Guwāhāti, India
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We present a cylindrically symmetric, Petrov type D, nonexpanding, shear-free, and vorticity-free solution of Einstein's field equations. The spacetime is asymptotically flat radially and regular everywhere except on the symmetry axis where it possesses a naked curvature singularity. The energy-momentum tensor of the spacetime is that for an anisotropic fluid which satisfies the different energy conditions. This spacetime is used to generate a rotating spacetime which admits closed timelike curves and may represent a Cosmic Time Machine. © 2017 Faizuddin Ahmed.


News Article | March 2, 2017
Site: www.eurekalert.org

This research article by Dr. Rita Mahanta et al has been published in Cardiovascular & Hematological Agents in Medicinal Chemistry Investigations by researchers of Zoology Department of Cotton College, Guwahati, and Gauhati University, Guwahati, Assam, India, have revealed that long term exposure to elevated doses of Anabolic Androgenic Steroids (AAS) can significantly affect aldosterone concentration and serum sodium/ potassium levels in albino mice. The research led by Dr. Rita Mahanta, Associate Professor (Retd.) in the Department of Zoology, Cotton College, Guwahati and Ph.D. student, Parmita Chowdhury from Gauhati University, Zoology Department, have discovered that prolonged administration of Nandrolone Decanoate, an AAS, upon a group of male albino mice significantly increased serum aldosterone and sodium ion levels when compared with a group of albino mice that did not receive such treatment. Post treatment alterations were also revealed through measuring the level of potassium ion but this change was reported to be insignificant. This study, published in the journal Cardiovascular and Hematological Agents in Medicinal Chemistry (Bentham Science), volume 14, issue 3, further emphasizes that a change of this kind where a marked increase in aldosterone levels occurred upon chronic exposure to Nandrolone Decanoate could be a possible indication of steroid related cardiovascular disorders as a number of literatures are available that support the correlation between aldosterone concentration and cardiovascular diseases. For more information about this article, please visit http://benthamscience.


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.


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.


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.


Devi N.,Cotton College | Narzary A.,Cotton College
International Journal of Polymeric Materials and Polymeric Biomaterials | Year: 2012

A novel hydrogel composed of gelatin, sodium salt of 2-acrylamido-2-methyl propane sulfonic acid (Na-AMPS), and acryl amide (AM) was using N,N-methylenebisacrylamide (MBA) as crosslinker and Potassium peroxodisulfate (KPS) as initiator in aqueous medium. The influence of various parameters on the equilibrium swelling ratio of the hydrogel were investigated. The drug release kinetics of the hydrogel loaded with tetracycline (TC) was studied at 370. The results obtained during experimental analysis showed that molar amount in cross linking agent as well as the monomers greatly affected the swelling ratio of the hydrogel and release kinetics of the model drug. The equilibrium release percent of TC reached about 80% release after 96 hours and the fractional release rate was controlled by the swelling of the hydrogel. © 2012 Taylor and Francis Group, LLC.


Kalita J.M.,Cotton College | Wary G.,Cotton College
Journal of Luminescence | Year: 2016

With the help of thermoluminescence (TL) analysis possible trap and recombination levels of natural biotite mineral have been estimated. Differential Scanning Calorimetric (DSC) analysis reveals that within 300-773 K there is no phase change of this mineral. However within this temperature range, some significant changes in trapping sites have been observed. For un-annealed sample one trap and one recombination center has been observed at depth around 1.01 and 3.57 eV respectively. However due to annealing at 473 and 573 K, initially present trap level has been found to shift towards the conduction band and produced a new shallow trap at depth around 0.78 eV. Further annealing at 673 K (or above) a new trap level is found to generate at the previously present site (at depth ~1.01 eV). But during the annealing treatments no significant change in recombination center is observed. Based on the analysis, a schematic band structure of biotite crystal has been proposed showing all possible trap and recombination centers. With reference to the band diagram the whole TL process in biotite have been discussed. © 2015 Elsevier B.V. All rights reserved.


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

Thermoluminescence (TL) glow curves of X-ray irradiated micro-grain natural kyanite have been recorded under annealed and un-annealed condition at various heating rates (2, 4, 6, 8 and 10 K s-1). TL parameters such as activation energy, order of kinetic and pre-exponential frequency factor have been investigated from the glow peak by a computerized glow curve deconvolution technique. Variation of peak integrals, peak maximum temperatures, FWHM and activation energy with heating rates have been investigated and the glow curves at higher rates have been found to be influenced by presence of thermal quenching. For annealed sample value of thermal quenching activation energy (W) and pre-exponential factor (C) are found to be 0.86 ± 0.02 eV and 2.5 × 109 s-1 respectively and for un-annealed sample these values are 1.68 ± 0.03 eV and 3.1 × 1010 s -1 respectively. Experimentally measured value of W and C have been verified by estimating thermal quenching efficiencies η(T) with the help of calculated value of W and C; quenched glow curves have been successfully reconstructed for each heating rate. The dose sensitivity of both types of samples is also reported. Annealed sample shows improved dose response than un-annealed sample. © 2013 Indian Association for the Cultivation of Science.


Kalita J.M.,Cotton College | Wary G.,Cotton College
Journal of Luminescence | Year: 2012

The Thermally Stimulated Luminescence (TSL) at room temperature X-ray irradiated natural biotite in form of micro-grain powder was studied under various heating rates. TSL peaks showed at temperatures 393 K, 399.6 K, 403.5 K, 404.5 K, 406.9 K at their respective heating rates 2 K/s, 4 K/s, 6 K/s, 8 K/s and 10 K/s. The effect of thermal quenching on thermoluminescence parameters such as peak maximum temperature, peak area, FWHM, geometrical symmetry factor, the activation energy were investigated. From the symmetry factor it is clear that the TL glow curve follows the first order kinetics for the lowest heating rate, but as the heating rate increases it defers from the first order. The activation energies for each heating rates were calculated by using Chen peak shape methods for general order kinetics and found to be decreased for higher heating rates. When activation energy is calculated by variable heating rate method it is observed that the method overestimated the value of activation energy and pre-exponential frequency factor significantly due to thermal quenching. © 2012 Elsevier B.V. All rights reserved.

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