A telescope made with cylinders – I. Some analytical results     

Ramesh Balasubramanyam 《Monthly notices of the Royal Astronomical Society》2004,354(4):1189-1193

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Exact relativistic model for a superdense star     

P. C. Vaidya  Ramesh Tikekar 《Journal of Astrophysics and Astronomy》1982,3(3):325-334

Assuming that the physical 3-spacet = const in a superdense star is spheroidal, a static spherically symmetric model based on an exact solution of Einstein’s equations is given which will permit densities of the order of 2 × 10¹⁴ gm cm^-3, radii of the order of a few kilometers and masses up to about four times the solar mass.  相似文献   

Some implications of escape of supermassive black holes from galactic nuclei due to plasmoid ejection     

Ramesh Chander Kapoor 《Astrophysics and Space Science》1983,95(2):425-429

Shklovsky (1982) has hypothesized escape of accreting supermassive black holes from galactic nuclei as a consequence of asymmetric ejection of plasma clouds from their accretion disks and their subsequent defunction for explaining evolutionary effects in quasars. It has been argued here that such an interpretation must accomodate the possibility of substantial capture of stars and gas by the black hole on its way out-which can prolong the life of the quasar-unless the mass of the black hole is less than ～10⁷ M _⊙ and a large enough initial recoil velocity is achieved.  相似文献   

The 1024 channel digital correlator receiver of the Gauribidanur radioheliograph     

R. Ramesh  M. S. Sundara Rajan  Ch. V. Sastry 《Experimental Astronomy》2006,21(1):31-40

A low frequency (40–150 MHz) radioheliograph for observations of the solar corona is in operation for the last few years at the Gauribidanur radio observatory, about 100 km north of Bangalore. The array has 32 antenna groups and a 1-bit digital correlator system consisting of 1024 channels is used as the back-end receiver. This paper describes the latter and results of the associated system tests.  相似文献   

Modeling and Mapping High Water Table for a Coastal Region in Florida using Lidar DEM Data     

Caiyun Zhang  Hongbo Su  Tiantian Li  Weibo Liu  Diana Mitsova  Sudhagar Nagarajan  Ramesh Teegavarapu  Zhixiao Xie  Fred Bloetscher  Yan Yong 《Ground water》2021,59(2):190-198

Predicting and mapping high water table elevation in coastal landscapes is critical for both science application projects like inundation risk analysis and engineering projects like pond design and maintenance. Previous studies of water table mapping focused on the application of geostatistical methods, which cannot predict values beyond an observation spatial domain or generate an ideal pattern for regions with sparse measurements. In this study, we evaluated the multiple linear regression (MLR) and support vector machine (SVM) techniques for high water table prediction and mapping using fine spatial resolution lidar-derived Digital Elevation Model (DEM) data, and designed an application protocol of these two techniques for high water table mapping in a coastal landscape where groundwater, tide, and surface water are related. Testing results showed that SVM largely improved the high water table prediction with a mean absolute error (MAE) of 1.22 feet and root mean square error (RMSE) of 2.22 feet compared to the application of the ordinary Kriging method which could not generate a reasonable water table. MLR was also promising with a MAE of around 2 feet and RMSE of around 3 feet. The study suggests that both MLR and SVM are valuable alternatives to estimate high water table elevation in Florida. Fine resolution lidar DEMs are beneficial for high water table prediction and mapping.  相似文献   

Multivariate water quality assessment from the Tamiraparani river basin,Southern India     

P. Kumarasamy  R. Arthur James  Hans-Uwe Dahms  Chan-Woo Byeon  R. Ramesh 《Environmental Earth Sciences》2014,71(5):2441-2451

The hydrochemistry of a perennial river has been investigated with multivariate cluster analysis (CA) and principal component analysis/factor analysis (PCA/FA). The aim was to investigate parameters responsible for spatial and temporal variations of river water quality. Water quality was monitored along the river basin at 20 different sites over a period of 1 year from July, 2008 to June, 2009. Multivariate statistics revealed that Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃ ^?, Cl^?, H₄SiO₄, SO₄ ^2?, NO₂ ^?, and PO₄ ^3? were influenced by seasonal and spatial variations and that water quality was in the first place determined more by natural weathering processes than by anthropogenic activities. We could prove by (a) Box and Whisker plot, (b) matrix scatter score mean plot, (c) ternary plot, and (d) Gibbs plot that the chemistry of river water is controlled by lithogenic weathering processes. The higher concentration of dissolved silica during summer and the pre-monsoon season is explained by natural and tropical climatic conditions of the environment.  相似文献   

Revisit to graphite-tungsten deposits of East Godavari district,Andhra Pradesh     

Ramesh M. Umathay  Anil M. Pophare 《Journal of the Geological Society of India》2014,84(4):417-430

The graphite-tungsten deposits under consideration in this study are located in the Burugubanda, Pydiputta, Tapasikonda, Marripalem and Madyaratigudem areas of the East Godavari district of Andhra Pradesh, India. These deposits were formed due to wide spread tectonothermal events associated with the evolution of Eastern Ghats Mobile Belt (EGMB). The graphite deposits of East Godavari district are epigenetic, rhombohedral fluid deposited type and are one of the four deposits of such type reported so far from Srilanka, Spain and England. The graphite deposits were formed due to granodioritic intrusion into the Narsipatnam shear zone, which caused migmatisation of khondalites along with mobilisation and concentration of graphite, as veins and lenses, into the graphite gneisses. The graphite gneisses were subsequently intruded by quartz rich pegmatites that were laden with tungsten mineralisation. The tungsten mineralisation occurs as thin bands, lenses, stringers and vein lets within the quartz matrix and also dispersed in the graphite gneisses. Inclusions of tungsten in graphite indicate that tungsten mineralisation succeeded graphite mineralisation. However, the low P-T phenomenon of tungsten (wolframite-ferberite) mineralisation resulted in low tenor of tungsten ore deposits (WO₃: 0.10%). Rare earth elements (REE) are associated with tungsten mineralisation in these areas. During the present study, these graphite-tungsten deposits have been re-examined, in the backdrop of shelving graphite-tungsten projects in these areas. The feed for mineral beneficiation tests was decided on the basis of dispersion of tungsten in quartz and graphite rich fractions of the ore zone. The feed (ROM material) on beneficiation gave recovery of +75% graphite concentrate, tungsten concentrate of consistent chemical grade, besides recovery of sizeable REE concentrate. It also rendered use of unutilised graphite tailing dumps at beneficiation plants, thereby effecting conservation. Thus, the association of tungsten and REE with the entire graphite deposits along with their value addition during beneficiation, as by-product, revived opportunities to restart graphite mining in the Burugubanda, Pydiputta and Tapasikonda areas in particular and East Godavari district, in general, as an economically viable venture. This will initiate opening of graphite mines in other districts of Andhra Pradesh and energise economics of working graphite mines within EGMB, in the states of Jharkhand, Odisha and Tamil Nadu.  相似文献   

MARSpline model for lead seven-day maximum and minimum air temperature prediction in Chennai,India     

K Ramesh  R Anitha 《Journal of Earth System Science》2014,123(4):665-672

In this study, a Multivariate Adaptive Regression Spline (MARS) based lead seven days minimum and maximum surface air temperature prediction system is modelled for station Chennai, India. To emphasize the effectiveness of the proposed system, comparison is made with the models created using statistical learning technique Support Vector Machine Regression (SVMr). The analysis highlights that prediction accuracy of MARS models for minimum temperature forecast are promising for short term forecast (lead days 1 to 3) with mean absolute error (MAE) less than 1 °C and the prediction efficiency and skill degrades in medium term forecast (lead days 4 to 7) with slightly above 1 °C. The MAE of maximum temperature is little higher than minimum temperature forecast varying from 0.87 °C for day-one to 1.27 °C for lag day-seven with MARS approach. The statistical error analysis emphasizes that MARS models perform well with an average 0.2 °C of reduction in MAE over SVMr models for all ahead seven days and provide significant guidance for the prediction of temperature event. The study also suggests that the correlation between the atmospheric parameters used as predictors and the temperature event decreases as the lag increases with both approaches.  相似文献   

Leaching behavior of lignite fly ash with shake and column tests     

Lal C. Ram  Nishant K. Srivastava  Ramesh C. Tripathi  Sanjay K. Thakur  Awadhesh K. Sinha  Sangeet K. Jha  Reginald E. Masto  Swapan Mitra 《Environmental Geology》2007,51(7):1119-1132

The maximum concentration of the majority of the trace metals in the leachates from shake and column test of lignite fly ash (LFA) was within the prescribed limits; however, total dissolved solids, total hardness, cations and anions (except K⁺), being above the prescribed limits, may lead to the increase in the hardness and salinity in the soil on the disposal of LFA. Present generation of huge amount of fly ash from thermal power plants (TPPs) is a big challenge concerning contamination of soil, crop produce and surface and ground water bodies due to the presence of some of the toxic trace metals in it. The leaching behavior of alkaline LFA (pH, 10.94), from TPP of Neyveli Lignite Corporation (NLC), India, was investigated by shake and column tests using water and sodium acetate buffer. The leaching of trace metals from LFA was governed by their concentrations, association with the ash particles, leaching duration and pH of the leachate (most influencing parameter). The leaching of metals followed the order: buffer column > aqueous column > aqueous shake > buffer shake test.  相似文献   

Absolute Calibration of TOPEX/Poseidon and Jason-1 Using GPS Buoys in Bass Strait, Australia     

Christopher Watson  Richard Coleman  Neil White  John Church  Ramesh Govind 《Marine Geodesy》2003,26(3):285-304

An absolute calibration of the TOPEX/Poseidon (T/P) and Jason-1 altimeters has been undertaken during the dedicated calibration phase of the Jason-1 mission, in Bass Strait, Australia. The present study incorporates several improvements to the earlier calibration methodology used for Bass Strait, namely the use of GPS buoys and the determination of absolute bias in a purely geometrical sense, without the necessity of estimating a marine geoid. This article focuses on technical issues surrounding the GPS buoy methodology for use in altimeter calibration studies. We present absolute bias estimates computed solely from the GPS buoy deployments and derive formal uncertainty estimates for bias calculation from a single overflight at the 40-45 mm level. Estimates of the absolute bias derived from the GPS buoys is -10 ± 19 mm for T/P and +147 ± 21 mm for Jason-1 (MOE orbit) and +131 ± 21 mm for Jason-1 (GPS orbit). Considering the estimated error budget, our bias values are equivalent to other determinations from the dedicated NASA and CNES calibration sites.  相似文献