Magnetic Fluid Model of Discharge Path in Internal Gears of E. D. M. Grinding

In this paper, the moving laws at any point of meshing discharge are stuied about internal gears E. D. M. grinding. It is the first time that the meshing theory of gears is combined with electric discharge machining, and the discharge principles of infernal gears of E. D. M. are described.     

中亚热带常绿阔叶林林隙动态与森林景观格局研究——以福建省万木林自然保护区为例

采用景观生态学方法对福建省万木林自然保护区中亚热带常绿阔叶林林隙动态与森林景观格局进行了研究。结果表明,随着林隙的不断发展,林隙冠空隙斑块形状的不规则性增强,林隙冠空隙斑块形状的破碎化程度加深,而林隙冠空隙斑块的分形维数减小。林隙冠空隙的斑块分形维数小于扩展林隙的斑块分形维数。     

Small understorey gaps created by subsistence harvesters do not adversely affect the maintenance of tree diversity in a sub-tropical forest

Understorey gaps are common in subtropical forests where pole-size trees are harvested for building materials. The creation of artificial understorey gaps has the potential to affect tree regeneration and the maintenance of forest tree diversity by locally increasing resource availability (light, nutrients, moisture). Understorey tree gaps had significantly lower foliage density in the 3-10-m stratum and higher soil moisture. However, fine root biomass and nutrient availability (N, P, K, C_org) were not different to controls in the intact understorey. Light intensity at the forest floor was a function of the age of the understorey gap, being greater in recent gaps but was not different between older gaps and the controls in intact understorey. The early regeneration community in gaps was different in composition from under intact understorey. Understorey gaps appeared to promote the regeneration of understorey species (density and species richness) by increasing community-wide seedling establishment of understorey species. However, understorey gaps had no effect on the early regeneration of canopy species. We argue that under low harvesting intensity (11.6% of the available pole-size stems), understorey gaps have a neutral role in the long-term maintenance of understorey species diversity and no apparent role in the long-term maintenance of canopy tree species diversity. These results suggest that low levels of subsistence harvesting of understorey species will not detrimentally affect the overall species composition of scarp forest.     

林隙及其对天然林更新的影响

林隙是森林中由自然或人为小规模干扰形成的,是森林演替和循环中必不可少而又经常发生的现象,为森林的更新提供了有利的微环境。本文通过对林隙尺度、特征和森林微环境变化等叙述,重点分析了我国对天然林林隙的研究现状、分布的区域和森林类型,林隙大小、年龄和边缘木等方面对天然林更新的影响,以及林隙理论在实践中的应用,指出,林隙更新理论是森林经营,尤其是天然林经营中最重要的方面之一。     

Canopy tree development and undergrowth bamboo dynamics in old-growth Abies–Betula forests in southwestern China: a 12-year study

Interactions between forest canopy characteristics and plants in the forest understory are important determinants of forest community structure and dynamics. In the highlands of southwestern, China the dwarf bamboo Bashania fangiana Yi is an understory dominant beneath a mixed canopy of the evergreen Abies faxoniana (Rheder & Wilson) and the deciduous Betula utilis (D. Don). The goal of this study was to better understand the role of bamboo dominance, canopy characteristics, and periodic bamboo dieback on forest development. To achieve this goal, we measured tree seedling, tree saplings, and trees, forest canopy characteristics, and bamboo cover in permanent forest (n = 4) and gap plots (n = 31) in a mixed A. faxoniana and B. utilis forest in Sichuan, China. Dwarf bamboos died off in 1983 in the gap plots, and in three of the four forest plots. Forest development was assessed for the period 1984–1996. The seedling bank in forest and gap plots increased after bamboo die-off. A. faxoniana seedlings increased more than B. utilis in forest plots; the opposite pattern characterized gap plots. The proportion of seedlings on raised micro-sites on the forest floor also changed and new seedling were more abundant on the forest floor. By 1996, bamboo seedling cover and biomass had recovered to ca. 45% or their pre-flowering values. Rates of bamboo seedling recovery were faster beneath canopy gaps and deciduous trees than beneath forest or evergreen trees. Tree mortality exceeded recruitment in plots with dense bamboo; the opposite pattern was found in the plot with little bamboo. The mortality rate for B. utilis trees (2.4% year⁻¹) was higher than that for A. faxoniana (0.8% year⁻¹) and forests with dense bamboos became more open over the census period. Tree mortality was size-dependent and intermediate sized trees had the lowest rates of mortality. Stand basal area increased mainly due to greater basal area gain than loss for A. faxoniana. Interactions between tree species life history, canopy type, and bamboo life-cycles create heterogeneous conditions that influence tree and bamboo regeneration and contribute to the coexistence of A. faxoniana and B. utilis in old-growth forests in southwestern China.     

英汉词汇空缺现象产生原因及翻译方法

词汇空缺现象越来越受人们重视，因为它给英汉互译造成一定障碍。本文通过理论和举例分析了词汇空缺产生的原因。并相应地提出英汉互译时处理词汇空缺现象的一些合理的方法：（1）音译法；（2）直译法；（3）意译法；（4）替代法；（5）用泛指词或特指词。     

Forest regeneration in artificial gaps twelve years after canopy opening in Acre State Western Amazon

The main objectives were to study the effect of gap size and canopy openness on the natural regeneration dynamics considering the parameters of sapling growth, recruitment, mortality, density, species composition and above-ground biomass accumulation. The study was carried out in 32 artificial gaps with sizes varying from 100 to 1200 m² and canopy openness from 10 to 45%, from the second to the twelfth year after gap creation. The gap size was measured using the vertical projection of the tree crowns on the ground (Brokaw's definition), and the canopy openness measurement by hemispherical photography. In the first five years, mean sapling growth (0.54 cm year⁻¹), mortality (3.9% year⁻¹) and AGB (26.2 Mg ha⁻¹ or 8.7 Mg ha⁻¹ year⁻¹) were significantly higher in the gaps than in the forest understorey (0.17 cm year⁻¹, 1.5% year⁻¹ and −0.59 Mg ha⁻¹ year⁻¹ respectively) and positively correlated with gap size and canopy openness. In the same period, recruitment was also significantly higher in the gaps (5.8% year⁻¹) than in the forest understorey (0.4% year⁻¹) but decreased with gap size and negatively correlated with canopy openness. In the first five years, the relative density of pioneer species was higher in the gaps but not significantly correlated with gap size or canopy openness. AGB increased linearly since canopy opening, and twelve years after gap creation it was still higher in larger (121.2 Mg ha⁻¹ or 10.1 Mg ha⁻¹ year⁻¹) rather than smaller (62.5 ha⁻¹ or 5.2 ha⁻¹ year⁻¹) gaps. Twelve years after gap creation there were no significant differences in the parameters of sapling growth, recruitment, and mortality which could be attributed to the original gap size and canopy openness.     

安徽查湾自然保护区甜槠林林隙森林物种多样性研究

采用样线法调查研究区内林隙分布,共获得36个林隙,大小不同林隙内植物种类组成表现出一定差异,大林隙(300~400m2)乔木树种18种,灌木、草本植物28种;小林隙(<100m2)乔木树种13种,中林隙(100~200m2)11种,两者灌木及草本植物均21种。大、中林隙内乔木树种以江南桤木居多,小林隙中暖木和甜槠占优势;3个林隙中灌木均以青栲幼苗占绝对优势,表明青栲将有可能进入林冠层而逐渐成为优势树种。林隙内乔木树种种数、丰富度指数均大于非林隙,均匀度小于非林隙;灌木、草本植物具有同样规律。乔木树种物种多样性以大林隙最高、中林隙最低;不同面积林隙SW多样性指数、均匀度指数依次为:大林隙>中林隙>小林隙;生态优势度为:中林隙>大林隙>小林隙。灌木、草本植物物种数、丰富度指数表现出300~400m2面积的大林隙内达最大值,并随林隙面积的减小而减小,灌、草层植物多样性最大值也出现在大林隙中;生态优势度指数中林隙最大,小林隙最小。     

京津冀水资源脆弱性评价

[目的]评价京津冀水资源脆弱性,为京津冀水资源管理提供理论依据与数据支撑。[方法]选取人口密集、经济发达、水资源问题极为突出的京津冀区域,采用水足迹的理论与方法,构建了集水资源压力—发展压力—污染压力—水资源管理压力(RDHM)于一体的水资源脆弱性评价指标体系,采用层次分析法确定不同指标的权重,对该区域2003—2013年水资源脆弱性进行了评价。[结果]京津冀地区面临着水资源禀赋差,开发利用强度大,污染严重,水资源管理力度区域差异大等问题。北京市在水资源管理方面水平相对较高,但水污染压力长期没有得到有效缓解;天津市虽然在水资源管理上获得了长足的进步,但水资源脆弱性有增无减,其水资源问题的解决亟需寻找新的途径;河北省水资源管理相对京津地区差距较大,水资源脆弱性逐年突显,成为京津冀地区水资源问题的短板。[结论]缓解区域水污染压力,正视河北省水资源管理的滞后性,统一配置水资源,缩小水资源脆弱性区域差异在京津冀一体化背景下势在必行。