Modelling of flocculation using a population balance equation

In this paper, a model based on a population balance equation (PBE) is developed. It aims at reproducing experimental floc size distributions obtained at steady state in a jar-test. The objective is to develop a simple model, based on physical phenomena, and that does not contain any adjustable parameters. Floc size distributions obtained using a part of a particle image velocimetry (PIV) device and image analysis are used to develop mathematical expressions for the aggregation and breakage kernels. A critical volume beyond which breakage is of significant importance is identified and related to the hydrodynamics. Hydrodynamic sequencing allows the distribution of the daughter particles resulting from a breakage event to be established. The model is finally successfully validated against experimental results.     

“边缘社区”探察——我国流动人口聚居区的现状特征透析

首先指出 ,所谓流动人口聚居区 ,即是以自发在社会经济部门从事经济和业务活动的城市暂住人口为居民主体、以房屋租赁为主导建构方式、以城乡结合部为区位选择的自发型集中居住区。在对京、宁、深三市典型的边缘性聚居区进行调研的基础上 ,着重从区位分布、居民构成、土地使用、空间布局、居住环境等方面入手 ,分析和归纳了各类聚居区不同的类型差别和特征分异 ,从而为其进一步的整合提供客观的依据     

粒子群算法种群结构与种群多样性的关系研究

本文采用种群熵刻画粒子群算法中种群的多样性,并通过一组标准测试函数分析了不同的种群结构及邻城关系对粒子群算法种群多样性变化和算法性能的影响。实验结果表明,不同的种群结构具有不同的信息传递特性,对粒子群种群多样性的变化及算法的搜索效果有着较大的影响,因此对于不同的问题需根据其特点选择不同的种群结构。     

Response of yellow perch in Les Cheneaux Islands,Lake Huron to declining numbers of double-crested cormorants stemming from control activities

The yellow perch (Perca flavescens) fishery of the Les Cheneaux Islands region of Lake Huron experienced an unprecedented collapse in 2000. Immediately prior to the collapse was the proliferation of double-crested cormorants (Phalacrocorax auritus) in the area. Subsequent investigations established that double-crested cormorant predation was chief among the forces shaping the local yellow perch population and contributing to the collapse of the fishery. A double-crested cormorant control program was implemented in 2004 with the objective of benefiting the yellow perch population and fishery. This study used creel survey and gillnet fish community assessment data to evaluate the response of the yellow perch population and fishery. In all, seven key yellow perch metrics were analyzed using regression analysis with double-crested cormorant abundance as the independent variable. As double-crested cormorant abundance declined, yellow perch abundance increased, total mortality rate decreased, the angler catch rate and harvest in the recreational fishery improved, yellow perch growth rate declined and mean age increased. Increased yellow perch recruitment was documented since 2003 but it was the longevity of these year classes, (improved survival) as much or more than their magnitude of the year class, that allowed for the progress towards recovery. Questions facing managers are the sustainable level of double-crested cormorants in the region and the long term prognosis for the yellow perch fishery to fully recover to pre-double-crested cormorant levels.     

Coupled population balance–CFD simulation of droplet breakup in a high pressure homogenizer

A framework for a one-way coupling between population balance equation (PBE) and computational fluid dynamics (CFD) for emulsions undergoing breakup in a turbulent flow-regime is implemented in the open-source CFD package OpenFOAM. The PBE is discretized using a volume conservative scheme. This framework was applied to emulsification of food-grade vegetable oil-in-water emulsions in a Niro Soavi high pressure homogenizer (HPH) with different pressure drops and using oils of varying viscosities. Different breakage rate models were implemented, as well as the model of Becker et al. (2014) which is an extension of the Luo and Svendsen (1996) model to account for the dispersed phase viscosity. The Becker et al. (2014) model was found to give better predictions after three consecutive passes, without the need for additional empirically determined parameters. The multi-scale PBE–CFD modelling approach allowed a detailed analysis of the breakup process in the gap and jet of the HPH valve.     

Hangzhou

Once an ancient capital of China, Hangzhou has transformed to a post-socialist city that faces profound changes and critical challenges in various aspects of urban development such as historical legacies, market-oriented urban economy, expansive urban spatial patterns, population management, land use restructuring, and affordable housing provision. Under the increasingly stronger market power, the city strives to reposition itself to be an important economic center in the Yangtze River Delta Region, through strategic and innovative urban growth agenda. This profile identifies some fundamental issues and processes that underscore Hangzhou’s recent urban development and presents future prospect for a coastal metropolis with regional significance.     

不同NPK配置对强筋小麦群体生物量与产量的效应研究

在关中川道灌区以强筋小麦陕253为材料,研究了不同NPK配置对其不同生育期生物产量、群体数量和产量的效应,结果表明提高施肥量可显著增加生物产量、群体数量及产量,处理平均值分别比常规处理增加11.9%~43.6%、4.1%~17.4%和8.3%,其最佳N、P、K配置依次为N135kg hm-2,P2O5和K2O各120kg hm-2、N135kg hm-2,P2O5225kghm-2,K2O120kg hm-2和N225kg hm-2,P2O5和K2O各120kg hm-2。在目前常规投肥水平下适度增加钾肥有利于生物产量的显著提高,增加磷肥和钾肥有利于群体数量的提高,增施氮钾肥有显著的增产效果。产量的最佳NPK配比较常规处理增产19.1%,其增加养分的平均产量4.44 kg kg-1,比各处理平均养分产量高1.6倍。     

Exploring dynamic self-adaptive populations in differential evolution

Although the Differential Evolution (DE) algorithm has been shown to be a simple yet powerful evolutionary algorithm for optimizing continuous functions, users are still faced with the problem of preliminary testing and hand-tuning of the evolutionary parameters prior to commencing the actual optimization process. As a solution, self-adaptation has been found to be highly beneficial in automatically and dynamically adjusting evolutionary parameters such as crossover rates and mutation rates. In this paper, we present a first attempt at self-adapting the population size parameter in addition to self-adapting crossover and mutation rates. Firstly, our main objective is to demonstrate the feasibility of self-adapting the population size parameter in DE. Using De Jong's F1–F5 benchmark test problems, we showed that DE with self-adaptive populations produced highly competitive results compared to a conventional DE algorithm with static populations. In addition to reducing the number of parameters used in DE, the proposed algorithm actually outperformed the conventional DE algorithm for one of the test problems. It was also found that that an absolute encoding methodology for self-adapting population size in DE produced results with greater optimization reliability compared to a relative encoding methodology.