应用低相干动态光散射法测量悬浮液中的颗粒粒径分布

利用低相干动态光散射法测量不同浓度悬浮液中的颗粒粒径分布。由低相干光源和迈克尔逊干涉仪,结合传统的动态光散射技术组成低相干动态光散射装置,通过检测单次背散射光的能谱分布,利用CONTIN算法得到不同浓度悬浮液中颗粒的粒径分布。结果表明,对于1%～10%体积浓度范围内的单分散悬浮液羊品测量得到的颗粒粒径精确度在4%以内。     

L-曲线准则在正则化图像复原中的应用

对因大气湍流引起的退化图像复原问题,采用Tikhonov正则化方法将其归结为一个适定的线性方程组的求解问题。当图像边界满足周期性条件时,利用二维离散傅里叶变换及其逆变换即可求得复原图像。在求解方程组中,利用L-曲线准则确定出能够平衡正则化函数和偏差函数的正则化参数,以得到较为理想的复原结果。仿真结果表明,当降质图像的噪声方差不是很大时,该方法能够得到较好的复原效果。     

基于颗粒粒度信息分布特征的动态光散射加权反演

宽分布和双峰分布颗粒的准确反演是动态光散射技术至今未能有效解决的难题,尤其峰值位置比小于2:1且含有大粒径颗粒(350 nm)的双峰分布.造成这一难题的主要原因包括:1)单角度测量数据的粒度信息含量不足;2)常规反演方法对测量数据的噪声抑制以及粒度信息利用缺乏针对性.对测量数据(即光强自相关函数)的研究发现,数据噪声主要分布在长延迟时段,而粒度信息集中分布在衰减延迟时段.基于此,本文提出了采用粒度信息分布为底数、调节参数为指数的权重系数对自相关函数进行加权反演的约束正则化方法.由于采用了与粒度信息分布一致的权重系数,该方法既充分利用了衰减延迟时段的粒度信息,又有效地抑制了长延迟时段的数据噪声.不同噪声水平下,宽分布和双峰分布颗粒体系的反演结果表明,与常规反演方法相比,这一方法可以获得更为准确的宽分布和近双峰分布的反演结果.     

细菌觅食优化算法在光散射法颗粒粒度反演中的应用

针对函数约束算法中传统的智能算法反演时存在鲁棒性差和易陷入局部最优的缺点,提出了将正则化理论与细菌觅食优化算法相结合应用在颗粒粒度的测量中。引入Tikhonov平滑泛函来构建算法的目标函数,采用L曲线法确定正则化参数;再利用细菌觅食优化算法通过趋向、聚群、复制和迁徙等四种智能行为,迭代计算来搜寻函数的最优解。实验仿真结果表明:利用细菌觅食优化算法实现了在不同程度的随机噪声下的服从J-SB分布的单峰分布的均匀球形颗粒粒度分布反演,其反演结果更稳定,反演精度高,对于实现稳定、快速、准确的颗粒粒度在线测量具有重要的意义。     

用于前向光散射颗粒粒度测量的基函数Tikhonov正则化算法

以前向光散射颗粒测试技术中的反演问题为研究对象,将颗粒粒径分布函数表示为一系列B-spline函数的线性组合以降低反演问题的病态性。模拟计算与实验表明:采用基函数形式的Tikhonov正则化方法可减少传统Tikhonov正则化反演带来的振荡,使其更加光顺。     

含噪动态光散射测量数据反演中正则化算法与Chahine算法的比较

采用两种常用的粒度反演方法——正则化和Chahine算法,对90nm与250nm单峰分布、50nm与200nm双峰分布、100nm与300nm双峰分布的模拟动态光散射数据,以及105nm、300nm标准颗粒的实测动态光散射数据进行了反演分析.结果表明:噪声水平的高低是影响粒度分布反演准确性的关键因素之一,反演结果的准确性随噪声水平的增加而降低,噪声水平超过某一阈值后,将无法得到有意义的反演结果;不同反演方法具有不同的抗噪能力,在低噪声水平下反演结果无显著差别,随着噪声水平的增加,反演结果表现出很大差异;正则化方法通过正则参数的选择可以有效抑制噪声影响,表现出强于Chahine算法的抗噪能力;与Chahine算法相比,正则化方法不需要假定初始分布,因此,在噪声较大的实验或生产过程中进行颗粒分布测量时,宜采用正则化方法.     

夫琅和费衍射颗粒粒度测量中的改进Chin-Shifrin反演算法

在基于线阵CCD的夫琅和费衍射颗粒粒度测量中,采用Chin-Shifrin积分变换反演算法使得反演的粒度分布出现假峰现象.为解决此问题,提出在该Chin-Shifrin积分变换反演算法中引入矩形窗函数,并在分析颗粒粒径与衍射光强导数最小值之间关系的基础上,确定矩形窗函数中心点位置及左右边界,利用该矩形窗函数对粒度分布进行截断处理,消除虚假峰,提高反演颗粒粒度分布的准确性.分别对两种标准颗粒进行了测量,并对不同算法的反演结果进行了对比.实验结果表明:引入矩形窗函数的改进Chin-Shifrin算法,能够有效排除粒度分布中的多假峰;粒度分布测量相对误差小于3%,重复性小于4%.     

L曲线方法在地基红外高光谱反演温度廓线中的应用

利用地基红外高光谱辐射数据可以反演得到高时间分辨率的边界层大气温度廓线。目前的AERIoe最优化反演算法相比于传统的“剥洋葱”算法有较大的改进,且对初值的依赖程度较低。但AERIoe算法中正则化算子的选择对反演结果的稳定性和反演时间有重要影响。目前主要采用经验的方法选择正则化算子,迭代步数较多,耗费大量的计算时间。提出了利用L曲线方法代替经验法选取正则化算子的改进方案,以提高AERIoe方法的反演速度。改进后的算法通过绘制解范数和残余范数的二维曲线图,取其拐点作为最优的正则化参数,相比于传统的经验法有着更好的理论基础。采用2011年美国大气辐射测量计划中SGP站点的晴空大气红外辐射数据进行反演实验。结果表明,利用该方法得到的反演结果具有很好的稳定性、收敛性和精度。相比于经验的方法,利用L曲线方法获得的正则化算子反演温度廓线时的收敛速度更快,迭代步数较少,可以节约大量的计算时间;在反演精度方面,L曲线方法在边界层中上层的反演精度更高,1～3 km高度上温度廓线的RMSE值提高了大约0.2 K。     

光全散射法颗粒测量中的一种自适应非独立模式算法

光全散射颗粒测量法中需求解第一类Ｆｒｅｄｈｏｌｍ积分方程。在不知道被测颗粒的尺寸范围的情况下如何确定积分方程的上下限、即测量范围，迄今仍是个问题。本文针对此问题提出了一种自适应非独立模式算法。该算法可根据双参数颗粒分布函数的分布参数Ｋ自动确定积分的上下限．数值模拟和实验都证实了此算法。     

Temperature Controlled Sequential Gelation in Composite Microgel Suspensions

Depending on the volume fraction and interparticle interactions, colloidal suspensions can exhibit a variety of physical states, ranging from fluids, crystals, and glasses to gels. For microgel particles made of thermoresponsive polymers, both parameters can be tuned using environmental parameters such as temperature and ionic strength, making them excellent systems to experimentally study state transitions in colloidal suspensions. Using a simple two‐step synthesis it is shown that the properties of composite microgels, with a fluorescent latex core and a responsive microgel shell, can be finely tuned. With this system the transitions between glass, liquid, and gel states for suspensions composed of a single species are explored. Finally, a suspension of two species of microgels is demonstrated, with different transition temperatures, gels in a sequential manner. Upon increasing temperature a distinct core–sheath structure is formed with a primary gel composed of the species with lowest transition temperature, which acts as a scaffold for the aggregation of the second species.     

用于光子相关光谱颗粒粒度测量的实数编码混合遗传算法

提出一种自动缩小反演范围的实数编码混合遗传算法,并用于光子相关光谱颗粒粒度测量中.该算法利用混沌遍历性质,融入模拟退火算法,具有较强的局部搜索能力.通过数值模拟,讨论在无噪声和多种噪声水平影响下单分散颗粒系的反演结果;分析90 nm聚苯乙烯标准颗粒样品的实验测量数据.结果表明,反演的粒径分布在峰值位置、峰宽度、峰对称性等方面很接近颗粒的真实分布,具有较强的抗噪声干扰能力.     

Ultrasonic Spectrometry for Particle Size Analysis in Dense Submicron Suspensions

Ultrasonic spectrometry was applied to the particle size analysis of disperse systems. The investigations were made for acoustic conditions called the long-wavelength regime (LWR). In the LWR the acoustic behaviour is governed by dissipative effects rather than by scattering. Two principal theoretical approaches to ultrasonic spectrometry — scattering theory and coupled phase models — are introduced. A model based on a newly developed coupled phase model and the scattering theory (ECAH theory) is implemented in the ultrasonic spectrometer Acousto Phor. Experiments were carried out for several suspensions with a high density contrast. It could be demonstrated that the model successfully describes acoustic attenuation and that the inversion algorithm finds particle size distributions comparable to those given by other measurement techniques. With regard to the particle size, a lower and an upper limit for the applicability were determined, which include three decades. As a further result, the model was validated at concentrations up to 10 vol.%. The model is considered to be open to development to cover even higher concentrations.     

高浓度超细颗粒的后向光子相关光谱测量技术研究

针对光子相关光谱颗粒粒径测量法不能在线测量高浓度超细颗粒的问题,通过分析溶液浓度对光子相关光谱测量法的影响,设计了一种后向散射光路,提出了后向光子相关光谱测量法.实验采用50 nm、100 nm以及500 nm三种标准乳胶球颗粒,在不同的浓度下分别用两种方法进行了测试.结果证明,后向光子相关光谱测量法能有效抑制多重散射的影响,适用于高浓度超细颗粒粒径的在线测量.     

Particle Sizing by Planar-Phase Doppler System

Conventional phase Doppler systems are useful for sizing particles in the order of microns, but sensitive to the Gaussian beam defect which can cause sizing errors. The defect can be significant when a large size is measured. In this paper, we present a new phase Doppler system using a planar optical layout which permits large particles to be measured in a forward scattering scheme without the Gaussian beam errors. The optical system design is discussed by numerical simulation based on the Mie theory.     

Lattice-Boltzmann Simulation of Particle Suspensions in Shear Flow

Inclusion of short-range particle–particle interactions for increased numerical stability in a lattice-Boltzmann code for particle-fluid suspensions, and handling of the particle phase for an effective implementation of the code for parallel computing, are discussed and formulated. In order to better understand the origin of the shear-thickening behavior observed in real suspensions, two simplified cases are considered with the code thus developed. A chain-like cluster of suspended particles is shown to increase the momentum transfer in a shear flow between channel walls, and thereby the effective viscosity of the suspension in comparison with random configurations of particles. A single suspended particle is also shown to increase the effective viscosity under shear flow of this simple suspension for particle Reynolds numbers above unity, due to inertial effects that change the flow configuration around the particle. These mechanisms are expected to carry over to large-scale particle-fluid suspensions.     

DLS粒度测量实验中噪声的影响与克服

噪声是始终存在于动态光散射实验的整个测量过程中,噪声的大小直接影响测量系统的信噪比大小与测量结果的准确性。根据噪声产生的物理原因,将动态光散射实验中的噪声分为外部环境噪声和设备内部噪声两大类。为了最大限度的降低噪声提高测量的准确性,在详细探讨影响动态光散射粒度测量实验中各种噪声的来源的基础上,分析了噪声对实验结果的影响,并提出相应解决的办法。     

Particle Sizing Using Frequency Domain Photon Migration

The transport properties of particulate process streams and their final product quality, are directly affected by critical parameters of particle size distribution, f(x), and volume, mass, or number density of particles or dispersed phase droplets. A method is proposed for the potential on-line monitoring of particle size distribution and volume fraction in real time, using frequency-domain photon migration measurements (FDPM). Theory, experimental measurements, and results for the determination of particle size distributions for both a polystyrene latex and a titanium dioxide suspension determined using the photon migration technique are presented. The critical issues associated with the application of photon migration to particulate and dispersed phase processes are discussed, including the effects of interparticle interactions on the transport of light.     

Calculating Shape Factors from Particle Sizing Data

It is well established that particle size and shape substantially influence the bulk properties of powdered materials. Although these characteristics are closely interrelated, the tendency has been to analyse the particle size independently from particle shape. The aim of this work was the assessment of particle shape through particle sizing data. For this purpose, three different particle shape materials – glass beads (spherical), crushed glass (moderately irregular) and mica (lamellar) – were tested, employing four particle sizers. The shape factor selected was the Wadell's sphericity, which was evaluated utilizing distinct equations. The comparison of the results reveals problems arising from the use of approximations rather than more fundamental equations.