Analytic ray curve tracing for outdoor sound propagation

Outdoor sound propagation, which propagates sound through inhomogeneous, moving media with complex obstacles, presents challenging scenarios for computational simulation. In this paper, we present a ray-tracing method that uses analytic ray curves as tracing primitives in order to improve the efficiency of outdoor sound propagation in fully general settings. This ray-curve tracer inherits the efficiency and flexibility of rectilinear ray tracers in handling boundary surfaces, and it overcomes the performance limitations imposed by approximating the curved propagation paths in inhomogeneous media with rectilinear rays. Adaptive media traversal, as well as acceleration structures for surfaces intersections, lead to further savings in computation. Our method’s speedup over existing ray models, at least an order of magnitude for simple 2D scenarios and up to two orders of magnitude for 3D complex scenes, is demonstrated on outdoor benchmark scenes.     

Complex ray tracing study of electron cyclotron resonance heating

In the up-to-date ray tracing study of electron cyclotron resonance heating (ECRH) of fusion plasmas, energy absorption effect has never been considered into the wave trajectory computation. Thus all the work has been done in real space so far. In this paper we consider coupling of energy absorption to wave trajectory for the first time, and numerically solve the formal complex Hamilton equations in complex space, then take the real-space-projected wave trajectories and group velocities to be the corresponding concrete ones. It is shown that both ordinary wave and extraordinary wave injected from the inner side of the tokamak plasmas approach the electron cyclotron resonance surface step by step and their group velocities become exceedingly small as they move toward this surface. Those clearly show that the resonance between the electron cyclotron waves and the fusion plasmas takes place in the electron cyclotron resonance region, which is just the case the ECRH experimental results and the plasma kinetic theory of waves demonstrate.     

等离子鞘套中毫米波大气窗口的衰减特性

为了探索出减缓飞行器在临近空间出现的通信黑障问题,结合毫米波大气窗口在大气传输的优越性,根据RAM C提供的飞行试验数据,建立双指数分布、Epstein分布和高斯分布三个等离子体鞘套模型,用Z-FDTD算法计算毫米波大气窗口在等离子体鞘套中传播的衰减特性。综合分析可得：可采用35 GHz所在的Ka频段和以220 GHz所在的太赫兹频段的双频测控工作通信系统,此搭配可较好满足对高超声速飞行器在临近空间巡航时的测控需求。     

Giving birth to the refined unambiguous statement of Snell's law in ray optics

This paper reports on the ambiguity present in the long-running Snell's law of refraction of light, which is based on the traditional ambiguous definitions of the angles of incidence and refraction in ray optics. To get rid of the said ambiguity, the refined unambiguous definitions of angles of incidence and refraction reported earlier by the author have been employed to give birth to the refined unambiguous statement of Snell's law of refraction. The most interesting physical insights that resulted from the refined unambiguous statement of Snell's law are: (i) in case of refraction of light of a particular colour while passing from one optical medium to another, the ratio of the sine of the angle of incidence and the sine of the angle of refraction is approximately equal to the refractive index of the second optical medium with respect to the first optical medium and (ii) the refractive index of an optical medium ‘b’ with respect to another optical medium ‘a’ is approximately equal to the reciprocal of the refractive index of the optical medium ‘a’ with respect to the optical medium ‘b’, and vice versa. These results are entirely novel and different from those existing in the traditional literature of ray optics.     

脉冲束流引出时的等离子体鞘层变化

采用一维无碰撞的动力学鞘层模型计算了脉冲等离子体在恒压引出时的等离子体鞘层厚度变化,分别对短脉冲和长脉冲放电时的离子源发射面演变进行了分析。结果表明：对于短脉冲放电,发射面位置的变化相对等离子体密度的变化存在一定时间的延迟;对于长脉冲的上升沿和直流放电的开启阶段,鞘层厚度变化的速度与离子初始速度相关,稳定后发射面的位置与离子初始速度和等离子体密度的乘积相关。     

不同成分等离子体鞘层的玻姆判据

在一维平板鞘层中采用流体模型分别研究了不同成分无碰撞等离子体鞘层的玻姆判据.通过拟牛顿法数值模拟了含有电子、离子、负离子以及二次电子的等离子体鞘层玻姆判据.结果表明二次电子发射增加了鞘层离子马赫数的临界值,且器壁发射二次电子温度越高,离子马赫数临界值越小.负离子使离子马赫数临界值减小.而在含有二次电子和负离子的等离子体鞘层中,当负离子较少时,二次电子发射对离子马赫数临界值影响较大;当负离子增加时,离子马赫数的临界值则主要受负离子的影响. 关键词： 鞘层 等离子体 玻姆判据     

太赫兹波在飞行器等离子体鞘套中的传输特性

针对临近空间飞行器的黑障问题,根据模拟的RAM C-III飞行器周围的流场分布结果,计算了等离子体电子密度和碰撞频率,并根据其分布建立了非均匀的等离子体模型。在此基础上,利用散射矩阵方法分析了太赫兹波在等离子体中的传输特性随着等离子体密度、等离子体厚度、等离子体碰撞频率的变化以及外加磁场对传输特性的影响。结果表明,太赫兹波的传输损耗随着等离子体电子密度和等离子体厚度的增加而增加,而碰撞频率的增加会使得透射率先减小后增加。在外加磁场的作用下,左旋太赫兹波的传输特性会得到改善;而对于右旋太赫兹波,磁场的施加会引入吸收峰,并且随着磁感应强度的增加向高频方向移动。     

等离子体鞘层中尘埃粒子的分布特性

采用柱槽状电极的流体模型，数值模拟了等离子体鞘层及鞘层中尘埃粒子的分布结构. 研究了尘埃粒子数、粒子大小、电极尺寸等因素对尘埃分布结构的影响. 研究表明：当等离子体密度较高时，鞘层较薄，反之鞘层较厚；当尘埃粒子数少时，尘埃分布形成一层结构，反之则形成多层结构；随电极尺寸的不同，尘埃粒子形成一些复杂而又有趣的结构. 关键词： 尘埃粒子 等离子体鞘层 电极     

具有非广延分布电子的碰撞等离子体磁鞘的结构

很多关于等离子体鞘层的研究工作都是基于电子满足经典的麦克斯韦速度分布函数,而等离子体中的粒子具有长程电磁相互作用,使用Tsallis提出的非广延分布来描述电子更为恰当.本文建立一个具有非广延分布电子的碰撞等离子体磁鞘模型,理论推导出受非广延参数q影响的玻姆判据,离子马赫数的下限数值会随着参数q的增大而减小.经过数值模拟,发现与具有麦克斯韦分布(q=1)电子的碰撞等离子体磁鞘对比,具有超广延分布(q<1)和亚广延分布(q>1)电子的碰撞等离子体磁鞘的结构各有不同,包括空间电势分布、离子电子密度分布、空间电荷密度分布.模拟结果显示非广延分布的参数q对碰撞等离子体磁鞘的结构具有不可忽略的影响.希望这些结论对相关的天体物理、等离子体边界问题的研究有参考价值.     

闪光照相中X光能谱对有效吸收系数的影响

研究闪光照相中影响材料有效吸收系数的两个主要因素,即X光的能谱效应和散射影响。用Monte-Carlo方法对闪光照相系统的客体各种组成材料的有效吸收系数进行数值模拟;求出不考虑散射而仅受能谱影响的有效吸收系数及其空间分布,发现该分布类似于医学CT数的分布规律,在高光程数对应的位置上该吸收系数较低;也得到了在20MeV闪光机情况下,客体各种组成材料的单个平均吸收系数。结果表明：钨、铝和铁的平均等效吸收系数分别近似为0.830,0.080和0.265cm-1。     

一种结合室内空间剖分的声线跟踪法

声线跟踪法是应用于室内声场预测的几何声学模拟经典方法之一,但该方法的计算效率随着室内空间布局复杂度的增加而降低。为了高效地应用于各种室内空间布局,提出了一种结合室内空间剖分的声线跟踪法,该方法将整个室内空间剖分成有限个凸多面体子空间,以减少在声线跟踪过程中与声线求交点的墙面数量,并省略了碰撞点有效性判断,显著提高了计算效率,尤其适用于大型复杂的室内空间布局。     

毫米波在等离子体中的衰减特性研究

为了研究毫米波与等离子体的相互作用,采用时域积分法对毫米波在等离子体中传输时的衰减特性进行了仿真,初步研究了毫米波在等离子体中传输时的衰减值与等离子体密度、碰撞频率及其工作频率之间的关系.通过理论结果和仿真结果的分析比较,验证了仿真可以为理论研究提供数据支撑的可行性. 关键词： 毫米波 等离子体 时域积分法 衰减     

Simulation and assessment of stray light effects in infrared cameras using non-sequential ray tracing

In this article, we have evaluated the stray light effects in infrared cameras operating in the 3–5 μm waveband having cooled focal plane array detectors. A non-sequential ray tracing method is used to model the multiple reflections from polished lens surfaces as well as diffused scattering from rough mechanical surfaces inside the camera housing. The flux signature on the detector surface due to the self-emission of in-band radiation from the lenses and camera housing is calculated. The flux signature due to sources beyond the nominal field-of-view of the camera is also calculated. Light splitting into multiple diffraction orders from diffractive lens surfaces is taken into account both in the transmission and the reflection paths. The wavelength and angle dependent reflection coefficient of the anti-reflection coatings on the polished lens surfaces is taken into account. The effect of local heating of camera mounts on the stray light signature on the detector surface is also evaluated. The results show that using the non-sequential ray tracing method, useful predictions can be made for the stray light signature in the infrared cameras. Such calculations can be used to identify areas in the camera housing which need to be temperature stabilized to reduce their detrimental stray-light signature.     

脉冲偏压上升沿特性对等离子体浸没离子注入鞘层扩展动力学的影响

等离子体浸没离子注入(PIII)是用于材料表面改性的一种廉价高效、非视线的技术.采用等离子体粒子模型，通过假设电子密度服从Boltzmann分布，求解Poisson方程和Newton方程，跟踪离子在等离子体鞘层中的运动形态及特性并进行统计分析，研究了不同上升速率和形状的6种波形上升沿对鞘层时空演化、离子注入能量和剂量的影响.结果表明，在PIII过程中，脉冲上升沿影响了等离子体鞘层的扩展，且不同波形诱导的鞘层厚度间存在最大差值.电场强度在鞘层的外边缘区域存在陡降区，离子的运动为非匀加速过程.可以通过调整脉冲 关键词： 等离子体浸没离子注入 鞘层 粒子模型 上升沿     

Experimental studies of plasma sheath near meshes of different transmissivity

<正>The measurements of the potential distributions in the boundary layer near meshes with different mesh spacing were conducted in weakly collisional plasmas using a fine-structured emissive probe and the results of the sheath thickness and electric field at the sheath-presheath edge were compared with theoretical models of collisional presheath and collisionless sheath.It was shown that,because the meshes are partially transparent to ions,the sheath is thinner and the electric field is stronger for the mesh of higher transmissivity,owing to the increased ion density in the sheath contributed from the ions transmitted from the other side of the mesh.However,the potential profiles in the presheath remain almost the same for different meshes except for the shift of the sheath-presheath edge.The thickness of the sheath decreases while the electric field at the edge increases with the increase of the neutral gas pressure.Furthermore, depending on the pressure,the measured electric fields at the edge are close to that from the models of a transition region.     

A skew ray tracing approach for the error analysis of optical elements with paraboloidal boundary surfaces

Using the error analysis methodology developed by the current author in previous studies for optical systems comprising elements with flat boundary surfaces, this study examines the errors induced in a light ray's path as it is reflected or refracted at a paraboloidal boundary surface. In analyzing the light path, two principal sources of error are considered, namely (1) translational errors (Δx_i, Δy_i and Δz_i) and rotational errors (ΔΓ_i, ΔΨ_i and ΔΦ_i), which collectively determine the deviation of the light path at each boundary surface, and (2) the differential changes induced in the incident point position and unit directional vector of the refracted/reflected ray as a result of differential changes in the position and unit directional vector of the light source. The validity of the proposed approach is verified using a generic parabaloidal boundary surface for illustration purposes. Overall, the results show that the proposed error analysis methodology provides a straightforward means of analyzing the performance of optical systems characterized by paraboloidal boundary surfaces such as headlight reflectors, optical telescope mirrors, flashlights and so forth.     

次声波在平流层波导中传播的数值模拟

对次声波在大气中传播进行了建模。通过结合保色散关系空间差分格式和Runge-Kutta时间格式的数值方法,建立了次声波传播模型。应用该次声波模型,研究了在耗散的重力分层大气中次声波的平流层导行传播。数值模拟结果表明,当次声波波包在平流层高度上被反射时,反射区域存在焦散现象,在声波的声压下降的同时,声波的能量得到聚焦。通过数值模拟结果与射线计算结果的对比表明,大气中声波传播的轨迹的精确描述需要应用全波解。     

利用射线追踪法研究超短外腔半导体激光器的输出特性

基于射线追踪法，推导了外腔半导体激光器的连续输出谱的隐函表达式.在此基础上，结合载流子速率方程，对超短外腔半导体激光器的输出谱及P-I特性进行了研究.结果表明：当外腔长度发生波长量级的变化时，超短外腔激光器的P-I特性将发生显著变化；随着外腔长度的变化，超短外腔激光器的激射波长在10nm范围内呈周期性跳变，当外腔长度介于40μm—70μm范围内，激射波长跳变范围最大.理论模拟结果与实验报道结果符合.     

衍射光学器件光线追迹公式的实验验证

本文介绍了一种衍射光学器件光线追迹的方法，并给出了计算公式。作为验证，在实验室里制作了具有连续相位的体全息器件，将其实际再现光斑与计算点列图进行比较。构造透射体全息片的物光为离轴的球面波，始于轴外点Ａ（０，１３２ｓｉｎ８°，－１３２ｃｏｓ８°），参考光为平面光束，其与Ｚ轴夹角为１７°。激光器采用氩离子激光器（Ｓｐｅｃｔｒａ－ｐｈｙｓｉｃｓＭｏｄｅｌ２０２０），波长４８８ｎｍ；干板感光胶为重铬酸明胶（ＤＣＧ），胶层厚为１５μｍ；通光口径３０ｎｍ。测试时把全息片放在干板的位置。挡住物光，让再现光以和参考光路相同的路径平行入射到全息片上，在全息片后垂直光轴放置毛玻璃片，平行光轴移动毛玻璃片，可观察到－１级衍射光的变化。在距离原点的距离分别为（ａ）４０ｍｍ，（ｂ）７０ｍｍ，（ｃ）８７ｍｍ，（ｄ）９５ｍｍ的地方用ＣＣＤ拍摄了衍射光的形状，与程序计算的点列图在形状和大小上都吻合     

电子温度对霍尔推进器等离子体鞘层特性的影响

采用二维粒子模拟方法研究了霍尔推进器通道中电子温度对等离子体鞘层特性的影响, 讨论了不同电子温度下电子数密度、鞘层电势、电场及二次电子发射系数的变化规律. 结果表明: 当电子温度较低时, 鞘层中电子数密度沿径向方向呈指数下降, 在近壁处达到最小值, 鞘层电势降和电场径向分量变化均较大, 壁面电势维持一稳定值不变, 鞘层稳定性好; 当电子温度较高时, 鞘层区内与鞘层边界处电子数密度基本相等, 而在近壁面窄区域内迅速增加, 壁面处达到最大值, 鞘层电势变化缓慢, 电势降和电场径向分量变化均较小, 壁面电势近似维持等幅振荡, 鞘层稳定性降低; 电子温度对电场轴向分量影响较小; 随电子温度的增大, 壁面二次电子发射系数先增大后减少. 关键词： 霍尔推进器 等离子体鞘层 电子温度 粒子模拟