Metamorphic reactions in dry and aluminous granulites: a Perple_X <Emphasis Type="Italic">P–T</Emphasis> pseudosection analysis of the influence of effective reaction volume     

P. Nasipuri  A. Bhattacharya  S. Das 《Contributions to Mineralogy and Petrology》2009,157(3):301-311

In high-Mg, Al metapelites, monophase sapphirine corona occur around spinel–corundum aggregates in monomineralic cordierite layers, and bi-phase orthopyroxene–sillimanite aggregates replace locally warped sapphirine in polygonized cordierite aggregates. P–T phase topologies computed (Perple_X software) using compositions of cordierite-rich layers that host the reaction textures did not match the assemblages for the discontinuous reactions spinel + corundum + cordierite → sapphirine and sapphirine + cordierite → orthopyroxene + sillimanite. Instead, the reaction assemblages were reproduced using P–T pseudosection analysis for micro-domain reaction volumes estimated from compositions of product phases in the volume proportion they occur. The results are consistent with known phase relations deduced using Schreinmakers P–T grids. Apparently, the compositions of cordierite-rich layers that hosted the reaction textures were inadequate chemical proxies for determining P–T–X relations of phase-boundary controlled reactions influenced by compositions of the nearest-neighbor minerals in the proportion they react (effective composition), and not in the proportion they existed in the layer/bulk rock. In other words, P–T–X phase topologies and reconstructed P–T paths in dry and aluminous rocks may be best understood by thermodynamic modeling of reactions using effective reaction volume compositions rather than the bulk composition of the rock or the mineralogical layer that host the reaction textures.  相似文献   

Orientation Course on Gemmology     

Jadaba Nanda Das 《Journal of the Geological Society of India》2009,74(1):142-143

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Book review     

Subhajyoti Das  B. P. Radhakrishna  P. Krishnamurthy 《Journal of the Geological Society of India》2009,73(2):289-290

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MNC’s appropriate water rights     

Subhajyoti Das 《Journal of the Geological Society of India》2009,73(6):874-874

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High Energy Emissions from Young Stellar Objects     

A. C. Das  Ashok Ambastha 《Journal of Astrophysics and Astronomy》2012,33(1):1-8

X-ray emissions from Young Stellar Objects (YSO) are detected by many X-ray missions that are providing important information about their properties. However, their emission processes are not fully understood. In this research note, we propose a model for the generation of emissions from a YSO on the basis of a simple interaction between the YSO and its surrounding circumstellar accretion disc containing neutral gas and charged dust. It is assumed that the YSO has a weak dipole type magnetic field and its field lines are threaded into the circumstellar disc. Considering the motion of ions and charged dust particles in the presence of neutral gas, we show that the sheared dust-neutral gas velocities can lead to a current along the direction of ambient magnetic field. Magnitude of this current can become large and is capable of generating an electric field along the magnetic field lines. It is shown how the particles can gain energy up to MeV range and above, which can produce high-energy radiations from the YSO.  相似文献   

Dust-acoustic soliton in a plasma with multi-species ions and kappa-distributed electrons     

M. P. Bora  B. Choudhury  G. C. Das 《Astrophysics and Space Science》2012,341(2):515-525

In this work, we consider the formation of electrostatic, dust-acoustic solitary structure in a unmagnetized plasma with Lorentzian electrons (kappa-distributed) and more than one species of thermal ions (Maxwellian). The work is inspired by results of different space-based observations of electrostatic solitary waves (ESW) in the near-earth and magnetospheric plasmas and recent experimental realization of existence of superthermal electron component in various space plasmas. We have, in this work, shown that existence of compressive potential structure is possible only with more than one species of thermal ions. Besides, formation of compressive double layers is also possible which depends on the amount of deviation of the electron thermal velocities from a Maxwellian distribution. We show that both dust-temperature and super-thermal electrons lead to a decrease in the soliton amplitude.  相似文献   

Dissipative accretion flows around a rotating black hole     

Santabrata Das  Sandip K. Chakrabarti 《Monthly notices of the Royal Astronomical Society》2008,389(1):371-378

We study the dynamical structure of a cooling dominated rotating accretion flow around a spinning black hole. We show that non-linear phenomena such as shock waves can be studied in terms of only three flow parameters, namely the specific energy     , the specific angular momentum (λ) and the accretion rate     of the flow. We present all possible accretion solutions. We find that a significant region of the parameter space in the     plane allows global accretion shock solutions. The effective area of the parameter space for which the Rankine–Hugoniot shocks are possible is maximum when the flow is dissipation-free. It decreases with the increase of cooling effects and finally disappears when the cooling is high enough. We show that shock forms further away when the black hole is rotating compared to the solution around a Schwarzschild black hole with identical flow parameters at a large distance. However, in a normalized sense, the flow parameters for which the shocks form around the rotating black holes are produced shocks closer to the black hole. The location of the shock is also dictated by the cooling efficiency in that higher the accretion rate     , the closer is the shock location. We believe that some of the high-frequency quasi-periodic oscillations may be due to the flows with higher accretion rate around the rotating black holes.  相似文献   

GIS-based vulnerability mapping of the coastal stretch from Puri to Konark in Odisha using analytical hierarchy process     

Behera  Rashmisikha  Kar  Abhipsa  Das  Manas Ranjan  Panda  Prachi Prava 《Natural Hazards》2019,96(2):731-751

Natural Hazards - The 485-km-long coastline of Odisha, a state in the northeastern part of the Indian peninsula, is potentially vulnerable to several disaster events that take place frequently. In...  相似文献   

Frequency dependence of the periodicity of the intensity of the non-magnetic component of solar radio emission     

T. K. Das  T. K. Nag 《Monthly notices of the Royal Astronomical Society》1999,303(2):221-226

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Computation of mass outflow rate from relativistic quasi-spherical accretion on to black holes     

Tapas K. Das 《Monthly notices of the Royal Astronomical Society》1999,308(1):201-206

We compute the mass outflow rate R _m˙ from relativistic matter that is accreting quasi-spherically on to the Schwarzschild black holes. Taking the pair-plasma pressure-mediated shock surface as the effective boundary layer (of the black hole) from where the bulk of the outflow is assumed to be generated, computation of this rate is done using combinations of exact transonic inflow and outflow solutions. We find that R _m˙ depends on the initial parameters of the flow, the polytropic index of matter, the degree of compression of matter near the shock surface and the location of the shock surface itself. We thus not only study the variation of the mass outflow rate as a function of various physical parameters governing the problem, but also provide a sufficiently plausible estimation of this rate.  相似文献