In the paper, the mixed parametric and self-oscillations in the presence of a nonlinear parametric action and a delay in friction causing self-oscillations have been studied. For this purpose, a model of a frictional self-oscillating system interacting with an energy source of limited power was used. The solution of nonlinear differential equations of motion was constructed using the direct linearization method. The relations of nonstationary and stationary oscillation modes were obtained. By application of the Routh – Hurwitz criteria, the conditions for the stability of stationary oscillations were derived. The calculations were carried out in order to gain information about the dynamics of fluctuations. An analysis of the data showed that the amplitude-frequency dependence changed its behavior under the influence of the delay. The latter also led to the appearance of stability regions on the lower branches of the amplitude curves, and a dependence arose on the steepness of the energy source characteristic.
Supercomputer simulation of several amino acid oligomers using the molecular dynamics method has made it possible for the first time to identify a complex of characteristics of both intrinsic intramolecular local vibrations, or normal modes, and forced vibrations when specifying an alternating electric field in the IR frequency range. Amplitude-time dependences of energy and electric dipole moment were obtained for oligomers of Gly, Ala, Trp, Val amino acids, the Fourier transform of which revealed their frequency spectra. The type of solvent model was shown to significantly affect the position of spectral peaks because of variations in local interactions and system dynamics. The interpretation of the obtained patterns made it possible to propose a non-contradictory model that satisfied the fundamental physical concepts of the intramolecular and intermolecular dynamics of groups of biomolecules. The model allows for intramolecular interactions of normal local vibrations, including those of the Fermi resonance type.
The effect of Ar+ and Cd+ ion implantation and subsequent thermal annealing has been studied on a single-crystal ZnTe (111) using a whole range of spectroscopy methods: ultraviolet photoelectron one (UPS), light absorption one, and Auger electron one (AES). The results showed that bombardment of the surface with Ar+ and Cd+ ions with an energy of E0 = 1 keV until a saturation dose of of Dsat = (6–8)·1016cm−2 was reached resulted in the destruction of the crystal structure of the ion-implanted layers and, as a consequence, in surface metallization. In particular, after implantation with Cd+ ions and subsequent annealing at T = 850 K, the formation of a homogeneous continuous Zn0,5Cd0,5Te film 30–35 Å thick was observed, which indicated the redistribution of components and the formation of a new phase state on the ZnTe surface. The results of the study of Zn0,5Cd0,5Te thin films demonstrate the presence of two clearly defined maxima in the valence electron spectra corresponding to binding energies of −1.4 eV and −5.2 eV.
In the paper, the results of numerical modeling of the formation and propagation of vortex structures generated by a pulsed turbulent buoyant jet have been presented for the Reynolds number Re = 1.5×104, the parameter P = 3.65, and the Grashof number Gr = 3.9×105. A three-dimensional turbulent flow model based on the unsteady Reynolds equations was adopted. The angle between the jet and gravity directions was varied from 0° to 180°. The vortex cloud movement was tracked up to the moment when the maximum velocity value in the cloud became equal to 3.5% of the inlet velocity. For various α values, the power-law relationships describing the propagation of the vortex cloud and a decrease in the maximum velocity value and temperature within the cloud were obtained.
This work has involved the simulation of technological operations of manufacturing a silicon (Si) avalanche photodiode and calculating its output characteristics. As a result, the values of its multiplication factor (from 49.5 to 63.3) and spectral sensitivity (from 15.8 to 19.6 A/W) depending on the shallow trench insulation defect type are presented for a Si avalanche photodiode. It has been shown that the technological defects causing narrowing of the width of the trench towards its bottom have the greatest impact on these parameters. As a result, the multiplication factor decreases to 18%. The dependence of the photodiode gain on the trench’s wall inclination angle was established to be described well by a linear function. It was also demonstrated that the trench narrowing led to an increase in the lateral component of the electric field strength near the groove, which reduced the breakdown voltage, but did not lead to an increase in multiplication.
Chromium nanocomposites MCr2O4 have been synthesized by a solid-state reaction. The synthesized samples were characterized using X-ray powder diffraction technology (XRD). The temperature of synthesis was 1000°C for NiCr2O4 and 900°C for Zn Cr2O4. Miller indices (hkl) were calculated for the production, and the compounds were shown to have cubic structure FCC. The lattice parameters were as follows: a = 8.26 Å, Z = 8, V = 564.26Å3 and a = 8.2650 Å, Z = 8, V = 564.58 Å3 for NiCr2O4 and ZnCr2O4 respectively. The space group of symmetry is Fd3m for the both. The grain sizes were calculated by the Debye – Scherrer formula for the two compounds and were 31.92 nm and 32.78 nm, respectively. The ZnCr2O4 and NiCr2O4 nanoparticles' morphology was examined using scanning electron microscopy (SEM). The SEM images showed the agglomeration of the nanoparticles, which were formed of square-shaped nanocrystallites.
In the paper, the efficiency of a parametric damping system for the oscillations of a linear, initially, lightly damped pendulum has been studied. A closed-loop stabilization system included the feedback based on the deviation of the simple pendulum's position from the prearranged one. Our system was equipped with a controller whose structure followed from the Mathieu equation, and the variable coefficients were selected taking into account the proposed methodology. The parametric controller (PC) was shown to be able to shorten the settling time via increasing the damping. Because of this, it makes sense to add the PC to a system with a traditional offset-based P-controller to improve dynamic performance and to increase accuracy in the steady state. Moreover, the PC successfully suppressed harmonic external disturbances. The PC based on the offset of one link was constructed for a planar two-link pendulum. The controller damped lower frequency oscillations, but this turned out to be enough to significantly improve the stabilization response.
In order to extend the serviceability of ferroelectric devices, this paper proposes an experimental approach (for the first time) to clearing up the mechanism of polarization fatigue development in a lead zirconate titanate-based ferroelectric thin film. For this purpose, the influence of the recording pulse sequence configuration on the polarization of a selected object has been analyzed. The coercive field (CF) and remanent polarization of ferroelectric hysteresis loops were compared under two electric field application modes (they differed in the order of positive and negative pulses). The change in CF components was found to be insignificant during cyclic switching, whereas the difference between CF values reached 10% or more after pauses between the measurements. Experiments showed that the polarity of the final pulse of the switching signal set favorable conditions for stabilizing domains in the film whose dipole moment was aligned with the pulse polarity, and after resuming the measurements, a field of higher intensity was required to reverse the polarization.
When measuring a coating thickness by X-ray fluorescent analysis, the preliminary calibration of the detection system is required using reference samples with a known coating thickness. This operation is quite time-consuming and gives results only for a certain detection system and a pair of elements (the base material and coating). In our study, the calibration curve has been obtained by the Monte Carlo calculation method using the MCC 3D software. In so doing, we calculated the dependences of the ratios of peak intensities of fluorescence lines from Fe Kα (substrate) and Zn Kα (coating), as well as Cu Kα (substrate) and Au Lα (coating) on the values of coating thickness. Moreover, the coating thickness determination errors were obtained. A conclusion was made about the possibility of using the Monte Carlo method to determine the coating thickness without preliminary calibration.
The paper presents the results of numerical simulation of fluid flow in a rectangular room when fluid is supplied from two opposing slotted holes. The Reynolds number (Re) based on the height of the supply opening was varied from 20 to 140. For the given ratio of the lengths of the sides of the room, intensive self-oscillations developed due to instability arising when the supply jets interacted at Re ≥ 50. Already at a value of Re = 100 the flow became chaotic with a continuous frequency spectrum. The Strouhal number values corresponding to the main frequency of the oscillations depended weakly on Re and were approximately 3·10−3.
The paper puts forward an extension of the Pythia8 software package, which makes it possible to calculate collisions of longitudinally polarized protons with the production of J/ψ mesons. The transverse momentum spectra of J/ψ mesons and the double longitudinal spin asymmetry of them at an energy of 510 GeV have been obtained. The calculated results were compared with experimental data, and a satisfactory agreement between them was established. This success served as the basis for predicting the results of the SPD experiment at the NICA collider. The corresponding calculations of the transverse momentum spectrum and the double longitudinal spin asymmetry of the J/ψ meson at an energy of 27 GeV were presented. All conclusions were based on the collinear parton model.
Nucleoprotein filaments formed by recombinase proteins on DNA are key structures of the homologous recombination process, which ensures the maintenance of the genome stability. Filament formation on DNA leads to a significant change in the mechanical properties of the complex, in particular to DNA lengthening, while the kinetics of filament assembly depends on mechanical tension. Using optical tweezers, this study has obtained data on the assembly dynamics of human RAD51 recombinase and bacteriophage T6 UvsX recombinase filaments on double-stranded DNA under varying mechanical tension. In the range between 3 and 12 pN, RAD51 efficiently bound to DNA, forming filaments with a high coverage. In contrast to RAD51, an efficient UvsX filament formation occurred only under high tension (12 pN), whereas UvsX binding to DNA was severely restricted at 3–6 pN. The different tendency of the two recombinases to interact with DNA reflected their adaptation to cellular environments and regulatory mechanisms governing homologous recombination.
The paper presents the results of calculating the nuclear modification factors of π0 mesons as a function of their transverse momentum and azimuthal angle at different collision centralities of Cu+Au at an energy of 200 GeV and U+U at 193 GeV. As a result of the analysis of the obtained data, it was established that the azimuthal dependence of the nuclear modification factors of π0 mesons in both collision systems demonstrated universality in the considered range of transverse momentum and could be explained by the dependence of parton energy losses on the length of their path in the quark-gluon plasma (QGP). It is advisable to use these azimuthal dependences of nuclear modification factors for clarification of the parameters in theoretical models describing the energy losses of partons in the QGP formed in collisions of deformed nuclei or in asymmetric collision systems.
Plasmonic materials based on noble metal nanostructures exhibit unique optical properties in the visible range. Currently, plasmons supported by metal nanoparticles or propagating along metal interfaces are attracting increasing attention in sensorics, medicine, imaging, nanophotonics, and optoelectronic technologies. This article has provided a brief overview of two main plasmonic modes: surface plasmon polaritons at metal interfaces and localized plasmons in nanostructures. It also discussed the physical principles of plasmon-enhanced sensors, such as colorimetric, plasmon-enhanced fluorescence, and surface enhanced Raman scattering ones. These sensors are widely used in healthcare, security, food processing, and environmental monitoring. The fabrication of plasmonic nanostructures in glasses using ion exchange and their application for detecting chemical compounds and biological objects was discussed.
This paper presents the results of a study of radiation damage accumulation in α-Ga2O3 under sequential bombardment with fluorine and phosphorus ions with varying energies of the keV range. A significant effect of the ion irradiation sequence on both the number and depth distribution profile of stable defects was established. The physical nature of this noncommutativity is discussed.
galkinkn@iacp.dvo.ru Abstract. In this work calcium silicide films grown by MBE method on a Si(111) substrate at a temperature of 500 degrees C with deposition flux ratios NCa : NSi = 3.49, 3.98, the formation of a epitaxial Ca5Si3 film with a thickness of up to 40 nm was detected, which was proven by XRD method. Reflection peaks in the region of interband transitions at 2.2, 2.75, 3.57 and 4.4 eV, a semi-metallic character of reflection at energies less than 0.5 eV, partial transmittance at 0.4-1.25 eV and a unique phonon structure with Raman shifts at 102, 110, 124, 160, 190, 220, 241, 344 and 379 cm-1 were detected for the first time in the reflection and Raman spectra of the Ca5Si3 film.
polyakov_a_1999@mail.ru Abstract. Magnesium silicide films were formed on n-type Si (111) substrates with resistivities ranging from 2 to 15 Ohm & centerdot;cm (samples 1 and 2) and from 0.1 to 0.5 Ohm & centerdot;cm (samples 3 and 4) using reactive epitaxy with layer-by-layer deposition of magnesium and silicon layers at a temperature of 250 degrees C. The article presents the results of a study of the morphology, optical and phononic properties, and the band gap of samples containing magnesium silicide films with thicknesses of 496, 682, 1143, and 414 nm, according to SEM data on a cross section. Atomic force microscopy showed that the films of all samples were formed by the Volmer-Weber mechanism, with the islands coalescing into clusters and grains. The island area of the film of the first sample ranges from 0.12 to 0.48 & micro;m2, the second-from 0.02 to 0.06 & micro;m2, the third-from 0.01 to 0.04 & micro;m2, and the fourth-from 0.04 to 0.09 & micro;m2. The islands coalesce into clusters and grains. In all grown films, Raman scattering (RS) peaks were detected at 258, 348, and 693 cm-1, which correspond to the formation of Mg2Si. In the IR spectra, the minimum transmittance at a wavenumber of 270 cm-1 varies from 0.04 to 0.01, which corresponds to an increase in the absorption of IR photons with an increase in the thickness of the Mg2Si films in the grown samples. The reflection and transmission spectra of the grown films revealed both interference peaks (below 1.5 eV) and a peak with an energy of 2.2-2.3 eV, corresponding to the interband transition in Mg2Si. Based on the infrared absorption spectra, the indirect band gap width was calculated for each film: 0.80 and 0.86 eV for samples 1 and 2; 0.77 and 0.79 eV for samples 3 and 4.
The technology of embedding metallic iron disilicide (alpha-FeSi2) nanocrystals (NCs) with different numbers of NCs multilayers and different doping levels of silicon multilayers with holes (1019 cm-3 and 1013 cm-3) was tested on SOI substrates, and composites with 4 and 8 layers of embedded alpha-FeSi2 NCs were grown using it. The maximum power factor 0.1 to 0.25 mW/(m & times;K2) at T = 450 K was observed in the composite with the maximum hole concentration in the silicon interlayers, and a decrease in the hole concentration led to a decrease in the power factor to 0.01 mW/(m & times;K2) at T = 450 K due to a sharp decrease in the sheet resistance with a weak increase in the Seebeck coefficient.
A methodological approach is presented for quantitative analysis of geometric parameters of nanoparticle arrays, in particular the measurement of interparticle spacings, using a Delaunay triangulation algorithm. The development is motivated by the critical role of interparticle spacings in the formation of "hot spots" in surface-enhanced Raman scattering (SERS). The algorithm for automatic identification of nanoparticle centers in microscopy images and calculation of distances between nearest neighboring particles via Delaunay triangulation is described, along with data filtering criteria and the accounting of boundary effects to improve statistical reliability. The methodology is demonstrated on self-assembled arrays of nanoparticles obtained by thermal annealing of thin Ag films. The advantages of the proposed method and its limitations are discussed. The originality of the approach and its applicability to nanometrology and morphological analysis of nanostructured surfaces are emphasized.
The laser-induced periodic surface structures (LIPSS) represent an effective tech-nique to modify optical, mechanical, and chemical surface characteristics. While most studies focus on one-dimensional (1D) LIPSS formation on bulk and thin-film materials with orien-tation direction depending on laser polarization state, more complex morphologies are highly demanded for advanced applications. Here, we demonstrate the formation of two-dimensional (2D) square and hexagonal LIPSS on metal (Cr, Hf) and phase-change material (Ge2Sb2Te5) thin films, driven by thermochemical and plasmonic mechanisms, respectively. These findings expand the potential for applications in tunable photonic devices, diffractive optical elements, and structurally colored metals with 2D anisotropic optical properties
