Mercury and cadmium concentrations in milk in Puerto Rico

Milk was collected over a four-month period from three representative sectors of Puerto Rico. Instrumental neutron activation analysis (INAA) performed on the samples showed that the mercury concentration was slightly higher than the safe upper limit set by the World Health Organisation on food products. INAA for cadmium yielded high values when compared with atomic absorption.     

Molecular weight dependent charge carrier mobility in poly(3,3' '-dioctyl-2,2':5',2' '-terthiophene)

Poly(3,3' '-dioctyl-2,2':5',2' '-terthiophene), a polymer recently used for the fabrication of organic field effect transistors, has been fractionated into five fractions distinctly differing in their molecular weights (Mn), with the goal of determining the influence of the degree of polymerization (DPn) on its principal physicochemical parameters. It has been demonstrated that within the Mn range studied (from 1.5 kDa to 10.5 kDa by SEC), corresponding to DPn from 10 to 38, the polymer band gap steadily decreases with growing molecular weight, which is clearly manifested by an increasing bathochromic shift of the band originating from the pi-pi* transition. The same trend is observed for the HOMO level, determined from the onset of the p-doping in cyclic voltammetry, which shifts from -5.10 eV to -4.90 eV for the lowest and the highest molecular weight fractions, respectively. The most pronounced influence of DPn has been found for the charge carriers' mobility-one of the most important parameters of field effect transistors (FETs) fabricated from this polymer. A fourfold increase in DPn results in an increase of the carriers' mobility by more than 3 orders of magnitude. Comparison of these results with those obtained for fractionated regioregular poly(3-hexylthiophene) shows a strikingly similar behavior of both polymers with respect to the molecular weight.     

Optical and structural characterization of KBr crystals doped cadmium bromide (CdBr2)

In this paper we demonstrate the presence of CdBr₂ and cadmium aggregates in KBr matrix during Czochralski growth of KBr crystals. The chemical decomposition of CdBr₂ due to high temperature of crystallisation and reformation of cadmium bromide seems to be responsible for this effect.     

Kansa-RBF algorithms for elliptic problems in regular polygonal domains

We propose matrix decomposition algorithms for the efficient solution of the linear systems arising from Kansa radial basis function discretizations of elliptic boundary value problems in regular polygonal domains. These algorithms exploit the symmetry of the domains of the problems under consideration which lead to coefficient matrices possessing block circulant structures. In particular, we consider the Poisson equation, the inhomogeneous biharmonic equation, and the inhomogeneous Cauchy-Navier equations of elasticity. Numerical examples demonstrating the applicability of the proposed algorithms are presented.     

On a third‐order Newton‐type method free of bilinear operators

This paper is devoted to the study of a third‐order Newton‐type method. The method is free of bilinear operators, which constitutes the main limitation of the classical third‐order iterative schemes. First, a global convergence theorem in the real case is presented. Second, a semilocal convergence theorem and some examples are analyzed, including quadratic equations and integral equations. Finally, an approximation using divided differences is proposed and used for the approximation of boundary‐value problems. Copyright © 2009 John Wiley & Sons, Ltd.     

A Chemotactic Model for Interaction of Antagonistic Microflora Colonies: Front Asymptotics and Numerical Simulations

This paper studies a two‐dimensional chemotactic model for two species in which one of them produces a chemo‐repellent for the other. It is shown asymptotically and numerically how the chemical inhibits the invasion of a moving front for the second species and how stable steady states, which depend on the chemical concentration, can be reached. The results qualitatively explain experimental observations by Swain and Ray [ 1 ] showing that colonies of bacteria produce metabolite agents which prevent the invasion of fungi.     

Discrimination of carotenoid and flavonoid content in petals of pansy cultivars (Viola x wittrockiana) by FT‐Raman spectroscopy

Fourier Transform Raman spectroscopy (FT‐Raman) has been applied for the non‐destructive in‐situ analysis of pigments on differently colored flower petals of pansy cultivars (Viola x wittrockiana). The main target of the present study was to investigate how far the Raman mapping technique through FT‐Raman spectroscopy and cluster analysis of the Raman spectra is a potential method for the direct, in‐situ discrimination of flavonoids (flavonols against anthocyanins) and of carotenoids occurring in flowers, using intact and differently colored flower petal of Viola x wittrockiana for this case study. In order to get more information about the reliability of the direct in‐situ flavonoid detection by the Raman method, pigments extracts of the petals were separated by thin‐layer chromatography (TLC) and investigated by Raman spectroscopy. Hierarchical cluster analysis (HCA) of the Raman spectra from reference pigments (carotenoids, anthocyanins and flavonols), from areas of the flower petals, and from the TLC extracts allowed discriminating the various pigments, in particular flavonoids (flavonols against anthocyanins) and carotenoids. With a two‐dimensional Raman mapping technique, which provides a chemical image of the sample under investigation, we determined by cluster analysis the distribution of carotenoids, anthocyanins and flavonols from the outer layer of the petals, and by integrating through suitable spectral regions selected as characteristic markers for particular pigments their relative concentration could approximately be determined. We found a satisfactory correlation between the patterns seen on the visible images and the patterns on the chemical images obtained by Raman mapping. Copyright © 2011 John Wiley & Sons, Ltd.     

A catalytic adsorptive stripping voltammetric procedure for trace determination of Cr(VI) in natural samples containing high concentrations of humic substances

A simple and fast catalytic adsorptive stripping voltammetric procedure for trace determination of Cr(VI) in natural samples containing high concentrations of humic substances has been developed. The procedure for chromium determination in the presence of DTPA and nitrates was employed as the initial method. In order to enhance the selectivity vs. Cr(III) the measurements were performed at 40°C. Interference from dissolved organic matter such as humic and fulvic acids was drastically decreased by adding Amberlite XAD-7 resin to the voltammetric cell before the deaeration step. The whole procedure was applied to a single cell, which allowed monitoring of the voltammetric scan. Optimum conditions for removing humic and fulvic acids due to their adsorption on XAD-7 resin were evaluated. The use of XAD-7 resin also minimize interferences from various cationic, anionic, and nonionic surfactants. The calibration graph for Cr(VI) for an accumulation time of 30 s was linear in the range 5 × 10⁻¹⁰ to 5 × 10⁻⁸ mol L⁻¹. The relative standard deviation for determination of Cr(VI) at a concentration of 1 × 10⁻⁸ mol L⁻¹ was 3.5% (n = 5). The detection limit estimated from 3 times the standard deviation for low Cr(VI) concentrations and an accumulation time of 30 s was about 1.3 × 10⁻¹⁰ mol L⁻¹. The proposed method was successfully applied to Cr(VI) determination at trace levels in soil samples.