Journal of Experimental and Theoretical Physics最新文献

In this study, we investigate the emergence of convective flows in graphene-modified hydrogels experiencing phase transition and determine the thermophysical characteristics of such systems; the results are compared with numerical simulation data. We analyze the effect of graphene on the heat-transfer properties of hydrogel materials as applied to 3D bioprinting technologies. Using holographic interferometry, gradient calorimetry, and resulting temperature dependences of refractive indices, we have developed the computational complex for calculating the thermophysical parameters of hydrogel materials with graphene admixtures. It has been established that even insignificant concentrations of graphene admixture substantially affects the thermophysical properties. It is also shown that a graphene admixture reduces the viscosity of hydrogel samples, which is measured by the Höppler viscometer. Using the experimentally obtained thermophysical and rheological properties of hydrogels with graphene and the results of numerical simulation, we have calculated the Rayleigh numbers for the corresponding convective heat-exchange modes in the experimental cells with a hydrogel. The Rayleigh number (Ra) demonstrates substantial differences in the heat transfer of the material and its convective properties that depend on the viscosity, density, thermal conductivity, and other parameters of the system. In our case, the variations of the Rayleigh number indicate the difference in the thermal and hydrodynamic properties of different hydrogels with graphene.

In the framework of the consistent microscopic theory, universal analytic expressions describing absorption of laser pulses of an arbitrary duration in an optically dense medium have been derived, and their limiting cases have been considered. For the Gaussian and Lorentzian spectral profiles, simple expressions have been obtained for the absorption coefficient as a function of dimensionless parameters (optical thickness of the medium, the pulse duration and carrier frequency). Based on the performed calculations, the effect of the optical thickness of the medium on the dependences of the absorption coefficient on the pulse parameters has been revealed.

In this work, we use quantum mechanics theory to investigate and calculate the resistivity of the electron gas in a GaP/AlP/GaP quantum well at zero temperature and arbitrary temperatures under the influence of a magnetic field parallel to the layer. The calculations are performed considering the surface roughness scattering mechanism and the ionized impurity scattering mechanism. The results indicate that the temperature and magnetic field significantly affect the electronic properties of the two-dimensional electron gas. Moreover, the investigation results also reveal the influence of scattering mechanisms on the resistivity of a two-dimensional electron gas. The effects of the localization field correction also impact the electronic properties of the two-dimensional electron system in the quantum well structure. The results of this study are highly important for gathering information about layer structure for electronic applications.

The influence of the dense plasma environment on the energy levels and transition rates of H-like N⁶⁺, Ne⁹⁺, and Al¹²⁺ ions have been examined. The structural and spectral properties have been analyzed by employing the relativistic configuration interaction (RCI) technique using the ion sphere model as the modified interactive potential between the nucleus and the electron. It is observed that for every transition, the transition energies are red shifted. The plasma screening effect on weighted oscillator strengths has also been examined. Additionally, the ground state thermodynamic pressure within the ion sphere and the radial wavefunctions of the spectral electron for the various states of N⁶⁺, Ne⁹⁺, and Al¹²⁺ ions at plasma density 1 × 10²³ cm^–3 were also studied. The line intensity ratio has also been computed for the first two spectral lines: [1s_1/2 – 2p_3/2 (1–3)] and [1s_1/2 – 2p_1/2 (1–2)]. Our computed data exhibits a good quantitative agreement with the other results reported in the literature as well as with the experimental results reported in the National Institute of Science and Technology (NIST) database. The current findings will be helpful in laboratory and astrophysical plasma modelling and characterization of hot dense plasma.

The magnetic-field dependence of the superparamagnetic-blocking temperature T_B of systems of antiferromagnetically ordered ferrihydrite nanoparticles has been investigated and analyzed. We studied two powder systems of nanoparticles: particles of “biogenic” ferrihydrite (with an average size of 2.7 nm), released as a result of vital functions of bacteria and coated with a thin organic shell, and particles of biogenic ferrihydrite subjected to low-temperature annealing, which cause an increase in the average particle size (to 3.8 nm) and burning out of the organic shell. The character of the temperature dependences of magnetization, measured after cooling in a weak field, as well as the shape of the obtained dependences T_B(H), demonstrate peculiar features, indicating the influence of magnetic interparticle interactions. A detailed analysis of the dependences T_B(H) within the random magnetic anisotropy model made it possible to estimate quantitatively the intensity of magnetic particle–particle interactions and determine the magnetic anisotropy constants of individual ferrihydrite particles.

In several recent years, a significant progress has been made in atomistic simulation of materials, involving the application of machine learning methods to constructing classical interatomic interaction potentials. These potentials are many-body functions with a large number of variable parameters whose values are optimized with the use of energies and forces calculated for various atomic configurations by ab initio methods. In the present paper a machine learning potential is developed on the basis of deep neural networks (DP) for Al–Cu alloys, and the accuracy and performance of this potential is compared with the embedded atom potential. The analysis of the results obtained implies that the DP provides a sufficiently high accuracy of calculation of the structural, thermodynamic, and transport properties of Al–Cu alloys in both solid and liquid states over the entire range of compositions and a wide temperature interval. The accuracy of the embedded atom model (EAM) in calculating the same properties is noticeably lower on the whole. It is demonstrated that the application of the potentials based on neural networks to the simulation on modern graphic processors allows one to reach a computational efficiency on the same order of magnitude as those of the embedded atom calculations, which at least four orders of magnitude higher than the computational efficiency of ab initio calculations. The most important result is that about the possibility of application of DP parameterized with the use of configurations corresponding to melts and perfect crystals to the simulation of structural defects in crystals and interphase surfaces.

We proposed a theoretical model and a method for its approximate analysis for flows induced by a uniform rotating magnetic field in a channel filled with a nonmagnetic fluid with a ferrofluid layer injected into it. One end of the channel is assumed to be blocked (thrombosed). This study is aimed at the development of the scientific basis of the magnetically induced intensification of drug transport in blocked blood vessels.

A spectral quasilinear approach to the problem of TEM-Weibel instability in an anisotropic collisionless plasma is developed, which takes into account only the integral nonlinear interaction of modes through the joint variation of the spatially averaged particle velocity distribution induced by these modes. Within this approximation, a closed system of equations is obtained for the one- and two-dimensional evolution of spatial modes (harmonics) of the distribution function of particles and the electromagnetic field under conditions when the plasma anisotropy axis, the wave vector, and the magnetic field of the modes are orthogonal to each other. The numerical solution of this system of equations is compared with the available results of one-dimensional analytical quasilinear theory in the region of its applicability, as well as with the results of two-dimensional simulation by the particle-in-cell method, which also takes into account the direct four-wave interaction of modes. It is established that in the simplest cases of one-dimensional and axially symmetric two-dimensional problems for a bi-Maxwellian plasma, quasilinear phenomena play the leading role at a quite long stage of nonlinear development of turbulence. It is noted that at a later stage of decay of turbulence and in a more general formulation of the problem, in particular, in the presence of an external magnetic field, the direct nonlinear interaction of modes can manifest itself along with quasilinear phenomena. Based on the analysis carried out, the contribution of certain nonlinear effects to the evolution of the spatial spectrum of Weibel turbulence is revealed, and the properties of this turbulence are studied, including the self-similar character and qualitatively different stages of the dynamics of unstable modes.

Cylindrically bent diamond single-crystal plates have a great potential for creating energy dispersive spectrometers and focusing crystal monochromators. When they are designed, it is necessary to take into account the significant stresses that appear on bending the plates. The strain tensor and the elastic stress fields in a cylindrically bent single-crystal (110) diamond plate are calculated. The calculations are based on experimental data obtained by local Laue diffraction. The calculation results can be used to design new X-ray optical devices with the ability to control their parameters.

We describe a new method for the formation of optical ghost images, in which radiation in the object arm is detected by several detectors. The advantage of the proposed method is demonstrated, which is the smaller number of illumination patterns required for reconstructing the object image as compared to traditional schemes of ghost imaging. We propose variants of algorithms for measurement reduction to the form relevant to the imaging of the object of investigation, which are aimed at improvement of the performance of the computing component of the endoscope. The fiber-optic version of ghost imaging considered here is suitable for investigating hard-to-reach abdomens and organs of human organism, which permit the introduction of a thin fiber-optic bundle, thus extending its applicability as compared to traditional optic endoscopic methods.