排序方式: 共有42条查询结果,搜索用时 15 毫秒
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Ramiz Aktar Santabrata Das Anuj Nandi H. Sreehari 《Journal of Astrophysics and Astronomy》2018,39(1):17
We examine the properties of the viscous dissipative accretion flow around rotating black holes in the presence of mass loss. Considering the thin disc approximation, we self-consistently calculate the inflow-outflow solutions and observe that the mass outflow rates decrease with the increase in viscosity parameter (\(\alpha \)). Further, we carry out the model calculation of quasi-periodic oscillation frequency (\(\nu _{\mathrm{QPO}}\)) that is frequently observed in black hole sources and observe that \(\nu ^\mathrm{max}_{\mathrm{QPO}}\) increases with the increase of black hole spin (\(a_k\)). Then, we employ our model in order to explain the High Frequency Quasi-Periodic Oscillations (HFQPOs) observed in black hole source GRO J1655-40. While doing this, we attempt to constrain the range of \(a_k\) based on observed HFQPOs (\(\sim \)300 Hz and \(\sim \)450 Hz) for the black hole source GRO J1655-40. 相似文献
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M. C. Ramadevi B. T. Ravishankar N. Sitaramamurthy G. Meena Brajpal Singh Anand Jain Reena Yadav Anil Agarwal V. Chandra Babu Kumar Ankur Kushwaha S. Vaishali Nirmal Kumar Iyer Anuj Nandi Girish V. Vivek Kumar Agarwal S. Seetha Dipankar Bhattacharya K. Balaji Manoj Kumar Prashanth Kulshresta 《Journal of Astrophysics and Astronomy》2017,38(2):32
We report the in-orbit performance of Scanning Sky Monitor (SSM) onboard AstroSat. The SSM operates in the energy range 2.5 to 10 keV and scans the sky to detect and locate transient X-ray sources. This information of any interesting phenomenon in the X-ray sky as observed by SSM is provided to the astronomical community for follow-up observations. Following the launch of AstroSat on 28th September, 2015, SSM was commissioned on October 12th, 2015. The first power ON of the instrument was with the standard X-ray source, Crab in the field-of-view. The first orbit data revealed the basic expected performance of one of the detectors of SSM, SSM1. Following this in the subsequent orbits, the other detectors were also powered ON to find them perform in good health. Quick checks of the data from the first few orbits revealed that the instrument performed with the expected angular resolution of 12’ \(\times \) 2.5\(^\circ \) and effective area in the energy range of interest. This paper discusses the instrument aspects along with few on-board results immediately after power ON. 相似文献
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Sahadeb Nandi 《Pure and Applied Geophysics》1971,89(1):139-150
Summary The problem of steady laminar hydromagnetic flow in a porous annulus of different permeability in the presence of a magnetic field is considered and solved by a method of perturbation. The case when the injection or the withdrawal rate at the outer wall, depending on the sign of the normal velocity at this wall, is greater than or equal to such rate at the inner wall is given in details. Some numerical results regarding the friction coefficients at the walls and the axial pressure coefficient and velocity distribution have been appended. 相似文献
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Tilak B. Kotoch Anuj Nandi D. Debnath J. P. Malkar A. R. Rao M. K. Hingar Vaibhav P. Madhav S. Sreekumar Sandip K. Chakrabarti 《Experimental Astronomy》2011,29(1-2):27-54
Cadmium Zinc Telluride (CZT) detectors are high sensitivity and high resolution devices for hard X-ray imaging and spectroscopic studies. The new series of CZT detector modules (OMS40G256) manufactured by Orbotech Medical Solutions (OMS), Israel, are used in the RT-2/CZT payload onboard the CORONAS-PHOTON satellite. The CZT detectors, sensitive in the energy range of 20 to 150 keV, are used to image solar flares in hard X-rays. Since these modules are essentially manufactured for commercial applications, we have carried out a series of comprehensive tests on these modules so that they can be confidently used in space-borne systems. These tests lead us to select the best three pieces of the ??Gold?? modules for the RT-2/CZT payload. This paper presents the characterization of CZT modules and the criteria followed for selecting the ones for the RT-2/CZT payload. The RT-2/CZT payload carries, along with three CZT modules, a high spatial resolution CMOS detector for high resolution imaging of transient X-ray events. Therefore, we discuss the characterization of the CMOS detector as well. 相似文献
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Iron and Manganese in Groundwater: Using Kriging and GIS to Locate High Concentrations in Buncombe County,North Carolina
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For health, economic, and aesthetic reasons, allowable concentrations (as suggested by the United States Environmental Protection Agency) of the secondary contaminants iron (Fe) and manganese (Mn) found present in drinking water are 0.3 and 0.05 mg/L, respectively. Water samples taken from private drinking wells in rural communities within Buncombe County, North Carolina contain concentrations of these metals that exceed secondary water quality criteria. This study predicted the spatial distribution of Fe and Mn in the county, and evaluated the effect of site environmental factors (bedrock geology, ground elevation, saprolite thickness, and drinking water well depth) in controlling the variability of Fe and Mn in groundwater. A statistically significant correlation between Fe and Mn concentrations, attributable to bedrock geology, was identified. Prediction models were created using ordinary kriging and cokriging interpolation techniques to estimate the presence of Fe and Mn in groundwater where direct measurements are not possible. This same procedure can be used to estimate the trend of other contaminants in the groundwater in different areas with similar hydrogeological settings. 相似文献
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A. Pirya S. Nandi D. J. Saikia C. Konar M. Singh 《Journal of Astrophysics and Astronomy》2011,32(4):471-474
We present the results of GMRT and VLA observations of five large radio sources over a wide frequency range to investigate
their structural and spectral asymmetries. The hot-spot brightness ratios suggest intrinsic source asymmetries, while the
spectral indices show evidence of re-acceleration of particles. 相似文献
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Sandip K. Chakrabarti S. Palit D. Debnath A. Nandi V. Yadav Ritabrata Sarkar 《Experimental Astronomy》2009,24(1-3):109-126
Combination of Fresnel Zone Plates (FZP) can make an excellent telescope for imaging in X-rays. We present here the results of our experiments with several pairs of tungsten made Fresnel Zone plates in presence of an X-ray source kept at a distance of about 45 ft. The quasi-parallel beam allowed us to study sources placed on the axis as well as off the axis of the telescope. We present theoretical study of the fringe patterns produced by the zone plates in presence of a quasi-parallel source. We compare the patterns obtained from experiments with those obtained by our Monte-Carlo simulations. The images are also reconstructed by deconvolution from both the patterns. We compare the performance of such a telescope with other X-ray imaging devices used in space-astronomy. 相似文献
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Sahadeb Nandi 《Pure and Applied Geophysics》1970,78(1):86-95
Summary The problem of unsteady hydromagnetic flow in a porous annulus when the inner boundary starts moving from rest with a constant longitudinal velocity is considered. For the case of equal Reynolds number and magnetic Reynolds number Laplace transforms of the solutions for the axial components of velocity and magnetic field are obtained in terms of modified Bessel functions. The inversions are effected for the cases of very large and small Reynolds number when the pressure gradient vanishes. 相似文献