Nutrient chemistry of groundwater in an intensively irrigated region of southern India   总被引：1，自引：0，他引：1  

N. Rajmohan  L. Elango 《Environmental Geology》2005,47(6):820-830

The concentration of nutrients in groundwater acts as an indicator to identify the influence of agricultural activities on the shallow subsurface environment. Hence, the present study was carried out to assess nutrient concentration (nitrate, phosphate and potassium) and understand its spatial and seasonal variations in the groundwater of Palar and Cheyyar River basin, Tamil Nadu, India. The groundwater samples collected from 43 wells were analyzed for nutrients once a month from January 1998 to June 1999. Results of the study suggested that agricultural activities, including application of fertilizers, soil mineralization processes and irrigation return flow, are major processes regulating the nutrients chemistry in the groundwater of this region. Groundwater in the sedimentary formation has comparatively higher concentration of nutrients than the groundwater in hard rock formations, which seems to be due to the adsorption of nutrients by the weathered rock materials. The seasonal water level fluctuation shows that rising water level increases nutrients concentration in groundwater due to the agriculture related activities. The results also indicate that nitrate and potassium concentrations are within the recommended drinking water limits, whereas phosphate concentration exceeds its drinking water limit and 35% of the samples are unsuitable for drinking purposes.Electronic Supplementary Material Supplementary material is available for this article at  相似文献   

Observation of surface and atmospheric parameters using “NOAA 18” satellite: a study on earthquakes of Sumatra and Nicobar Is regions for the year 2014 (M ≥ 6.0)     

Natarajan  Venkatanathan  Philipoff  Philip 《Natural Hazards》2018,92(2):1097-1112

Analysing pre-earthquake signals using satellite technology are getting importance among the scientific community, since round-the-clock survey for the wider region is possible compared to ground-based monitoring techniques. Several scientists are involved in various satellites and ground-based technologies to decode the complex physical mechanism of the earthquake process since 1980. They involved in measuring anomalous variations using space-based methodologies like EM signals, SAR interferometry, GPS for ionospheric sounding, satellite gravimetry, atmospheric sounding, Outgoing Longwave Radiation (OLR), radon gas and seismo-tectonic clouds. In this paper, the authors have considered surface latent heat flux (SLHF) and OLR satellite data for detailed analysis of earthquakes took place during the year 2014 in Sumatra and Nicobar Is regions. At the surface and atmospheric interface, the anomalous variations in SLHF were observed prior to the occurrence of the earthquake. Similarly, anomalous variations in OLR have been observed 3–30 days prior to the big earthquakes and it is measured above the cloud level. From the analysis, the author has found that variations in the SLHF and OLR flux can be utilized as efficient tools to identify the impending big earthquakes. SLHF and OLR variation level can give us a clue about the probable magnitude of earthquakes and also about earthquake preparation zones. Hence, by correlating the above-mentioned parameters, it is potential to key out the impending earthquakes with reasonable accuracy.

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Physiographic analysis for small scale soil and landuse mapping of Mewat area,Haryana, using LANDSAT imagery     

S. Natarajan  M. Y. Gajbe  M. L. Manchanda 《Journal of the Indian Society of Remote Sensing》1985,13(1):49-56

Visual interpretation of LANDSAT imagery of 1∶250,000 scale (band 5 and 7) and 1∶1 M (FCC) covering 1611 km² in Mewat area, Haryana was carried out for delineating the physiographic units. The physiographic units viz. hills, piedmont plain, intermontane basin and Yamuna alluvial plain were identified and delineated using interpretation elements. Soils and land use in relation to the physiographic units were studied during the field visit and are described in the paper.  相似文献   

Electrochemical aspects of grinding media-mineral interactions in magnetite ore grinding     

K.A. Natarajan  I. Iwasaki 《International Journal of Mineral Processing》1984,13(1):53-71

Electrochemical aspects of grinding media-mineral interactions in magnetite ore grinding are illustrated from the viewpoint of corrosive wear of grinding balls and changes in the surface properties of the ground minerals. The corrosive wear of mild steel and HCLA steel was found to be small in contact with magnetite, while the combined presence of pyrrhotite and oxygen accelerated the corrosion of the above ball materials. Austenitic stainless steel exhibited passive behavior under all the above conditions. Galvanic coupling of mild steel with magnetite or pyrrhotite resulted in the formation of a surface reaction product consisting of iron hydroxide species on the mineral.  相似文献   

High-redshift galaxies, their active nuclei and central black holes     

Martin G. Haehnelt  Priyamvada Natarajan  & Martin J. Rees 《Monthly notices of the Royal Astronomical Society》1998,300(3):817-827

We demonstrate that the luminosity function of the recently detected population of actively star-forming galaxies at redshift z  = 3 and the B -band luminosity function of quasi-stellar objects (QSOs) at the same redshift can both be matched with the mass function of dark matter haloes predicted by standard variants of hierarchical cosmogonies for lifetimes of optically bright QSOs anywhere in the range 10⁶ to 10⁸ yr. There is a strong correlation between the lifetime and the required degree of non-linearity in the relation between black hole and halo mass. We suggest that the mass of supermassive black holes may be limited by the back-reaction of the emitted energy on the accretion flow in a self-gravitating disc. This would imply a relation of black hole to halo mass of the form M _bh ∝  v ⁵_halo ∝  M ^5/3_halo and a typical duration of the optically bright QSO phase of a few times 10⁷ yr. The high integrated mass density of black holes inferred from recent black hole mass estimates in nearby galaxies may indicate that the overall efficiency of supermassive black holes for producing blue light is smaller than previously assumed. We discuss three possible accretion modes with low optical emission efficiency: (i) accretion at far above the Eddington rate, (ii) accretion obscured by dust, and (iii) accretion below the critical rate leading to an advection-dominated accretion flow lasting for a Hubble time. We further argue that accretion with low optical efficiency might be closely related to the origin of the hard X-ray background and that the ionizing background might be progressively dominated by stars rather than QSOs at higher redshift.  相似文献   

Gamma-ray bursts from stellar remnants: probing the Universe at high redshift     

Ralph A. M. J. Wijers  Joshua S. Bloom  Jasjeet S. Bagla  & Priyamvada Natarajan 《Monthly notices of the Royal Astronomical Society》1998,294(1):L13-L17

A gamma-ray burst (GRB) releases an amount of energy similar to that of a supernova explosion, which combined with its rapid variability suggests an origin related to neutron stars or black holes. Since these compact stellar remnants form from the most massive stars not long after their birth, GRBs should trace the star formation rate in the Universe; we show that the GRB flux distribution is consistent with this. Because of the strong evolution of the star formation rate with redshift, it follows that the dimmest known bursts have z  ∼ 6, much above the value usually quoted and beyond the most distant quasars. This explains the absence of bright galaxies in well-studied GRB error boxes. The increased distances imply a peak luminosity of 8.3 × 10⁵¹ erg s⁻¹ and a rate density of 0.025 per million years per galaxy. These values are 20 times higher and 150 times lower, respectively, than are implied by fits with non-evolving GRB rates. This means either that GRBs are caused by a much rarer phenomenon than mergers of binary neutron stars, or that their gamma-ray emission is often invisible to us due to beaming. Precise burst locations from optical transients will discriminate between the various models for GRBs from stellar deaths, because the distance between progenitor birth place and burst varies greatly among them. The dimmest GRBs are then the most distant known objects, and may probe the Universe at an age when the first stars were forming.  相似文献   

Strong lensing statistics in large, z≲ 0.2, surveys: bias in the lens galaxy population     

Ole Möller  Manfred Kitzbichler  Priyamvada Natarajan 《Monthly notices of the Royal Astronomical Society》2007,379(3):1195-1208

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The submillimetre properties of gamma-ray burst host galaxies     

N. R. Tanvir  V. E. Barnard  A. W. Blain  A. S. Fruchter  C. Kouveliotou  P. Natarajan  E. Ramirez-Ruiz  E. Rol  I. A. Smith  R. P. J. Tilanus  R. A. M. J. Wijers 《Monthly notices of the Royal Astronomical Society》2004,352(3):1073-1080

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Substructure and the cusp and fold relations     

Amir Babak Aazami  Priyamvada Natarajan 《Monthly notices of the Royal Astronomical Society》2006,372(4):1692-1698

Gravitational lensing of a background source by a foreground galaxy lens occasionally produces four images of the source. The cusp and the fold relations impose conditions on the ratios of magnifications of these four-image lenses. In this theoretical investigation, we explore the sensitivity of these relations to the presence of substructure in the lens. Starting with a smooth lens potential, we add varying amounts of substructure, while keeping the source position fixed, and find that the fold relation is a more robust indicator of substructure than the cusp relation for the images. This robustness is independent of the detailed spatial distribution of the substructure, as well as of the ellipticity of the lensing potential and the presence of external shear.  相似文献   

Identification and evolution of hydrogeochemical processes in the groundwater environment in an area of the Palar and Cheyyar River Basins,Southern India   总被引：5，自引：0，他引：5  

N.?Rajmohan  L.?ElangoEmail author 《Environmental Geology》2004,46(1):47-61

The Palar and Cheyyar River Basins in Tamil Nadu state of Southern India are characterised by different geological formations, and groundwater is the major source for domestic, agricultural and other water-related activities. Hydrogeochemical studies were carried out in this area with the objective of identifying the geochemical processes and their relation to groundwater quality. Groundwater samples were collected once a month from 43 groundwater wells in this area from January 1998 to July 1999. Sampling procedures and chemical analysis were carried out as per the standard methods. Chemical data are used for mathematical calculations and graphical plots to understand the chemical process and its relation to the groundwater quality. The chemical composition of groundwater in the central part of the study area mainly depends on the recharge from lakes and the river, which is explained by a mixing mechanism. In addition, weathering of silicate minerals controls the concentration of major ions such as sodium, calcium, magnesium and potassium in the groundwater of this area. Further, the activity ratios indicate that the groundwater is in equilibrium with kaolinite, smectite and montmorrillonite. The reverse ion exchange process controls the concentration of calcium, magnesium and sodium in hard rock formations, and dissolution of carbonate minerals and accessory minerals is the source of Ca and Mg, in addition to cation exchange in the sedimentary formations. In general, the chemical composition of the groundwater in this area is influenced by rock–water interaction, dissolution and deposition of carbonate and silicate minerals, ion exchange, and surface water interactions.  相似文献