稀土和锕系化合物中重费密子行为

本文采用周期Anderson哈密顿量研究了稀土和锕系化合物中的重费密子行为。对f电子间库仑关联项做了平均场近似并引入自能项反映多体作用的效应。对自能项采用了单格位近似,在准粒子表象中讨论了系统的性质,通过对f电子平均占据数的自洽计算,得到了准粒子有效质量,讨论了形成重费密子的条件,以及相应的磁性的变化,并做了数值计算。所得结果与最近的实验进行了比较。 关键词：     

Zitterbewegung in thin-film topological insulators in the presence of a terahertz pulse

Zitterbewegung (trembling motion) in thin-film topological insulators in the presence of a terahertz pump pulse has been considered. An analytical expression for the electric current density has been derived, which describes the electric current induced by the motion of an electron wave packet. The electron subsystem has been considered in the long-wavelength approximation, and the electromagnetic field has been described classically in the constant-pump approximation. The numerical analysis of the results has been carried out.     

Quasi-phase-matched modulation instability in birefringent fibers

The phase-sensitive nature of polarization modulation instability has been demonstrated in optical fibers whose birefringence has been manipulated to generate phase mismatches. Quasi-phase-matched modulation instability has been demonstrated, and the gain of the quasi-phase-matched sidebands has been investigated. The results are in good agreement with experiment.     

Extremely short optical pulses in strained graphene in terms of the gauge theory

Evolution of optical pulses, which propagate in strained graphene, has been investigated. The effective wave equation for the vector potential of the electromagnetic field has been derived. The tensile strain of graphene layers has been described using the effective vector-potential in terms of the gauge theory. The numerical solution of the derived wave equation has been presented and the dependence of the pulse strength and shape on the magnitude of the external strain has been analyzed.     

Bistability of a “chevron” smectic C* liquid crystal in an external electric field

The system of nonlinear equations describing a surface-stabilized ferroelectric smectic C* liquid crystal in the chevron geometry has been investigated by numerical methods in the framework of the continuum model of liquid crystals. Stable orientational and structural configurations have been studied, and the results obtained have been compared with those derived using simplified models. The height of the potential barrier separating two stable configurations has been determined, and the transition between them under the action of the external electric field has been examined. It has been demonstrated that this effect has a threshold character. The dependence of the threshold field on the film thickness has been analyzed.     

Current-induced spin polarization of holes in tellurium

The current-induced optical activity in a tellurium single crystal has been experimentally investigated in the mid-infrared spectral region. The phenomenological theory of the current-induced optical activity has been considered and the microscopic mechanism of this phenomenon has been described. The dependence of the degree of spin polarization of holes in tellurium on the electric current density has been determined. An approximate analytical expression relating the current-induced optical activity to the degree of spin polarization of holes has been obtained.     

Structure of organosilicon dendrimers of higher generations

The structure of organosilicon dendrimers of the ninth generation with the four-functional core and butyl terminal groups has been studied by small-angle neutron scattering. It has been demonstrated that the dendrimers are monodisperse objects with an anisometric shape. The partial volume and the average scattering density have been determined using the contrast variation technique. It has been shown that the dendrimers under study are identical in overall sizes and scattering density distribution. It has been revealed that 20% of the overall volume of the dendrimer is accessible for the penetration of the solvent. The distribution of the scattering length density in the dendrimers has been simulated and reconstructed using the Monte Carlo method, and a change in the excluded volume for different contrasts has been revealed. The specific features of the spatial structure of organosilicon dendrimers of higher generations have been discussed.     

Viscosity and electric properties of water aerosols

The flow of water mist in a narrow duct has been studied experimentally. The profile of the velocity of drops has been measured, and the viscosity of the mist has been calculated using the Navier–Stokes equation. It has been found that at low gradients of the rate of shear the viscosity of the mist can exceed that of clean air by tens and even hundreds of times. The electric charge of the drops has been measured. It has been found that the viscosity of the mist differs from that of clean air at gradients of the rate of shear that are less than the frequency of the establishment of electric equilibrium between the drops. A comparative analysis of the viscosities of the mist and a drop cluster has been carried out, and the dependence of the viscosity of the water aerosol on the radius and the charge of the drops has been predicted. The possible role of aerosols that contain submicron drops in the known “clear air turbulence” problem has been shown.     

BEPCⅡ国产500 MHz超导腔运行综述

北京正负电子对撞机二期(BEPCⅡ),国产500 MHz超导腔经过紧张的安装调试于2017年10月正式投入带束流运行。首先对此国产超导腔两次降温调试的相关参数进行了监测和对比分析;其次研究了通过高功率老练的方法改善超导腔的品质因数,并实时监测超导腔老练过程中的辐射剂量;最后对超导腔的带束流运行情况进行了介绍分析。结果表明:BEPCⅡ国产500 MHz超导腔虽然放置了6年,但是状态良好,通过高功率老练能够降低超导腔的辐射剂量,改善其性能,完全满足束流运行要求。     

Specific features of the structure of detonation nanodiamonds from results of electron microscopy investigations

The experimental results of a comprehensive investigation of the structure of detonation synthesis nanodiamonds by electron microscopy methods have been presented. The morphology of diamond nanoparticles has been investigated and the microdiffraction patterns have been analyzed. The method of characteristic fast electron energy loss spectroscopy in transmission electron microscopy has been used. The local density of structural components of a nanodiamond (diamond core and fullerene-like shell) has been obtained. The shape of the shell surrounding the nanocrystal has been determined using model calculations. A hypothesis explaining the charging of the nanodiamond surface has been proposed.     

Mean-field approximation for the potts model of a diluted magnet in the external field

The Potts model of a diluted magnet with an arbitrary number of states placed in the external field has been considered. Phase transitions of this model have been studied in the mean-field approximation, the dependence of the critical temperature on the external field and the density of magnetic atoms has been found, and the magnetic susceptibility has been calculated. An improved mean-field technique has been proposed, which provides more accurate account of the effects associated with nonmagnetic dilution. The influence of dilution on the first-order phase transition curve and the magnetization jump at the phase transition has been studied by this technique.     

Generalized classical mechanics

Generalized classical mechanics has been introduced and developed as a classical counterpart of the fractional quantum mechanics. The Lagrangian of generalized classical mechanics has been introduced, and equation of motion has been obtained. Lagrange, Hamilton and Hamilton-Jacobi frameworks have been implemented. Oscillator model has been launched and solved in 1D case. A new equation for the period of oscillations of generalized classical oscillator has been found. The interplay between the energy dependency of the period of classical oscillations and the non-equidistant distribution of the energy levels for fractional quantum oscillator has been discussed. We discuss as well, the relationships between new equations of generalized classical mechanics and the well-known fundamental equations of classical mechanics.     

Observation of bistability in a CO2 laser exhibiting passive Q-switching

Optical bistability has been investigated experimentally in a CO₂ laser containing CF₃Br as a saturable absorber. The frequency dependence of the hysteresis cycle of this laser containing a saturable absorber (LSA) has been studied. It has also been shown that the LSA may undergo simultaneously hysteresis cycles and Q-switching. The phase diagram of the LSA has been extended towards regions where this behavior has been observed.     

The phase transition in annealed mechanically alloyed Fe - Cu

Using M?ssbauer spectra and x-ray diffraction patterns, annealed mechanically alloyed Fe - Cu has been investigated in this paper. It is found that in [Formula: see text], after it has been milled, fcc-Cu has transformed into bcc-Cu, and some Cu atoms have diffused into the Fe. After the alloy has subsequently been annealed, it is found that bcc-Cu has transformed back into fcc-Cu, while the Cu atoms in the Fe have been separated. In [Formula: see text], after being milled, an fcc-Fe-rich phase has been formed, and after the alloy has subsequently been annealed, this has transformed back to bcc-Fe. The shorter the milling time and the higher the annealing temperature, the faster the transformation. In [Formula: see text], after it has been annealed, the fcc-Fe-rich phase has transformed to bcc-Fe also, and the fcc-Cu-rich phase remains when the annealing temperature increases. All of these results show that the fcc-Fe-rich phase in the milled samples is a metastable phase - it will transform to stable bcc-Fe when it is annealed - while the long-milling-product fcc-Cu-rich phase is a stable phase.     

Deflagration-to-detonation transition in spiral channels

The deflagration-to-detonation transition in hydrogen–air mixtures that fill spiral channels has been studied. A spiral channel has been produced in a cylindrical detonation tube with a twisted ribbon inside. The gas mixture has been ignited by means of a spark gap switch. The predetonation distance versus the twisted ribbon configuration and molar ratio between the gas mixture components has been determined. A pulling force exerted by the detonation tube after a single event of hydrogen–air mixture burnout has been found for four configurations of the twisted ribbon. Conditions under which the use of a spiral tube can be more effective (increase the pulling force) have been formulated.     

Approximate radiative solutions of the Einstein equations

In this paper the external field of a bounded source emitting gravitational radiation has been considered. A successive approximation method has been used to integrate the Einstein equations in Bondi's coordinates. A method of separation of angular variables has been worked out and the approximate Einstein equations have been reduced to the key equations (3.8)–(3.10). The losses of mass, momentum, and angular momentum due to gravitational multipole radiation have been found. It has been demonstrated that in the case of proper treatment a real mass occurs instead of a mass aspect in a solution of the Einstein equations. In Appendix C Bondi's news function has been given in terms of sources.     

Influence of density fluctuations on the equation of state

The influence of inhomogeneity of particle density on the equation of state has been considered in the approximation of homogeneous fluctuations. The formula for the relative mean square fluctuation has been derived taking into account intermolecular interaction. It has been shown that the density fluctuations cannot be neglected near the coexistence curve. This curve has been obtained without recourse to the Maxwell construction; unphysical parts of the van der Waals isotherms in fact never appear in the theory. Experimental parameters have not been used.     

Surfatron acceleration in electromagnetic waves with a low phase velocity

The possibility of unlimited surfatron acceleration of nonrelativistic charged particles by slow electromagnetic waves has been revealed. The capture into such an acceleration regime has been described. The region of the parameters in which the effect of the capture and acceleration exists has been considered. The contribution of this mechanism to an increase in the energy of charged particles in the Earth’s magnetosphere has been estimated.     

Influence of the surface curvature of carbon nanotubes on their conductivity in the dirac approximation

A method of surface curvature of carbon nanotubes has been proposed for quantitative estimation of the longitudinal conductivity of nanotubes. A dispersion relation for the electron spectrum of single-walled carbon nanotubes has been obtained analytically. The change in the zone structure of nanotubes of various types and diameters caused by taking into account the surface curvature has been analyzed. The temperature dependence of the longitudinal component of conductivity with allowance for the surface curvature for a series of nanotubes has been calculated. The comparison with the conductivity of a plane graphene has been performed. It has been shown that, in zig-zag tubes, the correction of the conductivity for the surface curvature decreases with an increase in temperature as well as with an increase in the radius of curvature.     

Study of the interaction of a palladium nanocontact with a hydrogen molecule

The interaction of a palladium nanocontact with a hydrogen molecule has been studied using molecular static method. The influence of impurity on the atomic structure and mechanical properties of the palladium nanocontact has been demonstrated. The characteristic interatomic distance has been determined in this contact. It has been found that the hydrogen molecule dissociates by interaction with nanocontact atoms.