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

Initial Conditions of Inflaton Field at the Quantum Bounce

Mohd Shahalam — 2026-03-30

In this paper, we explore the pre-inflationary evolution of the universe driven by a logarithmic potential in the context of Loop Quantum Cosmology. Our analysis focuses on identifying the physically admissible initial conditions for the inflaton field that result in a successful phase of slow-roll inflation. We also evaluate the corresponding number of e-folds and examine their consistency with current observational bounds. When the kinetic energy of the inflaton dominates at the initial stage, the cosmic evolution prior to reheating naturally separates into three successive phases: the bouncing phase, the transition phase, and the slow-roll inflationary phase. Throughout the bouncing phase, the dynamics of the scale factor are largely insensitive to both the chosen initial conditions and the detailed structure of the inflationary potential. In this regime, the evolution admits an explicit analytical solution, providing a clear and model-independent description of the background behavior before the onset of inflation. In this model, the quantum bounce is governed entirely by kinetic energy, since potential energy dominated initial conditions cannot be realized over the full range of inflaton field.

Energy conditions and late-time cosmic acceleration from a divergence-free deceleration parameter in f(R,T) gravity with non-minimal coupling

Umit Ismail — 2026-03-30

In this work, we study a divergence-free parameterization of the deceleration parameter within the simplest linear f(R,T) modified-gravity model featuring a non-minimal matter-geometry coupling, f(R,T)=R+2λT, where R is the Ricci scalar, T is the trace of the energy-momentum tensor, and λ is the coupling parameter. Using this parameterization, we derive the Hubble parameter as a function of redshift, H(z), and substitute it into the modified Friedmann equations. The model parameters are constrained with observational data from OHD (cosmic chronometers) and the Pantheon supernova compilation, and the present-day values of H_0, q_0, and the evolutionary component q_1 are numerically estimated; the results indicate a smooth transition of the Universe from decelerated to accelerated expansion. In addition, for different values of λ, we analyze the time evolution of the energy density ρ and the effective equation-of-state parameter ω, identify deviations from the ΛCDM scenario, and clarify the role of λ in shaping the global cosmological dynamics. The energy-condition analysis shows that the NEC and DEC are satisfied throughout the evolution, whereas the SEC is violated at late times, in agreement with the observed cosmic acceleration. Overall, the divergence-free parameterization within f(R,T) gravity provides a viable framework to account for late-time acceleration while remaining consistent with observational and theoretical constraints. The results also provide a basis for a comparative analysis with the standard ΛCDM model and for placing observational bounds on the coupling parameter λ.

Overview of the ²⁰Ne + ⁷⁶Ge reaction mechanisms at E_lab= 275 MeV

Lorenzo Federico Pappalardo — 2026-03-30

The study of the neutrino-less double beta decay by heavy-ions double charge exchange (HI-DCE) represents a crucial step toward understanding the fundamental properties of neutrinos and the possible violation of lepton number conservation. Among the candidate isotopes for this rare process, plays a central role in current and next-generation experimental searches. In this work, I investigate the nuclear structure aspects relevant to the decay of through the analysis of the reaction at . The reaction dynamics were modeled using the coupled-channels code FRESCO using the Distorted Wave Born Approximation (DWBA), which allows for a detailed description of inelastic excitations and single-nucleon transfer processes that are sensitive to nuclear transition densities. Complementary large-scale shell-model calculations were carried out with KSHELL to obtain spectroscopic amplitudes and nuclear matrix elements for the relevant states. The theoretical results were directly compared with experimental differential cross sections from the NUMEN Collaboration, showing good overall agreement in both magnitude and shape. This comparison validates the reliability of the adopted reaction and structure models and provides important constraints on the nuclear structure components that dominate the nuclear matrix elements.

Design and experimental study of a low-temperature Stirling engine model

Гульнар Баубекова — 2026-03-30

The aim of this paper is to study the physical principles of a low-temperature Stirling engine and develop a working model. Both ideal and realistic cycle parameters are considered. Actual energy losses occurring during engine operation are analyzed, and approaches for accounting for them in modeling are proposed, facilitating theoretical research on low-temperature heat engines. Various Stirling engine modifications are also considered, and their potential efficiency is analyzed depending on temperature, material properties, and operating conditions.

The construction of an experimental engine model contributes to a deeper understanding of the mechanisms of heat transfer and energy conversion in closed cycles, which is important for the development of heat engine theory. Experimental research also contributes to the development of a domestic scientific base in the field of alternative energy.

The study makes an educational and methodological contribution: a model has been proposed that can be used to clearly demonstrate the operation of a Stirling engine and conduct basic experiments, making it a useful tool in educational practice.

Failure Analysis of Spacecraft Onboard Control Complexes under the Influence of Space Environment Factors

Aizhan Oshmanova — 2026-03-30

During the operation of spacecraft (SC) designed for various purposes, failures occur in onboard electronic equipment, which may lead to the development of off-nominal situations and, in some cases, to the loss of satellites. As a rule, such failures arise in the spacecraft onboard control system (OCS). Many researchers attribute these failures to the effects of ionizing radiation in near-Earth space (NES). Therefore, assessing the performance of the spacecraft onboard control system under the combined influence of near-Earth space environmental factors is both critical and necessary.

The aim of this study is to assess the reliability of onboard electronic equipment by taking into account radiation-induced failures of various types using directed graph structures.

In this work, a reliability parameter for spacecraft control systems based on the direction of error propagation is developed. Directed graphs of the onboard control system characterizing error propagation are presented. A directed graph model of the onboard control system is considered, in which system elements and their interconnections are represented by vertices and edges. Based on the probabilistic characteristics of functional modules, a methodology is developed for identifying error propagation directions that determine the greatest structural vulnerability of the system.

It is shown that the reliability of the onboard control system is determined by the system architecture rather than by random fluctuations of model parameters. The proposed reliability parameter makes it possible to identify vulnerabilities of functional nodes that affect the operation of the control system under the combined influence of space environment factors. The obtained results can be used in the design of spacecraft onboard control systems in order to enhance their reliability and resistance to the combined effects of space environment factors and operating conditions.

The role of reactive phase transformations in composite ceramics in changing strength and thermal characteristics

Elshibekov R — 2026-03-30

The paper presents the results of the assessment of the influence of variations in the ratio of components in composite (1-x)ZrO₂ – xSiC ceramics on the change in phase composition caused by the initialization of reactive phase transformations, as well as determination of the role of phase transformations on the change in strength and thermal characteristics. It has been established that control over the phase composition of composite (1–x)ZrO₂–xSiC ceramics allows for the targeted optimization of their strength properties, and the most favorable combination of strength characteristics is achieved at intermediate SiC concentrations of 0.2 – 0.3 M, ensuring a high level of mechanical reliability of materials under conditions of intense external influences. The results of thermal shock tests confirm that the highest resistance to sudden temperature effects is achieved in composite (1–x)ZrO₂–xSiC ceramics with a SiC content of 0.2 – 0.3 M, which ensures an optimal balance between thermal conductivity, mechanical strength, and the ability of the structure to relax thermally induced stresses. The data obtained are of great practical importance for assessment of the performance of these materials under conditions of non-stationary temperature conditions and emergency situations typical for the operation of inert matrices of dispersed nuclear fuel.

Study of the influence of phase composition variation in (1-x)Fe3O4 – xZnO nanocomposites on the inhibition of corrosion mechanisms

Kamila Kaliyekperova — 2026-03-30

The paper presents the results of studies of the influence of changes in the phase composition of (1-x)Fe₃O₄ – xZnO nanocomposites on the resistance to corrosion processes that occur when nanoparticles come into contact with model phosphate buffer solutions that simulate the physiological environment of the body. A comparative analysis of the results at 25 °C and 45 °C makes it possible to conclude that temperature is the determining factor controlling the degree of structural changes of the spinel phase in a liquid medium. At room temperature, the nanocomposites exhibit high crystal chemical stability, whereas at 45 °C a gradual evolution of the cation distribution, leading to an increase in the inversion degree and an increase in cationic disorder in the structure of ZnFe₂O₄ spinel, is observed. During the conducted studies, it was established that the growth in the content of the amorphous phase correlates with the recorded increase in the degree of inversion of the spinel phase and the growth of cationic disorder, which indicates a single degradation mechanism, including cation migration, defect formation and partial amorphization of the structure. Moreover, even under the most severe degradation conditions (45 °C, 7 days), the total proportion of amorphous inclusions remains limited, which confirms the satisfactory structural stability of the studied nanocomposites.

Study of the dynamics of open quantum systems using Lie groups and algebras

Talgat Koshtybayev — 2026-03-30

Abstract. The paper proposes approaches to the description of quantum system states, as well as the properties of continuity and symmetry, through the density matrix, and explores symmetries in systems, operators, and their commutators using Lie groups and Lie algebras. Specifically, by solving the Neumann equation (or quantum Liouville equation) for a stationary Hamiltonian, information was obtained from all processes occurring in the system, and the underlying causes of these processes were analysed through Lie algebra. By considering the transition from temporal dependencies to the dependence of observables, unitary equations were obtained that describe the dynamics of observables in the Heisenberg representation while preserving the structure of the Lie algebra. The dynamics of open quantum systems weakly interacting with the environment are described through solutions of the Lindblad equation for a stationary super operator. The quantum-to-classical transition, for a system interacting with its environment, was demonstrated under the condition of Bloch sphere contraction. The conditions for transitions from one algebra to another newly formed algebra was established. The Lindblad equation and its solution were expressed in the Gell-Mann matrix representation. In the course of the calculations, the relations between the bases of internal algebras and generators were reduced to the four-dimensional case. For large values of the time variable, a mathematical formulation of the density matrix contractivity was presented.

Lithium borohydride (LiBH₄) as a promising material for neutron–gamma radiation shielding

Kanatbek Nalibay — 2026-03-30

Abstract. This review critically examines recent advances in neutron–gamma radiation shielding with a focus on lithium borohydride (LiBH₄) – based composite materials. The analysis centers on the study by Lotfalian et al. (2024), which employed Monte Carlo neutron transport simulations using the MCNPX code to evaluate LiBH₄ incorporated into high‑performance concrete (HPC). Rather than presenting original numerical calculations, the present article synthesizes published results, clarifies the underlying physical mechanisms, and evaluates the methodological assumptions, strengths, and limitations of LiBH₄‑containing shields in comparison with conventional materials. Particular attention is paid to fast‑neutron attenuation, shield compactness, and long‑term material stability.

Assessment of the Significance of FBG Sensors for Space Environments

Нұржігіт Смаилов — 2026-03-30

This paper presents a comprehensive assessment of the application of Fiber Bragg Grating (FBG) sensors under harsh conditions characteristic of space environments. The operational performance of the sensors is analyzed under vacuum, thermal cycling, mechanical loads, and extreme temperatures of 800–1000 °C. The spectral drift stability of Regenerated FBG technology is demonstrated. The linear sensitivity of the Bragg wavelength to strain provides a basis for high measurement accuracy. The capabilities of embedded FBG networks for multiparameter monitoring are confirmed.

A review of the literature reveals the lack of comprehensive evaluation of FBG sensors in space environments, as well as the absence of a system-level assessment of the “sensor–structure–measurement system” chain. To address this gap, a comprehensive experimental methodology is proposed. Simulation of LEO conditions and long-term stability analysis are performed. The results substantiate the use of FBG sensors as a reliable measurement platform for structural health monitoring (SHM) systems of spacecraft.

Controlled Hydrothermal Synthesis of ZnO Nanorods for High-Performance Gas Sensors

Abylay Tangirbergen — 2026-03-30

Controlled synthesis of ZnO nanorods with tailored crystallinity and morphology is of great importance for the development of high-performance gas sensors. In this study, ZnO seed layers were deposited on glass substrates by RF magnetron sputtering and subsequently annealed at 400 °C to improve crystallinity and surface uniformity. Hydrothermal growth of ZnO nanorods was then carried out under different precursor concentrations (0.01 M:0.01 M and 1 M:1 M zinc acetate/HMTA) to investigate the effects of solution chemistry on nanorod formation. X-ray diffraction (XRD) revealed a dominant (002) peak in all samples, confirming c-axis oriented growth, while scanning electron microscopy (SEM) demonstrated that higher precursor concentrations yielded longer, densely packed nanorods with well-defined hexagonal cross-sections. The results highlight that both seed layer annealing and precursor concentration strongly influence the structural and morphological evolution of ZnO nanorods. Optimized synthesis conditions lead to vertically aligned, highly crystalline nanorods with increased aspect ratios, which are expected to enhance gas adsorption and electron transport, making them highly suitable for resistive-type gas sensing applications.

Optical properties of BaTiO₃ at room temperature: DFT Modeling

Ulzhan Tolegen — 2026-03-30

The optical properties of the tetragonal phase of BaTiO₃ were investigated using density functional theory (DFT). To describe the static crystal lattice, the generalized gradient approximation with on-site Hubbard correlation (GGA+U) as well as a hybrid functional were employed. In order to account for the thermal motion of atoms, ab initio molecular dynamics calculations within the GGA+U framework were performed. Optical absorption spectra were calculated both for the static lattice and along the molecular dynamics trajectory.

The obtained results demonstrate that consideration of atomic thermal motion leads to a significant reduction in the calculated optical absorption threshold energy. This effect can be explained by two main factors. First, changes in atomic configuration induced by thermal motion transform electronic transitions that are optically forbidden (dark) in the static lattice into optically allowed (bright) transitions. Second, the optical absorption edge is reduced due to fluctuations in the energies of electronic transitions caused by atomic motion.

The calculations were performed separately for different k-points of the Brillouin zone.

On the derivation of the equations of motion and field from the law of conservation of energy

Gulnaziya Tugelbaeva — 2026-03-30

Abstract. The equations of motion in analytical mechanics and the equations in the theory of electromagnetic fields are derived using the principle of least action applied to the Lagrangian function. In this article, Hamilton’s and Lagrange’s equations are obtained without using variational principles. The equations determining the generalized momenta are derived under the condition that the energy is a function of the generalized coordinates and velocities, and the conservation of the system’s energy under changes in any degrees of freedom is also proven. It should be noted that, based on these assumptions, Hamilton’s equations were obtained with a completely undetermined Hamiltonian. To find the relations describing the dependence of momenta on coordinates and velocities, it is shown that the Lagrangian function must be determined by considering the system’s energy as a known quantity. It should be emphasized that all obtained results are valid for a phase space in which the degrees of freedom are maximally independent of each other. The methods applied in analytical mechanics were successfully used to derive the field theory equations in electrodynamics. More precisely, the energy of a charged particle in an electromagnetic field was determined for suitable values of the vector potential of the field. As suitable values, the longitudinal electric field and vector potentials corresponding to the positions of the particle were considered.