Template-based classification of SDSS-<Emphasis Type="BoldItalic">GALEX</Emphasis> point sources     

Ayesha Anjum  Mousumi Das  Jayant Murthy  S. B. Gudennavar  Rajesh Gopal  S. G. Bubbly 《Journal of Astrophysics and Astronomy》2018,39(5):61

We have classified a sample of 37,492 objects from SDSS into QSOs, galaxies and stars using photometric data over five wave bands (u, g, r, i and z) and UV GALEX data over two wave bands (near-UV and far-UV) based on a template fitting method. The advantage of this method of classification is that it does not require any spectroscopic data and hence the objects for which spectroscopic data is not available can also be studied using this technique. In this study, we have found that our method is consistent by spectroscopic methods given that their UV information is available. Our study shows that the UV colours are especially important for separating quasars and stars, as well as spiral and starburst galaxies. Thus it is evident that the UV bands play a crucial role in the classification and characterization of astronomical objects that emit over a wide range of wavelengths, but especially for those that are bright at UV. We have achieved the efficiency of 89% for the QSOs, 63% for the galaxies and 84% for the stars. This classification is also found to be in agreement with the emission line diagnostic diagrams.  相似文献   

Exact solution of anisotropic compact stars via mass function     

S. K. Maurya  Ayan Banerjee  Y. K. Gupta 《Astrophysics and Space Science》2018,363(10):208

Studying relativistic compact objects is important in modern astrophysics to understand several astrophysical issues. It is therefore natural to ask for an internal structure and physical properties of specific classes of compact stars from astrophysical observations. We obtain a class of new relativistic solutions with anisotropic distribution of matter for compact stars. More specifically, stellar models, described by an anisotropic fluid, establishing a relation between metric potentials and generating a specific form of mass function, are explicitly constructed within the framework of General Relativity. New solutions can be used to model compact objects, which adequately describe compact strange star candidates like SMC X-1, Her X-1 and 4U 1538-52, with observational data taken from Gangopadhyay et al. (Mon. Not. R. Astron. Soc. 431:3216, 2013). As a possible astrophysical application the obtained solutions could explain the physics of selfgravitating objects, and might be useful for strong-field regimes where data are currently inadequate.  相似文献   

Evidence for a spatially extensive hydrothermal system at the Ries impact structure,Germany          下载免费PDF全文

H. M. Sapers  G. R. Osinski  R. L. Flemming  E. Buitenhuis  N. R. Banerjee  L. L. Tornabene  S. Blain  J. Hainge 《Meteoritics & planetary science》2017,52(2):351-371

The ~15 Ma, 26 km diameter Ries impact structure in south‐central Germany was one of the first terrestrial impact structures where evidence of impact‐associated hydrothermal alteration was recognized. Previous studies suggested that pervasive, high‐temperature hydrothermal activity was restricted to the area within the “inner ring” (i.e., the crater‐fill impactite units). Here we present mineralogical evidence for localized hydrothermal activity in the ejecta beyond the crater rim in two previously unstudied settings: a pervasively altered lens of suevite ejecta directly overlying the Bunte Breccia at the Aumühle quarry; and suevite ejecta at depth overlain by ~20 m of lacustrine sediments sampled by the Wörnitzostheim 1965 drill core. A comprehensive set of X‐ray diffraction analyses indicates five distinct alteration regimes (1) surficial ambient weathering characterized by smectite and a minor illitic component; (2) locally restricted hydrothermal activity characterized by an illitic component and minor smectite; (3) hydrothermal activity at depth characterized by smectite, a minor illitic component, and calcite; (4) hydrothermal activity at depth characterized by smectite, a minor illitic component, calcite, zeolites, and clinochlore; and (5) pervasive hydrothermal activity at depth characterized by smectite, a minor illitic component, and minor clinochlore. These data spatially extend the Ries postimpact hydrothermal system suggesting a much more extensive, complex, and dynamic system than previously thought. Constraining the mineralogical alteration regimes at the Ries impact structure may also further our understanding of impact‐associated phyllosilicate formation on Mars with implications for climate models and habitability.  相似文献   

Geochemical and oxygen isotope perspective of a new R chondrite Dhofar 1671: Affinity with ordinary chondrites          下载免费PDF全文

Arshad Ali  Sobhi J. Nasir  Iffat Jabeen  Ahmed Al Rawas  Neil R. Banerjee  Gordon R. Osinski 《Meteoritics & planetary science》2017,52(9):1991-2003

Dhofar 1671 is a relatively new meteorite that previous studies suggest belongs to the Rumuruti chondrite class. Major and REE compositions are generally in agreement with average values of the R chondrites (RCs). Moderately volatile elements such as Se and Zn abundances are lower than the R chondrite values that are similar to those in ordinary chondrites (OCs). Porphyritic olivine pyroxene (POP), radial pyroxene (RP), and barred olivine (BO) chondrules are embedded in a proportionately equal volume of matrix, one of the characteristic features of RCs. Microprobe analyses demonstrate compositional zoning in chondrule and matrix olivines showing Fa‐poor interior and Fa‐rich outer zones. Precise oxygen isotope data for chondrules and matrix obtained by laser‐assisted fluorination show a genetic isotopic relationship between OCs and RCs. On the basis of our data, we propose a strong affinity between these groups and suggest that OC chondrule precursors could have interacted with a ¹⁷O‐rich matrix to form RC chondrules (i.e., ?¹⁷O shifts from ~1‰ to ~3‰). These interactions could have occurred at the same time as “exotic” clasts in brecciated samples formed such as NWA 10214 (LL3–6), Parnallee (LL3), PCA91241 (R3.8–6), and Dhofar 1671 (R3.6). We also infer that the source of the oxidation and ¹⁷O enrichment is the matrix, which may have been enriched in ¹⁷O‐rich water. The abundance of matrix in RCs relative to OCs, ensured that these rocks would be apparently more oxidized and appreciably ¹⁷O‐enriched. In situ analysis of Dhofar 1671 is recommended to further strengthen the link between OCs and RCs.  相似文献   

Mobility centre-oriented urban regeneration: examining place value of railway stations     

Banerjee  Iman  Saha  Apala 《GeoJournal》2022,87(4):567-581

Urban regeneration involves the notion of reconstruction of places, where regeneration initiatives are undertaken to ameliorate the quality of physical and social spaces, accrue economic profitability of space, and finally encourage environmental sustainability. Railway stations all around the world have a very important role to play in contemporary urban regeneration strategies as places of both social and material interest. With the progress of the twentieth century several issues like rapidly growing population, seemingly relentless urbanisation, an alarming rate of vehicle emission, and consequent pollution emphasised railway stations as critical places with great potentials of infrastructure development for the optimised functioning of urban centres. Thus the huge value of railway stations and their adjacent land has been acknowledged since the last quarter of the previous century. This paper aims to analyse the place value of railway stations and their immediate neighbourhoods within the urban fabric of a city using a relevant theoretical concept i.e. the ‘Node-Place Model’. Simultaneously it also draws attention to the notion of (re)development of functional spaces in and around the railway stations as a dimension of contemporary urban regeneration strategies, with the help of some global examples. This paper thereby reveals that in the urban centres throughout the entire world the railway stations are progressively attaining the focal position within integrated transport and land use planning strategies, either under the larger concept of 'Transit-Oriented Development' (TOD) or more simply, with the label of (re)development programme. This paper will significantly contribute to the ability of spatial policymakers to direct the future of urban growth towards public transit stations so as to achieve sustainable urban development.

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Anomalous behaviour of precursor resistivity in Shillong area, NE India     

J. R. Kayal  B. Banerjee 《Geophysical Journal International》1988,94(1):97-103

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Satellite detection of earthquake thermal infrared precursors in Iran   总被引：5，自引：1，他引：4  

Arun K. Saraf  Vineeta Rawat  Priyanka Banerjee  Swapnamita Choudhury  Santosh K. Panda  Sudipta Dasgupta  J. D. Das 《Natural Hazards》2008,47(1):119-135

Stress accumulated in rocks in tectonically active areas may manifest itself as electromagnetic radiation emission and temperature variation through a process of energy transformation. Land surface temperature (LST) changes before an impending earthquake can be detected with thermal infrared (TIR) sensors such as NOAA-AVHRR, Terra/Aqua-MODIS, etc. TIR anomalies produced by 10 recent earthquakes in Iran during the period of Jun 2002–Jun 2006 in the tectonically active belt have been studied using pre- and post-earthquake NOAA-AVHRR datasets. Data analysis revealed a transient TIR rise in LST ranging 2–13°C in and around epicentral areas. The thermal anomalies started developing about 1–10 days prior to the main event depending upon the magnitude and focal depth, and disappeared after the main shock. In the case of moderate earthquakes (<6 magnitude) a dual thermal peak instead of the single rise has been observed. This may lead us to understand that perhaps pre-event sporadic release of energy from stressed rocks leads to a reduction in magnitude of the main shock. This TIR temperature increment prior to an impending earthquake can be attributed to degassing from rocks under stress or to p-hole activation in the stressed rock volume and their further recombination at the rock–air interface. A precise correlation of LST maps of Bam and Zarand with InSAR-generated deformation maps also provides evidence that the thermal anomaly is a ground-related phenomenon, not an atmospheric one.  相似文献   

Characterization of an island aquifer from tidal response     

Pallavi Banerjee  Deepak Sarwade  V. S. Singh 《Environmental Geology》2008,55(4):901-906

Growing demand for potable water for various needs has lead to indiscriminate exploitation of groundwater resources, particularly, in the terrain where surface water resources are negligible. One such area is an island where groundwater is the only source of fresh water. Groundwater is the prime source of fresh water on most of the atolls in the world. Groundwater on these islands is in the form of thin fragile floating lens and is often vulnerable to overexploitation, draught, tidal waves, tsunami and cyclone resulting in seawater ingress. Sustainable development of this meager source of fresh groundwater for a longer time becomes a more difficult task on small atolls with a large population depending on this vital resource. To develop a sustainable management scheme and identify the vulnerable part of aquifer, characterization of the aquifer system on islands is imperative. Groundwater on an atoll is extremely vulnerable to seawater mixing through natural as well as human activities. One such natural process is the tides of the ocean. The response of sea tide to the water table on the island offers valuable data as well as cost-effective means to characterize an aquifer system. Such characterization is vital for the management of groundwater resources on an atoll. The obtained results have compared well with the parameters obtained through a conventional pumping test. Therefore, the use of tidal response to the water table, which can easily be recorded, provides a rapid and cost-effective means to characterization of the aquifer system on the island.  相似文献   

Non-adiabatic gravitational collapse in higher dimensional space-time and its junctions conditions     

B. Bhui  S. Chaterjee  A. Banerjee 《Astrophysics and Space Science》1995,226(1):7-18

Junction conditions are studied at the boundary of a higher dimensional spherical distribution containing an outgoing heat flow and radiation flux. Our analysis extends to higher dimension, an important observation of Santos that for a collapsing fluid with radial heat flow the isotropic pressure on the surface of discontinuity does not vanish. Some physically relevant parameters like luminosity, mass function for the bounded distribution and also the time required for horizon formation are also calculated and it is observed that the dimensionality of space-time does not qualitatively alter the analogous results of the standard space time.  相似文献   

MEM Analysis of Geomagnetic Field Variations Over Narssarssuaq     

M. Banerjee  M. K. Singh  Nagendra P. Singh  T. Lal 《Pure and Applied Geophysics》1997,150(2):329-340

—Maximum entropy spectral analysis (MESA) has been applied to 24 series of hourly daily data and only one daily mean series for the horizontal (H) and vertical (Z) components of the geomagnetic field for the year 1983 as observed at Narssarssuaq, Greenland (71.2°N, 36.7°E) (gm coordinate). The method has isolated some prominent medium frequency signal components. The maximum peaks for H are at 06 hr (0.174 cycles per day (cpd), 3.2 × 10⁴ db) and 08 hr (0.09 cpd, 3.5 × 10⁴ db). Similarly, the maximum peak in Z is observed at 04 hr (0.114 cpd, 5.7 × 10⁴ db). The spectral results for the daily-mean data indicate periods are greater than two days, with 178.5 days (nearly semiannual) being common to both H and Z. Other harmonics have been found for all the series of H and Z components which are mainly caused by the "Effective Period", i.e., the period produced by the combined effect of the sunspot numbers and the sun’s rotation period. Such frequencies correspond very well with those found in the geomagnetic indices A _p ?, C _p and AE. This suggests that the disturbance transient variations are caused by viscous interaction of the solar energies emanating from sunspot regions with the outermost magnetospheric boundary which, in turn, influences the magnetosphere-iono sphere coupling and produces the medium intensity long-duration continuous auroral activities (MILD CAAs) over high latitude regions. Thus, the higher latitude geomagnetic activities are nothing but the "effective period driven MILDCAAs" having a recurrence tendency of 27/n, where n is an integer.  相似文献