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Recently classes of conic and discrete conic functions were introduced. In this paper we use the term convic instead conic. The class of convic functions properly includes the classes of convex functions, strictly quasiconvex functions and the class of quasiconvex polynomials. On the other hand, the class of convic functions is properly included in the class of quasiconvex functions. The discrete convic function is a discrete analogue of the convic function. Recently the lower bound $3^{n-1}\log (2 \rho-1)$ for the number of calls to the comparison oracle needed to find the minimum of the discrete convic function defined on integer points of some $n$-dimensional ball with radius $\rho$ was obtained. But the problem of the existence of a polynomial (in $\log\rho$ for fixed $n$) algorithm for minimizing such functions has remained open. In this paper, we answer positively the question of the existence of such an algorithm. Namely, we propose an algorithm for minimizing discrete convic functions that uses $2^{O(n^2 \log n)} \log \rho$ calls to the comparison oracle and has $2^{O(n^2 \log n)} \mbox{poly }(\log \rho)$ bit complexity.

We study the proximity of the optimal value of the m-dimensional knapsack problem to the optimal value of that problem with the additional restriction that only one type of items is allowed to include in the solution. We derive exact and asymptotic formulas for the precision of such approximation, i.e. for the infinum of the ratio of the optimal value for the objective functions of the problem with the cardinality constraint and without it. In particular, we prove that the precision tends to 0.59136.../m if n tends to infinity and m is fixed. Also, we give the class of the worst multi-dimensional knapsack problems for which the bound is attained. Previously, similar results were known only for the case m=1., Comment: 7 pages submitted to MOTOR 2020

The common feature of sheared flows of an ideal fluid and plasma in magnetic field is the Kelvin-Helmholtz instability. This instability is described by identical equations in mentioned two cases. The wave equation for the eigenmodes in the plasma obtained by the kinetic method in the long-wave limit coincides with the Rayleigh equation known for an ideal fluid. Velocity profile with a transition layer of finite width is considered. Odd modes are investigated. Localized velocity shear layer is the source of perturbations propagating beyond the transition layer. The conditions of localization of the modes are studied., 8 pages, 6 figures

Electrostatic drift instabilities driven by ion and electron temperature gradients (ITG and ETG instabilities) are considered for the ranges of perpendicular wave number values from the inverse ion thermal gyroradius up to the electron thermal gyroradius. The analysis is carried out in the framework of the local kinetic approach. Scaling laws for instability parameters are presented. These scaling laws can be used as a basis of collisionless plasma transport rates in magnetic traps with purely poloidal magnetic field topology., 5 pages, 5 figures

We consider the bremsstrahlung of electrons of fully ionized plasma. Electron energy range extends from a few hundred electron volts before the extreme relativistic energies of several MeV. The results of calculations of effective slow-down rate of a single electron and the power emission from a volume of the plasma with Maxwellian electrons. At relativistic energies, the Born approximation yields highly accurate results. Correction to the Born approximation are considered for low-energy regimes. In the high-energy regimes numerical results are close to extreme relativistic analytic results. The formulas are suggested that approximate the results of numerical calculations., 6 pages, 3 figures, ver. 2 with corrected typos