Absorption and Transmission Power Coefficients for Millimeter Waves in a Weakly Ionised Vegetation Fire

A vegetation fire plume is a weakly ionised gaseous medium. Electrons in the plume are mainly due to thermal ionisation of incumbent alkali impurities. The medium is highly collisional with free electron - neutral particle been the dominant particle interaction mechanism. Signal strength of an incident millimetre wave (MM-Wave) may be significantly attenuated in the plume depending on the extent of ionisation. A numerical experiment was set to investigate signal power loss of a MM-Wave incident on a simulated weakly ionised fire plume with flame maximum (seat) temperature ranging from 1000–1150 K. The simulated fire plume had alkali impurities (potassium) content of 1.0% per unit volume. MM-Wave frequency range investigated in the experiment is from 30–60 GHz. The simulation has application in the prediction of MM-Wave propagation in a crown forest fire and may also be applied in remote sensing studies of forest fire environments. Simulated attenuation per unit path length for the MM-Wave frequencies ranged from 0.06–24.00 dBm⁻¹. Phase change per unit path length was simulated to range from 2.97–306.17°m⁻¹ while transmission power coefficients ranged from maximum of 0.9996 for a fire plume at 1000 K to a minimum value of 0.8265 for a plume at a temperature of 1150 K over a plume depth of 1.20 m. Absorption power coefficient ranged from a minimum value of 0.0004 to maximum value of 0.1585 at a seat temperature of 1150 K over the plume depth.     

低压下直流电弧热等离子体射流电子密度的光谱法测量

采用原子发射光谱仪研究低压直流电弧热喷涂等离子体射流的特性。利用Stark展宽法采集H_β谱线,使用其Δλ_1/2来计算等离子射流中的电子密度,研究了氢气流量、输入功率和探测距离对等离子体射流中电子密度的影响。使用Saha方程计算热等离子体的电离程度,研究了功率/氢气流量与等离子体电离程度的关系。结果表明:电子密度和电离程度随着电流强度的增大而增加;氢气流量增加可以明显提高等离子体射流的能量,但对电离程度影响不大。     

Binary Collision Density in a Non-Ideal Gas as a Function of Particle Density,Collision Diameter,and Temperature

Using molecular dynamics simulations, binary collision density in a dense non-ideal gas with Lennard-Jones interactions is investigated. It is shown that the functional form of the dependence of collision density on particle density and collision diameter remains the same as that for an ideal gas. The temperature dependence of the collision density, however, has a very different form at low temperatures, where it decreases as temperature increases. But at higher temperatures the functional form becomes the same as that for an ideal gas.     

气泡数密度对尾流光束衰减测量的影响

为准确地测量出尾流气泡群的衰减,提高前向光尾流探测的可靠性,研究了气泡数密度对尾流光束衰减测量的影响.基于辐射传输方程的小角度近似解,得到了探测截面上的约化功率和漫射功率的表达式.根据测量条件,引入了有尾流气泡和无尾流气泡时探测截面上接收到的辐射功率之比作为透射函数,并进一步引进了复散射校正因子,它表征了复散射效应的强弱.针对典型的尾流气泡分布,通过数值计算得到了不同测量条件下气泡数密度与复散射校正因子、透射函数的关系.数值计算结果表明：复散射校正因子都随气泡数密度的增大单调的增大,透射函数都随气泡数密度的增大单调的减小;测量条件不同,气泡数密度对光束衰减的影响也不同.研究结果表明,给定测量条件和透射比时,利用小角度辐射方程可以得到气泡群数密度的量化信息.     

光谱法诊断大气压等离子体电子密度

采用发射光谱方法对大气压氩气介质阻挡放电(DBD)系统中的电子密度进行了诊断。通过考虑放电等离子体中的各种加宽机制, 采用自编的非对称卷积程序对氩原子发射谱线的线型进行分析拟合, 再通过反卷积的方法将各种加宽机制分离开来, 最终将Stark展宽分离出来进行大气压氩气介质阻挡放电电子密度的计算。诊断结果表明, 在大气压氩气介质阻挡放电中当有三个放电丝存在, 电子温度为10000 K时, 电子密度约为4.06×1021 m-3, 诊断结果和模拟结果符合得很好。此方法不仅可以应用在大气压介质阻挡放电中, 还可以用于其他含有非氢气体的大气压等离子体电子密度的测量。     

微波大气吸收衰减特性分析及分层数值算法

 给出了微波在大气中传输受气体分子吸收导致衰减的较精确计算模型，该模型扩展了传统计算模式忽略温度、湿度、压力变化及传播距离受限制的近似算法。结合我国某地区的实测气象数据模拟计算了该地区的大气吸收衰减，最后根据数值计算结果分析了微波随频率、发射角度以及月份（季度）变化的传播特性，并简要说明了此研究在微波遥感中的实际意义。     

蒙特卡罗方法在低能电子致原子内壳层电离截面测量中的应用

在Monte Carlo方法模拟keV电子碰撞薄膜／厚衬底靶过程中,输入材料数据中采用的内壳层电离截面数据不同,得到的反映膜厚及村底对电离截面测量结果影响的修正因子值也有差别。讨论了Monte Carlo模拟得到的修正因子值受输入材料数据中内壳层电离截面影响的程度,并完成了入射keV电子在法拉第筒中逃逸率的估算工作。 The sensitivity of the correction factor, which describes the combined effect of finite film thickness and the thick substrate in the measurement of atomic inner-shell ionization cross-sections by low-energy electron impact, to the adopted ionization cross-sections in the Monte Carlo simulation is discussed. Moreover, the electron escape ratio from the Faraday cup in our experiment is also obtained by Monte Carlo method.     

微分吸收激光雷达在遥感大气密度过程中的探测误差、最优化发射功率和测量精度等问题的探讨

详细地讨论了微分吸收激光雷达测量气体密度时中心频率的漂移所引起的测量误差。计算结果表明,中心频率的漂移是微分吸收激光雷达主要的误差来源。还探讨了微分吸收激光雷达的发射功率的优化和探测精度的优化等问题。计算结果表明,优化前的中心频率的发射功率大于优化后的发射功率,随着探测距离的增大,两者的比值越来越大。而且优化后的精度高于优化前的精度,随着距离分辨率的减小,两者的比值也越来越大。因此,在探测距离比较大和距离分辨率比较小的情况下,微分吸收激光雷达的优化显得特别重要。     

Measurement and analysis of complex modulated motions in a weakly nonlinear system

The two-timing dynamics of a forced, weakly nonlinear system are considered. Experimental results on a roll-forced spherical pendulum verify the occurrence of slow-time, subharmonically and chaotically modulated oscillations in a frequency band near resonance; the modulatory behavior follows the occurrence of a Hopf bifurcation in the slow-time coordinates. A phase-sensitive detection method for experimentally isolating the slow-time behavior is described. A Lagrangian model for the pendulum is developed, and slow-time equations are presented. A two-thirds power scalling law relating roll angle to the appearance of the modulations is derived from the slow-time equations and tested with experimental results.     

Properties of the Collision Operators of the Electron Boltzmann Equation for a Weakly Ionized Plasma. II. Compactness Proof and Statements on the Spectrum

The compactness has been proved of the inscattering operator covering elastic, exciting and deexciting processes between electrons and heavy neutral particles. Starting point is the proof of the boundedness of the different inscattering operators for the individual collision processes using certain assumptions on the structure of the corresponding differential cross sections. Then, under somewhat more confined conditions the proff of compactness could be performed with the aid of the square integrability of an eightfold iterated kernel. On the basis of this property it was possible to draw conclusions with regard to the spectrum of the total collision operator. They are related to the continuous as well as the discrete part of the spectrum and are discussed in detail. For elastic collisions additional statements can be deduced from our investigation.     

电子碰撞引起的铜元素K壳层电离截面的测量与修正

 在电子碰撞的情形下,通过对铜靶的特征X射线测量,从而推算出它的K壳层电离截面。在实验中采用了薄靶厚衬底新方法。通过电子输运计算,由厚衬底产生的反射电子对计数的影响得以修正。用蒙特卡罗技术对质量厚度为23 mg∕cm²的铜靶的多次散射影响作了修正。     

Measurement of Titanium and Manganese K -shell Ionization Cross Sections by Electron Impact

报道了电子引起的钛、锰原子的Ｋ壳层电离截面实验值。实验中,采用了薄靶厚衬底技术,并将衬底中反射的电子对测量值的影响进行了修正。实验结果与其他文献报道的测量结果相吻合。最后,还将实验结果与Ｃａｓｎａｔｉ等人的经验公式进行了比较。     

Boltzmann Limit and Quasifreeness for a Homogenous Fermi Gas in a Weakly Disordered Random Medium

We discuss some basic aspects of the dynamics of a homogenous Fermi gas in a weak random potential, under negligence of the particle pair interactions. We derive the kinetic scaling limit for the momentum distribution function with a translation invariant initial state and prove that it is determined by a linear Boltzmann equation. Moreover, we prove that if the initial state is quasifree, then the time evolved state, averaged over the randomness, has a quasifree kinetic limit. We show that the momentum distributions determined by the Gibbs states of a free fermion field are stationary solutions of the linear Boltzmann equation; this includes the limit of zero temperature.     

Spectroscopic Measurement of Electron Temperature and Density in an Argon Plasma Jet Based on Collisional‐Radiative Model

The present paper describes a spectroscopic method or determining electron temperature T_e and density N_e in an argon plasma jet on the basis of a Collisional‐Radiative model of argon. Electron temperature and density in the argon plasma were measured by the method developed, and comparison of them was discussed with those obtained with a Langmuir probe. The results or T_e and N_e obtained by the spectroscopic method agreed roughly with those by the probe.     

Measurement of atomic number and mass attenuation coefficient in magnesium ferrite

Pure magnesium ferrite sample was prepared by standard ceramic technique and characterized by X-ray diffraction method. XRD pattern revealed that the sample possess single-phase cubic spinel structure. The linear attenuation coefficient (μ), mass attenuation coefficient (μ/ρ), total atomic cross-section (σ _tot), total electronic cross-section (σ _ele) and the effective atomic number (Z _eff) were calculated for pure magnesium ferrite (MgFe₂O₄). The values of γ-ray mass attenuation coefficient were obtained using a NaI energy selective scintillation counter with radioactive γ-ray sources having energy 0.36, 0.511, 0.662, 1.17 and 1.28 MeV. The experimentally obtained values of μ/ρ and Z _eff agreed fairly well with those obtained theoretically.      

A Novel Laser Heterodyne Technique for the Measurement of Electron Density in Gas Discharges: Application to a TEA CO2 Laser Plasma

We describe a novel intracavity laser heterodyne technique for the measurement of electron density in gas discharges. The method produces time-resolved data from a single pulse and we have used it to monitor electron densities in a TEA laser discharge with a typical CO2 laser gas mixture. Good agreement was found between the measured electron density and its value calculated from current density and drift velocity. A maximum value of 5 × 1013 cm-3 was observed.     

Sensitivity of Elastic Properties to Measurement Uncertainties in Laryngeal Muscles With Implications for Voice Fundamental Frequency Prediction

This paper discusses the effects of measurement uncertainties when calculating elastic moduli of laryngeal tissue. Small dimensions coupled with highly nonlinear elastic properties exacerbate the uncertainties. The sensitivity of both tangent and secant Young's Modulus was quantified in terms of the coefficient of variation, which depended on measurement of reference length and cross-sectional area. Uncertainties in the measurement of mass, used to calculate cross-sectional area of a small tissue sample, affected Young's Modulus calculations when tissue absorption of the hydrating solution was not accounted for. Uncertainty in reference length had twice the effect on elasticity than other measures. The implication of these measurement errors on predicted fundamental frequency of vocalization is discussed. Refinements on isolated muscle experimental protocols are proposed that pay greatest attention to measures of highest sensitivity.     

弓网电弧温度及导电特性的光谱分析

高铁提速受多方面因素制约,其中弓网离线对受流质量影响很大。在滑动接触模式下,受电弓与接触网的磨损均很严重。弓网离线产生的电弧是造成接触网和受电弓磨损的主要原因之一。电弧温度高,还具有电离特性,因此一般的传感器无法置于电弧中测量。光谱分析法在研究弓网电弧的温度及电子密度方面具有明显优势,基于此可进一步寻找耐磨损的新材料或者灭弧方法。因接触网使用铜合金材料,故选取铜元素特定光谱作为研究对象。采用Boltzman作图法,通过实验测得弓网电弧的光谱信息,进而计算电弧通道的温度。结果表明,由于单次电弧持续时间短又受弓网相对运动的影响,其温度并不很高,且电弧温度随着电弧持续时间的增加而增加。采用盲目反卷积的方法求解307.92 nm谱线的Stark展宽,再根据Stark展宽求得电弧的电子密度,结果表明弓网电弧通道的电子密度和其他种类电弧电子密度在同一数量级上;说明电弧引起的粒子电离效应明显。由此可知光谱法在电弧温度及电弧电离特性的分析中是较为方便和准确的。     

Measurements of Temperature and Electron Density Distributions in a Helium Plasma Produced Near Ceramic Surface

The temperature and electron density distributions in a helium plasma produced near ceramic surfaces at atmospheric pressure have been studied. The determination of these plasma parameters is based on spatial resolved line intensity measurements.     

不同原子的选择电离和测量产生腔场压缩的比较

研究了一个慢的二能级里德伯原子和一个快的三能级里德伯原子与腔场发生相互作用手腔场的压缩性质。结果表明,对快原子进行选择电离和测量,腔场不存在压缩;而对慢原子进行选择性电离和测量,腔场存在压缩,最大压缩处压缩参量可达２５％。