Moscow University Physics Bulletin最新文献

Since the formation of the Earth’s core, there has been a significant change in the thermal regime at the Earth’s surface and in the mantle. At the same time, according to palaeomagnetic observations, the dipole magnetic field has not undergone significant changes. Using a parametric model of core and mantle cooling, this paper discusses how this fact is consistent with the results of three-dimensional geodynamo modelling. It is shown that several-fold changes in the heat flux at the core–mantle boundary do not cause a transition from a dipole magnetic field to a multipole one.

This paper considers the method for designing a three-dimensional mirror collimator with rolled edges. The model is created based on its two-dimensional sections, each of which is preliminarily subjected to an optimisation procedure. Numerical simulation of the formation of the electromagnetic wave field reflected from such a three-dimensional collimator is carried out.

The paper describes the analytical calculation of helicity amplitudes for hard photon and gluon bremsstrahlung using the spinor formalism for processes such as (bar{q}qto ggamma) and (qgto qgamma). The presented amplitudes are expressed in terms of strength bivectors. The dependence on particle helicities and masses is taken into account. Numerical calculations have been performed for the annihilation process of a (bar{c}c) quark pair at energies of 24, 91, and 500 GeV in the center-of-mass frame, taking into account various combinations of the helicities of the quarks and the photon in the final state. The study is part of the ongoing development of a theoretical framework within the SANC system, aimed at analyzing polarized observables in proton–proton collisions at the NICA collider.

Within the framework of loop quantum gravity (LQG), a metric of a regular black hole is considered, in which the BH central singularity is replaced by a traversable tunnel. In addition, the investigated metric takes into account the effect of a tidal charge. Using the Newman–Janis algorithm, a rotating version of the given BH solution is obtained, for which the shadow profile is calculated. The shadow radii are compared with the constraints from the Event Horizon Telescope (EHT) observations. A slight discrepancy with the metrics of general relativity (GR) is revealed, which can be explained by the influence of quantum corrections on effects associated with rotation.

We investigate the structure of renormalization constants within the MS-like renormalization prescriptions for a version of dimensional regularization in which the dimensionful regularization parameter (Lambda) differs from the renormalization point (mu). Namely, we rewrite the all-loop equations relating coefficients at higher (varepsilon)-poles and higher powers of (lnLambda/mu) to the coefficients of the renormalization group functions in a simple unified form. It is argued that this form follows from the algebraic structure of the renormalization group.

Molecular dynamics simulation of the interaction processes of Ar({}_{n}) clusters with the Cu surface at different (E/n) ratios was performed. The mass distributions of sputtered fragments were calculated. It was shown that these distributions are described by a power law as a function of the fragment size. The dependences of the exponent on the energy and the size of the primary cluster were studied; it was shown that it correlates with the total sputtering yield similarly to the case of sputtering by atomic ions.

This study explores the potential for controlled surface topography modification of additively manufactured Ti6Al4V and AlSi10Mg alloys through 10 keV argon gas cluster ion irradiation. The effect of the ion incidence angle on the resulting surface morphology is examined. Under normal incidence, cluster ion irradiation reduces surface roughness from 6.2 to 0.89 nm for Ti6Al4V and from 16.8 to 4.27 nm for AlSi10Mg (as measured by atomic force microscopy over a (3times 3) (mu)m({}^{2}) scan area). The spatial wavelength range where significant surface smoothing occurs is identified. Oblique incidence irradiation induces uniform formation of an ordered ripple pattern, independent of crystallographic orientation and material phase.

The paper formulates the conditions and proves a theorem on the existence of a Lyapunov-stable steady-state solution to a reaction–diffusion system with slow and fast components in the two-dimensional case. A distinctive feature of the problem formulation is the singular Neumann boundary condition for the fast component. To obtain the result, the asymptotic method of differential inequalities is applied. The results obtained are of practical importance for various applications, for example, for modelling chemical reactions occurring inside rock in oil recovery problems, as well as for developing efficient numerical methods for solving boundary-value problems for elliptic equations.

Analytical expressions have been obtained describing the spatio-temporal dynamics of terahertz pulses in a medium with refractive index dispersion, representing a single-period oscillation of the electric field have been obtained. The calculation results made it possible to approximate the actual radiation from a photoconductive semiconductor antenna based on LT-GaN. Comparison with experimental spectra showed that the proposed formulae successfully describe the single-period emission of terahertz pulses generated by photoconductive antennas under the action of femtosecond laser pulses. It is shown that in the far-field diffraction zone, terahertz pulses undergo diffractive broadening, acquiring the character of a one-and-a-half-period oscillation.

Expressions for the magnetorefractive effect and the equatorial Kerr effect of collectivised ferromagnetic metal electrons in the terahertz spectral range are obtained using Maxwell’s equations and the Boltzmann kinetic equation. It is shown that the magnetorefractive effect (the change in the reflection coefficient upon reflection of unpolarized terahertz radiation from the surface of a magnetoresistive metal) is proportional to the magnetoresistance, and the Kerr effect can reach values of the same order of magnitude as for the visible spectral range. The possibility of using these effects is discussed.