复杂地形高空接闪线保护范围测定的一种方法

目前较多水电站采用高空接闪线进行雷电防护,高空接闪线一般距地面较高,线塔之间距离较远(有的甚至在不同山头),接闪线弧垂很难测量,接闪线本身又可能随风而动,因此其保护范围测定难度很大。为了解决复杂地形下水电站防雷检测中遇到的问题,建立了一种利用经纬仪等设备测定高空接闪线保护范围的方法,经过多次改进,该方法在没有其他先进设备的情况下已能有效解决问题。     

利用A-1B超轻型飞机喷洒白僵菌、溴氰菊酯防治马尾松毛虫

用A-1B超轻型飞机喷洒白僵菌纯孢子柴油乳剂,2.5％溴氰菊酯乳油1:100倍液防治马尾松毛虫,作业流量180ml/亩、喷幅30—40米,白僵菌纯孢子5g/亩、溴氰菊酯2ml/亩。经测试溴氰菊酯扩散比DR>0.67,平均雾滴直径127—173μm,白僵菌DR=0.62,平均雾滴直径约139μm,溴氰菊酯防治死亡率95.5％,白僵菌防治白僵率94.84％。防治费平均每亩1.89元。结果表明:在闽北马尾松毛虫的偶发性灾区,超轻型飞机是一种经济、有效、有发展前景的防治机械。     

螺旋锥齿轮研齿系统的动态响应

考虑齿侧间隙和齿轮传动误差的影响,建立了两自由度螺旋锥齿轮研齿系统的振动模型。通过数值计算,得到了不同制动转矩下,研齿系统的动态响应。根据时间历程和相图可知,制动转矩较小时,轮齿的啮合、碰撞和脱啮交替进行,随着制动转矩的增大,齿背碰撞消失,最后进入完全的齿面啮合状态。     

圆柱型迷宫式流道滴灌灌水器平面模型试验研究

在流道内的流体流动研究中引入PIV等先进的图像全场测速技术,关键是解决塑料灌水器模型本身的圆柱型以及不透明问题。以AutoCAD技术和读数显微镜相结合的方法测量灌水器迷宫式流道几何参数,探索性地借助不锈钢电火花线切割技术构建了圆柱型灌水器的平面模型,结果表明:平面模型与塑料原型的流态指数非常接近,利用电火花线切割技术可行;流量系数差异较大,应该选择粗糙度合适的平面模型上下表面材料;灌水器流道内部流动可以忽略材料极性引力的影响,流道深度对灌水器出流的影响主要是流量系数,而对于流态指数影响极小。     

Image-based estimation of crown volume of individual street trees by plane calculation of angle disparity

Street trees provide significant and widespread environmental benefits to the city and its citizens, such as improved air quality and adaptation to climate change. Crown volume (CV) indicates the geometric volume of crown, which is an essential indicator for the ecological service evaluation of street trees. The measurement of CV makes it possible to assess the carbon storage and input cost of urban trees. Because of the particularity of crown shape of street trees, the existing two-dimensional methods of calculating CV of forest trees become difficult except the three-dimensional techniques through the unmanned aerial vehicle, LiDAR equipment, and traditional harvest methods. In this study, a new virtual research method for plane calculation of angle disparity (PCAD) is proposed to calculate the CV of street trees. Two temporal satellite images of the exact location were first collected from Google Earth Pro, and then the angle disparity of images was adopted as a starting point to calculate tree height. Finally, CV was calculated from tree height, stem height, and crown diameter. The feasibility of the method was verified by a sample survey of street trees in Shanghai, China and the relative error of CV calculation by PCAD compared to that by field survey was 17.31 %. PCAD has the advantages of low-cost, quick operation, and suitability for a large area in studying CV of street trees.     

Comparing soil moisture under trickle irrigation modeled as a point and line source

The validity of the assumption that an irrigation event from point sources can be approximated as an infinite line source is investigated in this article. This is accomplished by comparing soil water dynamics under line and point sources. Two existing mathematical models which simulate point and line drip irrigation were used. The models consider root water uptake, evaporation of soil water from the soil surface and incorporate hysteresis in the soil water characteristic curve. The comparison was made for two soil types (loamy sand and silt).The results showed that the treatment of a point source as a line source underestimates the water content values for both the soil types. This difference decreases when the depth of comparison increases. For soil depths greater than 30 cm and for time greater than irrigation duration the two models gave very close results. For the same emitter spacing and for the horizontal direction perpendicular to the drip line on the emitter spot, when the distance from the point and the line sources increases the difference of water content values increases. On the contrary, in the direction parallel to the drip line when the distance from the emitter increases (the distance from the line source remains the same) the difference of water content decreases. Lastly, differences are greater in the case of coarse grained soil than in fine grained soil.     

数控微米刨切试验台的设计与试验

为解决传统热磨法加工微米薄木片及木纤维中高能耗、工序复杂、加工成本高的缺点,现改变加工方法,采用顺纹纵向刨切木材的方式,研发了数控微米刨切试验台。试验台主要由机架、纵向进给机构总成、工件夹具、控制面板、刨切机构总成、升降机构总成和限位机构组成,可对宽度为50 mm,长度为300～600 mm,高度为20～90 mm的木材工件进行纵向进给、切削量进给和刨切作业。笔者对试验台整机以及各机构进行设计,并通过ANSYSY对刀具进行强度校核。通过试验,确定刨切机构切削角δ取45°,刀刃伸出量h取0.05 mm,刀门宽度d取0.2 mm,刨得的木片平均厚度为18.7μm,最薄为15μm。最后通过显微镜观察发现经过刨切后的刀刃部分出现磨损,可通过表面改性提高刀具的耐磨性。     

Molecular approach of genetic affinities between wild and ornamental Platanus

Apart from the wild species P. orientalis and P. occidentalis, the cultivated plane trees constitute a wide and heterogeneous group, with uncertain genetic status and largely debated names. The recent canker stain problem in Europe makes it necessary at the present time to consider the genetic resources and to determine the genetic bases of all these trees. To attain this objective, a genetic molecular approach was used to analyze 60 trees of P. orientalis and P. occidentalis,different London planes (P. hispanicaand P. densicoma), a few controlledP. occidentalis × P. orientalishybrids and particular trees from arboreta and old parks. Molecular analysis involved thirty RAPD fragments generated with nine primers, PCR-RFLP in the 5S RNA genes and mitochondrial polymorphisms revealed by RFLP method. Clones were recognized amongP. hispanica and P. densicomatrees. A Correspondence Analysis and a dendrogram constructed according to the genetic distances confirmed the supposed hybrid origin of P. hispanica and P. densicoma between P. occidentalisand P. orientalis. Contribution ofP. orientalis to their constitution seems more important than that of P. occidentalis. Mitochondrial DNA polymorphisms indicated that crosses occurred in both directions. Moreover, P. occidentalis as female parent led toP. densicoma whereas P. orientalis as female parent led to P. hispanica. Low prevalence of pure species individuals and confusion risks with hybrid trees even for old trees are highlighted. This revised version was published online in August 2006 with corrections to the Cover Date.     

主动驱动条件下研磨轨迹均匀性的研

分析了主动驱动方式下平面研磨过程中工件的运动学特性,提出了研磨轨迹均匀性可以通过单位面积轨迹点的数量及其标准差来评价,理论分析了研磨盘和工件的转速比和偏心距对轨迹均匀性的影响.仿真表明,偏心距越小越有利于工件表面研磨轨迹的均匀分布,增大偏心距导致相对转速线速度偏差增大,不利于工件表面研磨轨迹的均匀分布.增大转速比使加工轨迹分布稀疏,轨迹曲线点的标准差大,加工均匀性差,研磨盘与工件具有相同的角速度时,更有利于轨迹均匀性的提高.     

浅谈花卉布展艺术

随着花卉业的蓬勃发展,以花卉展形式来推进花卉的技术交流、社会的文化交流、城市的商业交流具有重要的意义。成功的举办花卉展,首要是要进行花卉布展设计,即通过主题的确立,对布展区进行合理的区域划分及表现形式设计,突出对花的个体美、造型美、整体美、组合美的展示,使花卉展意境得到深化升华。