粮食烘干系统大型高效环保除尘装置模块化设计与分析

针对粮食烘干系统中所用大型除尘装备不易运输与安装的问题,采用离散的思想,将大型除尘设备分成容易运输和吊装的小单元,单元之间可以通过快速地定位和连接固定实现快速安装。设计装置能有效地减少运输和安装周期,推动粮食烘干过程中相关环保装备的应用与发展。

基于模块化设计的易维护型低压无功补偿装置

低压配网作为电力系统的末端,是在电力系统最为复杂的部分,其线损占电网总线损的一半以上。随着电网公司改革的推进,配电网逐渐向智能化、节能环保化、集约化的方向发展。本文研究一种新型的低压无功补偿装置,通过对无功补偿装置的补偿单元进行模块化设计,实现在无功补偿方面的容量可调整、分组定制化、维护便捷化的目标。

基于就业导向的矩阵结构模块课程体系构建——以高分子材料与工程专业为例

课程体系是学校办学理念、专业建设思路的集中体现,也是人才培养目标实现的关键途径。本文结合实践,分析了目前地方应用型院校专业课程设置问题所在,提出了构建以就业为导向的矩阵结构模块课程体系的策略。

Aging Characteristics of Lithium-Ion Battery Under Fast Charging Based on Electrochemical-thermalmechanical Coupling Model

The aging characteristics of lithium-ion battery(LIB)under fast charging is investigated based on an electrochemical-thermal-mechanical(ETM)coupling model.Firstly,the ETM coupling model is established by COMSOL Multiphysics.Subsequently,a long cycle test was conducted to explore the aging characteristics of LIB.Specifically,the effects of charging(C)rate and cycle number on battery aging are analyzed in terms of nonuniform distribution of solid electrolyte interface(SEI),SEI formation,thermal stability and stress characteristics.The results indicate that the increases in C rate and cycling led to an increase in the degree of nonuniform distribution of SEI,and thus a consequent increase in the capacity loss due to the SEI formation.Meanwhile,the increases in C rate and cycle number also led to an increase in the heat generation and a decrease in the heat dissipation rate of the battery,respectively,which result in a decrease in the thermal stability of the electrode materials.In addition,the von Mises stress of the positive electrode material is higher than that of the negative electrode material as the cycling proceeds,with the positive electrode material exhibiting tensile deformation and the negative electrode material exhibiting compressive deformation.The available lithium ion concentration of the positive electrode is lower than that of the negative electrode,proving that the tensile-type fracture occurring in the positive material under long cycling dominated the capacity loss process.The aforementioned studies are helpful for researchers to further explore the aging behavior of LIB under fast charging and take corresponding preventive measures.

大型数据中心规划与建设研究

文章简要论述了大型数据中心规划的概念,分析了数据中心主要系统对物理环境的要求,详细阐述了数据中心与民用建筑在结构上的区别,提出在规划建设上应关注IT、业务及场地等各方面的需求,优先满足数据中心用电、制冷、面积三个相互制约的基本条件,提高数据中心可用性级别,降低运营成本.

Spatial and Temporal Variability of Farm Size in China in Context of Rapid Urbanization

During the last 30 years, China has witnessed rapid economic growth and dramatic urbanization, with about 1.2 x 107 rural people migrating annually into urban areas. Meanwhile, especially since 1995, the rural population has been declining, which is closely linked to land circulation and the increase in farm size in many villages. Increasing scale of farming operations is often regarded as a key to avoiding the abandonment of farmland and to increasing the income of rural farmers. However, until now, there has been little research on the spatial and temporal variability of farm size at the national level in China. Using data from the national agricultural cen- sus and rural household surveys, this study examines the characteristics of land use circulation and the consequent changes in the area of farmland per household. The results show that： 1） 12.2% of rural households were involved in land circulation at the national level. The highest amounts of land circulation have occurred in those provinces where the farmland per capita is more than 0.2 ha or less than 0.1 ha; 2） over 80% of households operate less than 0.6 ha of farmland; 3） the proportion of mid-sized farms （between 0.2 ha and 0.6 ha per household） has decreased while the smallest and the largest farms have increased. This bears some similarity with the phenomenon known as the ＇disappearing middle＇, referring to the changes in farm size. This study establishes a framework for interpreting the factors affecting the changes in farm size in China, which include two promoting factors （urbanization and agriculture） and four hindering fac- tors （agricultual land system, household registration, stable clan system, and farmland loss）.

Analysis of Urbanization Based on Center-of-gravity Movement and Characteristics in Songhua River Basin of China and its Southern Source Sub-basin between 1990 and 2010

Urbanization in modern times led to a series of development strategies that brought new opportunities in China. Rapid urbanization caused severe stress to the ecosystems and the environment. Using the center-of-gravity(COG) method and parameters such as population, economy, and land, we studied the urbanization pattern in Songhua River Basin and its southern source sub-basin from 1990 to 2010. Urbanization was analyzed based on the COG position, eccentric distance, movement direction of COG, and distance of COG movement. Various characteristics of urbanization in the southern source sub-basin of the Songhua River were explained in relation to the whole Songhua River Basin. Urbanization in the southern source sub-basin of the Songhua River is balanced, relatively advanced, and stable compared to the whole Songhua River Basin. The average eccentric distance between the urbanization COGs in the Songhua River′s south source basin indicated rapid expansion of land urbanization during the span of this study. A basic pattern of urbanization COG in the whole Songhua Basin was observed, but there existed differences among the three aspects of urbanization process. Land urbanization is still in its active stage, so future studies should focus on analysis of such urbanization trends.

Formation of Los Angeles's low density and high car dependence

As a typical car-dependent city, Los Angeles （LA） is extensively used as an example in research to illustrate car influences on city form. Focusing on the features of LA＇s geologic conditions and civil circumstances, we argued that the relationship between LA＇s low-density pattern and car dependence is more involved than previously deemed simple causality. The low density should be primarily credited to the spacious requirement of the mining industry, frequent earthquakes and multiethnic population of the city. Off reserves in LA fueled its economic boom and fast urbanization that coincided with the start of mass production of cheap cars, and cars became medium-priced consumables for average families. Politicians preference for short constrnction-period projects enabled fast establishment of LA＇s highway infrastructure. The popularity of car use in return faciliatated further development of the low-density pattern of the city. The low-density urban form and car dependence created environmental and social problems for LA. Looking at P. R. China＇s motorization and urban development, we found that the trajectory of Beijing＇s motorization between 197g and 2003 coincides with that of the U.S. in the 1910s and 1920s. Lessons from LA＇s urban and transportation development should be suggestive to China＇s urban and transportation planning.

Simulation of Volume and Heat Transport along 26.5°N in the Atlantic

The observed meridional overtuming circula- tion （MOC） and meridional heat transport （MHT） estimated from the Rapid Climate Change/Meridional Circu- lation and Heat Flux Array （RAPID/MOCHA） at 26.5°N are used to evaluate the volume and heat transport in the eddy-resolving model LASG/IAP Climate system Ocean Model （LICOM）. The authors find that the Florida Cur- rent transport and upper mid-ocean transport of the model are underestimated against the observations. The simulated variability of MOC and MHT show a high correlation with the observations, exceeding 0.6. Both the simulated and observed MOC and MHT show a significant seasonal variability. According to the power spectrum analysis, LICOM can represent the mesoscale eddy characteristic of the MOC similar to the observation. The model shows a high correlation of 0.58 for the internal upper mid-ocean transport （MO） and a density difference between the western and eastern boundaries, as noted in previous studies.

From Sequential to Parallel Growth of Cities： Theory and Evidence from Canada

This paper examines city growth patterns and the corresponding city size distribution evolution over long periods of time using a simple New Economic Geography(NEG) model and urban population data from Canada. The main findings are twofold. First, there is a transition from sequential to parallel growth of cities over long periods of time: city growth shows a sequential mode in the stage of rapid urbanization, i.e., the cities with the best development conditions will take the lead in growth, after which the cities with higher ranks will become the fastest-growing cities; in the late stage of urbanization, city growth converges according to Gibrat′s law, and exhibits a parallel growth pattern. Second, city size distribution is found to have persistent structural characteristics: the city system is self-organized into multiple discrete size groups; city growth shows club convergence characteristics, and the cities with similar development conditions eventually converge to a similar size. The results will not only enhance our understanding of urbanization process, but will also provide a timely and clear policy reference for promoting the healthy urbanization of developing countries.

Fast Generation of Einstein–Podolsky–Rosen States for Two Cavity Modes with a Collection of Driven Atoms

We propose an efficient scheme for realizing two-mode squeezing for two cavity modes with an atomic ensemble trapped in the cavity and driven by two classical fields. Through a suitable choice of the driving classical fields, the evolution dynamics of the two cavity modes is decoupled with the atomic system and described by a two-mode squeezing operator. We show that a highly squeezed state can be obtained at the output even with a bad cavity. The required experimental techniques are within the scope of what can be obtained in the BEG-cavity setup.