Recent Contributions to Physics

Hydrothermal synthesis and characterization of ZnCo₂O₄ nanostructures

2025-08-20T12:10:53+00:00

In this work, three types of zinc cobaltite ZnCo₂O₄ structures, namely, nanorods, nanowires, and plates, were synthesized on nickel foam using a simple hydrothermal method. The morphology and structural characteristics of the synthesized samples were studied. The grown structures can be used as a basis for enzyme-free electrochemical biosensors. A detailed analysis of a series of six samples synthesized at different Zn:Co ratios (1:1, 1:10, and 10:1) was performed using scanning electron microscopy. The results of the study of the elemental composition of ZnCo₂O₄ nanostructures synthesized by the hydrothermal method on nickel foam showed that the composition of the obtained materials correlates with the composition of the initial growth solution, confirming the controllability of the doping process. The absence of any impurities indicates a high purity of the synthesized samples. The data obtained confirm the possibility of precise control of the stoichiometry of zinc cobaltite. It is shown that the morphology of the grown samples depends on the stoichiometry of the precursors, providing controlled growth of nanostructured materials. It is shown that the hydrothermal method for the synthesis of ZnCo₂O₄ nanostructures allows obtaining materials with a wide range of stoichiometry from cobalt- to zinc-containing phases, which opens up opportunities for fine-tuning the effective, functional properties of ZnCo₂O₄.

Investigation of the effect of short-pulsed ion irradiation on the stability of carbon nanowalls

2026-01-09T06:40:20+00:00

Carbon nanowalls (CNWs) are promising carbon-based nanomaterials for radiation-resistant electronic and optoelectronic applications due to their unique three-dimensional graphene-like architecture and outstanding physicochemical properties. In this work, the effect of short-pulsed high-current ion irradiation on the stability of carbon nanowalls was systematically investigated. CNWs were synthesized on quartz substrates by inductively coupled plasma–enhanced chemical vapor deposition and subsequently irradiated using the high-current pulsed ion accelerator INURA at current densities of 4, 7, and 10 A/cm². The radiation-induced changes in morphology, structure, optical transparency, and electrical properties were analyzed using atomic force microscopy, Raman spectroscopy, UV–Vis spectrophotometry, and four-point probe measurements. Atomic force microscopy revealed only moderate surface rearrangement and slight variations in roughness, while the characteristic vertically oriented nanowall morphology was preserved even at the highest irradiation density. Raman analysis confirmed the retention of the graphene-like sp² carbon structure, with minimal changes in the I_D/I_G ratio, indicating limited defect formation. Optical measurements showed moderate variations in transmittance correlated with surface restructuring, without spectral degradation. Electrical characterization demonstrated a stable or slightly reduced sheet resistance after irradiation, suggesting improved interwall electrical contact and structural stabilization. Overall, the results demonstrate the high resistance of carbon nanowalls to short-pulsed ion irradiation and confirm their suitability as functional materials for radiation-resistant electronic, optoelectronic, and sensor devices.

Harmonic analysis of a periodic electrical signal using the Mathcad package

2025-11-16T10:35:32+00:00

The article considers the harmonic analysis of periodic non-sinusoidal oscillations by Fourier series expansion. The features of decomposition of even and odd functions are revealed. Based on the symbolic method, the Fourier series was presented in a complex form. Examples are presented to provide clarity of the steps of the procedures for decomposing a function into a Fourier series.

Examples of Fourier series decomposition of periodic non-sinusoidal electric currents or signals using the Mathcad application software package are considered. Graphical, numerical, and analytical solutions of non-sinusoidal periodic currents or signals have been obtained using computational experiments. Methods for calculating the sum of the terms of the Fourier series for non-sinusoidal periodic signals, which consist of several stages, are presented.

It has been proven that complex even and odd functions describing periodic currents that are not sinusoidal (or cosine-shaped) consist of the sum of simple harmonic electrical oscillations. These fluctuations make up the frequency spectrum of these currents. The results of the approximation of periodic signals are presented as a Fourier series over the interval (p, p). Electrical signals are classified into a Fourier series, and the sum of the first two and four terms of this series is obtained. It has been shown that the more members of the signals classified in a row, these members more accurately describe the signal under study.

Effect of synthesis duration on the morphology and structure of carbon nanowalls on the surface of carbon paper

2025-12-29T09:34:53+00:00

This work investigates the evolution of the morphology and structural state of carbon nanowalls (CNWs) grown on carbon paper by capacitively coupled plasma-enhanced chemical vapor deposition (CCP-PECVD) as a function of synthesis duration (30-120 min) under fixed process parameters. The surface morphology of the coatings was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM), while structural changes were evaluated by Raman spectroscopy (λ = 473 nm). It is shown that at the early stage (30 min) CNWs form via island-like nucleation on defects of the carbon paper substrate, whereas increasing the deposition time to 60-90 min leads to intensive vertical growth and densification of the CNW array. AFM analysis reveals an increase in average and root-mean-square roughness (R_a: from 13.91 to 26.91 nm; R_ms: from 18.19 to 34.26 nm for 60-120 min), while the peak-to-valley roughness R_z increases up to 90 min (from 124.3 to 159.3 nm) and then reaches saturation (161.1 nm at 120 min). This behavior indicates a transition from predominantly vertical growth to a regime dominated by densification and secondary nucleation. Raman spectroscopy confirms a progressive increase in defect density and disorder of the sp² carbon network with increasing synthesis time: the I_D/I_G ratio rises from 0.61 to 1.84, the G-band full width at half maximum increases from 24.8 to 40.9 cm^-1, and the degree of graphitization decreases from 40.2 to 27.2 %. It is established that a synthesis duration of approximately 90 min provides an optimal balance between the development of vertical morphology and the preservation of structural ordering of the carbon phase, whereas 120 min results in maximum defect density and surface development, which is promising for applications requiring a high density of active sites.

Spectral characteristics of argon and argon-methane plasma obtained in an RF-DBD reactor at low pressure

2025-10-30T14:10:53+00:00

This paper investigates the properties and spectral characteristics of low-temperature argon plasma and argon-methane mixture plasma formed in a high-frequency dielectric barrier discharge (RF-DBD) at various powers and pressures. The experiments were conducted at an argon flow rate of 100 sccm for argon plasma and at a ratio of Ar:CH₄ = 95:5 for argon-methane plasma in the power range from 2 to 12 W and pressures of 0.5 and 1.0 Torr. It is shown that with an increase in the supplied power, the discharge area expands and the intensity of spectral lines increases, which is due to an increase in plasma density and the degree of ionisation. When the pressure increases, there is a decrease in the overall intensity of radiation due to a reduction in the free path length of electrons and an increase in collision losses. The introduction of methane leads to a decrease in the intensity of the spectral lines of molecular nitrogen and hydroxyl radicals (OH) compared to argon plasma, which indicates a redistribution of electron energy in favour of the excitation of argon atoms and active methane particles. The results obtained contribute to a deeper understanding of the physicochemical processes in Ar–CH₄ plasma and open up prospects for the application of RF-DBD discharges in plasma chemistry and materials science.

Quasi-periodic oscillations around compact objects within the Sen spacetime

2026-01-12T13:18:14+00:00

We investigate kilohertz (kHz) quasi-periodic oscillations (QPOs) observed in eight neutron-star low-mass X-ray binaries within the framework of the relativistic precession model (RPM). Fundamental (epicyclic) frequencies of test particles on circular orbits are computed in the static Sen spacetime. By fitting the Keplerian and epicyclic frequencies to the observed lower and upper QPO frequency pairs, (f_U, f_L) we infer the masses and electric charges of the compact objects and compare the results with those obtained in the Schwarzschild spacetime using the Akaike and Bayesian information criteria (AIC/BIC). We find that the Schwarzschild geometry provides physically consistent fits for four sources, while for GX 5–1 and GX 340+0 the Sen spacetime becomes effectively indistinguishable from Schwarzschild, indicating that no electric charge is required. Although the Sen metric yields statistically improved fits for the remaining four sources, the inferred large masses as well as large electric charges are incompatible with neutron-star physics. We therefore conclude that the static Sen spacetime does not provide a physically viable description of kHz QPOs in neutron-star systems.

Experience of using an infrared camera in the study of astronomical objects

2025-07-09T10:16:41+00:00

Based on the analysis of images of comet C/2023 A3 Tsuchinshan-ATLAS, obtained in both visible light and near-infrared range (wavelength over 850 nm) using CANON EOS 2000D and CANON EOS 1000DI (infrared) cameras, the influence of the observation spectral range on image contrast is studied. The image quality criterion is its contrast. Contrast coefficient calculations were performed using the standard ImageJ program used for image processing and analysis in various scientific applications. Several approaches to determining comet image contrast were used. Comparison of the obtained results did not reveal significant advantages of shooting in the mentioned spectral ranges. However, the analysis of noctilucent cloud images obtained using the same methodology revealed a significant advantage of infrared imaging, which sharply increases image contrast. A detailed analysis of shooting conditions suggested that the reduced effectiveness of infrared imaging is due to the transition from light scattering conditions of the daytime sky to twilight, and then to night conditions. A rationale is proposed for further studying methods of improving imaging efficiency when transitioning from the visible spectrum range to the near-infrared spectrum range.

Interrelation of fusion cross-section, reaction rate, and neutron production in a D-D reaction in a plasma focus device

2026-02-23T06:32:01+00:00

This study presents analysis of D-D thermonuclear fusion processes occurring in a plasma focus device by examining the interrelation between fusion cross-section, reaction rate, nuclear reaction time and neutron production. The goal of the study is to clarify the mechanisms of neutron production from the viewpoint of nuclear reaction kinetics governed by Coulomb barrier penetration and quantum tunneling effects. The fusion cross-section and reaction rate were calculated for deuteron energies in the range of 1-200 keV and compared with nuclear data libraries EXFOR and ENDF. The neutron particles which produced as a result of the D-D fusion reaction were registered using a silver activation foil detector. The corresponding effective deuterium ion energy region of 25-100 keV for D-D fusion reaction, cross-section 10^-3-10^-2 barn and nuclear reaction time 20-80 ns were found. It is consistent with experimentally observed neutron pulse durations producing during the pinch phase. In this case, the rate of nuclear fusion reactions in deuterium increases by approximately an order of magnitude compared to Maxwellian plasma, while the requirements for the magnetic confinement parameters of such plasma are significantly reduced.

Quantum-Noise–Induced Limits on Information Density in Confined Solid-State Systems

2026-01-21T07:46:27+00:00

The continuous miniaturization of solid-state systems has driven electronic materials into regimes where quantum noise and environmental coupling play a decisive role in determining physical performance. In this work, we develop an open quantum framework to investigate fundamental limits on information density in confined solid-state systems. By explicitly incorporating system environment interactions at the Hamiltonian level and describing the resulting non-unitary dynamics within the Lindblad formalism, we derive an intrinsic upper bound on the number of operationally distinguishable quantum states. Our analysis reveals that information density scaling is jointly constrained by geometric confinement and noise-induced coherence loss, leading to an apparent exponential growth only within an intermediate size regime. As system dimensions approach the nanoscale, increasing quantum noise enforces a crossover to sub-exponential, noise-limited behavior, signaling the breakdown of purely geometric scaling arguments. The results demonstrate that the observed scaling behavior arises as an emergent consequence of open quantum dynamics rather than technological optimization. Owing to its general formulation, the proposed framework is broadly applicable to a wide class of solid-state systems, providing a unified physical perspective on information-density limits imposed by quantum noise.