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31.
R. A. Angiras † C. J. Jog † A. Omar † K. S. Dwarakanath † 《Monthly notices of the Royal Astronomical Society》2006,369(4):1849-1857
The H i surface density maps for a sample of 18 galaxies in the Eridanus group are Fourier analysed. This analysis gives the radial variation of the lopsidedness in the H i spatial distribution. The lopsidedness is quantified by the Fourier amplitude A 1 of the m = 1 component normalized to the average value. It is also shown that in the radial region where the stellar disc and H i overlap, their A 1 coefficients are comparable. All the galaxies studied show significant lopsidedness in H i . The mean value of A 1 in the inner regions of the galaxies (1.5–2.5 scalelengths) is ≥ 0.2. This value of A 1 is twice the average value seen in the field galaxies. Also, the lopsidedness is found to be smaller for late-type galaxies; this is opposite to the trend seen in the field galaxies. These two results indicate a different physical origin for disc lopsidedness in galaxies in a group environment compared to the field galaxies. Further, a large fraction (∼30 per cent) shows a higher degree of lopsidedness ( A 1 ≥ 0.3). It is also seen that the disc lopsidedness increases with the radius as demonstrated in earlier studies, but over a radial range that is two times larger than done in the previous studies. The average lopsidedness of the halo potential is estimated to be ∼10 per cent, assuming that the lopsidedness in H i disc is due to its response to the halo asymmetry. 相似文献
32.
The elasto-plastic analysis of a circular underground opening using the finite element method (FEM), the coupled finite element and the boundary element method (FEBEM) is presented. The coupling procedure and elasto-plastic formulation are discussed. The effect of in situ stress ratio on yielded zone, displaced shape and principal stresses is presented. The results of FEBEM analysis are compared with those obtained from FEM. The computation time and the number of iterations as required by FEBEM and FEM are compared. 相似文献
33.
D. N. Avasthi G. Ramakotaiah S. Varadarajan N. D. J. Rao G. N. Behl 《Bulletin of Volcanology》1971,35(3):743-749
In the attempt to study the buried Deccan Trap layers in the Cambay Basin, the ground magnetic surveys have not been very useful as the data combine the effect due to the crystalline basement and the Trap thickness. In some parts of the basin, some reflections in the seismograms obtained in the course of seismic surveys, could be correlated to the Trap surface. These can be tied with wells drilled in the basin upto the Traps. The synthesis of the gravity and seismic data has enabled us to prepare a map of the Trap surface in the Cambay basin. The depth of the Trap surlace increases from about 2000 m in the northern part of the basin to about 600 m in its deepest part near Broach. The Trap surface rises gradually south of Narbada in an average direction of SE with depths running from 2500 m to 500 m. The interpretation of the gravity anomalies, assuming their cause to be the variations in the thickness of the Trap, has enabled the determination of the average thickness of the Traps in the basin. The maximum thickness of the Trap is in the central part of the basin and is estimated to be about 2.4 km. The Traps appear to gradually taper towards the flanks of the basin. 相似文献
34.
Jayadev Rajagopal G. Srinivasan K. S. Dwarakanath 《Journal of Astrophysics and Astronomy》1998,19(3-4):117-131
In the preceding paper (Paper I), we presented HI absorption spectra towards radio sources very close to the lines of sight
towards twenty five bright stars against which optical absorption spectra had been obtained earlier, In this paper we analyse
the results and draw some conclusions.
To summarize briefly, in most cases we found HI absorption at velocities corresponding to the optical absorption features
provided one restricted oneself to velocities ≲10 kms-1. At higher velocities we did not detect any HI absorption down to
an optical depth limit of 0.1 (except in four cases which we attribute to gas in systematic motion rather than clouds in random
motion). After discussing various scenarios, we suggest that this trend should perhaps be understood in terms of the high
velocity interstellar clouds being accelerated, heated and ablated by expanding supernova remnants. 相似文献
35.
Jayadev Rajagopal G. Srinivasan K. S. Dwarakanath 《Journal of Astrophysics and Astronomy》1998,19(3-4):97-116
This investigation is aimed at clarifying the nature of the interstellar gas seen in absorption against bright O and B stars.
Towards this end we have obtained for the first time HI absorption spectra towards radio sources very close to the lines of
sight towards twenty five bright stars previously studied. In this paper we describe the selection criteria, the details regarding
our observations, and finally present the absorption spectra. In the accompanying paper we analyse the results and draw conclusions. 相似文献
36.
The finite element method (FEM) and the boundary element method (BEM) are two well established numerical methods used for the analysis of underground openings. The advantages of both the methods are utilized by adopting FEBEM in which finite elements are coupled with boundary elements. A coupling procedure is presented in this paper. In using FEBEM, the effect of the location of interface boundary between finite element and boundary element regions, effect of Poisson's ratio and effect of stress ratio are discussed. It is shown that Poisson's ratio and stress ratio have significant effect on the accuracy of the results. Different discretization schemes are discussed to study their effect on accuracy and computation time. The use of different material properties in the FE region is presented. A comparative study is made with FEM for all the cases. It is shown that use of FEBEM is more advantageous than FEM. 相似文献
37.
DNAPL Removal from a Heterogeneous Alluvial Aquifer by Surfactant-Enhanced Aquifer Remediation 总被引：2，自引：0，他引：2
38.
K. S. Dwarakanath A. A. Deshpande N. Udaya Shankar 《Journal of Astrophysics and Astronomy》1990,11(3):311-322
A simple but effective modification to the conventional CLEAN algorithm is suggested. This modification ensures both stability
and speed when CLEAN is applied to maps containing a mixture of point sources and extended structures. The method has been
successfully applied to the recently-completed sky survey at 34.5 MHz (Dwarakanath & Udaya Shankar 1990). This survey was
made using the Gauribidanur T array (GEETEE)1 in 1-D aperture synthesis mode. Since in this case the ‘dirty beam’ (point spread
function) cannot be directly computed, a method to obtain this is discussed in detail. The results of this deconvolution procedure
have been encouraging in terms of reduced computing time and improved dynamic range in our maps. This algorithm should find
wider application in deconvolving maps which have both extended structures and point sources
This telescope is jointly operated by the Indian Institute of Astrophysics, Bangalore & the Raman Research Institute, Bangalore. 相似文献
39.
The HI content of galaxies in the Eridanus group is studied using the GMRT observations and the HIPASS data. A significant
HI deficiency up to a factor of 2–3 is observed in galaxies in the high galaxy density regions. The HI deficiency in galaxies
is observed to be directly correlated to the local projected galaxy density, and inversely correlated to the line-of-sight
radial velocity. Furthermore, galaxies with larger optical diameters are predominantly in the lower galaxy density regions.
It is suggested that the HI deficiency in Eridanus is due to tidal interactions. In some galaxies, evidences of tidal interactions
are seen. An important implication is that significant evolution of galaxies can take place in the group environment. In the
hierarchical way of formation of clusters via mergers of groups, a fraction of the observed HI deficiency in clusters could
have originated in groups. The co-existence of S0s and severely HI deficient galaxies in the Eridanus group suggests that
tidal interaction is likely to be an effective mechanism for transforming spirals to S0s. 相似文献
40.
The GMRTHI 21 cm-line observations of galaxies in the Eridanus group are presented. The Eridanus group, at a distance of ≈ 23 Mpc, is
a loose group of ≈200 galaxies. The group extends to more than 10 Mpc in projection. The velocity dispersion of the galaxies
in the group is ≈240 km s−1. The galaxies are clustered into different sub-groups. The overall population mix of the group is 30% (E + S0) and 70% (Sp
+ Irr). The observations of 57 Eridanus galaxies were carried out with the GMRT for ≈ 200 h. HI emission was detected from
31 galaxies. The channel rms of ≈ 1 mJy beam−1 was achieved for most of the image-cubes made with 4 h of data. The corresponding HI column density sensitivity (3σ) is ≈
1 × 1020 cm−2 for a velocity-width of ≈ 13.4 km s−1. The 3σ detection limit of HI mass is ≈ 1.2 X 107 Mpd for a line-width of 50 km s−1. Total HI images, HI velocity fields, global HI line profiles, HI mass surface densities, HI disk parameters and HI rotation
curves are presented. The velocity fields are analysed separately for the approaching and the receding sides of the galaxies.
These data will be used to study the HI and the radio continuum properties, the Tully-Fisher relations, the dark matter halos,
and the kinematical and HI lopsidedness in galaxies. 相似文献