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41.
M. R. Deshpande Hari Om Vats Harish Chandra P. Janardhan A. D. Bobra G. D. Vyas 《Astrophysics and Space Science》1994,218(2):249-265
This article describes in detail a burst from PSR 0950+08 on July 29, 1992. This event was observed by two radio telescopes (separated by ~ 200 km) operating at 103 MHz. There exists a very convincing indirect evidence that at the same time the pulsar also emitted large X-ray flux. The X-ray flux during the event compares with that during a solar X-ray flare. During the event the Sun was extraordinarily quiet as the solar X-ray flux 3 · 10–7 W/m2 only was observed. The cause for the burst is quite unknown and may be complex. However, a possibility of accretion of a comet-like object by pulsar may provide reasonable explanation of the observations. These results open some interesting questions about the pulsar physics. 相似文献
42.
43.
This study highlights the hydro-climatic features of the five wet periods contributing in different percentages to the annual
rainfall total over major river basins in India. Spatial and temporal variations in the parameters such as starting date,
duration and rainfall intensity of these wet periods throughout India have been discussed using daily gridded rainfall data
for the period 1951–2007. An attempt is also made here, to assess the impact of global SSTs on the start and duration of the
wet periods in Indian river basins. 相似文献
44.
Kopparapu Vijaya Kumar Chakradhar Chavan Sariput Sawant K. Naga Raju Prachiti Kanakdande Sangita Patode Krishna Deshpande S. K. G. Krishnamacharyulu T. Vaideswaran V. Balaram 《Contributions to Mineralogy and Petrology》2010,159(6):839-862
Spatial and temporal variations in the geochemistry of an extrusive basaltic section of Deccan traps record progressive changes
in mantle melting and crustal filtration and are relevant to understand continental flood basalt (CFB) magmatism. In the present
work we have carried out detailed field, petrographic, density and magnetic susceptibility, and geochemical investigations
on a small, semi-continuous extrusive section in the eastern Deccan Volcanic Province (DVP) to understand the role of shallow
magma chambers in CFB magmatism. Four formations, Ajanta, Chikhli, Buldhana and Karanja crop out in the Gangakhed–Ambajogai
area with increasing elevation. Our studies indicate that: (1) the Karanja Formation represents a major magma addition, as
indicated by abrupt change in texture, increases in MgO, CaO, Ni, Cr, and Sr, and drastic decreases in Al2O3, Na2O, K2O, Rb, Ba, REE, bulk-rock density and magnetic susceptibility; (2) assimilation fractional crystallization, crystal-laden
magmas, and accessory cumulus phases influence the trace element chemistry of Deccan basalts; (3) the predicted cumulate sequence
of olivine gabbro–leucogabbro–oxide-apatite gabbro is supported by the observed layered series in a shallow magma chamber
within the DVP; (4) the initial magma was saturated with olivine, plagioclase, and augite, and final the pressure of equilibration
for the Gangakhed–Ambajogai section basalts is ~2 kbar (~6 km depth); (5) petrophysical parameters act as proxies for magmatic
processes; (6) a small layer of oxide-rich basalts may represent the latest erupted pulse in a given magmatic cycle in the
DVP; (7) parental basalts to some of the red boles, considered as formation boundaries, might represent small degree partial
melts of the mantle; (8) SW Deccan basaltic-types continue into the eastern DVP; and (9) in addition to the magma chamber
processes, dynamic melting of the mantle may have controlled DVP geochemistry. The present study underscores the importance
of mapping specific stratigraphic intervals in limited areas to understand mantle and magma chamber processes relevant to
CFB magmatism. 相似文献
45.
A. A. Deshpande 《Journal of Astrophysics and Astronomy》1992,13(2):167-173
We discuss here the design details of an inexpensive programmable Sweeping Local Oscillator System (SLOS) built for use in
a ‘swept frequency dedispersion scheme’ for pulsar observations. A useful extension of the basic Divide-and-Add algorithm
for frequency synthesis is developed for this purpose. An SLOS based on this design has been built and used for high time-resolution
observations of pulsars at low radio-frequencies. 相似文献
46.
The behaviour of pulsars at low radio-frequencies (below ≈ 50 MHz) remains poorly understood mainly due to very limited observational
data on pulsars at these frequencies. We report here our measurements of pulse profiles at 34.5 MHz of 8 pulsars using the
Gauribidanur Radio Telescope. None of the 8 pulsars show any significant interpulse emission at this frequency which conflicts
with an earlier claim from 25 MHz observations. With the exception of one pulsar (PSR 0943 + 10) all the observed pulsars
show turnovers at frequencies above 35 MHz in their spectra. We also report our attempts to study the short and long term
variations in the pulsar signals at this low frequency. 相似文献
47.
This paper describes the design, tests and preliminary results of a real-time parallel signal processor built to aid a wide
variety of pulsar observations. The signal processor reduces the distortions caused by the effects of dispersion, Faraday
rotation, doppler acceleration and parallactic angle variations, at a sustained data rate of 32 Msamples/sec. It also folds
the pulses coherently over the period and integrates adjacent samples in time and frequency to enhance the signal-to-noise
ratio. The resulting data are recorded for further off-line analysis of the characteristics of pulsars and the intervening
medium. The signal processing for analysis of pulsar signals is quite complex, imposing the need for a high computational
throughput, typically of the order of a Giga operations per second (GOPS). Conventionally, the high computational demand restricts
the flexibility to handle only a few types of pulsar observations. This instrument is designed to handle a wide variety of
Pulsar observations with the Giant Metre Wave Radio Telescope (GMRT), and is flexible enough to be used in many other high-speed,
signal processing applications. The technology used includes field-programmable-gate-array(FPGA) based data/code routing interfaces,
PC-AT based control, diagnostics and data acquisition, digital signal processor (DSP) chip based parallel processing nodes
and C language based control software and DSP-assembly programs for signal processing. The architecture and the software implementation
of the parallel processor are fine-tuned to realize about 60 MOPS per DSP node and a multiple-instruction-multiple-data (MIMD)
capability. 相似文献
48.
Deformable alluvial channels are known to adjust their geometry and slope to achieve stable conditions for a specified influx of water and sediment. Designing the stable alluvial channel has been a captivating topic for scientists and engineers around the globe for years. The work which was commenced by Kennedy in 1895 has been continued and various approaches have been given so far, some of which are quite interrelated and others emerged with different ideas. In this comprehensive study, some of the classic and widely accepted approaches published in the literature have been thoroughly reviewed and have been verified with available river regime data. The data set has been sub divided into three categories based on the median bed material size (sand, gravel and cobble or boulder), in order to examine the applicability of various methods available for the design of stable alluvial channels. Detailed discussion related to the properties of the intercept coefficients in power function theory is not available in published literature. In this study, the coefficients are first calibrated and then applied with the respective exponents in order to derive the hydraulic geometry. Further, the derived hydraulic geometry from various approaches is summarized and discussed with comparative view point. The analysis shows that prediction from recently developed model based on the principle of maximum entropy and minimum energy dissipation is better than other approaches for the entire range of data set. The same model has been further generalized by assuming a wide trapezoidal channel cross-section through which an improvement in the prediction has been observed. 相似文献
49.
Precipitation samples were collected across the Himalayas from Kashmir (western Himalaya) to Assam (eastern Himalaya) to understand the variation of the stable isotopic content (\(\updelta ^{18}\)O and \(\updelta \)D) in precipitation associated with two dominant weather systems of the region: western disturbances (WDs) and Indian summer monsoon (ISM). Large spatial and temporal variations in isotopic values were noted with \(\updelta ^{18}\)O and \(\updelta \)D values ranging from \(-30.3\) to Open image in new window and \(-228\) to Open image in new window , respectively. The d-excess values also exhibit a large range of variation from \(-30\) to Open image in new window . In general, heavier isotopic values are observed in most of the samples in Jammu, whereas lighter values are observed in majority of the samples in Uttarakhand. Precipitation at Jammu seems to have undergone intense evaporation while that from Uttarakhand suggest normal Rayleigh fractionation/distillation of the air mass as it moves from the source region to the precipitation site and/or orographic lifting. The d-excess of rainfall in Kashmir has a distinctly higher median value of Open image in new window compared to other precipitation sites with a median of Open image in new window . Using distinct isotopic signatures, the regions receiving precipitation from two different weather systems have been identified. 相似文献
50.
Maji Kamal Jyoti Dikshit Anil Kumar Deshpande Ashok 《Arabian Journal of Geosciences》2017,10(18):1-20
Arabian Journal of Geosciences - The Ahnet and Tin Zaouatine terranes are located in the southern sector of the Algerian Desert and are part of the Tuareg Shield, which was built up during... 相似文献