A new class of skew distributions with climate data analysis

In this paper, we develop a new general class of skew distributions with flexibility properties on the tails. Moreover, such class can provide heavy and light tails. Some of its mathematical properties are studied, including the quantile function, the moments, the moment generating function and the mean of deviations. New skew distributions are derived and used to construct new models capturing asymmetry inherent to data. The estimation of the class parameters is investigated by the method of maximum likelihood and the performance of the estimators is assessed by a simulation study. Applications of the proposed distribution are explored for two climate data sets. The first data set concerns the annual heat wave index and the second data set involves temperature and precipitation measures from the meteorological station located at Schiphol, Netherlands. Data fitting results show that our models perform better than the competitors.     

回热器对制冷系统性能的影响

通过对制冷系统中回热器、蒸发器和压缩机工作过程的理论分析以及对蒸发器的热设计,定量地讨论了回热器出入口条件的改变对蒸发器尺寸、压缩机功率以及制冷系统成绩系数等的影响。降低制冷工质在回热器出口处的过热度,可以减小蒸发器的尺寸,但由此带来的不利因素,是需要增制冷工质的质量流量以及提高压缩机的压缩功率。     

起伏多相流管路持液率计算方法研究

起伏多相流管路持液率计算方法在工艺计算中具有重要的地位,但目前只能靠经验或半经验相关式计算。计算水平管持液率,Eaton和DuklerII相关式较好;在下坡管段使用BB相关式,易导致持液率小于0的情况,一般不采用BB相关式计算持液率;在上坡管段,如果对应水平持液率大于0.309 7时,宜采用其它方法计算持液率或者在程序中将持液率大于1时自动赋1处理;计算起伏管路的持液率采用BBE、BBD和MBX相关式误差较小。     

基于MATLAB的管壳式换热器优化设计

基于MATLAB 7.6开发了管壳式换热器,充分利用压降优化设计软件。通过改变换热器结构,充分利用管壳程压降,提高传热系数,减少换热面积。通过案例分析表明,充分利用压降后,换热器的传热系数提高了21%,换热面积减小了20%,大大减少了换热器的投资费用。     

铸型—冷铁—金属传热特性的研究

本文通过实验,测出冷铁在铸件凝固过程中的温度变化,找出铸件与冷铁间的等效界面热阻值,此值可供模拟铸件凝固时应用。     

Effects of urbanization on plant flowering phenology: A review

Studies of flowering and leafing phenology have dramatically increased during the last few decades because changes in plant phenology can be indicative of possible effects of climate change at multiple scales. This article reviews the available literature focusing on the effects of urbanization on flowering phenology. The literature of flowering phenology in urban environments suggests that spring-blooming plants in a variety of ecosystems in North America, Europe, and China tend to bloom earlier in the city than in the surrounding un-urbanized habitat. Moreover, ephemerals, early spring bloomers, and insect-pollinated plants in these environments tend to be more sensitive than perennials, mid- or late-spring bloomers, and wind-pollinated plants. Researchers attribute advanced flowering in urban environments to the Heat Island Effect. The potential ecological consequences of changes in flowering phenology in urbanized areas are not well understood or explicitly studied. However, studies in global biology have suggested that climate change may result in a series of important ecological consequences as well as human-related problems such as earlier and extended allergy seasons. More field-based studies are needed to elucidate this issue.     

热方程组的熄灭时间对初值的连续依赖性

利用极值原理和构造辅助函数的方法,我们证明了一类齐次二维热方程组解的熄灭时间连续依赖于初值.     

电水动力学强化管内凝结换热的能耗分析

利用电水动力学(EHD)强化换热能耗评价的新方法,对EHD强化水平管内R134a和垂直管内R123凝结换热的实验数据进行分析.结果表明,在给定的实验条件下,热通量相同时,对水平管内R134a,可用能获益系数随着电压的增加而减小;对垂直管内R123,可用能获益系数随着电压的增加而增加.强化系数大并不意味着可用能获益系数大.     

烟熏炉换热器进口主流道流动性改进

针对某一类型烟熏炉换热器进口主流道出口产生局部负压的问题,借助CFD仿真分析手段找出进口主流道结 构缺陷,提出了岔口几何形状的改变结构。分别对这2种不同结构的进口主流道管在Fluent平台上进行内流场分析,对 比两者之间的差异,表明改进后的进口管流速更加均匀,克服了原进口主流道管存在的问题,使得进入各组U型管的蒸 气相对均匀,换热效率得到提高。