Investigation of the magnetic behavior and structural chemistry within the pseudobinary silicide system CeOs x Ru2−x Si2

The crystal chemistry and the magnetism in the pseudobinary system CeOs _x Ru_2–x Si₂ has been investigated in the temperature range of 1.5 K to 1,100 K and for various concentrations. From Guinier X-ray powder diffractometry all alloys were found to be isostructural and to crystallize with the ThCr₂Si₂-type of structure. No significant deviations from the ThCr₂Si₂-atomic order and symmetry were observed in the as-cast alloys with respect to those heat treated at 1,000°C and at 500°C, quenched. From magnetic susceptibilities it is shown that the 4f-electrons demagnetize at low temperatures. The data were interpreted in terms of interconfiguration fluctuations, based on a model derived by Sales and Wohlleben. A maximum valence change is observed in CeOs_1.4Ru_0.6Si₂, ranging from 3.27 at 700 K to 3.70 at 5 K.     

Collisional redistribution of radiatively-excited levels of Tl and Ga atoms in an O2-acetylene-Ar flame

Several useful expressions for the population ratios of collisionally excited levels have been derived and different transitions of Tl and Ga atoms, seeded in a premixed atmospheric flame, have been excited in order to verify that the levels higher than the laser-excited level are populated approximately according to a Boltzmann equilibrium. This result confirms the possibility of using thermally assisted flourescence lines to measure local temperatures in flames. The Einstein spontaneous emission probability for the transition 6S_1/2→4P_3/2 at 2719.65Å of Ga has also been calculated (A_2719.65=0.41×10⁸s^-1) to fit the experimental point.     

Kinetics and mechanism of the oxidation of sulfite by chlorine dioxide in a slightly acidic medium

The sulfite-chlorine dioxide reaction was studied by stopped-flow method at I = 0.5 M and at 25.0 +/- 0.1 degrees C in a slightly acidic medium. The stoichiometry was found to be 2 SO(3)(2-) + 2.ClO(2) + H(2)O --> 2SO(4)(2) (-) + Cl(-) + ClO(3)(-) + 2H(+) in *ClO(2) excess and 6SO(3)(2-) + 2*ClO(2) --> S(2)O(6)(2-) + 4SO(4)(2-) + 2Cl(-) in total sulfite excess ([S(IV)] = [H(2)SO(3)] + [HSO(3)(-)] + [SO(3)(2-)]). A nine-step model with four fitted kinetic parameters is suggested in which the proposed adduct *SO(3)ClO(2)(2-) plays a significant role. The pH-dependence of the kinetic traces indicates that SO(3)(2-) reacts much faster with *ClO(2) than HSO(3)(-) does.     

Single- and Multi-Objective Cooperation for the Flexible Docking Problem

In this article, the impact of single-objective methods as intensification factors in a multi-objective approach is presented for the flexible docking problem. Based on a novel tri-objective model, a parallel multi-objective genetic algorithm has been designed. However, due to the high variability of the energy objective, intensification methods focused on this objective have been also included in order to improve the convergence speed of the genetic algorithm and the quality of the results. The corresponding approach, combining single- and multi-objective methods, has been proved efficient according to the tested instances and the quality criterion used.     

Stability and local bifurcation analyses of two-wheeled trailers considering the nonlinear coupling between lateral and vertical motions

Nonlinear Dynamics - Multistability is an area of interest in robotics and locomotion because the ability to achieve multiple configurations or generate multiple gaits allows a single robotic or...     

High performance ion chromatography of haloacetic acids on macrocyclic cryptand anion exchanger

A new high performance ion chromatographic method has been developed for the separation of the nine chlorinated-brominated haloacetic acids (HAAs) that are the disinfection by-products of chlorination of drinking water, using a macrocycle-based adjustable-capacity anion-exchange separator column (IonPac Cryptand A1). A gradient method based on theoretical and experimental considerations has been optimized in which 10 mM NaOH-LiOH step gradient was performed at the third minute of the analysis. The optimized method allowed us to separate the nine HAAs and seven possibly interfering inorganic anions in less than 25 min with acceptable resolution. The minimum concentrations detectable for HAAs were between 8.0 (MBA) and 210 (TBA) microg L(-1), with linearity included between 0.9947 (TBA) and 0.9998 (MBA). To increase sensitivity, a 25-fold preconcentration step on a reversed phase substrate (LiChrolut EN) has been coupled. Application of this method to the analysis of haloacetic acids in real tap water samples is illustrated.     

Diffusion of cationic polyelectrolytes into cellulosic fibers

The penetration of cationic polyelectrolytes into anionic cellulosic fibers was evaluated with fluorescent imaging techniques in order to clarify the mechanism and time scales for the diffusion process. The bulk charge of the cellulosic fibers indirectly creates a driving force for diffusion into the porous fiber wall, which is entropic in nature due to a release of counterions as the polyelectrolyte adsorbs. The individual bulk charges in the fiber cell wall also interact with the diffusing polyelectrolyte, such that the polyelectrolyte diffuses to the first available charge and consequently adsorbs and remains fixed. Thus, subsequent polyelectrolyte chains must first diffuse through the adsorbed polyelectrolyte layer before adsorbing to the next available bulk charges. This behavior differs from earlier suggested diffusion mechanisms, by which polyelectrolytes were assumed to first adsorb to the outermost surface and then reptate into the pore structure. The time scales for polyelectrolyte diffusion were highly dependent on the flexibility of the chain, which was estimated from calculations of the persistence length. The persistence length ultimately depended on the charge density and electrolyte concentration. The charge density of the polyelectrolyte had a greater influence on the time scales for diffusion. High charge density polyelectrolytes were observed to diffuse on a time scale of months, whereas the diffusion of low charge density polyelectrolytes was measured on the order of hours. An influence of the chain length, that is, steric interactions due the persistence length of the polyelectrolyte and to the tortuosity of the porous structure of the fiber wall, could only be noted for low charge density polyelectrolytes. Increasing the electrolyte concentration increased the chain flexibility by screening the electrostatic contribution to the persistence length, in turn inducing a faster diffusion process. However, a significant change in the diffusion behavior was observed at high electrolyte concentrations, at which the interaction between the polyelectrolyte charges and the fiber charges was almost completely screened.     

Quasi-isotropic analysis of anisotropic thin films on optical waveguides

Thin films assembled on a substrate are often anisotropic. Nevertheless, because of experimental limitations, sufficient parameters to characterize the anisotropy, even in the simplest (and perhaps most common) case of uniaxial thin films, which are birefringent, are not usually available. This paper examines the consequences of treating them as isotropic thin films, with particular reference to their characterization via perturbation of the propagation constants (effective refractive indices) of optical waveguides. It is shown that the refractive index and geometrical thickness of a thin film thus calculated are often unrealistic (especially when the thin film is positively birefringent), but the mass per unit area may be quite precise, depending on the sign and magnitude of the birefringence.