Simultaneous Measurement of Particle Size and Particle Velocity by the Spatial Filtering Technique

The objective of this study was to compare the measuring results of a fiber‐optical probe based on a modified spatial filtering technique with given size distributions of different test powders and also with particle velocity values of laser Doppler measurements. Fiber‐optical spatial filtering velocimetry was modified by fiber‐optical spot scanning in order to determine simultaneously the size and the velocity of particles. The fiber‐optical probe system can be used as an in‐line measuring device for sizing of particles in different technical applications. Spherical test particles were narrow‐sized glass beads in the range 30–100 μm and irregularly shaped test particles were limestone particles in the range 10–600 μm. Particles were dispersed by a brush disperser and the measurements were carried out at a fixed position in a free particle‐laden air stream. Owing to the measurement of chord lengths and to the influence of diffraction and divergent angle, the probe results show differences from the given test particle sizes. Owing to the particle‐probe collisions, the mean velocity determined by the probe is smaller than the laser Doppler mean velocity.     

Multiple scattering of short waves at a system of interacting particles

A plane wave incident on a classical nonideal gas is considered. The mean field is derived up to terms for pair collisions of the scattering particles subject to certain assumptions about the wavelength and the interaction potential.I am indebted to V. E. Zuev and S. D. Tvorogov for many discussions.     

Simultaneous Measurement of Velocity and Equivalent Diameter on Non-Spherical Particles

The performance of a laser-based optical technique to measure simultaneously the velocity and equivalent diameter of nonsphercial particles was evaluated. The size information was provided by the absolute intensity of diffractively scattered light by a particle crossing a single laser beam, which is concentric with a laser Doppler probe volume. The response curve (size-intensity relationship) of the technique was estimated by calculations using the Fraunhofer approximation. Experiments with spherical glass and polyethylene and non-spherical metal and ceramic particles ranging from 20 to 200 μm confirmed the operation of the technique and in all the measurements the maximum error of the average diameter was 10 μm as compared with size information provided by a microscope.     

Analysis of Particle Size Distribution by Particle Tracking

Particle tracking is performed using a combination of dark field or fluorescence video microscopy with automatic image analysis. The optical detection together with the image analysis software allows for the time resolved localization of individual particles with diameters between 100 and 1000 nm. Observation of their Brownian motion over a set of time intervals leads to the determination of their mean square displacements under the given room temperature and viscosity. Hereby, the radii of a set of particles visible within a given optical frame are derived simultaneously. Rapid data analysis leads to reliable particle size histograms. The applicability of this method is demonstrated on polystyrene latices and PMMA nanospheres with radii between 51 nm and 202 nm.     

Microfocusing options for the inelastic X‐ray scattering beamline at sector 3 of the Advanced Photon Source

Synchrotron radiation from third‐generation high‐brilliance storage rings is an ideal source for X‐ray microbeams. The aim of this paper is to describe a microfocusing scheme that combines both a toroidal mirror and Kirkpatrick–Baez (KB) mirrors for upgrading the existing optical system for inelastic X‐ray scattering experiments at sector 3 of the Advanced Photon Source. SHADOW ray‐tracing simulations without considering slope errors of both the toroidal mirror and KB mirrors show that this combination can provide a beam size of 4.5 µm (H) × 0.6 µm (V) (FWHM) at the end of the existing D‐station (66 m from the source) with use of full beam transmission of up to 59%, and a beam size of 3.7 µm (H) × 0.46 µm (V) (FWHM) at the front‐end of the proposed E‐station (68 m from the source) with a transmission of up to 52%. A beam size of about 5 µm (H) × 1 µm (V) can be obtained, which is close to the ideal case, by using high‐quality mirrors (with slope errors of less than 0.5 µrad r.m.s.). Considering the slope errors of the existing toroidal and KB mirrors (5 and 2.9 µrad r.m.s., respectively), the beam size grows to about 13.5 µm (H) × 6.3 µm (V) at the end of the D‐station and to 12.0 µm (H) × 6.0 µm (V) at the front‐end of the proposed E‐station. The simulations presented here are compared with the experimental measurements that are significantly larger than the theoretical values even when slope error is included in the simulations. This is because of the experimental set‐up that could not yet be optimized.     

Simultaneous measurement of moving particle size and velocity

An optical method that makes it possible to measure the size and velocity of particles in flows and mixtures independently and simultaneously is considered. Measurements are taken by analyzing a moving diffraction pattern using a multielement photodetector and a special signal processing algorithm. The shape of photocurrent pulses arising when the particle crosses a light beam is determined. Examples of applying this method to particles with internal optical inhomogeneities are given in comparison with other methods, such as the method of low-angle scattering.     

Measurement of optical constants for dense media by low-coherence dynamic light scattering

We perform the optical constants measurements for different absorption dense media by low-coherence dynamic light scattering (DLS) technique. The estimated particle size is used to calculate the scattering coefficient of particles suspended in dense media. The path-length resolved intensity distributions of light backscattered from the absorbing dense media are investigated experimentally by virtue of path-length resolved performance in low-coherence DLS measurements. The absorption coefficient can be obtained by applying the measured path-length resolved intensity distributions to the modified Lambert-Beer law. As a result, we proposed a new low-coherence DLS technique in simultaneous measurement of the scattering and absorption coefficients of absorbing dense media.     

三维面形测量数据的计算全息可视化

提出利用计算机制全息进行三维面形测量数据立体重现的技术。首先利用三维面形测量技术同时获取三维物体的强度和距离像；然后根据三维面形测量数据，设计和制作菲涅耳计算全息图；最后将计算全息和光学全息相结合，以菲涅耳计算全息图的光学再现像为对象，记录光学像全息。这样既解决了计算机制全息术中真实三维物体立体信息数据捕捉的问题，又为三维面形检测提供了一个行之有效的立体重构技术。给出了这种方法的原理、计算全息的设计、制作方案和实验验证结果。     

Trapping and manipulation of low-index particles in a two-dimensional interferometric optical trap

We demonstrate optical trapping and manipulation of low-index spheres in two dimensions, using the pattern produced by two interfering plane waves. This technique shows, for what is believed to be the first time, alignment of an array of hollow spheres and simultaneous manipulation of high- and low-index particles in the horizontal plane. Furthermore, rodlike particles (up to 30microm in length) are manipulated simultaneously with the low-index particles. This technique offers a practical method for manipulating bubbles, low-index droplets, or rodlike biological samples.     

大尺寸SiO2胶体颗粒的重力沉降自组装研究

采用两步法合成了直径分别为782，977，1027，1160和1324nm的SiO2胶体颗粒，透射电子显微镜显示颗粒尺寸的平均标准偏差小于5％.具有较好的单分散性.通过调节SiO2胶体颗粒悬浮液中介质粘度的方法，拓宽了重力沉降自组装的尺寸范围，得到了颗粒直径为700—1300nm的合成蛋白石 ，扫描电子显微镜图像显示它们为面心立方结构，透射谱表征显示它们具有一定的光子带隙. 关键词： SiO2胶体颗粒 重力沉降自组装 合成蛋白石 光子带隙     

退压式La_3Ga_5SiO_(14)晶体电光调QNd∶YAG激光器激光性能研究

通过对硅酸镓镧(LGS)晶体旋光性与电光效应的交互作用的理论研究,推导出晶体旋光性和电光效应共同作用下的光强表示式I=1-4B2(Asin 2ω-Ccos 2ω)2。利用此表示式设计计算了旋光晶体LGS尺寸为8 mm×8 mm×25 mm电光Q开关在1064 nm波长使用时的开关电压和偏振角分别为4995 V和27.3°。将理论研究得到的结论应用于LGS晶体电光调Q的Nd∶YAG晶体激光器的实验研究中,实验结果与理论计算结果基本一致。得到输出能量为361 mJ,脉冲宽度为7.8 ns的脉冲激光输出。     

双光路DOAS系统获取大气颗粒物粒谱分布方法研究

当前大气复合污染日趋严重,造成大气氧化性增强,气体向颗粒物的转化加快。大气颗粒物粒径大小及谱分布决定其在大气中的行为,以差分吸收光谱法（DOAS）为基础,结合双光路设计技术,开展实时、在线、获取近地面大气气溶胶颗粒物的粒谱分布的光谱方法研究。首先构建低噪声性能稳定的宽带氙弧灯为光源的双光路差分吸收光谱系统,基于干净天气条件下大气的能见度数据对系统进行校准,通过两个不同光路获得的光谱信号强度之比获取近地面紫外-近红外波段的大气总宽波段消光系数。基于宽波段消光系数,在去除瑞利散射以及气体吸收对消光系数的影响后,解析出气溶胶颗粒物的消光系数。基于核函数准则,利用均匀球型粒子的电磁场Mie理论来反演气溶胶物理特性,获得气溶胶粒子在该测量谱段的体积谱分布,利用体积谱与数密度谱的关系,反演出气溶胶粒子的数密度谱分布。开展利用直方图方法来表现颗粒物的粒谱分布方法研究,首先将DOAS测量波段近似等分为若干谱段,利用谱段处平均值,获取气溶胶粒谱直方分布图。最后把该系统和方法应用于外场实验,获得了气溶胶颗粒物在300～650 nm范围内的消光系数,将测量波段等分为11个谱段,反演了颗粒物的在0.1～1.25 μm粒径范围的数密度谱分布。该研究为整治我国灰霾天气,研究大气气相/粒子非均相化学反应提供科学依据。同时将推动DOAS技术的进一步发展和应用。     

介质中含孤立发光中心的纳米粒子的辐射寿命概率分布

含发光中心的纳米粒子在介质中随机分布,造成局域介质相对折射率的随机分布,导致了纳米粒子辐射寿命的涨落.分析纳米粒子数量在线度为发射光波长量级的体积内的概率密度,由此得出局域介质相对折射率的概率密度.通过纳米粒子辐射寿命对折射率的依赖关系,得到纳米粒子辐射寿命概率密度的解析表达.在此基础上,分析了Meltzer等人的实验中,含Eu³⁺离子的Y₂O₃粒子在甲醇溶液中辐射寿命的相对偏移量的涨落,并得出辐射寿命的不确定度(均方差)与纳米粒子体积、体积密度等物理量的关系.     

A Pulsed Field Gradient NMR Technique for the Determination of the Structure of Suspensions of Non-Brownian Particles with Application to Packings of Spheres

The internal structure of systems of particles in a liquid is studied with a novel NMR technique based on the measurement of the squared modulus of the magnetization in presence of a pulsed field gradient. The formalism is analogous to the one used in classical scattering techniques (light, X-rays, neutrons); it allows similar information to be obtained about the structure (in particular, the structure factorS(q)). The main improvement is that the range of particles sizes is 10 μm to 1 mm, as compared with the range of the scattering techniques (<5 μm). The NMR technique was validated by studying packings of spherical particles of mean diameter 240 μm created by sedimentation. The profile of the experimental squared modulus of the magnetization versus the wave vector provides results for the mean size of particles and the compacity. The main feature is that it depends on the pair distribution function, and the present results are in good agreement with a model based on the Percus–Yevick approximation. This technique is then particularly adapted to systems such as non-Brownian suspensions, fluidized beds, porous media, and sediments.     

Particle temperature and potassium release during combustion of single pulverized biomass char particles

This work investigated the combustion characteristics of single pulverized biomass-derived char particles. The char particles, in the size range 224–250 µm, were prepared in a drop tube furnace at pyrolysis temperatures of 1273 or 1473 K from four types of biomass particles – wheat straw, grape pomace, kiwi branches and rice husk. Subsequently, the char particles were injected upward into a confined region of hot combustion products produced by flat flames stabilized on a McKenna burner, with mean temperatures of 1460, 1580 and 1670 K and mean O₂ concentrations of 4.5, 6.5 and 8.5 vol%. The data reported include particle temperature, obtained using a two-color pyrometry technique, and potassium release rate, measured using a laser-induced photofragmentation fluorescence imaging technique. In addition, particle ignition delay time and burning time, obtained from the temporal evolution of the thermal radiation intensity of the burning char particles, are also reported. The results indicated that ignition of the char particles occurs simultaneously with the starting of the potassium release, then the particle burning intensity increases rapidly until it reaches a maximum, after which both the particle temperature and the potassium release rate remain approximately constant until the end of the char oxidation process. The char ignition process is temperature controlled, and the char oxidation process is oxygen diffusion controlled, with the total potassium release being independent of the oxygen concentration and the temperature of the combustion products. The combustion behavior of the chars studied is more affected by the char type than by the conditions used to prepare them.     

偏振相位偏移电子散斑干涉术及其应用于变形测量

本文叙述了一种用于测量漫射表面变形的使用偏振相位偏移技术的电子散斑干涉术.由于采用共光路光学相位偏移技术,因而具有较高的稳定性;用计算机图像处理可精确地获得相位图;用去包裹技术(unwrapping)可直接得到表面变形的精确数据.     

Superconducting terminals as sensitive probes for scarred states

When a quantum-chaotic normal conductor is coupled to a superconductor, the random-matrix theory (RMT) predicts that a gap opens up in the excitation spectrum which is of universal size E(g)(RMT) approximately 0.3 Planck/t(D), where t(D) is the mean scattering time between Andreev reflections. We show that a scarred state of long lifetime t(S)>t(D) suppresses the excitation gap over a window DeltaE approximately 2E(g)(RMT) which can be much larger than the narrow resonance width GammaS= Planck/t(S) of the scar in the normal system. The minimal value of the excitation gap within this window is given by GammaS/2相似文献   

Study of dispersion and absorption of an ensemble of spherical particles inside an optical cavity and new possibilities of predicting the optical characteristics of biological media by intracavity laser spectroscopy

Optical characteristics, namely, dispersion and absorption spectra of an ensemble of spherical particles randomly oriented inside an optical cavity are investigated. The study is based on the self-consistent matching of new data from the inhomogeneous optical cavity with data from the scattering of an ensemble of spherical particles of different size, randomly oriented in free space. As a result, a new model, which self-consistently accounts for multiple scattering in the optical cavity, has been developed to predict absorption and dispersion of ensembles of spherical particles. This model is supposed to enhance potentiality of the intracavity method for plotting wavelength dependences of optical characteristics of media. A specific calculation of dispersion and absorption dependences on the wavelength shows that this method can be used for investigation of biological media consisting of spherical particles, in particular, erythrocyte suspension.     

同材质颗粒不同填充密度的随机介质中光场的空间分布

用时域有限差分法研究了同一材质的颗粒在不同填充密度下的随机介质中光局域化问题. 依据随机介质激光的实验参数,模拟了颗粒填充密度不同的随机介质中光场的空间分布. 结果表明：当散射颗粒的散射平均自由程与波长相当时,随机介质中的光场分布呈现局域化的特征,而且随着颗粒填充密度增大,光场的局域化程度增强. 因此,在同样的抽运激励下,颗粒填充密度越大的随机增益介质越容易产生激光辐射. 数值模拟结果与实验定性符合. 关键词： 随机激光 时域有限差分法 颗粒填充密度 局域化