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141.
Soma Mukherjee Ujjwal Bhattacharya S. K. Parui Ranjan Gupta Ravi K. Gulati 《Astrophysics and Space Science》1996,239(2):361-373
In this paper we present an application of an artificial neural network model based on a multi-layered backpropagation algorithm for spectral classification of UV data from the International Ultraviolet Explorer (IUE) low dispersion spectra reference atlas. The model used is similar to that of von Hippel et al. (1994), and is found to reduce the classification error as compared to the recently reported results on the same data set (Gulati et al. 1994b). The improved version of the network is much simpler in structure and the training time is reduced by a factor of almost 20. Such networks will prove very useful in efficient classification of large databases
Subject headings: neural networks, stellar spectra, classification 相似文献
142.
We consider the second-order differential equations ofP-SV motion in an isotropic elastic medium with spherical coordinates. We assume that in the medium Lamé's parameters , r
p
and compressional and shear-wave velocities , r, wherer is radial distance. With this regular heterogeneity both the radial functions appearing in displacement components satisfy a fourth-order differential equation which provides solutions in terms of exponential functions. We then consider a layered spherical earth in which each layer has heterogeneity as specified above. The dispersion equation of the Rayleigh wave is obtained using the Thomson-Haskel method. Due to exponential function solutions in each layer, the dispersion equation has similar simplicity, as in a flat-layered earth. The dispersion equation is further simplified, whenp=–2. We obtain numerical results which agree with results obtained by other methods. 相似文献
143.
A. B. Bhattacharya S. K. Kar M. K. Chatterjee R. Bhattacharya 《Annales Geophysicae》1998,16(2):183-188
The records of VLF atmospherics over Calcutta and then over Kalyani (West Bengal) during the torrential rainfall, caused by violent monsoon and post-monsoon depressions, exhibit distinct long-period fadings both at day and night. Interesting results obtained from an analysis of round-the-clock atmospherics data and associated meteorological parameters are reported in this paper. A possible correlation between the severe meteorological activity with the solar geophysical phenomena was studied. The results are indicative of an interesting sequence of solar-terrestrial events. A tentative conclusion is reached, suggesting an origin of the fading from atmospheric gravity waves generated in the centre of activity of the depressions concerned.Currently at: Department of Physics, Serampore College, Serampore, 712 201 West Bengal 相似文献
144.
Sanjay Shitole Mayank Sharma Shaunak De Avik Bhattacharya Y. S. Rao B. Krishna Mohan 《Journal of the Indian Society of Remote Sensing》2017,45(3):451-462
In this paper, we propose an adaptive filtering technique for Synthetic Aperture Radar (SAR) images. A new windowing technique is introduced where the total window is divided into five equal sized overlapping sub-windows. The pixel to be filtered is a part of each of these sub-windows. A weighted mean of all sub-windows is computed for the pixel under consideration. The weights are accounted from a measure of heterogeneity calculated for each sub-windows. The filter is able to adapt automatically and adjust the speckle suppression strength based on local statistics. This allows the filter to preserve edges while strongly suppressing speckle over homogeneous areas. The proposed filter was compared with some well known SAR filtering techniques in terms of speckle suppression and edge preservation ability. Several experiments were performed on datasets acquired from both air-borne and space-borne SAR platforms. Some well known indices were used for quantitative comparison with other filters. Among the filters compared, the proposed filter shows good speckle suppression ability while still exhibiting reasonable edge preservation ability. 相似文献
145.
A. Akyüz D. Bhattacharya D. D. Dixon T. J. O'Neill O. T. Tümer R. S. White A. D. Zych 《Experimental Astronomy》1995,6(3):275-284
The proposed Tracking and Imaging Gamma-Ray Experiment (TIGRE), operating in the 0.3–100 MeV energy interval, will be an efficient polarimeter with a modulation factor of 50% at 0.5 MeV. The polarization detection parameters of TIGRE were estimated using a Monte Carlo simulation modified to include the polarization dependence of the Klein-Nishina formula. Using Compton scattering of low energy photons and approximately 3 acceptance angle after scattering, TIGRE will be able to measure strong sources with 20% fractional polarization at 3 significance in a typical balloon-borne exposure and 5% during a 4-week satellite observation. 相似文献
146.
C. Shobha T. Geeta Prasanna K. Nirmala K. Renuka Reddy B. Lakshmi K. J. Hebbar M. Suryanarayana M. V. V. Kamaraju A. Bhattacharya 《Journal of the Indian Society of Remote Sensing》1994,22(2):93-102
Aeromagnetic data processing refers to the processing of magnetic data acquired through airborne surveys. The total magnetic field at various points along the predetermined flight path is recorded using the on board cesium magnetometer. At each of these points, the positional information in terms of latitude, longitude obtained from Inertial Navigation System (INS) and attitude, time and date are also recorded. The track flown by the aircraft while data acquisition is also recorded using video flight path camera. A software package has been developed to process this data and generate outputs in a form amenable to visual interpretation. It is developed on a VAX 11/780 system using VAX FORTRAN and PLOT 10 GKS software. This paper gives an outline of the various functions available in this package and also highlights the problems encountered in choosing the most appropriate techniques/methods to be used in the gridding and contouring of the data. 相似文献
147.
Banded iron formations of the Iron Ore Group (Archean greenstone belts) of Jharkhand-Orissa region, India host a good number
of large iron ore deposits (Fe wt %> 62). Iron ore mineralization of Gandhamardan hill is one of them where iron ores occur
in two stratigraphic horizons. One is strictly confined within banded iron formation (stratabound mineralization) with irregular
geometry, and show fracture filling and replacement vein-type mineralization along the fringes of hard massive ores of the
core. This type of mineralization is exposed along the western slope of the hill. Hard massive and laminated ores dominate
this mineralization. The other type occurs as low dipping sheet like body above banded iron formation and covered by laterites
forming the top of the hill. Flaky ores dominate this mineralization with formation of hard goethitic crust near the top.
Both the mineralizations contain mineralized banded iron formation corestones surrounded by hard massive or flaky iron ores.
Hard massive ores are entirely represented by martite-microplaty hematite mineralogy. Hard laminated ores contain microplaty
hematite and few martite grains representing early magnetites of the banded iron formation. Flaky ores are high porosity ores
produced by leaching of silica, martite and microplaty hematite. Hard goethitic ores are developed due to replacement of martite
and microplaty hematite or precipitation of goethite in the pore spaces. 相似文献
148.
Anuj Nandi S. Palit D. Debnath Sandip K. Chakrabarti T. B. Kotoch R. Sarkar Vipin K. Yadav V. Girish A. R. Rao D. Bhattacharya 《Experimental Astronomy》2011,29(1-2):55-84
Imaging in hard X-rays of any astrophysical source with high angular resolution is a challenging job. Shadow-casting technique is one of the most viable options for imaging in hard X-rays. We have used two different types of shadow-casters, namely, Coded Aperture Mask (CAM) and Fresnel Zone Plate (FZP) pair and two types of pixellated solid-state detectors, namely, CZT and CMOS in RT-2/CZT payload, the hard X-ray imaging instrument onboard the CORONAS-PHOTON satellite. In this paper, we present the results of simulations with different combinations of coders (CAM & FZP) and detectors that are employed in the RT-2/CZT payload. We discuss the possibility of detecting transient Solar flares with good angular resolution for various combinations. Simulated results are compared with laboratory experiments to verify the consistency of the designed configuration. 相似文献
149.
Sharmila Bhattacharya Suryendu Dutta Ratul Dutta 《Journal of Earth System Science》2014,123(5):923-934
The present study reports the biomarker distribution of condensate belonging to the early Cretaceous time frame using gas chromatography–mass spectrometry (GC–MS). The early Cretaceous palaeoenvironment was inscribed into these molecular fossils which reflected the source and conditions of deposition of the condensate. The saturate fraction of the condensate is characterized by normal alkanes ranging from n-C9 to n-C29 (CPI-1.13), cycloalkanes and C14 and C15 sesquiterpanes. The aromatic fraction comprises of naphthalene, phenanthrene, their methylated derivatives and cyclohexylbenzenes. Isohexylalkylnaphthalenes, a product of rearrangement process of terpenoids, is detected in the condensate. Several aromatic sesquiterpenoids and diterpenoids have been recorded. Dihydro-ar-curcumene, cadalene and ionene form the assemblage of sesquiterpenoids which are indicative of higher plant input. Aromatic diterpenoid fraction comprises of simonellite and retene. These compounds are also indicative of higher plants, particularly conifer source which had been a predominant flora during the Cretaceous time. 相似文献
150.
M. K. Bera Kasturi Bhattacharya A. Sarkar A. Samanta Kishor Kumar Ashok Sahni 《Journal of the Geological Society of India》2010,76(3):275-282
Oxygen isotope composition (δ18O) of fossil bone and tooth enamel phosphate (bioapatite) is an important tool for estimating the isotopic composition of
past environmental water. Lack of analytical facility was a hindrance for studying such bioapatites in spite of large number
of fossil materials reported from various geological ages in India. We have established in our laboratory, based on available
methods, the chemical procedure for extraction of very small amount (<1000 μg) PO4
−3 from bioapatite and on-line mass spectrometric measurement of its δ18O composition by high temperature (∼1450°C) pyrolysis. The achieved precision is ∼± 0.3 ‰ similar to obtained elsewhere, with
interlaboratory calibration showing excellent agreement of standard phosphates. Inferred δ18O values of environmental water, based on the analysis of teeth and bones of sharks, fish and terrestrial mammals from the
Paleogene successions of the northwest sub-Himalayan and the Peninsular India show strong correspondence with animal habitats.
The freshwater δ18O values are much depleted having range similar to modern monsoon precipitation. However, owing to our small dataset it is
not possible at this stage to infer about the existence of monsoon over the Indian sub-continent during the Eocene-Oligocene
time. 相似文献