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1.
This paper describes a wide-field survey made at 34.5 MHz using GEETEE,1 the low frequency telescope at Gauribidanur (latitude
13°36′12′′N). This telescope was used in the transit mode and by per forming 1-D synthesis along the north-south direction
the entire observable sky was mapped in a single day. This minimized the problems that hinder wide-field low-frequency mapping.
This survey covers the declination range of-50° to + 70° (- 33° to +61° without aliasing) and the complete 24 hours of right
ascension. The synthesized beam has a resolution of 26′ x 42′ sec (δ- 14°. 1). The sensitivity of the survey is 5 Jy/beam (1σ). Special care has been taken to ensure that the antenna responds
to all angular scale structures and is suitable for studies of both point sources and extended objects
This telescope is jointly operated by the Indian Institute of Astrophysics, Bangalore and the Roman Research Institute, Bangalore. 相似文献
2.
The imbalance between incoming and outgoing salt causes salinization of soils and sub-soils that result in increasing the
salinity of stream-flows and agriculture land. This salinization is a serious environmental hazard particularly in semi-arid
and arid lands. In order to estimate the magnitude of the hazard posed by salinity, it is important to understand and identify
the processes that control salt movement from the soil surface through the root zone to the ground water and stream flows.
In the present study, Malaprabha sub-basin (up to dam site) has been selected which has two distinct climatic zones, sub-humid
(upstream of Khanapur) and semi-arid region (downstream of Khanapur). In the upstream, both surface and ground waters are
used for irrigation, whereas in the downstream mostly groundwater is used. Both soils and ground waters are more saline in
downstream parts of the study area. In this study we characterized the soil salinity and groundwater quality in both areas.
An attempt is also made to model the distribution of potassium concentration in the soil profile in response to varying irrigation
conditions using the SWIM (Soil-Water Infiltration and Movement) model. Fair agreement was obtained between predicted and
measured results indicating the applicability of the model. 相似文献
3.
4.
A. Varadarajan 《Engineering Geology》1975,9(1):53-62
A case study of an earth dam under construction in the Siwalik sedimentary rocks in North India is presented. The dam site is located in a seismically active zone. The shear zones incorporated in the rocks during folding control the stability of the dam foundations. Because the shear zones crop out in the river bed at different locations along the dam axis, the dam foundation is comprised of discrete blocks of varying resistance. The mechanism of stability is greatly influenced by the disposition of shear zones and the relevant analysis is three dimensional. 相似文献
5.
K. S. Dwarakanath W. M. Goss J. H. Zhao C. C. Lang 《Journal of Astrophysics and Astronomy》2004,25(3-4):129-141
We have imaged a region of ∼ 5′ extent surrounding Sgr A* in the HI 21 cm-line absorption using the Very Large Array. A Gaussian
decomposition of the optical depth spectra at positions within ∼ 2′ (∼ 5 pc at 8.5 kpc) of Sgr A* detects a wide line underlying
the many narrow absorption lines. The wide line has a mean peak optical depth of 0.32 ± 0.12 centered at a mean velocity of
V1sr = −4 ± 15 km s{−1}. The mean full width at half maximum is 119 ± 42 km s−1. Such a wide line is absent in the spectra at positions beyond ∼ 2′ from Sgr A*. The position-velocity diagrams in optical
depth reveal that the wide line originates in various components of the circumnuclear disk (radius ∼ 1.3′ ) surrounding Sgr
A*. These components contribute to the optical depth of the wide line in different velocity ranges. The position-velocity
diagrams do not reveal any diffuse feature which could be attributed to a large number of HI clouds along the line of sight
to Sgr A*. Consequently, the wide line has no implications either to a global population of shocked HI clouds in the Galaxy
or to the energetics of the interstellar medium as was earlier thought. 相似文献
6.
Srinivasan G. Bhattacharya D. Dwarakanath K. S. 《Journal of Astrophysics and Astronomy》1984,5(4):403-423
We conclude that pulsar-driven supernova remnants (SNRs) are extremely rare objects. Indeed an analysis of the known sample
of plerions suggests a very low birthrate ∼ 1 in 240 years. Long-lived and bright plerions like the Crab nebula are likely
to be produced only when the pulsar has an initial period ∼ 10–20 milliseconds and a field ∼ 1012 G. Such pulsars inside rapidly expanding shell remnants should also produce detectable plerions. The extreme rarity of SNRs
with such hybrid morphology leads us to conclude that these pulsars must have been born with an initial period larger than
∼ 35–70 milliseconds.
Joint Astronomy Program, Department of Physics, Indian Institute of Science, Bangalore 560012. 相似文献
7.
Rekhesh Mohan K. S. Dwarakanath G. Srinivasan Jayaram N. Chengalur 《Journal of Astrophysics and Astronomy》2001,22(1):35-50
Nearby interstellar clouds with high (|ν|≥10km s−1) random velocities although easily detected in NaI and CaII lines have hitherto not been detected (in emission or absorption)
in the HI 21cm line. We describe here deep Giant Metrewave Radio Telescope (GMRT) HI absorption observations toward radio
sources with small angular separation from bright O and B stars whose spectra reveal the presence of intervening high random
velocity CaII absorbing clouds. In 5 out of the 14 directions searched we detect HI 21cm absorption features from these clouds.
The mean optical depth of these detections is ∼0.09 and FWHM is ∼10km s−1, consistent with absorption arising from CNM clouds. 相似文献
8.
The use of the limit equilibrium method for the analysis of a dam foundation with a weak shear seam has many limitations. There is further uncertainty in such an analysis by this method when the seam is intercepted by a concrete key. The finite element method is the best alternative means of analysing such problems. In this paper, the finite element analysis of the Karjan Dam (India) foundation, which has a shear seam, is presented with and without the foundation treatment (i.e. the concrete key). The seam is simulated by joint elements. It has been found that a concrete key located near the toe of the dam significantly improves the stability of the foundation. 相似文献
9.
Ruta Kale K. S. Dwarakanath Joydeep Bagchi Surajit Paul 《Journal of Astrophysics and Astronomy》2011,32(4):533-536
The case of spectacular ring-like double radio relics in the merging, rich galaxy cluster A3376 is of great interest to study
non-thermal phenomena at cluster outskirts. We present the first low frequency (330 and 150 MHz) images of the double relics
using the GMRT. With our GMRT 330 MHz map and the VLA 1400 MHz map (Bagchi et al. 2006), we have constructed and analyzed the distribution of spectral indices over the radio relics. We find flat spectral
indices at the outer edges of both the relics and a gradual steepening of spectral indices toward the inner regions. This
supports the model of outgoing merger shock waves. The eastern relic has a complex morphology and spectral index distribution
toward the inner region. This will be discussed in the context of the effect of large-scale accretion flows on the outgoing
merger shocks as reported in the recent simulations. 相似文献
10.
A finite element analysis of a reinforced embankment-foundation system has been conducted using a coupled formulation and elastoplasticity theory. Such important factors as type of reinforcement, the type of clay, depth of foundation and drainage condition affecting the system have been systematically investigated using appropriate constitutive models to depict various components of the system and material parameters of two typical soft clay deposits found in India. The displacements, reinforcement force and maximum heights of the embankments are among the aspects presented and discussed. It is shown that the effectiveness of the reinforcement is dependent on its stiffness and the shear strength of the clay deposit. The foundation depth has significant effect on the nature and magnitude of displacement, the reinforcement force and the height of embankment. Drainage conditions are shown to markedly influence the effectiveness of reinforcement. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献