Magnetoacoustic-gravity surface waves

The linearized theory for the parallel propagation of magnetoacoustic-gravity surface waves is developed for an interface of a horizontal magnetic field above a field-free medium. The media either side of the interface are taken to be isothermal. The dispersion relation is obtained for the case of a constant Alfvén speed. In the absence of gravity the interface may support one or two surface modes, determined by the relative temperatures and magnetism of the two media. The effect of gravity on the modes is examined and dispersion diagrams and eigenfunctions are given. In the usual - k _x diagnostic diagram, the domain of evanescence is shown to be divided into two distinct regions determining whether a given mode will have a decaying or growing vertical velocity component. In the absence of a magnetic field the transcendental dispersion relation may be rewritten as a polynomial. This polynomial possesses two acceptable solutions only one of which may exist in any given circumstances (depending on the ratio of the densities). If the gas density within the field exceeds that in the field-free medium, then the f-mode may propagate. The f-mode exists in a restricted band of horizontal wavenumber and only when the field-free medium is warmer than the magnetic atmosphere. An analytical form for the wave speed of the f-mode is obtained for small values of the Alfvén speed. It is shown that the f-mode is related to the fast magnetoacoustic surface wave, merging into that mode at short wavelengths.     

Far beyond the Gulf: the implications of warfare for Asian labour migration

The implications of the Gulf War are assessed for the countries in Asia that send labor migrants to the Middle East. "This paper seeks to examine the effects of...the loss of remittances (and related issues, including return migration), primarily in terms of the long-term implications of the War for the future of contract labour migration in the Asian region...."     

Propagation of solar cosmic rays: Diffusion versus focused diffusion

This paper is designed to bring to the attention the fact that the effect of focusing of solar energetic particles is always essential as compared with scattering, no matter how small the value of the mean free path may be. That is why, an ordinary (focusing-free) diffusion approach can not be applied to the solar cosmic ray transport. In the case of high-energy solar particles, the focused diffusion is demonstrated to lead to a power law decay of energetic particle intensity much like an ordinary diffusion. However, the power law index of the decay is renormalized by the focusing.     

Rosat wide field camera data and the temperature of the interstellar medium

The shadowing effects of the molecular clouds in the nearby interstellar medium on the soft x-ray background has been investigated, using ROSAT WFC data in conjunction with previous rocket B and C band surveys. Shadowing over a 5° extent occurs only for a few percent of the sky, but the mixed model of the ISM is supported.Detailed modelling of the Draco shadowing region shows little evidence for a multi-temperature, hot ISM component.     

Radiation-hydrodynamic waves and global solar oscillations

We investigate nonadiabatic hydrodynamic waves in a nongrey, radiating, thermally conducting, homogeneous atmosphere in LTE with a finite mean free path of photons. Avoiding the Eddington approximation the remaining simplifications in the basic equations are discussed, the generalized dispersion relation is analysed, and some wave properties in a grey model are studied. The properties of waves in a stratified atmosphere are analysed as well. In connection with the predicted properties of the nonadiabatic waves we discuss observations ofp-modes by measuring brightness fluctuations.     

An integrable case of a rotational motion analogous to that of Lagrange and Poisson for a gyrostat in a Newtonian force field

The scope of the present paper is to provide analytic solutions to the problem of the attitude evolution of a symmetric gyrostat about a fixed point in a central Newtonian force field when the potential function isV ⁽²⁾.We assume that the center of mass and the gyrostatic moment are on the axis of symmetry and that the initial conditions are the following: (t ₀)=₀, (t ₀)=₀, (t ₀)=(t ₀)=₀, ₁(t ₀)=0, ₂(t ₀)=0 and ₃(t ₀)= ₃ ⁰ .The problem is integrated when the third component of the total angular momentum is different from zero (B ₁ 0). There now appear equilibrium solutions that did not exist in the caseB ₁=0, which can be determined in function of the value ofl ₃ ^r (the third component of the gyrostatic momentum).The possible types of solutions (elliptic, trigonometric, stationary) depend upon the nature of the roots of the functiong(u). The solutions for Euler angles are given in terms of functions of the timet. If we cancel the third component of the gyrostatic momentum (l ₃ ^r =0), the obtained solutions are valid for rigid bodies.     

H2 in interstellar and extragalactic ices: infrared characteristics, ultraviolet production, and implications

H2 is the most abundant molecule in the universe. We demonstrate that this molecule may be an important component of interstellar and possibly intergalactic ices, both because it can be formed in situ, within the ices, and because gas phase H2 can freeze out onto dust grains in some astrophysical environments. The condensation-sublimation and infrared spectral properties of ices containing H2 are presented. We show that solid H2 in H20-rich ices can be detected by an infrared absorption band at 4137 cm-1 (2.417 micrometers). The surface binding energy of H2 to H2O ice was measured to the delta Hs/k = 555 +/- 35 K. Surface binding energies can be used to calculate the residence times of H2 on grain surfaces as a function of temperature. Some of the implications of these results are considered.     

Origin of the hydrocarbon component of carbonaceous chondrites: the star-meteorite connection

We report the results of an experiment that produced a residue which closely matches the hydrocarbon component of the Murchison carbonaceous chondrite. This experiment suggests that the parent material of the meteoritic component originated as polycyclic aromatic hydrocarbon species in carbon stars during their later stages of evolution. The experiments also indicate that the pathway from those formation sites to eventual incorporation into the meteorite parent body involved hydrogenation in a plasma in the solar nebula or in H II regions prior to the solar nebula. This model is consistent with what is known about the meteoritic hydrocarbon component including deuterium abundance, the observation of cosmic infrared emission bands best attributed to polycyclic aromatic hydrocarbon molecules, and the inherent stability of these molecules that allows their formation in stars and subsequent survival in the interstellar medium.     

Room temperature solid-state detectors for Gamma ray burst spectroscopy

We have evaluated several solid state detectors which offer excellent energy resolution at room temperature for soft X-rays. For soft X-rays (< 1 keV to 20 keV), silicon P-intrinsic-N (PIN) and avalanche-mode photodiodes (APD's) have been studied. Using commercially available charge sensitive pre-amplifiers, these photodiodes provide 1 keV resolution without cooling. Their detection efficiencies are limited to about 20 keV and 15 keV, respectively. To overcome this constraint, we have studied thick (1.5 mm) PIN detectors made by Micron Semiconductor Ltd., U.K., as well as compound semiconducting materials with high Z constituents such as CZT and PbI₂. PbI₂ allows high detection efficiencies of photons up to 100 keV with detectors 100–300 microns thick. These new detectors offer the capability to study the low-energy spectral evolution of Gamma ray bursts (GRBs). A matrix of these detectors could be used as an image plane detector with moderate spatial resolution for imaging.     

New kinematic distances of NGC 7009 and BD+30°3639 from UV and radio data

Measurements of the equivalent width of the interstellar Lyman line from IUE spectra in the direction of the planetary nebulae NGC 7009 and BD+30°3639 are used to infer the H column density in these directions. Hydrogen 21 cm profiles are also used in connection with the ultraviolet data so that the expected rotation velocities and distances can be determined. The results are compared with recently published distances, in an attempt to distinguish between the short and long PN distance scales as applied to these objects.