Soil and stream sediment based geochemical mapping: A case study in Goa     

D. Purushothaman  J. P. Mohakul  Asit Saha  K. T. Vidyadharan  N. Rajendran 《Journal of the Geological Society of India》2009,73(6):744-746

Geochemical mapping has been carried out in Goa using soil/laterite and stream sediment as media. The geochemical maps for U, Th, Nb and Ta show a conspicuous pattern in the NW part of Goa. The anomaly axis shows a NE-SW trend which is across the formational trend. The nickel and copper distribution around Usgaon area, east of Ponda, have indicated anomalous signature in the northern continuation of the Usgaon ultramafic complex.  相似文献   

Natural radioactivity measurements in beach sand along southern coast of Orissa,eastern India   总被引：1，自引：1，他引：0  

N. Sulekha Rao  D. Sengupta  R. Guin  S. K. Saha 《Environmental Earth Sciences》2009,59(3):593-601

The beach placer deposits in the southern coastal Orissa, India may have significant levels of radiation due to the presence of Th and U bearing minerals such as monazite and zircon. In this study, Gopalpur and Rushikulya beach regions were selected to study the ambient radiation environment. The average activity concentrations of radioactive elements such as ²³²Th, ²³⁸U and ⁴⁰K of beach sand samples were measured by γ-ray spectrometry using a HPGe detector, and found to be much higher than the internationally accepted values. The cross plots of eTh/eU and eTh/K inferred that the sand samples of Gopalpur and Rushikulya beach placer deposit were deposited in leached uranium and an oxidising environment. The absorbed γ dose rate levels of the study areas are similar to other monazite sand-bearing HBRAs of southern and southwestern coastal regions of India and of world. Different radiation hazard indices were estimated for the present study area and were found to be much higher than the internationally accepted values. Hence, Gopalpur and Rushikulya beach placer region can be considered as a high background radiation area and a potential zone for radiogenic heavy mineral exploration.  相似文献   

Deep learning for predicting the monsoon over the homogeneous regions of India   总被引：1，自引：0，他引：1  

Moumita Saha  Pabitra Mitra  Ravi S Nanjundiah 《Journal of Earth System Science》2017,126(4):54

Indian monsoon varies in its nature over the geographical regions. Predicting the rainfall not just at the national level, but at the regional level is an important task. In this article, we used a deep neural network, namely, the stacked autoencoder to automatically identify climatic factors that are capable of predicting the rainfall over the homogeneous regions of India. An ensemble regression tree model is used for monsoon prediction using the identified climatic predictors. The proposed model provides forecast of the monsoon at a long lead time which supports the government to implement appropriate policies for the economic growth of the country. The monsoon of the central, north-east, north-west, and south-peninsular India regions are predicted with errors of 4.1%, 5.1%, 5.5%, and 6.4%, respectively. The identified predictors show high skill in predicting the regional monsoon having high variability. The proposed model is observed to be competitive with the state-of-the-art prediction models.  相似文献   

A hypothesis on onset,advance and withdrawal of the Indian summer monsoon     

Suranjana Saha  Kshudiram Saha 《Pure and Applied Geophysics》1980,118(2):1066-1075

The paper defines the intertropical convergence zone. (ITCZ) in the Indian monsoon region during the northern summer, identifies it with the northern boundary of the advancing monsoon and suggests that its seasonal movement can serve as an indicator of onset, advance and withdrawal of the monsoon. Evidence suggesting the movement of the ITCZ which is associated with the equatorial trough of low pressure is indirectly furnished by an analysis of the isallobaric or height-tendency field which reveals a distinct gradient towards the north/south during period of advance/withdrawal of the monsoon. A comparative study of the dates of onset of monsoon during two successive years appears to suggest that some of the problems encountered in using rainfall as the sole criterion for determining the onset and advance of the monsoon may be over-come by using the ITCZ concept as proposed in the present paper. Attention is drawn to the effects of synoptic-scale disturbances on the normal dates of onset, advance and withdrawal of the monsoon.  相似文献   

Unsteady boundary layer flows induced by a wavy plate     

L. M. Saha  L. Debnath 《Pure and Applied Geophysics》1973,105(1):802-809

Summary Unsteady boundary layer flows generated in an incompressible, homogeneous, nonrotating viscous fluid bounded by a rigid wavy plate are studied theoretically. The Laplace transform method is employed to obtain exact solutions of the unsteady boundary layer equations in a wavy plate configuration. The structures of the unsteady velocity distribution and the associated boundary layers are determined explicitly and several particular solutions are recovered as special cases of this analysis. The physical interpretation of the mathematical results are examined.  相似文献   

Kinetics of cadmium adsorption on aluminum precipitation products formed under the influence of tannate     

G. Yu  U.K. Saha  P.M. Huang 《Geochimica et cosmochimica acta》2006,70(20):5134-5145

The impeding effects of organic substances on the crystallization of Al precipitation products have been studied for more than three decades. However, the impacts of organics-induced structural perturbation and the resultant surface alteration of Al transformation products on their kinetics and mechanisms of the adsorption of trace metals still remain to be uncovered. This paper describes the kinetics of Cd adsorption on the short-range-ordered (SRO) Al precipitation products formed under the influence of tannate. The kinetics of Cd adsorption on the SRO Al precipitation products formed in the presence of tannate at initial tannate/Al molar ratios (MRs) of 0, 0.001, 0.01 and 0.1 was studied at an initial Cd concentration of 0.89 μM, pH 5.5, background electrolyte of 10⁻² M NaNO₃, and solid phase concentration of 0.08 g L⁻¹ at 278, 288, 298 and 313 K using the conventional batch method. The results show that, among the six empirical kinetic models tested, the second-order rate equation best described the kinetic data. Cadmium adsorption on SRO Al precipitation products was a multi-step process involving an initial fast reaction (0.083-0.75 h) followed by a slow reaction (0.75-4 h). The structural perturbation of Al precipitation products by tannate and the resultant development of their microporosity and alteration of surface and charge properties substantially enhanced the rate constants of both the fast and slow reaction processes of Cd adsorption. The heat of activation values for the fast reaction ranged from 27 to 41 kJ mol⁻¹, indicating that diffusion is the rate-limiting step in Cd adsorption. Except for the Al precipitation products formed at a tannate/Al MR of 0 and 0.001, the heat of activation was >47 kJ mol⁻¹ for the slow reaction, indicating that the rate-limiting step is a chemical process, which apparently involves bond breaking and formation on the surfaces of the SRO Al precipitation products. The pre-exponential factor, an index of the frequency of Cd collision with the surface of Al precipitation products, significantly increased with the increase of the initial tannate/Al MR, which is attributed to the development of microporosity and the increase in the specific surface area of the Al precipitation products formed under the influence of tannate ligands. The findings merit attention to the role of natural organics, which vary in the structure and functionality, in developing the microporous structure of Al precipitation products and the impact on the dynamics and mechanisms of Cd transformation and transport in natural environments.  相似文献   

Predation of the beetle Rhantus sikkimensis (Coleoptera: Dytiscidae) on the larvae of Chironomus Meigen (Diptera: Chironomidae) of the Darjeeling Himalayas of India     

Gautam Aditya  Goutam Kumar Saha   《Limnologica》2006,36(4):251-257

The dytiscid beetle Rhantus sikkimensis, Regimbart, 1899 (Coleoptera: Dytiscidae), a member of the freshwater insect communities of the Darjeeling Himalayas, were noted to predate on the coexisting larvae of Chironomus sp. Meigen. Evaluation of predation by R. sikkimensis on Chironomus sp. larvae, in the laboratory, revealed that a single adult morph of R. sikkimensis could kill and consume on an average 10–90 and 10–78 numbers of small and large Chironomus sp. larvae, respectively, per day, depending on the prey density. The attack rate ranged between 520 and 537, and the handling time ranged between 4.3 and 8.6 depending on the size of the preys. The predation varied with respect to predator density also, with a maximum of 151 larvae killed by three predators per day. Two indices of predation, ingestion rate (IR) ranging between 13.33 and 74.15 larvae/day/predator and clearance rate (CR) ranging between 19.67 and 39.99 L prey/day/predator, varied with the prey size and predator density, significantly, when the predation was observed for 9 consecutive days, at two predator densities. It was also noted that R. sikkimensis predated on an average 9.8 larvae of Chironomus sp. and 1 larva of Culex sp., when the larvae of both the species are present together as preys, showing a preference for the Chironomus sp. larvae.  相似文献   

Application of remote sensing to identify coalfires in the Raniganj Coalbelt,India     

Prasun K Gangopadhyay  Kuntala Lahiri-Dutt  Kanika Saha 《International Journal of Applied Earth Observation and Geoinformation》2006

Raniganj and Jharia regions together have been for long the single largest coal supplier in India, now contributing about a quarter of the total output in the country. Numerous reasons such as improper mining techniques and policy, as well as unauthorized mining caused surface and subsurface coalfires in these areas. These coalfires burn millions of tonnes of valuable coal resources, creating severe environmental problems and posing enormous operational difficulties of mining. After first use of remote sensing as a tool to identify coalfires in 1960s, with the time, the efficiency of remote sensing to identify and monitoring coalfires has been well established by several researchers. With the knowledge of local geological setting and density sliced surface temperature image the spatial distribution of coalfires can be revealed. The present paper makes an attempt to identify temperature anomalies of the Raniganj coalbelt to locate the spatial distribution of coalfires. Landsat Thematic Mapper (TM) thermal band data was used to calculate surface temperature along with NDVI (normalized vegetation index) derived emissivity.  相似文献   

Chemical weathering and gully erosion causing land degradation in a complex river basin of Eastern India: an integrated field,analytical and artificial intelligence approach     

Pal  Subodh Chandra  Chakrabortty  Rabin  Arabameri  Alireza  Santosh  M.  Saha  Asish  Chowdhuri  Indrajit  Roy  Paramita  Shit  Manisa 《Natural Hazards》2022,110(2):847-879

Hot and humid subtropical plateau regions are susceptible to land degradation in the form of weathering and gully erosion. Here, we investigate chemical weathering, gully erosion and cohesiveness through field-based measurements with a view to understand the controlling factors of potential land degradation, in complex river basin of the Chotanagpur plateau region in Eastern India. The layers of controlling factors of gully erosion were developed and prioritized considering boosted regression tree (BRT), alternative decision tree (ADT), particle swarm optimization (PSO) and random forest (RF) algorithms in the R software, and the results of these methods were also validated using receiver operating characteristic (ROC) curves. The spectroscopic analysis was carried out of collected soil samples to measure the degree of chemical weathering and cohesiveness. Furthermore, the climatic elements like temperature and rainfall were also considered for estimating the chemical weathering. The results of the gully erosion models (i.e., BRT, ADT, PSO and RF) show remarkable accuracy with ROC values of 0.93, 0.89, 0.91 and 0.84, respectively. An advanced decision tree model was integrated with the results of degree of chemical weathering and cohesiveness in geographical information system platform. The land degradation map developed from this approach shows that 10.53% of the study area is highly affected, whereas 17.36% area is moderately affected and the rest of the 73.85% area is less affected by land degradation. Our results provide essential information for policy makers in adopting measures for minimizing and controlling the land degradation. Our novel approach is significant to assess land degradation to a large scale.

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REFLECTION AND TRANSMISSION OF SHEAR WAVES IN MONOCLINIC MEDIA     

A. Chattopadhyay  S. Saha  M. Chakraborty 《国际地质力学数值与分析法杂志》1997,21(7):495-504

This paper deals with the propagation, reflection and transmission of shear waves in monoclinic media. The dispersion equation for a monoclinic layer overlying a monoclinic half-space has been obtained and curves are plotted. The amplitude ratios for both the reflected and transmitted waves due to reflection of shear waves at the interface of two monoclinic half-spaces have also been computed and the numerical results are presented graphically. The results are compared with the isotropic case. It has been observed that, in monoclinic media, the amplitude ratios for reflected and transmitted wave increases approximately by 25 and 50 per cent respectively, in comparison to the isotropic case. © 1997 John Wiley & Sons, Ltd.  相似文献