Locally Resolving Measurements of PSD,Particle Concentration and Particle Velocity by Means of TFS with Dual Beams

Transmission fluctuation spectrometry with spatial correlation (TFS‐SC) is based on transmitting two beams of radiation through a flowing suspension, whereby the distance of the beam centers is varied. Thus, the spatial correlation of the transmission fluctuations of the two beams is determined as a function of the beam distance. By numerical modeling, the transition functions of the correlation are found as a function of beam distance, beam diameters, particle diameter and beam intersection angle. Experimentally determined spatial correlation spectra can be inverted to obtain the particle concentration and particle size distribution by using the theoretical transition functions for mono‐sized particles. In addition, time correlations can be used to extract information on particle velocity. Some experimental results obtained by TFS‐SC are presented and discussed. This method appears promising for application in the local resolving of measurements of PSD, particle concentration and particle velocity in two‐phase flows, both in the laboratory and in process control.     

Transmission Fluctuation Spectrometry in Concentrated Suspensions Part Two: Particle Overlapping

Transmission fluctuations measured on a flowing suspension of particles with a high spatial and temporal resolution can be used to measure the particle size distribution and particle concentration. The theory of transmission fluctuation spectrometry (TFS) was recently developed, whereby the statistical behavior of the entire suspension is described on the basis of a single monolayer, in combination with a layer model describing the suspension as a series of independent monolayers. As the monolayers are assumed to be statistically independent from each other, the transmission through the 3‐dimensional suspension is modeled as the product of transmissions through the monolayers.     

The Fundamentals of Particle Size Analysis by Transmission Fluctuation Spectrometry.

A transmission signal measured on a flowing suspension of particles with a high spatial and temporal resolution shows significant fluctuations, which contain the complete information on particle size distribution and particle concentration. In Parts 1 and 2, the basic properties of signal fluctuations were studied for temporal averaging by a gliding time window and for spatial averaging by a circular beam of uniform intensity. However, the experimental implementation of such conditions is difficult. Now, the theory is extended for Gaussian beams of variable diameter and averaging by signal filtering in the frequency domain. This provides the basis for an experimental implementation by transmission of a laser beam and analog signal processing by an array of low pass filters.     

Experimental Study on Particle Size Distribution and Concentration Using Transmission Fluctuation Spectrometry with the Autocorrelation Technique

Based on the statistical characteristics of the transmission fluctuations in the particle suspension, transmission fluctuation spectrometry with autocorrelation (TFS‐AC) is described theoretically, with the assumptions of geometric ray propagation and completely absorbent particles in the suspension. The experiments presented here are realized in a focused Gaussian beam with the TFS‐AC technique. The acquisition of transmission fluctuation signals is achieved by using a high‐resolution digital oscilloscope. The transition function of TFS‐AC is obtained by varying the autocorrelation time. With a modified iterative Chahine inversion algorithm, solving a linear equation retrieves information on the particle size distribution and particle concentration. Some experimental results on spherical and non‐spherical particles are presented and discussed. The experiments cover a particle size range from 1μm to 1000 μm and a particle concentration of up to 12 %.     

透过率起伏光谱分析法测粒技术

提出的透过率起伏光谱分析法是一种新的颗粒测量方法。采用一细小光束照射匀速流动的颗粒系统,通过采集透射光起伏信号,经统计处理得到透过率的平均值与起伏谱。通过求解逆问题,从透过率的起伏谱中得到颗粒粒径分布信息,再结合透过率的平均值得到颗粒的体积分数信息。给出了关于单层颗粒透过率的平均值与起伏谱的理论表达式,并推广到三维单分散和多分散的颗粒系统。对粒径在32~425μm内的稀薄颗粒系进行了部分实验测试和模拟计算,结果表明该方法可同时对颗粒粒径分布和体积分数进行有效测量。     

Particle Size Analysis by Transmission Fluctuation Spectrometry: Experimental Results Obtained with a Gaussian Beam and Analog Signal Processing

Transmission fluctuation spectrometry (TFS) is a method for the analysis of particle size distributions based on the statistical fluctuations of a transmission signal. Complete information on the PSD and particle concentration can be retrieved by a special transformation of the transmission signal, whereby the expectancy of the transmission square (ETS) is determined after the signal has been subjected to a procedure of spatial and temporal averaging. By varying the averaging parameters over a wide range, a spectrum of ETSs is obtained and introduced into a linear equation system, which yields the PSD. In the experimental realization presented here, variable temporal averaging is realized in the frequency domain with a series of low pass filters at different cutoff frequencies while spatial averaging inevitably occurs as the particles pass through a focused Gaussian beam of finite cross section. Experimental results on spherical particles (glass beads) and non‐spherical particles (SiC) are presented. The PSDs are resolved in 30 intervals within a particle size range from 1–1000 μm, employing a modified Chahine inversion algorithm. So far, the measurements are limited to moderate particle concentrations. Some influences affecting the measurements, especially for higher particle concentrations, are discussed in detail.     

利用消光起伏信号测量颗粒平均粒径

窄光束照射流动颗粒系时,透过率会产生起伏.起伏的透过率信号可用来测量颗粒平均粒径和浓度.由于在测量原理和结构上非常简单,这种方法可用来实现在线、实时测量.Gregory提出的数据处理模型要求光束直径较小而且远大于颗粒直径,本文提出一种新的模型,可在光束直径接近甚至小于颗粒直径情况下对透过率起伏信号进行处理,模拟分析和实验测试表明,该方法可得到较满意的测量结果.     

Spot-scanning beam delivery with laterally-and longitudinally-mixed spot size pencil beams in heavy ion radiotherapy

The three-dimensional(3D) spot-scanning method is one of the most commonly used irradiation methods in charged particle beam radiotherapy.Generally,spot-scanning beam delivery utilizes the same size pencil beam to irradiate the tumor targets.Here we propose a spot-scanning beam delivery method with laterally-and longitudinallymixed size pencil beams for heavy ion radiotherapy.This uses pencil beams with a bigger spot size in the lateral direction and wider mini spread-out Bragg peak(mini-SOBP) to irradiate the inner part of a target volume,and pencil beams with a smaller spot size in the lateral direction and narrower mini-SOBP to irradiate the peripheral part of the target volume.Instead of being controlled by the accelerator,the lateral size of the pencil beam was adjusted by inserting Ta scatterers in the beam delivery line.The longitudinal size of the pencil beam(i.e.the width of the mini-SOBP) was adjusted by tilting mini ridge filters along the beam direction.The new spot-scanning beam delivery using carbon ions was investigated theoretically and compared with traditional spot-scanning beam delivery.Our results show that the new spot-scanning beam delivery has smaller lateral penumbra,steeper distal dose fall-off and the dose homogeneity(1-standard deviation/mean) in the target volume is better than 95%.     

基于二阶滤波器的消光起伏谱颗粒测量结果

消光起伏频谱法是一种新的测量两相流系统中颗粒粒径分布和浓度的方法,装置简单,操作方便,适合实时、在线测量。采用二阶低通滤波器对起伏的透射率信号分析,得到消光起伏频谱实验数据,并利用改进的Chahine循环方法计算得到颗粒的粒径分布和浓度信息。重点讨论高浓度情况,包括对特征函数频率响应的修正和对其阶高修正两个方面,得到修正参量并运用到反演算法中从而得到正确的测量结果。测量结果表明,通过高浓度修正,消光起伏频谱法可以在很大的颗粒浓度动态范围得到合理的测量结果,其可测颗粒最大体积分数视颗粒的大小而定。     

扇形多注强流相对论电子束的产生与传输研究

多注相对论速调管相对于常规相对论速调管, 每注电子束具有更低的导流系数和更低的空间电荷力, 却具有更高的束波转换效率. 本文基于这方面的需求, 通过三维软件模拟与实验研究了扇形多注强流相对论电子束的产生与传输. 通过建立电子枪的三维模型, 分析了阴极端面静电场的分布及其对电子束产生的影响; 通过粒子模拟获得了发射束流, 然后通过粒子跟踪仿真, 得到了电子束在空心漂移管和多扇形孔漂移管中传输的束斑图, 并对其进行了理论分析与解释. 模拟和实验结果表明, 电子束在空心漂移管传输过程中不仅绕束自身中心旋转, 还绕系统的中心旋转, 通过旋转多扇形孔漂移管实现对中的方法可提高传输效率.     

Tunable nonlinear beam shaping by non‐collinear interactions

A method is proposed for nonlinear beam shaping, employing a non‐collinear quasi phase‐matched interaction in a crystal whose nonlinear coefficient is encoded by a computer generated hologram pattern. In this method the same axis is used for both satisfying the phase‐matching requirements and encoding the holographic information, the result is a single shaped beam in the generated frequency. This allows to shape beams in one‐dimension using a very simple method to fabricate patterned nonlinear crystals and to shape beams in two‐dimensions with high conversion efficiency. The one‐dimensional case is experimentally demonstrated by converting a fundamental Gaussian beam into Hermite‐Gaussian beams at the second harmonic in a KTiOPO₄ crystal. The two‐dimensional case is demonstrated by generating Hermite‐Gaussian and Laguerre‐Gaussian beams in a stoichiometric lithium tantalate crystal. The suggested scheme enables broad wavelength tuning by simply tilting the crystal.     

消光起伏自相关频谱法颗粒测量技术

消光起伏相关频谱法(TFCS)是一种新的颗粒测量方法。采用一束窄光束照射两相流系统,照射区中颗粒浓度的起伏所导致的透射光起伏信号中包含了颗粒的粒径和浓度信息,对光束的透过率信号作相关处理得到消光起伏相关频谱,可用来同时测量两相流中颗粒的粒径分布和体积浓度。由于在测量原理和结构上非常简单,这种方法可用来实现在线、实时测量。本文介绍消光起伏自相关频谱的测量原理,并给出部分实测结果。     

Radiation damage to protein specimens from electron beam imaging and diffraction: a mini‐review of anti‐damage approaches,with special reference to synchrotron X‐ray crystallography

Recent research progress using X‐ray cryo‐crystallography with the photon beams from third‐generation synchrotron sources has resulted in recognition that this intense radiation commonly damages protein samples even when they are held at 100 K. Other structural biologists examining thin protein crystals or single particle specimens encounter similar radiation damage problems during electron diffraction and imaging, but have developed some effective countermeasures. The aim of this concise review is to examine whether analogous approaches can be utilized to alleviate the X‐ray radiation damage problem in synchrotron macromolecular crystallography. The critical discussion of this question is preceded by presentation of background material on modern technical procedures with electron beam instruments using 300–400 kV accelerating voltage, low‐dose exposures for data recording, and protection of protein specimens by cryogenic cooling; these practical approaches to dealing with electron radiation damage currently permit best resolution levels of 6 Å (0.6 nm) for single particle specimens, and of 1.9 Å for two‐dimensional membrane protein crystals. Final determination of the potential effectiveness and practical value of using such new or unconventional ideas will necessitate showing, by experimental testing, that these produce significantly improved protection of three‐dimensional protein crystals during synchrotron X‐ray diffraction.     

Particle Imaging Using a Transmission Wide‐Field Phase Confocal Microscope

A phase‐sensitive wide field transmission microscope, combining the advantages of both interferometric and confocal techniques, has been developed and applied to analysis of particulates, both in dry powder form and in suspensions. The microscope has also been used in detecting defects in crystals. Confocal operation is achieved by superimposing speckle illumination of a reference beam in a Mach‐Zehnder interferometer with a matched speckle pattern of the object beam. It is shown that the phase measurement enables particle size to be determined even when the particle is smaller than the focal spot size. The data acquisition time is below 1ms, making the system suitable for dynamic process measurement. The experimental results are in good agreement with modelled results giving rise to the possibility of simultaneous determination of both the size and refractive index of small particles.     

Transmission Fluctuation Spectrometry in Concentrated Suspensions. Part Three: Measurements

The theory of transmission fluctuation spectrometry (TFS) was developed for particle size analysis in flowing particle suspensions, whereby the statistical transmission fluctuations are used to extract the particle size distribution (PSD) and particle concentration. In the previous parts of this publication high concentration effects on TFS were investigated theoretically and by simulation. This work presents a study on TFS measurements in concentrated suspensions. By introducing an empirical correction to include the high concentration effects from both the monolayer structure and particle overlapping in the inversion algorithm, it is possible to obtain the particle size distribution and particle concentration over broad ranges of particle sizes and concentrations.     

无限细光束中透射起伏时间相关频谱法高浓度效应的模拟

时间或空间相关透射起伏频谱法是近年发展起来的一种新的颗粒测量方法,它可同时测量颗粒粒径分布和浓度,并可用来进行在线、实时测量。研究表明,随着浓度增大,逐渐增强的高浓度效应会导致测量值越来越严重地偏离理论值。本文采用模拟计算方法讨论无限细光束照射下的时间相关透射起伏频谱法高浓度效应并给出部分实验验证。分析表明,无限细光束照射时的透射起伏相关频谱主要受到层结构效应的影响,颗粒交叠效应不明显,表明为随着颗粒浓度增大,转换函数(特征函数)逐渐偏离低浓度理论值并向无因次相关时间小的方向移动,阶高始终保持不变。     

基于螺线盘聚焦径向电子束的理论分析与仿真研究

对径向电子束在浸没式聚焦条件下的传输特性进行了理论分析,得到了束流传输过程中轴向扩张幅值与外加引导磁场强度之间的解析表达式。阐述了螺线盘在空间中任意一点产生磁场的理论,给出了通以相反方向电流的螺线盘之间磁场的分布规律。设计了一种基于螺线盘聚焦径向电子束的引导磁场系统,并对电子束的传输特性进行了仿真研究,结果表明径向电子束能够在设计的引导磁场系统下实现束流的稳定传输。     

平顶高斯光束的相关概念和对称化变换

 对平顶高斯光束有关的一些重要概念,例如场分布和束宽等作了物理分析。进一步将二维平顶高斯光束推广到三维情况,并且对三维平顶高斯光束的对称化变换,包括在X和Y方向束宽相等和ｚ平面处曲率半径相等,进行了详细的研究。     

Optical formation and manipulation of particle and cell patterns using a tapered optical fiber

A method for optical formation and controllable manipulation of particle and cell patterns using a tapered optical fiber is demonstrated. With a laser beam at 980‐nm wavelength launched into the fiber, different sized silica particles were formed into particle patterns (both one‐dimensional chains and two‐dimensional arrays) with different particle numbers by optical binding. The formed particle patterns can be controllably manipulated in three dimensions. Using yeast cells as an example, it was demonstrated that the method is applicable for the formation of biological cell patterns, without damage to the yeast cell viability. This method provides a new facile way for biophotonic and biological researches with particles and cells in a highly organized manner.