Electron Pre-Acceleration at Nonrelativistic High-Mach-Number Perpendicular Shocks

We perform particle-in-cell simulations of perpendicular nonrelativistic collisionless shocks to study electron heating and pre-acceleration for parameters that permit extrapolation to the conditions at young supernova remnants. Our high-resolution large-scale numerical experiments sample a representative portion of the shock surface and demonstrate that the efficiency of electron injection is strongly modulated with the phase of the shock reformation. For plasmas with low and moderate temperature (plasma beta $\beta_{\rm p}=5\cdot 10^{-4}$ and $\beta_{\rm p}=0.5$), we explore the nonlinear shock structure and electron pre-acceleration for various orientations of the large-scale magnetic field with respect to the simulation plane while keeping it at $90^\circ$ to the shock normal. Ion reflection off the shock leads to the formation of magnetic filaments in the shock ramp, resulting from Weibel-type instabilities, and electrostatic Buneman modes in the shock foot. In all cases under study, the latter provides first-stage electron energization through the shock-surfing acceleration (SSA) mechanism. The subsequent energization strongly depends on the field orientation and proceeds through adiabatic or second-order Fermi acceleration processes for configurations with the out-of-plane and in-plane field components, respectively. For strictly out-of-plane field the fraction of supra-thermal electrons is much higher than for other configurations, because only in this case the Buneman modes are fully captured by the 2D simulation grid. Shocks in plasma with moderate $\beta_{\rm p}$ provide more efficient pre-acceleration. The relevance of our results to the physics of fully three-dimensional systems is discussed

Spatio-temporal evolution of the nonresonant instability in shock precursors of young supernova remnants

A nonresonant cosmic-ray-current-driven instability may operate in the shock precursors of young supernova remnants and be responsible for magnetic-field amplification, plasma heating and turbulence. Earlier simulations demonstrated magnetic-field amplification, and in kinetic studies a reduction of the relative drift between cosmic rays and thermal plasma was observed as backreaction. However, all published simulations used periodic boundary conditions, which do not account for mass conservation in decelerating flows and only allow the temporal development to be studied. Here we report results of fully kinetic Particle-In-Cell simulations with open boundaries that permit inflow of plasma on one side of the simulation box and outflow at the other end, hence allowing an investigation of both the temporal and the spatial development of the instability. Magnetic-field amplification proceeds as in studies with periodic boundaries and, observed here for the first time, the reduction of relative drifts causes the formation of a shock-like compression structure at which a fraction of the plasma ions are reflected. Turbulent electric field generated by the nonresonant instability inelastically scatters cosmic rays, modifying and anisotropizing their energy distribution. Spatial CR scattering is compatible with Bohm diffusion. Electromagnetic turbulence leads to significant nonadiabatic heating of the background plasma maintaining bulk equipartition between ions and electrons. The highest temperatures are reached at sites of large-amplitude electrostatic fields. Ion spectra show supra-thermal tails resulting from stochastic scattering in the turbulent electric field. Together, these modifications in the plasma flow will affect the properties of the shock and particle acceleration there.Comment: Accepted for publication in MNRAS. 16 pages, 15 figure

Kinetic simulations of nonrelativistic perpendicular shocks of young supernova remnants. I. Electron shock-surfing acceleration

Electron injection at high Mach-number nonrelativistic perpendicular shocks is studied here for parameters that are applicable to young SNR shocks. Using high-resolution large-scale two-dimensional fully kinetic particle-in-cell (PIC) simulations and tracing individual particles we in detail analyze the shock surfing acceleration (SSA) of electrons at the leading edge of the shock foot. The central question is to what degree the process can be captured in 2D3V simulations. We find that the energy gain in SSA always arises from the electrostatic field of a Buneman wave. Electron energization is more efficient in the out-of-plane orientation of the large-scale magnetic field because both the phase speed and the amplitude of the waves are higher than for the in-plane scenario. Also, a larger number of electrons is trapped by the waves compared to the in-plane configuration. We conclude that significant modifications of the simulation parameters are needed to reach the same level of SSA efficiency as in simulations with out-of-plane magnetic field or 3D simulations

Kinetic simulations of non-relativistic high-Mach-number perpendicular shocks propagating in a turbulent medium

Strong non-relativistic shocks are known to accelerate particles up to relativistic energies. However, for Diffusive Shock Acceleration electrons must have a highly suprathermal energy, implying a need for very efficient pre-acceleration. Most published studies consider shocks propagating through homogeneous plasma, which is an unrealistic assumption for astrophysical environments. Using 2D3V particle-in-cell simulations, we investigate electron acceleration and heating processes at non-relativistic high-Mach-number shocks in electron-ion plasma with a turbulent upstream medium. For this purpose slabs of plasma with compressive turbulence are separately simulated and then inserted into shock simulations, which requires matching of the plasma slabs at the interface. Using a novel procedure of matching electromagnetic fields and currents, we perform simulations of perpendicular shocks setting different intensities of density fluctuations ($\lesssim 10\%$) in the upstream. The new simulation technique provides a framework for studying shocks propagating in turbulent media. We explore the impact of the fluctuations on electron heating, the dynamics of upstream electrons, and the driving of plasma instabilities. Our results indicate that while the presence of the turbulence enhances variations in the upstream magnetic field, their levels remain too low to influence significantly the behavior of electrons at perpendicular shocks.Comment: Accepted for publication in ApJ, 17 pages, 10 figure

Запобігання професійних ризиків та зменшення шкідливого впливу на професійне здоров'я працівників компонентів металургійних відходів

Мета роботи: виявлення та аналіз ризиків від шкідливих чинників, пов’язаних із утворенням та зберіганням техногенних відходів, а також шляхів їх усунення. Підхід дослідження: в якості основного підходу дослідження застосовували ризик орієнтований підхід. Результати дослідження: виявлено та проаналізовано ризики для працівників металургійних підприємств та мешканців прилеглих територій від шкідливих чинників, пов’язаних із утворенням та зберіганням техногенних відходів металургійного виробництва. Визначено, яким чином можливо уникнути шкідливих чинників або знизити їх дію. Практична цінність дослідження: запропоновано заходи по зберіганню та переробці техногенних металургійних відходів, спрямовані на мінімалізацію ризику їх шкідливого впливу. Цінність дослідження: побудовано комплексну графічну схему причинно-наслідкового зв’язку між способами поводження із техногенними металургійними відходами різних видів та ризиками впливу шкідливих чинників із зазначенням найбільш раціональних шляхів поводження. Майбутні дослідження: розвиток майбутніх досліджень можливий в напрямку розширення використовуваних методів оцінки ризику. Тип статті: описовий та аналітичний

Підхід до розробки інформаційної системи для екстракції даних з веб

Today, the Internet contains a huge number of sources of information, which is constantly used in our daily lives. It often happens that similar in meaning information is presented in different forms on different resources (for example, electronic libraries, online stores, news sites and etc.). In this paper, we analyze the extraction of information from certain type of web sources that is required by the user. The analysis of the data extraction problem was carried out. When considering the main approaches to data extraction, the strengths and weaknesses of each were identified. The main aspects of the extraction of web knowledge were formulated. Approaches and information technologies for solving problems of syntactic analysis based on existing information systems are analyzed. Based on the analysis, the task of developing models and software components for extracting data from certain types of web resources were solving. A conceptual model of extracting data was developed taking into account web space as an external data source. A requirements specification for the software component was created, which will allow to continue working on the project and to clearly understand the requirements and constraints for implementation. During the process of modeling software, the following diagrams have been developed, such as activities, sequences and deployments, which will then be used to create the finished software application. For further development of the software, a programming platform and types of testing (load and modular) were defined. The obtained results allow to state that the proposed design solution, which will be implemented as a prototype of the software system, can perform the task of extracting data from different sources on the basis of a single semantic template.Сьогодні Інтернет містить величезну кількість джерел інформації, яка постійно використовується в нашому щоденному житті. Часто буває, що схожа за змістом інформація представлена в різній формі на різних ресурсах (наприклад, електронні бібліотеки, інтернет-магазини, новинні сайти). У даній роботі аналізується вилучення інформації з веб-джерел певного типу, яке потрібно користувачеві. Проведено аналіз проблеми вилучення даних. При розгляді основних підходів до екстракції даних були виділені сильні і слабкі сторони кожного. Сформульовано основні аспекти вилучення веб-знань. Проаналізовано підходи та інформаційні технології вирішення проблем синтаксичного аналізу на основі існуючих інформаційних систем. На основі проведеного аналізу була сформована задача розробки моделей і програмних компонентів для отримання даних з веб-ресурсів певного типу. Розроблено концептуальну модель вилучення даних з урахуванням веб-простору як зовнішнього джерела даних. Була створена специфікація вимог для програмного компонента, що дозволить продовжити роботу над проектом, щоб чітко розуміти вимоги і обмеження для реалізації. При моделюванні програмного забезпечення були розроблені наступні діаграми, такі як діаграми класів, активності, послідовності і розгортання, які потім будуть використовуватися для створення готового додатка. Для подальшої розробки програмного забезпечення була визначена платформа програмування і види тестування (навантажувальний і модульне). Отримані результати дозволяють стверджувати, що пропоноване проектне рішення, яке буде реалізовано у вигляді прототипу програмної системи, може виконувати завдання екстракції даних з різних джерел на основі одного семантичного шаблону

Using PIC and PIC-MHD to investigate cosmic ray acceleration in mildly relativistic shocks

Astrophysical shocks create cosmic rays by accelerating charged particles to relativistic speeds. However, the relative contribution of various types of shocks to the cosmic ray spectrum is still the subject of ongoing debate. Numerical studies have shown that in the non-relativistic regime, oblique shocks are capable of accelerating cosmic rays, depending on the Alfv\'enic Mach number of the shock. We now seek to extend this study into the mildly relativistic regime. In this case, dependence of the ion reflection rate on the shock obliquity is different compared to the nonrelativistic regime. Faster relativistic shocks are perpendicular for the majority of shock obliquity angles therefore their ability to initialize efficient DSA is limited. We define the ion injection rate using fully kinetic PIC simulation where we follow the formation of the shock and determine the fraction of ions that gets involved into formation of the shock precursor in the mildly relativistic regime covering a Lorentz factor range from 1 to 3. Then, with this result, we use a combined PIC-MHD method to model the large-scale evolution of the shock with the ion injection recipe dependent on the local shock obliquity. This methodology accounts for the influence of the self-generated or pre-existing upstream turbulence on the shock obliquity which allows study substantially larger and longer simulations compared to classical hybrid techniques.Comment: 38th International Cosmic Ray Conference, Proceedings of Science (ICRC2023) 54

Pre-acceleration in the Electron Foreshock II: Oblique Whistler Waves

Thermal electrons have gyroradii many orders of magnitude smaller than the finite width of a shock, thus need to be pre-accelerated before they can cross it and be accelerated by diffusive shock acceleration. One region where pre-acceleration may occur is the inner foreshock, which upstream electrons must pass through before any potential downstream crossing. In this paper, we perform a large scale particle-in-cell simulation that generates a single shock with parameters motivated from supernova remnants. Within the foreshock, reflected electrons excite the oblique whistler instability and produce electromagnetic whistler waves, which co-move with the upstream flow and as non-linear structures eventually reach radii of up to 5 ion-gyroradii. We show that the inner electromagnetic configuration of the whistlers evolves into complex non-linear structures bound by a strong magnetic field around 4 times the upstream value. Although these non-linear structures do not in general interact with co-spatial upstream electrons, they resonate with electrons that have been reflected at the shock. We show that they can scatter, or even trap, reflected electrons, confining around $0.8\%$ of the total upstream electron population to the region close to the shock where they can undergo substantial pre-acceleration. This acceleration process is similar to, yet approximately 3 times more efficient than, stochastic shock drift acceleration.Comment: 16 pages, 11 figures, accepted for publication in Ap

The Wetland Map Validation for Ukraine

This paper considers the topical issue of using data from a drone with a very high spatial resolution to solve the problems of validation of individual classes on land cover maps obtained at the national level with a 10-meter spatial resolution. In particular, this study validated the land cover map for the territory of Ukraine for 2020 and conducted a comparative analysis of orthophoto data with open Sentinel-2 satellite data, as well as validated some wetland locations from the classification map for Ukraine. Comparative analysis showed that orthophotoplane data have a correlation from 0.3 to 0.7 depending on the drone survey parameters with the Sentinel-2 satellite, and large wetlands on data with 10-meter spatial resolution are identified with an overall accuracy of 90%, but for more accurate details of wetlands contours correct will be the use of orthophotos data