采用改进型多目标粒子群算法的电力系统环境经济调度

电力系统多目标环境经济调度要求在满足发电成本最小的同时发电厂的污染气体排放也最小,为此提出了基于Pareto占优策略和拥挤距离排序方法的改进型粒子群算法求解该多目标问题。采用容量可动态调整的外部存档集合存储当前Pareto最优解,利用Pareto占优策略确定个体最优位置,进而根据粒子拥挤距离确定全局最优位置,并设置了动态惯性权重,引入了小概率变异机制,提高了算法搜索能力。算例结果验证了该算法的有效性。     

变步长和拥挤度因子的自适应人工鱼群算法

为了改进传统的人工鱼群算法会随着迭代的深入而导致算法易陷入局部最优的问题,以及固定的参数导致算法收敛慢和求解精度不高的问题,提出了一种改进的人工鱼群算法.首先结合迭代次数,为移动步长引入一个权值; 然后以每条人工鱼的视野范围所构成的子群为小生境,结合子群最优解与当前人工鱼状态,为拥挤度因子引入一个变异策略.数值实验结果表明,本文提出的算法收敛速度快、精度高、鲁棒性强,优于传统的人工鱼群算法和文献[4]提出的算法.     

Using Holographic Microscopy To Measure the Effect of Confinement on Crowding Agents in Lipid Vesicles

The hydrodynamic effects of macromolecular crowding inside cells are often studied in vitro by using polymers as crowding agents. Confinement of polymers inside cell-sized droplets has been shown to affect the diffusion of small molecules. Here we develop a method, based on digital holographic microscopy, to measure the diffusion of polystyrene microspheres that are confined within lipid vesicles containing a high concentration of solute. We apply the method to three solutes of varying complexity: sucrose, dextran, and PEG, prepared at ∼7 % (w/w). We find that diffusion inside and outside the vesicles is the same when the solute is sucrose or dextran that is prepared below the critical overlap concentration. For poly(ethylene glycol), which is present at a concentration higher than the critical overlap concentration, the diffusion of microspheres inside vesicles is slower, hinting at the potential effects of confinement on crowding agents.     

Effect of pad geometry on current density and temperature distributions in solder bump joints

Three-dimensional thermo-electrical finite element analyses were conducted to simulate the current density and temperature distributions in solder bump joints with different pad geometries.The effects of pad thickness,diameter and shape on current density and temperate distributions were investigated respectively.It was found that pads with larger thickness or/and diameter could reduce current density and temperature in solder bump significantly.Pad shapes affected the current density and temperature distributions in solder bumps.The relatively low current density and temperature didn＇t occur in the bump joint with traditional rounded pad but occurred in bump joints with octagonal and nonagonal pads respectively.Therefore,optimized pad geometry may be designed to alleviate the current crowding effect and reduce the bump temperature,and therefore delay electromigration failure and increase the mean-time-to-failure.     

Secondary Current Crowding Effect during Electromigration of Flip-Chip Solder Joints

In flip-chip interconnects under current stressing, the primary current crowding effect occurs at the entrance edge of the contact interface with the highest current density. In this study, an increased current density also occurred at the other edge of the contact interface, followed by a selective dissolution of under bump metallization. After primary current crowding, the rest of electrons flow to the metallization edge, followed by an abrupt change in direction toward the anode. Primary current crowding is attributed to the electrical field change whereas the secondary crowding effect is due to the physical blocking of the electron flow. Because this effect is not as great as that of primary current crowding, it must be assisted by thermal diffusion.     

Current density redistribution from no current crowding to current crowding in Pb-free solder joints with an extremely thick Cu layer

In order to remove the effect of current crowding on electromigration, thick Cu under-bump metallization has been widely adopted in the electronics industry. Three-dimensional (3-D) integrated circuits, using through Si via Cu column interconnects, is being developed, and it seems that current crowding may not be a reliability issue. However, statistical experiments and 3-D finite element simulation indicate that there is a transition from no current crowding to current crowding, caused by void growth at the cathode. An analysis of the electromigration-induced failure mechanism in solder joints having a very thick Cu layer is presented. It is a unique failure mechanism, different from that in flip chip technology. Moreover, the study of marker displacement shows two different stages of drift velocity, which clearly demonstrates the back-stress effect and the development of compressive stress.     

Indoor transmission of SARS-CoV-2

It is essential to understand where and how severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is transmitted. Case reports were extracted from the local Municipal Health Commissions of 320 prefectural municipalities in China (not including Hubei Province). We identified all outbreaks involving three or more cases and reviewed the major characteristics of the enclosed spaces in which the outbreaks were reported and their associated indoor environmental aspects. Three hundred and eighteen outbreaks with three or more cases were identified, comprising a total of 1245 confirmed cases in 120 prefectural cities. Among the identified outbreaks, 53.8% involved three cases, 26.4% involved four cases, and only 1.6% involved ten or more cases. Home-based outbreaks were the dominant category (254 of 318 outbreaks; 79.9%), followed by transport-based outbreaks (108; 34.0%), and many outbreaks occurred in more than one category of venue. All identified outbreaks of three or more cases occurred in indoor environments, which confirm that sharing indoor spaces with one or more infected persons is a major SARS-CoV-2 infection risk.     

基于拥挤距离排序的铝电解多目标优化

针对铝电解生产过程难以快速、准确地获得节能减排多目标优化Pareto前沿问题,提出一种基于拥挤距离排序的多目标细菌觅食算法。方法在保证铝电解槽平稳运行的基础上,建立电流效率最大和温室气体排放量最小的多目标优化模型;利用拥挤距离更新外部档案及对菌群步长进行自适应动态调整,以改进种群的收敛性和多样性,最后对优化模型求解。通过实验可知,改进后的算法能快速获得分布均匀的Pareto最优解,运用优化后的决策参数指导生产,能在提高电流效率的同时减少温室气体的排放量,实现铝电解生产过程节能减排的目的。     

基于改进粒子群优化算法的多目标铜卷加工生产调度研究

针对多目标铜卷加工生产调度问题,提出一种自适应的改进粒子群优化算法。该算法采用基于个体拥挤距离排序的外部种群保留策略以避免陷入局部极值,基于个体拥挤距离概率更新全局极值以及基于支配关系更新个体极值,同时采用基于非支配解和单点交叉的内部种群规模自适应调整策略以及自适应动态惯性权重来保持种群的多样性。通过应用实例验证了该方法求解多目标铜卷加工生产调度问题的有效性。