Monte Carlo simulation of radiative heat transfer and turbulence interactions in methane/air jet flames

A Photon Monte Carlo method combined with a composition PDF method is employed to model radiative heat transfer in combustion applications. Turbulence-radiation interactions (TRIs) can be fully taken into account using the proposed method. Sandia's Flame D and artificial flames derived from it are simulated and good agreement with experimental data is found. The effects of different TRI components are investigated. It is shown that, to predict the radiation field accurately, emission TRI must be taken into account, while, as expected, absorption TRI is negligible in the considered nonsooting methane/air jet flames if the total radiation quantities are concerned, but non-negligible for evaluation of local quantities. The influence of radiation on the turbulent flow field is also discussed.     

Nonlinear resonances in the near-field interaction between atoms

It has been shown that nonlinear near-field optical resonances occur in diatomic nanostructures consisting of identical or different two-level atoms in the presence of a radiation field when the dipole-dipole interaction is taken into account. The frequencies of these resonances depend strongly on the intensity of the external optical radiation, on the initial conditions, on the polarization of the external field with respect to the axis of the nanostructure, and on the interatomic distance. The interatomic interaction is taken into account beyond perturbation theory. For this reason, the effective polarizabilities of the atoms of the nanostructure are expressed in terms of the polynomials of both the interatomic distance and the electric field strength of the external optical wave. A “falling tower” effect that is caused by the nonlinear behavior of the local dipole moments of atoms in the nanostructure is predicted.     

Observation of a turbulence-induced large scale magnetic field

An axisymmetric magnetic field is applied to a spherical, turbulent flow of liquid sodium. An induced magnetic dipole moment is measured which cannot be generated by the interaction of the axisymmetric mean flow with the applied field, indicating the presence of a turbulent electromotive force. It is shown that the induced dipole moment should vanish for any axisymmetric laminar flow. Also observed is the production of toroidal magnetic field from applied poloidal magnetic field (the omega effect). Its potential role in the production of the induced dipole is discussed.     

Temporal dependence of the dipole moment of long-wavelength forms of n-dimethylaminobenzonitrile

The temporal dependences μ_e(t) of the dipole moment of n-dimethylaminobenzonitrile excited to different states by quanta with different energies are evaluated based on the experimental correlation functions of the shift of instantaneous spectra. It is found that, upon excitation into the maximum of absorption, the relaxation changes of the spectra are accompanied by an increase in the dipole moment from 9 D in the Franck-Condon state to 16 D in the stationary state. At the same time, the excitation of luminescence at the red absorption edge by radiation at 403 nm leads to a decrease in the range of variation of the dipole moment. In this case, the initial value of the dipole moment amounts to 14 D and, during the lifetime of the excited state, it increases to 17 D. This indicates that the nature of the radiation excited at the wavelength 403 nm is directly related to internal charge transfer states of n-dimethylaminobenzonitrile.     

Spectral polarization features of the macroscopic manifestation of parity violation in gaseous media

A formalism based on macroscopic Maxwell equations is developed for the case of media with violations of the space symmetry and time reversal. It is demonstrated that the parity violation in a medium is equivalent to the manifestation of spatial dispersion and natural optical activity. The proposed formalism makes it possible to uniquely calculate the macroscopic parameters of equations in terms of the microscopic theory. The parameters of gyrotropy and dichroism of a gaseous medium are determined within a model describing an interaction of resonance radiation with transitions to states that have different parities and are mixed by a weak interaction of an electron with the nucleus of the atom. It is established that, in the range of the resonance with a magnetic dipole transition, the effect of parity violation is enhanced as a result of the considerable difference between the natural broadenings of the electric and magnetic dipole transitions. This enhancement is suppressed when the dominant Doppler broadening of the atomic transitions is taken into account. It is shown that, owing to the unitarity of the weak interaction, the effects of parity violation are alternating functions of the radiation frequency and are integrally absent in the entire spectrum.     

Bloch–Siegert shift in application to the astrophysical determination of the fundamental constants variation

We have evaluated the Bloch–Siegert shift for the different values of magnetic field?s strengths defined at astrophysical conditions, i.e. when the stars with the strong surface magnetic fields are taken as a powerful pumping source of radiation. It is found that the additional shift of resonant frequency should be taken into account in the search for the time variation of the fundamental constants. The main conclusion is that the influence of the electromagnetic field should be considered carefully in each special case of the corresponding frequency determination.     

Light—induced nonlinear effects of dispersion relation of ultracold Bose gas

We have investigated the optical properties of Λ-configuration ultracold dense Bose gas interacting with two laser pulses, which usually result in electromagnetically induced transparency. With the nonrelativistic quantum electrodynamics and taking into account the atomic dipole－dipole interaction and local field effect, we have derived the Maxwell－Bloch equations of the system. The dispersion relation of an ultracold Bose gas has been obtained and the light-induced nonlinear effects have been analysed. The light-induced nonlinear effects are different from the effects induced by two-body collision of Bose－Einstein condensation atoms which have a frequency shift of transparent window.     

Near-field effect in a superthin film of resonance atoms

A boundary-value problem of nonlinear resonance optics in the interaction of intense light with a superthin film of two-level atoms is solved. In solving this boundary-value problem, the authors draw on the idea of a discrete-continuous system in which the atoms are distributed in a discrete manner in the vicinity of the point of observation. It is shown that detailed account of the dipole field leads to a near-field effect both inside the film and outside it in the near zone with respect to outer film surfaces. Various properties of the near-field effect in stationary irradiation of the film with quasi-resonance radiation with allowance for a resonance shift are investigated. It is shown, in particular, that, in the near zone, there is a nonexponential dependence of the fields of reflected and transmitted waves on the coordinate of the point of observation. Ul'yanovsk State University, 42, L. Tolstoi St., Ul'yanovsk, 432700, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 236–246, March–April, 1998.     

Effect of multiple reemission on the shape of the magnetic-depolarization contour

It is shown that in order to describe the level-intersection effect, taking into account repeated emission, it is necessary to solve the boundary problem. The passage of resonant polarized radiation through a plane-parallel layer under a magnetic field is considered. The method of invariant merging [8] is used to construct equations for the reflection and transmission functions. Reciprocity principles are established.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 25–30, December, 1976.     

The displacement-thickness theory of trailing edge noise

The problem of estimating the sound generated by turbulent boundary layer flow over the edge of a rigid half-plane is re-examined. A theory is proposed which is strictly valid at low Strouhal numbers based on boundary layer width, wherein the flow inhomogeneities are specified in terms of the fluctuations in the boundary layer displacement thickness. This enables account to be taken of changes in the properties of the turbulence as it translates past the edge, which are shown to result in the appearance of an acoustic dipole whose axis is aligned with the mean flow, and which supplements the radiation field predicted by conventional methods [1,2]. Detailed comparison is made with acoustic and surface pressures which are calculated according to the evanescent wave theory of edge noise [3–5].     

Quadrupole radiation from terahertz dipole antennas

We report what is to our knowledge the first detailed investigation of the polarization state of radiation from lens-coupled terahertz dipole antennas. The radiation exhibits a weak but measurable component that is polarized orthogonally to the orientation of the emitter dipole. The angular radiation pattern of this cross-polarized emission reveals that it is quadrupolar, rather than dipolar, in nature. One can understand this result by taking into account the photocurrent flowing in the strip lines that feed the dipole antenna. A Fresnel-Kirchhoff scalar diffraction calculation is used for calculating the frequency-dependent angular distribution of the radiation pattern, providing satisfactory agreement with the measurements.     

Optical size resonances in nanostructures

The existence of optical size resonances in atomic nanostructures is proved. The properties of optical size resonances strongly depend on the interatomic distances and on the polarization of an external radiation field. The properties of linear and nonlinear size resonances are considered in the case of two-dimensional nanostructures. The linear optical size resonances are described based on a closed system of equations for dipole oscillators and nonlocal field equations taking into account the dipole-dipole interactions of atoms in the radiation field. Using a stationary solution to these equations, it is demonstrated that two isotropic atoms with definite intrinsic frequencies form an anisotropic system in the radiation field, possessing two or four size resonances depending on whether the component atoms are identical or different. The nanostructure composed of two different atoms possesses two size resonances with positive dispersion and two other resonances with negative dispersion. The frequencies of the size resonances significantly differ from the intrinsic frequencies of isolated atoms entering into the nanostructure. By changing the angle of incidence of the external wave, it is possible to excite various size resonances. The properties of nonlinear optical size resonances excited by an intense radiation field were theoretically and numerically studied using the modified Bloch equations and nonlocal field equations. Dispersion relationships for the nonlinear resonances were derived and the inversion properties of atoms in the nanostructure were studied for various polarizations of the external optical wave.     

Dipole emission of a nanostructure system composed of two atoms and dimensional resonances

A stationary solution is obtained for the joint system of equations for atomic and field variables for two different atoms with dipole-dipole interaction in the radiation field taking into account the common radiative friction. The atoms are treated as an Lorentz oscillator with one isolated resonance. The interaction of atoms in the radiation field forms four dimensional resonances at frequencies that are substantially different from the natural frequencies of isolated atoms. Two of the four dimensional resonances are characterized by negative dispersion, and the intensity of dipole emission at these frequencies may be increased with respect to the intensity of emission at the frequencies of natural atomic resonances by a factor of about 10¹².     

Redistribution of energy flow in a material due to damping

The field lines of energy flow of the radiation emitted by a linear dipole in free space are straight lines, running radially outward from the source. When the dipole is embedded in a medium, the field lines are curves when the imaginary part of the relative permittivity is finite. It is shown that due to the damping in the material all radiation is emitted in directions perpendicular to the dipole axis, whereas for a dipole in free space the radiation is emitted in all directions except along the dipole axis. It is also shown that some field lines in the near field form semiloops. Energy flowing along these semiloops is absorbed by the material and does not contribute to the radiative power in the far field.     

等离子体中相对论电子的同步曲率辐射特性研究

根据同步曲率辐射理论推导了在等离子体环境中,不同磁场条件下的相对论性电子的吸收系数和发射系数表达式，计算了电子的发射强度，并且在此基础上研究了同步曲率辐射机制的脉泽效应.研究了两种磁场位型，第一种是强度均匀但弯曲的磁场，第二种是偶极磁场，结果发现了一些偶极磁场下特有的辐射特性.考虑到在天体的环境下电子具有的不同的能谱分布，分别选用了三种典型的能谱分布(幂率分布，高斯分布，热分布)进行了研究，通过计算负吸收和脉泽放大效应在发射强度上的表现后， 发现在某些天体物理环境中，同步曲率辐射在等离子体中的确存在脉泽放大效应.这些研究结果对太阳系中行星外层辐射的研究和宇宙中的射电高亮温度等问题的研究可能提供有益的帮助. 关键词： 同步曲率辐射 负吸收 脉泽效应     

Atomic beam focusing by a near-field atomic microlens

Atomic beam focusing by an atomic microlens formed by the optical field diffracted from a circular aperture in a metallic screen is considered for an aperture diameter smaller than the wavelength of the field. Analytic expressions are derived for the dipole gradient force acting on an atom in the field of diffracted radiation. It is shown that the action of the gradient force makes it possible to focus the atomic beam into a spot with a diameter on the order of a few nanometers. Numerical estimates are obtained for the focusing properties of the atomic microlens in the model describing the dipole interaction of Rb atoms with laser radiation in the vicinity of the D line.     

高能等离子体入射对磁场膨胀影响的模拟研究（已撤稿）

采用三维模型，使用混合网格质点法对等离子体入射偶极子磁场产生的磁场膨胀进行数值模拟.在模拟中考虑了高能等离子体注入两种不同类型磁场的情况：等离子体注入没有背景磁场的偶极子磁场和等离子体注入有背景磁场的偶极子磁场.研究表明背景磁场的存在不仅改变了粒子的分布，还改变了磁场膨胀的程度.还研究了注入的高能等离子体的速度对磁场膨胀的影响，结果表明入射的高能等离子体速度越大，磁场膨胀的程度就越大.对于低的入射速度，入射粒子在偶极子磁场中的回旋半径与偶极子磁场的特征长度相比较小，粒子被磁场束缚，对偶极子磁场的影响可以忽 关键词： 网格质点法 磁场膨胀 偶极子磁场     

与双模光场作用的Λ型三能级原子及其二能级近似

从多能级原子与多模光场的相互作用哈密顿量出发,导出了Λ型三能级原子与双模光场的相互作用哈密顿量．在大失谐条件下将其化成等效的二能级形式－双模喇曼耦合模型．提出了该模型的一个改进型等效哈密顿量．该哈密顿量由两部分构成：一部为通常所谓的等效哈密顿量,另一部分描述原子能级的动态斯塔克移动．研究表明,在双模喇曼耦合模型的研究中,只考虑前者是不够的,还必须考虑后者．最后,我们研究了该系统中原子的动力学行为,发现崩塌－复苏的数目、崩塌时间和复苏时间均呈现新的特性．     

与双模光场作用的Λ型三能级原子及其二能级近似

从多能级原子与多模光场的相互作用哈密顿量出发,导出了Λ型三能级原子与双模光场的相互作用哈密顿量。在大失谐条件下将其化成等效的二能级形式-双模喇曼耦合模型。提出了该模型的一个改进型等效哈密顿量。该哈密顿量由两部分构成:一部为通常所谓的等效哈密顿量,另一部分描述原子能级的动态斯塔克移动。研究表明,在双模喇曼耦合模型的研究中,只考虑前者是不够的,还必须考虑后者。最后,我们研究了该系统中原子的动力学行为,发现崩塌-复苏的数目、崩塌时间和复苏时间均呈现新的特性。     

Radiative Energy Shifts of an Atom Coupled to the Derivative of a Scalar Field near a Reflecting Boundary

We study the radiative energy level shifts of a two-level atom in dipole coupling to the derivative of a massless scalar quantum field in a spacetime with a perfectly reflecting boundary, and calculate the contributions of vacuum fluctuations and radiation reaction to the level shift. It is found that the energy level shift of the excited state is an oscillating function of the atom＇s distance from the boundary and it can either be positive or negative, while that of the ground state is always positive. The most remarkable feature is that the energy level shift of the ground state behaves like 1/z^4 when the atom＇s distance from the boundary, z, is very large as compared to the transition wavelength of the atom, while it behaves like 1/z^3 when z is very small