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21.
Ravi Shanker S. Nag A. Ganguly A. Absar B. P. Rawat G. S. Singh 《Journal of Earth System Science》2001,110(1):63-76
The diamond bearing pipe rocks in Majhgawan-Hinota (more than four pipes) occur as intrusives in sandstones of Kaimur Group.
These Proterozoic (974 ±30-1170 ±20 Ma) intrusive rocks, occupying the southeastern margin of Aravalli craton, were called
as ‘micaceous kimberlite’ in tune with the reported kimberlite occurrences from other parts of the world. Judging from the
definition of kimberlite, as approved by the IUGS Subcommission on Systematics of Igneous Rocks, it is not justified to call
these rocks as ‘micaceous kimberlite’. Rather the mineralogical assemblages such as absence of typomorphic mineral monticellite
(primary), abundance of phlogopite cognate, frequent presence of barite and primary carbonate mostly as calcite coupled with
ultrapotassic and volatile-rich (dominantly H2O) nature and high concentration of incompatible elements (such as Ba, Zr, Th, U), low Th/U ratios, low REE and no Eu-anomaly
clearly indicate a close similarity with that of South African orangeites. Thus orangeites of Proterozoic age occur outside
the Kaapvaal craton of South Africa which are much younger (200 Ma to 110 Ma) in age. 相似文献
22.
In the present paper we look for periodicities in the mean solar magnetic field observed at Stanford Observatory, using Fourier transform and autocorrelation techniques. Apart from the periodicity equal to that of the synodic rotational modulation of the Sun, other periods were also found by examining the time series formed at different epochs of the solar cycle. From the aforesaid analyses a 14-day periodicity has been confirmed, which is found to occur in all the cases taken under consideration. 相似文献
23.
Tapas Acharya Sisir Kanti Nag Sukumar Basumallik 《Journal of the Geological Society of India》2012,80(5):723-730
Filter analysis of lineaments in Precambrian metamorphic rocks was used to delineate fracture-correlated lineaments and hydraulically significant fractures. The unfiltered analysis technique fails to show correlation between major lineaments and fractures. Domain-based and discrete filtering techniques successfully identify fracture-correlated lineaments within the brittle-ductile shear zone in conjunction with fractures characterized by high fracture frequencies (>10/m). The locales of hydraulically significant fractures can thus be assessed if the geological controls governing the spatial distribution of fracture frequencies are computed using structural domain approach. The concurrence of fracture-correlated lineaments and hydraulically significant fractures within the brittle-ductile shear zone is evident. 相似文献
24.
Nandini Nag Sutapa Ghosh Roni Saha Somenath Chakrabarty 《Astrophysics and Space Science》2009,323(2):123-133
Following some of the recent articles on hole super-conductivity and related phenomena by Hirsch (Phys. Lett. A 134:451, 1989; Phys. Rev. B 68:184502, 2003a; Phys. Rev. B 71:184521, 2005a and Phys. Lett. A 345:453, 2005b) a simple model is proposed to explain the observed low surface magnetic field of the expected quark stars. It is argued
that the diamagnetic moments of the electrons circulating in the electro-sphere induce a magnetic field, which forces the
existing quark star magnetic flux density to become dilute. For the sake of completeness, we have also included the analyses
of instability at the normal-super-conducting interface due to excess accumulation of magnetic flux lines. The instability
at the interface has also been studied numerically.
相似文献
25.
Nag P 《Population geography : a journal of the Association of Population Geographers of India》1989,11(1-2):86-96
This paper surveys the contributions of the International Geographic Union (IGU) and the International Cartographic Association (ICA) to the field of population studies over the past 3 decades. Reviewing the various focal themes of conferences sponsored by the organizations since the 1960s, the author examines the evolution of population studies in IGU and ICA. During the 1960s, IGU began holding symposia addressing the issue of population pressure on the physical and social resource in developing countries. However, it wasn't until 1972, at a meeting in Edmonton, Canada, when IGU first addressed the issue of migration. But since then, migration has remained on the the key concerns of IGU. In 1978, the union hosted a symposium on Population Redistribution in Africa -- the first in a series of conferences focusing on the issue of migration. As an outgrowth of migration, the IGU also began addressing the related issue of population education. The interest in migration has continued through the 1980s. In addition to studies of regional migration, the IGU has also focused on conceptual issues such as migrant labor, environmental concerns, women and migration, and urbanization. In 1984, IGU began cooperating with ICA in the areas of census cartography and population cartography. The author concludes his review of IGU and ICA activities by discussing the emerging trends in population studies. The author foresees a more refined study of migration and more sophisticated population mapping, the result of better study techniques and the use of computer technology. 相似文献
26.
Influence of rock types and structures in the development of drainage network in hard rock area 总被引：6，自引：0，他引：6
Remote sensing techniques has proved to be an extremely useful tool in morphometric analysis and groundwater studies. Remote
sensing techniques with an emphasis on lineament identifications can play a great role in groundwater prospecting in semi-arid
hard rock areas of Purulia district. In the present study, morphometric analysis using remote sensing technique has been carried
out in parts of Baghmundi block, Purulia district, West Bengal. The parameters worked out include Bifurcation ratio (Rb), Stream length (Lu), Form factor (Rc), Circulatory ratio (Rc), and Drainage density (D). The morphometric analysis suggests that fractured, resistant, permeable rocks cover the area,
the drainage network not so affected by tectonic disturbances. Using satellite imageries of two dates of IRS, different hydrogeomorphological
units have been delineated. Among different hydrogeomorphic units (i) very shallow weathered pediment and (ii) Structural
hills/ residual hills/inselbergs have very poor ground water prospects, while moderately weathered pediplains and valley fills
are good prospective zones for groundwater exploration. 相似文献
27.
The basal component of radio emission is the radio intensity obtained after subtracting the sunspot-dependent (magneto-active) component from the observed flux and finally deducting the steady part from this subtracted value. The periodicity of this basal component of solar radio emission in the frequency band 0.245–15.4 GHz was studied both for the solar maximum (1980 and 1991) and minimum (1975 and 1986) periods. A constant periodicity of 35 days was observed in the entire radio band under study during the periods of maximum solar activity, whereas the periodicity fluctuates harmonically with frequency during the minimum periods, giving rise to an average time period of approximately 54 days. 相似文献
28.
K. R. Nag 《Pure and Applied Geophysics》1961,48(1):16-22
Summary The propagation of Rayleigh waves in three dimensions in alluvial soils which do not behave like ordinary isotropic elastic solids have been discussed in this paper. The frequency equation has been solved for different soil constants. 相似文献
29.
30.
S. K. Nag 《Journal of the Indian Society of Remote Sensing》2005,33(4):521-529
Groundwater being a valuable resource in today’s world needs proper evaluation and management for overall development within
the region for its judicious use. The Baghmundi Block of Purulia district, West Bengal is within the hard rock terrain of
Ayodhya hills and Matha Protected forest. The groundwater in this region is confined within the fracture zones and weathered
residuum. Hydrogeomorphologically, the entire area is classified into following categories such as - i) Very shallow weathered
pediment, ii) Moderately weathered pediment, iii) Valley fills, iv) Erosional gullies, v) Lateritic Upland and vi) Accumulation
gullies.
The hydrogeomorphic map of the area prepared by Department of Science and Technology, Govt. of West Bengal has been digitized
for the present study. The lineament map has been prepared from the satellite imagery. The lineament map has also been digitized
for the present study. From this the lineament density contour map has been prepared. An integrated remote sensing and Geographic
Information System (GIS) based methodology has been used for the delineating Groundwater potential zones in the study area.
Here the Geomorphology and Lineament density maps are overlaid following the Weighted Index Overlay Method, which delineates
groundwater potential zones. 相似文献