A High-Throughput Screening System Based on Fluorescence-Activated Cell Sorting for the Directed Evolution of Chitinase A

Chitinases catalyze the degradation of chitin, a polymer of N-acetylglucosamine found in crustacean shells, insect cuticles, and fungal cell walls. There is great interest in the development of improved chitinases to address the environmental burden of chitin waste from the food processing industry as well as the potential medical, agricultural, and industrial uses of partially deacetylated chitin (chitosan) and its products (chito-oligosaccharides). The depolymerization of chitin can be achieved using chemical and physical treatments, but an enzymatic process would be more environmentally friendly and more sustainable. However, chitinases are slow-acting enzymes, limiting their biotechnological exploitation, although this can be overcome by molecular evolution approaches to enhance the features required for specific applications. The two main goals of this study were the development of a high-throughput screening system for chitinase activity (which could be extrapolated to other hydrolytic enzymes), and the deployment of this new method to select improved chitinase variants. We therefore cloned and expressed the Bacillus licheniformis DSM8785 chitinase A (chiA) gene in Escherichia coli BL21 (DE3) cells and generated a mutant library by error-prone PCR. We then developed a screening method based on fluorescence-activated cell sorting (FACS) using the model substrate 4-methylumbelliferyl β-d-N,N′,N″-triacetyl chitotrioside to identify improved enzymes. We prevented cross-talk between emulsion compartments caused by the hydrophobicity of 4-methylumbelliferone, the fluorescent product of the enzymatic reaction, by incorporating cyclodextrins into the aqueous phases. We also addressed the toxicity of long-term chiA expression in E. coli by limiting the reaction time. We identified 12 mutants containing 2–8 mutations per gene resulting in up to twofold higher activity than wild-type ChiA.     

A robust locating multi-optima approach for damage identification of plate-like structures

This paper proposes a robust optimization approach for multiple damage identification of plate-like structures. Different from traditional particle swarm optimizations (PSOs), a combined PSO and niche technique (NPSO) is proposed to solve multimodal optimization problems, with the full consideration of subswarm creation, merging and absorbing mechanism. As a hypersensitive parameter to damage, the curvature mode shape is adopted to construct the objective function. Case studies are conducted to investigate the effectiveness and robustness of the algorithm on multi-damage identification. Simulation results show that the proposed algorithm exhibits robust search performance on identifying damage locations accurately with good convergence behavior. It is hoped that this study can provide guidance on robust damage detection, especially when the structure is subject to multiple damages and external disturbances.     

基于种群划分与变异策略的粒子群优化算法

粒子群算法因其形式比较简洁，参数设置灵活，操作简便易行，并且能够快速收敛，从而引起广泛关注。但是传统的粒子群算法也有缺陷：收敛速度慢以及容易陷入局部最优等。针对这些问题，本文借鉴小生境的方法，在进化初始阶段，对种群进行划分，将初始种群分为子种群，对不同的子种群进行不同的变异策略；在进化过程中，针对不同的子种群，设置不同的惯性权重因子ω，用来增强全局搜索能力与局部搜索能力。实验结果表明，本文提出的算法较传统的粒子群算法具有较快的收敛性以及找寻的全局最优解更接近真实解集，收敛精度比较高。     

基于粒子群优化和支持向量机的花粉浓度预测模型

为了提高花粉浓度预报的准确率，解决现有花粉浓度预报准确率不高的问题，提出了一种基于粒子群优化（PSO）算法和支持向量机（SVM）的花粉浓度预报模型。首先，综合考虑气温、气温日较差、相对湿度、降水量、风力、日照时数等多种气象要素，选择与花粉浓度相关性较强的气象要素构成特征向量；其次，利用特征向量与花粉浓度数据建立SVM预测模型，并使用PSO算法找出最优参数；然后利用最优参数优化花粉浓度预测模型；最后，使用优化后的模型对花粉未来24 h浓度进行预测，并与未优化的SVM、多元线性回归法（MLR）、反向神经网络（BPNN）作对比。此外使用优化后的模型对某市南郊观象台和密云两个站点进行逐日花粉浓度预测。实验结果表明，相比其他预报方法，所提方法能有效提高花粉浓度未来24 h预测精度，并具有较高的泛化能力。     

采用信息增益率的混合入侵检测模型设计

针对现有混合入侵检测模型仅定性选取特征而导致检测精度较低的问题，同时为了充分结合误用检测模型和异常检测模型的优势，提出一种采用信息增益率的混合入侵检测模型.首先，利用信息增益率定量地选择特征子集，最大程度地保留样本信息；其次，采用余弦时变粒子群算法确定支持向量机参数构建误用检测模型，使其更好地平衡粒子在全局和局部的搜索能力，然后，选取灰狼算法确定单类支持向量机参数构建异常检测模型，以此来提高对最优参数的搜索效率和精细程度，综合提高混合入侵检测模型对攻击的检测效果；最后，通过两种数据集进行仿真实验，验证了所提混合入侵检测模型具有较好的检测性能.     

PSO优化多核RVM的模拟电路故障预测

针对模拟电路健康管理的特点，提出了一种基于PSO优化多核RVM的模拟电路故障预测方法。利用参数分析得到电路的输出频域响应作为特征，计算其与电路无故障标准响应的欧氏距离来表征电路元件健康值，将多个核函数线性组合，并用PSO优化多核RVM参数后的模型实现对各个时间点元件的健康值变化轨迹进行预测。仿真结果表明，该方法在小样本情况下，预测效果优于单一核函数的RVM模型，适用于健康管理中实时预测，具有较好的实用性。     

复杂地形下风力机尾流数值模拟研究和激光雷达实验对比

以CFD数值计算和实验相结合的方法,对处于中国西南某多山地区陆上风电场的尾流特性进行研究,验证不同数值方法在复杂地形的适用性。首先采用2台激光雷达,测量目标风力机一个月内的自由来流风速和尾流廓线,在地形上坡加速效应下,不同大气稳定度下目标风力机的自由来流风速廓线均呈负梯度。然后分别采用经典致动盘和改进致动盘法,模拟目标风力机在主风向下的尾流发展。不同于只有风速与压降关系的经典致动盘法,改进致动盘法更考虑了叶片几何和气动参数(尺寸信息、攻角、桨距角、升阻力系数等)。通过与后置激光雷达尾流测试结果对比,这2种基于CFD技术的数值模拟方法,计算网格相同,计算时间相当,且均能较好地模拟因为复杂地形而引起的尾流偏转;其中改进致动盘的尾流形状与激光雷达相似,速度亏损也更接近激光雷达结果。因此,改进致动盘法更适合于复杂地形条件下风场模拟,较好平衡了计算的效率与精度。     

定子分段式永磁直线同步电机速度波动抑制方法研究

为了解决定子分段式永磁直线同步电机(PMLSM)存在的因磁阻效应、负载阻力、摩擦力、参数摄动以及动子进出定子时耦合面积变化所造成的控制性能下降的难题,根据动子和定子的耦合状态,提出一种在完全耦合阶段和动子退出定子阶段的分段式控制方法。首先,在动子与定子完全耦合阶段采用改进滑模控制器减小推力波动导致的速度波动,再通过加入扰动观测器降低滑模切换项所带来的抖振现象;在动子退出定子阶段,建立相关电磁参数与动子位置的函数关系,实时补偿由耦合面积变化引起的动子失速,使动子速度在退出时接近给定值。仿真及实验结果表明动定子完全耦合过程中的速度稳态误差为0.005 m/s,收敛时间为0.3 s,动子退出定子阶段的速度波动不超过0.04 m/s,满足定子分段式PMLSM用于长行程自动运输系统对平稳性及快速性的需求。     

Effect of paddy variety,milling status and aeration on the progeny emergence of Sitophilus oryzae L. (Coleoptera: Curculionidae)

In Sri Lanka, insects cause enormous losses in stored paddy; the rice weevil Sitophilus oryzae is a devastating insect. The magnitude of losses in stored paddy caused by insects varies with characteristics of paddy but has not yet been fully investigated. Due to the increased concerns on the use of synthetic chemicals, safer alternative pest management strategies for stored paddy are needed. Objectives of this study were to determine the effect of paddy variety, milling status and nature of aeration on the progeny emergence of S. oryzae. The experimental design was a three-factor factorial, completely randomized design (CRD).Freshly emerged S. oryzae adults were introduced to un-milled paddy or milled/polished rice belonging to traditional and improved varieties. The samples were maintained either open or airtight, and the progeny adults emerged was determined at monthly intervals. Progeny emergence was lower in the traditional varieties, un-milled paddy and under air-tight condition compared to improved varieties, milled/polished rice and aerated samples, respectively. Overall, the improved variety Bg 300 exhibited the maximum resistance to infestation by S. oryzae. Furthermore, white-colour and long-grain varieties produced lower progeny of S. oryzae than red-colour and short-grain varieties, respectively. It is concluded that the maximum protection in paddy/rice from insect infestation during storage can be achieved by using traditional varieties, stored as un-milled paddy (without dehusked) under airtight condition.     

基于粒子群优化算法的五自由度机械臂轨迹规划

为了让机械臂的工作时间达到最优,以自主研发的抛光机器人样机为研究对象,针对手表表壳表耳部分的抛光过程,提出PSO算法对五自由度机械臂轨迹规划进行优化,并通过MATLAB软件进行机械臂的仿真与分析。仿真结果表明,基于PSO算法的轨迹规划使机械臂在工作过程中加加速度不会产生突变,运动轨迹精度高,机械臂工作时间达到最优。