Mercury(II) ion-selective polymeric membrane sensors for analysis of mercury in hazardous wastes.

Two novel potentiometric sensors that are highly selective to Hg2+ ions are described. These are based on the use of 5,5'-dithio-bis(2-nitrobenzoic acid) (DTNB) and tricyclazole (TCZ) as neutral carriers in plasticized poly(vinyl chloride) membranes. Fast Nernstian responses are obtained for Hg2+ ions over the concentration ranges 7.0 x 10(-6) - 1.0 x 10(-2) and 7.7 x 10(-6) - 1.0 x 10(-2) mol l(-1) at pH 1.8 - 3.3 with lower detection limits of 5.0 x 10(-6) and 5.6 x 10(-6) mol l(-1) (approximately 1 microh ml(-1)) and calibration slopes of 30.0 and 29.7 mV decade(-1) with DTNB- and TCZ-based membrane sensors, respectively. Validation of the assay method reveals good performance characteristics, including long life span, good selectivity for Hg2+ ions over a wide variety of other metal ions, long term response stability, and high reproducibility. Applications for direct determination of mercury in hazardous wastes including dental amalgam, mercury bulbs, and fluorescent lamps give results with good correlation with data obtained using cold vapor atomic absorption spectrometry.     

Mechanism of electron transfer reaction of ternary nitrilotriacetatocobalt(II) complexes involving succinate and malonate as secondary ligands

The mechanism of oxidation of ternary complexes, [Co^II(nta)(S)(H₂O)₂]^3? and [Co^II(nta)(M)(H₂O)]^3? (nta = nitrilotriacetate acid, S = succinate dianion, and M = malonate dianion), by periodate in aqueous medium has been studied spectrophotometrically over the (20.0–40.0) ± 0.1°C range. The reaction is first order with respect to both [IO₄^?] and the complex, and the rate decreases over the [H⁺] range (2.69–56.20) × 10^?6 mol dm^?3 in both cases. The experimental rate law is consistent with a mechanism in which both the hydroxy complexes [Co^II(nta)(S)(H₂O)(OH)]^4? and [Co^II(nta)(M)(OH)]^4? are significantly more reactive than their conjugate acids. The value of the intramolecular electron transfer rate constant for the oxidation of the [Co^II(nta)(S)(H₂O)₂]^3?, k₁ (3.60 × 10^?3 s^?1), is greater than the value of k₆ (1.54 × 10^?3 s^?1) for the oxidation of [Co^II(nta)(M)(H₂O)]^3? at 30.0 ± 0.1°C and I = 0.20 mol dm^?3. The thermodynamic activation parameters have been calculated. It is assumed that electron transfer takes place via an inner‐sphere mechanism. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 103–113, 2008     

An exact solution for variable coefficients fourth-order wave equation using the Adomian method

This paper presents a novel approach for the analysis of a fourth-order parabolic equation dealing with vibration of beams by using the decomposition method. In this regard, a general approach based on the generalized Fourier series expansion is applied. The obtained analytic solution is simplified in terms of a given set of orthogonal basis functions. The result is compared with the classical modal analysis technique which is widely used in the field of structural dynamics. It is shown that the result of the decomposition method leads to an exact closed-form solution which is equivalent to the result obtained by the modal analysis method. Some examples are given to demonstrate the validity of the present study.     

Delayed feedback control of chaotic spinning disk via minimum entropy approach

Chaos control of a spinning disk model via delayed feedback method is presented. The feedback gain is obtained and adapted according to a minimum entropy (ME) algorithm. In this method, stabilizing an unstable fixed point of the system Poincare map is achieved by minimizing the entropy of point distribution on the Poincare section. Simulation results show the feasibility of the proposed method in applying the delayed feedback technique for chaos control of spinning disks.     

Determination of trace amount of carbon disulfide in water by the spectrophotometric reaction-rate method.

Carbon disulfide (CS2) was determined at trace levels by its induction effect on the reaction of triiodide with azide in acidic media. The reaction was monitored spectrophotometrically by the decreased absorbance of triiodide over a period of 30 - 180 s from the initiation of the reaction at 350 nm, with calibration linear range of 0.020 - 1.870 microg/ml CS2. The limit of detection is 0.013 microg/ml CS2. A carbon-active column was used for sample solution clean up. The proposed method was successfully applied to the determination of trace carbon disulfide in natural water.     

Evaporation of a thin film coated on a substrate induced by a pulsed laser

The two-dimensional Laplace integral transform technique has been applied to get the spatial and temporal temperature distributions in both the molten layer thickness of a thin film coated on a substrate, the still solid part of the thin film of the target and the temperature distribution in the substrate. Also a formula for the time dependence of the evaporated part of the thin film of the target as well as the molten layer thickness of the thin film were obtained. Calculations of the obtained relations were carried out during the irradiation with a pulsed laser. The derivation has taken into account the temperature-dependent absorption coefficient of the irradiated surface and the chemical reaction in the vapor of the thin film. As an illustrative example, computations were carried out on an aluminum thin film coated on a glass substrate.     

Effect of density-dependent nucleon-nucleon cross-section on elastic scattering

A linear form of density-dependent total nucleon-nucleon (NN) cross-section that depends on the coordinates of the projectile and target is applied in the Glauber phase shift formula. The only free parameter in these calculations is the density-dependent parameter , which is adjusted to obtain an agreement between the calculated angular distribution of the elastic-scattering cross-section and the corresponding experimental one. The elastic scattering of the ¹²C ion on the ¹²C ion target has been studied at incident energies of 300, 360, 1016, 1441 and 2400 MeV. The total reaction cross-section is also calculated with the obtained value of for the same reactions. The obtained values of are compared with those obtained from the optical-model analysis as well as those of the experimental value. Nuclear transparency effects are also discussed. Generally, the density-dependent NN cross-section improves the calculated results.Received: 11 February 2003, Revised: 8 July 2003, Published online: 26 January 2004PACS: 24.10.-i Nuclear-reaction models and methods - 25.70.-z Low and intermediate energy heavy-ion reactions