A case of commensurability induced by oblateness     

Ram Krishan Sharma  P. V. Subba Rao 《Celestial Mechanics and Dynamical Astronomy》1978,18(2):185-194

In the three-dimensional restricted three-body problem, it is known that there exists a near one-to-one commensurability ratio between the planar angular frequencies (s _{1, 2, 3}) and the corresponding angular frequency (S ₂) in thez-direction at the three collinear equilibria (L _{1, 2, 3}), which is significant for small and practically important values of the mass parameter (). When the more massive primary is treated as an oblate spheroid with its equatorial plane coincident with the plane of motion of the primaries, it is established that oblateness induces a one-to-one commensurability at the exterior pointL ₃ (to the right of the more massive primary) and at the interior pointL ₂ for 01/2 and that atL ₁ no such commensurability exists. However, the values of the oblateness coefficient (A ₁) involved atL ₂ are too high to have any practical significance, while those atL ₃ being small for small values of may be useful for generating periodic orbits of the third kind.  相似文献   

Suprathermal grains: On intergalactic magnetic fields     

Ajoy Kumar Dasgupta 《Astrophysics and Space Science》1979,60(2):455-464

Charged dust grains of radiia3×10^–63×10^–5 cm may be driven out of the galaxy due to radiation pressure of starlight. Once clear of the main gas-dust layer, dust grains may then escape into intergalactic space. Such grains are virtually indestructible-being evaporated only during galaxy formation. The dust grains, once injected into the intergalactic medium, may acquire suprathermal energy, thus suprathermal grains in collision with magnetized cloud by the Fermi process. In order to attain relativistic energy, suprathermal grains have to move in and out (scattering) of the magnetic field of the medium. It is now well established that high energy cosmic rays are of the order 10²⁰ eV or more. We have speculated that these high energy (>-10¹⁸ eV) cosmic ray particles are charged dust grains, of intergalactic origin. This is possible only if there exists a magnetic field in the intergalactic medium.  相似文献   

Bearing capacity of rectangular footing on reinforced soil   总被引：2，自引：4，他引：2  

Arvind Kumar  Swami Saran 《Geotechnical and Geological Engineering》2003,21(3):201-224

In the present paper, a method of analysis for calculating the pressure intensity corresponding to a given settlement for a rectangular footing resting on reinforced soil foundation has been presented. The process has been simplified by presenting non-dimensional charts for the various terms used in the analysis, which can be directly used by practicing engineers. An empirical method has been suggested to find out the ultimate bearing capacity of footing on reinforced soil. The results have been validated with large-scale model tests also. The procedure has been made clear by giving an illustrative example. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Study of the epicentral trends and depth sections for aftershocks of the 26th january 2001, Bhuj earthquake in Western India     

S. G. Gaonkar  B. V. Srirama  S. R. Samaddar  D. V. Punekar  Sagina Ram  Reena De  J. R. Kayal 《Journal of Earth System Science》2003,112(3):401-412

The Geological Survey of India (GSI) established a twelve-station temporary microearthquake (MEQ) network to monitor the aftershocks in the epicenter area of the Bhuj earthquake (M _w7.5) of 26th January 2001. The main shock occurred in the Kutch rift basin with the epicenter to the north of Bhachao village, at an estimated depth of 25 km (IMD). About 3000 aftershocks (M _d ≥ 1.0), were recorded by the GSI network over a monitoring period of about two and half months from 29th January 2001 to 15th April 2001. About 800 aftershocks (M _d ≥ 2.0) are located in this study. The epicenters are clustered in an area 60 km × 30 km, between 23.3‡N and 23.6‡N and 70‡E and 70.6‡E. The main shock epicenter is also located within this zone. Two major aftershock trends are observed; one in the NE direction and other in the NW direction. Out of these two trends, the NE trend was more pronounced with depth. The major NE-SW trend is parallel to the Anjar-Rapar lineament. The other trend along NW-SE is parallel to the Bhachao lineament. The aftershocks at a shallower depth (<10km) are aligned only along the NW-SE direction. The depth slice at 10 km to 20 km shows both the NE-SW trend and the NW-SE trend. At greater depth (20 km–38 km) the NE-SW trend becomes more predominant. This observation suggests that the major rupture of the main shock took place at a depth level more than 20 km; it propagated along the NE-SW direction, and a conjugate rupture followed the NW-SE direction. A N-S depth section of the aftershocks shows that some aftershocks are clustered at shallower depth ≤ 10 km, but intense activity is observed at 15–38 km depth. There is almost an aseismic layer at 10–15 km depth. The activity is sparse below 38 km. The estimated depth of the main shock at 25 km is consistent with the cluster of maximum number of the aftershocks at 20–38 km. A NW-SE depth section of the aftershocks, perpendicular to the major NE-SW trend, indicates a SE dipping plane and a NE-SW depth section across the NW-SE trend shows a SW dipping plane. The epicentral map of the stronger aftershocksM ≥ 4.0 shows a prominent NE trend. Stronger aftershocks have followed the major rupture trend of the main shock. The depth section of these stronger aftershocks reveals that it occurred in the depth range of 20 to 38 km, and corroborates with a south dipping seismogenic plane.  相似文献   

Depositional Record of Tidal-Flat Sedimentation in the Permian Coal Measures of Central India: Barakar Formation, Mohpani Coalfield, Satpura Gondwana Basin   总被引：1，自引：0，他引：1  

Chandan Chakraborty  Sanjoy Kumar  Ghosh  Tapan Chakraborty 《Gondwana Research》2003,6(4):817-827

The Permian Barakar Formation in the Mohpani coalfield, Satpura Gondwana basin, is composed of three broad lithologies that occur repetitively and are iterdigitated: (1) several metres thick coarse- to medium-grained sandstone bodies with scoured bases, (2) 5-20 m thick medium- to fine-grained sandstone bodies and (3) 5-20 m thick mudstone-dominated packages with variable proportions of centimetre- to decimetre-scale, fine- to medium-grained sandstone, carbonaceous shale and coal. The Barakar strata were previously interpreted as deposits of braided rivers and associated inter-channel flood basin in a continental setting. However, this study recognizes signatures of tidal current from the mudstone-dominated packages implying marine influence during Barakar sedimentation.

The mudstone-dominated sediment bodies are the focus of this paper and comprise of three lithofacies that bear imprints of tidal processes during Barakar sedimentation: (1) heterolith, (2) sandstone, and (3) coal-carbonaceous shale, which alternate with one another within individual bodies. The heterolithic facies show interlayering of sandstone and claystone resembling flaser, wavy and lenticular bedding, as well as pinstripe stratification. Successive sandstone-mudstone couplets indicate periodic waxing and waning of flows. Within individual heterolithic packages, the sandstone:claystone ratio along with the bedding style, varies cyclically upwards giving rise to alternate sandstone-dominated and claystone-dominated intervals suggesting tidal velocity fluctuation reflective of spring-neap lunar cycle. Thickness plots of successive sand-mud couplets also reveal cyclic variation with a conspicuous periodicity of around 12 couplets per cycle, which corroborates the spring-neap-spring (or neap-spring-neap) lunar cycle. Presence of abundant desiccation cracks indicates periodic emergence and points towards an intertidal setting. The sandstone facies is characterized by a variety of wave-generated features such as bundled and chevron upbuilding of lamina, bi-directional foreset orientations, offshooting and draping laminae, scour-and-drape feature, swollen lens-like geometries suggesting their emplacement under storm-induced combined-flow on the tidal-flat. The coal-carbonaceous shale facies represent supratidal marsh environment.  相似文献   

Productivity optimisation in weak sedimentary formations for improved coal production and roof stability—an approach     

V. M. S. R. Murthy  Santosh Kumar Ray 《Geotechnical and Geological Engineering》2002,20(3):273-290

Far-field peak particle velocity (PPV) measurements were made in the roof while blasting in coal development drivages at Tandsi Mine, Western Coalfields Limited, India. The roof was fragile at this mine and was posing constant support problems for mining, resulting in low productivity. The PPV measurements have been used to decipher the damage zone in the roof. The extent of damage obtained has been compared to establish the threshold limits for the damage zone. Conversely, the maximum charge per delay that can be exploded is calculated and a suitable blast design has been recommended for maintaining the roof stability and pull. A roof vibration predictor equation has been developed that shows a consistent trend indicating that it may have future use in a similar geo-mining setup. The blast pattern recommended has reduced the damage extent, though marginally, but helped in improving pull. Critical PPV for incipient rock damage in underground coal mine development drivages under fragile roof were computed. The PPV level for incipient crack growth was found to vary from 500 to 800 mm/s while for overbreak it varied from 800 to 1200 mm/s. It was also observed that the location of cut holes, charge concentration and firing sequence were found to be responsible for the difference in their damage potential.  相似文献   

Study of weathering and erosional status of basaltic rocks using remote sensing data     

Anup Kumar Das  Saumitra Mukherjee 《Journal of the Indian Society of Remote Sensing》2002,30(3):149-156

In the present study an attempt has been made in order to evaluate the weathering and erosional status of a part of the Konkan coast stretching between Mumbai and Rajpuri, using IRS-IB, LISS-II data supported by spectral reflectance and thin section study of the rock samples collected from the coastal plains. The study revealed that extensive erosion has been taking place in few pockets along the Konkan Coastal plain, which is evidenced by the presence of more weathered rocks in the coastal plains as compared to that of the hinterland, siltation of the coastal wetlands due to the deposition of eroded materials and high-suspended sediments in the coastal water. The thin section study of the basaltic rock samples collected from the coast also shows evidence of physical and chemical weathering. The lineaments of the coastal tract are found to exist in clusters mostly trending towards NNE—SSW and a few N—S trending, this supports the presence of a N-S trending fault parallel to the Konkan coast along the Western Ghats. It has also been found that remote sensing, in association with other conventional techniques is ideal for such type of studies.  相似文献   

Detection of seismic reflections from seismic attributes through fractal analysis   总被引：5，自引：0，他引：5  

Sankar Kumar Nath  Pawan Dewangan 《Geophysical Prospecting》2002,50(3):341-360

The concept of fractals is used here for the identification of seismic reflectors with special emphasis on thin‐bed delineation, which is generally overlooked during standard data processing. A new fractal analysis scheme is applied to both synthetic and real field seismic data. The fractal dimensions of the three seismic attributes – amplitude, phase, and instantaneous frequency – have been analysed and evaluated. A change in fractal dimension is found to occur whenever there is a reflection. However, the resolution in the delineation of reflectors varies, depending on the attribute under consideration and the method of fractal dimension estimation used. Fractal analysis is performed on both noise‐free and noisy synthetic data to establish the noise tolerance limit for both the ‘divider method’ and the ‘Hurst method’. It is then tested with different peak frequencies of the source wavelet to establish the criteria for using the divider method and the Hurst method. The divider method is found to be suitable for high peak frequency source wavelets (> 25 Hz), while the Hurst method is best suited for low peak frequency source wavelets (< 25 Hz). Finally, when applied to the digitally processed and migrated field seismic data, it could even delineate reflectors which otherwise went undetected on the migrated time section.  相似文献   

Passive diffusion sampling of sulfur dioxide in India: Impact assessment on arid areas     

S.Kumar  M.Mohan  R.Datta 《中国科学D辑(英文版)》2002,45(Z1)

Environmental constraints have drastically limited options of sustainable developmentand have severely offset many developmental schemes. In this paper, possibilities of acidic depo-sition, as a counter measure of desertification, are analyzed. Seasonal data of ambient sulfur di-oxide, pH of rain water and soil acidity are collected for over an year and analyzed. Arid environ-ment of surrounding areas of Delhi is considered and analyzed. Though ambient sulfur depositionis well below critical level, it might not be truly indicative of plant survival in arid areas. Results maybe useful in arid area afforestation, and polluting industries relocation, which holds tremendouspotential vis-a-vis sustainable development.  相似文献   

A receiver function perspective of the Dharwar craton (India) crustal structure   总被引：1，自引：0，他引：1  

Dipankar Sarkar  M. Ravi Kumar  Joachim Saul  Rainer Kind  P. S. Raju  R. K. Chadha  A. K. Shukla 《Geophysical Journal International》2003,154(1):205-211

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