String Cosmology in a Stationary Cylindrically Symmetric Space-Time     

Subenoy Chakraborty  Anusua Roy 《Astrophysics and Space Science》1998,262(3):245-248

We have studied string-dust cosmological model in a stationary cylindrically symmetric space-time. A one parameter family of solutions is obtained for the field equations of the system.  相似文献   

Utility of orbital surveillance system for snow monitoring in the Indian context     

K. Krishnanunni  D. K. Chakraborty  A. M. Rakshit  T. K. Kurien 《Journal of the Indian Society of Remote Sensing》1979,7(2):23-28

Since snow covered areas in the Himalayas contribute significantly to the discharge of the major rivers of North India, snow monitoring is essential for effective control and management of the available water resources, particularly in the lean period. As accumulation and melting of snow are dynamic processes the need arises for periodic monitoring. Conventional survey methods are time consuming and expensive due to adverse terrain conditions and weather. As such, updating information at reasonably frequent intervals calls for a strategy invoiving remote sensing techniques. Potentials of such techniques such as aerial and orbital photography and multispectral scanning systems as also microwave sensing systems are briefly discussed. Particular emphasis is laid on a Landsat type surveillance system, which is at the operational stage. As a case study demonstrating the system capability an area in the Sutlej catchment has been analysed on Landsat imagery acquired in October and December, 1972. The snow covered area is found to be considerably more in the December, 72 imagery. Such a map overlaid on a contoured 1:250,000 base updated every month can be useful input attempts at watershed modelling incorporating other dynamic features also.  相似文献   

Overview of some recent geophysical investigations in Himalaya     

Hari Narain 《Tectonophysics》1980,62(1-2)

Recent work on long-period surface wave dispersion investigations and other geophysical work have shown that in the Himalayan and Tibet Plateau region the crust is extremely thick and the velocities are low: However, the upper mantle below Tibet appears to have normal velocities. Seismic Research Observatories, being established in the vicinity of Himalaya, will be extremely useful for near-source investigations due to their digital data acquisition capabilities and much larger dynamic range. Quantitative seismicity maps prepared for the Himalayan region are useful in comprehending regional tectonics. With international collaboration, Deep Seismic Sounding surveys have been successfully carried out in western Himalaya. It is inferred that the northern boundary of the Indian Plate does not lie along the Main Central Himalayan Thrust or the Indus Suture line, but falls very much north of the combined Indo-Tibetan block. Focal mechanism studies are, by and large, consistent with the northward thrusting of the Indian Plate. Conflicting results regarding the prevalence of isostasy in the Himalayan region have been obtained from gravity surveys. Geophysical investigations and observational facilities need to be intensified for a better understanding of the tectonics.  相似文献   

Disturbances of cylindrical origin in an isotropic elastic medium     

S. K. Chakraborty 《Pure and Applied Geophysics》1956,33(1):9-16

Summary The paper deals with the investigations of disturbances in an infinite homogeneous isotropic and perfectly elastic medium produced by a source operating on a small portion of the inner surface of a cylindrical hole. Prof.S. K. Chakraborty, M. Sc., Surendranath College, 24 Harrison Road,Calcutta-9, India.  相似文献   

Disturbances in different types of elastic media     

Prof. S. K. Chakraborty 《Pure and Applied Geophysics》1956,35(1):25-32

Summary Disturbances generated by pressure on the surface of a spherical cavity inside (i) a dispersive medium, (ii) a medium having transverse isotropy about the radius vector have been considered. Finally, a brief discussion of the propagation of waves in visco-elastic media has been added.I wish to express my gratefulness to Professor B. B.Sen, for his kind help in the preparation of the paper.  相似文献   

Discussion     

S. Mukherjee  K. L. Chakraborty 《Mineralium Deposita》1974,9(1):91-92

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The protocontinental growth of the Indian Shield and the antiquity of its rift valleys   总被引：1，自引：0，他引：1  

S.M. Naqvi  V. Divakara Rao  Hari Narain 《Precambrian Research》1974,1(4):345-398

The evolution of the Indian Shield has been envisaged from the analysis of available tectono-lithostratigraphic, geochronological, geochemical and geophysical data. It appears that the Dharwar schist belts and their equivalents, except the Kolar schist belt, are not typical greenstone belts, but are representative of a transitional era of rapid transformation from simatic to sialic crust. In the Archaean—Proterozoic tract of India, relics of rocks older than 3.0 b.y. are identified in five widely separated regions of distinct tectono-litho-stratigraphic assemblages which probably represent the primordial continental nucleii. It is suggested that the growth of the Indian Shield has taken place through nucleation, accretion and merger into three protocontinents named Dharwar, Aravalli and Singhbhum. The cratonisation of the Indian unit seems to have been rapid and almost completed by the middle Proterozoic, as there is no significant variation in the composition of the clastic sediments and basalts from middle Proterozoic onwards. The continental nucleii appear to merge along the deep-seated lineaments, which are reflected on the tectonic map of India. Further, the Dharwar, Aravalli and Singhbhum protocontinents also seem to merge along a Y=shaped Narmada—Son—Godavari lineament which along with the Mahanadi lineament, between the two continental nucleii of the Singhbhum protocontinent have later developed into rift valleys.  相似文献   

Study of magnetic field geometry and extinction in Bok globule CB130     

A. Chakraborty  H. S. Das 《Astrophysics and Space Science》2016,361(9):321

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Dynamical behavior of size-graded dust grains levitated in rotating magnetized astroplasmas     

G. C. Das  Rupa Chakraborty 《Astrophysics and Space Science》2011,335(2):415-423

Our purpose is to examine the formation of different sheaths in rotating astroplasmas embedded in an ambient magnetic field. Sequel to our recent work (Das and Chakraborty in Astrophys. Space Sci., 2011) we remodeled our present study with the view to finding of robust sheath over the Earth’s Moon along with the formation of dust clouds therein. Based on using the pseudopotential analysis, a modified Sagdeev potential equation has been derived, which, in turns, quantifies the interaction of Coriolis force and magnetic field and to derive the different natures of sheath and dust atmosphere. The application of this result to the input numeric data of the lunar environment and dynamical behaviors of dust levitation has been studied. Our study finds that the dust particles having a spatial segregation within the sheath region form dust clouds in spaces.  相似文献   

Search for periodicities of the solar irradiance data from the Earth Radiation Budget Satellite (ERBS) using the periodogram method     

Sankar Narayan Patra  Gautam Bhattacharya  Koushik Ghosh 《中国天文和天体物理学报》2010,10(4)

We have analyzed the solar irradiance data from the Earth Radiation Budget Satellite(ERBS)during the time period from 1984 October 15 to 2003 October 15.By first filtering the data by Simple Exponential Smoothing,we have applied the periodogram method to the processed data in order to search for its time variation.The study exhibits multi-periodicities on these data around 110,118,574 and 740d with very high confidence levels(more than 99%).These periods are significantly similar to the periods of other solar activities which may suggest that solar irradiance may be associated with other solar activities.  相似文献