Journal of V. N. Karazin Kharkiv National University. Series Physics

OPTIMIZATION OF CONDITIONS FOR DISSIPATION-FREE TRANSFER OF ELECTRIC CURRENT USING TWO-LEVEL GRANULAR HIGH- TEMPERATURE SUPERCONDUCTORS OF VARIOUS COMPOSITIONS

2025-04-14T14:31:15+00:00

In order to optimize the conditions for dissipative-free electric current transport, the influence of chemical composition, temperature and magnetic field on phase transitions in model HTSC objects – granular high-temperature superconductors YBa₂Cu₃O_7-δ and DyBa₂Cu₃O_7-δ – was studied. The work investigated the peculiarities of magnetic field penetration into granular high-temperature superconductors of the 1:2:3 type, depending on the presence or absence of magnetically active atoms in their crystal lattice.Large-scale measurements of specific electrical resistance were carried out under conditions of continuous temperature change and discrete change in the external perpendicular magnetic field strength at a constant value of the transport current density.
The influence of the nature of filling the electron shells of the central atoms (Y or REM) in the 1:2:3 HTSC crystal lattice on the occurrence of phase transitions in superconducting granules and in the Josephson medium was investigated. It is shown that the presence of a magnetoactive Dy atom in the HTSC crystal structure has a weak effect on the critical temperatures of phase transitions in superconducting granules, but leads to a significant decrease in the critical temperatures of phase transitions in the Josephson medium. Thus, it is shown that from a wide class of granular superconductors of the 1:2:3 type, only granular superconductors based on HTSC YBa₂Cu₃O_7-δ can be used as the main material for dissipative-free transfer of electric current at the boiling point of liquid nitrogen.

SPHERICALLY SYMMETRIC SOLUTIONS OF GENERAL RELATIVITY WITH RADIAL MOTION

2025-04-14T14:31:19+00:00

In this paper, the model of radial motion of dusty matter for the spherically symmetric case in General Relativity (GR) was developed. The model can be used, in particular, to describe galactic halos of dark matter. The question of the qualitative and quantitative composition of dark matter is of great importance both for understanding the current structure of the Universe and for choosing the most realistic scenario of its evolution. Since dark matter effectively manifests itself only gravitationally, its pressure can be neglected, and the equation of state, despite its physical nature, can be considered dusty. The presence of supermassive black holes in the centers of galaxies and the scale of the phenomena necessitate the use of GR equations. The spherical shapes of galactic halos require the use of spherical symmetry. The aim of this work is to model the radial motion of dark matter for a spherically symmetric GR interval, taking into account a possible central mass. Dark matter is assumed to be dusty and moving both toward and away from the center. It is proved that such a stationary case corresponds to a static interval of spacetime in the coordinates of curvatures. The system of Einstein's equations for this case is significantly simplified and solved numerically. The Lichnerowicz-Darmois conditions of crosslinking the spacetime of the proposed model with the external spherically symmetric Schwarzschild spacetime are chosen as boundary conditions. In the proposed model, there is an event horizon, approaching which the motion of particles seems to “freeze”, similar to the motion near the event horizon in the Schwarzschild field. Thus, the model also takes into account the presence of a black hole in the center, which should have been formed as a result of the considered motion of matter. The proposed model can be applied to spherical galaxy clusters and even to stellar systems in space beyond the star, assuming the existence of a halo of cold dark matter particles around them.

FEATURES OF THE ORIGIN AND DEVELOPMENT OF CRACKS IN POLYCRYSTALLINE ALUMINUM SAMPLES

2025-04-14T14:31:22+00:00

CASIMIR HONEYCOMB DRIVE: ON THE FORCE ON PERFECTLY CONDUCTING HONEYCOMB ON A PLATE

2025-04-14T14:31:23+00:00

In this paper, the two-dimensional one-body Casimir effect is analyzed on the example of square-shaped nanocells. In the classical one-dimensional two-body Casimir effect a Casimir force appears between two plates as a difference of electromagnetic pressures of zero- point quantum-vacuum oscillation on different sides of each of the plates. The plates are pushed forwards each other by external quantum-vacuum oscillation fields, which in classical configuration exceed internal quantum-vacuum oscillation fields. It is possible to try to create a difference of electromagnetic pressures of quantum-vacuum oscillation on different sides of a single plate due to the difference of the geometry of vacuum resonators on different sides of the plate. For this purpose, it is necessary to grow nanocells on one of surfaces of a smooth metallic plate. As a result, it has been found that the formula for the force per unit area is very similar to the formula of the classical Casimir effect, except for the value of the proportionality coefficient.
The force applied to perfectly conducting honeycombs on a plate as a result of the difference in specific energy density on its different sides can be interpreted as the pressure of the zero-point electromagnetic oscillations. According to the formula presented in this work, for the gold nano-honeycomb with a size of about 2 microns the force should be equal to 8.55 dynes per square meter of the panel, which is quite an acceptable value for the practical use of the expected effect for satellite orbits correction.
Although the effect is small, an experimental confirmation could serve as a critical proof for the existence of Casimir's virtual quantum photons.

SPECIAL LABORATORY PRACTICUM IN THE DISTANCE FORM OF EDUCATION

2025-04-14T14:31:28+00:00

ANDRIY PETROVYCH SHYMKOV – PROFESSOR OF KHARKIV UNIVERSITY, OUTSTANDING ORGANIZER OF PHYSICAL EDUCATION, TEACHER, POPULARIZER OF SCIENCE AND PUBLIC FIGURE

2025-04-14T14:31:28+00:00

The article summarizes information about the life path, scientific, pedagogical and public activities of the famous physicist A.P.
Shymkov, Honored Professor of Kharkiv University. While studying at Kharkiv University, he was a member of a secret student democratic-revolutionary society. He was arrested and temporarily imprisoned in the Alekseevsky ravelin of the Peter and Paul Fortress. He graduated from Kharkiv University as an external student in 1860. In 1864 he defended his master's thesis, and in 1868 -his doctoral thesis. In 1866–1867, he successfully completed a scientific internship at universities in Germany, Switzerland, and France.
For 32 years (from 1867 to 1899), he headed the Department of Physics and managed the Lab of Physics at Kharkiv University. He worked part-time at the Kharkiv Institute of Technology and the Kharkiv Veterinary Institute. He published “Course of Experimental Physics”, which was used for a long time as the main physics textbook in universities of the Russian Empire, and also compiled the textbook “Theoretical Physics”, which was the first textbook on theoretical physics published at Kharkiv University. He constantly worked on replenishing the collection of physics lab instruments. He introduced a progressive system of training physicists at the Faculty of Physics and Mathematics of Kharkiv University, which was based on a combination of theoretical, experimental, and scientific and methodological training of specialists. He was one of the founders of the Society of Research Sciences at Kharkiv University. The most capable students of A. P. Shymkov were O. K. Pohorilko and M. D. Pylchykov, who, after graduating from Kharkiv University, on the recommendation of A. P. Shymkov, were left at the Department of Physics as fellows to prepare for teaching work. He translated and published several scientific and popular science books written by prominent foreign scientists. He edited the magazines “Svit” and “Khutoryanin”. While living in Kharkiv and Poltava, he was actively involved in public, educational, and charitable activities. He was a member of the Kharkiv and President of the Poltava Agricultural Society.