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161.
Abhay Anand Bourai Sunita Aswal Anoop Dangwal Mukesh Rawat Mukesh Prasad Nagendra Prasad Naithani Veena Joshi Rakesh Chand Ramola 《Acta Geophysica》2013,61(4):950-957
Radon in the Earth’s crust or soil matrix is free to move only if its atoms find their way into pores or capillaries of the matrix. 222Rn atoms from solid mineral grains get into air, filling pores through emanation process. Then 222Rn enters into the atmosphere from air-filled pores by exhalation process. The estimation of radon flux from soil surface is an important parameter for determining the source term for radon concentration modeling. In the present investigation, radon fluxes and soil-gas radon concentration have been measured along and around the Main Central Thrust (MCT) in Uttarkashi district of Garhwal Himalaya, India, by using Scintillation Radon Monitor (SRM) and RAD7 devices, respectively. The soil radon gas concentration measured by RAD7 with soil probe at the constant depth was found to vary from 12 ± 3 to 2330 ± 48 Bq·m?3 with geometrical mean value of 302 ± 84 Bq·m?3. Th significance of this work is its usefulness from radiation protection point of view. 相似文献
162.
163.
Uma Pandey Ashutosh K. Singh Om P. Singh Birbal Singh Vibhav K. Saraswat 《Acta Geophysica》2016,64(3):755-771
We present here the results of sub-ionospheric VLF perturbations observed on NWC (19.8 kHz) transmitter signal propagating in the Earth-ionosphere waveguide, monitored at our low latitude station Agra. During the period of observation (June-December 2011), we found 89 cases of VLF perturbation, while only 73 cases showing early character associated with strong lightning discharges. Out of 73 events, 64 (~84%) of the early VLF perturbations are found to be early/slow in nature; the remaining 9 events are early/fast. The onset duration of these early/slow VLF perturbations is up to ~ 5 s. A total of 54 observed early events show amplitude change lying between ± 3.0 dB, and phase change ± 12 degree, respectively, and found to occur mainly during nighttime. One of the interesting results we found is that the events with larger recovery time lie far away from the VLF propagation path, while events with smaller duration of recovery are within the ± 50–100 km of signal path. The World Wide Lightning Location Network (WWLLN) data is analysed to find the location of causative lightning and temporal variation. The lightning discharge and associated processes that lead to early VLF events are discussed. 相似文献
164.
Biman J. Medhi Maheswar G. J. C. Pandey T. S. Kumar Ram Sagar 《Monthly notices of the Royal Astronomical Society》2008,388(1):105-116
We present new B , V and R linear polarimetric observations for 61 stars towards the region of the young open cluster NGC 654. In this study we found evidence for the presence of at least two layers of dust along the line of sight to the cluster. The distances to the two dust layers are estimated to be ∼200 pc and ∼1 kpc which are located much closer to the Sun than the cluster (∼2.4 kpc). Both the dust layers have their local magnetic field orientation nearly parallel to the direction of the Galactic plane. The foreground dust layer is found to have a ring morphology with the central hole coinciding with the centre of the cluster. The foreground dust grains are suggested to be mainly responsible for both the observed differential reddening and the polarization towards the cluster. 相似文献
165.
Surface layer atmospheric and ocean observations have been collected along the cruise track from a special scientific expedition to Antarctica. Bulk estimates of surface momentum flux, sensible heat flux and latent heat flux have been computed applying bulk algorithms from the data collected along cruise track during the time period January 27 to March 31, 2006, and compared the results with National Centre for Environmental Prediction (NCEP) reanalysis. Underestimation of surface momentum flux in roaring forties (40°S–50°S) area of Indian Ocean is seen from NCEP reanalysis. Systemic differences in sensible and latent heat fluxes between observed and NCEP reanalysis have been found. Along the cruise track, the average sensible (latent) heat flux was 9.45 Wm?2 (67.46 Wm?2) and 3.75 Wm?2 (64.45 Wm?2) from the direct measurement and NCEP reanalysis, respectively. The NCEP reanalysis is being widely used in numerical modeling studies, and the discrepancies shown in the NCEP reanalysis in present study will be of immense use to the modeling community of the Indian Ocean in general and Southern Indian Ocean in particular. 相似文献
166.
The Kachchh Basin and the Jaisalmer Basin are two neighboring Mesozoic sedimentary basins at the western margin of the Indian
craton. The Jurassic succession of the Kachchh Basin is more complete and more fossiliferous than that of the Jaisalmer Basin.
Consequently, intrabasinal correlation of the sedimentary units has been possible in the Kachchh Basin, but not in the Jaisalmer
Basin. However, some marker beds existing in the Kachchh Basin can be recognized also in the Jaisalmer Basin. Ammonite evidence
shows that they are time-equivalent. The following four units form marker intervals in both basins: (1) the pebbly rudstone
unit with Isastrea bernardiana and Leptosphinctes of the Kaladongar Formation (Kachchh Basin) and the Isastrea bernardiana-bearing rudstone of the Jaisalmer Formation (Jaisalmer Basin) both represent transgressive systems tract deposits dated as
Late Bajocian; (2) bioturbated micrites with anomalodesmatan bivalves within the Goradongar Yellow Flagstone Member (Kachchh
Basin) and bioturbated units in the Fort Member (Jaisalmer Basin) represent maximum flooding zone deposits of the Middle to
Late Bathonian; (3) trough-crossbedded, sandy pack- to grainstones of the Raimalro Limestone Member (Kachchh Basin) and the
basal limestone-sandstone unit of the Kuldhar section of the Jaisalmer Formation (Jaisalmer Basin) correspond to Late Bathonain
transgressive systems tract deposits; and (4) ferruginous ooid-bearing carbonates with hardgrounds of the Dhosa Oolite member
(Kachchh Basin) and the middle part of the Jajiya Member (Jaisalmer Basin) are Oxfordian transgressive systems tract deposits.
The fact that in both basins similar biofacies prevailed during certain time intervals demonstrates a common control of their
depositional history. As the two basins represent different tectonic settings, the most likely controlling factors were the
relative sea-level changes produced by eustatic processes, a common subsidence history of the northwestern margin of the Indian
craton, and the paleoclimate. 相似文献
167.
168.
Arvind Chandra Pandey Swagata Ghosh M. S. Nathawat Reet Kamal Tiwari 《Journal of the Indian Society of Remote Sensing》2012,40(2):245-255
Accurate representations of the Earth’s surface in the form of digital elevation models (DEMs) are essential for a variety
of applications in glaciological and remote-sensing research. In the present study area change and thickness variation over
Pensilungpa glacier was attempted using remote sensing approach. It can be remarked that a net loss of 9.23 sq. km. which
is 38% of the glacier area mapped in 1962 indicate a drastic change over the glacier area during 1962–2007. Estimation of
glacier thickness change on Pensilungpa glacier based on ASTER DEM (2003) and Survey of India (SOI) contour based DEM (1962)
indicated increase in the glacier elevation in the accumulation zone mainly by 30 to 90 m and similar reduction by 30 to 90 m
in the ablation zone. 相似文献
169.
The great 1950 Assam Earthquake revisited: Field evidences of liquefaction and search for paleoseismic events 总被引:1,自引:0,他引:1
D.V. Reddy P. Nagabhushanam Devender Kumar B.S. Sukhija P.J. Thomas Anand K. Pandey R.N. Sahoo G.V. Ravi Prasad K. Datta 《Tectonophysics》2009,474(3-4):463-472
Extensive field investigations were carried out for the first time in the meizoseismal area of the great 1950 Assam Earthquake aimed at exploring the paleoseismic history of the NE Indian region through documentation of liquefaction features and radiocarbon (14C) dating. Trenching at more than a dozen locations along the Burhi Dihing River valley and within the alluvial fans adjoining the Brahmaputra and Dibang Rivers resulted in the identification of more than a dozen very prominent liquefaction features (sand dykes, sills, sand blows etc.) as evidences of large to great earthquakes. 14C dating of the organic material associated with some of the features indicates a paleoseismic record of about 500 yrs archived by the sediments in this region. Compelling geological evidence(s) of the great 1950 earthquake are well constrained by 14C dating. Out of the two historically reported seismic events (1548 AD and 1697 AD) from this region, 14C dating could constrain the 1548 AD event though not distinctly. Further studies using combined 14C and OSL dating may better constrain the seismo-chronology of the study region. 相似文献
170.
O. P. Pandey 《Journal of the Geological Society of India》2009,74(5):615-624
Indian shield has been frequented by number of large and moderate magnitude damaging earthquakes since historical times, including
the recent disastrous ones like Latur Mw 6.3 in 1993, Jabalpur Mw 5.8 in 1997 and Bhuj Mw 7.7 in 2001. Seismogenesis of these
events is still not understood well. Detailed study of nine such earthquake localities (as appended in Table 1), indicates
quite high P- and S- velocities (6.2–6.7 km/s and 3.65–3.90 km/s respectively) at a shallow depth of almost surface to six
kilometers. These seismogenic regions appear to be in a state of continuous uplift and erosion since geological times, which
brought mafic (granulitic/amphibolitic) crust to significantly shallow levels in which stresses are accummulated due to ongoing
local uplift and a high input of heatflow from the mantle. These stresses act over and above to the regional compressive stresses
generated by India-Eurasia collision. As against common belief, the role played by fluids in nucleation of such earthquakes,
in the relatively denser and high velocity Indian crust (compared to the other global stable continental regions), appears
limited. 相似文献