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排序方式: 共有207条查询结果,搜索用时 171 毫秒
171.
Arjun Kumar S. S. Rai Anand Joshi Himanshu Mittal Rajiv Sachdeva Rohtash Kumar Vandana Ghangas 《地震科学(英文版)》2013,26(2):99-105
Earthquakes began to occur in Koyna region (India) soon after the filling of Koyna Dam in 1962. In the present study, three datasets 1964–1993, 1993–1995, and 1996–1997 are analyzed to study the b-value and fractal dimension. The b-value is calculated using the Gutenberg–Richter relationship and fractal dimension D corr. using correlation integral method. The estimated b-value and D corr. of this region before 1993 are found to be in good agreement with previously reported studies. In the subsequent years after 1995, the b-value shows an increase. The estimated b-values of this region are found within the limits of global average. Also, the pattern of spatial clustering of earthquakes show increase in clustering and migration along the three zones called North-East Zone, South-East Zone (SEZ), and Warna Seismic Zone. The earthquake events having depth ≤5 km are largely confined to SEZ. After 1993, the D corr. shows decrease, implying that earthquake activity gets clustered. This seismic clustering could be helpful for earthquake forecasting. 相似文献
172.
Conformally flat tilted Bianchi type V cosmological models in presence of a bulk viscous fluid and heat flow are investigated. The coefficient of bulk viscosity is assumed to be a power function of mass density. Some physical andgeometric aspects of the models are also discussed. 相似文献
173.
K. K. Sinha Dibakar Ghosh S. D. Rai M. K. Khandelwal 《Journal of the Geological Society of India》2016,88(3):295-304
Low grade uranium mineralisation associated with phosphorites/ phosphatic sediments and carbonaceous shale has been well established at and/or close to Krol- Tal contact in some of sub-basins of inner Krol belt such as Nigalidhar, Mussoorie and Garhwal synclines in the realm of lesser Himalaya. Unlike the other sub-basins of the belt, though the Nainital syncline is sparsely phosphatic and carbonaceous, carbonate hosted uranium occurrence is reported for the first time from the syncline. The carbonate-hosted uranium occurrences in Krol D of Nainital syncline are of limited extent with values ranging from 200 ppm to 840 ppm eU3O8. Radioactivity is associated with fractured dolostone/ dolomitic limestone and pelloidal limestone. Uranium phases mostly occur in association with carbonaceous, ferruginous matters and clays. However, ultrafine pitchblende grains do occur associated with idiotopic pyrite aggregates suggesting initial trapping of uranium by organic matters present in sediments which later remobilised and precipitated as fine pitchblende. Subsequently, second phase of remobilisation of uranium under oxidising condition gave rise uraniferous goethite, limonite and other iron oxyhydoxides. In contrast to other sub-basins, the Krol-Tal contact in Nainital syncline does not appear to hold any promising phosphate and uranium mineralisation due to less suitable basinal morphology and low Ca/Mg ratio. 相似文献
174.
Sikta Patnaik G. N. Hegde A. Panneerselvam M. B. Verma R. Mohanty A. K. Rai 《Journal of the Geological Society of India》2016,88(2):151-158
Granite core samples (n=14) from the Gogi-Kurlagere fault zone in the central part of the Bhima basin were studied in terms of LREE, Y and Zr mobility during uranium mineralization. LREE, Zr and Y along with LILE (Ba, Rb) and P show behavioral differences in the mineralised and the non-mineralised samples. Average ΣLREE in mineralised granite (240 ppm) is higher than in non-mineralised samples (157 ppm). The average Zr and Y in the mineralised granite are 193 ppm and 17 ppm, while the corresponding abundances of these elements in non-mineralised portion are 148 ppm and 11 ppm respectively. Besides enrichment of U, Th, Ba, Pb and Rb and depletion of Sr are observed in mineralized granite in comparison to non-mineralized granite. Hydrothermal alteration has led to the mobility of these elements, which again dependent on the overall geochemical behavior of the migrating fluid. REE and Y in association with uranyl [(UO2)2+] ion were transported as carbonate complexes like [UO2(CO3)3]4- and [REE (CO3)3]3- and were later incorporated into favourable structural loci by precipitating minerals like pitchblende and coffinite. 相似文献
175.
Sea Surface Temperature (SST) is crucial for the development and maintenance of a tropical cyclone (TC) particularly below the storm core region. However, storm data below the core region is the most difficult to obtain, hence it is not clear yet that how sensitive the radial distribution of the SST impact the storm characteristic features such as its inner-core structures, translational speed, track, rainfall and intensity particularly over the Bay of Bengal. To explore the effects of radial SST distribution on the TC characteristics, a series of numerical experiments were carried out by modifying the SST at different radial extents using two-way interactive, triply-nested, nonhydrostatic Advanced Weather Research and Forecast (WRF-ARW) model. It is found that not only the SST under the eyewall (core region) contribute significantly to modulate storm track, translational speed and intensity, but also those outside the eyewall region (i.e., 2–2.5 times the radius of maximum wind (RMW)) play a vital role in defining the storm’s characteristics and structure. Out of all the simulated experiments, storm where the positive radial change of SST inducted within the 75 km of the storm core (i.e., P75) produced the strongest storm. In addition, N300 (negative radial changes at 300 km) produced the weakest storm. Further, it is found that SST, stronger within 2–2.5 times of the RMW for P75 experiment, plays a dominant role in maintaining 10 m wind speed (WS 10), surface entropy flux (SEF) and upward vertical velocity (w) within the eyewall with warmer air temperature (T) and equivalent potential temperature (??e) within the storm’s eye compared to other experiments. 相似文献
176.
177.
A.K. Mahajan J.J. Galiana-Merino C. Lindholm B.R. Arora A.K. Mundepi Nitesh Rai Neetu Chauhan 《Journal of Applied Geophysics》2011,73(3):196-206
The characterization of the sediments, down to bedrock, is very important from the seismological point of view in order to study the possible earthquake effects (site effects). Resonance frequency and shear-wave velocity profile are the main features used to estimate the thickness and stiffness of the sedimentary cover. To map these characteristics different geotechnical, geophysical and seismological methods have been developed and applied over a last few years. In this work, different soil investigation methods have been applied around the Himalayan foothills, focusing on three sites with different soil characteristics that span from the Doon valley to the Ganga foreland basin. Active and passive array experiments were carried out: Multichannel Analysis of Surface Waves (active MASW), Passive Remote MASW and f–k technique. A dispersion curve was estimated for every site covering a wider frequency band rather than if only one method would have been used. Moreover, ambient noise measurements were also recorded in order to apply the H/V method and to estimate the resonance frequencies. Combining the information provided from all methods and using the neighbourhood algorithm, the best suitable shear (S) wave velocity profiles were estimated for each area. In this way, soil sediments were characterized by the resonance frequency, the soil thickness and the mean S-wave velocity. It has been demonstrated that the use of different methods give coherent and more robust results than when only one method is applied. This greatly contributes to the credibility of the results. 相似文献
178.
In this article we investigate the nonlinear dynamics of 3D kinetic Alfvén waves (KAWs) and quasi-transverse weak whistler waves in a magnetized plasma. We have studied the problem numerically to examine the transient evolution of localized structures of 3D KAWs and whistler waves. The nonlinearity arises as a result of ponderomotive effects associated with 3D KAWs; consequently, the background density modifies. The weak whistler waves propagating in this modified density are localized and amplified. To improve our insight into the basic physics behind the formation of these localized structures, we have also solved the system semi-analytically. The power spectra show a Kolmogorov scaling (with a power of \(-5/3\)) in the inertial range that lies above the ion gyroradius. Below this scale, dispersive effects start to appear, and the power spectrum follows a steeper scaling (?2 to ?4). Our results show the important role that KAWs and whistler waves play in the energy cascading from larger to smaller scales. The results are consistent with the solar wind observations by the Cluster spacecraft. 相似文献
179.
Nuzhat Q. Qazi L. Adrian Bruijnzeel Shive Prakash Rai Chandra P. Ghimire 《水文科学杂志》2017,62(7):1114-1130
Baseflows have declined for decades in the Lesser Himalaya but the causes are still debated. This paper compares variations in streamflow response over three years for two similar headwater catchments in northwest India with largely undisturbed (Arnigad) and highly degraded (Bansigad) oak forest. Hydrograph analysis suggested no catchment leakage, thereby allowing meaningful comparisons. The mean annual runoff coefficient for Arnigad was 54% (range 44–61%) against 62% (53–69%) at Bansigad. Despite greater total runoff Qt (by 250 mm year–1), baseflow at Bansigad ceased by March, but was perennial at Arnigad (making up 90% of Qt vs. 51% at Bansigad). Arnigad storm flows, Qs, were modest (8–11% of Qt) and occurred mostly during monsoons (78–98%), while Qs at Bansigad was 49% of Qt and occurred also during post-monsoon seasons. Our results underscore the importance of maintaining soil water retention capacity after forest removal to maintain baseflow levels.
EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR D. Gerten 相似文献
180.
Kossitse Venyo Akpataku Shive Prakash Rai Masamaéya Dadja-Toyou Gnazou Lallébila Tampo Limam Moctar Bawa Gbandi Djaneye-Boundjou 《水文科学杂志》2019,64(8):983-1000
Hydrochemical, inverse geochemical modelling and isotopic approaches are used to assess the hydrogeochemical evolution of groundwater from the basement aquifers in the southeastern part of the Plateaux Region, Togo. Groundwater originates from present-day rainwater infiltration and is mostly fresh and slightly acidic to neutral. Hydrochemical facies are predominantly mixed cations-HCO3 associated with Ca/Mg-Cl, Na-HCO3 and Na-Cl water types in equilibrium with kaolinite and Ca/Mg-smectites. They are related to silicates hydrolysis, anthropogenic contamination, nitrification/denitrification, mixing along flowpaths and dissolution/precipitation of secondary minerals. The pattern of flow paths is in accordance with an increasing trend in total dissolved solids (TDS) toward the potentiometric depression located in the central and southern parts of the aquifer system. Inverse geochemical modelling using the NETPATH-WIN model showed the relative importance of biotite, plagioclase and amphibole weathering and dissolution of secondary carbonate minerals along the flowpath, suggesting that an abundance of minerals is not necessarily the main factor controlling the groundwater chemistry evolution. 相似文献