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101.
Barman Prakash Jade Sridevi Shrungeshwara T. S. Kumar Ashok Bhattacharyya Sanjeev Ray Jagat Dwipendra Jagannathan Saigeetha Jamir Wangshi Menla 《International Journal of Earth Sciences》2017,106(6):2025-2038
International Journal of Earth Sciences - The present study reports the contemporary deformation of the tectonically complex northeast India using 11 years (2002–2013) of GPS... 相似文献
102.
S. Bhattacharyya 《Astrophysics and Space Science》1987,136(1):77-82
This paper presents a critical analysis and partial modification of a very recent work by an author on the same topic with the help of a specific model. The proposed modifications bring closer agreements with the experimental data and give the basic model wider applicability. It is, however, emphasised that the suggested modifications do not alter the basic tenets of the model used by both the authors. 相似文献
103.
The formation of massive galaxies at the centre of a cluster is discussed here. The protogalaxies move with both rotation and random velocities through the gaseous medium pervading the cluster. Each galaxy is supposed to move through a resisting medium under the general gravitational field produced by the cluster as a whole. Also, the mass of the galaxy increases by accretion all the time as it moves through the medium. Using plausible laws for density of the medium and accretion of matter and solving equation of motion, we find that the galaxy loses angular momentum in the course of the time. The loss of angular momentum drives the galaxy towards the centre of the cluster. Thus over a sufficiently long time-scale several galaxies may merge in the central region of the cluster resulting in a single massive galaxy. The process can drive rise to several massive galaxies in the central region of the cluster. 相似文献
104.
D. P. Sharma B. V. Nagaraja J. C. Bhattacharyya S. Mohin A. V. Raveendran 《Astrophysics and Space Science》1983,95(1):65-77
We have monitored the X-ray source X-Per (4U 0352+30) on 31 August, 1979 through aU filter for about 1.5 hr using 102-cm telescope of Kavalur observatory. During this period intensity of X-Per fluctuated for some time, on time scales of few minutes but recovered in the end. It was again monitored from 27 December, 1979 to January 1980 through a standardU, B, V photometer attached to a 34-cm telescope. In this paper we present the data on the fast flickerings observed on 31 August, 1979 and on the long term monitoring from December 1979 to January 1980. 相似文献
105.
106.
Variation of the strength of recurrent geomagnetic activity, which occurs just before a sunspot minimum, with local time is studied for a network of observatories covering different latitude and longitude zones. For this purpose, hourly averages of horizontal intensity(H) for each UT hour for 173 days, which are totally free of disturbances due to solar transients, have been subjected to spectral analysis. Well-defined spectral peaks associated with periodicities of 28, 14 and 9 days were present in almost all the spectra. The pattern of daily variation of the strength of the 27-day signal changes from a diurnal one at low latitudes to a semi-diurnal one near the Sq focus and in this region, the 14-day signal appears to have an independent origin irrespective of the longitude zone. A study of 27-day oscillation in mean dailyH field also indicates that apart from ring current modulation, both Sq and electrojet fields also undergo 27-day oscillations during the declining phase of a solar cycle possibly through the ionospheric wind system. 相似文献
107.
Pyroclastic fragments of basaltic composition are obtained in a thick metabasaltic layer from the Singhbhum orogenic belt of Eastern India. Field relations indicate the basalts to be submarine lava flows. Chemically, the metabasalts represent an original dry basaltic magma, showing a differentiation trend of Fe-enrichment much like the abyssal tholeiites and the Skaergaard rocks. The fragments are sharply angular in shape and distinctly richer in FeO, MgO, and MnO relative to the enclosing matrices. It is shown that the fragments are least likely to represent solidified lavas. These are best explained as cumulates which were fragmented and erupted with the fractionated melts. 相似文献
108.
The Barda igncous complex of western Saurashtra (Gujarat) consists of a group of volcanic and subvolcanic igneous rocks, viz., pitchstone, rhyolite, felsite, granophyre and dioritic rocks. They are generally grouped under the Deccan Trap series and have been emplaced through the Deccan Trap basalt flows. Using different varieties of clinopyroxenes as characteristic phases several units of felsites and granophyres have been distinguished in the southeastern part of the Barda hills. The augites of the adjacent Deccan Trap basalt flows range between Ca33Mg61Fe6 and Ca41Mg44Fe15. (All compositions of minerals are derived from optical data). The clinopyroxene of a monzodiorite is Ca41Mg42.5Fe16.5. In the felsites and granophyres the clinopyroxenes range from salite (Ca46Mg31Fe23) through ferrosalite (Ca46Mg20Fe34) and ferroaugite (Ca43Mg17Fe46) to hedenbergite (Ca46Mg9Fe45). Beyond that a peralkaline trend is indicated by common occurrence of aegirine-augite granophyre in which the clinopyroxene is alkalic with 20 percent of NaFe3 Si2O6 (acmite) molecule. Several bodies of acmite-riebeckitebearing granophyres have been found; they also indicate a high degree of oxidation. A fayalitic olivine-bearing granophyre is of interest as it shows the strongest iron enrichment with 13 weight percent FeO + Fe2O3; its mineralogy indicates a very low oxygen fugacity of 1013 atmospheres during crystallization. 相似文献
109.
An analytical expression is derived for the cutoff rigidity of cosmic rays arriving at a point in an arbitrary direction, when the main geomagnetic field is approximated by that of an eccentric dipole. This expression is used to determine changes in geomagnetic cutoffs due to secular variation of the geomagnetic field since 1835. Effects of westward drift of the quadrupole field and decrease in the effective dipole moment are seen in the isorigidity contours. On account of the immense computer time required to determine the cutoff rigidities more accurately using the particle trajectory tracing technique, the present formulation may be useful in estimating the transmission factor of the geomagnetic field in cosmic ray studies, modulation of cosmogenic isotope production by geomagnetic secular variation, and the contribution of geomagnetic field variation to long term changes in climate through cosmic ray related modulation of the current flow in the global electric circuit. 相似文献
110.
We study the linear stability of nondissipative flow of an electrically conducting fluid subject to non-axisymmetric disturbances in the following cases: (i) the radial flow of an incompressible fluid between two concentric porous circular cylinders in the presence of a radial magnetic field and (ii) axial flow of a compressible fluid between two concentric circular cylinders permeated by a helical magnetic field (0,B
0(r),B
0z) in a cylindrical coordinate system. It is shown that in case (i), the flow is stable if the Alfvén velocity based on the undisturbed radial magnetic field exceeds the radial velocity due to suction or injection at the cylinder surfaces. In case (ii), it is found that under certain conditions the complex wave speed for an unstable mode lies within a circle of diameterW
max-W
min, whereW
max andW
min are the maximum and minimum values of the axial velocity in the flow region. In the presence of a purely axial magnetic field, however, the complex wave speed for an unstable mode always lies within the above circle. 相似文献