Vol 163, No 6 (2023)
Articles
Effekty konechnogo vremeni v odinarnom i dvoynom komptonovskom rasseyanii
Abstract
The process of Compton scattering by a free electron with subsequent reemission of one or two photons is considered in the assumption of finite interaction time. The corresponding cross sections are obtained in the framework of relativistic quantum electrodynamics using a modified form of fermion propagator with complex transmitted momentum. It is shown that finite time effects can be observable at sufficiently low energies of scattered photons. The proposed method also regularizes arising infrared divergence in the cross section of the double Compton effect. Possible experimental verification of considered theoretical approach is discussed.
Ionization transition rates in the intermediate regime of the Keldysh parameter for a (0,1)*LG spiral amplitude modulated laser field
Abstract
The mechanisms of the tunnel and multiphoton ionization transitions of hydrogen-like atoms and noble gas atoms are discussed. Atoms potassium and argon, with ionization energy of 4.34 and 15.76 eV, were chosen as the target. The atoms are exposed to Ti:Sapphire, (0,1)*LG, spiral amplitude modulated, laser beam at λ = 800 nm wavelength in a broad intensity range 1012 to 1015 W/cm2. The computational approach to describe tunnel and multiphoton processes was based on using the ADK theory. Stark and ponderomotive effects are also included to study their influence on the transition rate. Obtained results show that, for the lower γ values, the contribution of multiphoton ionization was less significant than the tunnel ionization contribution. In comparison, for higher γ values, multiphoton ionization dominated over tunnel ionization in a total transition rate. It is found that, in this particular case of spiral amplitude modulated mode, the intermediate regime, where both processes equally contribute, strongly depends on the atom selection and laser field intensity. Ionization in the intermediate regime occurs for γ ≈ 10 and 12 for low laser intensities, as γ ≈ 2 and 2.5 for the higher values, in the case of potassium and argon respectively. Our analysis indicated that the Stark and ponderomotive effects have a significant influence on the total transition rate. It is shown that these effects decrease the transition rate value and move the intermediate regime’s position toward lower values of the γ parameter, mainly in the case of higher laser field intensity.
Kompaktnyy generator opticheskoy chastotnoy grebenki na osnove lazernogo dioda s raspredelennoy obratnoy svyaz'yu i vysokodobrotnogo opticheskogo mikrorezonatora
Abstract
Optical frequency combs are a unique tool for fundamental metrology and spectroscopy; they are also used in various applications. High-Q microcavities are promising for generating coherent frequency combs. An approach based on the pulling effect, which is well-known in radiophysics, is proposed. The use of this effect makes it possible to develop a compact, commercially available source of an optical comb and microwave radiation based on a compact distributed-feedback laser diode with a low output power of 6 mW and a microcavity based on magnesium fluoride with a Q factor of 109. Different generation modes of optical frequency combs, corresponding to different numbers of generated solitons at a pump power of 6 mW and a wavelength of 1550 nm, as well as spectrally pure microwave radiation at a frequency of 12.94 GHz, are demonstrated.
Caustic-like Structures in UHECR Flux after Propagation in Turbulent Intergalactic Magnetic Fields
Abstract
UHECR propagation in a turbulent intergalactic magnetic field in the small-angle scattering regime is well understood for propagation distances much larger than the field coherence scale. The diffusion theory doesn’t work and unexpected effects may appear for propagation over smaller distances, from a few and up to 10–20 coherence scales. We study the propagation of UHECRs in this regime, which may be relevant for intermediate mass UHECR nuclei and nG scale intergalactic magnetic fields with 1 Mpc coherence scale. We found that the trajectories form a non-trivial caustic-like pattern with strong deviation from isotropy. Thus, measurements of the flux from a source at a given distance will depend on the position of the observer.
Vliyanie primesey na adsorbtsiyu kisloroda na poverkhnosti Ti5Si3(0001)
Abstract
The influence of simple and transition metal impurities, as well as interstitial impurities (B, C, and N), on the oxygen adsorption on the Ti5Si3 titanium silicide surface has been studied using the of projector augmented wave method within the electron density functional theory. It has been shown that titanium-substituting impurities belonging to the latter halves of the 3d–5d periods cause most significant changes in the adsorption energy. In addition, simple metals and interstitial impurities reduce the oxygen–surface interaction. By analyzing local electron densities of states, charge density difference distribution, charge transfer, and the overlap population of oxygen bonds to nearest-neighbor atoms, we have revealed special aspects of impurity influence on chemical bonding between the titanium silicide surface and oxygen. Factors responsible for an increase/decrease in the adsorption energy of oxygen on the doped surface are discussed. A correlation between the change in adsorption energy and the electronegativity of impurities has been found.
Akusticheskie solitony v gelikoidakh i spiral'nykh nanolentakh grafena
Abstract
The dynamics of local regions of longitudinal compression in graphene helicoids and spiral carbon nanoribbons has been numerically simulated. It has been shown that a supersonic acoustic soliton can constantly move without radiation of phonons only in helicoids with transverse radius R < 0.62 nm. Dimensionless velocity s of the soliton in this case falls into the interval 1.0–1.4. In larger radius helicoids and all spiral carbon nanoribbons, the motion of a soliton-like excitation is always accompanied by the intense radiation of phonons (the more the size of the spiral structure, the more intense the radiation).
Antiferromagnitnaya model' Pottsa na ob\"emno-tsentrirovannoy kubicheskoy reshetke
Abstract
We have studied phase transitions and thermodynamic properties of the antiferromagnetic Potts model with number of spin states q = 3 on a body-centered cubic lattice by the Monte Carlo method. Investigations have been performed with account for exchange interactions J1 and J2 between the first and second nearest neighbors. The phase transition order has been analyzed using the histogram method. It is found that in this model with J2 = 0, a second-order phase transition is observed. It is concluded that the inclusion of the interaction between the second nearest neighbors changes the type of the phase transition.
Narushenie kiral'noy simmetrii i neodnorodnye sostoyaniya v deformirovannykh ferromagnetikakh
Abstract
The general form of chiral terms associated with deformation of a ferromagnet is determined. The possibility of a transition from the helical state to the vortex state is demonstrated for a ferromagnetic rod subjected to elastic torsional strain. In the case of a single screw dislocation, the formation of the skyrmion state due to elastic strains and the helical distribution of magnetization induced by strains in the dislocation core is indicated. The conditions in which a transition from one chiral magnetization distribution to another distribution in an ensemble of identical dislocations are determined.
K teorii nukleatsii ionnykh soley iz vodnykh rastvorov
Abstract
The theory of nucleation of ionic salts from aqueous solution is critically analyzed and further developed in two limiting cases of sparingly and highly soluble strong electrolytes. In the case of sparingly soluble colloids with a relatively large screening length (compared to the radius of the critical nucleus), the classical nucleation theory is modified by taking into account the influence of the critical nucleus charge on the nucleation rate, which was disregarded in earlier models. In the opposite limit of highly soluble colloids which are characterized by a relatively small screening length, the influence of the critical nucleus charge on the nucleation rate can be neglected with good accuracy. However, the discrepancy with earlier models, mainly related to the value of the pre-exponential factor, can reach several orders of magnitude.
Indutsirovannyy zaryad v dikhal'kogenidakh perekhodnykh metallov
Abstract
We investigate the asymptotic behavior of the charge density ρind(r) induced by an azimuthally symmetric potential well of finite radius R. The analytic expression for ρind(r) at the distances r ≫≫ R is obtained. It is shown that, for a wide range of potential parameters, the induced charge density can be represented as ρind(r) = F(r)LV, where F(r) depends only on distance and LV depends on the parameters of the potential. We also investigate the behavior of the induced charge density when the potential well depth close to the critical value.
Vliyanie tolshchiny inkapsuliruyushchikh sloev na kachestvo geterostruktur na osnove MoSe2
Abstract
The dependence of the width of exciton and trion photoluminescence lines in MoSe2 monolayers on the thickness of hexagonal boron nitride encapsulating layers has been investigated. The possibility of variation of the exciton photoluminescence linewidth due to the interaction of excitons with the modes of resonator cavities made up of a silicon substrate and a boron nitride top layer has been checked. This interaction may significantly change the photoluminescence linewidth owing to the Parcell effect. Measurements taken of samples with different thicknesses of the bottom and top boron nitride layers have not revealed any influence of the Parcell effect on the linewidth. It has turned out however that the linewidth narrows by several times with increasing boron nitride bottom layer thickness from 10 to 100 nm and reaches 2 meV at a thickness of 100 nm. Supposedly, such narrowing of the photoluminescence line is associated with a decrease in the density of submicron bubbles, which takes place at longitudinal stress relaxation in the thicker layer of boron nitride.
Dipol'naya plazmonnaya moda v nanorazmernykh poluprovodnikovykh kvantovykh tochkakh tipa "yadro-obolochka" s geteroperekhodom vtorogo roda
Abstract
Excited states of nanosize two-component semiconductor core–shell crystals with a type II heterojunction are analyzed. It is demonstrated that the dipole plasmon resonance dominates in their photoabsorption spectra. It is found that the variation of the potential barrier height between the core and the shell in a comparatively narrow range leads to a fundamental change in the form of the collective mode from the surface plasmon resonance typical of the photoabsorption spectra of conducting nanosize particles to the rotational plasmon mode, for which only angular degrees of freedom are excited.
Generatsiya elektricheskogo polya v pylevoy plazme
Abstract
A nonuniform dusty plasma, micrometer-size particles or microdroplets of which are located in a dense gas or in atmospheric air, is excited by an energy pulse leading to the weak ionization of the gas. As a result, the particles charge through the attachment of gaseous ions to them. The stability of dusty plasma is determined by the low mobility of charged microparticles. The conditions under which the separation of negative and positive charges occurs in a dusty plasma with the creation the electric field are considered. The criteria are presented for the generation of atmospheric electricity in a dense cloud as a result of the gravitational falling of charged water microdroplets in the atmosphere, the weak ionization of which occurs under the action of cosmic rays. It is shown that this is possible only under a nonuniform space distribution of water microdroplets in the cloud. The peculiarities of a dusty plasma are considered. This plasma exists in Saturn’s rings and in the flow of coal combustion products, as well as in the dusty atmosphere of a coal mine.
Korrelyatsii zavikhrennosti vnutri kogerentnogo vikhrya
Abstract
We investigate fluctuations of vorticity inside a coherent vortex generated by the inverse energy cascade in two-dimensional turbulence. Temporal and spatial correlations can be characterized by the pair correlation function. The interaction of fluctuations leads to a nonzero third moment of vorticity. We analyze the pair correlation function and the third moment using a model in which the pumping is short-correlated in time and derive explicit expressions for the Gaussian spatial correlation function for the pumping force.