Radiation From Particles Moving in Small-Scale Magnetic Fields Created in Solid-Density Laser-Plasma Laboratory Experiments

Plasmas created by high-intensity lasers are often subject to the formation of kinetic-streaming instabilities, such as the Weibel instability, which lead to the spontaneous generation of high-amplitude, tangled magnetic fields. These fields typically exist on small spatial scales, i.e. "sub-Larmor scales". Radiation from charged particles moving through small-scale electromagnetic (EM) turbulence has spectral characteristics distinct from both synchrotron and cyclotron radiation, and it carries valuable information on the statistical properties of the EM field structure and evolution. Consequently, this radiation from laser-produced plasmas may offer insight into the underlying electromagnetic turbulence. Here we investigate the prospects for, and demonstrate the feasibility of, such direct radiative diagnostics for mildly relativistic, solid-density laser plasmas produced in lab experiments.Comment: 18 pages, 2 figures, (This version corrects numerous issues.

The shape evolution of cometary nuclei via anisotropic mass loss

Context. Breathtaking imagery recorded during the European Space Agency's Rosetta mission confirmed the bilobate nature of comet 67P/Churyumov-Gerasimenko's nucleus. Its peculiar appearance is not unique among comets. The majority of cometary cores imaged at high resolution exhibit a similar build. Various theories have been brought forward as to how cometary nuclei attain such peculiar shapes. Aims. We illustrate that anisotropic mass loss and local collapse of subsurface structures caused by non-uniform exposure of the nucleus to solar irradiation can transform initially spherical comet cores into bilobed ones. Methods. A mathematical framework to describe the changes in morphology resulting from non-uniform insolation during a nucleus' spin-orbit evolution is derived. The resulting partial differential equations that govern the change in the shape of a nucleus subject to mass loss and consequent collapse of depleted subsurface structures are solved analytically for simple insolation configurations and numerically for more realistic scenarios. Results. The here proposed mechanism is capable of explaining why a large fraction of periodic comets appear to have peanut-shaped cores and why light-curve amplitudes of comet nuclei are on average larger than those of typical main belt asteroids of the same size.Comment: 4 pages of the main text, 2 pages of appendix, 4 figure

On the application of cluster analysis for vegetation pollution assessment in the area of mining enterprise

The assessment of vegetation contamination in the influence area of mining enterprises is an important part of the research during the environment monitoring. There are different statistical methods that can be used for the analysis of data obtained in environmental monitoring. The article presents the results of cluster analysis of the chemical composition of agricultural vegetation samples collected in the area of copper-pyrite ore deposit location. During the analysis, all samples were divided into three clusters. One can suggest that this separation may be due to different mechanisms of pollutants entry into the particular sampling sites, as well as to the location of these sampling sites relatively to the enterprise industrial area. According to the results of the study, it can be concluded that cluster analysis is an effective tool for distinguishing the zones being characterized by different pollution mechanisms of grassy vegetation, when there are a small number of measurements and relatively low levels of the samples pollution. © 2019 Author(s)