Closed form charged fluid with t = constant hypersurfaces as spheroids and hyperboloids     

Naveen Bijalwan  Y. K. Gupta 《Astrophysics and Space Science》2012,337(1):455-462

In the present article models of well behaved charged superdense stars with surface density 2×10¹⁴ gm/cm³ are constructed by considering a static spherically symmetric metric with t = const hypersurfaces as spheroids and hyperboloids. Maximum mass of the star is found to be 7.66300M _Θ with radius 19.35409 km for spheroids case while 1.51360M _Θ with radius 13.72109 km for hyperboloid case satisfying ultra-relativistic conditions. The solutions thus found satisfy all the reality and causality conditions. For brevity we don’t present a detailed analysis of the derived solutions in this paper.  相似文献   

Coastal Placer Deposits of Central Tamil Nadu,India     

N. Angusamy  J. Dajkumar Sahayam  M. Suresh Gandhi  G. Victor Rajamanickam 《Marine Georesources & Geotechnology》2013,31(3):137-174

ABSTRACT

Placer mineral exploration has been undertaken along the beach of Central Tamil Nadu coast from Pondicherry to Vedaranyam. On the basis of the drainage network, geomorphology, and the coastal environment, the study area has been grouped into three sectors, North, Central, and South. Heavy mineral by Wt% shows a slightly higher abundance in the Northern sector, an enrichment of opaques in the Central sector from stations between Poompuhar and Karaikal, and a total depletion in the Southern sector. An abundance of heavies in the Northern sector is considered to be the result of a higher wave energy, and the cymatogenic downwarping of the basin during the present transgression. An enrichment of heavies in the Central sector from Poompuhar to Karaikal is attributable to the reworking of the beach ridges, which were submerged during the present transgression, and to the role of density sorting. A depletion of heavies in the Southern sector is accounted for by the absence of a terrigenous supply and the prevalence of wave shadow conditions throughout the year. The nature of the heavy mineral assemblage reflects the derivation of sediments principally from khondalites, granites, metamorphic rocks and paleo-sediments. Factor analysis also supplements the predominant role of a density factor in the segregation of heavy minerals in the study area. A five-stage model is proposed for the formation of placer deposits in the study region. The present study has disclosed rich concentrations of ilmenites in the central sector between Poompuhar and Karaikal that can be commercially exploited.  相似文献   

Nonsingular charged analogues of Schwarzschild’s interior solution     

Naveen Bijalwan  Y. K. Gupta 《Astrophysics and Space Science》2008,317(3-4):251-260

The problem of finding nonsingular charged analogue of Schwarzschild’s interior solutions has been reduced to that of finding a monotonically decreasing function f. The models are discussed in generality by imposing reality condition on f. It is shown that the physical solutions are possible only for surface density to central density ratio greater than or equal to 2/3 i.e. $\frac{\rho_{a}}{\rho_{0}}\ge2/3$ . The unphysical nature of solutions with linear equation state has been proved. A generalization procedure has been utilized to generalize solutions by Guilfoyle (1999). Recently found solutions by Gupta and Kumar (2005a, 2005b, 2005c) are generalized by taking particular form of f and seen to have higher mass and more stable. The maximum mass is found to be 1.59482 M _Θ . The models have been found to be stable once the physical requirements are established due to mass to radius less than 4/9, total charge to total mass ratio less than 1 and redshift quite low.  相似文献   

National Inventory of Rabi Pulses in India Using Remotely Sensed Data     

Nita Bhagia  G. D. Bairagi  Sandeep Pandagre  Gajendra Patel  S. P. Vyas  G. N. Naveen Kumar  Indal Ramteke  Pritam Mesharam 《Journal of the Indian Society of Remote Sensing》2017,45(2):285-295

A scheme called National Food Security Mission was launched by Government of India in 2007 for wheat, rice and pulses crops. At the request of Ministry of Agriculture for monitoring intensification of pulses a project called Pulses Intensification was taken up in Rabi season 2012–2013. Reliable statistics using advanced methods is very important for variety of pulse crops. Remotely sensed data can help in pre-harvest area estimation of pulse crops. Pulses in India are grown as partly scattered and partly contiguous crop. Growth in scattered areas and poor vegetation canopy of some of the pulse crops poses a challenge in its identification and discrimination using remotely sensed data. National Inventory of Rabi pulse crops in major growing regions of northern and southern parts of India was attempted. Multi-date AWiFS data and multi-date NDVI products of AWiFS of Rabi season 2014–2015 were used to study spectral-temporal behavior of pulse crops. Pulse crops accuracies of more than 95 % was observed in contiguous areas and 50–80.77 % in scattered regions. All India area estimate of Rabi pulses for the year 2014–2015 was 8963.327 ‘000 ha.  相似文献   

Larger floods of Himalayan foothill rivers sustained flows in the Ghaggar–Hakra channel during Harappan age     

Ajit Singh  Vikrant Jain  Michel Danino  Naveen Chauhan  Rahul Kumar Kaushal  Shantamoy Guha  V. N. Prabhakar 《第四纪科学杂志》2021,36(4):611-627

The human–landform interaction in the region of the Ghaggar–Hakra palaeochannel in the northwest Indo-Gangetic plains during the Bronze Age Indus/Harappan civilisation (~4.6–3.9 thousand years before the present, ka bp ) remains an enigmatic case due to a paucity of evidence regarding the hydrology of the then existing river. Here, we estimated the palaeohydrology of the foothill Markanda River in the sub-Himalayan catchment of the Ghaggar–Hakra (G–H) palaeochannel. Our morphology and chronology results show aggradation of a fan (57.7 ka) during the Late Pleistocene and T–1 to T–5 fluvial terraces (13.1 to 6.0 ka) during the terminal Pleistocene to Holocene, and deposition of palaeoflood sediments (3.9–3.8 ka) over the T–3 terraces during the Late Holocene. Considering the known uplift rates along the Himalayan frontal thrust, and our estimated aggradation rates, we derived channel palaeogeometry and calculated peak discharge at the site of palaeoflood deposits. We conclude that the Markanda River's peak discharge was several orders of magnitude higher during the Late Holocene than the modern-day peak discharge of 100-year return period. The palaeoflood deposits represent larger flooding of the foothill rivers that sustained flows in the downstream reaches of the Ghaggar–Hakra palaeochannel during the Late Harappan civilisation.  相似文献   

Tracer-based estimation of temporal variation of water sources: an insight from supra- and subglacial environments     

Naveen Kumar  Tirumalesh Keesari  S. Chidambaram  Shyam Ranjan  Mohd Soheb 《水文科学杂志》2013,58(11):1717-1732

ABSTRACT

The temporal variations in electrical conductivity and the stable isotopes of water, δD and δ¹⁸O, were examined at Chhota Shigri Glacier, India, to understand water sources and flow paths to discharge. Discharge is highly influenced by supraglacially derived meltwater during peak ablation, and subglacial meltwaters are more prominent at the end of the melt season. The slope of the best fit linear regression line for δD versus δ¹⁸O, for both supraglacial and runoff water, is lower than that for precipitation (snow and rain) and surface ice, indicating strong isotopic fractionation associated with the melting processes. The slope of the local meteoric water line (LMWL) is close to that of the global meteoric water line (GMWL), reflecting that the moisture source is predominantly oceanic. The d-excess variation in rainwater confirms that the southwest monsoon is the main contributor during summer while the remainder including winter is mostly influenced by westerlies.  相似文献   

Seismic microzonation of a nuclear power plant site with detailed geotechnical,geophysical and site effect studies     

Naveen James  T. G. Sitharam  G. Padmanabhan  C. S. Pillai 《Natural Hazards》2014,71(1):419-462

This paper highlights the seismic microzonation carried out for a nuclear power plant site. Nuclear power plants are considered to be one of the most important and critical structures designed to withstand all natural disasters. Seismic microzonation is a process of demarcating a region into individual areas having different levels of various seismic hazards. This will help in identifying regions having high seismic hazard which is vital for engineering design and land-use planning. The main objective of this paper is to carry out the seismic microzonation of a nuclear power plant site situated in the east coast of South India, based on the spatial distribution of the hazard index value. The hazard index represents the consolidated effect of all major earthquake hazards and hazard influencing parameters. The present work will provide new directions for assessing the seismic hazards of new power plant sites in the country. Major seismic hazards considered for the evaluation of the hazard index are (1) intensity of ground shaking at bedrock, (2) site amplification, (3) liquefaction potential and (4) the predominant frequency of the earthquake motion at the surface. The intensity of ground shaking in terms of peak horizontal acceleration (PHA) was estimated for the study area using both deterministic and probabilistic approaches with logic tree methodology. The site characterization of the study area has been carried out using the multichannel analysis of surface waves test and available borehole data. One-dimensional ground response analysis was carried out at major locations within the study area for evaluating PHA and spectral accelerations at the ground surface. Based on the standard penetration test data, deterministic as well as probabilistic liquefaction hazard analysis has been carried out for the entire study area. Finally, all the major earthquake hazards estimated above, and other significant parameters representing local geology were integrated using the analytic hierarchy process and hazard index map for the study area was prepared. Maps showing the spatial variation of seismic hazards (intensity of ground shaking, liquefaction potential and predominant frequency) and hazard index are presented in this work.  相似文献   

Multiwavelength observations of serendipitous Chandra X-ray sources in the field of A 2390     

C. S. Crawford  P. Gandhi  A. C. Fabian  R. J. Wilman  R. M. Johnstone  A. J. Barger †  L. L. Cowie ‡ 《Monthly notices of the Royal Astronomical Society》2002,333(4):809-824

We present optical spectra and near-infrared imaging of a sample of 31 serendipitous X-ray sources detected in the field of Chandra observations of the A 2390 cluster of galaxies. The sources have  0.5–7 keV  fluxes of  (0.6–8)×10^-14 erg cm^-2 s^-1  and lie around the break in the  2–10 keV  source counts. They are therefore typical of sources dominating the X-ray Background in that band. 12 of the 15 targets for which we have optical spectra show emission lines at a range of line luminosities, and half of these show broad lines. These active galaxies and quasars have soft X-ray spectra. Including photometric redshifts and published spectra, we have redshifts for 17 of the sources, ranging from   z ∼0.2  up to   z ∼3  , with a peak between   z =1–2  . 10 of our sources have hard X-ray spectra indicating a spectral slope flatter than that of a typical unabsorbed quasar. Two hard sources that are gravitationally lensed by the foreground cluster are obscured quasars, with intrinsic  2–10 keV  luminosities of  (0.2–3)×10⁴⁵ erg s^-1  , and absorbing columns of   N _H>10²³ cm^-2  . Both of these sources were detected in the mid-infrared by ISOCAM on the Infrared Space Observatory , which when combined with radiative transfer modelling leads to the prediction that the bulk of the reprocessed flux emerges at ∼100 μm.  相似文献   

4C +39.29 – extended emission around a powerful type 2 quasar     

P. Gandhi  A. C. Fabian  C. S. Crawford 《Monthly notices of the Royal Astronomical Society》2006,369(4):1566-1576

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Inclusion of earthquake strong ground motion in a geographic information system-based landslide susceptibility zonation in Garhwal Himalayas     

Naveen Pareek  Mukat L. Sharma  Manoj K. Arora  Shilpa Pal 《Natural Hazards》2013,65(1):739-765

Garhwal Himalayas are seismically very active and simultaneously suffering from landslide hazards. Landslides are one of the most frequent natural hazards in Himalayas causing damages worth more than one billion US$ and around 200 deaths every year. Thus, it is of paramount importance to identify the landslide causative factors to study them carefully and rank them as per their influence on the occurrence of landslides. The difference image of GIS-derived landslide susceptibility zonation maps prepared for pre- and post-Chamoli earthquake shows the effect of seismic shaking on the occurrence of landslides in the Garhwal Himalaya. An attempt has been made to incorporate seismic shaking parameters in terms of peak ground acceleration with other static landslide causative factors to produce landslide susceptibility zonation map in geographic information system environment. In this paper, probabilistic seismic hazard analysis has been carried out to calculate peak ground acceleration values at different time periods for estimating seismic shaking conditions in the study area. Further, these values are used as one of the causative factors of landslides in the study area and it is observed that it refines the preparation of landslide susceptibility zonation map in seismically active areas like Garhwal Himalayas.  相似文献