Occurrence of endophytes in grasses native to northern China

A survey of grass species associated with Neotyphodium and Epichloë fungal endophytes was made in the permanent grasslands of northern China. A total of 41 grass species, 56 sites and 172 local populations were examined to reveal endophytic infection of native grasses. Twenty‐five of the forty‐one species of grasses (proportionately 0·61) were infected by endophytes: twenty‐two species had a mean infection rate of 0·01–0·50 and only three species had a mean infection >0·50. Of the 172 local populations examined, however, proportionately 0·72 were not infected, 0·181 had an infection rate of 0·01–0·50 and 0·099 had an infection rate of 0·51–1·00. Two genera of grasses, Cleistogenes and Koeleria, as well as twenty plant species, were previously unknown endophytic hosts in China. High infection rates (0·86–1·00) of plants of Achnatherum sibiricum were detected at all eleven sites studied. Other grasses in which high infection rates were found were Agropyron mongolicum, Roegneria turczaninovii, Agropyron elongate, Poa palustris and Poaangustifolia. It was concluded that endophytes are found widely in natural grass populations and that endophyte–grass interactions may have effects on ecosystems and livestock in the grasslands of northern China.     

Model predicting dynamics of biomass, structure and digestibility of herbage in managed permanent pastures. 1. Model description

To investigate seasonal and annual interactions between management and grassland dynamics, a simple mechanistic model of the dynamics of production, structure and digestibility in permanent pastures was constructed. The model is designed to respond to various defoliation regimes, perform multiple‐year simulations and produce simple outputs that are easy to use as inputs for a model of ruminant livestock production. Grassland communities are described using a set of average functional traits of their constituent grass groups. The sward is subdivided into four structural compartments: green leaves and sheath, dead leaves and sheath, green stems and flowers, and dead stems and flowers. Each compartment is characterized by its biomass, age and digestibility. Only above‐ground growth is modelled, using a light‐utilization efficiency approach modulated by a seasonal pattern of storage and mobilization of reserves. Ageing of plant parts is driven by cumulative thermal time from 1 January and by biomass flows. Age affects senescence, abscission and digestibility of green compartments and, therefore, the quality of green leaves and stems can increase or decrease over time in relation to net growth and defoliation dynamics. The functional traits having the greatest impact on model outputs are seasonal effects, period of reproductive growth and effects of temperature on photosynthetic efficiency. The functional traits of the grass groups were parameterized for temperate pastures of the Auvergne region in France. The other model inputs are few: proportion of functional groups, basic weather data (incident photosynthetically active radiation, mean daily temperature, precipitation and potential evapotranspiration) and site characteristics (nitrogen nutrition index, soil water‐holding capacity). In the context of a whole‐farm simulator, the model can be applied at a field scale.     

结缕草属植物致死含水量的研究

为研究结缕草属(Zoysia)植物的耐旱能力,并对耐旱能力强的结缕草品种的选育以及极度干旱地区结缕草草坪的水分管理提供实验依据.在2005年对51份结缕草种源抗旱性初步鉴定的基础上,于2006年选择9份抗旱性代表种源,对其致死含水量进行研究,并对其与表征永久萎蔫系数进行相关分析.结果表明:9份材料致死含水量变异范围为3.01%∽6.14%,变异系数为25.21%,9份材料的致死含水量存在极显著差异(P<0.01);表征永久萎蔫系数相对于致死含水量存在极显著的线性正相关关系(P<0.01),回归方程为:Y=1.57X+3.88(R²=0.9217>R_0.01²=0.6354);根据表征永久萎蔫系数与致死含水量的线性回归方程,得出其他42份种源的致死含水量,其变异范围为3.62%∽5.64%,变异系数为10.85%.     

汽车42V电源系统及其发电机的研究

随着汽车用电设备对车用发电机发电量需求的提高,42 V汽车电源系统将取代目前的14 V电源系统。本文总结了42 V汽车电源系统的优点,分析了其运行模式,据此提出了其广阔的发展前景;分析了汽车42 V发电机的特点,指出了稀土永磁发电机是理想的42 V汽车发电机。     

饱水和气干状态杉木的压缩成型及其热处理永久固定

该研究采用烘箱热处理和真空热处理方法 ,在热处理温度都为 180℃ ,热处理时间分别为 6,10 ,15 ,2 5h的条件下 ,研究比较了饱水状态和气干状态杉木试材的径向压缩成型特性及其在不同方式热处理条件下热处理永久固定的效果 .研究结果表明 :①在相同条件下 ,与气干状态杉木试材相比 ,饱水并经蒸煮的试材在压缩成型后 ,或经热处理后 ,其回复率Rs 较小 ,各项物理力学性质较好 ;②在热处理过程中 ,对照试材的重量损失率WL随着热处理时间的延长而增大 ,而且 ,WL与Rs 之间呈近似线性负相关 ;③在相同条件下 ,与空气介质中热处理相比 ,真空中热处理后试材的材色变化较小 ,但回复率较大     

车用永磁式缓速器设计中漏磁影响因素分析

以优化设计和减少漏磁为目标,运用磁路分析法建立永磁式缓速器的漏磁场模型,得到设计参数的解析式。由于参数之间的复杂函数关系,采用区间数学算法来优化永磁式缓速器的设计参数,将影响漏磁系数的非线性方程组化简为线性方程组。选取满足设计要求的目标参数——转子鼓磁感应强度Bm、气隙磁感应强度Bg,ave、漏磁系数K的最佳取值区间。使用区间迭代法,求出自变量参数的取值区间和权数pi。运用Matlab语言编程直接搜索合理的设计参数,减少了计算量和循环次数。三维有限元漏磁分析和试验均证明了设计参数选取的合理性。结果表明：永磁体高度HPM、气隙ge对漏磁系数K影响较大;区间数学Tschernikow算法在永磁式缓速器设计中是有效的。     

基于损耗模型的永磁同步电机高效控制参数敏感性分析

针对分析参数变化对电机损耗效率的影响建立了永磁同步电机(Permanent Magnet Synchronous Motor)损耗模型,推导出电机损耗最小的最优定子电流。然后,分析铁损电阻、铜损电阻以及磁链变化对损耗精度的影响。结果表明,当铁损电阻变为原来的1.2倍时,总损耗效率增加1.0%;当铜损电阻变为原来1.5倍时,总损耗效率下降28%;当磁链变为原来的1.4倍时,总损耗效率下降1.4%。通过电机损耗的参数敏感性分析,为基于模型的电机高效率控制提供了重要参考。     

全封闭的霍尔接近开关

文章介绍一种基于霍尔元件的全封闭接近开关,设计了实际运用线路,并将其运用于齿轮转速测试。该霍尔接近开关是将两相同性能的霍尔元件与磁钢(夹在两者之间)封闭在一个隔磁材料中,配以高抗干扰的电路,可以在各个领域得到运用。     

顾及生态系统连通性的永久基本农田划定

在生态文明背景下，探索兼顾耕地资源保护与生态系统维护的永久基本农田划定方法对构建国土空间开发新格局具有重要意义。该研究通过最小累积阻力（minimum cumulative resistance，MCR）模型与电路理论等在识别生态源地、生态廊道和“踏脚石”基础上，将土地评价与立地条件分析（land evaluation and site assessment，LESA）方法及未来土地利用模拟（future land use simulation model，FLUS）模型相结合构建了一套顾及生态系统连通性的永久基本农田划定方法，以期为十堰市永久基本农田划定提供一定理论参考。结果表明：1）十堰市生态源地共计26个，主要以林地与水域为主，分布在南部和中部山地丘陵区；生态廊道共计66条，集中分布在竹溪县、竹山县、房县等境内；“踏脚石”共计121个。2）基于LESA方法划定的永久基本农田虽然满足了目标需求量，但与重要生态系统连通性用地存在严重冲突，与生态源地、生态廊道、“踏脚石”冲突面积分别为1772.64、4274.19、391.86 hm²。3）顾及生态系统连通性的永久基本农田划定方法，有效避开了划定的永久基本农田对生态源地、生态廊道与“踏脚石”等侵占，而且满足了未来城市用地增长需求，同时划定的永久基本农田质量高，集中连片性强，农田形状也较规则，便于机械化耕作，对保障中国粮食安全，推进农业供给侧结构性改革，实现乡村振兴具有重要作用。     

Nonlinear Analysis of Unloading RockMass Related to the Shiplock High Slopeof Three- Gorges Project

According to the characteristics of the shiplock high slope of Three- Gorges Project, this paper simplified the rock mass of the high slope as orthogonally anisotropical media.On the basis of recongnizing the nonlinear mechanics of excavation unloading,the paper prsents the nonlinear mechanics calculating method ,the theory of changing stiffen analysis. The calculating results agree fairly close to the measured one.By the excavating calculation of shiplock high slope, the paper shows that the rock mass will produce the large deformations,which have the large difference with the results of the old studies