Numerical simulation of flow hydrodynamics of struvite pellets in a liquid–solid fluidized bed

Phosphorus recovery in the form of struvite has been aroused in recent decades for its dual advantages in eutrophication control and resource protection.The usage of the struvite products is normally determined by the size which is largely depended on the hydrodynamics.In this study,flow behavior of struvite pellets was simulated by means of Eulerian–Eulerian two-fluid model combining with kinetic theory of granular flow in a liquid–solid fluidized bed reactor(FBR).A parametric study including the mesh size,time step,discretization strategy,turbulent model and drag model was first developed,followed by the evaluations of crucial operational conditions,particle characteristics and reactor shapes.The results showed that a cold model with the mesh resolution of 16 × 240,default time step of 0.001 sec and first order discretization scheme was accurate enough to describe the fluidization.The struvite holdup profile using Syamlal–O'Brien drag model was best fitted to the experimental data as compared with other drag models and the empirical Richardson–Zaki equation.Regarding the model evaluation,it showed that liquid velocity and particle size played important roles on both solid holdups and velocities.The reactor diameter only influenced the solid velocity while the static bed height almost took no effect.These results are direct and can be applied to guide the operation and process control of the struvite fluidization.Moreover,the model parameters can also be used as the basic settings in further crystallization simulations.     

城市热岛效应与景观格局相关性研究

城市下垫面的改变和人为热的增加是加剧热岛效应的重要原因,研究城市热岛效应对揭示城市景观的生态过程、城市空间结构的调整都有重要的指导意义,城市热岛效应与景观格局息息相关.遥感、地理信息系统与景观生态学理论共同形成了对大尺度城市空间格局独具特色的研究模式.卫星遥感数据反演法在城市热环境研究中具有举足轻重的地位,它实现了城市热岛效应的动态监测和内部结构分析.城市热岛与景观格局的相关研究往往转化为地表温度与土地覆盖/利用的相关研究,景观格局指数分析法是其重要研究方法,但仍存在界限不清、表现不敏感、生态学意义不明等问题,最后针对此类研究的重点难点提出建议.     

Forecasts of habitat loss and fragmentation due to urban growth are sensitive to source of input data

The conversion of natural habitat to urban settlements is a primary driver of biodiversity loss, and species' persistence is threatened by the extent, location, and spatial pattern of development. Urban growth models are widely used to anticipate future development and to inform conservation management, but the source of spatial input to these models may contribute to uncertainty in their predictions. We compared two sources of historic urban maps, used as input for model calibration, to determine how differences in definition and scale of urban extent affect the resulting spatial predictions from a widely used urban growth model for San Diego County, CA under three conservation scenarios. The results showed that rate, extent, and spatial pattern of predicted urban development, and associated habitat loss, may vary substantially depending on the source of input data, regardless of how much land is excluded from development. Although the datasets we compared both represented urban land, different types of land use/land cover included in the definition of urban land and different minimum mapping units contributed to the discrepancies. Varying temporal resolution of the input datasets also contributed to differences in projected rates of development. Differential predicted impacts to vegetation types illustrate how the choice of spatial input data may lead to different conclusions relative to conservation. Although the study cannot reveal whether one dataset is better than another, modelers should carefully consider that geographical reality can be represented differently, and should carefully choose the definition and scale of their data to fit their research objectives.     

Development pattern and enhancing system of automotive components remanufacturing industry in China

Along with the increasing number of automotive output and End-of-Life vehicles (ELVs) in China, resources shortage and environmental pollution are aggravating, so the tremendous need to reuse automotive components gives birth to the industry. The Chinese government becomes to realize that it is necessary to build a conservation-oriented and environment-friendly harmonious society. As the ultimate form of recycling, remanufacturing will be an effective method to promote the development of Chinese circular economy. The automotive remanufacturing industry in China is just at the preliminary stage, this paper presents some problems before remanufacturing, during remanufacturing and after remanufacturing, and then it points out several barriers, such as restrictive policies and regulations, consumer acceptance, scarcity of technologies, etc. Like many other developed countries, Chinese remanufacturing industry will also experience the primary stage, growth stage and developed stage. while the emphasis of resources input will not be the same. By analyzing the resources input characteristics at different development stages, three development patterns, such as the Government Incenting Pattern, Technology Driving Pattern and Market Leading Pattern, are put forward. At present, the cooperation of the government, industry, universities and research institutes, etc, will jointly construct the enhancing system of automotive components remanufacturing industry in China. Finally, it concludes with a summary and some suggestions in the field.     

福建乡村温泉旅游开发模式研究——以闽侯光明温泉为例

福建省温泉资源丰富,温泉旅游开发是福建省旅游业近阶段焦点之一.开发模式创新是温泉旅游企业赢得市场竞争,实现永续经营的关键.在总结国内外其他学者对温泉旅游开发模式研究的基础上,从发展推动力、资源利用集约程度、温泉与其他产业的对接、温泉主题文化、温泉度假区代系、温泉企业经营管理等六个方面对温泉旅游开发模式进行了系统解构,以闽侯县光明温泉为例,对福建乡村温泉旅游开发模式选择进行了探讨.     

农民工参加工伤保险的影响因素研究——基于政策和企业视角的实证分析

为了解我国农民工参加工伤保险的影响因素,提高农民工工伤保险的参保率,通过对全国9个省市共3 848名农民工的问卷调查,应用Logistic回归模型分析政策的因素和企业的因素对农民工参加工伤保险的影响。结果表明,农民工是否参加工伤保险受到各地工伤保险政策以及农民工所在企业两方面的影响。从政策的角度看,个体工商户参加工伤保险的规定、工伤保险基金的统筹水平以及工伤保险的偿付方式对农民工参加工伤保险有显著影响;从企业的角度看,农民工所在企业是否建有工会、企业所有制对农民工参加工伤保险有显著影响。建议各地进一步明确工伤保险政策中对个体工商户的参保要求,继续提高工伤保险基金的统筹水平,增加农民工领取工伤保险偿付的方式。建议劳动保障部门加强对未建有工会的企业,加强对私企,特别是个体工商户的监察力度。     

机械原因飞行事故诱因的分析与预测研究

为更好地预防机械原因飞行事故,提高安全管理和决策的水平,提出机械原因飞行事故诱因的分析与预测方法。首先借鉴"瑞士奶酪"模型的思想,建立了机械原因飞行事故诱因分析分类体系;而后构建了事故的二进制矩阵,通过进行比例矩阵分析和单一聚类分析来辨识重要的单诱因、两两诱因组合和事故主要诱发模式;最后采用Bootstrap方法对其进行预测。结果表明:所提出的方法能够辨识出机械原因飞行事故中的重要单诱因、两两诱因组合和主要诱发模式,并对其做出较为准确的预测,进而对制订事故防控预案,预防此类事故的发生具有重要意义。     

地下水曝气技术（AS）的国内外研究进展

地下水曝气法（Air Sparging,AS）凭借其高效、原位的优势已经成为治理土壤、地下水有机污染的重要技术,其修复机理是将加压空气注入到饱和含水层以下,有机污染物通过相间传质作用（溶解、挥发、解吸、生物降解等）转化为挥发性污染物,并随气流迁移至包气带,再由其他抽气装置收集到地表气体处理设备。本文总结了AS技术在理论模型、曝气性能影响因素（气体流型、曝气影响半径）等方面的研究现状,归纳了气体流型的发展过程以及测量曝气影响半径的常见方法。地下水曝气法在国外地下水、土壤有机污染修复中的应用越来越广泛,理论研究方面也比较成熟。文章比较了AS技术在国内外的研究和应用情况,认为目前该技术应朝着综合的方向发展,以提高污染物修复效率。     

基于可变模糊组合方法的瓦斯涌出量预测

矿井工作面瓦斯涌出是一个动态不确定过程。在分析了影响瓦斯涌出因素基础上,将可变模糊聚类与可变模糊模式识别两种模型相结合,提出了一种瓦斯涌出量预测的可变模糊组合方法。该方法首先利用粗糙集理论确定权重初值及各因素的重要性,然后利用可变模糊聚类模型求解最优模糊分类中心矩阵和最优权重,最后利用模式识别模型对待预测样本进行预测。以某矿井瓦斯涌出量预测为例,给出了具体预测过程。结果表明：可变模糊组合方法可行、有效。     

Open rivers: barrier removal planning and the restoration of free-flowing rivers

Restoration of unobstructed, free-flowing sections of river can provide considerable environmental and ecological benefits. It removes impediments to aquatic species dispersal and improves flow, sediment and nutrient transport. This, in turn, can serve to improve environmental quality and abundance of native species, not only within the river channel itself, but also within adjacent riparian, floodplain and coastal areas. In support of this effort, a generic optimization model is presented in this paper for prioritizing the removal of problematic structures, which adversely affect aquatic species dispersal and river hydrology. Its purpose is to maximize, subject to a budget, the size of the single largest section of connected river unimpeded by artificial flow and dispersal barriers. The model is designed to improve, in a holistic way, the connectivity and environmental status of a river network. Furthermore, unlike most previous prioritization methods, it is particularly well suited to meet the needs of potamodromous fish species and other resident aquatic organisms, which regularly disperse among different parts of a river network. After presenting an initial mixed integer linear programming formulation of the model, more scalable reformulation and solution techniques are investigated for solving large, realistic-sized instances. Results from a case-study of the Pike River Watershed, located in northeast Wisconsin, USA, demonstrate the computational efficiency of the proposed model as well as highlight some general insights about systematic barrier removal planning.