http://www.sciencedirect.com/science/article/pii/S1674987112000059     

Dilip Saha  Vikash Tripathy 《地学前缘(英文版)》2012,3(4):429-444

A lirst report on tuff beds from the Owk Shale in the Proterozoic Kurnool sub-basin in southern India is presented.The rhvolitic lo ihodacitic tuffs,overlying shclfal limestones formed at depths below storm wave base,have rheomorphic features indicative of viscoplaslic flow.and geochemical signatures of rhvolitic to rhyodacitic unwekled to welded tuffs,similar to those described from other Proterozoic intracratonie basins like Vindhvan and Chhattisgarh basins in India.Fragmentary naiure of altered glass with perlitic cracks and local admixture with intrabasinal sediments suggest phreatomagmatic reactions.The widespread and repealed occurrences of felsic luffs in these basins.possibly derived from low degree melting of continental crust.suggest intermittent(ectonothermal instability which likely intluenced hasinal topography and cyclic development of the carbonate platforms.  相似文献   

Mineralogical study of gabbro-anorthosite from Dumka, Chhotanagpur Gneissic Complex, Eastern Indian Shield     

Niladri Bhattacharjee  Jyotisankar Ray  Sohini Ganguly  Abhishek Saha 《Journal of the Geological Society of India》2012,80(4):481-492

The Chhotanagpur Gneissic Complex (CGC), bearing imprints of widespread high grade metamorphic and magmatic history since Palaeoproterozoic, represents an integral crustal segment of Eastern Indian Shield. The gabbroanorthosite intrusives constitute a part of mafic-ultramafic magmatism in the CGC. The study area around Dumka (24°16?? to 24°20??N: 87°13?? to 87°22??E) predominantly comprises of granite gneiss and charnockitic country rocks within which gabbro-anorthosite intrusions occur as lenses. Field relations and structural studies reveal that the country rocks of Dumka have suffered three phases of deformation represented by F₁, F₂ and F₃ folds. The gabbro-anorthosite intrusives maintain a sharp contact with the host rocks, deformed and metamorphosed. Relict igneous layering or primary igneous foliation (S_ig) is recorded where metamorphic overprint is minimal. Mineral phases of gabbro-anorthosite rocks suggest that clinopyroxene compositions from gabrro correspond to diopside and clinoferrosilite, while those from anorthosite are clinoferrosilite. Amphiboles from the gabbro-anorthosite rocks are calcic, and range from ferroan pargasite in gabbro to ferroan pargasitic hornblende in anorthosite. Plagioclase from gabbro and anorthosite belong to bytownite and andesine respectively. Chemical composition of garnet in gabbro is almandine. Thermobarometric estimates for Dumka gabbroanorthosites correspond to 511°C to 915°C and 5.0?C7.5 kb pressure, comparable to that estimated for Bengal Anorthosite (593?C795°C, 4.1?C7.3 kb). Fractionation trend of plagioclase substantiates a single parental magma in the evolution of Dumka gabbro-anorthosite intrusives.  相似文献   

Aerosol pollution and its impact on regional climate during Holi festival inferred from ground-based and satellite remote sensing observations     

C. P. Simha  P. C. S. Devara  S. K. Saha 《Natural Hazards》2013,69(1):889-903

In this paper, we report some salient features from a suit of special experiments that have been conducted over a coastal site (Mumbai) during February 23–March 03, 2010, encompassing an Indian festival, namely Holi, using solar radiometers and pyranometer. The results of the analysis of observations at the experimental site show higher (more than double) aerosol optical depth, water vapor, and lower down-welling short-wave radiative flux during the festival period. This is considered to be due to anthropogenic activities and associated meteorological conditions at the experimental location. To illustrate further, Angstrom parameters (alpha, denoting the aerosol size distribution, and beta, representing the loading) are examined. These parameters are found to be greater on Holi day as compared to those on the normal (control, pre-, and post-Holi) days, suggesting an increase in accumulation mode (smaller size) particle loading. The aerosol size spectra exhibited bimodal/power-law distribution with a dominant peak, modulated by anthropogenic activities, involving local and long-range transport of dust and smoke (emanated from biomass-burning) aerosols, which is consistent with MODIS satellite observations. The aerosol direct radiative forcing estimation indicated cooling at the bottom of the atmosphere.  相似文献   

The thickness of H i in galactic discs under MOdified Newtonian Dynamics: theory and application to the Galaxy     

F. J. Sánchez-Salcedo  K. Saha  C. A. Narayan 《Monthly notices of the Royal Astronomical Society》2008,385(3):1585-1596

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On the tidally driven circulation in the South China Sea: modeling and analysis     

Varjola Nelko  Abhishek Saha  Vivien P. Chua 《Ocean Dynamics》2014,64(3):413-428

The South China Sea is a large marginal sea surrounded by land masses and island chains, and characterized by complex bathymetry and irregular coastlines. An unstructured-grid SUNTANS model is employed to perform depth-averaged simulations of the circulation in the South China Sea. The model is tidally forced at the open ocean boundaries using the eight main tidal constituents as derived from the OSU Tidal Prediction Software. The model simulations are performed for the year 2005 using a time step of 60 s. The model reproduces the spring-neap and diurnal and semidiurnal variability in the observed data. Skill assessment of the model is performed by comparing model-predicted surface elevations with observations. For stations located in the central region of the South China Sea, the root mean squared errors (RMSE) are less than 10 % and the Pearson’s correlation coefficient (r) is as high as 0.9. The simulations show that the quality of the model prediction is dependent on the horizontal grid resolution, coastline accuracy, and boundary locations. The maximum RMSE errors and minimum correlation coefficients occur at Kaohsiung (located in northern South China Sea off Taiwan coast) and Tioman (located in southern South China Sea off Malaysia coast). This may be explained with spectral analysis of sea level residuals and winds, which reveal dynamics at Kaohsiung and Tioman are strongly influenced by the seasonal monsoon winds. Our model demonstrates the importance of tidally driven circulation in the central region of the South China Sea.  相似文献   

Recharge mechanism and processes controlling groundwater chemistry in a Precambrian sedimentary terrain: a case study from Central India     

R. K. Ray  T. H. Syed  Dipankar Saha  B. C. Sarkar  D. V. Reddy 《Environmental Earth Sciences》2017,76(3):136

Unplanned and unsustainable extraction has created stress on groundwater resources in many parts of India. The stress symptoms are more pronounced in hard rock areas, where the aquifer potentials are comparatively low. Present research targeted an area of 3000 km² in the interstream region between the Kharun and Seonath rivers, which is one such region in Central India. In spite of being a water-stressed area, so far, little is understood about processes of recharge, amount of recharge and processes controlling chemical quality, which are key inputs for groundwater management in the area. This study presents an appraisal of recharge mechanism, recharge rate and prevailing water–rock interactions in the study area. Stable isotope composition of groundwater when compared to that of rainfall indicates monsoon rainfall as the primary source of groundwater recharge. Winter rains, which are characteristically enriched in heavier isotopes, do not contribute notably to groundwater recharge. Recharge is rapid with minor or no evaporative enrichment before recharge. Further, analysis of stable isotopes show that ‘macropore recharge’ is dominant in limestone or calcareous shale, covering more than 70% of the study area. Also apparent is the vertical connectivity amongst the aquifers. However, active intermixing of surface water and groundwater is not a predominant process. Annual groundwater recharge from rainfall, as derived from chloride mass balance, is 105.26 million cubic metre. Groundwater is predominantly of bicarbonate type, irrespective of its hydrostratigraphic (lithology) setting. Dissolution of carbonates and gypsum (occurring as veins), weathering of feldspar and ion exchange of clay minerals are amongst the most likely processes controlling the regional groundwater chemistry.  相似文献   

Groundwater contamination with arsenic in Sherajdikhan,Bangladesh: geochemical and hydrological implications     

M. A. Halim  R. K. Majumder  S. A. Nessa  K. Oda  Y. Hiroshiro  B. B. Saha  S. M. Hassain  Sk. A. Latif  M. A. Islam  K. Jinno 《Environmental Geology》2009,58(1):73-84

An integrated study has been carried out to elucidate the distribution and occurrence of arsenic in selected groundwater samples in the area of Sherajdikhan, Bangladesh. Arsenic and other parameters (T, pH, EC, Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, NO₃ ⁻, SO₄ ²⁻, HCO₃ ⁻, PO₄ ³⁻, Fe, Mn and DOC) have been measured in groundwater samples collected from shallow/deep tube wells at different depths. Hydrogeochemical data suggest that the groundwaters are generally Ca–Mg–HCO₃ and Mg–Ca–HCO₃ types with bicarbonate (HCO₃ ⁻) as the dominant anion, though the other type of water has also been observed. Dissolved arsenic in groundwater ranged from 0.006 to 0.461 mg/l, with 69% groundwater samples exceeded the Bangladesh limit for safe drinking water (0.05 mg/l). Correlation and principal component analysis have been performed to find out possible relationships among the examined parameters in groundwater. Low concentrations of NO₃ ⁻ and SO₄ ²⁻, and high concentrations of DOC, HCO₃ ⁻ and PO₄ ³⁻ indicate the reducing condition of subsurface aquifer where sediments are deposited with abundant organic matter. Distinct relationship of As with Fe and Mn, and strong correlation with DOC suggests that the biodegradation of organic matter along with reductive dissolution of Fe–Mn oxyhydroxides has being considered the dominant process to release As in the aquifers studied herein.  相似文献   

On particle trajectories in restricted 3-body problem including the effect of radiation: Sun-Jupiter system     

M. K. Das  Pankaj Narang  M. Yuasa  L. M. Saha 《Astrophysics and Space Science》2008,314(1-3):59-71

In this work, we have simulated orbits of a particle moving in gravitational field of the Sun-Jupiter system. The effect of solar radiation pressure, including Poynting Robertson drag, on the evolution of particle orbits in phase space have been studied for different values of the parameter β ₁ (the ratio of radiation to gravitational force) and initial conditions. Characteristics of various computed trajectories have been studied using wavelet transform (WT), Fourier transform (FT) and Poincare surface of section method. We use wavelet analysis to identify transitions of a trajectory in time-frequency plane and further apply it to classify it as regular or chaotic in phase space. Unlike the Fourier transform method (FT), we observe that the wavelet transform (WT) also provides a basis to identify ‘sticky’ trajectories in the present dynamical system.  相似文献   

Hazardous Waste Pollution Prevention Using Clay with Admixtures     

Papita Saha  Siddhartha Datta  Shyamal Kanti Sanyal 《洁净——土壤、空气、水》2008,36(2):230-238

Landfill is the most commonly used method for disposal of waste materials since it is one of the least expensive methods. In order to dispose of any hazardous material to a landfill, a liner is used, which protects the underlying land and groundwater since it acts as a barrier to fluid movement. Of the various methods available for providing improved and more effective properties of landfills, methods involving the use of bentonite, cement, lime, gypsum, etc., have been explored in the laboratory. The aim is to overcome the problem and deficiencies of the existing liners. It is observed from the experimental results that the metal concentrations of the input waste solution can be reduced to 80–98% using a soil‐cement admixture, 60–95% using a soil‐gypsum mixture, 45–95% using a soil‐bentonite mixture, 50–90% for soil, 35–80% using a soil‐lime mixture, as liner materials. The permeation rate of different metals through the different soil‐admixture media depends on various factors. A simple mathematical treatment of the phenomenon related to the permeation of liquid through the admixture of the clay and other components has been developed. The experimental results show satisfactory agreement with the predictions.  相似文献   

Experimental studies on sloshing behavior due to horizontal movement of liquids in baffled tanks     

P.K. Panigrahy  U.K. Saha  D. Maity 《Ocean Engineering》2009,36(3-4):213-222

A series of experiments have been carried out in a developed liquid sloshing setup to estimate the pressure developed on the tank walls and the free surface displacement of water from the mean static level. The square tank attached to a shaking table can be moved to and fro by a cam arrangement driven by a DC motor. Pressure and displacement studies are done on the basis of changing excitation frequency of the shaking table and fill level in the tank. Experiments were carried out without and with baffles, and the consequent changes in the parameters are observed.  相似文献