An Easy Spectrophotometric Method for the Determination of Hypochlorite Using Thionin

A simple, rapid, and sensitive spectrophotometric method has been developed for the determination of hypochlorite using thionin. The method is based on the reaction of hypochlorite with potassium iodide in acidic medium to liberate iodine. The liberated iodine bleaches the violet color of thionin, which is measured at 600 nm. The decrease in absorbance is directly proportional to the concentration of hypochlorite. Beer’s law is obeyed in the range 0.2– 1.2 µg/mL of hypochlorite. The molar absorptivity, Sandell’s sensitivity, detection limit, and quantitation limit are found to be 1.489 × 10⁴ L/(mol cm), 3.25 × 10⁻³ µg cm⁻², 0.1026 µg/mL, and 0.3112 µg/mL, respectively. The method has been successfully applied to the determination of hypochlorite in various samples of natural water, tap water, milk, etc.__________From Zhurnal Analiticheskoi Khimii, Vol. 60, No. 8, 2005, pp. 798–801.Original English Text Copyright © 2005 by Narayana, Mathew, Vipin, Sreekumar, Cherian.The text was submitted by the authors in English.     

Measurement of Fractal Aggregates of Polydisperse Particles Using Small-Angle Light Scattering

The effect of primary particle polydispersity on the structure of fractal aggregates has been investigated through the salt-induced, diffusion-limited aggregation of mixtures of hematite. The fractal dimension was determined experimentally using three independent methods: q dependence of static light scattering, kinetic scaling, and correlation of aggregate mass and linear size both determined from Guinier scattering. The fractal dimensions D(f) obtained were 1.75+/-0.03, 1.76+/-0.03, and 1.70+/-0.05, respectively. The use of a previously derived fractal mean particle size was validated in allowing data collapse to master curves for the aggregation kinetics data. The fractal mean particle size is shown to have general utility by taking a number weighting to describe polydisperse aggregation kinetics and a mass weighting to describe small q scattering behavior. Copyright 2000 Academic Press.     

On Different Approaches to Estimate the Mass Fractal Dimension of Coal Aggregates

Several methods to measure the structures of coal aggregates are compared. Loose and compact coal aggregates were generated through flocculation of ultrafine coal particles (mean volume diameter of 12 μm) under specific shearing conditions. Aggregate structure in terms of mass fractal dimension, D_f, was determined using various methods; namely 2D and 3D image analysis, interpretation of intensity patterns from small angle light scattering, changes in aggregation state through light obscuration, and settling behavior. In this study, the measured values of D_f ranged from 1.84–2.19 for coal aggregates with more open structures, and around 2.27–2.66 for the compact ones. All of these approaches could distinguish structural differences between aggregates, albeit with variation in D_f values estimated by the different techniques. The discrepancy in the absolute values for fractal dimension is due to the different physical properties measured by each approach, depending on the assumptions used to infer D_f from measurable parameters. In addition, image analysis and settling techniques are based on the examination of individual aggregates, such that a large number of data points are required to yield statistically representative estimations. Light scattering and obscuration measure the aggregates collectively to give average D_f values of the particulate systems; consequently ignoring any structural variation between the aggregates, and leaving possible small contaminations undetected (e.g. by dust particles or air bubbles). Appropriate utilization of a particular method is thus largely determined by system properties and required data quality.     

Preparation and characterization of thermally evaporated titanium phthalocyanine dichloride thin films

Titanium phthalocyanine dichloride (TiPcCl₂) thin films are prepared on glass substrates by vacuum-sublimation technique. The optical constants of thin films are obtained by means of thin film spectrophotometry. Planar structures for the study of electrical properties are fabricated with TiPcCl₂ as active layer and silver as the contact electrodes. The effects of post-deposition annealing on the optical band gap have been studied. The optical transition is found to be direct allowed in nature. The invariance in the optical band gap shows the thermal stability of the material. The activation energies are determined using the Arrhenius plots between electrical conductivity and inverse temperature. The variation in activation energy with post-deposition annealing is investigated. The unit cell dimensions of TiPcCl₂ thin films are also determined by indexing the powder diffraction data. The variations of the surface morphology and grain size with annealing have also been studied.     

An engineering predictive approach of fatigue crack growth behavior: The case of the lug-type joint

The present attempt proposes a predictive approach of the fatigue crack growth (FCG) behavior of a lug-type joint used in an aeronautic context. The crack tip residual stress distribution and material dispersions are considered. The developed approach was implemented by coupling the Extended Finite Element Method (XFEM), the Residual Corrected Stress Intensity Factor (RC-SIF), developed by the authors, and the Monte Carlo simulation (MCS) method. The Lemaitre–Chaboche model, developed upon the ABAQUS commercial code, was considered for characterizing material behavior. The developed approach treats FCG life by considering the stochastic behavior of material parameters and the crack tip residual stress field during propagation. Comparing with experimental data, the proposed approach exhibits a good ability in evaluating the FCG reliability of a cracked lug-type joint subjected to different loading conditions. The iso-probabilistic P–a–N curves can be used as an efficient tool for ensuring the safety behavior of cracked components.     

The Formation of Nano-sized Selenium–titanium Dioxide Composite Semiconductors by Photocatalysis

Nano-sized selenium (Se) particles were deposited onto titanium dioxide (TiO₂) by the photocatalytic reduction of selenate (Se(VI)) and selenite (Se(IV)) ions. Se particles deposition on TiO₂ was only observed in the presence of formic acid, which acted as the organic hole scavenger. The Se particles formed were crystalline. Se particles of different size could be formed onto the TiO₂ particles by manipulating experimental parameters such as pH and the Se precursor used. When Se(VI) ions were used as the precursor, the Se particles formed on TiO₂ were found to be spherical in shape, up to 6 times bigger than the TiO₂ particles (up to 145nm) and discretely formed on the TiO₂ particles. The growth and sphericity of the Se particles were explained in terms of electron transfer across the p–n junctions formed by the p-type Se and n-type TiO₂ semiconductors under illumination and the adsorption of the Se(VI) ions. The size of the Se particles were found to be dependent on the amount of Se(VI) photoreduced. When Se(IV) ions were used as the precursor for Se particles formation, the particles formed were much smaller than that of TiO₂ crystals (less than 25nm) and also more evenly dispersed on the TiO₂ particles.     

Acid-catalyzed ortho-alkylation of anilines with styrenes: an improved route to chiral anilines with bulky substituents

[reaction: see text] Reaction of para-substituted anilines with styrene derivatives at elevated temperatures, when catalyzed by CF3SO3H, results in highly chemoselective ortho-alkylation of the aniline. When R = H, dialkylation can be achieved by varying the ratio of styrene to aniline. Several different substituted anilines and styrenes were examined, and good yields (42-87%) were obtained, except in the case where electron-withdrawing substituents are present on the styrene.     

Analog Integrated Circuit for Motion Detection against Moving Background Based on the Insect Visual System

A network for displaying the velocity signal of a target edge which has larger velocity than the background was proposed and designed based on an insect visual system. In the insect visual system, the velocity signals generated by the background are inhibited by the signals generated by averaging the velocity signals from each cell and can only display the velocity signals of the target. The proposed network was constructed with simple analog circuits. The measured results of the test chip fabricated with the 1.2$mUm complementary metal-oxide-semiconductor (CMOS) process showed that the edge detection circuit inserted to the first stage of the proposed network can detect the edge position. It was apparent from the measured results of the test circuit constructed with discrete metal-oxide-semiconductor (MOS) transistors that the proposed unit circuit constructing the network can generate the velocity signals by inputting the edge signals. The results with the simulation program with integrated circuit emphasis (SPICE) showed that the proposed network can only display the velocity signals of the target edges but not those of the background. Thus, it was clarified that the various motion directions of the target can be detected independent of the background by using the proposed network.