An explosion model in magne to gasdynamics     

B. G. Verma  J. B. Singh 《Astrophysics and Space Science》1980,73(2):469-479

By taking into account the interaction with magnetic field, in an axially symmetric inhomogeneous medium and assuming Gaussian density profile in radial direction instead of the cusped exponential law, a point explosion has been investigated by generalising the method suggested by Laumbach and Probstein (1969). The shock envelope becomes increasingly elongated along the axis of rotation, until it finally breaks through into the intergalactic space before it can spread considerably in equatorial directions as in ordinary gasdynamics. A comparison has been made between our results and those obtained in ordinary gasdynamics.Explosion models of double radio sources and related objects are suggested.  相似文献   

SciMeasure Wavefront Sensor Cameras and their Application in the Palomar Adaptive Optics System     

Ray DuVarney  Charlie Bleau  Garry Motter  Richard Dekany  Mitchell Troy  Gary Brack 《Experimental Astronomy》2001,11(3):237-249

SciMeasure, in collaboration with Emory University and the Jet Propulsion Laboratory, has developed a very versatile CCD controller for use in adaptive optics, optical interferometry, and other applications requiring high-speed readout rates and/or low read noise. The overall architecture of this controller system will be discussed and its performance using both EEV CCD39 and MIT/LL CCID-19 detectors will be presented. This controller is used in the adaptive optics system, developed by JPL, for the 200′′ Hale telescope at Palomar Mountain. Early diffraction-limited science results, recently achieved by the AO system, are presented. We gratefully acknowledge the financial support of NASA through SBIR contracts NAS8–97195 and NAS8–98081.  相似文献   

Generation and amplification of HM emissions by ion-cyclotron instabilities     

S. N. Singh  R. Y. Prasad 《Astrophysics and Space Science》1973,23(2):269-273

This paper describes the analysis of the growth rate of hydromagnetic waves in the magnetosphere in ion-cyclotron mode considering multicomponent thermal plasma. Effects upon growth rate have been estimated due to (a) Thermal velocity of background plasma; (b) Presence of Heliumions in background plasma; (c) Beam Velocity; (d) Beam density.  相似文献   

Numerical performance of some finite element schemes for analysis of seepage in porous elastic media     

Ranbir S. Sandhu  Honho Liu  Kamar J. Singh 《国际地质力学数值与分析法杂志》1977,1(2):177-194

Several finite element schemes for analysis of seepage in porous elastic media, based on different spatial and temporal discretization, were implemented in computer programs. Their numerical performance is evaluated by comparison with the exact solution for Terzaghi's problem of one-dimensional consolidation.  相似文献   

Normal doppler shifted cyclotron radiation from a cold plasma     

R.P. Singh 《Planetary and Space Science》1973,21(7):1268-1269

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Propagation of plane relativistic shock waves     

G. Deb Ray 《Astrophysics and Space Science》1979,61(1):81-89

Similarity solutions for propagation of plane shock waves in a relativistic gas, where the nucleon number density varies linearly as distance from its edge at near vacuum is obtained. The shock front moves with constant speed and the solutions are applicable only to an isothermal medium or cold gas.  相似文献   

High-Resolution 0.33-0.92 μm Spectra of Iapetus, Hyperion, Phoebe, Rhea, Dione, and D-Type Asteroids: How Are They Related?     

Bonnie J. BurattiMichael D. Hicks  Kimberly A. TrykaMicah S. Sittig  Ray L. Newburn 《Icarus》2002,155(2):375-381

New high-resolution spectra in the 0.33 to 0.92 μm range of Iapetus, Hyperion, Phoebe, Dione, Rhea, and three D-type asteroids were obtained on the Palomar 200-inch telescope and the double spectrograph. The spectra of Hyperion and the low-albedo hemisphere of Iapetus can both be closely matched by a simple model that is the linear admixture of the spectrum of a medium-sized, high-albedo icy saturnian satellite and D-type material. Our results support an exogenous origin to the dark material on Iapetus; furthermore, this material may share a common origin and a similar means of transport with material on the surface of Hyperion. The recently discovered retrograde satellites of Saturn (Gladman et al., Nature412, 163-166) may be the source of this material. The leading sides of Callisto and the Uranian satellites may be subjected to a similar alteration mechanism as that of Iapetus: accretion of low-albedo dust originating from outer retrograde satellites. Phoebe does not appear to be related to either Iapetus or Hyperion. Separate spectra of the two hemispheres of Phoebe show no identifiable global compositional differences.  相似文献   

Cosmological models in generalized scalar-tensor theory with cosmological term and bulk viscosity     

Tarkeshwar Singh  G.P. Singh  A. Beesham 《Astrophysics and Space Science》2001,275(3):275-283

Exponential and power law solutions for homogeneous cosmological modelshave been discussed in a generalized scalar-tensor theory where both thecosmological term and coupling parameter are taken tobe functions of the scalar field , along with the bulk viscousstress of the cosmic fluid. Assuming simple relationships of the scalarfield with the cosmological term and the coupling parameter, all thesolutions are studied in Dicke's revised units. By use of a conformaltransformation, the solutions are also expressed in atomic units.  相似文献   

Early cosmological models in Lyra's geometry     

C.P. Singh 《Astrophysics and Space Science》2001,275(4):377-383

A spatially homogeneous and isotropic Robertson-Walker model withzero-curvature of the universe is studied within the frame-work of Lyra'smanifold. The gauge-function in Lyra's manifold is taken to betime-dependent. Exact solutions of Einstein equations are obtained for twodifferent early phases of the universe viz. Inflationary phase andradiation-dominated phase by using `gamma-law' equation of statep = ( - 1) . The -index, describing the material content,varies continuously with cosmic time so that in the course of itsevolution, the universe goes through a transition from an inflationaryphase to a radiation-dominated phase. The physical properties of themodels are also discussed.  相似文献   

A comparison of aggregation behavior in aqueous humic acids     

Christi?Young  Ray?von WandruszkaEmail author 《Geochemical transactions》2001,2(1):16

The ability of six humic acids (HAs) to form pseudomicellar structures in aqueous solution was evaluated by five techniques: size exclusion chromatography; pyrene fluorescence enhancement; the pyrene I₁/I₃ ratio; the cloud point of dilute HA solutions; and the fluorescence anisotropy of HAs. Soil HAs were found to aggregate most easily, both on microscopic and macroscopic scales. The formation of amphiphilic structures was chiefly related to HA-solvent interactions: highly solvated HAs aggregated poorly, while a lignite derived material underwent intermolecular, rather than intramolecular, rearrangements. A newly discovered algal HA was found to have minimal aggregative properties.  相似文献