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201.
A total of 103 surface sediment samples collected from the water depth range of 15—3300 m along Vijaydurg-Karwar stretch of central west coast of India were analyzed for foraminiferal content. Relict benthic foraminiferal assemblage was noted within 50—135 m water depth.The relict benthic foraminiferal assemblage that includes Amphistegina,Operculum and Alveolinetta in sediment samples within the water depth of 85—135 m indicates presence of coral reef at this depth during Early Holocene. The presence of barnacle fouling on Relict foraminifera at 60—90 m confirms the paleo-shoreline. The shallow depth zone is characterized by presence of agglutinated relict foraminifera.The agglutinated forms indicate freshwater influx,which eventually increased the sea level and subsequently deteriorated the paleo-coral reef. 相似文献
202.
Validation of Indian National DEM from Cartosat-1 Data 总被引:1,自引:0,他引:1
S. Muralikrishnan Abhijit Pillai B. Narender Shashivardhan Reddy V. Raghu Venkataraman V. K. Dadhwal 《Journal of the Indian Society of Remote Sensing》2013,41(1):1-13
CartoDEM is an Indian National DEM generated from Cartosat-1 stereo data. Cartosat-1, launched in May, 2005, is an along track (aft ?5°, Fore +26°) stereo with 2.5 m GSD, give base-height ratio of 0.63 with 27 km swath. The operational procedure of DEM generation comprises stereo strip triangulation of 500?×?27 km segment with 10 m posting along with 2.5 m resolution ortho image and free—access posting of 30 m has been made available (bhuvan.nrsc.gov.in). A multi approach evaluation of CartoDEM comprising (a) absolute accuracy with respect to ground control points for two sites namely Jagatsinghpur -flat and Dharamshala- hilly; second site i.e. Alwar-plain and hilly with high resolution aerial DEM, (b) relative difference between SRTM and ASTERDEM (c) absolute accuracy with ICESat GLAS for two sites namely Jagatsinghpur-plain and Netravathi river, Western Ghats-hilly (d) relative comparison of drainage delineation with respect to ASTERDEM is reported here. The absolute height accuracy in flat terrain was 4.7 m with horizontal accuracy of 7.3 m, while in hilly terrain it was 7 m height with a horizontal accuracy of 14 m. While comparison with ICESat GLAS data absolute height difference of plain and hilly was 5.2 m and 7.9 m respectively. When compared to SRTM over Indian landmass, 90 % of pixels reported were within ±8 m difference. The drainage delineation shows better accuracy and clear demarcation of catchment ridgeline and more reliable flow-path prediction in comparison with ASTER. The results qualify Indian DEM for using it operationally which is equivalent and better than the other publicly available DEMs like SRTM and ASTERDEM. 相似文献
203.
The photo-coulomb neutrino process has been considered in the electro-weak theory and the influence of this process to the evolution of stars has been outlined. The scattering cross-section of this process is calculated in both low and high energy limit. The neutrino mass has been taken into account in this calculation. In the low-energy limit the neutrino luminosity is computed in the temperature range 108–109 K and is also compared to the previous result obtained according to the current-current coupling theory. The process may be significant for the evolution of stars in the later phases. 相似文献
204.
Sudip Bhattacharyya M. Coleman Miller Duncan K. Galloway 《Monthly notices of the Royal Astronomical Society》2010,401(1):2-6
Precision measurements of neutron star radii can provide a powerful probe of the properties of cold matter beyond nuclear density. Beginning in the late 1970s, it was proposed that the radius could be obtained from the apparent or inferred emitting area during the decay portions of thermonuclear (type I) X-ray bursts. However, this apparent area is generally not constant, preventing a reliable measurement of the source radius. Here, we report for the first time a correlation between the variation of the inferred area and the burst properties, measured in a sample of almost 900 bursts from 43 sources. We found that the rate of change of the inferred area during decay is anticorrelated with the burst decay duration. A Spearman rank correlation test shows that this relation is significant at the <10−45 level for our entire sample, and at the 7 × 10−37 level for the 625 bursts without photospheric radius expansion. This anticorrelation is also highly significant for individual sources exhibiting a wide range of burst durations, such as 4U 1636–536 and Aql X-1. We suggest that variations in the colour factor, which relates the colour temperature resulted from the scattering in the neutron star atmosphere to the effective temperature of the burning layer, may explain the correlation. This in turn implies significant variations in the composition of the atmosphere between bursts with long and short durations. 相似文献
205.
Michael A. Dopita Daniela Calzetti Jesús Maíz Apellániz William P. Blair Knox S. Long Max Mutchler Bradley C. Whitmore Howard E. Bond John MacKenty Bruce Balick Marcella Carollo Michael Disney Jay A. Frogel Robert O’Connell Donald Hall Jon A. Holtzman Randy A. Kimble Patrick McCarthy Francesco Paresce Abhijit Saha Alistair R. Walker Joe Silk Marco Sirianni John Trauger Rogier Windhorst Erick Young 《Astrophysics and Space Science》2010,330(1):123-131
We present narrow band, continuum subtracted Hα, [S ii], Hβ, [O iii] and [O ii] data taken with the Wide Field Camera 3 on the Hubble Space Telescope in the nearby dwarf starburst galaxy NGC 4214. From these images, we identify seventeen new planetary nebula candidates, and seven supernova remnant candidates. We use the observed emission line luminosity function of the planetary nebulae to establish a new velocity-independent distance to NGC 4214. We conclude that the PNLF technique gives a reddening independent distance to NGC 4214 of 3.19±0.36 Mpc, and that our current best-estimate of the distance to this galaxy ids 2.98±0.13 Mpc. 相似文献
206.
Malay Mukul Sridevi Jade Anjan Kumar Bhattacharyya Kuntala Bhusan 《Journal of the Geological Society of India》2010,75(1):302-312
Deformation in active mountain belts like the Himalaya is manifested over several spatial and temporal scales and collation
of information across these scales is crucial to an integrated understanding of the overall deformation process in mountain
belts. Computation and integration of geological shortening rates from retrodeformable balanced cross-sections and present-day
convergent rates from deforming mountain belts is one way of integrating information across time-scales. The results from
GPS measurements carried out in NE India indicate that about 15–20 mm/yr of convergence is being accommodated there. Balanced-cross
sections from the NE Himalaya indicate about 350–500 km of shortening south of the South Tibet Detachment (STD). Geothermobarometry
suggest that the rocks south of the STD deformed under peak metamorphic conditions at ∼ 22 Ma. This indicates a geological
convergence rate of ∼ 16–22 mm/yr which appears to be fairly consistent with the GPS derived convergence rates. Approximately
1.5 to 3.5 mm/yr (∼ 10–20 %) of the total N-S of the present-day convergence in the NE Himalaya is accommodated in the Shillong
Plateau. In addition, ∼ 8–9 mm/yr of E-W convergence is observed in the eastern and central parts of the Shillong Plateau
relative to the Indo-Burman fold-thrust belt. Balanced cross-sections in the Indo-Burman wedge together with higher resolution
GPS measurements are required in the future to build on the first-order results presented here. 相似文献
207.
Abhijit Basu 《Journal of the Geological Society of India》2009,73(4):528-536
Typically or arguably Ediacaran fossils (635 Ma to 543 Ma) are reported by several research groups from one unit of the Chhattisgarh
and two units of the Vindhyan Supergroups in peninsular India. Depositional ages of the host sediments, however, are inferred
to be ∼1000 Ma and ∼ 1630 Ma as determined by U-Pb dating of magmatic and detrital zircons in rhyolitic tuff (∼ porcellanite)
and sandstones, provenance considerations and paleopole positions. The contradiction of absolute ages results from inferring
the Ediacaran age strictly on the basis of fossils. I argue that the fossils reported from the Chhattisgarh and Vindhyan Supergroups
should be considered mostly Mesoproterozoic and late Proterozoic in age. I also argue that although the Ediacaran Period records
explosive diversity of preserved fossils, many forms very likely appeared much earlier with variable degrees of preservation
or none at all at times, and, that their age-ranges extend to the Paleoproterozoic. I hypothesize that the rate of increase
of biological diversity was lower than the rate of preservation in certain geological intervals, especially immediately after
extinction events. 相似文献
208.
Recent observations of the rotation curves of large disk galaxies of all Hubble-types have shown that they possess flat or slowly rising rotation curves up to large distances from the centre. It has been suggested here that such rotation curves are understood under normal fluid dynamical considerations provided that viscous (and/or magnetic) transfer of mass and angular momentum from inner to outer regions of these galaxies is efficient. Flow of gas from halo to the disk in regions close to the axis of rotation is also suggested. The existence of rising rotation curves in some galaxies with varying gradients and flat rotation curves in others suggest that probably these galaxies are not coeval. The formers are probably of more recent origin. 相似文献
209.
The antiproton-proton flux ratio has been estimated from the closed galaxy model of Peters and Westergaard by using the latest primary nucleon spectrum and
inclusive reaction accelerator results. The derived
flux ratio is about three times higher than those expected from the leaky box model. The results have been compared with the previous estimates by different authors. 相似文献
210.
Marine organisms must possess strategies enabling them to initiate calcite precipitation despite the unfavorable conditions for inorganic precipitation in surface seawater. These strategies are poorly understood. Here we compare two potential strategies of marine calcifyers to manipulate seawater chemistry in order to initiate calcite precipitation: Removal of Mg2+ and H+ ions from seawater solutions. An experimental setup was used to monitor the onset of inorganic precipitation on seed crystals as a function of the Mg2+ concentration and pH in artificial seawater. We focused on precipitation rates typical for biogenic calcification in planktonic foraminifera (∼10−3 mol m−2 h−1) and time scales typical for the initiation of calcification in these organisms (minutes to hours). We find that the carbonate ion concentration has to increase by a factor of ∼13 when [Mg2+] increases from 0 to 53 mmol kg−1 in order to maintain a typical biogenic precipitation rate. Model calculations for the energy requirement for various scenarios of Mg2+ and H+ removal including Ca2+ exchange and CO2 diffusion are presented. We conclude that the more cost-effective strategy to initiate calcite precipitation in foraminifera is H+ removal, rather than Mg2+ removal. 相似文献