Table of contents

Manmade media (MMMs) consisting of uniaxial photonic crystals with inserts of layers (films) or cylinders embedded in a periodic way into a dielectric substrate with dielectric permeability (DP) are considered. Approximate model-based and accurate electrodynamic methods for describing such MMMs, which are referred to in the case of metal (conductive) or ferrite (metaatom) inserts as a 'hyperbolic metamaterial' (HMM), are analyzed. Homogenization methods, the role of dissipation, spatial dispersion (SD), and slow plasmon-polaritons are reviewed. The feasibility of obtaining the hyperbolic dispersion law in a macroscopic description of DP of inserts using the Drude–Lorentz model is studied. In the general case with dissipation and SD, the surface of the Fresnel-equation isofrequencies is shown to differ from a rotation hyperboloid and to be bounded. The ambiguity of a description based on effective material parameters, the effect of dissipation and SD on hyperbolicity, currently observable and possible physical phenomena, and HMM applications are discussed.

Magnetic helicity is one of the integrals of nonviscous flows in magnetohydrodynamics that determines the number of linkages of magnetic field lines in a medium. It is among a number of helicities that characterize the degree of mirror asymmetry of velocity and magnetic fields. The helicities play a crucial role in driving the generation of large-scale magnetic fields in stars and spiral galaxies. Until recently, measurements of various helicities were based on astronomical observations of the Sun's active regions, but not in the Sun's deep layers where the solar dynamo is operative. Galaxies are transparent to some extent and are therefore very attractive in this sense for observing the helicity of its magnetic field. Theoretical advances and the first successful attempts at such observations are reviewed.

Increasing the strength of the static magnetic field is the main trend in modern magnetic resonance imaging (MRI) of humans. Performing MRI in ultrahigh fields (7 T or more) involves many effects both enhancing and diminishing the image quality, and some effects previously unobservable in weaker fields. We review the main impacts of using ultrahigh fields in human MRI, including new challenges and the solutions proposed. We also discuss new magnetic-resonance scan methods that were unavailable with lower field strength (below 7 T).

Increased interest in the development of negative ions sources is related to the emergence of important applications of negative-ion beams. These are, first of all, tandem accelerators, high-energy implantation and accelerator-based mass spectrometry, supercollimated beams, charge-exchange injection into cyclic accelerators and storage rings, charge-exchange extraction of beams from cyclotrons, injectors of high-energy neutrals in plasma systems, and charge-exchange beam separation. The development of sources of negative ions and their use in academic research and industry are reviewed. Physical bases and designs of surface-plasma sources of negative ions, as well as the history of their development, are presented.

We consider the interpretation of quantum mechanics on the basis of the so-called 'pilot-wave' concept from the point of view of its adequacy in the light of both already-realized and possible and gedanken experiments, including those that involve photons. It is shown that this concept, despite undoubtedly being useful, can hardly ensure compliance of quantum-theory predictions with the postulate that particle coordinates and velocities objectively exist, while splitting the wave function into empty and nonempty wave packets seems to contradict to the results of feasible experiments and their interpretations.

In this letter, we demonstrate the fallacy of the provisions and conclusions set forth in the letter to the editors of Physics–Uspekhi by V V Klimov [Phys. Usp.62 (10) 1058 (2019)]. The author discusses the review by M V Rybin and M F Limonov [Phys. Usp.62 (8) 823 (2019)] and makes a number of conclusions that have nothing to do with the content of the review and the original work on which the review is based. Also, V V Klimov's conclusions contradict well-known data in the literature.