Uspehi fizičeskih nauk

Atomic processes of ionization, recombination, and electron capture in collisions of positive ions with atoms, ions, electrons, and molecules are considered. The impact of these processes on the interaction of ion beams with media in a wide range of energies—from low to super-relativistic—is discussed, focusing primarily on energies $E \sim 10$ keV–100 GeV per nucleon. The main features of the effective cross sections of the processes are described as a function of the collision energy, atomic structure, and density effects in gases, solids, and plasmas. The role of dielectronic recombination in the interaction of beams of heavy multi-electron ions with a plasma is considered in detail. The progress in experimental and theoretical studies in accelerator physics and the physics of collisions of heavy ions with atomic systems, achieved over the last five to ten years is reviewed.

The article deals with the influence of stochastic dynamics of the brain's neural ensembles on the perception and processing of sensory information, as well as on decision-making based on it. The review considers sources of noise in the nervous system during sensory information processing, as well as some nervous system strategies of compensating for or taking into account stochastic processes. Experiments and mathemat„ical models are discussed in which stochastic brain dynamics begins to play a significant role in the perception of sensory information. Particular attention is paid to brain noise research paradigms such as the perception of weak stimuli close to the sensitivity threshold and bistable ambiguous stimuli. Methods for assessing brain noise using both psychophysical experiments and direct analysis of neuroimaging data are described. Finally, some issues in applying the concept of stochastic brain dynamics to problems in the biomedical diagnosis of various neurological diseases are considered.

Microwave exposure is one possible promising heating method that can be used to create porous carbon materials. Activated carbon materials obtained by microwave heating can serve as an adsorbent or electrode material in energy storage devices such as supercapacitors. The paper investigates the processes of carbonization and activation of cotton lint using microwaves. A comparison is made with the traditional thermal method of heating, as well as with the mass-produced highly porous carbon fiber Busofit T1.

We revisit the modal analysis of small perturbations in Keplerian ideal gas flows with a constant vertical magnetic field leading to magnetorotational instability (MRI) using the nonlocal approach. In the general case, MRI modes are described by a Schr$\ddot o$dinger-like differential equation with some effective potential, including ‘repulsive’ ($1/r^{2}$) and ‘attractive’ ($-1/r^{3}$) terms, and are quantized. In shallow potentials, there are no stationary ‘energy levels.’ In thin Keplerian accretion discs, the perturbation wavelengths $\lambda =2\pi /k_{z}$ are smaller than the disc semi-thickness $h$ only in ‘deep’ potential wells. We find that there is a critical magnetic field for the MRI to develop. The instability arises for magnetic fields below this critical value. In thin accretion discs, at low background Alfv$\acute e$n velocity $c_A\ll (c_A)_cr$, the MRI instability increment $\omega $ is suppressed compared to the value obtained in the local perturbation analysis, $\omega \approx -\sqrt {3}ic_Ak_{z}$. We also investigate for the first time the case of a radially variable background magnetic field.