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Sourav Palit Sandip Kumar Chakrabarti Dipak Debnath A. R. Rao Anuj Nandi Vipin K. Yadav V. Girish 《Experimental Astronomy》2009,27(1-2):77-93
We present the results of simulations of shadows cast by a zone plate telescope which may have one to four pairs of zone plates. From the shadows we reconstruct the images under various circumstances. We discuss physical basis of the resolution of the telescope and demonstrate this by our simulations. We allow the source to be at a finite distance (diverging beam) as well as at an infinite distance (parallel beam) and show that the resolution is worsened when the source is nearby. By reconstructing the zone plates in a way that both the zone plates subtend the same solid angles at the source, we obtain back high resolution even for sources at a finite distance. We present simulated results for the observation of the galactic center and show that the sources of varying intensities may be reconstructed with accuracy. Results of these simulations would be of immense use in interpreting the X-ray images from recently launched CORONAS-PHOTON satellite. 相似文献
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Dipankar Chakraborti Mohammad Mahmudur Rahman Bhaskar Das Amit Chatterjee Dipankar Das Biswajit Nayak Arup Pal Uttam Kumar Chowdhury Sad Ahmed Bhajan Kumar Biswas Mrinal Kumar Sengupta Md. Amir Hossain Gautam Samanta M. M. Roy Rathindra Nath Dutta Khitish Chandra Saha Subhas Chandra Mukherjee Shyamapada Pati Probir Bijoy Kar Adreesh Mukherjee Manoj Kumar 《Hydrogeology Journal》2017,25(4):1165-1181
During a 28-year field survey in India (1988–2016), groundwater arsenic contamination and its health effects were registered in the states of West Bengal, Jharkhand, Bihar and Uttar Pradesh in the Ganga River flood plain, and the states of Assam and Manipur in the flood plain of Brahamaputra and Imphal rivers. Groundwater of Rajnandgaon village in Chhattisgarh state, which is not in a flood plain, is also arsenic contaminated. More than 170,000 tubewell water samples from the affected states were analyzed and half of the samples had arsenic >10 μg/L (maximum concentration 3,700 μg/L). Chronic exposure to arsenic through drinking water causes various health problems, like dermal, neurological, reproductive and pregnancy effects, cardiovascular effects, diabetes mellitus, diseases of the respiratory and gastrointestinal systems, and cancers, typically involving the skin, lungs, liver, bladder, etc. About 4.5% of the 8,000 children from arsenic-affected villages of affected states were registered with mild to moderate arsenical skin lesions. In the preliminary survey, more than 10,000 patients were registered with different types of arsenic-related signs and symptoms, out of more than 100,000 people screened from affected states. Elevated levels of arsenic were also found in biological samples (urine, hair, nails) of the people living in affected states. The study reveals that the population who had severe arsenical skin lesions may suffer from multiple Bowens/cancers in the long term. Some unusual symptoms, such as burning sensation, skin itching and watering of eyes in the presence of sun light, were also noticed in arsenicosis patients. 相似文献
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K. Vinod Kumar Arup Palit A. K. Chakraborti S. K. Bhan 《Journal of the Indian Society of Remote Sensing》1994,22(4):195-201
Conventional techniques of monitoring both long-term and short-term changes in river morphology is time consuming and expensive. Remote sensing with its synoptic and temporal capability is an effective tool to study river metamorphosis. The present study is carried out in lower Ganga basin where Hooghly river is an important river contributing sediment to this vast fertile plain. A time series planform analysis is carried out between 1971 to 1991 period. Thematic maps generated from Landsat MSS and IRS-IA LLSS-I satellite data for 1986 and 1991 period respectively is compared with 1971 topographic maps. The migratory character of paleocourse of Hooghly river is deciphered through the paleochannels, oxbow takes and meander scars deciphered from satellite imagery. The shortterm river metamorphosis like cut-offs, bar migration and point bar accretion morphology are mapped and compared with 1971 topographic maps. The critical zone with respect to cut-offs and future channel migration are identified for river stabilization work. 相似文献
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The India Remote Sensing data on 1:50,000 scale revealed the occurrence of permanent waterlogging in low-lying flats and depressions
of the Indira Gandhi Nahar Pariyojona (IGNP) command area. Such data also indicated seasonal dynamics of waterlogging and
soil salinization (Salt efflorescence/crusting) in irrigated areas. Mixed spectral signatures of high moisture content and
poor crop stand indicated the presence of shallow aquifers close to the main canal. Digital analysis facilitated some indicators
for segregating such land uses, limited to optical range. Ground truth study found patchy crop stand, moist soil profile and
subsurface soil salinization indicating the presence of high water table (<1.5 m). It also found fluctuating (1.5–6.0 m) water
table with poor vegetative growth indicating areas sensitive to waterlogging These were classified as potential waterlogging.
Moderate to high soil salinity was found at surface and at the control section (0.2–0.8 m) of soil profiles indicating initiation
of secondary salinization. Coarse to medium soil texture facilitated capillary rise of salts with the advancing water table
in irrigated zone. The presence of fine textured and impermeable calcium carbonate layers at a depth below the surface enhanced
waterlogging and rise of water table. The preponderance of chlorides and sulfates of sodium, calcium and magnesium was found
in the salinized areas. The quality of ponded water was extremely poor and unfit for its reuse. The ground water was saline
in some areas but normally lies within the prescribed limit. The quality of drainage water was poor in saline depression and
unsuitable for reuse. These were moderate in other areas suggesting its safe reuse if mixed with good quality water. Suitable
soil and water management practices are necessary for sustainable crop production in the irrigated areas 相似文献
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Dipankar Chakraborti Mohammad Mahmudur Rahman Bhaskar Das Bishwajit Nayak Arup Pal Mrinal Kumar Sengupta Md. Amir Hossain Sad Ahamed Manabendranath Sahu Kshitish Chandra Saha Subhash Chandra Mukherjee Shyamapada Pati Rathindra Nath Dutta Quazi Quamruzzaman 《Environmental Earth Sciences》2013,70(5):1993-2008
The authors’ survey of the Ganga–Meghna–Brahmaputra (GMB) plain (area 569,749 km2; population >500 million) over the past 20 years and analysis of more than 220,000 hand tube-well water samples revealed groundwater arsenic contamination in the floodplains of the Ganga–Brahmaputra river (Uttar Pradesh, Bihar, Jharkhand, West Bengal, and Assam) in India and the Padma–Meghna–Brahmaputra river in Bangladesh. On average, 50 % of the water samples contain arsenic above the World Health Organization guideline value of 10 μg/L in India and Bangladesh. More than 100 million people in the GMB plain are potentially at risk. The authors’ medical team screened around 155,000 people from the affected villages and registered 16,000 patients with different types of arsenical skin lesions. Arsenic neuropathy and adverse pregnancy outcomes have been recorded. Infants and children drinking arsenic-contaminated water are believed to be at high risk. About 45,000 biological samples analyzed from arsenic-affected villages of the GMB plain revealed an elevated level of arsenic present in patients as well as non-patients, indicating that many are sub-clinically affected. In West Bengal and Bangladesh, there are huge surface water in rivers, wetlands, and flooded river basins. In the arsenic-affected GMB plain, the crisis is not over water scarcity but about managing the available water resources. 相似文献
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Turbulent flow structures and geomorphic characteristics of a mining affected alluvial channel 
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下载免费PDF全文 Sediment mining in rivers may have a major impact on river geomorphology and research is required to quantify these impacts. In this research, experimental studies were conducted to analyse the morphological changes of channel bed and the turbulent characteristics of flow in the presence of mining. The channel bed profile shows erosion at the bank of the pit and that the erosion expands to the whole width of the channel and propagates downstream with time. The deposition of sediment occurs along the upstream edge of the pit and the depth of the pit decreases with time. Velocity reversal occurs at the central bottom of the pit related to a recirculation zone. Reynolds shear stress and the turbulent intensities become higher in the mining pit region and downstream of it as compared to the upstream section, causing a more rapid movement of bed particles. Analysis of the bursting phenomenon shows that the contribution of sweep and ejection events to the total Reynolds shear stress is more dominant over outward and inward interaction events. The dominance of the sweep event over ejection is observed at the near‐bed region for all the sections, but the depth range of dominance of sweep events in the pit and downstream of the pit is found to be more than the upstream. The increase in thickness is responsible for the increase in bed material transport. The increased sediment transport capacity at the mining pit and downstream of it caused the deformation and lowering of channel bed downstream. An empirical formulation of bedload transport for mining induced channels is derived from two different sized uniform bed materials. Copyright © 2018 John Wiley & Sons, Ltd. 相似文献
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Research on in-channel sand mining is imperative as it may have a significant impact on channel morphology. Following this quest to quantitatively comprehend the phenomenon, experimental studies were done to investigate the dynamic characteristics of the migration of a mining pit. The evaluation of the migration rate of a mining pit in a physical scale model has found a rise in the migration rate of the pit's upstream edge with increasing discharge. A wavelet analysis applied for analyzing scale-dependent migration of the bed profile of a mining pit also revealed similar findings. Additionally, the wavelet analysis examined the length-scale dependent migration of a mining pit and a decrease in the migration rate has been observed with an increase in the length scale. The plan form of a pit (length-to-width ratio) governs the erosion and deposition processes around the pit. Both physical and statistical approaches show an increase in the migration rate with an increase in the length-to-width ratio of the pit. An empirical formulation has been developed for calculating the migration rate of the upstream edge of a mining pit based on pit geometry (length-to-width ratio), average flow velocity, and critical shear stress of the bed material. The results also show a higher bed load transport rate in the channel subjected to mining as compared to a plain bed channel. 相似文献
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