree of orientational order depends on the temperature and undergoes odd-even fluctuations according to the parity of the number of carbon atoms contained in the flexible part of the monomer unit. Extrapolation of the order parameter to the isotropization temperature leads to a value of about 0.63 for even-type polymers and to about 0.47 for odd-type polymers. An intermediate value is found for a copolymer containing equal amounts of even and odd monomer units along the polymer chain.     

Passivity and complementarity

This paper studies the interaction between the notions of passivity of systems theory and complementarity of mathematical programming in the context of complementarity systems. These systems consist of a dynamical system (given in the form of state space representation) and complementarity relations. We study existence, uniqueness, and nature of solutions for this system class under a passivity assumption on the dynamical part. A complete characterization of the initial states and the inputs for which a solution exists is given. These initial states are called consistent states. For the inconsistent states, we introduce a solution concept in the framework of distributions.     

Finite element and implicit Runge–Kutta implementation of an acoustics–convection upstream resolution algorithm for the time‐dependent two‐dimensional Euler equations

The second of a two‐paper series, this paper details a solver for the characteristics‐bias system from the acoustics–convection upstream resolution algorithm for the Euler and Navier–Stokes equations. An integral formulation leads to several surface integrals that allow effective enforcement of boundary conditions. Also presented is a new multi‐dimensional procedure to enforce a pressure boundary condition at a subsonic outlet, a procedure that remains accurate and stable. A classical finite element Galerkin discretization of the integral formulation on any prescribed grid directly yields an optimal discretely conservative upstream approximation for the Euler and Navier–Stokes equations, an approximation that remains multi‐dimensional independently of the orientation of the reference axes and computational cells. The time‐dependent discrete equations are then integrated in time via an implicit Runge–Kutta procedure that in this paper is proven to remain absolutely non‐linearly stable for the spatially‐discrete Euler and Navier–Stokes equations and shown to converge rapidly to steady states, with maximum Courant number exceeding 100 for the linearized version. Even on relatively coarse grids, the acoustics–convection upstream resolution algorithm generates essentially non‐oscillatory solutions for subsonic, transonic and supersonic flows, encompassing oblique‐ and interacting‐shock fields that converge within 40 time steps and reflect reference exact solutions. Copyright © 2005 John Wiley & Sons, Ltd.     

A globally well-posed finite element algorithm for aerodynamics applications

A finite element CFD algorithm is developed for Euler and Navier-Stokes aerodynamic applications. For the linear basis, the resultant approximation is at least second-order-accurate in time and space for synergistic use of three procedures: (1) a Taylor weak statement, which provides for derivation of companion conservation law systems with embedded dispersion-error control mechanisms; (2) a stiffly stable second-order-accurate implicit Rosenbrock-Runge-Kutta temporal algorithm; and (3) a matrix tensor product factorization that permits efficient numerical linear algebra handling of the terminal large-matrix statement. Thorough analyses are presented regarding well-posed boundary conditions for inviscid and viscous flow specifications. Numerical solutions are generated and compared for critical evaluation of quasi-one- and two-dimensional Euler and Navier-Stokes benchmark test problems. Of critical importance, essentially non-oscillatory solutions are uniformly attained for a range of supercritical flow situations with shocks.     

Liquid crystal behaviour of linear copolymers—II

A family of linear copolymers, characterized by the presence along the polymer chain of variable amounts of two atomic groups of different mesogenic potentiality, has been studied by differential scanning calorimetry and X-ray diffraction methods. The range of composition that allows enantiotropic mesophasic behaviour is defined for four homologous sets of copolymers. The experimental phase diagram gives, by extrapolation, indications about the potential mesophasic properties of that extreme composition (corresponding to a homopolymer) that shows no direct mesophasic properties.