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981.
目的利用频域子结构方法(FBSM,FRF Based Sub-structuring Method)对结构的力学环境进行准确高效地预示。方法分别对处理子结构间为刚性连接和弹性连接两种问题的FBSM进行理论推导。为了验证FBSM的正确性,设计连接为刚性连接和弹性连接两种算例结构,并将FBSM对算例结构频响函数的计算结果与有限元方法(FEM,Finite Element Method)的对应计算结果进行对比。其中,弹性连接利用空间梁单元进行等效,并将该等效方法与利用六自由度标量弹簧的等效方法进行对比。结果对于刚性连接和弹性连接两种情况,FBSM对频响函数的计算结果均与FEM的对应计算结果吻合程度良好。此外,空间梁单元的结点刚度矩阵为非对角阵,与六自由度标量弹簧相比,可更为准确地等效工程实际中的弹性连接。结论FBSM可对结构的力学环境进行准确高效的预示,且在处理具有弹性连接结构的力学环境预示问题时,可采用空间梁单元等效弹性连接。 相似文献
982.
针对高超声速、结构轻量化带来的航天器复杂结构声振耦合动力学环境难以精准预示问题,提出一种基于有限元-边界元(FEM-BEM)方法的声振耦合问题数值仿真方法。分析国内外求解声振耦合问题的主要数值仿真方法,从影响航天器性能设计的低中频声振耦合动力学特性入手,采用有限元-边界元方法,以航天器典型结构截锥壳为研究对象,开展混响噪声作用下的声振耦合研究。建立了声振耦合模型,获得了主体结构、主要支撑结构及设备的声振耦合响应。提出的数值仿真方法和仿真分析过程,为航天器声振耦合分析提供了理论基础和仿真手段。 相似文献
983.
经对呼和浩特盆地西部深层水1000km ̄2、浅层水600km ̄2范围内进行水质检测分析,发现其深、浅两层地下水均富砷,浅水有18.8%、深水有40.9%的水样砷含量超过国家饮用水卫生标准。测得水体总砷中以三价砷为主。溶解氧含量低,铁、锰离子为痕量,硫酸盐、亚硝酸盐氮含量也均低,同时有低硒、高氟现象,提示该地区为富含有机质的强还原环境,有利于砷的迁移富集,对饮水型砷中毒起着促进作用。 相似文献
984.
稀土元素日允许摄入限量的差异与农用安全性讨论 总被引:2,自引:0,他引:2
比较不同时期提出的稀土元素日允许摄入量(AD I)的差异性发现,随着研究的深入,近期提出的AD I值明显低于早期的AD I值,反映了人们对稀土元素毒性效应有了进一步的认识。根据农产品中稀土元素残留量及其可通过食物链为人们所摄入的现状,分析了稀土农用、稀土厂“三废”对生态环境的污染影响以及潜在的食品安全性问题。 相似文献
985.
本文研究了广东五华县牛角塘综合治理试验区几种典型森林生态系统土壤的物质迁移、肥力特性及元素迁移与富集传性,结果表明,生态类型的差异不仅会影响到土壤的肥力状况,同时由于水土流失等因素的影响,还会造成土壤机械组成、元素迁移富集特点以及其它发生学特性的差异,林地、半林地及光山地之间在这些方面也存在着明显的差异性. 相似文献
986.
煤中痕量元素与三态硫关系的模型 总被引:12,自引:0,他引:12
将青山烟煤按不同比重分级后,分别测定了各级煤粉中痕量元素Be、Cd、Pb、Co,Cr,Cu,Ni,As以及三态硫的含量,发现痕量元素与三态硫之间有一定的相关关系,本文用回归分析法建立了痕量元素与三态硫关系的模型,并用该模型对青山烟煤某一比重范围内煤粉中的痕量元素含量进行预报,结果令人满意。 相似文献
987.
The impacts of a functional and a demolished copper processing works on the aquatic and terrestrial environment in the vicinity of the works was investigated by determining the levels of selected trace metals in river water, river sediments, channel margin sediments and overbank soils. Samples were taken at five sites within an area of the Churnet Valley in Staffordshire, where the River Churnet flows through the two works. Analysis of river water samples by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) has shown that only copper is present above background levels considered to typify uncontaminated rivers. Analysis of river sediments, channel margin sediments and overbank soils by nitric-perchloric acid digestion and Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) analysis has indicated contamination by arsenic, cadmium and copper in the vicinity of both works. Arsenic and copper are deposited primarily within the aquatic environment, although some contamination of the terrestrial environment by copper is also observed. Cadmium is deposited primarily within the terrestrial environment. The deposition of arsenic and copper in river and channel margin sediments respectively is also related to current and historical contamination. 相似文献
988.
Spread of metals through an invertebrate food chain as influenced by a plant that hyperaccumulates nickel 总被引:6,自引:0,他引:6
Lynsey R. Peterson Victoria Trivett Alan J.M. Baker Carlos Aguiar A. Joseph Pollard 《Chemoecology》2003,13(2):103-108
Summary. Hyperaccumulation of metals in the shoot system of
plants is uncommon, yet taxonomically and geographically widespread. It
may have a variety of functions, including defense against herbivores.
This study investigated the effects of hyperaccumulation on metal
concentrations across trophic levels. We collected plant material, soil,
and invertebrates from Portuguese serpentine outcrops whose vegetation
is dominated by the nickel hyperaccumulator Alyssum pintodasilvae.
Samples were analyzed for nickel, chromium, and cobalt. Grasshoppers,
spiders, and other invertebrates collected from sites where A.
pintodasilvae was common had significantly elevated concentrations of
nickel, compared to nearby sites where this hyperaccumulator was not
found. Chromium and cobalt, occurring in high concentrations in the
serpentine soil but not accumulated by A. pintodasilvae, were not
elevated in the invertebrates. Therefore, it appears likely that a flux
of nickel to herbivore and carnivore trophic levels is specifically
facilitated by the presence of plants that hyperaccumulate this metal.
The results may be relevant to the development of phytoremediation and
phytomining technologies, which use plants to extract metals from the
soil.
Reveived 22 August 2002; accepted 2 April 2003.
R1D="
Correspondence to: A. J. Pollard, e-mail:joe.pollard@furman.edu 相似文献
989.
The relationship between epilithic periphyton (biofilm) bound metals and metals bound to sediments in freshwater systems 总被引:1,自引:0,他引:1
Surficial sediments and epilithic periphyton (biofilm) were sampled from six sites on the River Churnet and five sites on the River Manifold in Staffordshire and analysed for cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn). The sites demonstrated a wide range of sediment trace metal concentrations determined by inductively coupled plasma optical emission spectrometry (ICP-OES) and atomic absorbtion spectroscopy (AAS). Biofilm was removed from the substrate using physical abrasion and 0.005 M ethylenediaminoethanetetra-acetic acid (EDTA) extractant. The European Standards, Measurements and Testing Programmes (BCR) operationally defined geochemical speciation scheme was used to determine the exchangeable, acid soluble fraction of the sediments. Significant positive correlations were determined between the EDTA extractable biofilm and the exchangeable sediment fraction for Cd, Cu and Zn but not for Pb. Natural epilithic periphyton may be a potential metal biomonitor particularly of Cu, Cd and Zn in aquatic systems and provide supporting information in relation to potential sediment toxicity. 相似文献
990.