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31.
Sarkar K. Chakraborty C. Mazumder B. S. 《Stochastic Environmental Research and Risk Assessment (SERRA)》2015,29(3):995-1017
Stochastic Environmental Research and Risk Assessment - This work presents a study of spatiotemporal changes of scour-holes around sand embedded submerged circular and non-circular cylinders with... 相似文献
32.
John-Mark Davies Weston H. Nowlin Blake Matthews Asit Mazumder 《Aquatic Sciences - Research Across Boundaries》2010,72(4):393-402
Ideas on how various measures of nutrient limitation relate to plankton biomass and species composition are re-examined. While
long-term and multi-lake studies typically focus on determining overall biomass, seasonal studies are more focused toward
understanding species composition. We use physiological assays to assess short-term nutrient deficiency of nitrogen and phosphorus
in two moderately fertile lakes. While biomass in the lakes was considered to ultimately be limited by total phosphorus, nutrient
assays were variable in time. Nutrient ratios (TN:TP, PN:PP, PC:PP and PC:PN) did not predict short-term deficiencies, notably
that nitrogen deficiency occurred in these phosphorus-limited lakes. In one of our study lakes, there was a relaxation of
phosphorus deficiency despite phosphate concentrations occurring below traditional detection limits. Following this period,
there was an autumn bloom of Aphanizomenon flos-aquae. This relationship corresponds with other studies that have found A. flos-aquae to be a poor competitor for phosphorus. In contrast, phosphorus deficiency remained high prior to the autumn diatom bloom
in our other study lake. Deficiency measures remain an excellent means of assessing physiological status of plankton communities
and provide greater insight into species compositional changes, especially when other potential indicators like dissolved
nutrient concentrations are inconclusive. Regardless of the nutrient limitation indicator used for a given study, it is critical
to consider the appropriate scale of the measure. 相似文献
33.
This paper addresses the development of a flow region associated with turbulence and stress characteristics over a series of 2-D asymmetric dunes placed successively at the flume surface. Experiments were conducted over twelve asymmetric dunes of mean length 32 cm, crest height 3 cm and the dune width almost as wide as width of the flume, using 3-D Micro-ADV at the Indian Statistical Institute, Calcutta. The variations of turbulence statistics along the flow affected by the wavy bottom roughness have been studied. Quadrant decomposition of the instantaneous Reynolds shear stress has been adopted to calculate the contribution of ejection and sweeping events in shear stress generation. The relative dominance of two events are found to contribute in a cyclic manner (spatially) in the near bed region, whereas such phenomenon seems to be disappeared towards the main flow. 相似文献
34.
Anirban?BiswasEmail author Arabinda?Das Debasree?Deb Aloke?Ghose Debendra?Nath?Guha Mazumder 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(4):1035-1050
Inorganic arsenic is a carcinogen and consumption in low dose may lead to cancer. We estimated the cancer risk of the participants from arsenic endemic regions of West Bengal, India. The probable cancer risk was estimated following the assessment of daily inorganic arsenic intake through drinking water and diets of 20 participants for three consecutive years who had been using low arsenic water in the Indian context (median arsenic concentration in the study Years-I, II and III were 22, 16, 13 µg/l respectively). Probable cancer risk of the population was 2.80 × 10?4, 2.94 × 10?4, 3.12 × 10?4 in the three respective study years (Year-I, II and III); just higher than the US EPA risk level of concern. The arsenic species content of the paired raw, cooked rice and urine was estimated in the as is taken basis. The major diet component, rice contained 72–86% inorganic arsenic whereas urine contains 70% organic arsenic on an average. The cancer risk assessment has been proposed to be modified by inclusion of urine arsenic release, considering the fact of arsenic release through urine. The risk became 1.28 × 10?5, 1.13 × 10?5, 1.01 × 10?5 in the study Year-I, II and III respectively, considering urinary arsenic release, attributed the consideration of urine arsenic release into probable cancer risk estimation. 相似文献
35.
The relation between grain-size distribution of the bed and in suspension was critically examined under a uniform flow velocity of 50 cm/s over two beds: one of mainly fine sands and the other of medium sands. Two sections – one 2.85 m downstream and the other 6.35 m downstream in the experimental channel-were selected for sampling to study the grain-sorting pattern in the vertical direction along the direction of transport. The shape and type of the grain-size distribution pattern were critically studied with height above the bed. The change in the distribution pattern has been attributed to the change of local bed roughness causing scouring against the protruded relatively coarse grains on the bed. Such trends are important to predict the nature of river bed topography. The sand of Bed-1 initially exhibits a log-skew-Laplace distribution at different heights of suspension. The distribution pattern, however, changes but this changing pattern is not consistent along the upstream side. For Bed-2, which initially exhibits a log-normal distribution, the same pattern persists from the height of suspension at 5 cm up to 20 cm. Such consistency in log-normality is also observed at the downstream points of measurement. It is generally expected that the mean grain-size would reduce with increases of suspension height but the results of the experiments, in some occasions, differ significantly from the gradual fining upward trend. This result has been attributed to local changes of bed roughness arising from the protruded relatively coarse grains causing eddies, scouring, and turbulent phenomena which moves coarse particles higher in suspension adding a coarse tail to the distribution increasing the mean grain-size. 相似文献
36.
Rakesh Mazumder 《天文和天体物理学研究(英文版)》2019,(6):43-50
A filament is a cool, dense structure suspended in the solar corona. The eruption of a filament is often associated with a coronal mass ejection(CME), which has an adverse effect on space weather. Hence,research on filaments has attracted much attention in the recent past. The tilt angle of active region(AR)magnetic bipoles is a crucial parameter in the context of the solar dynamo, which governs the conversion efficiency of the toroidal magnetic field to poloidal magnetic field. Filaments always form over polarity inversion lines(PILs), so the study of tilt angles for these filaments can provide valuable information about generation of a magnetic field in the Sun. We investigate the tilt angles of filaments and other properties using McIntosh Archive data. We fit a straight line to each filament to estimate its tilt angle. We examine the variation of mean tilt angle with time. The latitude distribution of positive tilt angle filaments and negative tilt angle filaments reveals that there is a dominance of positive tilt angle filaments in the southern hemisphere and negative tilt angle filaments dominate in the northern hemisphere. We study the variation of the mean tilt angle for low and high latitudes separately. Investigations of temporal variation with filament number indicate that total filament number and low latitude filament number vary cyclically, in phase with the solar cycle. There are fewer filaments at high latitudes and they also show a cyclic pattern in temporal variation. We also study the north-south asymmetry of filaments with different latitude criteria. 相似文献
37.
A total of 25 surficial sediment samples (Peterson grab, gravity and piston cores), collected during the Pilot Expedition
to Southern Ocean (PESO) 2004 cruises 199C and 200 onboard the ORV Sagar Kanya along a N–S transect between 9.69°N and 55.01°S, and 80 and 40°E in the Indian Ocean sector of the Southern Ocean (SW Indian
Ocean), have been investigated for various morphological features—test size, mean proloculus size and coiling direction (dextral/sinistral
forms)—of the planktic indicator species Neogloboquadrina pachyderma (Ehrenberg). The results show that the coiling directions co-vary with temperature and salinity, the abundances of sinistrally
coiled forms increasing towards higher latitudes (south of 40°S), whereas dextrally coiled forms show a reverse trend. Similarly,
overall test and proloculus sizes depend largely on the physicochemical properties (salinity, temperature, nutrients, calcium
saturation) of the ambient water masses. These observations suggest that, particularly at the boundaries between different
water masses, variations in morphological features of N. pachyderma can meaningfully be used to reconstruct paleoceanographic conditions from Indian Ocean sediments. 相似文献
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39.
Md. Abu Sayeed Mostafa Ali Reza Hossain Md. Abdul Wahab Md. Tawheed Hasan Kumar Das Simon Sabuj Kanti Mazumder 《中国海洋湖沼学报》2015,33(4):895-904
A study was conducted to investigate the status of the water and sediment quality in the Chalan Beel——a major fresh water fish reservoir of the country for a period of one year from July 2007 to June 2008. The mean values of water quality parameters(depth: 214.73±152.22 cm, temperature 27.68±4.26℃, transparency 123±82 cm, p H 9.7±0.47, total alkalinity 137±42 mg/L, conductivity 307±147 μs/cm, total dissolved solids 183±89 mg/L, ammonia-N 0.27±0.39 mg/L, nitrate-N 0.09±0.07 mg/L, phosphate-P 2.01±2.53 mg/L) and sediment quality parameters(p H 7.21±0.35, organic matter 2.59±0.52%, total nitrogen 0.09±0.04%, available phosphorus 5.4±3.6 Meq./100 g and exchangeable potassium 0.43±0.14 Meq./100 g) were within the range recommended for most of the inland fishes of Bangladesh. Although the water and sediment quality parameters except ammonia and phosphate are in the suitable range, the overall results suggest that better management techniques should be practiced in order to overcome the declining trend of associated aquatic life(fauna and flora) of this important fresh water body of Bangladesh. 相似文献
40.
A total of 103 surface sediment samples collected from the water depth range of 15—3300 m along Vijaydurg-Karwar stretch of central west coast of India were analyzed for foraminiferal content. Relict benthic foraminiferal assemblage was noted within 50—135 m water depth.The relict benthic foraminiferal assemblage that includes Amphistegina,Operculum and Alveolinetta in sediment samples within the water depth of 85—135 m indicates presence of coral reef at this depth during Early Holocene. The presence of barnacle fouling on Relict foraminifera at 60—90 m confirms the paleo-shoreline. The shallow depth zone is characterized by presence of agglutinated relict foraminifera.The agglutinated forms indicate freshwater influx,which eventually increased the sea level and subsequently deteriorated the paleo-coral reef. 相似文献