Signal-levelling agents for eliminating the interferences of iron,aluminium, barium and calcium in the determination of lead by flame atomic absorption spectrometry

The interferences of iron, aluminium, barium and calcium on the determination of lead by flame atomic absorption spectrometry are discussed; a titration procedure was used. Ascorbic acid, citric acid, EDTA and nitric acid were used successfully for levelling the interfering effects from the cations.     

Spectrophotometric microdetermination of copper(II), silver(I), and gold(III) using azastyrene Schiff bases

A new method for the spectrophotometric microdetermination of Cu(II), Ag(I), and Au(III) using β-2-hydroxybenzyl-5-bromo- (I_a), 5-chloro- (I_b), and 3-methoxy-2-hydroxyazastyrene (I_c) is given. The optimum conditions favoring the formation of the colored complexes are extensively studied. The molecular structure was found to be (1:1) and (1:2) (M:L). Beer's law is obeyed up to 5.00, 8.64, and 11.82 ppm for Cu(II), Ag(I), and Au(III), respectively, while the optimum concentration ranges using the Ringbom method are 0.6–5.00, 1.00–8.60, and 2.00–11.80 ppm for the same metal ions, respectively.     

Export Performance and Export Policy: Evidence from the U.K. Clothing Industry

This paper examines the relationship between a number of export policy measures and the export sales performance of a sample of companies in the U.K. clothing industry. Policy measures are used first in a discriminant analysis of above- and below-average exporters and, second, to explain a multi-dimensional measure of export performance using canonical correlation. The "jack-knife" technique is used to test the stability of these analyses.     

Fireworks algorithm framework for Big Data optimization

This paper presents a novel optimization framework based on the Fireworks Algorithm for Big Data Optimization problems. Indeed, the proposed framework is composed of two optimization algorithms. A single objective Fireworks Algorithm and a multi-objective Fireworks Algorithm are proposed for solving the Big Optimization of Signals problem “Big-OPT” which belongs to the Big Data Optimization problems class. The single objective Fireworks Algorithm adopts a modified search mechanism to ensure rapidity and preserve the explorative capacities of the basic Fireworks Algorithm. Afterward, the algorithm is extended to handle multi-objective optimization of Big-OPT with a supplementary special sparks phase and a novel strategy for next generation selection. To validate the performance of the framework, extensive tests on six EEG datasets are performed. The framework is also compared with several approaches from recent state of the art. The study concludes the competitive performance of the proposed framework in comparison with the other techniques reported in this paper.     

The new one‐dimensional coordination polymer catena‐poly[[diaquasodium(I)]‐μ‐oxalato‐[diaquairon(III)]‐μ‐oxalato]

The oxalate dianion is one of the most studied ligands and is capable of bridging two or more metal centres and creating inorganic polymers based on the assembly of metal polyhedra with a wide variety of one‐, two‐ or three‐dimensional extended structures. Yellow single crystals of a new mixed‐metal oxalate, namely catena‐poly[[diaquasodium(I)]‐μ‐oxalato‐κ⁴O¹,O²:O^1′,O^2′‐[diaquairon(III)]‐μ‐oxalato‐κ⁴O¹,O²:O^1′,O^2′], [NaFe(C₂O₄)₂(H₂O)₄]_n, have been synthesized and the crystal structure elucidated by X‐ray diffraction analysis. The compound crystallizes in the noncentrosymmetric space group I4₁ (Z = 4). The asymmetric unit contains one Na^I and one Fe^III atom lying on a fourfold symmetry axis, one μ₂‐bridging oxalate ligand and two aqua ligands. Each metal atom is surrounded by two chelating oxalate ligands and two equivalent water molecules. The structure consists of infinite one‐dimensional chains of alternating FeO₄(H₂OW1)₂ and NaO₄(H₂OW2)₂ octahedra, bridged by oxalate ligands, parallel to the [100] and [010] directions, respectively. Because of the cis configuration and the μ₂‐coordination mode of the oxalate ligands, the chains run in a zigzag manner. This arrangement facilitates the formation of hydrogen bonds between neighbouring chains involving the H₂O and oxalate ligands, leading to a two‐dimensional framework. The structure of this new one‐dimensional coordination polymer is shown to be unique among the A^IM^III(C₂O₄)₂(H₂O)_n series. In addition, the absorption bands in the IR and UV–Visible regions and their assignments are in good agreement with the local symmetry of the oxalate ligand and the irregular environment of iron(III). The final product of the thermal decomposition of this precursor is the well‐known ternary oxide NaFeO₂.     

On the Dirichlet problem for asymmetric zero-range process on increasing domains

In order to obtain hitting time estimates for the asymmetric zero-range process (AZRP) on ^d, in dimensions d3, we characterize the principal eigenvalue of the generator of the AZRP with Dirichlet boundary on special domains. We obtain a Donsker-Varadhan variational representation and show that the corresponding eigenfunction is unique in a natural class of functions.Mathematics Subject Classification (2000):60K35, 82C22, 60J25     

Variations in Physicochemical Properties and Bioconversion Efficiency of <Emphasis Type="Italic">Ulva lactuca</Emphasis> Polysaccharides After Different Biomass Pretreatment Techniques

Green macroalgae are an abundant and undervalued biomass with a specific cell wall structure. In this context, different pretreatments, namely ethanol organosolv (Org), alkaline, liquid hot water (LHW), and ionic liquid (IL) pretreatments, were applied to the green macroalgae Ulva lactuca biomass and then evaluated. Their effects on chemical composition, biomass crystallinity, enzymatic digestibility, and theoretical ethanol potential were studied. The chemical composition analysis showed that the Org and LHW pretreatments allowed the highest glucan recovery (80.8 ± 3.6 and 62.9 ± 4.4 g/100 g DM, respectively) with ulvan (80.0 and 99.1%) and hemicellulose (55.0 and 42.3%) removal. These findings were in agreement with both thermogravimetric analysis and scanning electron microscopy results that confirm significant structural changes of the pretreated biomasses. It was found that the employed pretreatments did not significantly affect the cellulose crystallinity; however, they both increased the whole crystallinity and the enzymatic digestibility. This later reached 97.5% in the case of LHW pretreatment. Our results showed high efficiency saccharification of Ulva lactuca biomass that will constitute the key step of the implementation of a biorefinery process.     

Metastability for the Exclusion Process with Mean-Field Interaction

We consider an exclusion particle system with long-range, mean-field-type interactions at temperature 1/β. The hydrodynamic limit of such a system is given by an integrodifferential equation with one conservation law on the circle $C$ : it is the gradient flux of the Kac free energy functional F _β. For β≤1, any constant function with value m ∈ [?1, +1] is the global minimizer of F _β in the space $\{ u:\int_C {u(x)} \,dx = m\} $ . For β>1, F _β restricted to $\{ u:\int_C {u(x)} \,dx = m\} $ may have several local minima: in particular, the constant solution may not be the absolute minimizer of F _β. We therefore study the long-time behavior of the particle system when the initial condition is close to a homogeneous stable state, giving results on the time of exit from (suitable) subsets of its domain of attraction. We follow the Freidlin–Wentzell approach: first, we study in detail F _β together with the time asymptotics of the solution of the hydrodynamic equation; then we study the probability of rare events for the particle system, i.e., large deviations from the hydrodynamic limit.     

An explicit characterization of the convex envelope of a bivariate bilinear function over special polytopes

In this paper, we constructively derive an explicit characterization of the convex envelope of a bilinear function over a special type of polytope in ². Our motivation stems from the use of such functions for deriving strengthened lower bounds within the context of a branch-and-bound algorithm for solving bilinear programming problems. For the case of polytopes with no edges having finite positive slopes, that is polytopes with downward sloping edges (which we call D-polytopes), we obtain a direct, explicit characterization of the convex envelope. This case subsumes the analysis of Al-Khayyal and Falk (1983) for constructing the convex envelope of a bilinear function over a rectangle in ². For non-D-polytopes, the analysis is more complex. We propose three strategies for this case based on (i) encasing the region in a D-polytope, (ii) employing a discretization technique, and (iii) providing an explicit characterization over a triangle along with a triangular decomposition approach. The analysis is illustrated using numerical examples.