Adsorption kinetic control of As(III &; V) mobilization and sequestration by Mangrove sediment     

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   

Torsional surface wave in an elastic half-space with void pores     

S. Dey  S. Gupta  A. K. Gupta 《国际地质力学数值与分析法杂志》1993,17(3):197-204

  相似文献   

Aquifer Sensitivity to Pesticide Leaching: Testing a Soils and Hydrogeologic Index Method     

Edward Mehnert  Donald A. Keefer  William S. Dey  H. Allen Wehrmann  Steven D. Wilson  Chittaranjan Ray 《Ground Water Monitoring & Remediation》2005,25(4):60-67

  相似文献   

Old high-redshift galaxies and primordial density fluctuation spectra     

Peacock  Jimenez  Dunlop  Waddington  Spinrad  Stern  Dey  & Windhorst 《Monthly notices of the Royal Astronomical Society》1998,296(4):1089-1097

We have discovered a population of extremely red galaxies at z  ≃ 1.5 which have apparent stellar ages of ≳ 3 Gyr, based on detailed spectroscopy in the rest-frame ultraviolet. In order for galaxies to have existed at the high collapse redshifts indicated by these ages, there must be a minimum level of power in the density fluctuation spectrum on galaxy scales. This paper compares the required power with that inferred from other high-redshift populations: damped Lyα absorbers and Lyman-limit galaxies at z  ≃ 3.2. If the collapse redshifts for the old red galaxies are in the range z _c ≃ 6–8, there is general agreement between the various tracers on the required inhomogeneity on 1-Mpc scales. This level of small-scale power requires the Lyman-limit galaxies to be approximately ν ≃ 3.0 fluctuations, implying a very large bias parameter b  ≃ 6. If the collapse redshifts of the red galaxies are indeed in the range z _c = 6–8 required for power spectrum consistency, their implied ages at z  ≃ 1.5 are between 3 and 3.8 Gyr for essentially any model universe of current age 14 Gyr. The age of these objects as deduced from gravitational collapse thus provides independent support for the ages estimated from their stellar populations. Such early-forming galaxies are rare, and their contribution to the cosmological stellar density is consistent with an extrapolation to higher redshifts of the star formation rate measured at z  < 5; there is no evidence for a general era of spheroid formation at extreme redshifts.  相似文献   

Geology,geomorphology and mineral resources of khodana and adjoining areas (Haryana) and their significance in landuse planning     

R. C. Dey 《Journal of the Indian Society of Remote Sensing》1985,13(1):57-68

The area around Khodana, Bhiwani district, Haryana forms a part of the semi-arid region of western India. As vegetation is sparse and mainly xerophytic, photointerpretation technology was effectively utilised in bringing out the broad geology and structural pattern of the mature Precambrian terrain, which were ground-checked and correlated with the results of detailed integrated surveys carried out for base metal sulphide mineralisation in the area. A number of shear/fault zones, sub-parallel to the formational contacts and the regional fold axes, could be recognised in aerial photographs and on ground checking, were found to be intensely limonitised. The possibility of direct application of the pyrite-pyrthotite, encountered in drilling through shear zones, in landuse planning has been discussed. Discrete use of the quartzites as road ballasts, building stone and bund material, use of clay-rich pockets within pasture lands or micro-depressions in the surrounding terrain for locally-constructed brick kilns and ochreous material as pigments are some other uses of finite land resources of Haryana State.  相似文献   

Distribution of suspended sediment concentration in wide sediment‐laden streams: A novel power‐law theory          下载免费PDF全文

Francisco Nicolás Cantero‐Chinchilla  Oscar Castro‐Orgaz  Subhasish Dey 《Sedimentology》2016,63(6):1620-1633

The diffusion equation of suspended sediment concentration in a wide sediment‐laden stream flow is dependent on the vertical gradient of streamwise velocity and the sediment diffusivity. This study aims at investigating the influence of the streamwise velocity laws on the suspended sediment concentration distributions, resulting from the solution of the diffusion equation. Firstly, the sediment concentration distributions are obtained numerically from the solution of the diffusion equation using different velocity laws and compared with the experimental data. It is found that the power‐law approximation produces good computational results for the concentration distributions. The accuracy of using a power‐law velocity model is comparable with the results obtained from other classical velocity laws, namely log‐law, log wake‐law and stratified log‐law. Secondly, a novel analytical solution is proposed for the determination of sediment concentration distribution, where a power‐law, wall‐concentration profile is coupled with a concentration wake function. The power‐law model (for velocity and concentration) is calibrated using the experimental data, and then a generalized wake function is obtained by choosing a suitable law. The developed power‐law model involving the wake function adjusted by an exponent predicts the sediment concentration distributions quite satisfactorily. Finally, a new explicit formula for the suspended‐load transport rate is derived from the proposed theory, where numerical computation of integrals, as needed in the Einstein theory, is avoided.  相似文献   

Time series effects of dissolved oxygen and nitrogen on Long Island Sound lobster harvest     

Zinnia Mukherjee  Dipak K. Dey  Rangan Gupta 《Natural Hazards》2016,84(3):1849-1858

  相似文献   

Estimating threshold-exceeding probability maps of environmental variables with Markov chain random fields   总被引：2，自引：2，他引：0  

Weidong Li  Chuanrong Zhang  Dipak K. Dey  Shanqin Wang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(8):1113-1126

Estimating and mapping spatial uncertainty of environmental variables is crucial for environmental evaluation and decision making. For a continuous spatial variable, estimation of spatial uncertainty may be conducted in the form of estimating the probability of (not) exceeding a threshold value. In this paper, we introduced a Markov chain geostatistical approach for estimating threshold-exceeding probabilities. The differences of this approach compared to the conventional indicator approach lie with its nonlinear estimators—Markov chain random field models and its incorporation of interclass dependencies through transiograms. We estimated threshold-exceeding probability maps of clay layer thickness through simulation (i.e., using a number of realizations simulated by Markov chain sequential simulation) and interpolation (i.e., direct conditional probability estimation using only the indicator values of sample data), respectively. To evaluate the approach, we also estimated those probability maps using sequential indicator simulation and indicator kriging interpolation. Our results show that (i) the Markov chain approach provides an effective alternative for spatial uncertainty assessment of environmental spatial variables and the probability maps from this approach are more reasonable than those from conventional indicator geostatistics, and (ii) the probability maps estimated through sequential simulation are more realistic than those through interpolation because the latter display some uneven transitions caused by spatial structures of the sample data.  相似文献   

Response of multiply supported secondary systems to earthquakes in frequency domain     

Aparna Dey  Vinay K. Gupta 《地震工程与结构动力学》1998,27(2):187-201

A new formulation of the transfer function has been proposed for the seismic analysis of linear, multiply supported secondary systems. The transfer function for a given response quantity has been formulated by directly using the fixed-base modes of the primary and secondary systems. This approach is exact and does not involve the determination of the combined system properties. Further, it is applicable to the secondary systems with various mass ratios and configurations. A few example primary–secondary systems have been considered to illustrate the proposed formulation in case of different mass ratios. It has also been shown how the proposed formulation can be used to obtain reasonably accurate stochastic estimates of the secondary system responses. © 1998 John Wiley & Sons, Ltd.  相似文献   

A time-domain nonlinear effective-stress non-Masing approach of ground response analysis of Guwahati city,India     

Basu  Devdeep  Boga  Madhulatha  Dey  Arindam 《地震工程与工程振动(英文版)》2019,18(1):61-75

The response of subsoil strata subjected to seismic excitations plays an important role in governing the response of the overlying superstructures at any site. Ground response analysis(GRA) helps to assess the influence of soil characteristics on the propagating seismic stress waves from the bedrock level to the ground surface during an earthquake. For the northeastern region of India, located in the highest seismic zone in the country, conducting an extensive GRA study is of prime importance. Conventionally, most of the GRA studies are carried out using the equivalent linear method, which, being a simplistic approach, cannot capture the nonlinear behavior of soil during seismic shaking. This paper presents the outcomes of a one-dimensional effective stress based nonlinear GRA conducted for Guwahati city(located in northeast India) incorporating the non-Masing load/unload/reload characteristics. The various ground response parameters evaluated from this study help in assessing the ground shaking, soil amplification, and site responses expected in this region. 2D contour maps, which are representative of the distribution of some of these parameters throughout Guwahati city, are also developed. The results presented herein can serve as guidelines for the design of foundations and superstructures in this region.  相似文献