三相异步电动机智能节能器的研制   总被引：1，自引：0，他引：1  

李伟凯  孟臣 《黑龙江八一农垦大学学报》1998,10(4):38-42

本文对三相异步电动机的经济运行电压进行了计算分析,并以单片机为核心研制出一种智能节能器,可根据电动机负载经的变化情况,自动调节电动机的端电压值,使电动机运行于高效节能状态,达到节能目的,本文对节能器的节能原理,系统构成了较详细的论述。  相似文献   

输水管道装置增压泵的节能分析     

杨建国  把多铎  杨彦勤 《西北农林科技大学学报(自然科学版)》1998,26(4):41-44

在输水管道均匀分流和沿管长水力坡降不变的情况下,对一级集中供水泵站、中间加设加压泵站及管道增压泵三种方案的能耗进行了分析。结果表明,采用管道增压泵节能效果最好,并确定了加压泵站及管道增压泵的最佳位置计算式。  相似文献   

受控与自控棉田生态系统的能量流动研究     

竺锡武  汪世泽 《西北农林科技大学学报(自然科学版)》1998,26(5):76-80

对陕西关中棉区受控与自控两类棉田生态系统的能量流动作了比较研究。结果表明：（１）两类棉田系统的食物网结构、营养层、生态锥体、生态效率等基本特征相似,在能量分配方面有量的差异;（２）天敌的利用效率在两类系统间有显著差异;（３）受控棉田系统的现存量与摄能量的营养级金字塔具有更快的递降率。  相似文献   

Nutrient content of Prosopis africana seeds     

Barminas  J.T.  Maina  H.M.  Ali  J. 《Plant foods for human nutrition (Dordrecht, Netherlands)》1998,52(4):325-328

The proximate and mineral compositions of Prosopis africana seeds used in the preparation of a local condiment in Nigeria and as animal feed were investigated. The proximate analysis showed that protein, ash and fiber values were comparable to Parkia africana seeds. However, the crude lipid content was lower than Parkia filicoidea seeds and decorticated groundnut. Phosphorus, potassium and calcium were the major mineral elements of the seeds, thereby suggesting that they could contribute partially to the overall daily intake of these elements.  相似文献   

木荷幼苗对常绿阔叶林不同光环境的光合响应   总被引：9，自引：0，他引：9       下载免费PDF全文

王荣  郭志华 《林业科学研究》2007,20(5):688-693

在夏季晴天,对生长在旷地、林窗和林下的木荷幼苗光合作用的日变化、光响应曲线及对短暂遮荫的响应等进行观测,结果表明:(1)旷地的日平均光合有效辐射约为1 230 μmol·m-2·s-1,分别是林窗和林下的1.7和12.3倍左右,并且旷地的气温显著大于林窗和林下的,而空气相对湿度却明显低于其它2个光环境;(2)木荷幼苗在旷地和林窗均出现光合"午休"现象,旷地木荷"午休"时净光合速率的降幅约60%,而林窗的降幅约为30%;旷地中木荷幼苗的最大净光合速率约为17.8 μmolCO2·m-2·s-1,约是林窗和林下的1.8和3.4倍;此外,木荷幼苗的光饱和点、光补偿点和暗呼吸速率均随环境光强的增大而增大;(3)短暂遮荫时,随着光合有效辐射的降低,各光环境中木荷幼苗的气孔导度和蒸腾速率不断降低,胞间CO2浓度逐渐升高,水分利用率在旷地和林窗中呈下降趋势,而在林下一定低光范围内(约130～800 μmol·m-2·s-1)则维持了较高水平;(4)受光斑照射时,光斑区域的光合有效辐射和净光合速率分别比受光斑前以及未受光斑区域提高了10倍和4倍以上.  相似文献   

菜蛾绒茧蜂的寄主选择性及寄生对寄主发育和取食的影响   总被引：19，自引：0，他引：19  

施祖华  刘树生 《植物保护学报》1999,26(1):25-29

研究了菜蛾绒茧寄生对寄主幼虫龄期的选择性及对寄主生长发育、取食量的影响。结果表明,该蜂能寄生小菜蛾各个龄期的幼虫,但当２－４龄幼虫同时存在时,偏爱寄生２、３龄幼虫,对２、３、４龄幼虫的选择系数分别为０．３７、０．３９、０．２４。该蜂对４龄幼虫的寄生能力随寄主日龄增大而急剧下降,对进入４龄并发育至该龄期４０％时间以上的幼虫不能寄生。产卵寄生的雌蜂比例也随４龄幼虫日龄增大而急剧下降。小菜蛾幼虫被寄主后  相似文献   

How can we feign sustainability with an increasing population?     

South  David B. 《New Forests》1999,17(1-3):193-212

Attitudes of human societies toward tree plantations can be a critical factor in determining the source of wood supply in the future. Because human populations will expand substantially in the next century, considerable increases in the demands on native forests will occur. Currently, only a limited amount of tree plantations have been established specifically to provide firewood in developing countries. This may be the result, in part, of a world society that has evolved a general preference for pastures, but an aversion to tree plantations. In total, pastureland and tree plantations amount to 26 percent and 1 percent of the world's land base, respectively. Nevertheless, our actions today will determine whether children in the future collect firewood from natural stands or from tree plantations. It is estimated that a substantial afforestation program could increase the amount of tree plantations to equal 5 percent of the world's land base by the year 2050. Ten billion dollars (United States) is a rough estimate of the annual costs for such a program (assuming no overhead or administrative costs). Most of the wood needs could be met from tree plantations. However, if the world's society wants most of its wood in 2050 to come from natural stands (>80 percent), then tree plantations can be limited to just 1 percent of the land base.  相似文献   

我国杉木林生物量与能量利用率的研究   总被引：8，自引：0，他引：8       下载免费PDF全文

肖文发  聂道平  张家诚 《林业科学研究》1999,12(3):237-243

根据作者的研究和文献资料系统分析了我国杉木的能量利用,分配及生物生产力的特征和规律,结果表明：杉木不同器官的热值差异明显,平均为１９．９５１ｋＪ．ｇ＾－１。生物量与密度和年龄呈较好的线性相关。  相似文献   

火炬松制造中密度纤维板工艺的研究     

黄洛华  曲岩春 《木材工业》1999,13(5):11-13

通过对火炬松制造中纤维板制板工艺条件的研究,探索降低中密度纤维板制造过程中纤维施胶量的可能性。结果表明,火炬松制造中密度纤维板是可行的;采用８％的施胶量制板;板材的主要物理力学性能可达到美国ＭＤＦ国家标准ＡＮＳＴＡ２０８．２－１９９４和我国ＭＤＦ国家标准７０型及８０型特级品的要求。  相似文献   

Improved Design of Energy Dissipators for Pipe Outlets     

Arun Arun Goel  D.V.S. Verma 《Irrigation and Drainage Systems》1999,13(4):313-320

This paper presents an experimental study on thedevelopment of an efficient energy dissipator ascompared to Garde's energy dissipator (Garde et al.1986) for pipe outlets. The recommended designs werelaboratory tested on scale models with pipe outletdiameter of 10 cm and 7.5 cm for Froude number rangingfrom 1.70 to 5.50. The performance of the newdissipator improved tremendously by using new shapes,sizes and locations of the appurtenances for the samelength of stilling basin. This was possible due tobetter spreading of efflux jet by using a propersplitter block. The formation of a strong vortexinfront of the solid impact wall, in place of a grid,and an additional horizontal shear at the bottomproduced more fine grained eddies and turbulence,which finally reduced the energy of the outgoing flow. The low bottom velocities at the end of the basinresulted in reduction of the scour. The performanceof various models has been compared by estimating thescour index based on maximum depth of scour and itslocation at the end of run time.  相似文献