Search

Using solid state reaction method, ceramic pellets of NaNbO 3 , Na 0.6 K 0.4 NbO 3 and Na 0.5 K 0.5 NbO 3 have been prepared. Temperature and frequency dependence of dielectric constant and loss tangent of the prepared samples have been studied. It has been observed that, at the transition temperature, dielectric constant peak shifts to lower temperature, and the dielectric constant and loss tangent peak heights decrease, with increasing frequency; which shows the relaxational behavior of this system. [ABSTRACT FROM AUTHOR]

In the present paper, a methodology has been developed for the mapping of snow cover in Beas basin, Indian Himalaya using AWiFS (IRS-P6) satellite data. The complexities in the mapping of snow cover in the study area are snow under vegetation, contaminated snow and patchy snow. To overcome these problems, field measurements using spectroradiometer were carried out and reflectance/snow indices trend were studied. By evaluation and validation of different topographic correction models, it was observed that, the normalized difference snow index (NDSI) values remain constant with the variations in slope and aspect and thus NDSI can take care of topography effects. Different snow cover mapping methods using snow indices are compared to find the suitable mapping technique. The proposed methodology for snow cover mapping uses the NDSI (estimated using planetary reflectance), NIR band reflectance and forest/vegetation cover information. The satellite estimated snow or non-snow pixel information using proposed methodology was validated with the snow cover information collected at three observatory locations and it was found that the algorithm classify all the sample points correctly, once that pixel is cloud free. The snow cover distribution was estimated using one year (2004-05) cloud free satellite data and good correlation was observed between increase/decrease areal extent of seasonal snow cover and ground observed fresh snowfall and standing snow data. [ABSTRACT FROM AUTHOR]

To understand the effect of contamination and mixed objects on snow reflectance, field experiments were carried out in Indian Himalaya during the winters of 2004-2005 and 2005-2006. The observations suggest, as the amount of contamination increases, the peak of snow reflectance in the visible region shifts toward the higher wavelength range. For snow and soil cover mix, as the proportion of soil cover increases, reflectance increases in SWIR region. For snow and vegetation mix areas, a red edge can be observed if vegetation cover is more than 25%. A significant change in the reflectance is observed in the visible region for snow thickness below 5 cm. Normalized Difference Snow Index (NDSI) and S3 based snow indexes can map soil and ash contaminated snow. In snow-soil mixing (patchy snow), NDSI underestimates the snow cover area and S3 index overestimates. Both the snow indexes can map the snow under vegetation and mixed snow-soil-vegetation areas. Thin snow cover areas can also be mapped using both the indexes. This study will be helpful in developing new indexes and selection of threshold value for snow cover mapping. [ABSTRACT FROM AUTHOR]

The specific heat of an anharmonic BaxSr1—xTiO3 ferroelectric crystal is calculated in its paraelectric phase from the Silverman–Joseph Hamiltonian augmented with fourth order phonon coordinates using double time Green's functions. The soft mode contribution to specific heat is described by appropriate Einstein terms. The variation of specific heat with temperature and defect parameters is discussed. The effect of defects on specific heat can be observed in the presence of anharmonicity. Around the Curie temperature the Cochran soft mode is held to be responsible for the anomalous behaviour of specific heat. [ABSTRACT FROM AUTHOR]