Based on model calculations, we show that ion-acoustic oscillations can be excited by heat fluxes in a plasma. We discuss the probable effect of ion-acoustic oscillations on the formation of temperature gradients at critical heat fluxes. The local critical heat flux in the transition region of the solar atmosphere is close to the well-known experimental heat flux from the corona into the chromosphere.
We present a catalogue of galaxy clusters detected in the Planck all-sky Compton parameter maps and identified using data from the WISE and SDSS surveys. The catalogue comprises about 3000 clusters in the SDSS fields. We expect the completeness of this catalogue to be high for clusters with masses larger than M500 ≈ 3 × 10 14 M , located at redshifts z < 0.7. At redshifts above z ≈ 0.4, the catalogue contains approximately an order of magnitude more clusters than the 2nd Planck Catalogue of Sunyaev-Zeldovich sources in the same fields of the sky. This catalogue can be used for identification of massive galaxy clusters in future large cluster surveys, such as the SRG/eROSITA all-sky X-ray survey.
At present, the capture of a suitable asteroid into an Earth satellite orbit is proposed as one
of the methods for investigating asteroids within the framework of manned missions. Once the asteroid
has been transferred to such an orbit, an expedition with the participation of astronauts is planned to the
asteroid surface, where research is carried out and asteroid rock samples are selected and subsequently
delivered to the Earth. It is in this way that the American Keck project is described at the current planning
and preliminary design stage. In this paper, we solve the capture problem by a method alternative to that
planned in the Keck project
Amethod for preventing the collisions of hazardous celestial objects with the Earth by diverting
them from the trajectory of their encounter with the Earth is investigated. For this purpose, we propose to
use small near-Earth asteroids that are transferred to the trajectories of a gravity-assist maneuver near
the Earth by imparting a comparatively small velocity impulse to them. As a result of such a maneuver, a
small asteroid is thrown into the hazardous object’s interception orbit. The asteroids suitable for achieving
this goal are chosen by solving Lambert’s problem. The same concept is investigated for the problem of
transferring asteroids to orbits resonant with the Earth’s orbit so as to open up the possibility of regular
missions to such asteroids with the goal of studying them and using their resources. The choice is made by
minimizing the mentioned velocity impulse, whose admissible value is assumed to be within the limits that
do not exceed 20 m s−1 .
The connection of between the formation and properties of areas characterized by the sharp gradient of electron temperature, with electrostatic turbulence, providing high a high effective electrons collision frequency and a low thermal conductivity of medium, is discussed. Simple dependences for the thermal conductivity, effective collision frequency and noise electric fields are obtained. For a tube with a relatively weak magnetic field, which passes from the chromosphere into the crown, on the basis of the known experimental models of solar atmosphere, an altitude dependence of the thermal conductivity and value of noise electric fields is estimated.