Gravitational collapse of a circularly symmetric star in an anti-de Sitter spacetime     

Ranjan Sharma  Shyam Das  Farook Rahaman  Gopal Chandra Shit 《Astrophysics and Space Science》2015,357(1):1-9

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Evidence of Meteoroid Fragmentation in Specular Trail Echoes Observed Using Gadanki MST Radar     

A. Patil  A. Malhotra  A. K. Patra  T. R. Prasad  J. D. Mathews 《Earth, Moon, and Planets》2015,114(3-4):89-99

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Automated star–galaxy segregation using spectral and integrated band data for TAUVEX/ASTROSAT satellite data pipeline     

Archana Bora  Ranjan Gupta  Harinder P. Singh  K. Duorah 《New Astronomy》2009,14(8):649-653

We employ an Artificial Neural Network (ANN) based technique to develop a pipeline for automated segregation of stars from the galaxies to be observed by Tel-Aviv University Ultra-Violet Experiment (TAUVEX). We use synthetic spectra of stars from UVBLUE library and selected International Ultraviolet Explorer (IUE) low-resolution spectra for galaxies in the ultraviolet (UV) region from 1250 to 3220 Å as the training set and IUE low-resolution spectra for both the stars and the galaxies as the test set. All the data sets have been pre-processed to get band integrated fluxes so as to mimic the observations of the TAUVEX UV imager. We also perform the ANN based segregation scheme using the full length spectral features (which will also be useful for the ASTROSAT mission). Our results suggest that, in the case of the non-availability of full spectral features, the limited band integrated features can be used to segregate the two classes of objects; although the band data classification is less accurate than the full spectral data classification.  相似文献   

Relative performances of central and dipole frequency soundings over a layered earth     

H. P. Patra  N. L. Shastri 《Pure and Applied Geophysics》1982,120(3):527-537

Variable frequency soundings in the audio-range replaces shallow conventional direct current methods for determination of layer parameters when surface layer resistivity is high. Central frequency soundings (CFS) is one such method that involves measurement of the existing vertical magnetic field component induced at the centre of a horizontal circular or square loop. Dipole method of frequency sounding using small horizontal coplanar loops (abbreviated DFS) measuring the same field component is also considered. Theoretical studies on CFS and DFS over two- and three-layer horizontally stratified earth are carried out and the response characteristics computed and analysed.Theoretical response curves for CFS and DFS over two- and three-layer earth models are presented in convenient forms. Response curves under similar geological-physical conditions are compared. The study indicates that the relative superiority of a method is controlled largely by the nature of the conductivity contrast and the ratio of the first layer thickness to loop radius or dipole separation. While CFS shows a better resolution of conductivity contrast, DFS works better at high frequencies. For resistive substratum, however, both lack proper resolution.  相似文献   

Electrokinetic retention, migration and remediation of nitrates in silty loam soil under hydraulic gradients   总被引：1，自引：0，他引：1  

Krishnapillai Manokararajah  Ramanathan Sri Ranjan   《Engineering Geology》2005,77(3-4):263-272

Contamination of groundwater by nitrates leaching from intensive agricultural and livestock operations have become a major concern for surrounding communities that use groundwater as their water supply. High levels of nitrate in drinking water poses a significant risk to human health, i.e., methaemoglobinaemia (“blue baby” syndrome).

The traditional pump-and-treat method is ineffective in medium to fine-textured agricultural soils due to the low hydraulic conductivity. This paper presents the results of a laboratory experiment investigating the feasibility of using electrokinetic treatment in retaining, accumulating, moving and remediating nitrates in a silty loam soil under hydraulic gradients.

A hydraulic gradient of 1.25 was applied to the horizontal soil columns to simulate a groundwater movement system. The study was performed in two stages. During the first stage of the experiment, the anode located at the inflow end of the columns was able to retard the movement of nitrates even under a hydraulic gradient of 1.25. After 15 days of flow, the effluent nitrate concentration in the control column rose to 90 mg l⁻¹ while no nitrates were detected in the effluent from columns subjected to the electrokinetic treatment.

After 15 days, the polarity of the electrodes was switched and this second stage lasted another 20 days. The cathode near the inflow end promoted the conversion of nitrates entering the column to other forms. The anode near the outflow end promoted the migration and accumulation of negatively charged nitrate ions towards the outflow end. By the 12th day, the nitrate concentrations in the electrokinetically treated columns were brought down to <5 mg NO₃-N l⁻¹. Electrokinetic treatment retarded nitrate movement against a hydraulic gradient of 1.25 and effectively restored a medium-textured soil contaminated with NO₃-N.

The NO₂-N level remained below 1 mg l⁻¹ throughout the experiment. The hydraulic conductivity varied between 1.0E–7 and 3.6E–7 m s⁻¹. The current requirement varied between 3 and 6 mA.  相似文献   

Water quality assessment of Gautami — Godavari mangrove estuarine ecosystem of Andhra Pradesh, India during September 2001     

S. C. Tripathy  A. K. Ray  S. Patra  V. V. Sarma 《Journal of Earth System Science》2005,114(2):185-190

Some chemical and biological parameters were analysed at sixteen stations in the mangrove ecosystem, of the neighbouring Gautami-Godavari (GG) river estuary and Kakinada (KKD) bay to understand the present status of water quality and the impact of external terrigenous inputs during southwest (SW) monsoon in the study areas. High concentrations of nutrients in the mangrove ecosystem compared to the bay and estuarine ecosystems reveal the importance of this zone as a source of nutrients to the adjacent coastal ecosystems. Low Si:N:P (29:4:1) ratios in these ecosystems are due to the enrichment of these nutrients through external anthropogenic inputs even after the utilization by phytoplankton in the biological cycle. The mean Chl b/Chla and Chl c/Chla ratios and high phaeopigments (Pp) concentrations compared to Chlb and high ratios of Chl a/Pp suggests the possibility of the potential growth of phytoplankton populations in lower light intensity and low turbulent areas of these mangrove ecosystems.  相似文献   

Investigation of Hemispherical Variations of Soft X-Ray Solar Flares during Solar Cycles 21 to 24     

Prasad  Amrita  Roy  Soumya  Ghosh  Koushik  Panja  Subhash Chandra  Patra  Sankar Narayan 《Solar System Research》2021,55(2):169-182

Solar System Research - In the current investigation we have studied the distribution as well as the asymmetry of solar X-ray flares during the period 1976–2017 which corresponds to solar...  相似文献   

Numerical and experimental investigations on inelastic cyclic performance of mid‐span gusset plate connections          下载免费PDF全文

P. C. Ashwin Kumar  Dipti Ranjan Sahoo 《地震工程与结构动力学》2018,47(9):1921-1941

The design and detailing of gusset plate connections greatly influence the seismic performance of a special concentrically braced frame (SCBF). Recently, a balanced design approach has been proposed in order to develop significant inelastic deformation from multiple yield mechanisms and to delay the failure of connections of SCBF system. Although extensive studies have been conducted on the corner gusset plate connections of SCBFs, research on the detailing of mid‐span beam gusset plates is rather limited. This study aims at investigating the required free length for the detailing of the mid‐span gusset plates with different brace slenderness ratios. A nonlinear finite element analysis has been conducted for a braced frame with 4 different values of linear clearance in the mid‐span gusset plates and 2 values of brace slenderness ratios. In all simulation models, the corner gusset plates have been designed using balanced design approach and detailed using an elliptical clearance of 8 times the gusset plate thickness. An experimental study has also been conducted on 2 gusset plate sub‐assemblages having similar brace slenderness ratio but with 2 different values of linear clearance in the middle gusset plates. The lateral drift capacity corresponding to the brace fracture and the level of damage are found to be dependent on the detailing of the gusset plates. Based on the results of numerical and experimental studies, the required free length has been recommended for the detailing of middle gusset plates of SCBFs of different brace slenderness ratios.  相似文献   

Switch in chemical weathering caused by the mass balance variability in a Himalayan glacierized basin: a case of Chhota Shigri Glacier     

Naveen Kumar  Martyn Tranter  Parmanand Sharma  Manish Pandey  Prabhat Ranjan 《水文科学杂志》2019,64(2):179-189

Long-term data (2003–2015) on meltwater chemistry, mass balance and discharge of a benchmark glacier (Chhota Shigri Glacier, India) were studied to determine any association between these variables. To infer the factors governing the alteration of chemical weathering processes in glacierized basins, multi-annual records of the hydrochemical indices (Ca²⁺+Mg²⁺/Na⁺+K⁺) and the C-ratio were also examined. A succession of negative mass balance years has resulted in a decline in solute concentrations in the runoff, as discharge has increased. The (Ca²⁺+Mg²⁺/Na⁺+K⁺) and C-ratio are highest during periods of negative annual mass balance, when the spatial extent of the channelized drainage system increases. Conversely, these ratios are lowest in positive mass balance years, when the spatial extent of the channelized drainage system decreases, and chemical weathering in the distributed drainage system becomes more dominant. This paper is the first to show the inter-annual linkages between meltwater chemistry, mass balance and discharge for a valley glacier.  相似文献   

GIS based spatial data analysis for landslide susceptibility mapping   总被引：5，自引：4，他引：1  

S. Sarkar  D. P. Kanungo  A. K. Patra  Pushpendra Kumar 《山地科学学报》2008,5(1):52-62

Landslide susceptibility map delineates the potential zones for landslides occurrence. The paper presents a statistical approach through spatial data analysis in GIS for landslide susceptibility mapping in parts of Sikkim Himalaya. Six important causative factors for landslide occurrences were selected and corresponding thematic data layers were prepared in GIS. Topographic maps,satellite image,field data and published maps constitute the input data for thematic layer preparation. Numerical weights for different categories of these factors were determined based on a statistical approach and the weighted thematic layers were integrated in GIS environment to generate the landslide susceptibility map of the area. The landslide susceptibility map classifies the area into five different landslide susceptible zones i.e.,very high,high,moderate,low and very low. This map was validated using the existing landslide distribution in the area.  相似文献