Inhomogeneous perfect fluid universe with electromagnetic field     

Anirudh Pradhan  Vineet K. Yadav  Lallan Yadav  A. K. Yadav 《Astrophysics and Space Science》2007,312(3-4):267-273

Cylindrically symmetric inhomogeneous cosmological model for perfect fluid distribution with electromagnetic field is obtained. The source of the magnetic field is due to an electric current produced along the z-axis. F ₁₂ is the non-vanishing component of electromagnetic field tensor. To get the deterministic solution, it has been assumed that the expansion θ in the model is proportional to the shear σ. Physical and geometric aspects of the models are also discussed in presence and absence of magnetic field.   相似文献   

A new class of Inhomogeneous string cosmological models in general relativity     

Anirudh Pradhan  Anil Kumar Yadav  R. P. Singh  Vipin Kumar Singh 《Astrophysics and Space Science》2007,312(3-4):145-150

A new class of solutions of Einstein field equations has been investigated for inhomogeneous cylindrically symmetric space-time with string source. To get the deterministic solution, it has been assumed that the expansion (θ) in the model is proportional to the eigen value σ ¹  ₁ of the shear tensor σ ⁱ    _j . Certain physical and geometric properties of the models are also discussed.  相似文献   

A subgrid parameterization of orographic precipitation   总被引：6，自引：0，他引：6  

L. Ruby Leung  S. J. Ghan 《Theoretical and Applied Climatology》1995,52(1-2):95-118

Summary Estimates of the impact of global climate change on land surface hydrology require climate information on spatial scales far smaller than those explicitly resolved by global climate models of today and the foreseeable future. To bridge the gap between what is required and what is resolved, we propose a subgrid-scale parameterization of the influence of topography on clouds, precipitation, and land surface hydrology. The parameterization represents subgrid variations in surface elevation in terms of probability distributions of discrete elevation classes. Separate cloud, radiative, and surface processes are calculated for each elevation class. Rainshadow effects are not treated by the parameterization; they have to be explicitly resolved by the host model. The simulated surface temperature, precipitation, and snow cover for each elevation class are distributed to different geographical locations according to the spatial distribution of surface elevation within each grid cell.The subgrid parameterization has been implemented in the Pacific Northwest Laboratory's climate version of the Penn State/NCAR Mesoscale Model. The scheme is evaluated by driving the regional climate model with observed lateral boundary conditions for the Pacific Northwest and comparing simulated fields with surface observations. The method yields more realistic spatial distributions of precipitation and snow cover in mountainous areas and is considerably more computationally efficient than achieving high resolution by the use of nesting in the regional climate model.With 17 Figures  相似文献   

Accuracy assessment in cotton acreage estimation using Indian remote sensing satellite data     

Sujay Dutta  S.A. Sharma  A.P. Khera  Ajai  M. Yadav  R.S. Hooda  K.E. Mothikumar  M.L. Manchanda 《ISPRS Journal of Photogrammetry and Remote Sensing》1994,49(6)

The accuracy of cotton crop classification using satellite data has been assessed with respect to a detailed land cover map prepared by field survey. The effect of spatial resolution on classification accuracy was studied using LISS-I (spatial resolution 72.6 m) and LISS-II data (spatial resolution 36.25 m) of the Indian remote sensing satellite IRS-1B. The performances of the maximum likelihood and the minimum distance to mean as classifiers have also been assessed. LISS-II data have been found to give a higher classification accuracy. The estimate of cotton acreage using LISS-II data was closer to that obtained from the base map. The maximum likelihood classifier (MXL) and the minimum distance to mean (MDM) classifier performed equally well.  相似文献   

Recent sedimentary records from the Arabian Sea   总被引：1，自引：0，他引：1  

B. L. K. Somayajulu  D. N. Yadav  M. M. Sarin 《Journal of Earth System Science》1994,103(2):315-327

An attempt is made to understand the redox conditions that prevailed in the north eastern continental margins of the Arabian Sea and in the nearby deep water regions during the past few centuries using short undisturbed sediment cores. The geochronology is accomplished using²¹⁰Pb excess method and the proxy indicators chosen for productivity and associated redox changes are CaCO₃, organic matter (OM), Mn and U along with major elements Fe and Al. Such changes in principle are related to high productivity in the overlying waters which in turn depend on monsoonal intensity that causes upwelling responsible for increase in productivity. Alongwith the published data on gravity cores from the same region, our measurements suggest the following: At ∼ 300 m water depth, south of 21°N, the sediment-water interface at depths of ∼ 300 m had been anoxic during the time span represented by the presently studied cores for approximately ∼ 700y as evidenced by low Mn/Al (< 0.7 × 10⁻²) and high U/Al (> 10⁻⁴) weight ratios. In some adjacent deeper regions, however, the environment turned oxic around ∼ 200 y BP. Whereas both Mn and Ra were lost to the overlying waters in the anoxic regions (depth ∼340m), the Mn that diffused from deeper sections appears to have mineralized at the sediment-water-interface. Studies of this type on long undisturbed cores from the margins of the Arabian Sea and the Bay of Bengal, involving several proxies and geochronology by more than one method are needed to understand short term environmental (and monsoonal intensity) changes of the recent past with high resolution.  相似文献   

Seismic ray direction anomalies and relative residuals of earthquakes recorded at Gauribidanur array     

Avadh Ram  Lalaji Yadav  O P Singh 《Journal of Earth System Science》1981,90(1):63-74

Slowness and azimuthal anomalies provide valuable information about lateral inhomogeneities within the crust and mantle of the earth. Over 300 earthquakes (distance range 14°–36° and azimuth 0°–360°) recorded at Gauribidanur seismic array (GBA) in southern India, were analysed using adaptive processing techniques. Slowness anomalies upto 1·3 sec/deg and azimuthal anomalies upto 8° have been observed in the present analysis. Slowness anomaly patterns for Java trench, Mid-Indian oceanic ridge earthquakes are more consistent as compared to the events originating in the Himalayan and Hindukush regions. A significant feature of the azimuthal anomaly pattern was the distinct absence of any positive anomalies from earthquakes occurring in mid-oceanic ridge. These anomalies have also been analysed as a function of epicentral distance and are mainly attributed to the transition zones occurring between 400–700 km depth ranges in the Indian upper mantle regions. Relative residuals between the stations of GBA have very little dependence on azimuth and distance. An anomalous structure beneath the array in the direction of the Java trench region (azimuth 116–126°) has been postulated on the basis of large systematic slowness vectors observed.  相似文献   

Geoelectrical soundings for the study of suitable aquifers in the Gangetic alluvium of Allahabad region     

C L Singh  G S Yadav 《Journal of Earth System Science》1982,91(1):21-28

Sixteen geoelectrical soundings were taken in the western part of the district Allahabad lying between the rivers Ganga and Yamuna during the month of April 1976. The area of investigation forms the eastern part of Doab of rivers Ganga and Yamuna. Schlumberger configuration of geoelectrical soundings was used and the data were interpreted mainly by curve matching technique and theoretically calculated multi-layer model curves. Based on the results of the investigation it has been possible to draw geoelectrical section along two profiles and prepare a contour map of resistant substratum representing the base of the alluvial cover. A fence diagram has been constructed to represent the result of all the sounding data. The results of the present geophysical study have provided valuable information regarding the subsurface geology of this virgin area and also the potential aquifer zones which could be exploited for regular supply of groundwater for irrigation and drinking purposes.  相似文献   

TheUrquiola oil spill,La Coruña,Spain: Impact and reaction on beaches and rocky coasts     

Erich R. Gundlach  Christopher H. Ruby  Miles O. Hayes  Anne E. Blount 《Environmental Geology》1978,2(3):131-143

The supertankerUrquiola grounded, exploded, and burned at the entrance to La Coruña harbor (Spain) on May 12, 1976. A total of 100,000 tons of Persian Gulf crude oil was lost, of which about 30,000 tons washed onto shoreline environments. From May 17 to June 10, 1976, the impact and interaction of oil on fine-sand, coarse-sand, and gravel beaches and on sheltered and exposed rocky coasts was monitored in detail. At 32 localities, the beach was profiled, trenched, extensively sampled, and photographed. Another 67 stations were examined for surficial oil coverage and distribution. The surficial distribution of oil on the beaches was influenced primarily by wave activity, tidal stage, and oil quantity. Heaviest accumulations formed along the high-tide swash line. Within beach sediments, oil was present at distinct oiled sediment layers, which were often deeply buried. The depth of burial was related to wave energy and sediment type. Deepest burial (1 m) was on a high-energy, coarse-sand beach (M_z=0.82φ). Burial on fine-sand beaches was less than 30 cm. The thickness of oiled sediment depended on sedimentary characteristics, the quantity of oil present, wave action, and capillary forces. Oil-soaked sediment, as much as 65-cm thick, occurred on coarse-grained beaches. On fine-sand beaches, oiled sediment was limited to thicknesses of 10 cm or less. On rocky shores, oil distribution was determined primarily by wave energy. Along high-energy, cliffed, or steeply dipping rocky areas, wave reflection kept the oil approximately 5 m offshore and contamination was minimal. In low-energy, sheltered areas, oil readily accumulated, causing apparent environmental damage.  相似文献   

On magneto-elastic disturbaces in a visco-elastic cylinder placed in a magnetic field     

B. Yadav 《Pure and Applied Geophysics》1970,81(1):86-90

Summary The present note is an attempt to discuss the disturbances in a cylinder characterised by a visco-elasticity of general linear type, which is subjected to a magnetic field.  相似文献   

Spectral models for estimation of chlorophyll content, growth and yield of wheat crop     

Mahender Singh  Ram Niwas  M. L. Khichar  Manoj K. Yadav 《Journal of the Indian Society of Remote Sensing》2006,34(1):1-5

Field experiments were conducted during 1998–99 and 1999–2000 at research farm of the Department of Agricultural Meteorology, CCS Haryana Agricultural University, Hisar. Five wheat cultivars: WH 542, PBW 343, UP 2338, Raj 3765 and Sonak were sown on 25^th November, 10^th and 25^th December with four nitrogen levels viz., no nitrogen. 50, 100 and 150% of recommended dose. Leaf area index, dry matter at anthesis, final dry biomass and grain yield were recorded in all the treatments. Chlorophyll and wax contents of wheat leaves were estimated at different growth stages. Multiband spectral reflectance was measured using hand-held radiometer. Spectral indices such as simple ratio, normalized difference, transformed vegetation index, perpendicular vegetation index and greenness index were computed using the multiband spectral data. Values of all the spectral indices were maximum in 25 November sown crop with maximum dose of nitrogen (180 kg N ha^-1). PBW 343 showed higher values of all the spectral indices in comparison with other cultivars. The spectral indices recorded during maximum leaf area index stage were correlated with crop parameters. Using stepwise regression, empirical models for chlorophyll, leaf area index, dry biomass and yield prediction were developed. The ’R²’ values of these models ranged between 0.87 and 0.95.  相似文献