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321.
Lead (Pb) and cadmium (Cd) concentrations were determined in muscle, gonad, liver and brain of tilapia fish caught from fish ponds in Machakos and Kiambu counties in Kenya. A total of 217 fish samples were randomly sampled from the two counties. Acid digestion method and atomic absorption spectrophotometer were used for analysis. Heavy metal concentrations varied significantly depending on the type of tissue analyzed. Generally, the highest concentration of Pb was detected in brain and the liver. Fish organs contained Pb in the following order: brain > liver > muscle > gonad, while Cd followed the order: brain > liver > gonad > muscle. Kiambu county recorded higher concentration of the studied heavy metals compared to Machakos county although statistically there was no difference. Lead and Cd content in both counties studied exceeded the maximum allowable limit. The study recommended controlling industrial and agricultural effluents into surface water and proper sitting of ponds to minimize the risk of contamination of farmed fish by heavy metals. 相似文献
322.
以二甲胺、二乙胺、甲乙胺、吗啉和N-甲基苄胺5种二级胺代表物质为例,分别使用气相色谱-氢火焰(GC-FID)技术和气相色谱-质谱(GC-MS)技术检测饮用水中二级胺质量浓度。结果表明,使用优化的预处理方法处理后进样分析,5种代表物质的线性范围在20~2 000μg/L,相对标准偏差(RSD)≤0.46%,最低检出限在3.18~24.19μg/L。FID比MSD具有较强优势。该方法对于直链脂肪类和杂环类的二级胺都有良好的检测效果,可用于对饮用水二级胺类物质的检测。 相似文献
323.
为提供煤尘爆炸事故预防和缓解所需的科学依据,对煤尘爆炸火焰传播过程进行试验研究。所用试验装置,其主要部分为直径0.3 m的圆形管道与断面边长为80 mm的方形管道对接形成的一个长2 m的爆炸腔体。在其中共进行9次煤尘爆炸试验。结果表明,煤尘爆炸火焰传播具有速度快,波动大,稳定性较差的特点,火焰区长度远大于扬尘区长度,最大火焰速度和传播距离与煤尘量均不存在正比例关系,但存在一个特定的煤尘质量浓度。在这个特定质量浓度处,最大火焰速度达到最大值。当煤尘质量浓度大于这个特定质量浓度时,火焰传播速度曲线整体下降,暂时缺氧被认为是导致这一情况的重要因素。 相似文献
324.
甲烷煤尘燃烧爆炸试验研究 总被引:2,自引:0,他引:2
为揭示甲烷煤尘空气混合物爆炸波的传播规律,采用试验分析的方法,建立甲烷煤尘空气混合物燃烧爆炸的3种试验方案,分析不同体积分数的甲烷和不同质量浓度的煤尘消耗不同体积空气时的爆压和爆速等参数的发展趋势,探究爆轰波传播的稳定性,阐明了甲烷煤尘燃烧爆炸的基本特征。试验结果表明,在最优配比条件下,与单一甲烷空气、煤尘空气混合物相比,甲烷煤尘空气混合物的爆压、爆速明显增加。甲烷煤尘空气混合物爆轰比单一的气相、固相混合物爆轰的爆炸压力、爆速明显增加、爆轰更稳定。 相似文献
325.
326.
在工程应用中,初始压力的增高一般都能提高预混合可燃性气体爆炸的强度,缩小反应设备的体积.因此研究在小环境密闭空间下初始压力的变化对预混合可燃性气体爆炸的特性与规律是十分必要的.本文运用AutoReaGas爆炸仿真模拟器定量研究了小环境密闭空间的初始压力对预混合可燃性气体爆炸的影响.其结果表明,在相同小环境密闭空间尺寸下利用AutoReaGas爆炸仿真模拟器充入相同条件的预混合可燃性气体.其预混合气体密度、冲击波产生的超压都随着初始压力的增加而增大;并且爆炸超压与初始压力呈近似的线性关系;但各个观测点的温度和速度并不随着初始压力的增加而变化.研究所取得的成果可为今后的工程应用提供一定的理论数据指导. 相似文献
327.
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329.
Motomu Toda Masayuki Yokozawa Akihiro Sumida Tsutomu Watanabe Toshihiko Hara 《Ecological modelling》2009
A simulation study was carried out to investigate simultaneously the effects of eco-physiological parameters on competitive asymmetry, self-thinning, stand biomass and NPP in a temperate forest using an atmosphere–vegetation dynamics interactive model (MINoSGI). In this study, we selected three eco-physiological relevant parameters as foliage profiles (i.e. vertical distribution of leaf area density) of individual trees (distribution pattern is described by the parameter η), biomass allocation pattern in individual tree growth (χ) and the maximum carboxylation velocity (Vmax). The position of the maximal leaf area density shifts upward in the canopy with increasing η. For scenarios with η < 4 (foliage concentrated in the lowest canopy layer) or η > 12 (foliage concentrated in the uppermost canopy layer), a low degree of competitive asymmetry was produced. These scenarios resulted in the survival of subordinate trees due to a brighter lower canopy environment when η < 4 or the generation of spatially separated foliage profiles between dominant and subordinate trees when η > 12. In contrast, competition between trees was most asymmetric when 4 ≤ η ≤ 12 (vertically widespread foliage profile in the canopy), especially when η = 8. In such cases, vertically widespread foliage of dominant trees lowered the opportunity of light acquisition for subordinate trees and reduced their carbon gain. The resulting reduction in carbon gain of subordinate trees yielded a higher degree of competitive asymmetry and ultimately higher mortality of subordinate trees. It was also shown that 4 ≤ η ≤ 12 generated higher self-thinning speed, smaller accumulated NPP, litter-fall and potential stand biomass as compared with the scenarios with η < 4 or η > 12. In contrast, our simulation revealed small effects of χ or Vmax on the above-mentioned variables as compared with those of η. In particular, it is notable that greater Vmax would not produce greater potential stand biomass and accumulated NPP although it has been thought that physiological parameters relevant to photosynthesis such as Vmax influence dynamic changes in forest stand biomass and NPP (e.g. the greater the Vmax, the greater the NPP). Overall, it is suggested that foliage profiles rather than biomass allocation or maximum carboxylation velocity greatly govern forest dynamics, stand biomass, NPP and litter-fall. 相似文献
330.
Stefan Lüpold George M. Linz Tim R. Birkhead 《Behavioral ecology and sociobiology》2009,63(6):899-909
Post-copulatory sexual selection (PCSS) is thought to be one of the evolutionary forces responsible for the rapid and divergent
evolution of sperm design. However, whereas in some taxa particular sperm traits are positively associated with PCSS, in other
taxa, these relationships are negative, and the causes of these different patterns across taxa are poorly understood. In a
comparative study using New World blackbirds (Icteridae), we tested whether sperm design was influenced by the level of PCSS
and found significant positive associations with the level of PCSS for all sperm components but head length. Additionally,
whereas the absolute length of sperm components increased, their variation declined with the intensity of PCSS, indicating
stabilising selection around an optimal sperm design. Given the diversity of, and strong selection on, sperm design, it seems
likely that sperm phenotype may influence sperm velocity within species. However, in contrast to other recent studies of passerine
birds, but consistent with several other studies, we found no significant link between sperm design and velocity, using four
different species that vary both in sperm design and PCSS. Potential reasons for this discrepancy between studies are discussed.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献