Exact solution of the equation of transfer in a finite exponential atmosphere by the method of laplace transform and linear singular operators

An approximate solution of the transfer equation for coherent scattering in stellar atmospheres with Planck's function as a nonlinear function of optical depth, viz.,

Shear-induced instability and arch filament eruption: A magnetohydrodynamic (MHD) numerical simulation

We investigate, via a two-dimensional (nonplanar) MHD simulation, a situation wherein a bipolar magnetic field embedded in a stratified solar atmosphere (i.e., arch-filament-like structure) undergoes symmetrical shear motion at the footpoints. It was found that the vertical plasma flow velocities grow exponentially leading to a new type of global MHD-instability that could be characterized as a Dynamic Shearing Instability, with a growth rate of about 8{ovV} _A a, where {ovV} _A is the average Alfvén speed and a ^–1 is the characteristic length scale. The growth rate grows almost linearly until it reaches the same order of magnitude as the Alfvén speed. Then a nonlinear MHD instability occurs beyond this point. This simulation indicates the following physical consequences: the central loops are pinched by opposing Lorentz forces, and the outer closed loops stretch upward with the vertically-rising mass flow. This instability may apply to arch filament eruptions (AFE) and coronal mass ejections (CMEs).To illustrate the nonlinear dynamical shearing instability, a numerical example is given for three different values of the plasma beta that span several orders of magnitude. The numerical results were analyzed using a linearized asymptotic approach in which an analytical approximate solution for velocity growth is presented. Finally, this theoretical model is applied to describe the arch filament eruption as well as CMEs.     

Catastrophic landslip activity in two hard rock terrains of peninsular India

This paper presents the case histories of two catastrophic landslips in hard rock terrains with varied climatic and geological environments. The first slip is associated with a power project in very close proximity (200 m) of the Porthimund Dam (11°22N, 76°3430E), in a charnockitic terrain in the Nilgiri hills (Tamil Nadu), and the second is associated with a railroad structure (19°525N, 78°1720E), in Adilabad district (Andhra Pradesh), in a basaltic terrain.The landslip in the charnockites is attributable to: (1) a high degree of saprolitization in the charnockites, with maximum intensity in the crest portion; (2) the coincidence of a major joint pattern in a NE-SW direction, with the strike of the foliation; and (3) the poor-to-fair physical rock quality in the crest and scarp portions.The slips in the basaltic terrain are due to: (1) the partially altered, highly jointed nature of the regional trap rocks with boulder sizes varying from 20 cm to 250 cm in diameter and the debris accumulating in a precarious condition on the northeast side of the rail track, with unfavorable alignment direction; and (2) the instability created in the weak rock mass by the vibrational forces of heavily loaded running trains.The weathered state of the rock masses in both the cases, showing good agreement with their physical state, accounts for the landslips. The remedial measures suggested are also discussed.     

Heat and mass transfer of a viscous heat generating fluid with Hall currents

A study of natural convection in hydrodynamic flows of a viscous heat generating fluid in the presence of Hall currents and variable suction has been carried out. The governing equations for the magnetohydrodynamic fluid flow and heat transfer are solved. The effects of Hall currentm and heat source parameter on the velocity and temperature distributions are discussed.     

Re-analysis of close binary systems

Line-forming regions around close binaries with strong winds ( /4r _* v 10^–4 g cm^–2) are large in extent compared with the stars, large enough to screen them. Their orbitally-modulated Doppler shifts can overestimate the mass function, because of a larger rotational lever arm. In particular, most of the black-hole candidates need not involve companions more massive than a neutron star.The solar-wind problem is reconsidered. An extrapolation to Wolf-Rayet stars suggests that their winds are centrifugally driven. Their mass-loss rates tend to have been overestimated.Seemingly single (massive) stars can hide a (compact) companion.     

The nonlinear solar dynamo and differential rotation: A Taylor number puzzle?

We consider dynamically consistent mean-field dynamos in a spherical shell of incompressible fluid. The generation of magnetic field and differential rotation is parameterized by the - and -effects, respectively. Extending previous investigations, we include now the cases of moderate and rapid rotation in the sense that the inverse Rossby number can approach or exceed unity: This can lead to disk-shaped -contours, which are in better accordance with recent results of helioseismology than cylindrical -contours. On the other hand, in order to obtain -dynamo cycles the Taylor number has to be so large, that eventually cylindrical -contours become unavoidable (cf. Taylor-Proudman theorem). We discuss the different possibilities in a state diagram, where the inverse Rossby number and the relative correlation length are taken as the elementary parameters for mean-field dynamos.     

Phase transition in K2Cd2(SO4)3: Order parameter and microscopic distortions

The transition from P2₁3(T ⁴) to P2₁2₁2₁(D ₂ ⁴ ) in the langbeinite K₂Cd₂(SO₄)₃ has been analyzed using group theoretical methods and previously published structural data above and below the transition. We find that because the transition is strongly first-order, the primary-order parameter has relatively large values at the transition temperature, and higher order terms which involve the order parameter, the strain, and the coupling of the two must be included in the Landau expansion for the free energy. Complex displacements occur at the transition for all atoms of the unit cell, but these displacements can be resolved into contributions which can be shown from symmetry considerations to transform as the _{2 3} irrep of P2 ₁ 3(T ⁴) as well as contributions from symmetry-preserving displacements which transform under the irrep ₁. Therefore, the transition is not a simple one and involves sulfate rotations and cadmium and potassium ion displacements.     

Investigation of the electrostatic charging of dust particles in a Paul-trap

Dust particles (glass, tungsten, and nickel) with sizes ranging from 0.25 to 3m were levitated in a Paul-trap and charged by ions or electrons. For ions the particle potential is limited at field strength of about 1×10⁹ V m^–1 by a temperature-dependent discharge mechanism. The particles interaction with 2 to 20 keV electrons always leads to positive surface potentials which can be explained in terms of a decreased absorption of electrons by small particles. Micrometer sized agglomerates were used for the investigation of the electrostatic fragmentation. Fragmentation takes place in a twofold manner: small surface flufl can be removed or the parent particle can be disrupted into smaller agglomerates.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Multifrequency behayiour of the dwarf nova SS Cygni

Several years of coordinated multifrequency observations of the dwarf nova SS Cygni have been performed in order to study the accretion behaviour of this system in particular, and in general to clarify this crucial problem for the cataclysmic variables.From IUE measurements, together with those from optical and IR ground based telescopes, we have found orbital modulations in the continuum and in the equivalent widths of the emission lines. During quiescent phases the behaviour of SS Cygni are dependent on the type of the preceding outburst (long-type or short-type).In this paper we will discuss the physical implications one can derive from these results.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.Based on the observations performed with IUE (VILSPA) satellite, and with the telescopes of the Loiano and Roque de los Muchachos Observatories.     

Interstellar medium parameters derived from low-frequency variability

Complete infraredJ andK light curves of the RS CVn system XY UMa have been obtained at the beginning of 1989. We point out some interesting morphological changes observed in these light curves.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.