排序方式： 共有32条查询结果，搜索用时 31 毫秒
21.
J. K. Biswas B. Bera R. Chanda S. K. Sarkar J. Majumdar S. Majumder S. Hazra 《International Journal of Environmental Science and Technology》2018,15(9):1867-1878
Lakes are functionally integral and biologically complex freshwater ecosystems which provide a vast array of ecosystem goods and services to society. Nowadays aquatic ecosystems are being used, misused and abused by diverse anthropogenic activities at an unprecedented rate. The management of lake water quality is usually directed to resolution of conflicts between maintenance of desirable water quality and human-induced degradation of aquatic environment. Nutrients play a decisive role in determining lake’s environmental state through regulation of its primary production. The present study on Saheb Bundh Lake located in Purulia District, West Bengal, India, was undertaken to assess the status of nutrients (nitrogen and phosphorus) subject to certain anthropogenic activities, and to construct models using best subset method which could be adopted as a nutrient management tool. The water samples were monitored for different physicochemical parameters adopting standard methods. It was found that the set of variables including turbidity, temperature, pH, redox potential and total hardness has been championed as the best subset of water quality explaining the dynamics of total phosphorus concentration of freshwater Saheb Bundh Lake. The suite of factors comprising dissolved oxygen, pH, temperature, turbidity and total hardness has been proved as the best subset for estimating total nitrogen concentration. The models developed have been validated for total phosphorus and total nitrogen concentration. For total phosphorus, the model values were found to be very close to the measured values but the values varied widely for total nitrogen, championing the former as a very potent down-to-earth model. 相似文献
22.
S. K. Mandal N. Majumder C. Chowdhury D. Ganguly M. Dey T. K. Jana 《Environmental Earth Sciences》2012,65(7):2027-2036
Elevated concentrations of arsenic in the sediment and pore water in the Sundarban wetlands pose an environmental risk. Adsorption
and desorption are hypothesized to be the major processes controlling arsenic retention in surface sediment under oxic/suboxic
condition. This study aims to investigate sorption kinetics of As(III & V) and its feedback to arsenic mobilization in the
mangrove sediment. It ranges from sand to silty clay loam and shows the adsorption of As(III & V) following the Langmuir relation.
Estimates of the maximum adsorption capacity are 59.11 ± 13.26 μg g−1 for As(III) and 58.45 ± 8.75 μg g−1 at 30°C for As(V) in the pH range 4 to 8 and salinity 15–30 psu. Extent of adsorption decreases with increasing pH from 4
to 8 and desorption is the rate-limiting step in the reaction of arsenic with sediment. Arsenic in the sediment could be from
a Himalayan supply and co-deposited organic matter drives its release from the sediment. Arsenic concentration in the sediment
is well below its maximum absorption capacity, suggesting the release of sorbed arsenic in pore water by the microbial oxidation
of organic matter in the sediment with less feedback of adsorption. 相似文献
23.
Himadri Sekhar Das Abinash Suklabaidya Saonli Datta Majumder Asoke Kumar Sen 《中国天文和天体物理学报》2010,10(4)
The observed linear polarization data of comet Hyakutake are studied at wavelengths λ=0.365 μm,λ=0.485 μm and 0.684 μm through simulations using Ballistic Particle-Cluster Aggregate and Ballistic Cluster-Cluster Aggregate aggregates of 128 spherical monomers.We first found that the size parameter of the monomer,x～1.56-1.70,turned out to be the most suitable which provides the best fits to the observed dust scattering properties at three wavelengths:λ=0.365 μm,0.485 μm and 0.684 μm.Thus,the effective radius of the aggregate(r)lies in the range 0.45 μm ≤ r≤ 0.49 μm at λ=0.365 μm;0.60μm < r < 0.66 μm at λ=0.485 μmand 0.88 μm < r < 0.94 μm at λ=0.684 μm.Now using superposition T-MATRIX code and the power-law size distribution,n(r)～r-3,the best-fitting values of complex refractive indices are calculated for the observed polarization data at the above three wavelengths.The best-fitting complex refractive indices(n,k)are found to be (1.745,0.095)at λ=0.365 μm,(1.743,0.100)at λ=0.485 μm and(1.695,0.100)at λ=0.684 μm.The refractive indices derived from the present analysis correspond to a mixture of both silicates and organics,which are in good agreement with the in situ measurement of comets by different spacecraft. 相似文献
24.
Mirza A. T. M. Tanvir Rahman Ratan Kumar Majumder Syed Hafizur Rahman Md. Abdul Halim 《Environmental Earth Sciences》2011,63(2):363-373
Twenty groundwater samples were collected from two different areas in Satkhira Sadar Upazila to identify the source of salinity
in deep groundwater aquifer. Most of the analyzed groundwater is of Na–Cl–HCO3 type water. The trends of anion and cation are Cl− > HCO3
− > NO3
− > SO4
2− and Na+ > Ca2+ > Mg2+ > K+, respectively. Groundwater chemistry in the study area is mainly governed by rock dissolution and ion exchange. The dissolved
minerals in groundwater mainly come from silicate weathering. The salinity of groundwater samples varies from ~1 to ~5%, and
its source is possibly the paleo-brackish water which may be entrapped during past geologic periods. 相似文献
25.
Singrauli Coalfield of Central India was studied through analysis of remotely sensed and other available data for evaluation of impact due to mining and related industrial activities on the environment The comparison of scenarios between pre-mining and industeialisatioa periods for a time span of about 100 years depicted through multilevel-multidata remotely sensed and other available data reveals that the face of entire Singrauli coalfield has changed progressively especially with the establishment of mining, hydel power project, thermal power stations and related industrial units. This has resulted in increasing urbanisation, transportation and communication network during the present years. A few measures against the environmental threat are also suggested to minimise the various effects of hazards and to uphold symbiosis in the eco-sphere. 相似文献
26.
Multiresolution tectonic features over the Earth inferred from a wavelet transformed geoid 总被引：2，自引：0，他引：2
Geoid signals give information about the underlying density structure and can be used to locate the source depth of the mass anomalies. Wavelet analysis allows a multiresolution analysis of the signal and permits one to zoom into a specific area bounded by a particular length scale. The ability of wavelets to resolve the geoid signal into individual wavelength components without losing the spatial information makes this method superior to the more common spherical harmonic method. The wavelet analysis allows one to zoom into a specific area and look at the regional geology. We have used a wavelet transform of the geoid to study the regional geology of Japan and the Philippine Plate, South America, Europe, North America, East Africa and the Middle East, India and the Himalayas, China and Southeast Asia, and Australia. By filtering the Earth’s geoid anomalies with 2-D Gaussian wavelets at various horizontal length scales, one can detect the subduction zones along South America, the Aleutians, and the western Pacific; the Himalayas; the Zagros Mountains; the Mid-Atlantic ridge; and the island chains of the mid-Pacific. We have processed geoid data with a horizontal resolution down to approximately 200 km. Using an adjustable wavelet, one can detect structures that can only be picked up visually with much higher resolution spherical harmonic gravity data. We have also looked at the wavelength at which the maximum signal occurs over a range of scales. This method, known as E-max and k-max, is especially effective for detecting plate tectonic boundaries and ancient suture zones along with areas of strong non-isostatic gravitational potential due to high differential stress. These areas are likely to be at high risk of earthquakes. These methods will be especially useful to future studies of the geoid potentials of other planets, such as Mars and Venus, since they will allow careful studies of the regional geology variations with geoid data of the resolution available from satellites. 相似文献
27.
Phosphorus (P) cycling in mangroves plays an important role in productivity but the magnitude of atmospheric input in the mangrove P budget is still uncertain. This study applied a box model approach to assess P budget in the Indian Sundarban, the world’s largest mangrove ecosystem for conceptual understanding of P cycling and for better representation of transport and transformation of P within the mangrove ecosystem. The P content in the sediment (0.19–0.67 μg g?1) was found much below its maximum retention capacity (322 μg g?1) and was lower than the mean marine sediment (669 μg g?1). The C:N and C:P ratios were correlated (r 2 = 0.66, P < 0.01) and the major fraction of available P was recycled within the organic structure of mangrove ecosystem, thus maintaining productivity through conservation strategies. Atmospheric input accounted for 56.7% of total P input (16.06 Gg year?1) and 50% of total P output (14.7 Gg year?1) was attributed to plant uptake. Budget closing or unaccounted P (1.36 Gg) was only 8.5% of the total input. Two feedback pathways, i.e., input of P from dust fallout and biochemical mineralization of organic matter, significantly affected P availability. The findings of the study suggest that atmospheric deposition is of major importance as a natural and/or anthropogenic forcing function in the Sundarban mangrove system. 相似文献
28.
In this study, a new strain of microorganism Shewanella putrefaciens was used for biofiltration of a pyridine laden air stream in a corn‐cob packed biotrickling filter. In the biotrickling filter tested with S. putrefaciens, the maximum removal of pyridine is determined to be 100% at less than the average inlet concentration of 0.653 g m–3 and more than 93% at a higher average inlet concentration of 1.748 g m–3 (phase VIII) with an empty bed residence time (EBRT) of 106 s. However, when the biotrickling filter was operated at a low EBRT of 53 s and almost the same average inlet concentration of 1.752 g m–3 (phase VII), the removal level attained was not greater than 85%. The maximum elimination capacity (EC) of the biotrickling filter was 102.34 g m–3h–1 at an inlet pyridine load of 119.62 g m–3h–1 with an EBRT of 53 s in phase VII. The maximum deviation of the EC from the 100% conversion line varied from 0.257 to 10.166% when going from phase I to VIII. Kinetic analysis showed that the maximum removal rate, rmax, and saturation constant, Ks, values for pyridine were calculated as 0.24 g m–3h–1 and 6.44 g m–3, respectively, with a correlation coefficient, R2, of 0.9939 and a standard deviation of error of 23.94%. The information contained herein indicates that the corn‐cob packed biotrickling filter inoculated by S. putrefaciens should provide excellent performance in the removal of gaseous pyridine. 相似文献
29.
Catherine A. Hier Majumder David A. Yuen Erik O. Sevre John M. Boggs Stephen Y. Bergeron 《Visual Geosciences》2002,7(1):1-53
Finite Prandtl number thermal convection is important to the dynamics of planetary bodies in the solar system. For example,
the complex geology on the surface of the Jovian moon Europa is caused by a convecting, brine-rich global ocean that deforms
the overlying icy “lithosphere”. We have conducted a systematic study on the variations of the convection style, as Prandtl
numbers are varied from 7 to 100 at Rayleigh numbers 106 and 108. Numerical simulations show that changes in the Prandtl number
could exert significant effects on the shear flow, the number of convection cells, the degree of layering in the convection,
and the number and size of the plumes in the convecting fluid. We found that for a given Rayleigh number, the convection style
can change from single cell to layered convection, for increasing Prandtl number from 7 to 100. These results are important
for determining the surface deformation on the Jovian moon Europa. They also have important implications for surface heat
flow on Europa, and for the interior heat transfer of the early Earth during its magma ocean phase. Electronic Supplementary
Material is available if you access this article at . On that page (frame on the left side), a link takes you directly to the supplementary material.
Electronic Supplementary Material is available if you access this article at . On that page (frame on the left side), a link takes you directly to the supplementary material. 相似文献
30.
Two-dimensional numerical simulations were conducted of the growth of thermal plumes from a point heat source at Rayleigh
numbers up to 108 and Prandtl numbers up to 1000. Scaling the convection equations by the free fall velocity rather than the
thermal diffusivity, increased the Prandtl number range available to numerical simulation by one order of magnitude from Prandtl
number 100 to 1000. We present animations showing how the plumes grow with time for different Prandtl numbers. Plumes with
Prandtl numbers around 7 (water) were found to be unstable to sinuous instabilities; whereas those at Prandtl numbers of 1000
had straight stems and fewer sinuous instabilities. Wavelet analysis was used to analyze the scales at which plumes initiated,
and the scales at which sinuous instabilities occurred. The scale of both the plume structures and instabilities was found
to decrease with Prandtl number. 相似文献