Measurement of coronal properties of Seyfert galaxies from NuSTAR’s hard X-ray spectrum     

Priyanka Rani  C. S. Stalin 《Journal of Astrophysics and Astronomy》2018,39(1):15

Precise measurement of the coronal properties of Active Galactic Nuclei (AGN) requires the availability of high signal-to-noise ratio data covering a wide range of X-ray energies. The Nuclear Spectroscopic Telescope Array (NuSTAR) which is highly sensitive to earlier missions in its operational energy range of 3–79 keV, allows us to arrive at precise estimates of the coronal parameters such as cut-off energy (\(E_\mathrm{cut}\)), coronal temperature (\(\textit{kT}_e\)) and geometry of the corona at least for sources that have \(E_\mathrm{cut}\) within the energy range of NuSTAR. In this paper, we present our preliminary results on the spectral analysis of two Seyfert galaxies namely 3C 120 and NGC 4151 using NuSTAR observations in the 3–79 keV band. We investigated the continuum and coronal parameters, the photon index \(\Gamma \), \(E_\mathrm{cut}\) and \(\textit{kT}_{e}\). By fitting the X-ray spectrum of 3C 120 and NGC 4151 with a simple phenomenological model, we found that both the sources showed a clear cut-off in their spectrum.  相似文献   

Geochemical and thermodynamic aspects of sorption of strontium on kaolinite dominated clay samples at Kalpakkam     

R. Deepthi Rani  P. Sasidhar 《Environmental Earth Sciences》2012,65(4):1265-1274

The mobility of strontium in subsurface is largely influenced by sorption on to clay minerals. In the present study, kaolinite clay samples collected from the Kalpakkam nuclear plant site were employed to understand the sorption characteristics of strontium by batch method. The effect of several parameters such as time, strontium ion concentration, pH, temperature and ionic strength was investigated. The kinetic studies suggested pseudo-second-order mechanism. The experimental sorption data was fitted to Langmuir adsorption model for obtaining the sorption capacity of the sorbent. The maximum sorption capacity was 5.77 mg/g at 298 K and was found to increase with an increase in temperature. It was observed that the distribution coefficient (K _d) of strontium on clay increased as the pH of the solution increased. The distribution coefficient was found to decrease with an increase in concentration of Na⁺ and Ca²⁺ ions. This variation of K _d suggests that cation exchange is the predominant sorption process. It was also observed that sorption process is endothermic. The thermodynamic parameters such as ∆G ⁰, ∆H ⁰ and ∆S ⁰ were calculated. The negative values obtained for ∆G ⁰ indicated that the sorption of strontium on clay was spontaneous at all studied concentrations. ∆G ⁰ becomes more negative with an increase in temperature, suggests that the sorption process is more favorable at higher temperatures.  相似文献   

Near hydrothermal alteration of obsidian glass: Implications for long term performance assessments     

Nishi Rani  J. P. Shrivastava  R. K. Bajpai 《Journal of the Geological Society of India》2012,79(4):376-382

Obsidian glass alteration experiments under near hydrothermal conditions were performed to study mechanism and conditions of formation of altered minerals. X-ray diffraction patterns and cell dimensions of the specimens treated at 150, 200 and 300°C (pH = 8.03) revealed appearance of three main minerals — illite (9.5–10 Å), chlorite (7.04 Å) and halloysite (10.25Å). Further increase in the pH favours matrix dissolution with the formation of secondary altered layers. SEM-EDS study show that the alteration causes smoothing of the grain surfaces. These surfaces exhibits etch pits and series of depressions, formed by the process of dissolution. SEM — Back Scattered Electron images of obsidian specimens show thin laminae of smectite, with foliated bulky rims and cellular honeycomb texture, formed by precipitation from the solution as well as by direct transformation of glass during alteration. This mechanism is resulting from the alteration of alkalis by ionic inter-diffusion with H₃O⁺ and H⁺ and inward diffusion of H₂O, leading to free diffusion of silica into solution and then to a local rearrangement of the glass framework. Thus, a direct transformation of glass into clay minerals is the major reaction mechanism as evidenced by the mechanism of glass dissolution and subsequent mineral precipitation.  相似文献   

Generalized teleparallel gravity via some scalar field dark energy models     

M. Sharif  Shamaila Rani 《Astrophysics and Space Science》2013,345(1):217-223

We consider generalized teleparallel gravity in the flat FRW universe with a viable power-law f(T) model. We construct its equation of state and deceleration parameters which give accelerated expansion of the universe in quintessence era for the obtained scale factor. Further, we develop correspondence of f(T) model with scalar field models such as, quintessence, tachyon, K-essence and dilaton. The dynamics of scalar field as well as scalar potential of these models indicate the expansion of the universe with acceleration in the f(T) gravity scenario.  相似文献   

A set of linked optimization models for an inter-basin water transfer     

D. Rani  D.K. Srivastava  T.R. Gulati 《水文科学杂志》2013,58(2):371-392

ABSTRACT

A set of linked optimization models was used to evaluate planning and operation of the proposed Pamba-Achankovil-Vaippar (PAV) water transfer project in India. The shortage of water for irrigation in the Vaippar basin has led to the need for water import. The project consists of three reservoirs. The models were applied at three levels. At Level-1, the projections of water requirement for irrigation in the Vaippar basin at Reservoir-1 were estimated using an LP model. Level-2 was operated at three sub-levels: the first was the determination of the export requirements from the Pamba basin (Reservoir-2) to the Achankovil basin (Reservoir-1); the second was determining the capability of Reservoir-2 to export and sizing of the three reservoirs to meet the above targets was the third sub-level. Integrated reservoir operation and canal irrigation water distribution were done at Level-3. DP models were employed at levels-2 and 3. The linked LP, DP and simulation models were found effective for planning water transfers.  相似文献   

Charged Particle Monitor on the Astrosat Mission     

A. R. Rao  M. H. Patil  Yash Bhargava  Rakesh Khanna  M. K. Hingar  A. P. K. Kutty  J. P. Malkar  Rupal Basak  S. Sreekumar  Essy Samuel  P. Priya  P. Vinod  D. Bhattacharya  V. Bhalerao  S. V. Vadawale  N. P. S. Mithun  R. Pandiyan  K. Subbarao  S. Seetha  K. Suryanarayana Sarma 《Journal of Astrophysics and Astronomy》2017,38(2):33

Charged Particle Monitor (CPM) on-board the Astrosat satellite is an instrument designed to detect the flux of charged particles at the satellite location. A Cesium Iodide Thallium (CsI(Tl)) crystal is used with a Kapton window to detect protons with energies greater than 1 MeV. The ground calibration of CPM was done using gamma-rays from radioactive sources and protons from particle accelerators. Based on the ground calibration results, energy deposition above 1 MeV are accepted and particle counts are recorded. It is found that CPM counts are steady and the signal for the onset and exit of South Atlantic Anomaly (SAA) region are generated in a very reliable and stable manner.  相似文献   

Modelling spatial variation of fluoride pollutant using geospatial approach in the surrounding environment of an aluminium industries     

Prem Chandra Pandey  Pavan Kumar  Vandana Tomar  Meenu Rani  Swati Katiyar  Mahendra Singh Nathawat 《Environmental Earth Sciences》2015,74(12):7801-7812

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A review of b-value imaging and fractal dimension studies in the Andaman Sumatra subduction     

Srivastava  Kirti  Rani  Swaroopa  Srinagesh  D. 《Natural Hazards》2014,73(1):97-110

The present study analyses the spatial pattern of quaternary gravitational slope deformations (GSD) and historical/present-day instabilities (HPI) inventoried in the Swiss Rhone Valley. The main objective is to test if these events are clustered (spatial attraction) or randomly distributed (spatial independency). Moreover, analogies with the cluster behaviour of earthquakes inventoried in the same area were examined. The Ripley’s K-function was applied to measure and test for randomness. This indicator allows describing the spatial pattern of a point process at increasing distance values. To account for the non-constant intensity of the geological phenomena, a modification of the K-function for inhomogeneous point processes was adopted. The specific goal is to explore the spatial attraction (i.e. cluster behaviour) among landslide events and between gravitational slope deformations and earthquakes. To discover if the two classes of instabilities (GSD and HPI) are spatially independently distributed, the cross K-function was computed. The results show that all the geological events under study are spatially clustered at a well-defined distance range. GSD and HPI show a similar pattern distribution with clusters in the range 0.75–9 km. The cross K-function reveals an attraction between the two classes of instabilities in the range 0–4 km confirming that HPI are more prone to occur within large-scale slope deformations. The K-function computed for GSD and earthquakes indicates that both present a cluster tendency in the range 0–10 km, suggesting that earthquakes could represent a potential predisposing factor which could influence the GSD distribution.  相似文献   

Modified QCD ghost f ( T,T G ) gravity     

Abdul Jawad  Shamaila Rani  Surajit Chattopadhyay 《Astrophysics and Space Science》2015,357(2):1-7

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Measuring statistical isotropy of CMB anisotropy     

Tarun Souradeep  Amir Hajian  Soumen Basak   《New Astronomy Reviews》2006,50(11-12):889

The statistical expectation values of the temperature fluctuations and polarization of cosmic microwave background (CMB) are assumed to be preserved under rotations of the sky. We investigate the statistical isotropy (SI) of the CMB maps recently measured by the Wilkinson microwave anisotropy probe (WMAP) using the bipolar spherical harmonic formalism proposed in Hajian and Souradeep [Hajian, A., Souradeep, T. (2003) Astrophys. J. Lett. 597, L5] for CMB temperature anisotropy and extended to CMB polarization in Basak, Hajian and Souradeep [Basak, S., Hajian, A., Souradeep, T. (2006) Phys. Rev. D74, 02130(R)]. The Bipolar Power Spectrum (BiPS) had been measured for the full sky CMB anisotropy maps of the first year WMAP data and now for the recently released three years of WMAP data. We also introduce and measure directional sensitive reduced Bipolar coefficients on the three year WMAP ILC map. Consistent with our published results from first year WMAP data we have no evidence for violation of statistical isotropy on large angular scales. Preliminary analysis of the recently released first WMAP polarization maps, however, indicate significant violation of SI even when the foreground contaminated regions are masked out. Further work is required to confirm a possible cosmic origin and rule out the (more likely) origin in observational artifact such as foreground residuals at high galactic latitude.  相似文献