Geophysical anomalies associated with uranium mineralization from Beldih mine, South Purulia Shear Zone, India     

Animesh Mandal  Arkoprovo Biswas  Saurabh Mittal  William K. Mohanty  Shashi Prakash Sharma  Debashish Sengupta  Joydip Sen  A. K. Bhatt 《Journal of the Geological Society of India》2013,82(6):601-606

Beldih mine at the central part of the South Purulia Shear Zone (SPSZ) has been reported with low grade uranium-bearing formation within quartz-magnetite-apatite host in kaolinized formation. Therefore, the present integrated geophysical study with gravity, magnetic, radiometric, very low frequency electromagnetic (VLF) and gradient resistivity profiling methods around the known mineralized zones aimed at identifying the exact geophysical signatures and lateral extent of these uranium mineralization bands. The closely spaced gravity-magnetic contours over the low to high anomaly transition zones of Bouguer, reduced-to-pole magnetic, and trend surface separated residual gravity-magnetic anomaly maps indicate the possibility of high altered zone(s) along NW-SE direction at the central part of the study area. High current density plots of VLF method and the low resistive zones in gradient resistivity study depict the coincidence with low gravity, moderately high magnetic and low resistivity anomalies at the same locations. Moderate high radioactive zones have also been observed over these locations. This also suggests the existence of radioactive mineralization over this region. Along profile P2, drilled borehole data revealed the presence of uranium mineralization at a depth of ～100 m. The vertical projection of this mineralization band also identified as low gravity, low resistivity and high magnetic anomaly zone. Thus, the application of integrated geophysical techniques supported by geological information successfully recognized the nature of geophysical signatures associated with the uranium mineralization of this region. This enhances the scope of further integrated geophysical investigations in the unexplored regions of SPSZ.  相似文献   

Carbon dioxide exchange in a temperate grassland ecosystem   总被引：18，自引：0，他引：18  

Joon Kim  Shashi B. Verma 《Boundary-Layer Meteorology》1990,52(1-2):135-149

Carbon dioxide exchange was measured, using the eddy correlation technique, over a tallgrass prairie in northeastern Kansas, U.S.A., during a six-month period in 1987. The diurnal patterns of daytime and nocturnal CO₂ fluxes are presented on eight selected days. These days were distributed throughout most of the growing season and covered a wide range of meteorological and soil water conditions. The midday CO₂ flux reached a maximum of 1.3 mg m^-2 (ground area) s^-1 during early July and was near zero during the dry period in late July. The dependence of the daytime carbon dioxide exchange on pertinent controlling variables, particularly photosynthetically active radiation, vapor pressure deficit and soil water content is discussed. The nocturnal CO₂ flux (soil plus plant respiration) averaged -0.4 mg m^-2 (ground area) s^-1 during early July and was about -0.2 mg m^-2 s^-1 during the dry period.Published as Paper No. 9061, Journal Series, Agricultural Research Division, University of Nebraska-Lincoln, U.S.A.Research Associate and Professor, respectively.  相似文献   

Carbon dioxide,water vapor and sensible heat exchanges of a grain sorghum canopy   总被引：3，自引：0，他引：3  

Dean E. Anderson  Shashi B. Verma 《Boundary-Layer Meteorology》1986,34(4):317-331

With the aid of eddy correlation instrumentation, the components of the energy budget and CO₂ flux were measured over grain sorghum grown at Mead, Nebraska. Diurnal patterns of sensible heat, latent heat, CO₂ and momentum flux are examined for typical days. On a mostly clear day when the crop leaf area index was 3.7, net radiation reached a mid-day peak of 560 W m^-2, while sensible and latent heat fluxes peaked at 50 and 460 W m^-2, respectively. The peak CO₂ flux occurring just prior to solar noon was 1.5 mg m^-2(ground area) s^-1. CO₂ flux (respiration from plants, soil and roots) in the early evening was about -0.28 mg m^-2 (ground area) s^-1.A relationship between CO₂ flux and photosynthetically active radiation (PAR) was developed. Except during the late stage of growth (growth stage 8.5, toward the initiation of senescence), the crop showed no evidence of saturation up to PAR 1800 Ei m^-2s^-1. The light compensation point was found to be about 211 Ei m^-2s^-1. Examination of CO₂ flux-PAR relationships for selected days through the season indicated an aging effect in terms of a decrease in photosynthetic activity of the sorghum canopy. Measurements made on two consecutive days demonstrate the effects of weather conditions on CO₂ flux and carbon-water flux ratio (a measure of water use efficiency of the crop). The occurrence of regional sensible heat advection with concommitant high vapor pressure deficit and air temperature-limited CO₂ exchange reduced the carbon-water flux ratio.Published as Paper No. 7717, Journal Series, Nebraska Agricultural Research Division. The work was conducted under Regional Research Project 11-33 and Nebraska Agricultural Research Division Project 27-003.Formerly Post Doctoral Research Associate (now at the University of Connecticut Department of Renewable Natural Resources Storrs CT)  相似文献   

Analyzing hyper-spectral and multi-spectral data fusion in spectral domain     

H. Pande  Poonam S. Tiwari  Shashi Dobhal 《Journal of the Indian Society of Remote Sensing》2009,37(3):395-408

Image fusion is the combination of two or more different images to form a new image by using a certain algorithm. Despite the fact that the number and kind of satellite imagery are daily increasing, using fusion techniques, in a proper way, to eliminate the redundancy in data and increase the quality of data is an important challenge in Remote Sensing Image Processing. Fusion of multispectral images with a hyperspectral image generates a composite image which preserves the spatial quality from the high resolution (MS) data and the spectral characteristics from the hyperspectral data. For the present study three fusion algorithms (Principal Component Transformation, Colour Normalized and Gram-Scmidt Transformation) were analysed for Hyperion and IKONOS MSS data. Their ability to preserve the spectral quality of fused data, in comparison with original hyper-spectral image, has been investigated.  相似文献   

Period–luminosity relations for Galactic Cepheid variables with independent distance measurements     

Chow-Choong Ngeow  Shashi M. Kanbur 《Monthly notices of the Royal Astronomical Society》2004,349(3):1130-1136

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Period–colour and amplitude–colour relations in classical Cepheid variables – III. The Large Magellanic Cloud Cepheid models     

Shashi M. Kanbur  Chow-Choong Ngeow 《Monthly notices of the Royal Astronomical Society》2006,369(2):705-722

Period–colour (PC) and amplitude–colour (AC) relations are studied for the Large Magellanic Cloud (LMC) Cepheids under the theoretical framework of the hydrogen ionization front (HIF)–photosphere interaction. LMC models are constructed with pulsation codes that include turbulent convection, and the properties of these models are studied at maximum, mean and minimum light. As with Galactic models, at maximum light the photosphere is located next to the HIF for the LMC models. However, very different behaviour is found at minimum light. The long-period  ( P > 10 d)  LMC models imply that the photosphere is disengaged from the HIF at minimum light, similar to the Galactic models, but there are some indications that the photosphere is located near the HIF for the short-period  ( P < 10 d)  LMC models. We also use the updated LMC data to derive empirical PC and AC relations at these phases. Our numerical models are broadly consistent with our theory and the observed data, though we discuss some caveats in the paper. We apply the idea of the HIF–photosphere interaction to explain recent suggestions that the LMC period–luminosity (PL) and PC relations are non-linear with a break at a period close to 10 d. Our empirical LMC PC and PL relations are also found to be non-linear with the F -test. Our explanation relies on the properties of the Saha ionization equation, the HIF–photosphere interaction and the way this interaction changes with the phase of pulsation and metallicity to produce the observed changes in the LMC PC and PL relations.  相似文献   

Excitation mechanism ofNi 5199 Å lines in the day Airglow     

Gupta  Shashi K. 《Astrophysics and Space Science》1971,13(1):203-210

Production rates of N(² D) metastable atoms in the daytime atmosphere have been calculated for different possible processes, using positive ion composition and reaction rate data, available presently. Emission rates of the 5199 Å doublet of Ni are calculated by separately and jointly considering the deactivation of N(² D) atoms by electrons and molecular oxygen.From a comparison of the computed results with the observational data, an attempt has been made to identify the processes of importance to the production and deactivation of N(² D). For further confirmation of the proposed mechanism the variation of integrated intensity of this radiation with solar activity has been obtained. The calculated values may be compared with intensity data obtained in future at different levels of solar activity.  相似文献   

Hydrogeologic and hydraulic characterization of aquifer and nonaquifer layers in a lateritic terrain (West Bengal,India)     

Sabinaya Biswal  Madan K. Jha  Shashi P. Sharma 《Hydrogeology Journal》2018,26(6):1947-1973

The hydrogeologic and hydraulic characteristics of a lateritic terrain in West Bengal, India, were investigated. Test drilling was conducted at ten sites and grain-size distribution curves (GSDCs) were prepared for 275 geologic samples. Performance evaluation of eight grain-size-analysis (GSA) methods was carried out to estimate the hydraulic conductivity (K) of subsurface formations. Finally, the GSA results were validated against pumping-test data. The GSDCs indicated that shallow aquifer layers are coarser than the deeper aquifer layers (uniformity coefficient 0.19–11.4). Stratigraphy analysis revealed that both shallow and deep aquifers of varying thickness exist at depths 9–40 and 40–79 m, respectively. The mean K estimates by the GSA methods are 3.62–292.86 m/day for shallow aquifer layers and 0.97–209.93 m/day for the deeper aquifer layers, suggesting significant aquifer heterogeneity. Pumping-test data indicated that the deeper aquifers are leaky confined with transmissivity 122.69–693.79 m²/day, storage coefficient 1.01?×?10^?7–2.13?×?10^?4 and leakance 2.01?×?10^?7–34.56?×?10^?2 day^?1. Although the K values yielded by the GSA methods are generally larger than those obtained from the pumping tests, the Slichter, Harleman and US Bureau Reclamation (USBR) GSA methods yielded reasonable values at most of the sites (1–3 times higher than K estimates by the pumping-test method). In conclusion, more reliable aquifers exist at deeper depths that can be tapped for dependable water supply. GSA methods such as Slichter, Harleman and USBR can be used for the preliminary assessment of K in lateritic terrains in the absence of reliable field methods.  相似文献   

B.K. Dhruva Rao (1936–2016)     

K. T. Shashi Kumar  C. V. Seshadri 《Journal of the Geological Society of India》2017,89(2):225-225

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Period–colour and amplitude–colour relations in classical Cepheid variables – V. The Small Magellanic Cloud Cepheid models     

Shashi M. Kanbur  Chow-Choong Ngeow  Greg Feiden 《Monthly notices of the Royal Astronomical Society》2007,380(2):819-827

Period–colour (PC) and amplitude–colour (AC) relations at maximum, mean and minimum light are constructed from a large grid of full amplitude hydrodynamic models of Cepheids with a composition appropriate for the Small Magellanic Cloud (SMC). We compare these theoretical relations with those from observations. The theoretical relations are, in general, in good agreement with their observational counterparts, though there exist some discrepancy for short period  (log [ P ] < 1)  Cepheids. We outline a physical mechanism which can, in principle, be one factor to explain the observed PC/AC relations for the long and short period Cepheids in the Galaxy, Large Magellanic Cloud (LMC) and SMC. Our explanation relies on the hydrogen ionization front (HIF)–photosphere interaction and the way this interaction changes with pulsation period, pulsation phase and metallicity. Since the PC relation is connected with the period–luminosity (PL) relation, it is postulated that such a mechanism can also explain the observed properties of the PL relation in these three galaxies.  相似文献