An Upper Limit on the Ratio Between the Extreme Ultraviolet and the Bolometric Luminosities of Stars Hosting Habitable Planets     

Sujan Sengupta 《Journal of Astrophysics and Astronomy》2016,37(2):11

A large number of terrestrial planets in the classical habitable zone of stars of different spectral types have already been discovered and many are expected to be discovered in the near future. However, owing to the lack of knowledge on the atmospheric properties, the ambient environment of such planets are unknown. It is known that sufficient amount of Extreme Ultraviolet (EUV) radiation from the star can drive hydrodynamic outflow of hydrogen that may drag heavier species from the atmosphere of the planet. If the rate of mass loss is sufficiently high, then substantial amount of volatiles would escape causing the planet to become uninhabitable. Considering energy-limited hydrodynamical mass loss with an escape rate that causes oxygen to escape alongwith hydrogen, an upper limit for the ratio between the EUV and the bolometric luminosities of stars which constrains the habitability of planets around them is presented here. Application of the limit to planet-hosting stars with known EUV luminosities implies that many M-type of stars should not have habitable planets around them.  相似文献   

GIS-enabled historiography to determine travel routes during the Western Han period via agent-based models and least-cost path analysis     

Raja Sengupta  Griet Vankeerberghen  Ruoxuan Wen  Jing Rao  Yanbing Chen 《Transactions in GIS》2023,27(4):1090-1103

GIS-enabled historiography allows us to shed light on missing or poorly understood aspects of historical events. Here, we use agent-based models (ABMs), least cost path analysis (LCPA), and space–time paths to recreate and evaluate possible modes and routes of travel undertaken by Shi Rao, a Western Han official. A diary was found in Shi Rao's tomb that includes information about his travels over 1 year (11 BCE), including start and end times of his journeys. But it leaves out details regarding modes of transport or exact routes. Using Tan Qixiang's historical atlas, we digitized river networks and utilized modern topographic data to digitally recreate the landscape as it was during Shi Rao's travels. This was then used to evaluate possible journeys via rivers (using ABMs) and roads (using LCPA), and compared to historical speed of boats, carts and horses, with findings indicating that horseback may have been the viable option.  相似文献   

Evolution of high-Mg–Al granulites from Sunkarametta, Eastern Ghats, India: evidence for a lower crustal heating–cooling trajectory     

Bose    Fukuoka    Sengupta  & Dasgupta 《Journal of Metamorphic Geology》2000,18(3):223-240.

A suite of high-Mg–Al granulites from Sunkarametta, Eastern Ghats Belt, India, shows contrasting prograde assemblages of extremely aluminous orthopyroxene+cordierite+sapphirine and similarly aluminous orthopyroxene+Ti-rich spinel in closely associated domains. Textural and compositional characteristics indicate that both were derived from prograde dehydration–melting of biotite–plagioclase–quartz-bearing protoliths. The former assemblage was stabilized at relatively more magnesian bulk composition. Geothermobarometric data and petrogenetic grid considerations place 'peak' metamorphic conditions at c. 950 °C and 9 kbar. Subsequent to peak metamorphism, the rocks cooled to c . 700–750 °C, with slight lowering of pressure, and the retrograde reactions also involved melt–solid interaction. The inferred P – T  trajectory is one of heating–cooling at lower crustal (25–30 km) depths.  相似文献   

Mathematical techniques for paleocurrent analysis: Treatment of directional data     

J. S. Rao  Supriya Sengupta 《Mathematical Geology》1972,4(3):235-248

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Geochemistry of the Chakradharpur granite—Gneiss complex—A Precambrian trondhjemite body from West Singhbhum,Eastern India     

S. Sengupta  P.K. Bandyopadhyay  H.J. Van Den Hul 《Precambrian Research》1983,23(1):57-78

The Chakradharpur Granite—Gneiss complex (CKPG) is exposed as an elliptical body within the arcuate metamorphic belt sandwiched between the Singhbhum Granite in the south and the Chotonagpur Granite—Gneiss to the north. It consists of an older bimodal suite of grey gneiss and amphibolites, intruded by a younger unit of pegmatitic granite. The bimodal suite represents the basement to the enveloping metasediments.The average major-element chemistry of the grey gneiss conforms to the definition of trondhjemite and includes both low-Al₂O₃ and high-Al₂O₃ types. The amphibolites can be grouped into a low-MgO and a high-MgO type. Rocks of the younger unit range in composition from granodiorite to quartz monzonite. The two granitic units also differ significantly in their Rb, Sr and Ba contents, and in the REE distribution pattern. The grey gneiss shows a highly fractionated REE pattern and a distinct positive Eu anomaly, with Eu/Eu^* values increasing with increase in SiO₂ %. In samples of the younger granite, the REE pattern is less fractionated, with higher HREE abundance relative to the grey gneiss and usually shows a negative Eu anomaly. The two types of REE patterns in amphibolites are interpreted to represent the two broad groups identified on the basis of major element chemistry.On the basis of chemical data, a two-stage partial melting model for the genesis of grey gneiss is suggested, involving separation of hornblende and varying amounts of plagioclase in the residual phase. Varying amounts of plagioclase in the residuum result in the wide range of Al₂O₃ content of the partial melt from which the trondhjemites crystallised. Residual hornblende produces the highly fractionated REE pattern, but a relatively higher HREE content of the trondhjemites compared to those produced by separation of garnet in the residual phase. The high level of Ba together with moderate levels of Sr in the trondhjemites can also be explained by plagioclase in the residue, whose effectiveness in partitioning Ba compared to Sr is lower. Of the two groups of amphibolites, the low-MgO type shows relative depletion of LREE compared to the high-MgO type. It contains varying amounts of plagioclase and is tentatively suggested to represent the residue. The other group, with a slightly fractionated REE pattern (Ce_N/ Yb_N = 2.01), is generally considered to represent the source material for the trondhjemites. This may have been generated by 5–15% partial melting of mantle peridotites, containing higher concentrations of LIL elements than those which produced average Precambrian tholeiites. This first phase of partial melting resulted in the slightly fractionated REE pattern of these amphibolites. Derivation of the younger granitic unit from the trondhjemites can be ruled out on the basis of REE data alone. REE data suggest partial melting of metasediments to be the origin of these rocks. It is also possible that deeply buried volcanic rocks, similar to calc-alkaline components of greenstone belts, are the parent for this component.  相似文献   

Obituary     

Sudipta Sengupta 《Journal of the Geological Society of India》2009,74(2):277-278

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Petrology of gedrite-bearing rocks in mid-crustal ductile shear zones from the Eastern Ghats Belt, India   总被引：1，自引：0，他引：1  

Dasgupta  Sengupta  PR. Sengupta  Ehl  & Raith 《Journal of Metamorphic Geology》1999,17(6):765-778

A suite of metapelitic, basic and quartzofeldspathic rocks intruded by enderbitic gneiss from the southernmost tip of the Eastern Ghats Belt, India, and metamorphosed at c. 750–800  °C, 6  kbar, were subjected to repeated ductile shear deformation, hydration, cooling and accompanying alkali metasomatism along narrow shear zones. Gedrite-bearing assemblages developed in the shear zones traversing metapelitic rocks. Interpretation of the reaction textures in an appropriate P–T  grid in the system FMASH, an isothermal–isobaric μ _H2O– μ _Na2O grid in the system NFMASH, and geothermobarometric data suggest a complex evolutionary history for the gedrite-bearing parageneses. Initially, gedrite-bearing assemblages were produced due to increase in μ _Na2O at nearly constant but high μ _H2O accompanying cooling. Gedrite was partially destabilized to orthopyroxene+albite due to progressively increasing μ _Na2O. During further cooling and at increased μ _H2O a second generation of gedrite appeared in the rocks.  相似文献   

Behavior of braced excavation in sand under a seismic condition: experimental and numerical studies   总被引：1，自引：1，他引：0  

Sanku Konai  Aniruddha Sengupta  Kousik Deb 《地震工程与工程振动(英文版)》2018,17(2):311-324

The behavior of braced excavation in dry sand under a seismic condition is investigated in this paper. A series of shake table tests on a reduced scale model of a retaining wall with one level of bracing were conducted to study the effect of different design parameters such as excavation depth, acceleration amplitude and wall stiffness. Numerical analyses using FLAC 2D were also performed considering one level of bracing. The strut forces, lateral displacements and bending moments in the wall at the end of earthquake motion were compared with experimental results. The study showed that in a post-seismic condition, when other factors were constant, lateral displacement, bending moment, strut forces and maximum ground surface displacement increased with excavation depth and the amplitude of base acceleration. The study also showed that as wall stiffness decreased, the lateral displacement of the wall and ground surface displacement increased, but the bending moment of the wall and strut forces decreased. The net earth pressure behind the walls was influenced by excavation depth and the peak acceleration amplitude, but did not change significantly with wall stiffness. Strut force was the least affected parameter when compared with others under a seismic condition.  相似文献   

Performance of sand and shredded rubber tire mixture as a natural base isolator for earthquake protection     

Srijit Bandyopadhyay  Aniruddha Sengupta  G. R. Reddy 《地震工程与工程振动(英文版)》2015,14(4):683-693

The performance of a well-designed layer of sand, and composites like layer of sand mixed with shredded rubber tire(RSM) as low cost base isolators, is studied in shake table tests in the laboratory. The building foundation is modeled by a 200 mm by 200 mm and 40 mm thick rigid plexi-glass block. The block is placed in the middle of a 1m by 1m tank filled with sand. The selected base isolator is placed between the block and the sand foundation. Accelerometers are placed on top of the footing and foundation sand layer. The displacement of the footing is also measured by LVDT. The whole setup is mounted on a shake table and subjected to sinusoidal motions with varying amplitude and frequency. Sand is found to be effective only at very high amplitude( 0.65 g) of motions. The performance of a composite consisting of sand and 50% shredded rubber tire placed under the footing is found to be most promising as a low-cost effective base isolator.  相似文献   

Tectonic amalgamation of crustal blocks along Gadag-Mandya Shear Zone in Dharwar Craton of southern India     

Siladitya Sengupta  Abhinaba Roy 《Journal of the Geological Society of India》2012,80(1):75-88

The crustal scale Shear Zone that can be traced from Gadag in the north to Mandya in the south in Dharwar Craton of southern India is considered as the boundary between two subcratonic blocks namely the Eastern Dharwar Craton (EDC) and the Western Dharwar Craton (WDC) in published literature. The present study on the Gadag-Mandya Shear Zone (GMSZ) in the Javanahalli-Hagalvadi sector has brought out a detailed account on the disposition, geometry and kinematics of the shear zone, and also the distinctive structural patterns of the two adjacent supracrustal belts, namely the Chitradurga schist belt (CSB) in the west and Javanahalli schist belt (JSB) in the east. The JSB has an overall N-S striking and gentle easterly dipping geometry, the structural features of which are indicative of a predominant noncoaxial deformation and westward transportation of the supracrustal assemblage. In contrast, deformation in the CSB, which is defined mainly by a flattening type of strain, has produced an overall verticality of the structures (dominant foliation, axial planes of regional folds).  相似文献