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.     

Preparation and characterization of polyaniline nanostructures via a interfacial polymerization method

Polyaniline nanostructures have been formed successfully via a interfacial polymerization method using different organic solvents. These materials were characterized by using IR, UV–vis, TGA, SEM, TEM and AC-impedance spectroscopy. In impedance plot of polyaniline (interfacial polymerization) using different organic solvents, different equivalent circuits with distinct nature of arcs have been observed indicating different distribution ratio indicating diffusion-limited interfacial control of nucleation and growth of polyaniline nanostructures dependent on the different distribution ratio and different rates of transfer of aniline from organic phase to aqueous phase in different solvents.     

Delineation of waterlogged area in inaccessible underground workings at Hingir Rampur Colliery using 2D resistivity imaging: a case study

Resistivity imaging (RI) survey was carried out along two profiles in the Hingir-Rampur Colliery to assess how far it would be practical to extend the workings in Seam I towards the waterlogged previous workings, whilst leaving at least 60 m of coal between the two sections of mine. In order to corroborate the results of the geophysical survey, two boreholes were drilled along the profiles. Analysis confirmed hard, compact and dry strata between 60 and 146 m depth.     

Nanogold based electrochemical sensor for determination of norepinephrine in biological fluids

A stable layer of gold nano particles (AuNPs) was deposited on the surface of indium tin oxide (ITO) and was used as an electrode for the detection of norepinephrine (NE) by square wave voltammetry (SWV) and cyclic voltammetry (CV). This modified electrode exhibits potent and persistent electron-mediating behavior and a well-defined oxidation peak towards NE was observed. The peak potential of NE was observed at less positive potential with increase in peak current as compared to bare ITO and bare gold electrodes. NE exhibited two quasi-reversible couples at AuNPs modified ITO over the potential range from −0.6 to 0.8 V in phosphate buffer solution (PBS) (pH 7.2). At optimal experimental condition, the catalytic oxidative peak current was responsive with the NE concentrations ranging from 100 nM to 25 μM. The detection limit was found to be 87 nM. Also, the effect of pH revealed that the oxidation of NE at the AuNPs modified ITO involved the transfer of equal number of protons and electrons. The interfering effect of common coexisting metabolites in blood and urine has also been reported. The modified electrode exhibited high stability and reproducibility. A comparison of results with high performance liquid chromatography (HPLC) signalizes a good agreement.     

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