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51.
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
52.
53.
Jyoti Shah Deepak C. Srivastava Vipul Rastogi Rajit Ghosh Aditi Pal 《Journal of the Geological Society of India》2010,75(1):89-97
Most of the existing methods of strain analysis can estimate strain in a single form of distorted brachiopod, or trilobite
provided independent evidence, such as the association of the fossil with cleavage and/or stretching lineation is available
for inferring the direction of maximum principal strain. This article proposes a simple computer graphics based method and
its MATLAB code that determine the minimum amount of strain in a single distorted fossil form even if data for inferring the
maximum principal strain direction are lacking. Our method is a rapid computer-graphics alternative to some of the existing
analytical methods.
In a distorted fossil form of original bilateral symmetry, the relative senses of angular shears along the hinge line and
the median line are mutually opposite to each other. It follows, therefore, that the maximum principal strain direction lies
within the acute angle between the hinge and the median lines in the plane of the fossil. Using this principle, our method
performs several simulations such that each simulation retrodeforms the distorted fossil by assuming a particular orientation,
lying within the acute angle between the hinge line and the median line, as the potential direction of the maximum principal
strain. Each simulation of retrodeformation yields a potential strain ratio. The distribution of all the potential strain
ratios, obtained by assuming different orientations as the potential directions of the maximum strain, is typically a parabola-like
curve with a distinct vertex that corresponds to the minimum amount of strain in the distorted fossil. An entirely computer
graphical approach is somewhat time-intensive because it involves a large number of retrodeformational simulations. We, therefore,
give a MATLAB code, namely, the Minstrain, that rapidly retrodeforms the fossil and determines the minimum strain with precision. 相似文献
54.
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
55.
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
56.
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
57.
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
58.
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
59.
Madhuri?Khambete Aditi?DivekarEmail author 《Journal of the Indian Society of Remote Sensing》2014,42(1):249-255
Remote sensing offers a wide variety of image data with different characteristics in terms of spatial and spectral resolutions. For optical sensor systems, imaging systems have a trade-off between high spatial and high spectral resolution, and no single system offers both. Hence, in the remote sensing application, an image with ‘greater quality’ often means higher spatial and higher spectral resolution. It is, therefore, necessary and very useful to merge images with higher spectral information and higher spatial information. Pansharpening combines spatial information from the high-resolution panchromatic image and color information from multispectral bands to create a high-resolution color image. Here we propose Discrete Cosine Transform (DCT) based pansharpening algorithm using Adaptive Linear model which preserves spectral information from Multispectral image and retains spatial resolution of Panchromatic image. 相似文献
60.
Suresh Kumar N. R. Patel Aditi Sarkar V. K. Dadhwal 《Journal of the Indian Society of Remote Sensing》2013,41(3):609-618
The present study demonstrated the methodology to assess agro-climatic suitability of the soybean crop through integration of crop suitability based on FAO framework of land evaluation and biophysical (water limited) yield potential in the rainfed agro-ecosystem. A long term climatic database (1980–2003) was prepared to compute decadal rainfall and temperature variations of 13 IMD stations in part of Madhya Pradesh state. The climatic database was used in soil water balance software–BUDGET to compute crop specific length of growing period (LGP) and biophysical production potential such as water limited crop yield potential of each soil types for soybean crop. Water limited crop yield potential of soils were found to be varied from 33 to 100 and LGP ranged from 65 to 180 days in the area. FAO based land suitability was analyzed in association with the water limited yield potential for better appraisal of land potential and assess their suitability in rainfed area. FAO based land suitability indicated 2.45 % area as highly suitable and 57.49 % area as moderately suitable. However, integration of water limited crop yield potential with FAO based land suitability lead to agro-climatic suitability analysis indicated 17.60 % and 40.03 % area, respectively as highly suitable and moderately suitable. FAO based land evaluation showed 88.13 % of plains as moderately suitable whereas agro-climatic suitability indicated only 47.79 %. Agro-climatic suitability analysis revealed undulating plateau and undulating plains as most suitable for soybean crop. 相似文献