Biparametric potentiometric analytical microsystem for nitrate and potassium monitoring in water recycling processes for manned space missions

The construction and evaluation of a Low Temperature Co-fired Ceramics (LTCC)-based continuous flow potentiometric microanalyzer prototype to simultaneously monitor the presence of two ions (potassium and nitrate) in samples from the water recycling process for future manned space missions is presented. The microsystem integrates microfluidics and the detection system in a single substrate and it is smaller than a credit card. The detection system is based on two ion-selective electrodes (ISEs), which are built using all-solid state nitrate and potassium polymeric membranes, and a screen-printed Ag/AgCl reference electrode. The obtained analytical features after the optimization of the microfluidic design and hydrodynamics are a linear range from 10 to 1000 mg L⁻¹ and from 1.9 to 155 mg L⁻¹ and a detection limit of 9.56 mg L⁻¹ and 0.81 mg L⁻¹ for nitrate and potassium ions respectively.     

Minimalist peptidomimetic cyclophanes as strong organogelators

L-Valine containing cyclophanes have been shown to gelate organic solvents leading to soft materials with a clear expression of their chirality at the supramolecular level.     

Stochastic Order and Generalized Weighted Mean Invariance

In this paper, we present order invariance theoretical results for weighted quasi-arithmetic means of a monotonic series of numbers. The quasi-arithmetic mean, or Kolmogorov–Nagumo mean, generalizes the classical mean and appears in many disciplines, from information theory to physics, from economics to traffic flow. Stochastic orders are defined on weights (or equivalently, discrete probability distributions). They were introduced to study risk in economics and decision theory, and recently have found utility in Monte Carlo techniques and in image processing. We show in this paper that, if two distributions of weights are ordered under first stochastic order, then for any monotonic series of numbers their weighted quasi-arithmetic means share the same order. This means for instance that arithmetic and harmonic mean for two different distributions of weights always have to be aligned if the weights are stochastically ordered, this is, either both means increase or both decrease. We explore the invariance properties when convex (concave) functions define both the quasi-arithmetic mean and the series of numbers, we show its relationship with increasing concave order and increasing convex order, and we observe the important role played by a new defined mirror property of stochastic orders. We also give some applications to entropy and cross-entropy and present an example of multiple importance sampling Monte Carlo technique that illustrates the usefulness and transversality of our approach. Invariance theorems are useful when a system is represented by a set of quasi-arithmetic means and we want to change the distribution of weights so that all means evolve in the same direction.     

Electronic Tongues Employing Electrochemical Sensors

This review presents recent advances concerning work with electronic tongues employing electroanalytical sensors. This new concept in the electroanalysis sensor field entails the use of chemical sensor arrays coupled with chemometric processing tools, as a mean to improve sensors performance. The revision is organized according to the electroanalytical technique used for transduction, namely: potentiometry, voltammetry/amperometry or electrochemical impedance. The significant use of biosensors, mainly enzyme‐based is also presented. Salient applications in real problem solving using electrochemical electronic tongues are commented.     

Investigation on the structural and electrical properties of NdSrNi1−xCrxO4+δ (0.1≤x≤0.9) system

The phases NdSrNi_1−xCr_xO_4+δ (0.1≤x≤0.9) have been synthesized by modified sol-gel method and subsequent annealing at 1250 °C in 1 atm of flowing argon. X-ray diffraction (XRD) analysis and electrical resistivity have been measured at room temperature. Rietveld refinement shows that all compositions with x>0.1 were found to crystallize in the tetragonal K₂NiF₄ type structure in the space group I4/mmm, while for x=0.1, a mixture of two phases with the tetragonal space group I4/mmm and the orthorhombic space group Fmmm. Variations of a and c parameters show a complex behavior with increasing chromium content. It was established that compounds with chromium content less then x≤0.5 are oxygen-deficient, while for x>0.5 the sample are oxygen-overstoichiometric. The NdSrNi_0.5Cr_0.5O_4+δ compound exhibits semiconductive behavior and the electrical transport mechanism agrees with the non-adiabatic small polaron hopping model in the temperature ranges 298-493, 493-573 and 573-703 K separately.     

Regularity of the Extremal Solution of Some Nonlinear Elliptic Problems Involving the <Emphasis Type="Italic">p</Emphasis>-Laplacian

We consider the equation on a smooth bounded domain of with zero Dirichlet boundary conditions where p ≥ 2, λ > 0 and f satisfies typical assumptions in the subject of extremal solutions. We prove that, for such general nonlinearities f, the extremal solution u ^* belongs to L ^∞(Ω) if N < p + p/(p − 1) and if N < p(1 + p/(p − 1)). This work was partially supported by MCyT BMF 2002-04613-CO3-02.     

Simultaneous Titration of Ternary Mixtures of Pb(II), Cd(II) and Cu(II) with Potentiometric Electronic Tongue Detection

An automatic titration method is reported to resolve ternary mixtures of transition metals (Pb²⁺, Cd²⁺ and Cu²⁺) employing electronic tongue detection and a reduced number of pre‐defined additions of EDTA titrant. Sensors used were PVC membrane selective electrodes with generic response to heavy‐metals, plus an artificial neural network response model. Detection limits obtained were ca. 1 mg L^?1 for the three target ions and reproducibilities 3.0 % for Pb²⁺, 4.1 % for Cd²⁺ and 5.2 % for Cu²⁺. The system was applied to contaminated soil samples and high accuracy was obtained for the determination of Pb²⁺. In the determination Cd²⁺ and Cu²⁺, sample matrix showed a significant effect.