Fabrication of a bimetallic Cu/Pt particle-modified carbon nanotube paste electrode and its use for the electrocatalytic oxidation of methanol

In this work, carbon nanotube paste electrode (CNTPE) was used as a substrate for deposition of bimetallic Cu/Pt particles. At first, a Cu film was prepared by electrochemical reduction of Cu ions onto the CNTPE in 0.1 M H₂SO₄ solution. Cu/Pt catalysts were prepared by partial galvanic replacement of Cu with Pt by simply immersion of the Cu-coated CNTPE in 2.0 mM H₂PtCl₆ solution. The nature and surface morphology of the bare CNTPE and fabricated Cu/Pt species were characterized by scanning electron microscopy and energy dispersive X-ray spectrometry. The Cu/Pt-modified CNTPE exhibits remarkable electrocatalytic activity towards methanol oxidation. It has been shown that carbon nanotubes improve the electrocatalytic activity of the catalysts towards oxidation. Then, the influence of various parameters such as Cu source concentration, electrodeposition time, replacement time, and methanol concentration on its oxidation as well as long-term stability of the modified electrode have been investigated by electrochemical methods.     

Catechol as an electrochemical indicator for voltammetric determination of <Emphasis Type="Italic">N</Emphasis>-acetyl-<Emphasis Type="SmallCaps">l</Emphasis>-cysteine in aqueous media at the surface of carbon paste electrode

The utilization of catechol as an electrochemical indicator in the presence of N-Acetyl-l-cysteine (NAC) at a carbon paste electrode (CPE) has been investigated in aqueous media using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and double-step potential chronoamperometry methods. The results show that NAC participates in Michael type addition reaction with electrogenerated quinone from electrooxidation of catechol at CPE to form the corresponding thioquinone derivative. The reoxidation of the adduct leads to increase in the oxidative current which is proportional to the concentration of NAC. Therefore, in the optimum condition (pH = 6.00) by CV, the oxidation of NAC occurs at a potential about 400 mV versus Ag|AgCl|KCl_sat in the presence of catechol at the surface of CPE. The practical utility of the method showed that low detection limit and high sensitivity for voltammetric determination of NAC. The proposed method is useful for the routine analysis of NAC in pharmaceutical formulations.     

Electrocatalytic reduction of nitrite using ferricyanide; Application for its simple and selective determination

The electrocatalytic reduction of nitrite has been studied by ferricyanide at the surface of carbon paste electrode. Cyclic voltammetry and chronoamperometry techniques were used to investigate the suitability of ferricyanide as a mediator for the electrocatalytic nitrite reduction in aqueous solution with various pH. Results showed that pH 0.00 is the most suitable for this purpose. In the optimum pH, the electrocatalytic ability about 700 mV can be seen and the homogeneous second-order rate constant (k_s) for nitrite coupled catalytically to ferricyanide was calculated 2.75 × 10³ M⁻¹ s⁻¹ by Nicholson-Shain method. Also, electron transfer coefficients (α) for ferricyanide was determined by using various electrochemical approaches such as Tafel plot in the absence and presence of nitrite 0.556 and 0.760, respectively. The catalytic reduction peak current was linearly dependent on the nitrite concentration and the linearity range obtained was 5.00 × 10⁻⁵ to 1.00 × 10⁻³ M. Detection limit has been found to be 2.63 × 10⁻⁵ M (2σ). This method has been applied as a selective, simple and precise method for determination of nitrite in real sample.     

Capacity of Wireless Communication Systems Employing Antenna Arrays,a Tutorial Study

A tutorial study is performed on thecapacity of multiple antenna wireless communication systems.Multiple antenna structures can be classified into single-inputmultiple-outputs (SIMO), multiple-inputs single-output (MISO), andmultiple-inputs multiple-outputs (MIMO) systems. Assuming that thechannel is known at receiver, capacity expressions are providedfor each structure, under the conditions of quasi-static flatfading. Also, information rate limits are provided in each casefor some suboptimal structures or detection techniques that may beused in practice. Using simulations for the case of flat Rayleighfading, capacities of optimal/suboptimal implementations arecontrasted for each multi-antenna structure. Discussions are madeon system design, regarding implementation complexity andpractical limitations on achieving these capacities. Inparticular, the problem of fading correlation and required antennaspacing, effect of fast channel fading, and lack of channelknowledge at receiver are discussed. Providing the results of themost recent researches considering the capacity of multi-antennasystems, as well as some new results, this paper can give a goodperspective for designing appropriate architectures in differentwireless communication applications.     

Copper-poly(2-aminodiphenylamine) as a novel and low cost electrocatalyst for electrocatalytic oxidation of methanol in alkaline solution

In the present work we demonstrate the carbon paste as a new electrode substrate for the electropolymerization of 2-aminodiphenylamine and fabrication of polymer film modified electrode. Then transition metal of copper is incorporated into the polymer by electrodepositing of Cu(II) from CuCl₂ acidic solution using potentiostatic technique. The electrocatalytic oxidation of methanol was studies by cyclic voltammetry and chronoamperometry methods at the surface of obtained Cu/P(2ADPA)/MCPE. It has been found that in the course of an anodic potential sweep, the electro-oxidation of methanol follows the formation of Cu(III) and is catalyzed by this species through a mediated electron transfer mechanism. The obtained current density for this catalytic oxidation is very high which could be come from high surface area of caused by the P(2ADPA) modification. The effects of various parameters such as the copper loading, scan rate and methanol concentration on the electrocatalytic oxidation of methanol were also investigated at the surface of Cu/P(2ADPA)/MCPE. Finally, using a chronoamperometric method, the catalytic rate constant (k) for methanol was found to be 0.2 × 10⁵ cm³ mol⁻¹ s⁻¹ that the high k can be ascribed for the fast electron transfer process due to electrode modification.     

A novel, effective and low cost catalyst for methanol oxidation based on nickel ions dispersed onto poly(o-toluidine)/Triton X-100 film at the surface of multi-walled carbon nanotube paste electrode

In this work, for the first time an aqueous solution of Triton X-100 (TX-100) [t-octyl phenoxy polyethoxy ethanol] non-ionic surfactant is used as an additive for electropolymerization of o-toluidine (OT) onto multi-walled carbon nanotube paste electrode (CNTPE), which is investigated as a novel matrix for dispersion of nickel ions. The growth of polymeric film in the absence of TX-100 is poor, while it considerably increases in the presence of the surfactant and its growth is continued up to 60th cycle. The as-prepared substrate is used as porous matrix for dispersion of transition metal ions of Ni(II) to POT/TX-100 film by immersing the modified electrode in a 0.1 M nickel sulfate solution. The electrochemical characterization of this modified electrode exhibits redox behavior of Ni(III)/Ni(II) couple. It has been shown that POT/TX-100 at the surface of CNTPE improves catalytic efficiency of the dispersed nickel ions toward methanol oxidation. Then, using a chronoamperometric method, the catalytic rate constant, k, for methanol oxidation is found to be 7.40 × 10⁴ cm³ mol⁻¹ s⁻¹. At the end of this work, long-term stability of this modified electrode has been investigated.     

Synchronisation conjointe rythme et phase en CDMA optimisée dans un contexte multi-utilisateur

This paper is concerned with the problem of joint phase and delay synchronization fords-cdma signals in a multi-user context. We propose a novel version of a standard algorithm optimized for the multi-user case. A brief study of the standard algorithm shows that the task of timing recovery is the most degraded. So the improvement will concern this timing recovery. The optimized version consists in inserting a prefilter in the delay loop, and in calculating its coefficients in order to minimize the timing variance. The resolution of such a problem with the Lagrange-multiplier method yields an analytical expression of the prefilter coefficients. The optimized algorithm performances are then evaluated by simulations. The main result of this study shows that a very short prefilter can increase the timing recovery performances and the phase recovery performances too, due to the interaction between those two tasks.     

Effect of variations in the plate modulus of elasticity on the failure modes of FRP plated R.C. beams

In the absence of FRP plate/glue/concrete interface bond failure (i.e. interfacial debonding), eight possible flexural modes of failure are identified for reinforced concrete beams experiencing lateral loading, and strengthened in flexure with external FRP or steel plates glued to their soffits. All possible changes in such modes of failure, as a result of variations in the modulus of elasticity of the FRP material (assuming an associated constant value of ultimate tensile strength for the FRP plate in a given beam design), have been addressed in some detail, with a quantitative treatment of the critical values of the FRP modulus of elasticity associated with various failure mode transitions (i.e. changes).     

Electrocatalytic oxidation of glutathione at carbon paste electrode modified with 2,7-<Emphasis Type="Italic">bis</Emphasis> (ferrocenyl ethyl) fluoren-9-one: application as a voltammetric sensor

Electrooxidation of glutathione (GSH) was studied at the surface of 2,7-bis (ferrocenyl ethyl) fluoren-9-one modified carbon paste electrode (2,7-BFEFMCPE). Cyclic voltammetry (CV), double potential-step chronoamperometry, and differential pulse voltammetry (DPV) were used to investigate the suitability of this ferrocene derivative as a mediator for the electrocatalytic oxidation of GSH in aqueous solutions with various pH. Results showed that pH 7.00 is the most suitable pH for this purpose. At the optimum pH, the oxidation of GSH at the surface of this modified electrode occurs at a potential of about 0.410 V versus Ag|AgCl|KCl_sat. The kinetic parameters such as electron transfer coefficient, α = 0.61, and rate constant for the chemical reaction between GSH and redox site in 2,7-BFEFMCPE, k _h = 1.73 × 10³ cm³ mol⁻¹ s⁻¹, were also determined using electrochemical approaches. Also, the apparent diffusion coefficient, D _app, for GSH was found to be 5.0 × 10⁻⁵ cm² s⁻¹ in aqueous buffered solution. The electrocatalytic oxidation peak current of GSH showed a linear dependence on the glutathione concentration, and linear calibration curves were obtained in the ranges of 5.2 × 10⁻⁵ M to 4.1 × 10⁻³ M and 9.2 × 10⁻⁷ M to 1.1 × 10⁻⁵ M with cyclic voltammetry and differential pulse voltammetry methods, respectively. The detection limits (3σ) were determined as 1.4 × 10⁻⁵ M and 5.1 × 10⁻⁷ M for the CV and DPV methods, respectively. This method was also examined as a selective, simple, and precise new method for voltammetric determination of GSH in real sample such as hemolysed erythrocyte.