Magic Squares of Cubes Modulo a Prime Number

This work is dedicated to the properties of the 3 × 3 magic squares of cubes modulo a prime number. Its central concept is the number of distinct entries of these squares and the properties associated with this number. We call this number the degree of a magic square. The necessary conditions for the magic square of cubes with degrees 3, 5, 7, and 9 are examined. It was established that there are infinitely many primes for which magic squares of cubes with degrees 3, 5, 7, and 9 exist. I apply n-tuples of consecutive cubic residues to prove that there are infinitely many Magic Squares of Cubes with degree 9. Furthermore I use Brauer’s theorem, that guarantees the existence of a sequence of consecutive integers of any length, to construct Magic Squares of Cubes whose entries are all cubic residues. Such analytic tools as Modular Arithmetic, Legendre symbol, Fermat’s Little Theorem, notions of quadratic and cubic residues were employed in the process of research

Multi-frequency study of relativistic jets in active galactic nuclei

The thesis at hand presents the results of multi-frequency Very Long Baseline Interferometry (VLBI) observations of jets associated with active galactic nuclei. The results are discussed in the context of broad-band jet emission models and used to constrain physical properties of the parsec-scale core -- inner part of the jet which is likely related to the observed high-energy emission. The analysis of the frequency-dependent core position shift supports interpretation of the parsec-core as the integral part of the jet; the observed core position is determined by opacity. Synchrotron self-absorption is found to be the dominating opacity mechanism in the observed sources. A comparison between radio sources possessing jets aligned closely to the line of sight with those aligned at large angles to it supports the idea that the bright extragalactic gamma-ray sources are associated with jets affected by relativistic beaming

Geostrophic tripolar vortices in a two-layer fluid : linear stability and nonlinear evolution of equilibria

We investigate equilibrium solutions for tripolar vortices in a two-layer quasi-geostrophic flow. Two of the vortices are like-signed and lie in one layer. An opposite-signed vortex lies in the other layer. The families of equilibria can be spanned by the distance (called separation) between the two like-signed vortices. Two equilibrium configurations are possible when the opposite-signed vortex lies between the two other vortices. In the first configuration (called ordinary roundabout), the opposite signed vortex is equidistant to the two other vortices. In the second configuration (eccentric roundabouts), the distances are unequal. We determine the equilibria numerically and describe their characteristics for various internal deformation radii. The two branches of equilibria can co-exist and intersect for small deformation radii. Then, the eccentric roundabouts are stable while unstable ordinary roundabouts can be found. Indeed, ordinary roundabouts exist at smaller separations than eccentric roundabouts do, thus inducing stronger vortex interactions. However, for larger deformation radii, eccentric roundabouts can also be unstable. Then, the two branches of equilibria do not cross. The branch of eccentric roundabouts only exists for large separations. Near the end of the branch of eccentric roundabouts (at the smallest separation), one of the like-signed vortices exhibits a sharp inner corner where instabilities can be triggered. Finally, we investigate the nonlinear evolution of a few selected cases of tripoles.PostprintPeer reviewe

Problems of socio-geographical assessment of the tourist attractiveness of the region

The article deals with the problems of the study of tourist attractiveness, identifies the main differences of the conceptual apparatus used in tourist studies of the regions, systematizes the criteria for evaluating the tourist attractiveness of the region, analyzes the existing methods and determines the factors of tourist attractiveness, determines the main stages of determining the rating of the tourist rating

Modeling the evolution of intrathermocline lenses in the Atlantic Ocean

The existence of a tongue of Mediterranean Water (MW) at the depths of 500–1500 m is a characteristic feature of the hydrological regime in the northeastern part of the Atlantic Ocean. Anticyclonic eddies filled with MW (meddies or lenses) are observed in this region. They are identified via their high temperature and salinity anomalies, which compensate in density, yielding nearly homogeneous meddy cores. The analysis of historical observations has showed that approximately 100 lenses can exist simultaneously in this part of the ocean. High concentration of large water volumes (\u3e4000 km3 each) can be found both in the region of their origin near the Iberian Peninsula and near the Azores Frontal Zone. The latter is precisely the region in which merging of eddies can occur to form larger lenses. The existence of long-living lenses at large distances from the region of their formation is an indirect indication of the fact that merging of lenses occurs (MESOPOLYGON lens, SM1 lens in the SEMAPHORE experiment, and a lens in the Sargasso Sea). Here, we analyze the results of model experiments on interaction between two anticyclonic eddies applying the contour dynamics method (CDM) to a three-layer ocean. In these experiments, the vertical distribution of layerwise density in the layers, the horizontal size of the eddies (assumed to be cylindrical structures), and their depth location correspond to the observed conditions in the Atlantic Ocean. We show that the evolution of intrathermocline eddies and the evolution of barotropic eddies differ significantly. We found the behavior of interacting eddies in the middle layer depends on the Froude number. We determined the critical distances between the lenses when their merger begins and the destruction\u27 criterion for the elliptical intrathermocline eddies

Vortex merger in surface quasi-geostrophy

The merger of two identical surface temperature vortices is studied in the surface quasi- geostrophic model. The motivation for this study is the observation of the merger of sub- mesoscale vortices in the ocean. Firstly, the interaction between two point vortices, in the absence or in the presence of an external deformation field, is investigated. The rotation rate of the vortices, their stationary positions and the stability of these positions are determined. Then, a numerical model provides the steady states of two finite-area, constant-temperature, vortices. Such states are less deformed than their counterparts in two-dimensional incom- pressible flows. Finally, numerical simulations of the nonlinear surface quasi-geostrophic equations are used to investigate the finite-time evolution of initially identical and sym- metric, constant temperature vortices. The critical merger distance is obtained and the deformation of the vortices before or after merger is determined. The addition of external deformation is shown to favor or to oppose merger depending on the orientation of the vor- tex pair with respect to the strain axes. An explanation for this observation is proposed. Conclusions are drawn towards an application of this study to oceanic vortices.PostprintPeer reviewe

N-symmetric interaction of N hetons. Part I. Analysis of the case N = 2

Funding: This work was carried out as part of a joint project funded by the Russian Foundation for Basic Research (grant 20-55-10001) and UK Royal Society (grant IEC\R2\192170). MAS was also supported by the program 0147-2019-0001 (State Registration No.AAAA-A18-118022090056-0) and by the Ministry of Science and Education of the Russian Federation (Project No. N14.W03.31.0006), KVK was supp orted by RFBR project No.20-05-00083.We examine the motion of N symmetric hetons (oppositely signed vertical dipoles) in a two-layer quasi-geostrophic model. We consider the special case of N-fold symmetry in which the original system of 4N ordinary differential equations reduces to just two equations for the so-called “equivalent” heton. We perform a qualitative analysis to classify the possible types of vortex motions for the case N = 2. We identify the regions of the parameter space corresponding to unbounded motion and to different types of bounded, or localized, motions. We focus on the properties of localized, in particular periodic, motion. We identify classes of absolute and relative “choreographies” first introduced by Simó [“New families of solutions to the N-body problems,” in Proceedings of the European 3rd Congress of Mathematics, Progress in Mathematics Vol. 201, edited by C. Casacuberta, R. M. Miró-Roig, J. Verdera, and S. Xambó-Descamps (Birkhäuser, Basel, Barcelona, 2000), pp. 101–115]. We also study the forms of vortex trajectories occurring for unbounded motion, which are of practical interest due to the associated transport of heat and mass over large distancesPostprintPeer reviewe