Superconducting and ferromagnetic phases induced by lattice distortions in SrFe2As2

Single crystals of SrFe2As2 grown using a self-flux solution method were characterized via x-ray, transport and magnetization studies, revealing a superconducting phase below T_c = 21 K characterized by a full electrical resistivity transition and partial diamagnetic screening. The reversible destruction and reinstatement of this phase by heat treatment and mechanical deformation studies, along with single-crystal X-ray diffraction measurements, indicate that internal crystallographic strain originating from c-axis-oriented planar defects plays a central role in promoting the appearance of superconductivity under ambient pressure conditions in ~90% of as-grown crystals. The appearance of a ferromagnetic moment with magnitude proportional to the tunable superconducting volume fraction suggests that these phenomena are both stabilized by lattice distortion.Comment: 4 pages, 4 figure

Aerosol Characteristics at a high-altitude station Nainital during the ISRO-GBP Land Campaign-II

During the second land campaign (LC-II) organised by ISRO-GBP, extensive ground-based measurements of aerosol characteristics were carried out over Manora Peak (29.4oN; 79.5oE; 1951 metres above mean sea level), Nainital (a high altitude station located in the Shivalik ranges of Central Himalayas) during the dry, winter season (December) of 2004. These measurements included the spectral aerosol optical depths (AOD), columnar water vapour content (W), Total Columnar Ozone (TCO), total number concentration (NT) of near surface aerosols, mass concentration of black carbon (MB), aerosol mass loading (MT), and Global Solar Radiation. Based on these measured parameters, we present the results on the near-surface and columnar properties of atmospheric aerosols at Nainital.Comment: Published in the Proceedings of the ISRO-GBP Land-Campaign-II meeting, Physical Research Laboratory, Ahmadabad (Inida), March 200

Modeling Metal Oxide Surge Arrester for the Modern Polarization Based Diagnostics

Recently a number of new non-destructive diagnostic techniques have been investigated for the reliable condition assessment of the ageing of metal oxide surge arrester (MOSA). Among them polarizationrdepolarization current and return voltage measurement techniques showed very promising results. This paper presents an insulation polarization model for investigating polarization-based diagnostics for metal oxide surge arrester. The simulations of the proposed model are validated and verified by comparing the data from the polarization/depolarization current measurements. The simulation of return voltage for MOSA is also performed to validate the insulation polarization model. Finally, the usefulness of this model for MOSA diagnostics has been highlighted in this paper

Optical properties of perovskite alkaline earth titanates : a formulation

In this communication we suggest a formulation of the optical conductivity as a convolution of an energy resolved joint density of states and an energy-frequency labelled transition rate. Our final aim is to develop a scheme based on the augmented space recursion for random systems. In order to gain confidence in our formulation, we apply the formulation to three alkaline earth titanates CaTiO_3, SrTiO_3 and BaTiO_3 and compare our results with available data on optical properties of these systems.Comment: 19 pages, 9 figures, Submitted to Journal of Physics: Condensed Matte

Some Precautions for the Field Users of PDC Measurement for Transformer Insulation Condition Assessment

The need for economic, reliable and effective delivery of electric power has lead to the search for new, efficient and effective methods for diagnosing the insulation of the HV equipments in the industries all over the world. One of the methods currently being investigated as a potential nondestructive diagnostic tool for condition monitoring of the oilpaper insulation of power transformers is the Polarisation and Depolarisation Current (PDC) measurement. This paper starts with a theoretical and physical description of the PDC technique. Several practical aspects of the technique have been discussed in the paper along with corresponding experimental and field test results. These physical considerations can be used as 'precautions' for the potential field users of the PDC technique for insulation condition assessment of transformers

A Simplified Lightning Model for Metal Oxide Surge Arrester

Lightning strike has been one of the major factors that lead to failure of electrical power systems. In recent years, metal oxide surge arrester has been widely used and it is now an essential item in the insulation coordination for power systems based on its excellent electrical characteristics. Recently, the study of dynamic lightning model of metal oxide arrester has been conducted to provide an accurate performance in the operation. This paper presents a simplified lightning model for distribution-class metal oxide surge arrester derived from the IEEE Working Group (WG) 3.4.11 model. The model parameters were calculated from the standard data sheets obtained from the manufacturer. The effectiveness of the model was tested and compared with the residual voltage test results for typical lightning surges of 8/20ms