Spectral study of GX 339-4 with TCAF using Swift and NuSTAR observation     

Santanu Mondal  Sandip K. Chakrabarti  Dipak Debnath 《Astrophysics and Space Science》2016,361(9):309

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Geochemistry of the Neoproterozoic Narji limestone,Cuddapah Basin,Andhra Pradesh,India: implication on palaeoenvironment     

Adrika Roy  Gopal Chakrabarti  Debasish Shome 《Arabian Journal of Geosciences》2018,11(24):784

The Neoproterozoic Narji Formation of Cuddapah Basin, Southern India is mainly composed of limestones with minor amount of clastic rocks. Limestones are massive as well as laminated and occasionally chert bearing. Geochemistry (major, trace, and REE) of limestones is studied to strengthen the knowledge on depositional environment of Narji Formation in the direction to better figure out the development of Cuddapah Basin during Neoproterozoic era. Average SiO₂ (25.97), Al₂O₃/TiO₂ (16.67), and K₂O/Al₂O₃ (0.21) ratios suggest clastic contamination in the Narji limestones. PAAS (Post Archean Australian Shale) normalized REE?+?Y pattern of Narji limestones are showing seawater like REE?+?Y pattern. The Er/Nd and Y/Ho ratios (average 0.17 and 35.68, respectively) of Narji limestones indicate the retention of normal seawater character with the signatures of terrigenous input and diagenesis process. Positive Ce anomaly, high U/Th (>?1.25), and V/(V?+?Ni) (>?0.5) ratios of Narji limestones clearly indicate their deposition in dyoxic to anoxic condition.  相似文献   

Economically viable rare earth element deposits along beach placers of Andhra Pradesh,eastern coast of India     

Jyothirmayi Palaparthi  Ramananda Chakrabarti  Santanu Banerjee  Rasmohan Guin  Shayantani Ghosal  Sudha Agrahari  Debashish Sengupta 《Arabian Journal of Geosciences》2017,10(9):201

A comprehensive study was carried out in order to determine the radioelement and rare earth element (REE) concentrations in beach placer deposits at selected locations along the eastern coast of Andhra Pradesh in India. This was done to evaluate the economic value of these deposits. The findings of this study suggest that high Th and low K concentrations delineate the prospective regions having REE deposits. The beach placers, in general, can be characterized by high thorium and moderate uranium concentrations. The concentrations of REEs vary in the following order: Ce > La> Nd > Pr > Sm > Gd > Dy. Rapid in situ thorium prospectivity coupled with laboratory-based techniques like ICP-MS, as proposed in this study, would help in the identification of prospective REE sources along the coastal placers. The development of indigenous resources of light rare earth elements (LREEs), medium rare earth elements (MREEs), and heavy rare earth elements (HREEs) would decrease the dependence on imports, which have a strategic hold on the production and supply of the REEs, globally.  相似文献   

Evolution of Palaeo-Mesoproterozoic open coast ramp-clues from stromatolite-bearing carbonate facies of Vempalle Formation,Cuddapah Basin,India     

Suparna Bose  Gopal Chakrabarti  Debasish Shome 《Arabian Journal of Geosciences》2017,10(10):226

The carbonate-dominated Palaeo-Mesoproterozoic Vempalle Formation of the Cuddapah Basin, Southern India, represents deposition in a supratidal-subtidal setting. The facies associations, deciphered from this study, are consistent with continued gradual rise of sea level with little or no sedimentary influx during the deposition of sediments, wherein gradual deposition of carbonates are recorded with increased accommodation. The broad development of stromatolites in different layers of sediments across the coast indicates a moderately high-energy open coastline. The prolific volcanism as recorded at the top of the succession ultimately shuts down the Vempalle carbonate factory.  相似文献   

Wave interaction with an upright breakwater structure     

Subrata K. Chakrabarti 《Ocean Engineering》1999,26(10):446

Breakwaters are often built in coastal waters to facilitate navigation and recreation, both inside and outside regions of the breakwater. This requires that the reflection and transmission characteristics of the structure be both minimized at the same time. This is achieved by a design that will allow dissipation of wave energy by multiple reflection. Such structures will need the knowledge of these characteristics in their design. Model tests were performed on a shallow water breakwater concept of this type to determine the reflection and transmission coefficients. The concept of the breakwater was to reduce both the reflection and transmission of waves. It was found that the breakwater design was effective at certain wave characteristics. Nondimensional loads and local pressures on the breakwater panels are also reported which will facilitate the structural design of such breakwaters.  相似文献   

Study of high energy phenomena from near space using low-cost meteorological balloons     

Sandip K. Chakrabarti  Ritabrata Sarkar  Debashis Bhowmick  Arnab Bhattacharya 《Experimental Astronomy》2017,43(3):311-338

Indian Centre for Space Physics has taken a novel strategy to study low energy cosmic rays and astrophysical X-ray sources which involve very light weight payloads up to about five kilograms on board a single or multiple balloons which are used for meteorological purposes. The mission duration could be anywhere from 3-12 hours. Our strategy provides extreme flexibility in mission preparation and its operation using a very economical budget. There are several limitations but our innovative approach has been able to extract significant amount of scientific data out of these missions. So far, over one hundred missions have been completed by us to near space and a wealth of data has been collected. The payloads are recovered and are used again. Scientific data is stored on board computer and the atmospheric data or payload location is sent to ground in real time. Since each mission is different, we present here the general strategy for a typical payload and provide some results we obtained in some of these missions.  相似文献   

Spectral properties of shocked accretion flows— a self-consistent study     

Sandip K. Chakrabarti  Samir Mandal 《Astrophysics and Space Science》2007,309(1-4):163-166

Magnetized accretion flows around black holes which include standing or oscillating shock waves can produce very realistic spectrum till a few MeV. These shocks accelerate hot electrons which produce power-law spectrum. The post-shock region intercepts soft-photons from an external source, namely, a Keplerian disk and also from distributed sources such as the synchrotron photons emitted from thermal and non-thermal electrons originated in the pre-shock and post-shock flow. These photons are inverse Comptonized by the thermal and the non-thermal electrons present in the CENBOL region. Computations show that the emitted radiation is extended till a few MeV. We include the bulk motion Comptonization as well and discuss its importance vis-a-vis the power-law spectrum produced by non-thermal electrons.   相似文献   

Multiple shocks in the rotating winds from self-gravitating discs     

Sandip K. Chakrabarti 《Journal of Astrophysics and Astronomy》1989,10(3):261-277

We present the analytic theory of dissipative and non-dissi-pative shocks in the rotating outflows in both the pseudo-Newtonian and the Schwarzschild geometry. We include the effects of the self gravity of the surrounding massive disc and show that the flow may have as many as five critical points when the angular momentum and the disc mass are sufficiently high. This leads to the possibility of the multipleannular shocks within the flow. We derive the expressions correlating the pre-shock and the post-shock quantities for all the three principal types of discontinuities. From these relations it is shown that for given initial flow parameters such as the angular momentum and the energy there could be as many as eighteen formal shock locations out of which at most two are chosen in reality. Detailed classification of the parameter space in terms of the initial flow parameters will be discussed elsewhere  相似文献   

Smoothed particle hydrodynamic simulations of viscous accretion discs around black holes     

Giuseppe Lanzafame  D. Molteni  & Sandip K. Chakrabarti 《Monthly notices of the Royal Astronomical Society》1998,299(3):799-804

Viscous Keplerian discs become sub-Keplerian close to a black hole since they pass through sonic points before entering into it. We study the time evolution of polytropic viscous accretion discs (both in one- and two-dimensional flows) using smoothed particle hydrodynamics. We discover that for a large region of the parameter space spanned by energy, angular momentum and polytropic index, when the flow viscosity parameter is less than a critical value, standing shock waves are formed. If the viscosity is very high then the shock wave disappears. In the intermediate viscosity, the disc oscillates very significantly in the viscous time-scale. Our simulations indicate that these centrifugally supported high density regions close to a black hole play an active role in the flow dynamics, and consequently, the radiation dynamics.  相似文献   

Technical Note: On the formulation of Jonswap spectrum     

Subrata K. Chakrabarti 《Applied Ocean Research》1984,6(3):175-176

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