arXiv subjects

Alexander Kutsenko

Publications and source records attributed to Alexander Kutsenko.

4 recordsLinked to original sources

arXiv2024

The Spectro-Polarimeter (SP) of the Andrei B. Severny Solar Tower Telescope (STT) at the Crimean Astrophysical Observatory: Optical Design and Implementation

The Spectro-Polarimeter (SP) is a new instrument installed at the upgraded Andrei B. Severny Solar Tower Telescope (STT) at the Crimean Astrophysical Observatory. The instrument is a traditional echelle slit dual-beam spectropolarimeter with temporal modulation of the polarization. STT-SP provides simultaneous spectropolarimetric observations of the Sun within three 15 Angstrom wide spectral ranges around photospheric Fe I 5250, Fe I 5324, and chromospheric Mg I b2 5172 spectral lines. The spectral resolution of the instrument reaches 70,000 with the seeing-constrained slit width of 1 arcsec. The field-of-view of STT-SP is 200 arcsec allowing one to map a moderate size active region within a single raster scan. The instrument will provide new opportunities in the analysis of magnetic fields and thermodynamics of the lower atmosphere of the Sun. In this paper we describe the optical design of STT-SP and present the preliminary results acquired during the commissioning of the instrument.

astro-ph.SR↗

arXiv2024

Estimation of the lifetime of slow-decaying unipolar active regions in the framework of the turbulent erosion model

We explore properties and behavior of slow-decaying unipolar sunspot groups in the framework of the turbulent erosion model suggested by Petrovay and Moreno-Insertis (1997). The basic concept of the model is the suppression of a turbulent diffusivity inside a magnetic flux tube by strong magnetic fields. As a result, the outer turbulent plasma detaches magnetic features primarily from the external border of a magnetic flux tube. The radius of the tube exhibits inward progression at a constant rate. The model predicts older sunspots to decay slower and it seems to be very promising to explain the slow decay of long-living unipolar sunspot groups. By analyzing the magnetic structure associated with a sunspot, we did reveal a gradual decrease of the magnetic structure radius at a constant rate implying the validity of the model. However, in some cases the derived velocity of the radius decrease was too low: our calculations provided implausibly high estimations for the lifetime and maximal area of such sunspots. We discuss possible additional mechanisms affecting the decay rate of such peculiar sunspots.

astro-ph.SR↗

arXiv2020

On the Sixth International Olympiad in Cryptography NSUCRYPTO

NSUCRYPTO is the unique cryptographic Olympiad containing scientific mathematical problems for professionals, school and university students from any country. Its aim is to involve young researchers in solving curious and tough scientific problems of modern cryptography. From the very beginning, the concept of the Olympiad was not to focus on solving olympic tasks but on including unsolved research problems at the intersection of mathematics and cryptography. The Olympiad history starts in 2014. In 2019, it was held for the sixth time. In this paper, problems and their solutions of the Sixth International Olympiad in cryptography NSUCRYPTO'2019 are presented. We consider problems related to attacks on ciphers and hash functions, protocols, Boolean functions, Dickson polynomials, prime numbers, rotor machines, etc. We discuss several open problems on mathematical countermeasures to side-channel attacks, APN involutions, S-boxes, etc. The problem of finding a collision for the hash function Curl27 was partially solved during the Olympiad.

cs.CR↗

arXiv2019

Improvements of the Longitudinal Magnetic Field Measurement from the Solar Magnetic Field Telescope at Huairou Solar Observing Station

The weak-field approximation implying linear relationship between Stokes $V/I$ and longitudinal magnetic field, $B_{\Vert}$, often suffers from saturation observed in strong magnetic field regions such as sunspot umbra. In this work, we intend to improve the magnetic field observations carried out by the \textit{Solar Magnetic Field Telescope} (SMFT) at Huairou Solar Observing Station, China. We propose using non-linear relationship between Stokes $V/I$ and $B_{\Vert}$ to derive the magnetic field. To determine the form of the relationship, we perform a cross-calibration of the observed SMFT data and magnetograms provided by the \textit{Helioseismic and Magnetic Imager} on board the \textit{Solar Dynamics Observatory}. The algorithm of the magnetic field derivation is described in details. We show that using non-linear relationship between Stokes $V/I$ and $B_{\Vert}$ allows us to eliminate magnetic field saturation inside sunspot umbra. The proposed technique enables one to enhance the reliability of the SMFT magnetic field data obtained even long before the space-based instrumentation era, since 1987.

astro-ph.SR↗