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We report radial velocity studies of photospheric absorption lines from spectral time series of the late O-type runaway supergiant HD 188209. Radial velocity variations with a quasi-period ∼ 2 days have been detected in high-resolution echelle spectra and most probably indicate that the supergiant is pulsating. Night-to-night variations in the position and strength of the central emission reversal of the Hα profile have been observed. The fundamental parameters of the star have been derived using state-of-the-art plane-parallel and unified non-LTE model atmospheres, these last including the mass-loss rate. The binary nature of this star is not suggested either from Hipparcos photometry or from radial-velocity curves.
Spacecraft encounters with comets Giacobini-Zinner and Halley revealed a great variety of collective plasma phenomena accompanying the interaction of the solar wind with comets. In this review, we discuss the theory and in situ measurements of the Alfvén wave turbulence and the solar wind loading by cometary ions, and the structure of the cometary bow shock.
In this work we address the studies of enhancement in diamond growth on Ti-6AI-4V metal alloy by modifying the surface using the excimer laser ablation technique, prior to deposition of diamond. Ti-6Al-4V is chosen for its technological importance in aerospace industry, dental and bio-implant applications. Analysis of the structures of the film is done using X-ray diffraction, scanning electron microscopy and Raman spectroscopy. Ablation of the alloy by excimer laser pulses produces periodically hill/valley structures on the surface, thus increasing the density of diamond nucleation and film adhesion. The roughness of the alloy surface was measured to be in the 0.5μm – 1μm range with an average distance between peaks of the hill/valley structure measuring 1.5μm.
The loss-cone instability of plasma confined in a mirror-type trap is considered. Relaxation of the particle distribution in the trap with a length larger than the mean free path between ‘turbulent’ collisions is described by conventional quasilinear theory. A quasi-linear equation for the ion distribution is solved analytically for the case of a small loss-cone volume of particles in velocity space (it takes place, for instance, in the case of a trap with a larger mirror ratio).
A new mechanism is suggested that draws non-resonant thermal electrons into a higher-velocity range, where they can be effectively accelerated by waves. We argue that the acceleration of a small number of pre-existing resonant particles influences the dynamics of the bulk plasma and results in a macroscopic electric field. The solution for the spatial dependence of this electric field is obtained, and it appears to be a new type of electrostatic shock, which forms only in the presence of background turbulence. This field enriches the region of resonant particles with thermal electrons, which leads to a build-up of an excess of accelerated particles. The number of accelerated particles is calculated. This mechanism appears as a good candidate to explain electron acceleration in the foot of quasi-perpendicular shocks.