Self-similar model of magnetohydrodynamic radiative shock waves with increasing density     

S. N. Ojha  D. S. Pandey 《Astrophysics and Space Science》1988,148(1):143-148

The magnetohydrodynamic model of shock waves has been discussed in an atmosphere with gravitation and radiation. The disturbance is headed by a strong shock of increasing density. The medium ahead of the shock is assumed to be inhomogeneous and at rest. Variation of magnetic field radiation flux, and other flow variables are given in tabular form.  相似文献   

On penetrative instabilities     

S. K. Pandey 《Astrophysics and Space Science》1980,71(2):499-506

The investigation of instabilities in a penetrative atmosphere discussed in our earlier paper (Pandeyet al., 1979) is extended to include thermal dissipation in a more realistic approximation. It is shown that the convective modes are not very sensitive to the presence of an overlying stable layer. The overstabilization of gravity modes is, however, found to occur under very stringent conditions, while the acoustic overstability is enhanced by the presence of an overlying stable layer.  相似文献   

Self-similar magnetogasdynamic cylindrical shock waves,I     

J. B. Singh  S. K. Pandey 《Astrophysics and Space Science》1988,146(1):71-78

Similarity solutions describing the flow of a perfect gas behind a cylindrical shock wave with transverse magnetic field are investigated in an inhomogeneous medium. The total energy of the shock wave is assumed to be constant. A comparative study has been made between the results with and without magnetic field.  相似文献   

General relativistic treatment of magnetofluid disk around compact objects     

U. S. Pandey 《Astrophysics and Space Science》1988,141(2):251-256

Solutions of magnetofluid accretion disk with negligible self-gravitation have been obtained in the background of the Schwarzschild spacetime for differential as well as rigid rotation. The constraint equations for the magnetic field components have also been derived. It is shown that the magnetic field plays an important role in confining the fluid flow.  相似文献   

Correlation of Heat Flow and Crustal Topography in the Indian Region     

Janardan G. Negi  Om Prakash Pandey 《Geophysical Journal International》1976,45(2):201-217

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Some Bianchi Type I Viscous Fluid Cosmological Models with a Variable Cosmological Constant     

Anirudh Pradhan  Purnima Pandey 《Astrophysics and Space Science》2006,301(1-4):127-134

Some Bianchi type I viscous fluid cosmological models with a variable cosmological constant are investigated in which the expansion is considered only in two direction i.e. one of the Hubble parameter is zero. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density whereas the coefficient of shear viscosity is considered as constant in first case whereas in other case it is taken as proportional to scale of expansion in the model. The cosmological constant Λ is found to be positive and is a decreasing function of time which is supported by results from recent supernovae Ia observations. Some physical and geometric properties of the models are also discussed.  相似文献   

Artificial Neural Network (ANN) Based Inversion of Benthic Substrate Bottom Type and Bathymetry in Optically Shallow Waters - Initial Model Results     

P. V. Nagamani  Prakash Chauhan  Nivedita Sanwlani  M. M. Ali 《Journal of the Indian Society of Remote Sensing》2012,40(1):137-143

Ocean-colour remote sensing in optically shallow waters is influenced by contribution from the water column depth as well as by the substrate type. Therefore, it is required to include the contribution from the water column and substrate bottom type for bathymetry estimation. In this report we demonstrate the use of Artificial Neural Network (ANN) based approach to spectrally distinguish various benthic bottom types and estimate depth of substrate bottom simultaneously in optically shallow waters. We have used in-water radiative transfer simulation modeling to generate simulated top-of-the-water column reflectance the four major benthic bottom types viz. sea grass, coral sand, green algae and red algae using Hydrolight simulation model. The simulated remote sensing reflectance, for the four benthic bottom types having benthic bottom depth up to 30 m were generated for moderately clear waters. A multi-layer perceptron (MLP) type neural network was trained using the simulated data. ANN based approach was used for classification of the benthic bottom type and simultaneous inversion of bathymetry. Simulated data was inverted to yield benthic bottom type classification with an accuracy of ~98% for the four benthic substrate types and the substrate depth were estimated with an error of 0% for sea grass, 1% for coral sand and 1–3% for green and red algae up to 25 m, whereas for substrate bottom deeper than 25 m depth the classification errors increased by 2–5% for three substrate bottom types except sea grass bottom type. The initial results are promising which needs validation using the in-situ measured remote sensing reflectance spectra for implementing further on satellite data.  相似文献   

Vulnerability and adaptation to climate variability and water stress in Uttarakhand State, India   总被引：1，自引：0，他引：1  

Ulka Kelkar  Kapil Kumar Narula  Ved Prakash Sharma  Usha Chandna   《Global Environmental Change》2008,18(4):564

This paper presents a participatory approach to investigate vulnerability and adaptive capacity to climate variability and water stress in the Lakhwar watershed in Uttarakhand State, India. Highly water stressed microwatersheds were identified by modelling surface runoff, soil moisture development, lateral runoff, and groundwater recharge. The modelling results were shared with communities in two villages, and timeline exercises were carried out to allow them to trace past developments that have impacted their lives and livelihoods, and stimulate discussion about future changes and possible adaptation interventions.  相似文献   

Detection and extraction of signals from the epoch of reionization using higher-order one-point statistics     

Geraint J. A. Harker  Saleem Zaroubi  Rajat M. Thomas  Vibor Jeli&#;  Panagiotis Labropoulos  Garrelt Mellema  Ilian T. Iliev  Gianni Bernardi  Michiel A. Brentjens  A. G. de Bruyn  Benedetta Ciardi  Leon V. E. Koopmans  V. N. Pandey  reas H. Pawlik  Joop Schaye  Sarod Yatawatta 《Monthly notices of the Royal Astronomical Society》2009,393(4):1449-1458

Detecting redshifted 21-cm emission from neutral hydrogen in the early Universe promises to give direct constraints on the epoch of reionization (EoR). It will, though, be very challenging to extract the cosmological signal (CS) from foregrounds and noise which are orders of magnitude larger. Fortunately, the signal has some characteristics which differentiate it from the foregrounds and noise, and we suggest that using the correct statistics may tease out signatures of reionization. We generate mock data cubes simulating the output of the Low Frequency Array (LOFAR) EoR experiment. These cubes combine realistic models for Galactic and extragalactic foregrounds and the noise with three different simulations of the CS. We fit out the foregrounds, which are smooth in the frequency direction, to produce residual images in each frequency band. We denoise these images and study the skewness of the one-point distribution in the images as a function of frequency. We find that, under sufficiently optimistic assumptions, we can recover the main features of the redshift evolution of the skewness in the 21-cm signal. We argue that some of these features – such as a dip at the onset of reionization, followed by a rise towards its later stages – may be generic, and give us a promising route to a statistical detection of reionization.  相似文献   

LO Pegasi: an investigation of multiband optical polarization     

J. C. Pandey  Biman J. Medhi  R. Sagar  A. K. Pandey 《Monthly notices of the Royal Astronomical Society》2009,396(2):1004-1011

We present BVR polarimetric study of the cool active star LO Pegasi (LO Peg) for the first time. LO Peg was found to be highly polarized among the cool active stars. Our observations yield average values of polarization in LO Peg:   P_B = 0.387 ± 0.004 per cent, θ_B= 88°± 1°; P_V = 0.351 ± 0.004 per cent, θ_V= 91°± 1°  and   P_R = 0.335 ± 0.003 per cent, θ_R= 91°± 1°  . Both the degree of polarization and the position angle are found to be variable. The semi-amplitude of the polarization variability in B, V and R bands is found to be  0.18 ± 0.02, 0.13 ± 0.01  and  0.10 ± 0.02  per cent, respectively. We suggest that the levels of polarization observed in LO Peg could be the result of scattering of an anisotropic stellar radiation field by an optically thin circumstellar envelope or scattering of the stellar radiation by prominence-like structures.  相似文献