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171.
The protocontinental growth of the Indian Shield and the antiquity of its rift valleys 总被引:1,自引:0,他引:1
The evolution of the Indian Shield has been envisaged from the analysis of available tectono-lithostratigraphic, geochronological, geochemical and geophysical data. It appears that the Dharwar schist belts and their equivalents, except the Kolar schist belt, are not typical greenstone belts, but are representative of a transitional era of rapid transformation from simatic to sialic crust. In the Archaean—Proterozoic tract of India, relics of rocks older than 3.0 b.y. are identified in five widely separated regions of distinct tectono-litho-stratigraphic assemblages which probably represent the primordial continental nucleii. It is suggested that the growth of the Indian Shield has taken place through nucleation, accretion and merger into three protocontinents named Dharwar, Aravalli and Singhbhum. The cratonisation of the Indian unit seems to have been rapid and almost completed by the middle Proterozoic, as there is no significant variation in the composition of the clastic sediments and basalts from middle Proterozoic onwards. The continental nucleii appear to merge along the deep-seated lineaments, which are reflected on the tectonic map of India. Further, the Dharwar, Aravalli and Singhbhum protocontinents also seem to merge along a Y=shaped Narmada—Son—Godavari lineament which along with the Mahanadi lineament, between the two continental nucleii of the Singhbhum protocontinent have later developed into rift valleys. 相似文献
172.
P. C. Sinha Y. R. Rao S. K. Dube C. R. Murthy A. K. Chatterjee 《Estuarine, Coastal and Shelf Science》1999,48(6):649
This paper has two purposes. The first is to study the circulation and salinity in Hooghly Estuary, along the east coast of India and the second is to compare the performance of two turbulence closure schemes by modelling it. A breadth averaged numerical model using a sigma co-ordinate system in the vertical is briefly described. Vertical diffusion of momentum and salt are parameterized by a simple first-order turbulent closure or by a one equation model for turbulent kinetic energy (TKE) which uses a specified mixing length. The results are compared with the available neap and spring tide observations along the estuary for both low and high discharge periods.The computed elevations and currents are in reasonable agreement with the observations showing no major differences in vertical current profiles by both the turbulent schemes. However, there is a slight under-prediction of bottom currents. The salinity profiles predicted by TKE model show better matching with observations. Statistical tests are also conducted to study the comparative performance of the turbulent closure schemes. The maintenance of two layer structure in residual currents and salt variability are also studied by using the model. 相似文献
173.
This paper presents a new computational tool for probabilistic stability assessment of earth slopes/embankments. The method involves high dimensional model representation (HDMR) that facilitates lower dimensional approximation of the original limit state, response surface generation of HDMR component functions, and Monte Carlo simulation. HDMR is a general set of quantitative model assessment and analysis tools for capturing the high-dimensional relationships between sets of input and output model variables. It is a very efficient formulation of the system response, if higher-order variable correlations are weak, allowing the physical model to be captured by the first few lower-order terms. Once the approximate form of the original limit state is defined, the failure probability can be obtained by statistical simulation. Results of four numerical examples indicate that the proposed method provides accurate and computationally efficient estimates of the failure probability of earth slopes/embankments. 相似文献
174.
Akkur V. Raman Rayaroth Damodaran Lisa A. Levin Thiruchitrambalam Ganesh Yannamani K. V. Rao Sateesh Nanduri Rakhesh Madhusoodhanan 《Marine Ecology》2015,36(3):679-700
The Bay of Bengal remains one of the least studied of the world's oxygen minimum zones (OMZs). Here we offer a detailed investigation of the macrobenthos relative to oxygen minimum zone [OMZ – DO (dissolved oxygen), concentration <0.5 ml·1?1] at 110 stations off the North East Indian margin (160 and 200 N) featuring coastal, shelf and slope settings (10–1004 m). Macrobenthos (>0.5 mm) composition, abundance and diversity were studied in relation to variations in depth, dissolved oxygen, sediment texture and organic carbon. Using multivariate procedures powered by SIMPROF analysis we identified distinct OMZ core sites (depth 150–280 m; DO 0.37 ml·1?1) that exhibited dense populations of surface‐feeding polychaetes (mean 2188 ind. m?2) represented by spionids and cossurids (96%). Molluscs and crustaceans were poorly represented except for ampeliscid amphipods. The lower OMZ sites (DO > 0.55 ml·l?1) supported a different assemblage of polychaetes (cirratulids, amphinomids, eunicids, orbinids, paraonids), crustaceans and molluscs, albeit with low population densities (mean 343 ind. m?2). Species richness [E(S100)], diversity (Margalef d; H’) and evenness (J’) were lower and dominance was higher within the OMZ core region. Multiple regression analysis showed that a combination of sand, clay, organic carbon, and dissolved oxygen explained 62–78% of the observed variance in macrobenthos species richness and diversity: E(S100) and H’. For polychaetes, clay and oxygen proved important. At low oxygen sites (DO <1 ml·l?1), depth accounted for most variance. Residual analysis (after removing depth effects) revealed that dissolved oxygen and sediment organic matter influenced 50–62% of residual variation in E(S100), H’ and d for total macrofauna. Of this, oxygen alone influenced up to ~50–62%. When only polychaetes were evaluated, oxygen and organic matter explained up to 58–63%. For low oxygen sites, organic matter alone had the explanatory power when dominance among polychaetes was considered. Overall, macrobenthic patterns in the Bay of Bengal were consistent with those reported for other upwelling margins. However, the compression of faunal gradients at shallower depths was most similar to the Chile/Peru margin, and different from the Arabian Sea, where the depth range of the OMZ is two times greater. The Bay of Bengal patterns may take on added significance as OMZs shoal globally. 相似文献
175.
Indian Ocean humpback dolphins Sousa plumbea inhabit nearshore waters from South Africa to eastern India. Humpback dolphins are vulnerable to conservation threats due to their naturally small population sizes and use of nearshore habitats, where human activities are highest. We investigated the abundance and residency of this species inhabiting Mossel Bay, South Africa, using photographic mark-recapture. Data were collected during 81 surveys in Mossel Bay between 2011 and 2013. Open population modelling using the POPAN parameterisation produced a ‘super-population’ estimate of 125 individuals (95% CI: 61–260) and within-year estimates of between 33 and 86 individuals (2011: 71 [95% CI: 30–168]; 2012: 33 [15–73], 32 [15–70]; 2013: 46 [20–108]). Although less appropriate, closed capture models were also run for comparison with previous studies in the region and generated similar, but slightly smaller, population estimates within each year. We compared our catalogue with opportunistic data collected from East London, Plettenberg Bay, De Hoop and Gansbaai. The only catalogue matches attained were between Plettenberg Bay (n = 44 identified) and Mossel Bay (n = 67 identified), separated by 140?km. Population exchange was moderate, with nine individuals resighted in multiple years between these two areas. This study supports previous findings of long-range movements for this species and provides a baseline from which to assess future impacts on the population. 相似文献
176.
Tilak B. Kotoch Anuj Nandi D. Debnath J. P. Malkar A. R. Rao M. K. Hingar Vaibhav P. Madhav S. Sreekumar Sandip K. Chakrabarti 《Experimental Astronomy》2011,29(1-2):27-54
Cadmium Zinc Telluride (CZT) detectors are high sensitivity and high resolution devices for hard X-ray imaging and spectroscopic studies. The new series of CZT detector modules (OMS40G256) manufactured by Orbotech Medical Solutions (OMS), Israel, are used in the RT-2/CZT payload onboard the CORONAS-PHOTON satellite. The CZT detectors, sensitive in the energy range of 20 to 150 keV, are used to image solar flares in hard X-rays. Since these modules are essentially manufactured for commercial applications, we have carried out a series of comprehensive tests on these modules so that they can be confidently used in space-borne systems. These tests lead us to select the best three pieces of the ??Gold?? modules for the RT-2/CZT payload. This paper presents the characterization of CZT modules and the criteria followed for selecting the ones for the RT-2/CZT payload. The RT-2/CZT payload carries, along with three CZT modules, a high spatial resolution CMOS detector for high resolution imaging of transient X-ray events. Therefore, we discuss the characterization of the CMOS detector as well. 相似文献
177.
We present the photometric solutions of the variable star V30 that is in the foreground of intermediate open cluster NGC 7789.The observations were done in the V passband using the 2 m telescope at the IUCAA-Girawali Observatory in India.The analysis is done using the Wilson-Devinney Code (2003) and the fitted light curve is presented.The photometric solutions reveal a W-subtype contact configuration.The photometric mass ratio is found to be 0.395 and the absolute masses and radii for the components are ded... 相似文献
178.
We present the combined BVI multicolor photometric solutions of seven EW variables in the old open cluster Berkeley 39.The observations were carried out in the B and V passbands from the 2 m telescope at the IUCAA-Girawali Observatory in India.The analysis is done using the 2003 version of the Wilson-Devinney code and the fitted light curves are presented.The light curves appear to be symmetric in all the passbands.The photometric solutions suggest that the variables are W-type systems.The new ephemeris ind... 相似文献
179.
Hipparcos photometric data for the massive O-type binary UW CMa were analysed within the framework of the Roche model. Photometric solutions were obtained for five mass ratios in the q = M2/M1 = 0.5–1.5 range. The system is found to be in a contact configuration. Independently of q, the best-fitting model solutions correspond to the orbital inclination i ~ 71° and the temperature of the secondary component T2 ~ 33500 K, at the fixed temperature of the primary T1 = 33750 K. Considering that the spectrum of the secondary is very weak, photometric solutions corresponding to the contact configuration favor the mass ratio q smaller than unity (in which case the luminosity of the secondary is smaller than that of the primary). The absolute parameters of the system are estimated for different values of the mass ratio. 相似文献
180.