A theoretician's analysis of the supernova data and the limitations in determining the nature of dark energy     

T. Padmanabhan  T. Roy Choudhury 《Monthly notices of the Royal Astronomical Society》2003,344(3):823-834

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The multifrequency angular power spectrum of the epoch of reionization 21-cm signal     

Kanan K. Datta  T. Roy Choudhury  Somnath Bharadwaj 《Monthly notices of the Royal Astronomical Society》2007,378(1):119-128

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X-ray spectroscopy of Cygnus X-3     

M. Choudhury  A. R. Rao 《Journal of Astrophysics and Astronomy》2002,23(1-2):39-43

We have analysed the X-ray spectra of the highly variable X-ray source Cygnus X-3 over a wide energy range from 5 keV to 150 keV using data selected from the RXTE archives. Separate analysis of the low and hard states show the presence of a hard powerlaw tail in both the states. Here we present the result of the wide band spectral study of the source.  相似文献   

Estimation of seismic hazard in Gujarat region, India   总被引：1，自引：1，他引：0  

Sumer Chopra  Dinesh Kumar  B. K. Rastogi  Pallabee Choudhury  R. B. S. Yadav 《Natural Hazards》2013,65(2):1157-1178

The seismic hazard in the Gujarat region has been evaluated. The scenario hazard maps showing the spatial distribution of various parameters like peak ground acceleration, characteristics site frequency and spectral acceleration for different periods have been presented. These parameters have been extracted from the simulated earthquake strong ground motions. The expected damage to buildings from future large earthquakes in Gujarat region has been estimated. It has been observed that the seismic hazard of Kachchh region is more in comparison with Saurashtra and mainland. All the cities of Kachchh can expect peak acceleration in excess of 500?cm/s² at surface in case of future large earthquakes from major faults in Kachchh region. The cities of Saurashtra can expect accelerations of less than 200?cm/s² at surface. The mainland Gujarat is having the lowest seismic hazard as compared with other two regions of Gujarat. The expected accelerations are less than 50?cm/s² at most of the places. The single- and double-story buildings in Kachchh region are at highest risk as they can expect large accelerations corresponding to natural periods of such small structures. Such structures are relatively safe in mainland region. The buildings of 3?C4 stories and tall structures that exist mostly in cities of Saurashtra and mainland can expect accelerations in excess of 100?cm/s² during a large earthquake in Kachchh region. It has been found that a total of 0.11 million buildings in Rajkot taluka of Saurashtra are vulnerable to total damage. In Kachchh region, 0.37 million buildings are vulnerable. Most vulnerable talukas are Bhuj, Anjar, Rapar, Bhachau, and Mandvi in Kachchh district and Rajkot, Junagadh, Jamnagar, Surendernagar and Porbandar in Saurashtra. In mainland region, buildings in Bharuch taluka are more vulnerable due to proximity to active Narmada-Son geo-fracture. The scenario hazard maps presented in this study for moderate as well as large earthquakes in the region may be used to augment the information available in the probabilistic seismic hazard maps of the region.  相似文献   

Estimation of site amplification functions in Gujarat region, India     

Sumer Chopra  Dinesh Kumar  B. K. Rastogi  Pallabee Choudhury  R. B. S. Yadav 《Natural Hazards》2013,65(2):1135-1155

Site response in the Gujarat region is studied using local earthquake data recorded at 32 sites spread all over Gujarat region, India. Out of these 32 sites, 15 sites are located in Kachchh region, 8 in Saurashtra and 9 in mainland Gujarat region. These sites are underlain by different types of rocks/sediments of different ages. Out of 32 stations, 7 stations are on Quaternary deposits, 6 on Tertiary, 11 on Deccan, 3 on Jurassic, 3 on Cretaceous and 2 on Proterozoic rocks. The predominant frequencies at these sites depend strongly on the local geology. The average predominant frequencies of the sites on Quaternary sediments are 2.4?Hz, 5.3?Hz on Tertiary, 7.5?Hz on Jurassic, 7.2?Hz on Deccan, 4.6?Hz on Cretaceous and 7.5?Hz on Proterozoic formations. The average site amplification values at predominant frequencies are 3.7 for the sites of Quaternary deposits, 3.3 for Tertiary, 3.3 for Cretaceous rock, 4.2 for Deccan trap, 4.1 for Jurassic sites and 4.6 for Proterozoic. The damage to the houses during 2001 Bhuj earthquake is compared with the amplification at predominant frequencies at those sites. The spatial variation of predominant frequencies and the site amplifications at different frequencies corresponding to the natural frequencies of different storey buildings are studied, which will be useful in the evaluation of seismic hazard in the region.  相似文献   

Triggered/migrated seismicity due to the 2001 M w7.7 Bhuj earthquake, Western India     

B. K. Rastogi  Sandeep Kumar Aggrawal  Nagabhushan Rao  Pallabee Choudhury 《Natural Hazards》2013,65(2):1085-1107

Paper describes triggered seismicity to 200?km distance and for a decade due to the 2001 M _w7.7 Bhuj earthquake. The Kachchh region is seismically one of the most active intraplate regions of the World due to the occurrence of two large earthquakes 1819 (M _w7.8) and 2001 (M _w7.7). Though, it has high hazard but was known to have low seismicity in view of the occurrence of fewer smaller shocks. However, the status seems to have changed after 2001. Besides the strong aftershock activity for over a decade, seismicity has spread to nearby faults in Kachchh peninsula and at several places southward for 200?km distance in Saurashtra peninsula. Beyond the rupture zone of the 2001 Bhuj earthquake, more than 40 mainshocks of M _w?~?3?C5 have occurred at 20 different locations, which is unusual. The increased seismicity is inferred to be caused by stress perturbation due to the 2001 Bhuj earthquake by viscoelastic process. In Saurashtra, over and above the viscoelastic stress increase, the transient stress increase by water table rise in monsoons seems to be affecting the timing of mainshocks and associated sequences of earthquakes.  相似文献   

Agricultural Area Diversification and Crop Water Demand Analysis: A Remote Sensing and GIS Approach     

B. U. Choudhury  Anil Sood  S. S. Ray  P. K. Sharma  S. Panigrahy 《Journal of the Indian Society of Remote Sensing》2013,41(1):71-82

Large scale adoption of input intensive rice–wheat cropping system in the centrally located Jalandhar district of Indian Punjab has led to over-exploitation of ground water resources, intensive use of chemical fertilizers and deterioration of soil health. To overcome these shortfalls, in the present study, agricultural area diversification plan has been generated from agricultural area and crop rotation maps derived from remote sensing data (IRS P6-AWiFS and RADARSAT ScanSAR) along with few agro-physical parameters in GIS environment. Cropping system indices (area diversity, multiple cropping and cultivated land utilization) were also worked out from remote sensing data .Analysis of remote sensing data (2004–05) revealed that rice and wheat individually remained the dominant crops, occupy 57.8% and 64.9% of total agricultural area (TAA), respectively. Therefore, in the diversified plan, it is suggested that at least 39% of the current 40% TAA under rice–wheat rotation should be replaced by other low water requiring, high value and soil enriching crops, particularly in coarse textured alluvial plain having good quality ground water zones with low annual rainfall(<700 mm). This will reduce water requirement to the tune of 15,660 cm depth while stabilizing the production and profitability by crop area diversification without further degradation of natural resources.  相似文献   

“Events and failures are our only means for making policy changes”: learning in disaster and emergency management policies in Manitoba,Canada     

Haque  C. Emdad  Choudhury  Mahed-Ul-Islam  Sikder  Md. Sowayib 《Natural Hazards》2019,98(1):137-162

Natural Hazards - The Canadian Province of Manitoba has experienced many severe floods and other natural disasters, and in response municipal, provincial, and federal governments have developed...  相似文献   

Passive microwave remote sensing contribution to hydrological variables     

Bhaskar J. Choudhury 《Surveys in Geophysics》1991,12(1-3):63-84

Physical principles governing passive microwave remote sensing of hydrological variables are outlined and illustrated by actual observations by ground-based, air-borne and space-borne microwave radiometers operating at different frequencies. Specific hydrological variables addressed in this paper are soil moisture, seasonal inundation of rivers and swamps, vegetation, snow, and rainfall. Passive remote sensing provides measurements of electromagnetic radiation emitted by the land-atmosphere system, which can be related more directly to the radiative characteristics of the system than to physical or physiological characteristics. Estimation of hydrological variables from microwave observations necessarily involves models relating the radiative to the physical characteristics, and in general more than one physical characteristics determine the microwave observations. This non-uniqueness in the relationship between microwave observations to a particular hydrological variable leads to uncertainties in the estimation of the variable. Notwithstanding this limitation, the principles and the examples given in this paper illustrate the value of passive microwave observations to regional and global hydrology at a temporal resolution of days aggregated to a decade.  相似文献   

The albedo of snow for partially cloudy skies     

B. J. Choudhury  A. T. C. Chang 《Boundary-Layer Meteorology》1981,20(3):371-389

The albedo of snow for different cloudiness conditions is an important parameter in the Earth's radiation budget analysis and in the study of snowpack's thermal conditions. In this study an efficient approximate method is derived to calculate the incident spectral solar flux and snow-cover albedo in terms of different atmospheric, cloud, and snow parameters. The global flux under partially cloudy skies is expressed in terms of the clear sky flux and a coefficient which models the effect of scattering and absorption by cloud patches and multiple reflections between the cloud base and snowcover. The direct and the diffuse components of the clear sky flux are obtained using the spectral flux outside the atmosphere and the spectral transmission coefficients for absorption and scattering by molecules and aerosols.The spectral snow reflectance model considers both specular surface reflection and volumetric multiple scattering. The surface reflection is calculated by using a crystal-shape-dependent bidirectional reflectance distribution function; the volumetric multiple scattering is calculated by using a crystal-size-dependent approximate solution in the radiative transfer equation. The input parameters to the model are atmospheric precipitable water, ozone content, turbidity, cloud optical thickness, the size and shape of ice crystals of snow and surface pressure. The model yields spectral and integrated solar flux and snow reflectance as a function of solar elevation and fractional cloudcover.The model is illustrated using representative parameters for the Antarctic coastal regions. The albedo for a clear sky depends inversely on the solar elevation. At high elevations the albedo depends primarily upon the grain size; at low elevation the albedo depends on grain size and shape. The gradient of the albedo-elevation curve increases as the grains become larger and faceted. The albedo for a densely overcast sky is a few percent higher than the clear-sky albedo at high elevations. A simple relationship between grain size and the overcast albedo is obtained. For a set of grain size and shape, the albedo as a function of solar elevation and fractional cloud cover is tabulated.  相似文献