Heat and mass transfer in rotating fluid with Hall current,I

Hall effects on the hydromagnetic free convection resulting from the combined effects of thermal and mass diffusion of an electrically conducting liquid past an infinite vertical porous plate in a rotating system have been analysed. The expressions for the mean velocity, mean temperature in the boundary layer and the mean skin friction, the mean rate of heat transfer on the plate are derived. The effects of magnetic parameterM, Hall parameterm, Schmidt number Sc, and Ekman numberE on the flow field, are discussed with the help of graphs and tables.     

Adiabatic radial pulsations of a composite stellar model

Small adiabatic radial oscillations of composite models have been investigated. The effect of central condensation ρ_c√ρ on the period of pulsation have also been examined. In has been shown that the second moment of mass concentration characterize the periods of pulsation more effectively than central condensation.     

Limiting wave growth for electron cyclotron waves

Quasilinear weak diffusion theory presented by Kennel and Petschek (1966) and advanced by Schulz and Davidson (1988) is further extended to put an upper limit on the growth of electron cyclotron waves. It is shown that the power gain of whistler mode electron cyclotron wave (other than plasmaspheric hiss) can not exceed 40 dB. Inside the outer radiation belt, the upper limit of temporal wave growth is 350 rad s^–1 and normalised wave growth is 0.017. The limits are independent of the kind of the electron diffusion and are applicable for on the equator/off the equator locations of wave-particle interactions.     

B-D Field Interaction with the Gravitation Field in the Robertson-Walker Universe Filled With Perfect Fluid

The study of Einstein field equations describing the Robertson-Walker universe with the Brans-Dicke field and perfect fluid has been made. It is found that the exact solutions to the B-D field interacting with perfect fluid reduce to a false vaccum with cosmological constant and without cosmological constant the solution reduce to the exact solution of the matter dust distribution in the Brans-Dicke cosmology. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pointing of HAGAR telescope mirrors

An array of seven atmospheric Cherenkov telescopes was commissioned at a high altitude site in Hanle in the Ladakh region of the Himalayas. The array called HAGAR has been designed to observe celestial γ-rays of energy >100 GeV. Each telescope is altitude-azimuth mounted and carries seven parabolic mirrors whose optic axes are co-aligned with the telescope axis. The telescopes point and track a celestial source using a PC-based drive control system. Two important issues in positioning of each HAGAR telescope are pointing accuracy of telescope axis and co-alignment of mirrors’ optic axes with the telescope axis. We have adopted a three pronged strategy to address these issues, namely use of pointing models to improve pointing accuracy of the telescopes, RA-DEC scan technique to measure the pointing offsets of the mirrors and mechanical fine-tuning of off-axis mirrors by sighting a distant stationary light source. This paper discusses our efforts in this regard as well as the current status of pointing and monitoring of HAGAR telescopes.     

Stability of an anisotropic plasma jet

The instability arising in a slab model of a jet moving in an external plasma is investigated, assuming the plasmas to be governed by the Chew, Goldberger, and Low (CGL) equations. Numerical results on the growth rates of unstable modes are obtained both for symmetric and asymmetric perturbations for equal aligned and transverse fields in wide and slender jet approximations. Special cases of an incompressible jet moving in a static CGL plasma and of a CGL plasma jet moving in an incompressible environment are also considered and conditions of instability derived.     

A magnetized homogeneous inflationary cosmological model in general relativity

In this paper we have investigated the effect of magnetic field on an orthogonal Bianchi type-I inflationary cosmological model using the concept of Higgs field. It has been investigated that the expansion and inflation in the model increases as the magnetic field increases. To get inflationary model we have assumed a mass less scalar field with flat potential V(φ)that has flat region. This revised version was published online in July 2006 with corrections to the Cover Date.     

A new class of Inhomogeneous string cosmological models in general relativity

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.     

Bulk viscous LRS Bianchi-I Universe with variable G and decaying Λ

The present study deals with spatially homogeneous and totally anisotropic locally rotationally symmetric (LRS) Bianchi type I cosmological model with variable G and Λ in presence of imperfect fluid. To get the deterministic model of Universe, we assume that the expansion (θ) in the model is proportional to shear (σ). This condition leads to A=ℓB ⁿ , where A, B are metric potential. The cosmological constant Λ is found to be decreasing function of time and it approaches a small positive value at late time which is supported by recent Supernovae Ia (SN Ia) observations. Also it is evident that the distance modulus curve of derived model matches with observations perfectly.     

Systematic analysis of low/hard state RXTE spectra of GX 339–4 to constrain the geometry of the system

One of the popular models for the low/hard state of black hole binaries is that the standard accretion disk is truncated and the hot inner region produces, via Comptonization, hard X-ray flux.This is supported by the value of the high energy photon index, which is often found to be small,～ 1.7( 2), implying that the hot medium is starved of seed photons. On the other hand, the suggestive presence of a broad relativistic Fe line during the hard state would suggest that the accretion disk is not truncated but extends all the way to the innermost stable circular orbit. In such a case, it is a puzzle why the hot medium would remain photon starved. The broad Fe line should be accompanied by a broad smeared reflection hump at ～ 30 ke V and it may be that this additional component makes the spectrum hard and the intrinsic photon index is larger, i.e. 2. This would mean that the medium is not photon deficient, reconciling the presence of a broad Fe line in the observed hard state. To test this hypothesis,we have analyzed the RXTE observations of GX 339–4 from the four outbursts during 2002–2011 and identify observations when the system was in the hard state and showed a broad Fe line. We have then attempted to fit these observations with models, which include smeared reflection, to understand whether the intrinsic photon index can indeed be large. We find that, while for some observations the inclusion of reflection does increase the photon index, there are hard state observations with a broad Fe line that have photon indices less than 2.