BULLETIN OF THE L.N. GUMILYOV EURASIAN NATIONAL UNIVERSITY. PHYSICS. ASTRONOMY SERIES

Dr. Constraining power-law cosmology with observational Hubble data

2025-09-25T09:07:30+00:00

In this work, we analyze observational constraints on power-law cosmology, which is characterized by two key parameters: the Hubble constant (H0) and the deceleration parameter (q). Using the latest 31 data points of observational Hubble data, we obtain bounds on these parameters. Our results indicate that power-law cosmology provides a good fit to the Hubble data, with the estimates closely matching recent findings reported in the literature. Nevertheless, while this model captures several major aspects of cosmic evolution, it falls short in accounting for finer details, particularly the dynamical transition of cosmic acceleration.

Решение для F(R,Q,X,φ) модели в сферической метрике

2025-09-28T18:36:07+00:00

В работе рассматриваются аналитические и численные подходы к построению решений в рамках обобщённой гравитационной модели вида F(R,Q,X,φ). Особое внимание уделено исследованию метрик сферической симметрии, позволяющих изучить поведение гравитационных и скалярных степеней свободы в компактных объектах и космологических моделях. Показано, что введение нелинейной зависимости функции действия от комбинации F(R,Q,X,φ) существенно расширяет класс допустимых решений по сравнению с традиционной F(R)–гравитацией. Анализируются условия существования статических и динамических решений, их устойчивость, а также возможные физические интерпретации в контексте модифицированной теории гравитации и астрофизики. Полученные результаты открывают перспективы для описания тёмной материи, тёмной энергии и гравитационных коллапсов в рамках единого формализма. Дополнительно рассматриваются возможные проявления модели в сценариях ранней Вселенной, включая инфляционную динамику и фазовые переходы, а также влияние на образование структур и эволюцию космологических возмущений. Подчёркивается роль численных методов в исследовании сложных режимов, где аналитические решения оказываются недоступными. Особое внимание уделяется сравнительному анализу с известными решениями в общей теории относительности, что позволяет выявить новые физические эффекты и ограничения на параметры модели. Представленные результаты могут быть полезны при разработке альтернативных космологических сценариев и в дальнейшем применены к анализу астрофизических наблюдений, включая гравитационно-волновые сигналы и динамику компактных звёздных объектов.

Comparative analysis of cast and flux-cored wire based coatings during electric arc metallisation

2025-05-12T04:34:50+00:00

The paper presents the results of investigation of properties of coatings obtained by electric arc metallisation on 65G steel substrate using different types of wire - cast and powder. A comparative analysis of the influence of chemical composition and technological parameters of sputtering (wire feed rate, gas pressure, sputtering distance, substrate preheating) on thickness, porosity, micro-hardness, roughness and adhesion of coatings has been carried out. It is found that cored wire provides lower porosity, improved structure uniformity and increased hardness compared to cast wire. Optimal parameters of the spraying mode allowed to achieve the maximum coating thickness up to 712 microns and minimum porosity of 4.3%. The results of the research confirm the prospectivity of powder wires application for formation of wear-resistant and corrosion-resistant coatings in machine-building and other industries.

Ғарыш инфрақұрылымындағы деформацияны FBG сенсорларымен дәл бақылау

2025-08-27T13:59:32+00:00

Annotation. The use of FBG sensors is considered effective for the purpose of accurate monitoring of structural deformation in space infrastructure . In the space environment, structures are subjected to various mechanical and temperature loads. These effects can lead to structural damage, defects, or accidents over time. Therefore, real-time deformation control is an important condition for ensuring safety and durability. The main advantages of sensors are compactness, light weight, resistance to electromagnetic interference. These properties make them effective for use in conditions of a limited resource in outer space. This article will describe the principles of operation of FBG sensors, methods for their installation in space structures, accuracy and stability in determining various types of deformation.

Оценка фоновой радиации на территории Казахстана методом ЭПР дозиметрии по зубной эмали

2025-09-02T12:52:13+00:00

This review article provides a comprehensive analysis of contemporary studies devoted to EPR dosimetry using tooth enamel. The fundamental aspects of radiation-induced signal formation, their physico-chemical nature, and specific interactions with intrinsic paramagnetic centers are considered. The structural and dosimetric properties of tooth enamel and its model systems, including synthetic apatites, are analyzed, along with advanced approaches for the registration, identification, and quantitative evaluation of EPR spectra.

Special attention is given to the practical aspects of dosimetry, including sample preparation, irradiation conditions, and algorithms for extracting dose-related information. Issues of dose–response linearity, energy dependence of the signal, and sources of uncertainty are critically discussed.

The relevance of the study arises from the increasing demand for reliable methods of individual dose assessment in cases of radiation accidents, as well as in medical and environmental dosimetry. EPR dosimetry based on tooth enamel demonstrates high potential as an independent tool for retrospective dose reconstruction, characterized by long-term signal stability and high sensitivity to ionizing radiation. The review integrates both theoretical and applied aspects of the method, contributing to a holistic understanding of its capabilities, limitations, and avenues for further development.

In conclusion, the prospects for advancing the method are outlined, including improvements in spectral analysis, refinement of signal formation models, and the broadening of EPR dosimetry applications in radiation protection and biomedical research.

Stable Formation of BiVO4/ZnO Heterostructure via a Soft Deposition Method

2025-08-27T14:20:25+00:00

This work presents the results of a mild two-step layer-by-layer deposition of bismuth vanadate (BiVO₄) onto hydrothermally synthesized zinc oxide (ZnO) nanorods using the spin-coating method. Controlling the viscosity and precursor concentration plays a key role in tuning the thickness, uniformity, and stability of the BiVO₄ films formed on ZnO. The synthesized samples were characterized using a range of analytical techniques. First, UV–Vis spectroscopy was used to determine the absorption spectrum in the visible range after BiVO₄ deposition. Next, X-ray diffraction (XRD) confirmed the presence of the monoclinic phase of BiVO₄ and the wurtzite phase of ZnO, as well as the degree of crystallinity of the samples. Finally, scanning electron microscopy (SEM) revealed the morphology of ZnO nanorods and the stable coating of their surface with a BiVO₄ layer. To evaluate the practical performance of the BiVO₄/ZnO heterostructures, photoelectrochemical (PEC) measurements were conducted under natural outdoor conditions using linear sweep voltammetry, demonstrating the operability of the films in real environments. The obtained results confirm that the proposed two-step spin-coating method with optimized solution viscosity enables the formation of stable heterostructures suitable for use in photoelectrochemical devices.

New manganese hexaboride: stability and mechanical properties

2025-09-01T19:19:04+00:00

Through ab initio evolutionary crystal structure prediction, we have discovered a novel monoclinic phase of manganese hexaboride (MnB₆) with the space group P2/m. This new polymorph is energetically favorable over the previously known hexagonal Pm2 structure at pressures below 58 GPa. Although metastable with respect to decomposition into MnB₄ and B, the P2/m phase is demonstrated to be dynamically and mechanically stable at ambient pressure, as confirmed by the absence of imaginary phonon modes and the satisfaction of the Born stability criteria. Calculations of the elastic properties reveal that MnB₆-P2/m is a hard, brittle material with a high Vickers hardness of 33 GPa, which surpasses that of common industrial ceramics like tungsten carbide and silicon carbide. Its bulk modulus (273 GPa), shear modulus (220 GPa), and Young modulus (519 GPa) indicate superior resistance to elastic deformation. The compound exhibits significant elastic anisotropy, as visualized by the directional dependence of its moduli and hardness. These properties establish the new MnB₆-P2/m polymorph as a promising candidate for experimental synthesis and potential application as a hard material.

Хлоридіндегі гидроний иондарының динамикасына атомдық түсініктер және отын ұяшықтарын қолдану үшін декан қышқылы негізіндегі терең эвтектикалық еріткіш

2025-08-27T14:13:01+00:00

Proton-exchange membrane fuel cells require high-strength, inexpensive, and environmentally friendly proton-permeable media. However, traditional proton-conducting electrolytes face problems such as limited thermal stability and reduced proton mobility in anhydrous or low-humidity environment. In this study, we consider deep eutectic solvents based on choline chloride and decanoic acid as a potential alternative medium for the transport of hydroxonium ions. Calculations of the density functional theory with dispersion correction were used to optimize the structures of deep eutectic solvents without and in the presence of hydroxonium ion, providing accurate information about their structural and electronic properties. The optimized geometry shows a network of hydrogen bonds between choline chloride and decanoic acid, which are further regulated by the fusion of the hydroxonium ion. Molecular electrostatic potential mapping identifies regions that effectively bind protons, while boundary molecular orbital investigation reveals changes in electron distribution and stability caused by the interaction of hydroxonium ions. The results show that the matrix of choline chloride and decanoic acid can stabilize hydroxonium ions due to strong hydrogen bonding and improve proton transport. This work provides knowledge about the interactions of solvent and hydroxonium at the atomic level, lays the foundation for the rational design of electrolytes based on special deep eutectic solvents for the use of fuel cells, and directs future research towards experimental verification and integration into proton-exchange membrane systems of fuel cells.

Computational and experimental studies of processes of non-activation release of tritium from beryllium-containing materials of research nuclear reactors

2025-07-21T10:32:31+00:00

Under neutron irradiation lithium-6 is produced in beryllium components of nuclear reactors, which further interacts with neutrons to form tritium. The concentration of lithium-6 grows to some equilibrium value, when the rate of its formation compares with the Li burnup rate. Numerous studies of tritium interaction with irradiated beryllium were conducted, where reliable data were obtained that the main process influencing tritium release rate is diffusion. Diffusion processes become significant at high temperatures (above 700℃), when beryllium recrystallization begins. However, it was found that significant amounts of tritium may be released into the water surrounding beryllium reflector. A possible mechanism for such release may be the release of tritium directly from the near-surface layer of beryllium units. Since the reaction Li⁶+n_th -->He⁴+H³
produces high-energy helium and tritium ions (with energies >2 MeV), they can leave the near-surface beryllium layer in the beryllium units of the reactor (estimates show that the width of such a layer exceeds 2 µm).

The paper presents a method for calculating tritium ions amount emitted from beryllium reflectors of nuclear reactors in non-activation way. Experiments on method verification consisted in irradiation of various lithium-containing samples wrapped in aluminum foils. Irradiation was conducted during 21 days at temperature 50℃ until achieving thermal neutron fluence 9.1·10¹⁹n/cm² and fast neutrons fluence (E˃0.1 MeV) 1.8·10¹⁹n/cm². Tritium amount accumulated in aluminum foils was estimated and compared with calculation. Results showed applicability of proposed calculation method for estimating tritium ions amount emitted from beryllium reflectors of nuclear reactors in non-activation way.

Оптические и люминесцентные свойства монокристаллов YAG:Ce облученных ионами Xe132 с энергией 231 МэВ

2025-09-02T18:35:47+00:00

The study investigates the effect of 230 MeV xenon ion irradiation on the optical and luminescent properties of Y₃Al₅O₁₂:Ce (YAG:Ce) crystals. Irradiation leads to the formation of Frenkel defects (F, F⁺), antisite defects, as well as the suppression of Ce³⁺ ion emission due to the intensification of nonradiation processes and charge transfer Ce³⁺ Ce⁴⁺ . It is shown that with increasing fluence, the luminescence intensity of Ce³⁺ decreases as a result of the formation of crystals lattice defects such as oxygen vacancies and antisite disorders. Changes in the valence state of cerium (Ce³⁺ Ce⁴⁺) are also possible. The obtained results provide insight into radiation-induced processes in YAG:Ce, which are important for its application in radiation-resistant scintillation detectors.

Charged particle spectrometer for the investigation of nuclear reactions induced by fast neutrons

2025-09-02T18:47:19+00:00

A spectrometer for detecting charged particles has been developed, designed for high-precision research in nuclear physics and applied tasks. The instrument is based on a two-section ionization chamber with a Frisch grid, providing high detection efficiency, nearly isotropic solid angle (~4π), and minimal background noise levels, which is critically important for reliable determination of small reaction cross-sections. The relevance of this development is driven by growing interest in studying neutron-induced reactions related to nuclear energy development, radiation protection, and fundamental research into nuclear structure, as well as the lack of modern spectrometers capable of working with both solid and gaseous targets without loss of efficiency. The device is effectively used in systematic studies of charged particle emission reactions induced by fast neutrons on light and medium-mass nuclei. It enables obtaining energy distributions of reaction products, total and differential cross-sections, as well as angular distributions of charged particles. A key advantage of the spectrometer is its ability to work with both solid and gaseous samples, significantly expanding its application scope in scientific research.

Fluctuations in large classical systems

2025-09-11T10:45:14+00:00

Based on statistical regularities, this paper describes fluctuations in a multi-particle system of the Gibbs ensemble that is in thermal equilibrium with a thermostat. In particular, using Gibbs' canonical distributions, we calculate energy fluctuations during random thermal exchanges, the variance of particle number fluctuations, and the mean square of random energy. According to the results of these calculations, a formula for the relative energy fluctuations of a monoatomic ideal gas was also obtained. To calculate the fluctuations of any physical quantity, it is necessary to express the entropy variation in terms of that quantity. Based on this widely used thermodynamic principle, and taking into account the relationship between entropy probabilities and non-equilibrium states, a generalized formula for the variance of thermodynamic quantity fluctuations was derived, along with a formula for calculating the probability density of a non-equilibrium state. Using the resulting formula, it was shown that the probability density of a non-equilibrium state is a function of small random deviations of thermodynamic quantities from their equilibrium values. Based on these results, expressions were derived for the variances of temperature, volume, and density fluctuations in a monoatomic ideal gas, as well as for the relative fluctuations of these quantities. Additionally, internal energy fluctuation was calculated. Using a method that considers the transition of a system from an equilibrium state to a fluctuating one, along with thermodynamic parameter fluctuations, a criterion was presented that enables the calculation of fluctuations in mechanical quantities that describe the state of a macroscopic body in a given medium. In particular, the transition of a resting body to a fluctuating state due to molecular impacts from a fluid (or gas) was considered, and the probability density and variance of the fluctuating velocity of the body were calculated.

Modeling Defect States and the Role of 4f Electrons in Gd₃Ga₅O₁₂ Using DFT Methods

2025-09-12T05:47:40+00:00

Gadolinium gallium garnet (Gd₃Ga₅O₁₂, GGG) is an important synthetic crystal widely used in laser systems, magneto-optics, and radiation-resistant electronics. A fundamental understanding of its electronic structure and defect states is essential for optimizing optical and functional properties. This study aims to investigate the role of 4f electrons and oxygen vacancies in shaping the band structure and optical response of GGG using modern density functional theory (DFT) methods. Calculations were performed with the VASP package using GGA-PBE, SCAN, mBJ, and hybrid HSE06 functionals. Comparative analysis shows that Gd³⁺ 4f electrons significantly affect the band gap and density of states: their inclusion creates localized levels near the valence band edge and narrows the band gap, whereas their exclusion overestimates the gap and neglects local effects. Charged [GGG]²⁺ vacancies shift the Fermi level without forming defect levels, while neutral [GGG]⁰ vacancies create localized states within the gap, reducing transparency and deteriorating the optical properties of the crystal.

The results have both fundamental and applied significance. Scientifically, they clarify the role of strongly correlated 4f electrons in garnets and the mechanism of oxygen defect effects. Practically, they provide a basis for predicting radiation resistance and designing next-generation optical materials. This work contributes to the physics of defect states and theoretical modeling of functional crystals.