On the gravitational instability of a medium in non-uniform rotation and magnetic field

The effect of a non-uniform magnetic field on the gravitational instability for a non-uniformly rotating, infinitely extending axisymmetric cylinder in a homogeneous medium has been studied. The Bel and Schatzman criterion of gravitational instability for a non-uniformly rotating medium is modified under the effect of a non-uniform/uniform magnetic field acting along the tangential and axial directions. As a consequence the stabilizing and destabilizing effect of the non-uniform magnetic field is obtained, a new criterion for the magneto-gravitational instability is deduced in terms of Alfven’s wave velocity; and it is also found that the Jeans criterion determines the gravitational instability in the absence of rotation and when the non-uniform/uniform magnetic field acts along the axis of the cylinder.     

Characteristic actionsħ (s) in the structure of the universe and the problem of the origin of galaxies

From the characteristic actions ^(s), we can derive various relations between the basic characteristic quantities of objects and the fundamental constants in known physical laws. The main physical processes which lead to the formation of objects should be included in some such reletions through the fundamental constants. The problem of the origin of galaxies has been considered on the basis of the theory of actions ^(s). It has been shown that in addition to gravitational effect, the dissipation process of the adiabatic density perturbations arising from the Thomson scattering in the early universe is a crucial process in forming galaxies; and if the Hubble constant has a valueH ₀ 50 km s^–1 Mpc^–1, the protogalaxies might be formed just before recombination.     

Plasma wave properties of the Schwarzschild magnetosphere in a Veselago medium

We re-formulate the 3+1 GRMHD equations for the Schwarzschild black hole in a Veselago medium. Linear perturbation in rotating (non-magnetized and magnetized) plasma is introduced and their Fourier analysis is considered. We discuss wave properties with the help of wave vector, refractive index and change in refractive index in the form of graphs. It is concluded that some waves move away from the event horizon in this unusual medium. We conclude that for the rotating non-magnetized plasma, our results confirm the presence of Veselago medium while the rotating magnetized plasma does not provide any evidence for this medium.     

Nonlinear stability in the restricted three-body problem with oblate and variable mass

This study investigates the nonlinear stability of the triangular equilibrium points when the bigger primary is an oblate spheroid and the infinitesimal body varies (decreases) it’s mass in accordance with Jeans’ law. It is found that these points are stable for all mass ratios in the range of linear stability except for three mass ratios depending upon oblateness coefficient A and β, a constant due to the variation in mass governed by Jeans’ law.     

Out-of-plane equilibrium points and their stability in the Robe’s problem with oblateness and triaxiality

This paper examines the existence and stability of the out-of-plane equilibrium points of a third body of infinitesimal mass when the equations of motion are written in the three dimensional form under the set up of the Robe’s circular restricted three-body problem, in which the hydrostatic equilibrium figure of the first primary is an oblate spheroid and the second one is a triaxial rigid body under the full buoyancy force of the fluid. The existence of the out of orbital plane equilibrium points lying on the xz-plane is noticed. These points are however unstable in the linear sense.     

On the covering of a Hill’s region by solutions in the restricted three-body problem

We consider two classical celestial-mechanical systems: the planar restricted circular three-body problem and its simplification, the Hill’s problem. Numerical and analytical analyses of the covering of a Hill’s region by solutions starting with zero velocity at its boundary are presented. We show that, in all considered cases, there always exists an area inside a Hill’s region that is uncovered by the solutions.     

Evolution effects in the distribution of distant galaxies?

The amplitudes of the two-point correlation function for galaxies are compared for galaxy catalogues extending to different depths. Strong evolution effects in the pattern of galaxy distribution seem to be present suggesting a secular increase of the clustering amplitude. Other explanations would involve large errors in the identification of faint objects as galaxies or a considerable contamination of the counts by very young highly redshifted galaxies as recently proposed by TINSLEY .     

On ‘out of plane’ equilibrium points in the elliptic restricted three-body problem with radiating and oblate primaries

We locate and examine the stability of the ‘out of plane’ equilibrium points, L _6,7 of an infinitesimal body in the field of stellar-oblate binary systems moving in elliptic orbits around their common center of mass. Their positions and stability depend on the oblateness as well as radiation coefficients of the primaries and the eccentricity of their orbits. A numerical application of this problem for the systems: Gamma Leporis and Altair are given.     

Solving the mysteries of the diffuse interstellar medium with high-resolution UV spectroscopy

Understanding the complex structure, dynamics, and ionization of gas in the nearby interstellar medium is required before one can realistically model interstellar gas in other galaxies. High-resolution ultraviolet spectra provide the essential data for such studies because the resonance lines of most important atoms, ions, and molecules are located in the ultraviolet, and high spectral resolution is needed to resolve line profiles and determine the velocity structure along a line of sight. I list ten important physical questions concerning interstellar gas that require a more sensitive spectrometer than STIS and the desired spectral resolution to answer these questions.     

Exact solution of the equation for the problem of diffuse reflection and transmission with a scattering function ω0(1 +x cos⊙) by the method of laplace transform and theory of linear singular integral equation

Neutrinos couple through a weak neutral current to the density of matter, in particular to the neutron density. Density fluctuations, or phonons, in the neutron fluid may be emitted or absorbed by neutrinos passing through the matter. At high densities, temperatures and neutrino energies the neutrino mean free paths for phonon emission and absorption can be 10⁶ cm. Significant changes in the neutrino momentum and energy accompany these processes. We present a model calculation for neutrino scattering by phonons, and representative numerical results for the neutrino mean free path and mean energy and momentum changes fork _B T andE _v both ranging from 1 to 27 MeV.Research supported by the National Research Council of Canada.     

Is the ‘superhot’ hard x-ray component in solar flares consistent with a thermal source?

It has been shown by Brown and Emslie (1988) that any optically thin thermal bremsstrahlung source must emit an energy spectrumL () (keV s^–1 keV^–1) which has the property that higher derivatives alternate in sign, i.e., (–) ^j L(^j)() > 0 for allj. In this short note, we apply this test to the superhot component discussed by Linet al. (1981) in order to determine whether a strictly thermal interpretation of this component is valid. We find that all statistically significant higher derivatives do indeed have the correct sign; this strengthens the identification of this component as due to a thermal source.Presidential Young Investigator.     

The mean transmission of the neutral intergalactic medium in the LYα -line from a sample of high-resolution quasar spectra

We present our measurements of the mean transmission \(\overline F \left( z \right)\) of the neutral intergalactic medium in the Lyα line. For this purpose we used the sample of 33 high-resolution (R = 5300…45 000) spectra selected from the public available archive of the European Southern Observatory with the help of the Virtual Observatory tools. For continuum determination in each spectra the points with maximum flux in Lyα-forest region were selected and fitted by spline. The obtained values of the mean transmission \(\overline F \left( z \right)\) was fitted by power-law τ_eff = α(1 + z)^β, where α = (4.4 _?0.2 ^+4.4 )× 10^–3, β = 3.278 _?0.054 ^+0.083 for averaging of the F(z) over the redshift bins Δz = 0.1 and α = (10.6 _?1.0 ^+1.1 )× 10^–3, β = 2.685 _?0.071 ^+0.081 for averaging over each quasar. The results were compared with those ones from previous studies of high- and low-resolution quasar spectra.     

Evolution Toward the Observational Features of a Stripped Envelope Type Ⅱb Supernova in a Binary System

Type Ⅱb supernovae(SNe Ⅱb) that have a thin layer of hydrogen left in their outer envelope have been believed to belong to core collapse supernovae.Mass transfer via Roche lobe overflow can significantly change the nucleosynthesis and surface chemical elements of the progenitors of SNe Ⅱb.We aim to explore what conditions a close binary can meet with the observational features of SNe Ⅱb.We find that an observed low mass SN Ⅱb cannot be produced by a low mass isolated star with M <20,M_⊙ due t...     

Structure and Evolution of the Transition Region Network Observed in he ii λ304

The length scale and life time of the transition region network cells were studied using Heii 304 filtergrams. The temporal structure function was calculated from spatially aligned Heii 304 images. The estimated life time of the network cell was about 27 hr. We compared this life time with the life time of photospheric magnetic network and of the extrapolated magnetic network. The spatial structure function was calculated from the Heii 304 filtergrams. The calculated spatial structure function saturates at 25000 km. The transition region network elements are bigger in size than the photospheric magnetic network element. The magnetic network element equals the size of the Heii 304 network element when the photospheric magnetic field is extrapolated to a height of 3000 km above the photosphere where the magnetic fluxes are deployed. The derived value of the diffusion speed of the network elements was 0.098 km s^–1.     

A Monte Carlo Study of the Evolution of the Scale Height of Normal Pulsars in the Galaxy

Based on the undisturbed, finite thickness disk gravitational potential, we carried out 3-D Monte Carlo simulations of normal pulsars. We find that their scale height evolves in a similar way for different velocity dispersions (σv): it first increases linearly with time, reaches a peak, then gradually decreases, and finally approaches a stable asymptotic value. The initial velocity dispersion has a very large influence on the scale height. The time evolution of the scale height is studied. When the magnetic decay age is used as the time variable, the observed scale height has a similar trend as the simulated results in the linear stage, from which we derive velocity dispersions in the range 70- 178km s-1, which are near the statistical result of 90 - 270km s-1 for 92 pulsars with known transverse velocities. If the characteristic age is used as the time variable, then the observed and theoretical curves roughly agree for t > 108 yr only if σv < 25km s-1.     

Asymmetric periodic solutions of the averaged Hill problem with allowance for a planet’s oblateness

We consider asymmetric periodic solutions of the double-averaged Hill problem by taking into account oblateness of the central planet. They are generated by steady-state solutions, which are stable in the linear approximation and correspond to satellite orbits orthogonal to the line of intersection of the planet’s equatorial plane with the orbital plane of a disturbing point. For two model systems [(Sun+Moon)-Earth-satellite] and [Sun-Uranus-satellite], these periodic solutions are numerically continued from a small vicinity of the equilibrium position. The results are illustrated by projecting the solutions onto the (pericenter argument-eccentricity) and (longitude-inclination) planes.     

On the Evolution of the Lower Energy Cutoff of Nonthermal Electrons in Solar Flares

1 INTRODUCTION Gan, Li and Chang (2001a) proposed a quantitative method to obtain the lower energycutoff (Er) of power-law electrons from the observed broken-down double power-law hard Xray spectrum. Most recently Can et al. (2002) improved the method and let it be moreself-consistent. They applied their improved method to the 54 hard X-ray events observed withBATSE/CGRO and acquired more general results in comparison with those obtained by Canet al. (2001b). Despite the data is rel…     

Evidence of Evolution in the Dense Cores in Massive Star Forming Regions

The excitation of H2O masers usually needs very high density gas, hence it can serve as a marker of dense gas in HII region. We selected a sample of H2O maser sources from Plume et al. (four with, and four without detected CS(J = 7-6) emission), and observed them in 13CO(J=1-0) and C18O (J=1-0). C18O (J=1-0) emission was detected only in three of the sources with detected CS(J=7-6) emission. An analysis combined with some data in the literature suggests that these dense cores may be located at different evolutionary stages. Multi-line observation study may provide us clues on the evolution of massive star forming regions and the massive stars themselves.     

Equilibrium points of the restricted three-body problem with equal prolate and radiating primaries,and their stability

Paper presents a complete discussion of the existence, location and stability of the equilibrium points of the coplanar restricted three-body problem with equal prolate and radiating primaries. Depending on the values of the radiation and negative oblateness parameters, two or four additional collinear equilibrium points exist, in addition to the three Eulerian points of the classical case, making up a total of up to seven collinear points. Four of these additional points, as well as the classical central equilibrium point located at the origin, are stable for certain ranges of the parameters. Also, depending on the values of the parameters, up to six additional non-collinear equilibrium points exist, in addition to the triangular Lagrangian points of the classical case. Two of these additional points are located symmetrically above and below the origin and are stable, while the other four are located symmetrically in the four quadrants and are unstable.