Equatorial ionospheric responses in relation to the occurrence of main phase of intense geomagnetic storms in the local dusk sector     

R. Hajra  S.K. Chakraborty 《Journal of Atmospheric and Solar》2011,73(7-8):760-770

During five intense geomagnetic storms with main phases occurring around local dusk sector, equatorial ionosonde and electrojet data, VHF/UHF scintillation data of Calcutta, and several solar wind parameters are investigated to ascertain the polarity of prompt penetration electric field (PPEF). Abrupt increases in AE, ASY-H and/or sharp decreases in D_st/SYM-H with strong southward IMF B_z may symbolize eastward PPEF to equatorial latitude leading to evolution of density irregularities if the period is associated with arrival and sustenance of large magnetospheric shock compression. On the contrary, westward PPEF is more feasible if the shock reduces suddenly or fluctuates with small values.  相似文献   

New technologies, old divides: linking internet access to social and locational characteristics of US farms     

Pratyusha Basu  Jayajit Chakraborty 《GeoJournal》2011,76(5):469-481

Access to new information and communication technologies is widely viewed as a prerequisite for participation in the global economy, so that inequalities in such access have become a significant policy concern. Rural areas are especially underserved in terms of internet providers, and this is true in both developed and less developed economies. This article focuses on access to the internet within farming operations in the US as an important aspect of understanding the digital divide within rural areas. Using county level data from the 2007 US Census of Agriculture and multivariate regression analysis, our study examines the statistical relationship between farm internet access and a set of explanatory factors which include demographic characteristics of operators, economic characteristics of farms, and geographic location (region and metropolitan status) of the farm. Further, it seeks to understand whether access to the internet can be socially and locationally differentiated from access to high speed internet. Our findings indicate that existing social divides are replicated in terms of the digital divide, so that social inequalities are potentially a more pressing problem than infrastructural gaps in terms of rural access to the internet in the US.  相似文献   

A multi-method approach for the study of lanthanum speciation in coastal and estuarine sediments     

Parthasarathi Chakraborty  P.V. Raghunadh BabuV.V. Sarma 《Journal of Geochemical Exploration》2011

Two independent analytical methods (sequential extraction and kinetic extraction methods) were applied in order to understand the distribution and speciation of La in the coastal and estuarine sediments from the central east coast of India. Sequential extraction study revealed that La was primarily present as inert complexes (~ 50–60% of the total La) in all the sediments. Amounts of ~ 20–30% of the total La in all the sediments were found to associate with the total organic carbon (TOC) in the sediments. The dissociation rate constants of La–sediment complexes obtained from kinetic extraction studies revealed that the concentration of thermodynamically weak complexes of La gradually increased with the increasing La/TOC ratio in the sediments.  相似文献   

Movement of seasonal eddies and its relation with cyclonic heat potential and cyclogenesis points in the Bay of Bengal     

Bishnu Kumar  Arun Chakraborty 《Natural Hazards》2011,59(3):1671-1689

Movement of seasonal eddies in the Bay of Bengal (BOB) and its relation with cyclonic heat potential (CHP) and cyclogenesis points have been investigated in this study using 6 years (2002–2007) of global ocean monthly analysis datasets based on the Simple Ocean Data Assimilation (SODA) package (SODA v2.0.4) of Carton et al. (2005) and Indian Meteorological Department cyclogenesis points. The region dominated by anticyclonic eddies with CHP greater than 70 × 10⁷ J/m² as well as good correlations (>0.9) with sea surface height (SSH) and 26°C isothermal depth (D ₂₆) can be a potential region of cyclogenesis. The region dominated by cyclonic eddies with CHP greater than 50 × 10⁷ J/m² and good correlation (>0.9) with both SSH and D ₂₆ can serve as a potential region of high-level depression. Potential cyclogenesis regions are the southern BOB (5°N–12°N) for the post-monsoon season and the head of BOB (north of 15°N) during southwest monsoon. Seven potential regions are identified for the eddy formation for different seasons, which are consistent with the cyclogenesis points. The CHP distributions alone are able to explain the cyclone tracks for the pre-monsoon and post-monsoon seasons but not for the monsoon season.  相似文献   

A study on soil physico-chemical, microbial and metal content in Sukinda chromite mine of Odisha, India   总被引：1，自引：1，他引：0  

S. Das  S. S. Ram  H. K. Sahu  D. S. Rao  A. Chakraborty  M. Sudarshan  H. N. Thatoi 《Environmental Earth Sciences》2013,69(8):2487-2497

Soil samples from chromite mining site and its adjacent overburden dumps and fallow land of Sukinda, Odisha, were analysed for their physico-chemical, microbial and metal contents. Chromite mine soils were heterogenous mixture of clay, mud, minerals and rocks. The pH of the soils ranges between 5.87 and 7.36. The nutrient contents of the mine soils (N, P, K and organic C) were found to be extremely low. Analysis of chromite mine soils revealed accumulation of a number of metals in high concentrations (Fe > Cr > Mn > Ni > Zn > Pb > Sr) which exceeded ecotoxicological limits in soil. Correlation and cluster analysis of metals revealed a strong relation between Cr, Ni, Fe, Mn among the different attributes studied. Assessment of different microbial groups such as fungi, actinomycetes and bacteria (heterotrophic, spore forming, free-living nitrogen fixing, phosphate solubilising and cellulose degrading) from mine soils were found to be either extremely low or absent in some soil samples. Further chromium tolerant bacteria (CTB) were isolated using 100 mg/L Cr(VI) enriched nutrient agar medium and were screened for their tolerance towards increasing concentrations of hexavalent chromium and other toxic metals. Out of 23 CTB isolates, three bacteria tolerated up to 900 mg/L, 6 up to 500 mg/L, 20 up to 200 mg/L of Cr(VI). These bacteria were also found to be sensitive towards Cu > Co > Cd and very few CTB strains could show multiple metal tolerance. These strains have great scope for their application in bioremediation of toxic chromium ions in presence of other metals ions, which needs to be explored for their biotechnological applications.  相似文献   

Velocity measurements in some classes of alternative gravity theories     

Sumanta Chakraborty 《Astrophysics and Space Science》2013,347(2):411-421

The general misconception regarding velocity measurements of a test particle as it approaches black hole is addressed by introducing generalized observer set. For a general static spherically symmetric metric applicable to both Einstein and alternative gravities as well as for some well known solutions in alternative gravity theories, we find that velocity of the test particle do not approach that of light at event horizon by considering ingoing observers and test particles.  相似文献   

Sodium Arsenite Induced Alteration of Hemocyte Density of Lamellidens marginalis – An Edible Mollusk from India     

Sudipta Chakraborty  Mitali Ray  Sajal Ray 《洁净——土壤、空气、水》2008,36(2):195-200

Lamellidens marginalis (Molluska Bivalvia Eulamellibranchiata) is an important member of the freshwater ecosystem of India, which is sustained by filtering phytoplankton, bacteria and other particulate organic matter from the available water. Hemocytes, the circulating blood cells of bivalves, function as immunological effector cells under exposure to toxins and/or parasites. The hemocytes of Lamellidens marginalis have been identified morphologically and enumerated as being qualified for use as a biomarker to analyze the threat of freshwater contamination by sublethal concentrations of sodium arsenite, a natural pollutant of freshwater ecosystems. Diverse subpopulations of hemocytes were identified as blast‐like cells, granulocytes, agranulocytes, hyalinocytes and asterocytes. Supression in the total count of hemocytes and blast‐like cells was recorded under the exposure of all the concentrations of sodium arsenite tested. Sodium arsenite elevated the relative density of granulocytes, hyalinocytes, and asterocytes. Partial restoration of the total count of the hemocytes was recorded after the post‐treated animals were maintained in arsenic‐free water for periods of 15 and 30 days. The data predict a shift in the immunological parameters of this bivalve in arsenic contaminated environments. The present study is aimed at quantifying the arsenic induced stress in Lamellidens marginalis and establishing the hemocyte density as a biomarker of aquatic pollution in selected geographical regions of India.  相似文献   

Cenozoic geodynamic evolution of the Andaman–Sumatra subduction margin: Current understanding     

Partha P.  Chakraborty  Prosanta K.  Khan 《Island Arc》2009,18(1):184-200

The Andaman–Sumatra margin displays a unique set‐up of extensional subduction–accretion complexes, which are the Java Trench, a tectonic (outer arc) prism, a sliver plate, a forearc, oceanic rises, inner‐arc volcanoes, and an extensional back‐arc with active spreading. Existing knowledge is reviewed in this paper, and some new data on the surface and subsurface signatures for operative geotectonics of this margin is analyzed. Subduction‐related deformation along the trench has been operating either continuously or intermittently since the Cretaceous. The oblique subduction has initiated strike–slip motion in the northern Sumatra–Andaman sector, and has formed a sliver plate between the subduction zone and a complex, right‐lateral fault system. The sliver fault, initiated in the Eocene, extended through the outer‐arc ridge offshore from Sumatra, and continued through the Andaman Sea connecting the Sagaing Fault in the north. Dominance of regional plate dynamics over simple subduction‐related accretionary processes led to the development and evolution of sedimentary basins of widely varied tectonic character along this margin. A number of north–south‐trending dismembered ophiolite slices of Cretaceous age, occurring at different structural levels with Eocene trench‐slope sediments, were uplifted and emplaced by a series of east‐dipping thrusts to shape the outer‐arc prism. North–south and east–west strike–slip faults controlled the subsidence, resulting in the development of a forearc basins and record Oligocene to Miocene–Pliocene sedimentation within mixed siliciclastic–carbonate systems. The opening of the Andaman Sea back‐arc occurred in two phases: an early (～11 Ma) stretching and rifting, followed by spreading since 4–5 Ma. The history of inner‐arc volcanic activity in the Andaman region extends to the early Miocene, and since the Miocene arc volcanism has been associated with an evolution from felsic to basaltic composition.  相似文献   

A Study of the Thermodynamics and Kinetics of Copper Adsorption Using Chemically Modified Rice Husk     

Hasanur Jaman  Debarati Chakraborty  Papita Saha 《洁净——土壤、空气、水》2009,37(9):704-711

The use of rice husk as a low cost adsorbent for the removal of copper from wastewater has been explored in a laboratory scale experiment. The rice husk used for the study was treated with alkali to increase the sorption properties. The influence of metal ion concentration, weight of biosorbent, stirring rates, temperature and pH were also evaluated, and the results are fitted using adsorption isotherm models. From the experimental results it was observed that almost 90–98% of the copper could be removed using treated rice husk. The Langmuir adsorption isotherm, Freundlich isotherm and Tempkin isotherm models were used to describe the distribution of copper between the liquid and solid phases in batch studies, and it was observed that the Langmuir isotherm better represented the adsorption phenomenon. The experimental rate constant, activation energy, Gibbs free energy, enthalpy and entropy of the reaction were calculated in order to determine the mechanism of the sorption process.  相似文献   

Evaluation of RADARSAT ScanSAR synthetic aperture radar data for rice crop inventory and monitoring     

S. Panigrahy  M. Chakraborty  K. R. Manjunath  N. Kundu  J. S. Parihar 《Journal of the Indian Society of Remote Sensing》2000,28(1):59-65

Radarsat ScanSAR Narrow (SN2) data acquired on July 24 and August 17, 1997 were used to analyse the signature of rice crop in West Bengal, India. The analysis showed that the lowland practice of cultivation gives a distinct signature to rice due to the initial water background. The relatively stable backscatter from water bodies in temporal data enhanced the separability of rice fields from water using two date data. Around 94 per cent classification accuracy was achieved for rice crop using two date data. It was feasible to discriminate rice sub-classes based on their planting period like early and late crop. The analysis indicates the suitability of ScanSAR data for large area rice crop monitoring as it has a wide swath of 300 km.  相似文献