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取代传统避雷针的一种新型防雷装置——半导体消雷器已经问世。本文根据半导体消雷器的性能特征,以电力系统为应用领域,提出了将半导体消雷器组成联合保护网带的方法,总结了运用半导体消雷器的实际经验。 相似文献
3.
本文从防盗报警、电视监控系统的布线及供电系设计二方面,论述了在进行防盗报警电视监控系统设计时,必须严格按有关设计规范布线,尽量做到经济合理、安全可靠。 相似文献
4.
本文介绍了用成套小样园作为典型众数抽样调查单元的方法测定两个不同林分小班的蓄积,并与用点抽样和不同形状样地的系统抽样结果相比较,表明用成套小样园作为典型众数抽样调查单元的方法能满足90%以上的精度,而且工效很高;作者也探讨了使用此法的条件. 相似文献
5.
随着我国城市化进程的加快,越来越多的农村人口变成了城市人口,导致数以千万计的农民失去了自己的土地,一些地方农民的利益没有得到很好的保障,使处于新生存环境的农民面临着被"边缘化"的危险.失地农民问题是我国城市化进程中出现的新问题,是一个事关我国城市化能否实现可持续发展和整个社会改革发展稳定的大问题.为此,从我国征地补偿标准过低、征地程序不完善和政府角色错位在征地过程中存在失范行为等视角探悉我国城市化进程中农村征地存在的问题,以寻求解决之道. 相似文献
6.
随着全国野生动植物保护和自然保护区建设工程的实施 ,自然保护区在我省生态环境建设中的地位与作用越来越重要 ,运用生物多样性管护区的理论指导我省的自然保护区建设将是正确认识自然保护区地位与作用的关键所在。 相似文献
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S. Langton 《Agroforestry Systems》1990,12(2):173-185
A number of different types of edge effects on experimental plots are defined, and it is shown that they are frequently important in agroforestry experiments. Methods of eliminating edge effects, either at the design or the analysis stage, are described. Computer simulations, based on uniformity data, are used to investigate the efficacy of neighbour-balanced designs, with and without neighbour terms, for reducing the problem of neighbour effects between different treatments. It is concluded that, while neighbour-balanced designs may be useful in certain situations or in combination with other methods, it is preferable to eliminate edge effects by using adequate guard rows. Recommendations are therefore made concerning the correct use of guard areas in agroforestry experimentation. 相似文献
9.
The conversion of anthropogenic into more natural, self-regenerating forests is one of the major objectives of forestry throughout
Europe. In this study, we present investigations on permanent plots with different silvicultural treatment in NE German pine
stands. Management of old-growth pine stands on acidic and nutrient-poor sandy sites differs in fencing, thinning, and planting
of certain tree species. The investigations were carried out on the community, population, and individual level of the pine
forest ecosystems. Thus, vegetation changes, size and height of tree populations, and height increment of tree individuals
were observed over a time span of 6 years. Special attention was paid to short-lived tree species such as, e.g., Frangula alnus and Sorbus aucuparia, as well as to Fagus sylvatica as one of the most typical forest tree species of Central Europe. Vegetation changes are interpreted as a consequence of
natural regeneration of formerly degraded forest sites, involving an increase in nutrient availability. High browsing pressure
can be considered as a key factor for the inhibition of tree seedlings and growth of saplings. Some Sorbus aucuparia individuals, however, succeeded in growing out of the browsing height also in unfenced stands. Few found specimens of Fagus sylvatica proved that this species is able to establish spontaneously on these relatively dry, acidic sites under continental climate
influence. Such natural regeneration processes, also including spontaneous rejuvenation of trees, can be integrated into silviculture
as passive forest conversion management. An active management like thinning of stands, planting of trees, and fencing can
accelerate forest conversion with regard to height growth and species number of trees. 相似文献
10.
On the basis of nine Norway spruce (Picea abies (L.) Karst.) and ten European beech (Fagus sylvatica L.) thinning experiments in Germany, for which both residual and removed stock had been registered first during 1870, I scrutinize
how moderate and heavy thinning from below (B-, C-grade) affects the production of merchantable volume compared with light
thinning (A-grade). In relation to A-grade, cumulative merchantable volume (CV) of B- and C-grade amounts in average to 103–107%
in juvenile and to 97–102% in mature Norway spruce stands. The corresponding findings for European beech are 101–106% and
94–102%. CV of individual stands varies between 89% and 130% for Norway spruce and 73% and 155% for European beech (CV of
A-grade = 100%). These findings are substantiated by the relation between stand density (SDI) and periodic annual increment
(PAI). On the B- and C-grade plots of spruce and beech, respectively, SDI was reduced down to 41–91% and 31–83% of the A-grade.
When SDI is reduced in young stands, PAI follows a unimodal curve. Norway spruce’s PAI culminates in 109% if SDI is reduced
to 59%; European beech’s PAI culminates in 123% when density is reduced to 50%. Whereas Norway spruce’s growth reacts most
positively on thinning under poor site conditions and with increment reduction on favourable sites, European beech behaves
oppositely. With stand development the culmination point of the unimodal relation moves towards maximum density, so that in
older stands PAI follows the increasing pattern, which is the left portion of a unimodal curve. A model is presented which
apparently unifies contradictory patterns of stand density–growth reactions by integrating relative stand density, average
tree size and site fertility effects, and makes the findings operable for forest management. 相似文献