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111.
Selection of a set of dominant echo features to classify seafloor sediments using a multilayer perceptron neural network is
investigated at two acoustic frequencies (33 and 210 kHz). Several sets of inputs with different combinations of two, three,
four, five, and six echo features are exploited with three-layer neural networks. The performances of the networks are analyzed
to assess the most discriminating set of echo features for classification of seafloor sediments. The results of the overall
average performances reveal that backscatter strength and time spread are the two most important echo features at 33 kHz,
whereas backscatter strength has higher discriminating characteristics at 210 kHz for seafloor sediment classification. In
addition, a set of four echo features consisting of backscatter strength, time-spread, statistical skewness, and Hausdroff
dimension gives the highest success at both the acoustic frequencies. 相似文献
112.
Improving multimodel weather forecast of monsoon rain over China using FSU superensemble 总被引:3,自引:0,他引:3
In this paper we present the current capabilities for numerical weather prediction of precipitation
over China using a suite of ten multimodels and our superensemble based forecasts. Our suite of models includes
the operational suite selected by NCARs TIGGE archives for the THORPEX Program. These are: ECMWF, UKMO, JMA,
NCEP, CMA, CMC, BOM, MF, KMA and the CPTEC models. The superensemble strategy includes a training and a forecasts
phase, for these the periods chosen for this study include the months February through September for the years 2007
and 2008. This paper addresses precipitation forecasts for the medium range i.e. Days 1 to 3 and extending out to
Day 10 of forecasts using this suite of global models. For training and forecasts validations we have made use of
an advanced TRMM satellite based rainfall product. We make use of standard metrics for forecast validations that
include the RMS errors, spatial correlations and the equitable threat scores. The results of skill forecasts of
precipitation clearly demonstrate that it is possible to obtain higher skills for precipitation forecasts for Days
1 through 3 of forecasts from the use of the multimodel superensemble as compared to the best model of this suite.
Between Days 4 to 10 it is possible to have very high skills from the multimodel superensemble for the RMS error of
precipitation. Those skills are shown for a global belt and especially over China. Phenomenologically this product
was also found very useful for precipitation forecasts for the Onset of the South China Sea monsoon, the life cycle
of the mei-yu rains and post typhoon landfall heavy rains and flood events. The higher skills of the multimodel
superensemble make it a very useful product for such real time events. 相似文献
113.
This is the second paper of the series where we have considered Brans-Dicke (B-D) theory as well as general scalar tensor
theory of gravitation in higher dimensional space-time model in the false vacuum state. We have examined whether inflationary
solutions are possible both for constant or variable coupling parameter ω. Also the nature of the scalar field and the coupling
parameter are discussed in the asymptotic limit.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
114.
The expression for nonlinear shift of a wave number of a whistler wave propagating through the ionosphere has been derived and the results have been discussed. It is seen that nonlinear shift of a wave number of a whistler is significant in some physical situations. From numerical estimations it is observed that wave number shifts of a whistler for both the LCP and RCP waves become significant when the frequency of the waves are nearly equal to the ion-cyclotron frequency. 相似文献
115.
T. K. Chakraborty 《Astrophysics and Space Science》1980,68(2):469-474
Similarity solutions for the propagation of plane relativistic shock waves in a slowly moving medium, where the nucleon number density obeys an exponential law ofx/t, is obtained in this paper. The shock surface moves with constant velocity and the total energy of the disturbance is dependent on time. The solutions are applicable only to an isothermal medium. 相似文献
116.
Sandip More Rajarshi Rit Mahasin Ali Khan Dipak Kumar Paruya Suchana Taral Tapan Chakraborty Subir Bera 《Journal of the Geological Society of India》2018,91(3):301-306
Fossil leaf impressions and pollen grains comparable to modern Sloanea sp. of Elaeocarpaceae collected from the middle part of the Siwalik sediments (Geabdat Sandstone Formation; Pliocene) in Darjeeling foothills of eastern Himalaya are reported in the present communication. On the basis of macro morphological features, leaf remains are described as a new species Sloanea siwalika sp. nov. This is the first authentic record of the occurrence of leaf and pollen grains comparable to the genus Sloanea L. from the Cenozoic sediments of India and Asia as well. The recovery of this species and other earlier-described evergreen taxa from the same formation, suggests the existence of a tropical, warm and humid climatic conditions during the depositional period. The present study further suggests that after Pliocene the taxon might have shifted from Darjeeling Himalayan region to the adjoining southeast Asian land masses, due to possible climate change caused by post-Pliocene orogenic movement of the Himalaya. 相似文献
117.
Maitrayee Chakraborty Sayan Biswas Pulak Sengupta 《International Geology Review》2015,57(11-12):1619-1632
The Arcuate Singhbhum Shear Zone (SSZ) forms an integral part and occurs at the southern fringe of the Palaeoproterozoic North Singhbhum Fold Belt (NSFB) of the East Indian Shield. Repeated folding, ductile shearing, and accompanying hydrothermal activities in the SSZ during the late Palaeoproterozoic (ca. 1.66–1.60 Ga) orogeny resulted in a highly tectonized ensemble of rocks including a suite of peraluminous kyanite-rich quartzite (KQR). Near Kanyaluka village, the KQR shows millimetre- to decimetre-thick alternation of kyanite- and quartz-rich bands. The banded rock is intensely sheared and is cross-cut by weakly deformed to undeformed kyanite-quartz veins. In many places, kyanite-rich bands show sea-green coloured pods rich in lazulite. Textural studies reveal that deformed kyanite and quartz grains are sequentially replaced by augelite and lazulite (XMg > 0.97) at the terminal phase of shearing in the SSZ. Modelling of observed textures and mineral compositions with the C-Space program shows the following augelite- and lazulite-forming reactions:
1.829Kyanite + 0.998P + 1.5H2O + 0.001Ca = 1Augelite + 1.666Al + 0.001 Mg + 1.822SiO2 + 0.002Fe + 0.0002Na
1.778Kyanite + 0.667Augelite + 1.294P + 1.011 Mg + 0.011Fe + 0.0001Na = 1Lazulite + 2.833Al + 1.78SiO2 + 0.001 Ca
118.
A granite-granodiorite-gabbro-ultramafic rock association occurs in the southern sector of Chhotanagpur Gneissic Complex in Central India. Field relations show mingling and mixing of mafic and granodioritic magmas along the contacts of the intrusives. Petrographic studies, coupled with analyses of phase compositions and bulk rock major and trace element compositions favor origin of mafic magma from partial melting of sub-continental hybridized lithospheric mantle and subsequent two stage emplacement. Initial ponding of mafic magma at basal crust elevated the geothermal gradient so as to cause partial melting of lower crustal materials and generation of granodioritic melt. Simultaneous emplacement of granodioritic and mafic magmas tapped from basal crustal reservoir at mid-crustal depth resulted in restricted mingling-mixing along the contacts of the contrasting magma types locally producing rocks of dioritic composition. The mode of evolution of this cogenetic mafic-felsic association, when combined with available geochronological data, has important implications in demarcation of the extent of Grenvellian orogen that resulted in amalgamation of the Southern Crustal Province of India (SCP) with the Bundelkhand Craton or Northern Crustal Province (NCP). 相似文献
119.
S. Mohanto K. Singh T. Chakraborty D. Basu 《Geotechnical and Geological Engineering》2014,32(3):601-616
The compressed air energy storage (CAES) method is a viable method of storing surplus energy underground when there is a mismatch between energy generation and demand. Wellbores embedded in rock are an integral part of energy storage structures, and are used for injecting and extracting the compressed air. During injection and production cycles, the storage reservoir and wellbore are subjected to cyclic change in external pressure and temperature, which may cause failure of the wellbore. In this paper, cyclic thermo-mechanical analysis of a horizontal wellbore in an underground CAES cavern is performed using finite element analysis. The rock behavior is simulated using the Mohr-Coulomb constitutive law. The reduction in the yield strength of rock with increase in the number of loading cycles is taken into account in the analysis. Parametric sensitivity studies are carried out to study the effects of dilation and friction angles of rock, the ratio of in situ horizontal and vertical stresses, loading frequency, and the magnitude of the temperature cycles in the cavern on the wellbore performance for different types of rock. The thermo-mechanical cyclic behavior leads to plastic strains that are greater than those obtained by performing mechanical analysis only. Significantly large deformation is generated in rock for large dilation angle and high loading frequencies. 相似文献
120.
Nairwita Mazumder Ritabrata Biswas Subenoy Chakraborty 《Astrophysics and Space Science》2011,334(1):183-186
Recent observational evidences demand that the universe is going through an accelerating phase and hence in the frame work
of Einstein gravity the matter should be exotic in nature. In the present work, we study the evolution of the apparent and
event horizons across phantom barrier (a cosmological constant) and examine the validity of the generalized second law of
thermodynamics (GSLT) for the universe bounded by the horizons. 相似文献