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Sarkar S.,Gauhati University | Mahanta C.R.,Cotton College
General Relativity and Gravitation | Year: 2013

Dark energy model with the equation of state pDE = -ρDE-Aρα DE, is characterised by four finite life time future singularity of the universe for different values of the parameter and A and α [Nojiri et al. in Phys Rev D 71:063004, 2005]. Since from the matter dominated era to the dark energy dominated era the ratio of the dark energy density to the matter energy density increases as the universe expand for these future singularities, the universe passes through a significant time when the dark energy density and the matter energy density are nearly comparable. Considering 1/r0 < r = ρDE/ρM < r0, where r0 is any fixed ratio, we calculate the fraction of total life time of the universe when the universe passes through the coincidental stage for these singularities. It has been found that the fractional time varies as α varies within the range for which these finite life time future singularities occur and the fraction is smaller for smaller values of r0. Importance of the fractional time and observational limits onto the values of the parameter A and α has also been discussed. © 2012 Springer Science+Business Media New York.

Sarkar S.,Gauhati University | Mahanta C.R.,Cotton College
International Journal of Theoretical Physics | Year: 2013

In this paper, we have studied a homogeneous and anisotropic universe filled with matter and holographic dark energy components. Assuming deceleration parameter to be a constant, an exact solution to Einstein's field equations in axially symmetric Bianchi type-I line element is obtained. A correspondence between the holographic dark energy models with the quintessence dark energy models is also established. Quintessence potential and the dynamics of the quintessence scalar field are reconstructed, which describe accelerated expansion of the universe. © 2013 Springer Science+Business Media New York.

Kalita J.M.,Cotton College | Wary G.,Cotton College
Journal of Luminescence | Year: 2014

The thermoluminescence (TL) glow curves of X-ray irradiated micro-grain natural muscovite were recorded within 298-520 K at various linear heating rates (2 K/s, 4 K/s, 6 K/s, 8 K/s and 10 K/s). Natural TL of muscovite was checked, but no significant TL was observed within 298-520 K in any heating rate. Within the heating rate 2-10 K/s only a low temperature distinct peak was observed in the temperature range 348-357 K. The TL parameters such as activation energy, order of kinetic, geometrical symmetry factor and pre-exponential frequency factor were investigated from the glow peak by Peak Shape (PS) method and Computerized Glow Curve Deconvolution (CGCD) technique. At lowest heating rate the glow peak obeys non-first order kinetic and at the highest heating rate it follows the second order kinetic. The variation of peak integrals, peak maximum temperatures, FWHM and activation energy with heating rates were investigated, and the glow curves at higher rates were found to be influenced by the presence of the thermal quenching. The thermal quenching activation energy and pre-exponential factor were calculated and found to be 2.31±0.02 eV and 3.46×1014 s-1, respectively. © 2013 Elsevier B.V.

Kalita J.M.,Cotton College | Wary G.,Cotton College
Thermochimica Acta | Year: 2014

Thermoluminescence (TL) of X-ray irradiated natural biotite annealed at 473, 573, 673 and 773 K were studied within 290-480 K at various linear heating rates (2, 4, 6, 8 and 10 K/s). A Computerized Glow Curve Deconvolution technique was used to study various TL parameters. Thermal quenching was found to be very high for un-annealed sample, however it decreased significantly with increase in annealing temperature. For un-annealed sample thermal quenching activation energy (W) and pre-exponential frequency factor (C) were found to be W = (2.71 ± 0.05) eV and C = (2.38 ± 0.05) × 1012 s -1 respectively. However for 773 K annealed sample, these parameters were found to be W = (0.63 ± 0.03) eV, C = (1.75 ± 0.27) × 1014 s-1. Due to annealing, the initially present trap level at depth 1.04 eV was vanished and a new shallow trap state was generated at depth of 0.78 eV which contributes very low thermally quenched TL signal. © 2014 Elsevier B.V.

Lahkar K.,Cotton College | Mahanta R.,Cotton College
Academic Journal of Cancer Research | Year: 2012

Hormone act as a promoter in the carcinogenic process by inciting cell to produce substances that are carcinogenic. The thyroid provides the simplest example of association of cancer and hormone through its profound mutagenic effects on the growth and development of the body. However, the relationship between thyroid hormones and carcinogenesis is still not very conclusive. This investigation was therefore conducted to evaluate further the effect of thyroxine on T3, T4 and TSH status during 3-methylcholanthrene (3MC) induced carcinogenesis. In this investigation a significantly higher mean values of T3, T4 and TSH (P<0.01) were observed in the group of animals treated with 0.5 mg 3-methylcholanthrene from the 10th day onwards to the 120 th day, the end of the experiment suggesting a hypersecretion of thyroxine. Daily administration of 10μg thyroxine alone exhibited biphasic trend and inhibitory effect on T3 and T4 content where T3 showed steep decline of -1.75% on 120th day and T4 with -26.72% below the normal base line. On the contrary there is highly significant initial increase (P<0.01) in the mean TSH values with percent deviation of 320.17%. In the animal group treated with thyroxine-3MC combination, a decrease in the thyroid function i.e. both T3 and T4 content throughout the experimental period up to 120th day was observed which may be due to some amount of suppression in the thyroid function caused by supplementation of thyroxine. However, comparative decrease of TSH content after combined treatment of thyroxine-3MC than that of 3MC alone may suggest some amount of recovery with both 3MC which act as a thyroid function enhancer and thyroxine supplementation though it did not touch the normal base line. © IDOSI Publications, 2012.

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