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R V Krishnamurthy D P Agrawal V N Misra S N Rajaguru 《Journal of Earth System Science》1981,90(2):155-160
Radiocarbon dates on pedogenic CaCO3, accumulated at various depths in a stabilised dune at Budha Pushkar, Rajasthan, show inversion with respect to ‘stratigraphy’. Occurrence of younger carbonates overlain by older ones at various levels, is interpreted in terms of a shift in climatic conditions causing pedogenic carbonates to be leached to greater depths. Based on this model, several wetter regions during the last 6000 years have been identified. The most significant shift from a dry to a wet phase seems to have taken place between 5000 and 4500 years ago. Conclusions drawn from this study is in agreement with that based on pollen data and extends this method as a potential palaeoclimatic indicator. 相似文献
3.
B. N. Ashoka G. C. Anupama T. P. Prabhu S. Giridhar K. K. Ghosh S. K. Jain A. K. Pati N. Kameswara Rao 《Journal of Astrophysics and Astronomy》1987,8(2):195-209
The evolution of the spectrum of SN1987a is traced from 1987 February 26 to March 31. Based on the low-resolution spectroscopic
data we identify the lines of H, He I, Na I, Fe II, Sc II, Ca II which are known to be present in Type II Supernovae, and
also present evidence for the existence of lines of Mg I, CaI, O I, and N I. We discuss the evolution of the Hα profile, and draw attention to its complex structure around March 30. Close
to the rest wavelength of Ha a double-peaked structure appeared in the profile with a peak-to-peak separation of ∼ 1400 km
s−1, suggestive of an expanding shell or disc of gas.
Using the available broadband photometric information, we also trace the evolution of the photosphere of SN1987a assuming
that it radiates like a supergiant. 相似文献
4.
Optical spectroscopic data are presented on nova LW Serpentis 1978, obtained during its decline fromV 9.0 to ≃10.2 (compared to a value of ∼ 8.0 at recorded maximum). The spectrum and its evolution compare well with a typical
nova, though the principal absorption (∼ −750 km s−l) was very weak in comparison with the diffuse-enhanced absorption (∼ −1300 km s−1). The principal absorption could be identified only in the lines of O I λλ7774, 8446, and in moderate-resolution observations
of Hα. The salient features of spectral evolution follow: The near-infrared triplet of Ca n continuously weakened. O I λ8446
was always brighter than O I λ 7774, indicating continued importance of Lyman Β fluorescence. The lines due to [O I], [N II]
and N n brightened considerably near the end of our observations (37 days from maximum). The Hα emission line was asymmetric
all through with more emission towards the red. Its emission profile showed considerable structure. Based on the individual
peaks in the Hα line profile, a kinematical model is proposed for the shell of LW Ser. The model consists of an equatorial
ring, and a polar cone on the side away from the earth. The nearer polar cone did not show significant emission of Hα during
our observations. The polar axis of the shell is inclined at a small angle (∼ 15‡) to the line of sight. 相似文献
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N. S. Krishnamurthy V. Ananda Rao Dewashish Kumar K. K. K. Singh Shakeel Ahmed 《Journal of the Geological Society of India》2009,73(5):639-650
Exploration and exploitation of coal seams is one of the major resources for the energy sector in any country but at the same
time water filled voids/water logged areas in the old workings of these seams are very critical problems for the coal mining
industry. In such situations, disasters like inundation, landslides, collapsing of the old seams may occur. In this regard,
it is necessary to find out the water saturated/water filled voids and zones in the mining areas. Since no established technique
is available to find such zones, an experimental study using Electrical Resistivity Imaging (ERI) has been carried out in
one of the coal mining areas near Dhanbad, to find out the feasibility of finding the barrier thickness and the water logged
area in underground coal mines. The area under study forms part of Jharia coalfield in Dhanbad district, Jharkhand state.
The coal bearing rocks of Barakar Formation of Lower Permian age (Gondwana period) occur in the area under a thin cover (10
m to15 m) of soil and or alluvium. Coal bearing Barakar Formations consist mainly of sandstone of varying grain size, intercalation
of shale and sandstone, grey and carbonaceous-shale and coal seams.
Since the water saturation reduces the resistivity of a formation to a large extent, water filled voids and old coal workings
are expected to have significant resistivity contrast with the surrounding host rock. Hence, ERI technique was applied in
such an environment as this technique uses high-density data acquisition both laterally and vertically by using multiple number
of electrodes. Along with ERI, mise-à-la-masse (also called charged body) technique was also employed at one of the promising
sites to find out the connectivity of water logged areas and also detection of these old workings from the surface measurements
was analyzed. The interpreted 2D resistivity sections have clearly indicated the water bearing zone(s) along the profile which
was well confirmed with the existing water level in the nearby borewells. On the other hand, this technique did not identify
the size of the coal pillar and gallery (air filled voids), which might be due to the small size of the voids (i.e. about
2 m × 2 m) below a depth of 15m and more but have indicated altogether as a high resistive zone ranging from 600–1000 Ohm-m. 相似文献
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8.
J. Krishnamurthy 《国际地球制图》2013,28(3):39-52
In order to evaluate the potentials of IRS‐1A Linear Imaging Self‐scanning Sensor (LISS‐I) data for geological and geomorphological applications and also to compare the IRS‐1A LISS‐I data with Landsat Thematic Mapper (TM) data, a study has been attempted for parts of Uttar Pradesh and Madhya Pradesh in Northern India. The first four spectral bands of Landsat TM sensor data which are similar and close to IRS‐1A LISS‐I senor have been utilised for the comparative evaluation. Various techniques employed for both the data set to derive the required geology and geomorphology related information include (i) band combination (ii) spectral response analysis (iii) principal component analysis (iv) supervised classification techniques and (v) visual observation of various outputs generated by the above methods. The Optimum Index Factor (OIF) method adopted for selecting suitable band combinations showed similar OIF rankings for IRS‐1A LISS‐I data and Landsat TM data. It has been visually observed that the band combination 1, 3 & 4 offers relatively better feature display. The spectral responses derived for various major geologic rock units such as Deccan Trap, Vindhyan Formation, Bundelkhand Granite and for a few landcovers such as surface water bodies and black soil show striking similarity in pattern for both LISS‐I and TM. The Principal Component (PC) analysis of both data sets suggested that the total scene brightness tends to dominate in the first PC. The percentage information contributed by PCs 1&2 as also by PCs 1,2 & 3 in both the LISS‐I and TM are comparable. It was observed from the classified image generated by performing supervised classification with a maximum likelihood algorithm that major geomorphic landforms were clearly distinguishable. Thus the qualitative and quantitative evaluation of both IRS‐1A LISS‐I and Landsat TM data showed that significant similarities exist between them. The study also revealed that IRS‐1A LISS‐I data can be effectively used for deriving geology and geomorphology related details. 相似文献
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