Heavy metal concentrations in fish,shellfish and fish products from internal markets of India vis-a-vis international standards

Heavy metals are an important group of chemical contaminants and food is the major vehicle for entry into the system. Fish constitute a major source of heavy metals in food. Concentration of heavy metals in commercially important species of fish, shellfish and fish products from fish markets in and around the Cochin area was evaluated using an atomic absorption spectrometer. The concentration ranges of Cd, Pb, Hg, Cr, As, Zn, Cu, Co, Mn, Ni, and Se in the samples were <0.07–1, <0.07–1.32, <0.05–2.31, <0.05 to 3.65, <0.1–4.14, 0.6 to 165, 0.15 to 24, <0.02 to 0.85, <0.08 to 9.2, <0.032–1.38 and; <0.03–1.35 mg/kg, respectively. The present study showed that different metals were present in the samples at different levels but within the maximum residual levels prescribed by the EU and USFDA and the fish and shellfish from these areas, in general, are safe for human consumption.     

Changes in Effective Thermal Conductivity During the Carbothermic Reduction of Magnetite Using Graphite

Knowledge of the effective thermal diffusivity changes of systems undergoing reactions where heat transfer plays an important role in the reaction kinetics is essential for process understanding and control. Carbothermic reduction process of magnetite containing composites is a typical example of such systems. The reduction process in this case is highly endothermic and hence, the overall rate of the reaction is greatly influenced by the heat transfer through composite compact. Using Laser-Flash method, the change of effective thermal diffusivity of magnetite-graphite composite pellet was monitored in the dynamic mode over a pre-defined thermal cycle (heating at the rate of 7 K/min to 1423 K (1150 °C), holding the sample for 270 minutes at this temperature and then cooling it down to the room temperature at the same rate as heating). These measurements were supplemented by Thermogravimetric Analysis under comparable experimental conditions as well as quenching tests of the samples in order to combine the impact of various factors such as sample dilatations and changes in apparent density on the progress of the reaction. The present results show that monitoring thermal diffusivity changes during the course of reduction would be a very useful tool in a total understanding of the underlying physicochemical phenomena. At the end, effort is made to estimate the apparent thermal conductivity values based on the measured thermal diffusivity and dilatations.     

Determination of interface-state parameters in a MOS capacitor by DLTS

A modification of the DLTS (Deep Level Transient Spectroscopy) technique for interface-state measurement is described in which the surface potential is used to determine the energy of the interface states contributing to the emission signal. This technique allows an accurate and unambiguous determination of interface-state energies and cross sections. Expressions are determined for interface-state emission as a function of surface potential. Measurements of interface-state density and majority-carrier cross sections as functions of energy for n- and p-type MOS samples are presented.     

M.O.S. switched-capacitor amplifiers

Switched-capacitor voltage gain elements, in which the gain is precisely controlled by the ratio of two capacitors, are presented. The voltage gain is obtained by means of a transconductance element operating into a switched-capacitor resistor. Circuit configurations use a single operational amplifier or a unity-gain buffer. In some of these configurations, the offset voltage of the operational amplifier or the buffer is not amplified.     

Enhanced and selective fluoride sorption on Ce(III) encapsulated chitosan polymeric matrix

Chitosan beads (CB) possesses low defluoridation capacity (DC) have been suitably modified by carboxylation followed by chelation with Ce(III) to enhance its DC. The carboxylated chitosan beads (CCB), which has a desirable DC of 1385 mgF^?/kg, has been further chemically modified by incorporating Ce³⁺ ion into CCB (Ce‐CCB) and its DC was found to be 4798 mgF^?/kg, whereas raw chitosan beads (CB) possesses 52 mgF^?/kg only. The maximum DC of Ce‐CCB was observed at pH 7 and showed selectivity toward fluoride in presence of other coanions. The sorbent was characterized using FTIR and SEM with EDAX analysis. The sorption data was fitted with Freundlich and Langmuir isotherms and kinetic models. The calculated thermodynamic parameters, viz., ΔG°, ΔH° and ΔS° indicate the nature of fluoride sorption. A field trial was carried out with fluoride water collected from a nearby fluoride‐endemic village to test the suitability of Ce‐CCB at field conditions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Surface studies on activated and hydrided CaNi5 alloy

X-ray photoelectron spectroscopic studies on the activated pure CaNi₅ alloy as well as the hydride formed at 1 atm pressure and room temperature, CaNi₅H_4.8, showed that on activation calcium segregates to the surface and forms the oxide, whereas most of the nickel on the surface is present in the metallic form. This indicates that the coexistance of the oxide phase and the metal phase is essential for the facile hydriding behaviour of CaNi₅.     

Ion beam and thermally-induced interface reaction between highT c superconductor thin film and metal overlayer

Ion beam and thermally-induced interface reactions between highT _c superconducting thin film of Y₁Ba₂Cu₃O_7−x and metal overlayer of Ag are studied with a view to control the interfacial property of contact resistance. The interface reaction is induced by 100 keV Ar⁺ ion beam with different ion dose values ranging from 5 × 10¹³ to 3×10¹⁴ ions/cm². The YBaCuO film-metal interface is characterized by using the small angle XRD to study the structural properties of the interfacial phases. The electrical property of the interface, specifically contact resistance, has been investigated for different dose values and thermal treatments. Three-probe vs four-probe configuration has been adopted to measure the contact resistance.     

Determination of the structure and orientation of organic molecules tethered to flat graphitic carbon by ATR-FT-IR and Raman spectroscopy

Mono- and multilayers of nitroazobenzene (NAB), azobenzene (AB), nitrobiphenyl (NBP), biphenyl (BP), and fluorene (FL) were covalently bonded to flat pyrolyzed photoresist films (PPF) by electrochemical reduction of their diazonium derivatives. The structure and orientation of the molecular layers were probed with ATR-FT-IR and Raman spectroscopy. A hemispherical germanium ATR element used with p-polarized light at 65 degrees incidence angle yielded high signal/noise IR spectra for monolayer coverage of molecules on PPF. The IR spectra are dominated by in-plane vibrational modes in the 1000-2000-cm(-1) spectral range but also exhibit weaker out-of-plane deformations in the 650-1000-cm(-1) region. The average tilt angle with respect to the surface normal for the various molecules varied from 31.0 +/- 4.5 degrees for NAB to 44.2 +/- 5.4 degrees for FL with AB, NBP, and BP exhibiting intermediate adsorption geometries. Raman intensity ratios of NAB and AB for p- and s-polarized incident light support the conclusion that the chemisorbed molecules are in a predominantly upright orientation. The results unequivocally indicate that molecules electroreduced from their diazonium precursors are not chemisorbed flat on the PPF surface, but rather at an angle, similar to the behavior of Au/thiol self-assembled monolayers, Langmuir-Blodgett films, and porphyrin molecules chemisorbed thermally on silicon and PPF from alkyne and alkene precursors.