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21.
本文是通过10个月的日射、日照资料对比观测、统计的乔唐、康氏和光电式日照计记录阈值的平均值和标准偏差,分析了乔唐日照计进光孔径、涂药方式对感光迹线的影响,测定了感光药的吸收光谱,并根据日出日没时直接日射辐照度的平均变化率,估算了由阈值的不确定度引起的日照时数的误差,从而为我国几十年的乔唐日照资料的评价提供依据。 相似文献
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Maintaining forest landscape connectivity is one of the most effective ways to alleviate natural forest fragmentation and biodiversity loss problems. Recently, graph theory based metrics have been used as powerful tools in the assessment of landscape connectivity. However, the functional features of landscape units at different structure levels, based on which outcomes can be enriched and advice can be given for practical applications, have been overlooked. In this study, a series of graph-based connectivity indices was calculated to 1) evaluate the optimal threshold distance, 2) identify the key landscape units at the component and patch levels, and 3) classify the functional types of components and patches and analyze functional patterns at different structural levels. The relationship between patch size and patch functional performance in maintaining landscape connectivity was discussed. With a natural forest area in Minqing County of China as the study area, recommendations regarding forest conservation and connectivity enhancement were provided based on the research conclusions. This study provides a way to comprehensively analyze habitat fragmentation and functional patterns for local forest conservation. 相似文献
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在海岸带,沙粒粒径和水分含量是决定沙粒起动风速的最主要因素。闽江口南岸海滩沙的平均粒径为2.0Φ,水分含量多在0.3%~1.0%之间。运用Johnson的经验公式,可计算出海滩沙的起动风速为6~7m/s。这一结果与实际观测值十分吻合。由于海岸环境因素的影响,使得同等条件下海岸带沙粒的起动风速明显大于内陆沙漠沙,而风沙流的输沙率明显小于内陆沙漠沙。海岸带是风速剧变带,在引用陆地气象台站的风速记录分析海岸风况和研究风沙运动规律时,必须对风速进行订正。 相似文献
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引入小波分析方法对大坝变形监测数据的处理,实现了对离散型的变形数据的尺度分解,对变形趋势的分析。并且对变形数据在滤波、消噪等方面,对分解层次中的偶然误差特性分析,以及阀值的选取方法进行了比较,表明利用小波变换的方法对变形数据的分析处理是有效、可行的。 相似文献
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Marleen Coetsiers Petra Blaser Kristine Martens Kristine Walraevens 《Environmental Geology》2009,57(5):1155-1168
Aquifers from the same typology can have strongly different groundwater chemistry. Deducing the groundwater quality of less
well-characterized aquifers from well-documented aquifers belonging to the same typology should be done with great reserve,
and can only be considered as a preliminary approach. In the EU’s 6th FP BRIDGE project “Background cRiteria for the IDentification
of Groundwater thrEsholds”, a methodology for the derivation of threshold values (TV) for groundwater bodies is proposed.
This methodology is tested on four aquifers in Flanders of the sand and gravel typology. The methodology works well for all
but the Ledo-Paniselian aquifer, where the subdivision into a fresh and saline part is disproved, as a gradual natural transition
from fresh to saline conditions in the aquifer is observed. The 90 percentile is proposed as natural background level (NBL)
for the unconfined Pleistocene deposits, ascribing the outliers to possible influence of pollution. For the Tertiary aquifers,
high values for different parameters have a natural origin and the 97.7 percentile is preferred as NBL. The methodology leads
to high TVs for parameters presenting low NBL, when compared to the standard used as a reference. This would allow for substantial
anthropogenic inputs of these parameters. 相似文献
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By using GDS dynamic hollow cylinder torsional apparatus, a series of cyclic torsional triaxial tests under complex initial consolidation condition are performed on Nanjing saturated fine sand. The effects of the initial principal stress direction α0, the initial ratio of deviatoric stress η0, the initial average effective principal stress p0 and the initial intermediate principal stress parameter b0 on the threshold shear strain y, of Nanjing saturated fine sand are then systematically investigated. The results show that y, increases as η0, P0 and b0 increase respectively, while the other three parameters remain constant. α0 has a great influence on y,, which is reduced when α0 increases from 0° to 45° and increased when α0 increases from 45° to 90°. The effect of α0 on γt plays a leading role and the effect of η0 will weaken when α0 is approximately 45°. 相似文献
30.
Representative sediment sizes in predicting the bed-material load for nonuniform sediments 总被引:1,自引:0,他引:1
《国际泥沙研究》2016,(1):79-86