The oxidation of ascorbate at copolymeric sulfonated poly(aniline) coated on glassy carbon electrodes

Self-doped poly(aniline)s as electrode coatings to catalyze ascorbate oxidation are revisited in this article. Sulfonated poly(aniline) (SPAN) was deposited on glassy carbon electrodes as a copolymer of aniline and its sulfonated derivative, 2-aminobenzenesulfonic acid (2-ABSA). The resulting deposits are reproducible and show good stability and electroactivity at pH > 7, enabling studies at typical physiological pH values. Calibration curves were obtained using a rotating disc electrode at a sampling potential of 0.2 V, displaying linear dependence in the region 0–20 mM ascorbate. A kinetic model based on the Michaelis–Menten reaction mechanism, previously validated for poly(aniline) composites, was used to analyse the form of the calibration curve leading to values of the effective reaction constants K_ME and k′_ME. New calibration curves constructed for different sampling potentials were used to elucidate the rate limiting step at saturated kinetics. Rotating disc voltammetry performed at increasing pH (from pH 2 to 9) showed a dramatic decrease in the limiting current, without any evidence for a change in the reaction mechanism.     

Synthesis of Ni3V2O8@graphene oxide nanocomposite as an efficient electrode material for supercapacitor applications

Journal of Solid State Electrochemistry - In the present investigation, we have synthesized Ni3V2O8@GO composite by co-precipitation method and designed as a new anode material for supercapacitor...     

On the numerical study of an obstacle optimal control problem with source term

In the present work, we study the numerical aspect of the optimality system given by R. Ghanem (Positivity 13:321–338, 2009). A numerical algorithm is given and its practical feasibility is investigated by several numerical tests in one and two dimensional spaces.     

Heuristic spectral estimation of bivariate nonstationary processes

A heuristic technique is developed for the estimation of auto-spectra and cross-spectra of multivariate nonstationary random processes which are used as models of earthquake accelerograms. The spectra are estimated by considering the statistical moments of the energy of linear systems (filters) excited by the stochastic seismic processes. The usefulness of the proposed technique is demonstrated by examples.

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Sommario Si propone una tecnica euristica per la determinazione degli spettri di processi aleatori non-stazionari multivariati, che vengono usati come modelli di accelerogrammi sismici. Gli spettri sono valutati considerando i momenti statistici dell'energia di sistemi lineari (filtri) eccitati dai processi sismici aleatori. Alcuni esempi dimostrano l'utilità della tecnica proposta.

     

Mesoporous platinum hosts for electrodeliquidliquid – Triple phase boundary redox systems

Mesoporous metal hosts are attractive electrode materials for complex electrode reactions, for example those involving a system of two immiscible liquids. Here we show that a solution of tetraphenylporphyrianto manganese (MnTPP) in 4-(3-phenylpropyl)-pyridine (PPP) organic liquid can be immobilized into mesoporous platinum thin films electrodeposited from a liquid crystalline template. When immersed in an aqueous solution, the organic liquid remains immobilized inside the mesoporous platinum framework. Well-defined, stable, and reproducible ion transfer voltammograms are recorded. The effects of mesoporous platinum membrane thickness (volume), scan rate, and the type of aqueous electrolyte anion (for Cl⁻, , , CN⁻, SCN⁻ and ) are investigated. Mesoporous platinum is proposed as a very effective electrode material for liquidliquid anion sensing and for other applications of electrochemically driven liquidliquid redox systems.     

Quantifying uncertainty in chemical systems modeling

This study compares two techniques for uncertainty quantification in chemistry computations, one based on sensitivity analysis and error propagation, and the other on stochastic analysis using polynomial chaos techniques. The two constructions are studied in the context of H₂? O₂ ignition under supercritical‐water conditions. They are compared in terms of their prediction of uncertainty in species concentrations and the sensitivity of selected species concentrations to given parameters. The formulation is extended to one‐dimensional reacting‐flow simulations. The computations are used to study sensitivities to both reaction rate pre‐exponentials and enthalpies, and to examine how this information must be evaluated in light of known, inherent parametric uncertainties in simulation parameters. The results indicate that polynomial chaos methods provide similar first‐order information to conventional sensitivity analysis, while preserving higher‐order information that is needed for accurate uncertainty quantification and for assigning confidence intervals on sensitivity coefficients. These higher‐order effects can be significant, as the analysis reveals substantial uncertainties in the sensitivity coefficients themselves. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 368–382, 2005     

Stochastic Finite Element Analysis for Multiphase Flow in Heterogeneous Porous Media

This study is concerned with developing a two-dimensional multiphase model that simulates the movement of NAPL in heterogeneous aquifers. Heterogeneity is dealt with in a probabilistic sense by modeling the intrinsic permeability of the porous medium as a stochastic process. The deterministic finite element method is used to spatially discretize the multiphase flow equations. The intrinsic permeability is represented in the model via its Karhunen–Loeve expansion. This is a computationally expedient representation of stochastic processes by means of a discrete set of random variables. Further, the nodal unknowns, water phase saturations and water phase pressures, are represented by their stochastic spectral expansions. This representation involves an orthogonal basis in the space of random variables. The basis consists of orthogonal polynomial chaoses of consecutive orders. The relative permeabilities of water and oil phases, and the capillary pressure are expanded in the same manner, as well. For these variables, the set of deterministic coefficients multiplying the basis in their expansions is evaluated based on constitutive relationships expressing the relative permeabilities and the capillary pressure as functions of the water phase saturations. The implementation of the various expansions into the multiphase flow equations results in the formulation of discretized stochastic differential equations that can be solved for the deterministic coefficients appearing in the expansions representing the unknowns. This method allows the computation of the probability distribution functions of the unknowns for any point in the spatial domain of the problem at any instant in time. The spectral formulation of the stochastic finite element method used herein has received wide acceptance as a comprehensive framework for problems involving random media. This paper provides the application of this formalism to the problem of two-phase flow in a random porous medium.     

Capillary electrophoresis with microwave-enhanced electrochemical detection

A new experimental development concerning microwave-assisted electrochemical detection in conjunction with capillary electrophoresis is presented. Focused microwaves are readily incorporated into end-column detection systems for capillary electrophoresis, they induce strong localised thermal activation at microelectrodes, and they affect and modulate, in particular, signals for chemically irreversible redox processes.     

True and false reversal of the elution order of barbiturates on a bonded cellulose-based chiral stationary phase

A set of racemic N-alkylated barbiturates were investigated for their direct enantioselective HPLC separation on a new chiral stationary phase (CSP) containing cellulose tris(3,5-dimethylphenylcarabamate) immobilized onto silica gel (Chiralpak IB) and its coated version (Chiralcel OD). They were online detected by UV and optical rotation detectors to trace the elution order of their enantiomers. Surprisingly, examples of false and true reversal of the elution order of enantiomers of barbiturates were observed and reported.     

Chiral separations of piperidine-2,6-dione analogues on Chiralpak IA and Chiralpak IB columns by using HPLC

Recently, two new immobilized polysaccharides based CSPs, namely tris-(3,5-dimethylphenylcarbamate) derivatives of amylose and cellulose known as Chiralpak IA and Chiralpak IB were introduced, which may be used with a wide range of solvents including standard and prohibited ones. Several racemic piperidine-2,6-dione analogues [aminoglutethimide, p-nitro-glutethimide, p-nitro-5-aminoglutethimide, cyclohexylaminoglutethimide, phenglutarimide and thalidomide] have been resolved on Chiralpak IA and Chiralpak IB columns (25 cm × 0.46 cm). The non-conventional mobile phases used were methyl-tert-butyl ether-THF (90:10, v/v) [I], 100% dichloromethane [II] and 100% acetonitrile [III] separately at a flow rate of 1.0 mL/min using a UV detector at 254 nm. The resolution factors for Chiralpak IA and Chiralpak IB columns were 1.00-5.33 and 0.33-0.67, respectively. Chiralpak IA column gave better results than Chiralpak IB column for the reported molecules using the developed HPLC conditions. Experimental conditions and the possible chiral recognition mechanisms have been discussed.