On the entropy of radiation reaction

The inexorable development of ever more powerful laser systems has re-ignited interest in electromagnetic radiation reaction and its significance for the collective behavior of charged matter interacting with intense electromagnetic fields. The classical radiation reaction force on a point electron is non-conservative, and this has led some authors to question the validity of methods used to model ultra-intense laser–matter interactions including radiation reaction. We explain why such concern is unwarranted.     

复燃对液体火箭尾焰红外辐射特性的影响

为了定量研究复燃对液体火箭尾焰红外辐射特性的影响,建立了一个可以计算液体火箭尾焰复燃流场和红外辐射特性的模型.首先,使用FLUENT软件计算液体火箭尾焰复燃流场,其中尾焰中的复燃反应使用有限速率化学反应模型计算;然后,使用基于HITEMP数据库的窄带模型计算尾焰内气体的辐射参量;最后,使用有限体积法求解尾焰中的辐射传输方程.通过比较该模型计算的Titan IIIB尾焰光谱辐射强度与(美国)国家航空航天局公布结果的一致性,证明了该模型的正确性.最后,利用该模型计算了复燃对某液体火箭尾焰光谱和波段红外辐射强度的影响,结果表明,复燃反应可以显著增加尾焰红外光谱辐射强度,在2.5~3.0 μm和4.2~4.7 μm两个主要辐射波段平均辐射强度的增加比例分别达到了30.8%和28.3%,所以,在计算液体火箭尾焰准确的红外辐射特性时,需要考虑复燃的影响.     

化学反应机理对液氧煤油发动机尾焰红外特性影响研究

提出了一种液氧煤油发动机尾焰红外辐射特性计算方法,首先采用计算流体力学软件对液氧煤油发动机内流场进行计算,然后以获得喷管喉部截面参数作为入口边界条件计算发动机尾焰流场,最后以发动机尾焰流场参数分布为基础,采用有限体积法对发动机尾焰红外光谱辐射特性和成像特性进行计算,并对比验证了模型和方法的准确性。在此基础上,研究了化学反应机理和复燃反应过程对尾焰红外辐射特性影响。结果表明,采用多步化学反应能够准确模拟液氧煤油发动机内流场,温度相比热力学计算大3.34%,压力相比试车测量大2.89%;考虑复燃反应使尾焰红外辐射强度增强显著,在采用单步化学反应和多步化学反应两种工况下2~5波段红外辐射强度分别增大50%~100%和150%~170%,但不会影响尾焰红外光谱辐射特性和红外总辐射强度随探测角变化趋势;采用单步化学反应和多步化学反应都能够获得清晰结构的红外成像图像,但是前者2~5尾焰红外辐射强度要比后者增大90%~190%,且两种工况下发动机尾焰红外光谱辐射特性差别很大,尾焰红外总辐射强度随探测角变化趋势也不同。     

Influence of 30-MeV α-particle beams on wave propagation in the Belousov-Zhabotinsky reaction

The generation of leading centers in the Belousov-Zhabotinsky reaction under the action of collimated radiation with a high linear energy transfer has been investigated. To get insight into the mechanism of the effect of radiation on the Belousov-Zhabotinsky reaction, the radicalator model was modified to involve the interaction of the reactants with the ^•OH radical produced by water radiolysis.     

Dynamics of an electron in a relativistically intense laser field including radiaion reaction

The dynamics of an electron in a relativistically intense laser pulse field is described with the radiation reaction being taken into account. The study is based on solving the Newton equation with the Lorentz and the radiation reaction forces. Validation is provided for an iteration technique which makes it possible to remove the discrepancies found in the theoretical models of radiation reaction. It is demonstrated that an electron having a high initial velocity and colliding head-on with a laser pulse sheds a considerable part of its kinetic energy due to the radiation reaction. A broadening of the electromagnetic pulse emitted by the electron occurs as a result of the same effect. The findings obtained can be used to experimentally verify the effect of radiation reaction.     

On the derivation of Hawking radiation associated with the formation of a black hole

We show how in gravitational collapse the Hawking radiation at large times is precisely related to a scaling limit on the sphere where the star radius crosses the Schwarzschild radius (as long as the back reaction of the radiation on the metric is neglected). For a free quantum field it can be exactly evaluated and the result agrees with Hawking's prediction. For a realistic quantum field theory no evaluation based on general principles seems possible. The outcoming radiation depends on the field theoretical model.     

The 51V(n, γ)52V reaction studied with polarized neutrons and polarized vanadium nuclei

Circular polarization of γ- radiation following capture of polarized thermal neutrons by unoriented nuclei and the angular distribution of such radiation, using polarized neutrons and polarized nuclei, made it possible to assign spins to 13 levels of ⁵²V. In addition the admixtures of spin-3 and spin-4 reaction channels could be derived for 20 primary γ-ray transitions. With this information interference phenomena in the ⁵¹V(n, γ) reaction were studied. The low-lying levels of ⁵²V are compared with shell-model calculations. The capture mechanism is discussed in terms of a doorway-state model.     

Travelling waves in a radiation-combustion free-boundary model for flame propagation

We study a combustion-radiation model which models premixed flames propagating in a gaseous mixture with inert dust. This model combines diffusion of mass and temperature with reaction at the flame front. We choose a free boundary model to describe the propagating flames and take a linearized approximation to model the radiation, but we keep a nonlinear reaction term which is temperature dependent. The radiative transfer of thermal energy emitted and absorbed by dust is modelled using the Eddington equation. We analyse the bifurcation diagram of the travelling wave solution curve. In a specific parameter plane, travelling waves are given by a single smooth curve which is parameterized by the flame temperature.     

Soot and NO formation in counterflow ethylene/oxygen/nitrogen diffusion flames

Formation of soot and NO in counterflow ethylene/oxygen/nitrogen diffusion flames was numerically investigated. Detailed chemistry and complex thermal and transport properties were used. A simplified two-equation soot model was adopted. The results indicate that NO emission has negligible influence on soot formation. However, soot formation affects the emission of NO through the radiation induced thermal effect and the reaction induced chemical effect. When the oxygen index of the oxidant stream is lower, the relative influence of chemical reaction caused by soot on NO emission is more important, while the relative influence of the radiation induced thermal effect becomes more important for the flame with a higher oxygen index in the oxidant stream.     

基于高光谱技术的甲烷层流预混火焰自由基特性研究

高光谱技术提供了空间和光谱维度的信息,同时基于传统黑体模型的实验技术和计算方法不适用于甲烷火焰的辐射特性,而火焰中自由基的高光谱信息反映了火焰结构、组分浓度分布等燃烧的多方面特征,能够为燃烧模型的完善提供依据。利用高光谱技术在不同当量比和不同流量下研究了甲烷预混火焰中自由基的空间和光谱特性。对不同当量比的研究表明,随着当量比的增加,火焰中心处的CH^*和C^*₂自由基的辐射强度先增加后降低,而燃烧区域内二者的平均辐射强度一直增加,火焰中心处的点可以表征局部的燃烧状态,而燃烧区域内辐射均值表征热释率等整体燃烧状态,定量给出了两种方法的不同趋势。火焰中心处的CH^*自由基辐射强度在当量比为1.01时达到峰值,而C^*₂自由基辐射强度在当量比为1.12时达到峰值,两种自由基的辐射峰值可以分别作为燃烧中反应强度和稳定性的判据。当量比可以由C^*₂和CH^*辐射强度之比来表征,修正了C^*     

Linear Motion under Constant Force and Radiation Reaction

The classical relativistic equation of motion with radiation reaction is solved exactly when the motion is along the lines of force due to a constant electric field. For physically admissible solutions, there is no contribution due to the radiation reaction. The general motion without radiation reaction is not linear.     

Spontaneous excitation of a circularly accelerated atom coupled with vacuum Dirac field fluctuations

We study the spontaneous excitation of a circularly accelerated atom coupled with vacuum Dirac field fluctuations by separately calculating the contribution to the excitation rate of vacuum fluctuations and a cross term which involves both vacuum fluctuations and radiation reaction, and demonstrate that although the spontaneous excitation for the atom in its ground state would occur in vacuum, such atoms in circular motion do not perceive a pure thermal radiation as their counterparts in linear acceleration do since the transition rates of the atom do not contain the Planckian factor characterizing a thermal bath. We also find that the contribution of the cross term that plays the same role as that of radiation reaction in the scalar and electromagnetic fields cases differs for atoms in circular motion from those in linear acceleration. This suggests that the conclusion drawn for atoms coupled with the scalar and electromagnetic fields that the contribution of radiation reaction to the mean rate of change of atomic energy does not vary as the trajectory of the atom changes from linear acceleration to circular motion is not a general trait that applies to the Dirac field where the role of radiation reaction is played by the cross term.     

Uniformly Accelerated Charge in a Quantum Field: From Radiation Reaction to Unruh Effect

We present a stochastic theory for the nonequilibriurn dynamics of charges moving in a quantum scalar field based on the worldline influence functional and the close-time-path (CTP or in-in) coarse-grained effective action method. We summarize (1) the steps leading to a derivation of a modified Abraham-Lorentz-Dirac equation whose solutions describe a causal semiclassical theory free of runaway solutions and without pre-acceleration patholigies, and (2) the transformation to a stochastic effective action, which generates Abraham-Lorentz-Dirac-Langevin equations depicting the fluctuations of a particle’s worldline around its semiclassical trajectory. We point out the misconceptions in trying to directly relate radiation reaction to vacuum fluctuations, and discuss how, in the framework that we have developed, an array of phenomena, from classical radiation and radiation reaction to the Unruh effect, are interrelated to each other as manifestations at the classical, stochastic and quantum levels. Using this method we give a derivation of the Unruh effect for the spacetime worldline coordinates of an accelerating charge. Our stochastic particle-field model, which was inspired by earlier work in cosmological backreaction, can be used as an analog to the black hole backreaction problem describing the stochastic dynamics of a black hole event horizon.     

A two-dimensional multispecies fluid model of the plasma in an ACplasma display panel

A time dependent, two-dimensional model for simulating the plasma evolution in an AC plasma display panel (AC-PDP) is described. Reaction-convection (mobility)-diffusion equations for charged particles and excited heavy neutral species are solved along with Poisson's equation, a radiation transport equation, a surface charge buildup equation, and an external L-R-C circuit equation using a fully implicit numerical method. Electron-driven rate coefficients are computed with a 0-D Boltzmann solver in the local field approximation. For studying the particle dynamics in pure helium, we consider a reduced model in which radiation transport is ignored and the excited species manifold is collapsed to composite metastable and excited states. The model predictions of breakdown voltage are quite sensitive to the value of the secondary electron emission coefficient assumed and the uncertainties in the electron-driven reaction rates. An initial comparison between the model predictions and I-V measurements from a specially constructed helium-filled panel is made with qualitatively similar behavior. The lack of quantitative agreement can be explained by a combination of uncertainties in the model input data and uncertainty in the initial surface charge state in the experiments     

Modal vibrations of a cylindrical radiator over an impedance plane

The problem of acoustic radiation from an infinite cylinder undergoing harmonic modal surface vibrations near a locally reacting planar boundary is considered. The formulation utilizes the appropriate wave field expansions, the classical method of images, and the translational addition theorem for cylindrical wave functions, along with a simple local surface reaction model involving a complex amplitude wave reflection coefficient applied to simulate the relevant boundary conditions for the given configuration. The analytical results are illustrated with a numerical example in which the cylindrical surface is immersed near a layer of fibrous material set on an impervious rigid wall. The numerical results reveal the important effects of interface local surface reaction and source position on the computed modal impedance component values and the radiated on-axis far-field pressure. The benchmark solution presented can lead to a better understanding of acoustic radiation from near-interface two-dimensional sources, which are commonly encountered problems in outdoor acoustics and noise control engineering. Eventually, it could be used to validate those found by numerical approximation techniques.     

Gravitational radiation reaction on the motion of particles in general relativity

We examine the problem of deducing the geodesic motion of test particles from Einstein's vacuum field equations and its extension to include gravitational radiation reaction. In the latter case we obtain an equation of motion for a particle which incorporates radiation reaction of the electrodynamical type, but due to shearing radiation, together with a mass-loss formula of the Bondi-Sachs type.Work supported in part by the National Science Foundation under Grant PHY-8306104.     

Force approach to radiation reaction

The difficulty of the usual approach to deal with the radiation reaction is pointed out, and under the condition that the radiation force must be a function of the external force and is zero whenever the external force be zero, a new and straightforward approach to radiation reaction force and damping is proposed. Starting from the Larmor formula for the power radiated by an accelerated charged particle, written in terms of the applied force instead of the acceleration, an expression for the radiation force is established in general, and applied to the examples for the linear and circular motion of a charged particle. This expression is quadratic in the magnitude of the applied force, inversely proportional to the speed of the charged particle, and directed opposite to the velocity vector. This force approach may contribute to the solution of the very old problem of incorporating the radiation reaction to the motion of the charged particles, and future experiments may tell us whether or not this approach point is in the right direction.     

厚靶低中能9Be(d,xn)反应加速器中子源特性研究

利用PHITS程序评价计算了厚靶9Be(d, xn)反应加速器中子源的能谱和角分布数据，重点讨论了JQMD、INCL和INCL/DWBA三种核反应物理模型计算厚靶9Be(d, xn)反应中子辐射场分布的适用性。研究结果显示，基于INCL/DWBA耦合模型的PHITS程序计算所得到的厚靶9Be(d, xn)反应中子能谱和角分布数据能够较好地与实验数据符合，可以为厚靶9Be(d, xn)反应中子源特性研究及应用提供较为准确的中子辐射场数据。此外，设计了水冷大面积旋转铍靶的方案，并在5~25 MeV/5 mA入射氘能量下条件下，开展了靶面温度模拟研究，结果显示，靶面最高温度可控制在100 oC以下。