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21.
《Scandinavian Journal of Forest Research》2012,27(1-4):245-250
Natural regeneration was registered on 97 clear‐felled and scarified sites in northeastern Sweden ten growing seasons after planting. On each site, three fix plots were laid out at planting and the planted seedlings were mapped. Ten years later all healthy non‐planted seedlings were registered in an anulus of size 15.7 m2. Non‐planted seedlings were also observed in four 4 m2 squares on each fix‐plot to estimate the zero‐square frequency. Species were classified as Pinus sylvestris, L., Picea abies (L) Karst. and deciduous species (Betula pendulajpubescens Roth./Ehrh., Populus tremula L., Alnus incana (L) Moench.). On average, 7 133 non‐planted seedlings ha‐1 were found, of which 29% were conifers. Among the conifers, 71% were P. abies. More than 2 500 conifer non‐planted seedlings ha‐1 were found on 27% of the plots. The number of non‐planted seedlings was correlated to the presence of neighbouring seed‐producing stands within 100 m and decreased with rising altitude. Pinus sylvestris seedlings were more frequent on dry soils while the deciduous seedlings were more frequent on wet sites. In the 4 m2 squares, the zero‐square frequency was 29% if both conifers were and deciduous seedlings were considered and 63% if only conifers were considered. Mean height of the tallest seedling per species and square was 62 cm for P. sylvestris, 42 cm for P. abies and 107 cm for the deciduous seedlings. Key words: Alnus incana, Betula, broad‐leaves, deciduous, Norway spruce, Picea abies, Pinus sylvestris, Populus tremula, reforestation, Scots pine. 相似文献
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Junjie LIU 《干旱区科学》2019,11(5):764-773
The non-rectangular hyperbola (NRH) equation is the most popular method that plots the photosynthetic light-response (PLR) curve and helps to identify plant photosynthetic capability. However, the PLR curve can't be plotted well by the NRH equation at different plant growth phases due to the variations of plant development. Recently, plant physiological parameters have been considered into the NRH equation to establish the modified NRH equation, but plant height (H), an important parameter in plant growth phases, is not taken into account. In this study, H was incorporated into the NRH equation to establish the modified NRH equation, which could be used to estimate photosynthetic capability of herbage at different growth phases. To explore photosynthetic capability of herbage, we selected the dominant herbage species Potentilla anserina L. and Elymus nutans Griseb. in the Heihe River as the research materials. Totally, twenty-four PLR curves and H at different growth phases were measured during the growing season in 2016. Results showed that the maximum net photosynthetic rate and the initial slope of PLR curve linearly increased with H. The modified NRH equation, which is established by introducing H and an H-based adjustment factor into the NRH equation, described better the PLR curves of P. anserina and E. nutans than the original ones. The results may provide an effective method to estimate the net primary productivity of grasslands in the study area. 相似文献
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对轴线相交的柱—柱、柱—锥、锥—锥相贯线的性状进行了解析分析,得出在轴线正交情况下相贯线特殊点的图解方法,轴线斜交情况下相贯线的特殊点也可根据本文中的分析方法应用仿射原理得出。 相似文献
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自2018年《CNAS-GL006化学分析中不确定度的评估指南》颁布后,不确定度计算方法的需求日益增强。本研究依据GB 23200.8-2016《水果和蔬菜中500种农药及相关化学品残留量的测定气相色谱-质谱法》,采用气相色谱-质谱法,结合内标定量法,对草莓中丙溴磷、亚胺硫磷、五氯硝基苯和氯氟氰菊酯的残留进行了测量不确定度的详细评定,共涉及标准品纯度、储备液配制、工作液配制、称样量和前处理过程5个B类评定分量,以及标准溶液峰面积、样品溶液峰面积和添加回收率3个A类评定分量。结果显示:在0.08 mg/kg添加水平下,丙溴磷、亚胺硫磷、五氯硝基苯和氯氟氰菊酯的测量合成相对标准不确定度依次为3.55%、3.22%、2.20%和3.66%,样品溶液峰面积和添加回收率2个A类不确定度分量对4种农药合成不确定度的贡献较高,其中丙溴磷、亚胺硫磷和氯氟氰菊酯均超过60%,五氯硝基苯超过31%。本研究中4种农药在草莓样品中的测量结果在95%的置信限(k=2)内可表示为:丙溴磷,0.085±0.006 mg/kg;亚胺硫磷,0.084±0.005 mg/kg;五氯硝基苯,0.079±0.003 mg/kg;氯氟氰菊酯,0.082±0.006 mg/kg。不确定度评定结果将最大限度地减少待测物在最大残留限量附近的残留值判定可能存在的争议。 相似文献
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基于ARIZ算法的方草捆收集车改进设计与试验 总被引:3,自引:0,他引:3
针对方草捆收集车作业时草捆在喂入过程中发生歪斜严重影响其稳定性的问题,应用ARIZ算法对技术系统进行了优化设计,并完成了试验验证。根据分析造成草捆歪斜的主要原因,确定问题发生的技术系统,建立系统组件功能模型,并针对技术系统存在的问题,应用矛盾分析、物-场分析等方法进行了系统性分析,通过应用创新原理、分离原理、知识库查询及标准解等工具形成了一系列创新设计方案,通过使用Pro/Innovator软件对新产生的方案进行了综合评价,并从中得到最优方案。对改进后的方草捆收集车进行了试验,结果表明:改进后的草捆收集车收集效率高,稳定性好。 相似文献
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By using mixed triangle series,this paper discusses the calculation of rectangular stiffened plates with simply supported edge along direction of stiffeners under several local loads,such as uniform load on local rectangular area,concentrated force,concentrated moment of couple,line loads,line moments of equal and some equivalent concentrated forces acting on a line with equaldistance among them.All analytical solutions of both displacements and internal forces are derived.A numerical example to treat an engineering problem is given. 相似文献
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土壤质地一定程度上决定土体中水、气、热、盐/溶质的传输特征及其机械力学性能,是进行工农业生产活动、建立土壤转换函数及开展土壤水热数值模拟研究所必需的关键参数。因此,土壤质地分类是土壤学、农学、环境科学及工程等多门学科的研究基础。迄今为止,世界各国制定了数十种土壤质地分类系统,并建立了对应的三角图/三元相图用于土壤质地查询或制图。经过历代土壤工作者的不懈努力,中国土壤质地分类在不断吸收美国制、卡庆斯基制和国际制经验的基础上,结合我国实际制定了1986版的质地分类系统,但该分类系统仍存在分类标准不清晰及无法制作土壤质地三角图的局限。本研究基于现行的1986版土壤质地分类系统提出了一种改进的修订方案供讨论,目的是明确各个质地类型的界限,并首次创建方便使用的土壤质地平面正三角和直角三角坐标图,同时编写了基于Origin的查询/制图工具包。鉴于我国土壤学界普遍使用国际制、美国制或混用的现状,国内迫切需要在各个行业中大力推广和应用中国土壤质地分类制,这既可以统一标准,也是我国土壤科学发展水平的重要体现。此外,为了便于国际交流,未来还应重点研究中国制和其他分类系统之间的定量转换关系并开发相关自动转换程序。 相似文献