Determination of Arsenic in Honey,Propolis, Pollen,and Honey Bees by Microwave Digestion and Hydride Generation Flame Atomic Absorption

The toxic properties of arsenic are well known. Honey has been widely used for monitoring this element. The present work reports a novel method for the determination of arsenic in honey, bees, pollen, and propolis, based on the coupling of microwave digestion and hydride generation. Method development included the quantitative reduction of arsenic(V) to arsenic(III), the acid used for dilution, and the complete removal of the gases following digestion. The method performance was satisfactory with recoveries between 83% and 111% and corresponding relative standard deviations between 3.1% and 24%. Among the 32 samples of honey, propolis, pollen, and honey bees analyzed, arsenic was detected in four out of six propolis samples at the method limit of detection (0.4?µg?g^?1). The results indicate that propolis may be an efficient indicator for arsenic.     

Determination of surface ζ‐potential and isoelectric point of carbon surfaces using tracer particle suspensions

Carbon materials are widely used in a range of applications from biomaterials to sensing and electronics. Many of these applications rely on the ability to control carbon/water interfacial properties, in particular, surface charge density. This work reports a study of the electrokinetic properties of amorphous carbon thin films as a function of pH and surface chemistry. Surface ζ‐potential (SZP) and isoelectric point were determined using the tracer particle method. Initially, the use of sulfonated and amine‐terminated latex bead suspensions as tracer particles for the determination of SZP of reference polymer surfaces was validated. The tracer particle method was then applied to the determination of SZP and isoelectric point of macroscopic carbon surfaces with different surface chemistry. Highly graphitic and sp³‐rich hydrogenated carbon surfaces were found to display negative SZP, as expected for hydrophobic surfaces. The isoelectric point of the most highly graphitic surface was found to be pH_iso = 3.7. Surface oxidation of these films resulted in a decrease of SZP at all pH values and in a downshift of pH_iso to values lower than 1.5, consistently with the presence of surface acidic groups arising from oxidation. Results indicate that the specific choice of acid/base chemistry for the tracer particles does not significantly affect either SZP or pH_iso determinations. These results show that the tracer particle method in combination with widely available latex beads as tracers can be applied for the determination of carbon SZP as a function of pH. Copyright © 2017 John Wiley & Sons, Ltd.     

A novel method for separating Cs<Superscript>+</Superscript> from liquid radioactive waste using ionic liquids and a selective extractant

Selective separation of Cs ⁺ from liquid radioactive waste by “precipitation” was observed in a hydrophobic ionic liquid containing the Cs ⁺ -selective extractant dicyclohexano-18-crown-6. The precipitate was formed by the cation exchange mechanism, which simplified the treatment of Cs ⁺ after extraction. Solid–liquid extraction is a more economical extraction system than liquid–liquid extraction because it uses smaller quantities of ionic liquids. This work showed the possibility of developing a new method for removing Cs ⁺ from liquid radioactive waste using solid–liquid phase separation instead of the conventional liquid–liquid separation in an ionic liquid extraction system.     

Thin films of V2O5/MoO3 and their applications in electrochromism

Journal of Solid State Electrochemistry - Pure and doped vanadium pentoxide (V2O5, V2O5/MoO3) thin films were prepared by sol-gel method and dip coating technique. Furthermore, they were...     

New eco-friendly low-cost binders for Li-ion anodes

In the production of commercial Li-ion batteries, the active materials slurries are generally prepared using polyvinylidene fluoride (PVdF) as binder because of its good adhesion properties and electrochemical stability. Unfortunately, there are some disadvantages related to the use of PVdF: the most important is the use of toxic and environmentally unfriendly solvents, such as N-methyl-pyrrolidone (NMP), and the second is the high costs. In the light of these considerations, it seemed straightforward to investigate the suitability of some water-soluble, inexpensive, and eco-friendly materials to test as alternative binders (sodium alginate, chitosan tragacanth gum, gelatin). The rheological properties of these materials have been investigated in addition to the electrochemical characterization. Furthermore, graphite electrodes with PVdF, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) binders have been considered for sake of comparison. We found that some of these water-soluble binders, besides good electrochemical performances, showed a high adhesion to the current collector and a good electrochemical stability under the experimental conditions employed, which makes them interesting for the next generation of Li-ion batteries.     

Mathematical modelling and the learning trajectory: tools to support the teaching of linear algebra

In this article we present a didactic proposal for teaching linear algebra based on two compatible theoretical models: emergent models and mathematical modelling. This proposal begins with a problematic situation related to the creation and use of secure passwords, which leads students toward the construction of the concepts of spanning set and span. The objective is to evaluate this didactic proposal by determining the level of match between the hypothetical learning trajectory (HLT) designed in this study with the actual learning trajectory in the second experimental cycle of an investigation design-based research more extensive. The results show a high level of match between the trajectories in more than half of the conjectures, which gives evidence that the HLT has supported, in many cases, the achievement of the learning objective, and that additionally mathematical modelling contributes to the construction of these linear algebra concepts.     

On Litoff’s theorem

We give a short proof of Litoff’s theorem from the viewpoint of completely reducible modules.     

A fractional step method for 2D parabolic convection-diffusion singularly perturbed problems: uniform convergence and order reduction

In this work, we are concerned with the efficient resolution of two dimensional parabolic singularly perturbed problems of convection-diffusion type. The numerical method combines the fractional implicit Euler method to discretize in time on a uniform mesh and the classical upwind finite difference scheme, defined on a Shishkin mesh, to discretize in space. We consider general time-dependent Dirichlet boundary conditions, and we show that classical evaluations of the boundary conditions cause an order reduction in the consistency of the time integrator. An appropriate correction for the evaluations of the boundary data permits to remove such order reduction. Using this correction, we prove that the fully discrete scheme is uniformly convergent of first order in time and of almost first order in space. Some numerical experiments, which corroborate in practice the robustness and the efficiency of the proposed numerical algorithm, are shown; from them, we bring to light the influence in practice of the two options for the boundary data considered here, which is in agreement with the theoretical results.     

Averaged Decay Estimates for Fourier Transforms of Measures over Curves with Nonvanishing Torsion

We study averaged decay estimates for Fourier transforms of measures when the averages are taken over space curves with non-vanishing torsion. We extend the previously known results to higher dimensions and discuss sharpness of the estimates.     

On the mean value parametrization of natural exponential families — a revisited review

It is well known that any natural exponential family (NEF) is characterized by its variance function on its mean domain, often much simpler than the corresponding generating probability measures. The mean value parametrization appeared to be crucial in some statistical theory, like in generalized linear models, exponential dispersion models and Bayesian framework. The main aim of the paper is to expose the mean value parametrization for possible statistical applications. The paper presents an overview of the mean value parametrization and of the characterization property of the variance function for NEF’s. In particular it introduces the relationships existing between the NEF’s generating measure, Laplace transform and variance function as well as some supplemental results concerning the mean value representation. Some classes of polynomial variance functions are revisited for illustration. The corresponding NEF’s of such classes are generated by counting probabilities on the nonnegative integers and provide Poisson-overdispersed competitors to the homogeneous Poisson distribution.