Screening of Fish Tissue for Methyl Mercury Using the Enzyme Invertase in a Solvent Interface

This paper describes a simple and rapid screening system for the extraction and determination of methyl mercury in tissue samples from fish. A novel clean-up procedure based on the use of two immiscible phases, an organic one containing methyl mercury and an aqueous one containing invertase, was developed. Methyl mercury was selectively extracted from the organic into the aqueous phase by its irreversible reaction with thiol groups of invertase, and the resulting inhibition of enzymatic activity served as a measure of methyl mercury concentration. Enzyme activity was measured with a spectrophotometric method using 3,5-dinitrosalicylic acid as a reagent. After parameter optimisation including pH, substrate concentration, and enzyme reaction time, it was possible to determine methyl mercury in the ppb range with this technique. Concentrations as low as 10ppb of methyl mercury in the extract, corresponding to 0.2ppm of methyl mercury in fish, were detected. The proposed procedure was successfully demonstrated as a simple screening method for methyl mercury in fish samples.     

Existence, uniqueness and analyticity for periodic solutions of a non-linear convolution equation

We study existence, uniqueness and analyticity for periodic solutions ofu(x)=( _IR J(y)u(x–y)dy) forxIR.     

Occurrence of rare events in ergodic interacting spin systems

We give asymptotics for the occurrence time of rare events in infinite spin systems whose invariant measure satisfies a Logarithmic Sobolev inequality. We then describe the typical paths close to this occurrence time. Finally, in the case of non-interacting spins, we obtain sharper estimates for the expected value of the occurrence time.     

Dirichlet-to-Neumann semigroup acts as a magnifying glass

The first aim of this paper is to illustrate numerically that the Dirichlet-to-Neumann semigroup represented by P. Lax acts as a magnifying glass. In this perspective, we used the finite element method for discretizing of the correspondent boundary dynamical system using the implicit and explicit Euler schemes. We prove by using the Chernoff’s Theorem that the implicit and explicit Euler methods converge to the exact solution and we use the (P1)-finite elements to illustrate this convergence through a FreeFem++ implementation which provides a movie available online. In the Dirichlet-to-Neumann semigroup represented by P. Lax the conductivity \(\gamma \) is the identity matrix \(I_n\) , but for a different conductivity \(\gamma \) , the authors of Cornean et al. (J Inverse Ill-posed Prob 12:111–134, 2006) supplied an estimation of the operator norm of the difference between the Dirichlet-to-Neumann operator \(\Lambda _\gamma \) and \(\Lambda _1\) , when \(\gamma =\beta I_n\) and \(\beta =1\) near the boundary \(\partial \Omega \) (see Lemma 2.1). We will use this result to estimate the accuracy between the correspondent Dirichlet-to-Neumann semigroup and the Lax semigroup, for \(f\in H^{1/2}(\partial \Omega )\) .     

Scheduling with uncertainties on new computing platforms

New distributed computing platforms (grids) are based on interconnections of a large number of processing elements. A most important issue for their effective utilization is the optimal use of resources through proper task scheduling. It consists of allocating the tasks of a parallel program to processors on the platform and to determine at what time the tasks will start their execution. As data may be subject to uncertainties or disturbances, it is practically impossible to precisely predict the input parameters of the task scheduling problem.     

Adsorptive properties of X zeolites modified by transition metal cation exchange

The ionic exchange of the NaX zeolite by Ni²⁺ and Cr³⁺ cations was progressively driven and studied by adsorption of nitrogen and carbon dioxide. For each cation-exchanged X zeolite sample, the development of characteristics such as profile of isotherms, RI criterion, isosteric adsorption heat and microporous volume using both the Dubinin–Radushkevich (DR) equation and the t-plot, was followed through the nitrogen adsorption. Results show that the cationic exchange process, in the case of Cr³⁺ introduced at middle degree, is accompanied by a textural damage for Cr(x)X, in contrast to Ni²⁺-exchanged X zeolites. This degradation occurs without significant presence of mesopores, because the RI criterion values were found to be much lower than 2.2. The CO₂ adsorption isotherms were measured at intervals of 30 K from 273 K and the equilibrium pressures ranged from 0.5 to 600 Torr. The experimental data were correlated by the Toth model. The associated three adjustable parameters were estimated by nonlinear least-squares analysis. The effect of temperature on the model parameters and the Henry’s law slope, K _H , represented by the product of Toth parameters, are discussed.     

Glyphosate–Exonuclease Interactions: Reduced Enzymatic Activity as a Route to Glyphosate Biosensing

N-phosphonomethyle-glycine (glyphosate) is the most widely used pesticide worldwide due to its effectiveness in killing weeds at a moderate cost, bringing significant economic benefits. However, owing to its massive use, glyphosate and its residues contaminate surface waters. On site, fast monitoring of contamination is therefore urgently needed to alert local authorities and raise population awareness. Here the hindrance of the activity of two enzymes, the exonuclease I (Exo I) and the T5 exonuclease (T5 Exo) by glyphosate, is reported. These two enzymes digest oligonucleotides into shorter sequences, down to single nucleotides. The presence of glyphosate in the reaction medium hampers the activity of both enzymes, slowing down enzymatic digestion. It is shown by fluorescence spectroscopy that the inhibition of ExoI enzymatic activity is specific to glyphosate, paving the way for the development of a biosensor to detect this pollutant in drinking water at suitable detection limits, i.e., 0.6 nm .