由 Mie 散射光强反演颗粒粒度分布的一种改进正则化法

基于Mie散射的激光粒度仪广泛地应用在颗粒粒度测量中,其中由光强分布演算出粒度分布的计算方法一直是关注的热点。此反演问题属于第一类Fredholm算子方程,具有不适定性,难以得出准确的稳定解,需要用高效的数值算法。本文提出一种应用于该类仪器颗粒粒度分布反演问题的改进正则化法,采用广义交叉验证法(GCV)来选择正则参数,并引入松弛技术,将迭代值加工成一种松弛值以改善精度,得出了稳定的正则拟解(近似解)。经标准颗粒的验证和计算机模拟证实,此算法是可行和有效的。     

An improved hybrid self-inertia weight adaptive particle swarm optimization algorithm with local search

As an evolutionary computing technique, particle swarm optimization (PSO) has good global search ability, but the swarm can easily lose its diversity, leading to premature convergence. To solve this problem, an improved self-inertia weight adaptive particle swarm optimization algorithm with a gradient-based local search strategy (SIW-APSO-LS) is proposed. This new algorithm balances the exploration capabilities of the improved inertia weight adaptive particle swarm optimization and the exploitation of the gradient-based local search strategy. The self-inertia weight adaptive particle swarm optimization (SIW-APSO) is used to search the solution. The SIW-APSO is updated with an evolutionary process in such a way that each particle iteratively improves its velocities and positions. The gradient-based local search focuses on the exploitation ability because it performs an accurate search following SIW-APSO. Experimental results verified that the proposed algorithm performed well compared with other PSO variants on a suite of benchmark optimization functions.     

A Bayesian inversion method for estimating the particle size distribution of latexes from multiangle dynamic light scattering measurements

A statistical Bayesian method is proposed for estimating the particle size distribution (PSD) of polymeric latexes from multiangle dynamic light scattering (MDLS) measurements. The procedure includes two main steps: 1) the calculation of the angle-dependent average diameters of the PSD from the MDLS autocorrelation measurements, and 2) the PSD estimation through a Bayesian method (that is solved with a Markov chain Monte Carlo sampling strategy implemented in the form of a Metropolis-Hasting algorithm). First, the method was evaluated through two simulated examples that involved unimodal and bimodal PSDs of different shapes. Then, the method was employed for estimating two bimodal PSDs obtained by mixing two narrow polystyrene standards. For comparison, all examples were also solved by numerical inversion of the raw MDLS autocorrelation measurements through a classical regularization technique typically used for inverting ill-conditioned linear problems. The proposed method appears as an effective and robust tool for characterizing unimodal or multimodal PSDs without requiring any a priori assumption on the number of modes or on their shapes. For unimodal PSDs exhibiting high asymmetries and for bimodal PSDs with modes of different particle concentration, the Bayesian method produced more accurate results than those obtained with the classical regularization technique.     

多输出回归算法在超声粒径分布反演中的研究

悬移质粒径分布作为研究水体运动规律和水利建设中的关键参数,通过对Epstein-Carhart-Allegra-Hawley(ECAH)模型和超声衰减实验这类先验信息的研究,结合机器学习算法对悬移质颗粒粒径进行预测。根据超声衰减实验和其他相关物性参数提取特征,结合筛分法确定的粒径分布种类制作训练数据集和验证数据集,通过对单种粒径预测的梯度提升决策树(Gradient Boosting Decision Tree,GBDT)算法进行组合构建多输出回归算法对粒径分布进行预测。结果表明:三种样品单种粒径的最大相对误差在±10%以内,中位径误差分别为0.07%、?0.10%和?2.20%;在实验范围内,预测分布结果与筛分法结果一致,有较高的可行性和准确度,可为粒径分布测量提供一种新的思路。     

均匀粒度分布的双壳相变储湿微胶囊制备

分别以正十八烷、甲基丙烯酸甲酯和壳聚糖作为核材料、内壳和外壳,采用细乳液原位聚合法及界面聚合法制备双壳相变储湿微胶囊。通过均匀设计与径向基函数神经网络结合,考察因素(如乳化剂用量、助乳化剂用量、引发剂用量、超声乳化时间和搅拌速度)对双壳相变储湿微胶囊粒度分布的影响,并且对最均匀粒度分布双壳相变储湿微胶囊进行表征与测试。结果表明,当扩展系数为0.55时,径向基函数神经(Radial Basis Function,RBF)网络具有最佳的逼近效果。最均匀粒度分布双壳相变储湿微胶囊的制备工艺参数:乳化剂用量为3.58wt%、助乳化剂用量为0.53wt%、引发剂用量为1.86wt%、超声乳化时间为11.35 min,搅拌速度为632r·min~(-1)。基于上述制备参数,d_(10)为3 352.0nm、d50为4 474.9nm,d_(90)为6 108.4nm,d_(90)-d_(10)实测值为2 756.4nm,实测值与预测值吻合较好,相对误差为2.69%。在相对湿度35%~65%的平衡含湿量为0.0547~0.1259g·g~(-1),相变温度为28.87℃,相变焓为78.45J·g~(-1)。     

A particle size distribution analysis method to quantitatively evaluate coagulation of fine particles in aqueous solutions

A laser particle size analysis method was proposed to quantitatively evaluate the fine particles coagulation. Laser particle size analyzer was used to measure the particle size distribution of coal slime at different stirring rates and different concentrations of Ca²⁺ or Na⁺. The value of d₁₀, d₅₀, and d₉₀ can be used to quantitatively evaluate the coagulation performance of fine particles, the greater value of d₁₀, d₅₀, and d₉₀ they are, and the better coagulation performance it is. It was found that the addition of Ca²⁺ could promote easier coagulation for fine particles than the addition of Na⁺, and the best coagulation performance, in which d₉₀ was greater than 700?µm, occurred at the conditions of 1000?rpm stirring speed and Ca²⁺ concentration above 5?mmol/L. It is because that the electronegativity of coal and clay particles would be weakened in the presence of Ca²⁺, and the electrostatic repulsive force of fine particles would be reduced, resulting in the fine particles becoming easy to coagulate. Moderate stirring speed could provide kinetic energy for particle to cross the energy barrier of two colloidal particles. On the contray, coagulated particles broke up when the stirring speed reached a high level.     

Modeling of particle size distribution and energy consumption of wet milled maize at varying soaking period and method in the production of Ogi

Energy consumptions and particles size distribution of soaked maize grains at varying time were studied and modeled. Rosin–Rammler–Bennet (RRB) model well fitted first milling size distribution with a high coefficient of determination (R²) and low root mean square error (RSME). The milling energy of maize grains decreased significantly (p?<?0.05) with increase in soaking time. The milling energy decrease from 32 to 8.72?kWh/kg and 32.00 to 9.00?kWh/kg for maize variety E9W at 24th hour soaking conditions of 28 and 65°C, respectively. Similar observations for A4W, B2Y and C3Y at 24?h of soaking were recorded. The Work index, Kick’s and Rittinger’s constants decreased with increase in soaking time. There was significant difference (p?<?0.05) in values obtained for Bond work index, Rittinger’s and Kick’s constants; these decreased with increase in soaking time. Predicted energy consumption followed similar trend. The interaction effect between energy consumption, Moisture content, and Milling time showed a high R² (0.8767–0.99349); while the regressed model for determining energy consumption from relationship between the mass, moisture content, milling time and the ratio of the geometric diameter mean and final size of the product were also established in this work with R² ranging from 0.9355 to 0.967.     

Determination of particle size by using the angular distribution of backscattered light as measured with low-coherence interferometry

We employ a novel interferometer to measure the angular distribution of light backscattered by a turbid medium. Through comparison of the measured data with the predictions of Mie theory, we are able to determine the size of the scatterers comprising the medium with subwavelength precision. As the technique is based on low-coherence interferometry, we are able to examine the evolution of the angular distribution of scattered light as it propagates into the medium. The effects of multiple scattering as a function of penetration depth in the medium are analyzed. We also present various considerations for extending this technique to determining structural information in biological tissues, such as the effects of a distribution of particle sizes and the need to average out speckle contributions.     

超声法纳米颗粒悬浮液粒径测量中温度影响的实验研究

针对医药、化工领域高浓度纳米悬浮液颗粒粒径超声检测中温度影响,采用超声衰减谱法(UAS)对体积浓度30%的纳米铟锡金属氧化物(ITO)水性悬浮液在循环流速800 r/min,温度298～358 K时颗粒粒径分布进行实验。结果表明:温度升高,超声幅值A减小,超声衰减系数增大,颗粒中位径D50增大,颗粒系分布曲线整体朝大颗粒方向偏移,但是分布宽度保持稳定的趋势。同时,将室温(298K)测量结果与CPS离心沉降颗粒测量仪对比,结果较吻合。通过线性回归的方法修正温度对测量结果的影响,超声衰减法能够应用于358K的高温下高浓度纳米颗粒检测。     

激光光散射法测定聚乳酸分子量及其分子量分布

介绍了一种用于测定聚乳酸分子量及其分布的多角度激光光散射法；给出了该方法的实验步骤及结果。该法以四氢呋喃为溶剂和流动相，凝胶渗透色谱柱为分离体系，结合十八角激光散射仪和示差折光仪等检测器进行联机测量。实验测得合成聚乳酸重均分子量在30000-150000g／mol之间，分子量分布（Mw／Mn）为1.3～1．8。     

A pitch distribution in slow-wave structure of STWT using Cauchy mutated cat swarm optimization with gravitational search operator

Space traveling-wave tube (STWT) is a special power amplifier used in the space technology field to perform high-power conversion of signals; the pitch distribution is core parameter in slow-wave structure to ensure energy exchange between the electron beam and electromagnetic wave. A novel Cauchy mutated cat swarm optimization with gravitational search operator (GS-CMCSO) is proposed and applied to slow-wave structure design of STWT, electron beam efficiency is used as the objective function, and 1-D CHRISTINE code is introduced to obtain the output value of STWT, the pitch distribution to obtain best beam efficiency can be calculated. Experiments are carried out based on GS-CMCSO; quantum particle swarm optimization (QPSO) and Cauchy mutated cat swarm optimization (CMCSO) algorithms are introduced for optimization performance comparison. The experimental results demonstrate that the best beam efficiency (42.6%) generated by GS-CMCSO is larger than those of CMCSO (40.5%) and QPSO (34.9%); when the STWT is saturated, the output power and gain optimized by GS-CMCSO are excellent. Thus, the proposed method is very suitable for pitch distribution optimization in the slow-wave structure of STWT and performs better than those on QPSO and CMCSO.     

Improvement of pressure distribution to arbitrary geometry with boundary condition represented by polygons in particle method

The boundary condition represented by polygons in the moving particle semi‐implicit method can accurately represent geometries and treat complex geometry with high efficiency. However, inaccurate wall contribution to the Poisson's equation leads to drastic numerical oscillation. To address this issue, in this research, we analyzed the problems of the Poisson's equation used in the boundary condition represented by polygons. The new Poisson's equation is proposed based on the improved source term (Tanaka and Masunaga, Trans Jpn Soc Comput Eng Sci, 2008). The asymmetric gradient model (Khayyer and Gotoh, Coastal Engineering Journal, 2008) is also adopted to further suppress the numerical oscillation of fluid particles. The proposed method can dramatically improve the pressure distribution to arbitrary geometry in three dimensions and keep the efficiency. Four examples including the hydrostatic simulation, dam break simulation, and two complex geometries are verified to show the general applicability of the proposed method. Copyright © 2017 John Wiley & Sons, Ltd.