An Evaluation of Methods for Neuromagnetic Image Reconstruction

In this paper, we discuss several aspects of a potential new medical imaging modality for producing a quantitative three-dimensional map of neuron current densities associated with brain function. The neuromagnetic image is produced by reconstructing a current dipole field from external magnetic field measurements made with an array of superconducting quantum interference device (SQUID) detectors. This field is produced by numerical inversion of the Biot-Savart equation. The purpose of the work is to investigate fundamental limits on the feasibility of the proposed system under ideal conditions. The following problems are addressed: 1) What are the factors limiting resolution of the system? 2) What is a suitable model for neural activity in the brain? 3) What classes of algorithms are suitable for estimating the model parameters? The major conclusion of this work is that the inversion problem is severely ill-posed and the choice of model and estimation algorithm are crucial in obtaining reasonable solutions. A class of solutions, termed minimum dipole, is proposed as a means of obtaining more acceptable results.     

A comparative study on the processing, dielectric and electrical properties of PMN based solid solutions

Lead magnesium niobate (PMN) based binary with lead titanate (PT), lead iron niobate (PFN) and lead zinc niobate (PZN) and ternary with PZN-PT and PFN-PT solid solutions have been synthesized. In depth characterization using X-ray diffraction and SEM techniques have revealed the major perovskite phase formation. Amongst all the solid solutions, PMN-PZN-PT has given the highest values of permittivity as 19,740 and 23,700 withT _c as 34°C when sintered at 1080°C and 1180°C respectively on the one hand and on the other, PFN containing solid solutions exhibited distinct deviation from the relaxor behaviour.     

Role of hydrogen in electrical and structural characteristics of bilayer CdTe/Mn diluted magnetic semiconductor thin films

Bilayer thin films of diluted magnetic semiconductor CdTe/Mn have been prepared using vacuum thermal evaporation method at pressure of 10⁻⁵ torr. Annealing of bilayer thin films has been performed in atmospheric condition at constant temperature 400 °C for 1 hour. Hydrogenation of as-grown and annealed bilayer thin films has been performed by keeping these in hydrogenation cell. Structural characteristics of as-grown and heat treated thin films have been performed by X-ray diffractometer. Current–voltage characteristics of both as-grown hydrogenated and annealed hydrogenated bilayer thin films have been studied to find out the effect of hydrogenation. Surface topography of as-grown and annealed bilayer thin films has been confirmed by optical microscopy.     

Photoluminescence and photoluminescence excitation spectra of In0.2Ga0.8N-GaN quantum wells: comparison betweenexperimental and theoretical studies

InGaN-GaN represents an important heterostructure with applications in electronics and optoelectronics. It also offers a system where we can study the effects of interface roughness, alloy clustering, and the piezoelectric effect. In the paper, we examine how these factors influence the photoluminescence and excitation photoluminescence in InGaN-GaN quantum wells. We examine the Stokes shift as a function of the excitation level and doping and relate the values to the piezoelectric effect and disorder in the system. Detailed comparisons are made with experimental results     

Efficient algorithms to compute Hankel transforms using wavelets

The aim of the paper is to propose two efficient algorithms for the numerical evaluation of Hankel transform of order ν, ν>−1 using Legendre and rationalized Haar (RH) wavelets. The philosophy behind the algorithms is to replace the part xf(x) of the integrand by its wavelet decomposition obtained by using Legendre wavelets for the first algorithm and RH wavelets for the second one, thus representing Fν(y) as a Fourier-Bessel series with coefficients depending strongly on the input function xf(x) in both the cases. Numerical evaluations of test functions with known analytical Hankel transforms illustrate the proposed algorithms.     

Kinetics of adsorption of sulfur mustard on Al2O3 nanoparticles with and without impregnants

BACKGROUND: Chemical warfare (CW) agents are highly toxic compounds and have been used in war to produce physical immobilization, so safe and effective ways to detoxify them without endangering human life or the environment is of great concern. One of the important ways to achieve protection against CW agents contaminating air is to utilize suitable adsorbent materials, e.g. activated carbon, nanoparticles, etc. In the present study nanoparticles, synthesized through sol–gel processes and loaded with reactive compounds have been used for the degradation of CW agents and to understand their adsorption kinetics using Fickian and linear driving force models. RESULTS: Nanoparticles of AP‐Al₂O₃ (aerogel‐produced alumina) in the size range 2–30 nm with high surface area (375 m² g^?1) were produced by an alkoxide‐based synthesis, and then characterized using N₂‐Brunauer–Emmet–Teller (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD) and thermogravimetric analysis (TGA) techniques. Thereafter, these were impregnated, and finally tested for kinetics of adsorption of sulfur mustard (HD) under static conditions. The kinetics was studied using linear driving force and Fickian diffusion models and the kinetics parameters determined. CONCLUSION: AP‐Al₂O₃ with 10% impregnation of 9‐molybdo‐3‐vanadophosphoric acid (10%, w/w) showed the maximum uptake (640 mg g^?1) of HD. The highest adsorption potential indicated that the adsorption was due not only to physisorption but also involved chemisorption. Values of the diffusional exponent indicated the mechanism to be Fickian and anomalous. Hydrolysis, dehydrochlorination and oxidation reactions (identified using gas chromatography‐mass spectrometry (GC/MS)) were found to be the route of degradation of HD over the prepared nanoparticle based adsorbents. Copyright © 2009 Society of Chemical Industry