High iridium concentration of alkaline rocks of Deccan and implications to K/T boundary     

P. N. Shukla  N. Bhandari  Anirban Das  A. D. Shukla  J. S. Ray 《Journal of Earth System Science》2001,110(2):103-110

We report here an unusually high concentration of iridium in some alkali basalts and alkaline rocks of Deccan region having an age of about 65Ma, similar to the age of the Cretaceous-Tertiary boundary. The alkali basalts of Anjar, in the western periphery of Deccan province, have iridium concentration as high as 178pg/g whereas the alkaline rocks and basalts associated with the Amba Dongar carbonatite complex have concentrations ranging between 8 and 80 pg/g. Some of these values are more than an order of magnitude higher than the concentration in the tholeiitic basalts of Deccan, indicating the significance of alkaline magmatism in the iridium inventory at the Cretaceous-Tertiary boundary. Despite higher concentration, their contribution to the global inventory of iridium in the Cretaceous-Tertiary boundary clays remains small. The concentration of iridium in fluorites from Amba Dongar was found to be <30 pg/g indicating that iridium is not incorporated during their formation in hydrothermal activity.  相似文献   

Mapping of tropical dry deciduous forest and landuse in part of Vindhyan range using satellite remote sensing     

Pant  D N  Das  K K  Roy  P S 《Journal of the Indian Society of Remote Sensing》1992,20(1):9-20

Forest vegetation of Vindhyan range located in the north of G.B. Pant Sagar (dam) has been subjected to degradation due to high biotic pressure caused by the installation of thermal power plants, coal mining, heavy cattle grazing etc. In the present study Landsat TM FCC of 1∶250,000 scale was visually analysed with respect to forest vegetation types, crown density and structure along with other landuse/land cover classes. ExceptShorea robusta (Sal) andLagerstroemia parviflora (Lendia) all forest vegetation types show higher percentage of degradation and under-stocked condition with respect to their areal extent under study. Overall classification accuracy of the forest types has been found to be 88.94%. This indicates that for obtaining reliable mapping accuracy in dry deciduous areas, satellite remote sensing data of appropriate season is essential.

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Simulation Of Salt-Water Encroachment In A Multi-Layer Groundwater System,Bangkok, Thailand     

S. Gangopadhyay  A. Das Gupta 《Hydrogeology Journal》1995,3(4):74-88

Salt-water encroachment in the multi-layer groundwater system underlying the Bangkok metropolitan area was simulated with a quasi-three-dimensional flow and solute-transport model. The quasi-three-dimensional model used in this study is based on the model SUTRA. Accurate conceptualization of the initial state of the system with regard to the distribution of salt-water concentration is very important for modeling, especially in areas where localized zones of high salt concentration exist in the groundwater. Data adequacy and model results were evaluated by a geostatistical analysis. The model is capable of simulating the regional trend of potentiometric levels and salt concentration. However, lack of monitoring data in areas where localized zones of high salt concentration exist resulted in large model residuals. RÉSUMÉ: L'empiétement des eaux salées dans le système hydrologique multi-couche sous-jacent la zone métropolitaine de Bangkok a été simulé à l'aide d'un modèle quasi-tridimensionnel représentant l'écoulement des eaux et le transport d'éléments en solution. Le modèle quasi-tridimensionnel utilisé dans cette étude est basé sur le modèle SUTRA. Une conceptualisation exacte de l'état initial du système en ce qui concerne la répartition de la concentration des eaux salines est très important, particulièrement dans les endroits localisés où l'eau souterraine presente une forte concentration en sel. La qualité des donnés et des résultats a été estimée à l'aide d'une analyse géostatistique. Le modèle est capable de simuler la tendance régionale des niveaux potentiométriques et de la concentration en sel. Cependant, le manque de données de contrôle dans les endroits à forte concentration a donné lieu à des résiduels importants. RESUMEN: La intrusión de agua salina en el sistema multicapa bajo el área metropolitana de Bangkok se simuló mediante un modelo de flujo y transporte de solutos casi-tridimensional, basado en el modelo SUTRA. La conceptualizacián precisa de la distribución inicial de concentraciones de agua salina es muy importante para el modelo, especialmente en áreas donde existen zonas locales de alta concentración salina en el agua subterránea. La exactitud de los datos y del modelo se evaluaron mediante un análisis geoestadístico. El modelo permite simular la tendencia regional de los niveles piezométricos y la concentración de sales. Sin embargo, la falta de datos de muestreo en las zonas locales de alta salinidad resultaron en valores altos de los residuos calculados por el modelo.  相似文献   

On coda waves of earthquakes     

Sushil Chandra Das Gupta 《Pure and Applied Geophysics》1959,43(1):45-74

Summary Coda waves viz. the tail portion of an earthquake record have been observed and analysed byCarder, Macelwane and others. They showed that the periods of such waves increase with the increase of epicentral distances.Carder observed that these waves have very little transverse component so that these may be considered as of the type of Rayleigh waves. RecentlyOmote showed that the Coda waves contain three periodsT ₁,T ₂,T ₃ of whichT ₁ increases with epi-central distances as observed by previous observers. ButT ₂,T ₃ remain constant for all earthquakes from different epicentral distances.Omote tried to explain this phenomenon by considering that the surface of the earth consists of several layers andT ₂,T ₃ are free oscillation periods of the surface layers.T ₁ period has been explained bySezawa and also byJeffreys which has been shown byGutenberg. The author has attempted to explain the periodsT ₂,T ₃ by considering passage of cracks at the focal region. The Rayleigh wave character of Coda waves and low velocity of such waves have been explained.  相似文献   

"A study on the direct interpretation of dipole sounding resistivity measurements over layered earth"     

U. C. Das  D. P. Ghosh 《Geophysical Prospecting》1973,21(4):800-800

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Waves and stresses produced in an elastic medium due to impulsive radial forces and twist on the surface of a spherical cavity     

Sushil Chandra Das Gupta 《Pure and Applied Geophysics》1954,27(1):1-6

Summary Displacements and stresses produced by impulsive radial pressure and by impulsive twists have been determined. In the former case total flow of energy across a spherical boundary has been obtained.  相似文献   

Evening and morning twilight airglow emissions of 5577 Å and 5893 Å lines at Calcutta and Allahabad and their correlation with flare index     

S. K. Midya  G. Tarafder  T. K. Das 《Earth, Moon, and Planets》1993,63(3):199-207

Evening and morning twilight enhancements of 5577 Å and 5893 Å lines were observed by Dunn-Manring type photometer at Calcutta during the period 1983–1985 and that of 5577 Å have been collected from Allahabad observatory. The following paper presents the correlation between the enhanced intensity of airglow lines (A _G ) and solar flare index (I _f ) which is calculated considering all the flares which occurred 24 hr before the times of occurrence of enhancements. It is observed that the intensity of airglow lines varies with the flare index in an oscillatory manner upto a certain limiting value ofI _f . Afterwards intensity of both lines increases with the increase ofI _f . The nature of variation is the same for both sunspot maximum and minimum periods. A possible explanation of such type of variation has also been invoked.  相似文献   

OnH-functions of radiative transfer     

S. R. Das Gupta 《Astrophysics and Space Science》1974,30(2):327-342

Chandrasekhar'sH-functionH(z) corresponding to the dispersion functionT(z)=| _rs –frs(z)|, where [f _rs (z)] is of rank 1, is obtained in terms of a Cauchy integral whose density functionQ(x, ₁, ₂,...) can be approximated by approximating polynomials (uniformly converging toQ(x)) having their coefficients expressed as known functions of the parameters _r 's. A closed form approximation ofH(z) to a sufficiently high degree of accuracy is then readily available by term by term integration.  相似文献   

Exact solution of a problem in a stellar atmosphere using the Laplace transform and the Wiener-Hopf technique     

Rabindra Nath Das 《Astrophysics and Space Science》1979,63(1):155-170

The general equation for radiative transfer of line scattering intensity — including the effects of scattering, absorption and thermal emission — in the Milne-Eddington model is considered here. The scattering function is assumed to be quadratically anisotropic in the cosine of the scattering angle, and Planck's intensity function is assumed for thermal emission. The exact solutions for emergent intensity from the bounding face and the intensity at any optical depth are obtained by the method of the Laplace transform in combination with the Wiener-Hopf technique.  相似文献   

Geo-engineering properties of expansive soil treated with xanthan gum biopolymer     

Suresh Prasad Singh  Ritesh Das 《Geomechanics and Geoengineering》2020,15(2):107-122

ABSTRACT

This paper presents the effectiveness of xanthan gum (XG) biopolymer in stabilising the expansive soil. The XG biopolymer is mixed with expansive soil in different proportions such as 0%, 0.2%, 0.5%, 0.8% and 1.0% by weight of the dry soil mass. The plasticity, compaction, swelling, compressibility, hydraulic conductivity, strength and durability characteristics of the treated and un-treated expansive soil are examined. Results show that the plasticity index of the treated soil mass initially increases but beyond 0.5% biopolymer addition it decreases sharply. The optimum moisture content and maximum dry density of treated soil, found out from light and heavy compaction tests, do not follow any definite trend. It is also found that increasing XG content increases compressibility slightly but, it reduces swelling pressure, differential free swelling value and hydraulic conductivity remarkably. On the other hand, time-dependent compressive strength and resistance to mass loss increases with increasing XG content. Microscopic examination confirms the formation of gel-like linkage, which brings about the modifications in the treated expansive soil.  相似文献