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Search Results: 1 - 10 of 465617 matches for " A. A. Sen "
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Cosmology in scalar tensor theory and asymptotically de-Sitter Universe
A. A. Sen,S. Sen
Physics , 2001, DOI: 10.1142/S021773230100442X
Abstract: We have investigated the cosmological scenarios with a four dimensional effective action which is connected with multidimensional, supergravity and string theories. The solution for the scale factor is such that initially universe undergoes a decelerated expansion but in late times it enters into the accelerated expansion phase. Infact, it asymptotically becomes a de-Sitter universe. The dilaton field in our model is a decreasing function of time and it becomes a constant in late time resulting the exit from the scalar tensor theory to the standard Einstein's gravity. Also the dilaton field results the existence of a positive cosmological constant in late times.
Observational Constraints on Cardassian Expansion
S. Sen,A. A. Sen
Physics , 2002, DOI: 10.1086/373900
Abstract: In this work, we have studied the observational constraints on the Cardassian Model for the dark energy. We have compared the model with existing Supernova data. The dependence of the location of the Cosmic Microwave Background Radiation (CMBR) peaks on the parameters of the model have also been studied. We find, in particular, that observational data arising from Archeops for the location of the first peak, BOOMERANG for the location of the third peak, together with the Supernova data, constrain significantly the parameter space.
WMAP constraints on Cardassian model
A. A. Sen,S. Sen
Physics , 2003, DOI: 10.1103/PhysRevD.68.023513
Abstract: We have investigated the constraints on the Cardassian model using the recent results from the Wilkinson Microwave Anisotropy Probe (WMAP) for the locations of the peaks of the Cosmic Microwave Background (CMB) anistropy spectrum. We find that the model is consistent with the recent observational data for certain range of the model parameter $n$ and the cosmological parameters. We find that the Cardassian model is favoured compared to $\Lambda$CDM model, for a higher spectral index ($n_s \approx 1$) together with lower value of Hubble parameter $h$ ($h\leq 0.71$). But for smaller values of $n_s$, both $\Lambda$CDM and Cardassian are equally favoured. Also, irrespective of Supernova constraint, CMB data alone predicts current acceleration of the universe in this model. We have also studied the constraint on the $\sigma_{8}$, the rms density fluctuations at $8h^{-1}$ Mpc scale.
Late time acceleration in Brans Dicke Cosmology
S. Sen,A. A. Sen
Physics , 2000, DOI: 10.1103/PhysRevD.63.124006
Abstract: In this work we have investigated the possibility of having a late time accelerated phase of the universe, suggested by recent supernova observation, in the context of Brans Dicke (BD) theory with a symmetry breaking potential and a matter field. We find that a perfect fluid matter field (pressureless and with pressure) cannot support this acceleration but a fluid with dissipative pressure can drive this late time acceleration. We have also calculated some cosmological parameters in our model to match with observations.
BTEX in Ambient Air of a Metropolitan City  [PDF]
D. Majumdar, A. K. Mukherjeea, S. Sen
Journal of Environmental Protection (JEP) , 2011, DOI: 10.4236/jep.2011.21002
Abstract: The environmental fate, global warming effect and human health risk from mono aromatic VOCs are of major concerns among many consequences of their anthropogenic emission. In more than a yearlong study (November 2003 to February 2005) of the city air in Kolkata, India at different seasons in three different sites, the seasonal mean benzene and toluene concentrations varied between 13.8–72.0 μg/m3 and 21.0–83.2 μg/m3 respectively along all the sites. The environmental distribution and load of BTEX (Benzene, Toluene, Ethylbenzene and isomers of Xylene) in different environmental compartment was estimated using a multimedia mass balance model, TaPL3. The total environmental load of BTEX together was estimated to be 9.7 × 104 kg. Contribution of Kolkata metropolitan city towards global warming due to environmental emission of BTEX has been estimated as 1.9 × 105 tons of carbon dioxide equivalent per year which is about 1.1% of yearly direct CO2 emission the city. The consequence of BTEX emission towards human health has been estimated in terms of non-cancer and cancer risk in population due to their inhalation exposure. The cumulative lifetime cancer risk for benzene and ethylbenzene was found to be higher than the acceptable value and range between 3.0 × 105 and 8.9 × 106 in three sites, although the non-cancer health risk was found to be within acceptable limit.
Antioxidant and chemoprotective properties of Momordica charantia L. (bitter melon) fruit extract
A Semiz, A Sen
African Journal of Biotechnology , 2007,
Abstract: Momordica charantia, commonly known as bitter melon, is used as a vegetable in number of countries. Extracts of M. charantia plant, fruit pulp, and seed have been reported to have a wide medicinal use in the traditional medical systems, most often as hypoglycemic and anti-diabetic agents. We have studied the effect of M. charantia, collected from Kazdaglari (Mount Ida) in Balikesir, fruit extract on glutathione S-transferases (GSTs), cytochrome P450s (CYPs), and antioxidant enzymes in rats. Male Wistar rats, aged 12 weeks and weighing 200-250 g, were given 200 mg M. charantia fruit extract per kg body weight, i.p., for four consecutive days. At the end of the experimental period, the animals were sacrificed, and liver, kidney, and lung were isolated. Our results have indicated significant increase in especially hepatic antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) activities. The strongest increase (about 9-fold) was observed in GPx activities while about 2 to 5-fold increases were observed in SOD and CAT. M. charantia fruit extract also exhibited hepatoprotective effects in CCl4-intoxicated rats. In addition, about 50% increase was also noted with hepatic cytosolic GSTs. On the other hand, treatments of rats with M. charantia significantly reduced both ethoxyresorufin O-deethylase (EROD) and methoxyresorufin O-deethylase (MROD) activities in rat liver microsomes, which are known to be catalyzed by CYP1A isoforms These results suggest that the M. charantia fruit extract possesses the anti-oxidant effects besides having protective activities in rats.
Deviation from $\Lambda$CDM: Pressure Parametrization
Sen, A. A.
High Energy Physics - Phenomenology , 2007, DOI: 10.1103/PhysRevD.77.043508
Abstract: Most parametrizations for dark energy involve the equation of state $w$ of the dark energy. In this work, we choose the pressure of the dark energy to parametrize. As $p = constant$ essentially gives a cosmological constant, we use the Taylor expansion around this behavior $p = -p_{0} + (1-a)p_{1} + ....$ to study the small deviations from the cosmological constant. In our model, the departure from the cosmological constant behavior has been modeled by the presence of extra K-essence fields while keeping the cosmological constant term untouched. The model is similar to assisted inflation scenario in a sense that for any higher order deviation in terms of Taylor series expansion, one needs multiple K-essence fields. We have also tested our model with the recent observational data coming from Supernova type Ia measurements, the baryon oscillations peak (BAO) and the gas mass fraction of the galaxy clusters inferred from X-ray observations and obtain constraints for our model parameters.
Sporadic hemiplegic migraine in children: A report of two new cases
Chakravarty A,Sen A
Neurology India , 2010,
Abstract: Two cases of sporadic hemiplegic migraine, which fulfilled the diagnostic criteria as laid down in International Classification of Headache Disorders (ICHD)-2, are reported in children. In the first case, two unusual features were noted, namely, the occurrence of dysphsia in association with a left hemiparesis and the spread of sensory symptoms to the contralateral side during attacks. The second case is perhaps the youngest patient reported with this disorder.
Deviation from $Λ$CDM: Pressure Parametrization
A. A. Sen
Physics , 2007, DOI: 10.1103/PhysRevD.77.043508
Abstract: Most parametrizations for dark energy involve the equation of state $w$ of the dark energy. In this work, we choose the pressure of the dark energy to parametrize. As $p = constant$ essentially gives a cosmological constant, we use the Taylor expansion around this behavior $p = -p_{0} + (1-a)p_{1} + ....$ to study the small deviations from the cosmological constant. In our model, the departure from the cosmological constant behavior has been modeled by the presence of extra K-essence fields while keeping the cosmological constant term untouched. The model is similar to assisted inflation scenario in a sense that for any higher order deviation in terms of Taylor series expansion, one needs multiple K-essence fields. We have also tested our model with the recent observational data coming from Supernova type Ia measurements, the baryon oscillations peak (BAO) and the gas mass fraction of the galaxy clusters inferred from X-ray observations and obtain constraints for our model parameters.
Superconducting cosmic string in Brans-Dicke theory
A. A. Sen
Physics , 1998, DOI: 10.1103/PhysRevD.60.067501
Abstract: In the present work, the gravitational field of superconducting cosmic string has been investigated in the context of Brans-Dicke theory of gravity. We have presented two kind of solutions for the spacetime in the far field zone of the string. When the B-D scalar field is switched off, one of the solutions reduces to the solution earlier obtained by Moss and Poletti in General Relativity.
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