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721.
Schulmeister MK Healey JM Butler JJ McCall GW 《Journal of contaminant hydrology》2004,69(3-4):215-232
Discrete-depth sampling of inorganic groundwater chemistry is essential for a variety of site characterization activities. Although the mobility and rapid sampling capabilities of direct-push techniques have led to their widespread use for evaluating the distribution of organic contaminants, complementary methods for the characterization of spatial variations in geochemical conditions have not been developed. In this study, a direct-push-based approach for high-resolution inorganic chemical profiling was developed at a site where sharp chemical contrasts and iron-reducing conditions had previously been observed. Existing multilevel samplers (MLSs) that span a fining-upward alluvial sequence were used for comparison with the direct-push profiling. Chemical profiles obtained with a conventional direct-push exposed-screen sampler differed from those obtained with an adjacent MLS because of sampler reactivity and mixing with water from previous sampling levels. The sampler was modified by replacing steel sampling components with stainless-steel and heat-treated parts, and adding an adapter that prevents mixing. Profiles obtained with the modified approach were in excellent agreement with those obtained from an adjacent MLS for all constituents and parameters monitored (Cl, NO(3), Fe, Mn, DO, ORP, specific conductance and pH). Interpretations of site redox conditions based on field-measured parameters were supported by laboratory analysis of dissolved Fe. The discrete-depth capability of this approach allows inorganic chemical variations to be described at a level of detail that has rarely been possible. When combined with the mobility afforded by direct-push rigs and on-site methods of chemical analysis, the new approach is well suited for a variety of interactive site-characterization endeavors. 相似文献
722.
723.
浅析相关因子对空气负离子水平的影响 总被引:10,自引:0,他引:10
张翔 《湖南环境生物职业技术学院学报》2004,10(4):346-351
空气负离子是一种重要的森林旅游资源,其保健功能迎合了人们追求生态健康的旅游心理.论文着重对其影响因素进行分析,借助于SPSS统计软件对若干因子进行一元回归分析.在分析结果的基础上,对森林旅游地有关保健设施的规划和设计提供一定的建议。 相似文献
724.
本文介绍了光、温敏核不育水稻在生态及生理生化方面取得的主要成就.着重概述了光、温敏核不育水稻雄性育性转换的光温生态条件,育性转换过程中蛋白质、氨基酸、酶活性、ATP及内源植物激素持续变化.另外,对光、温敏不育水稻研究存在的问题进行了分析. 相似文献
725.
Dynamics of Turbulence in Low-Speed Oscillating Bottom-Boundary Layers of Stratified Basins 总被引:1,自引:0,他引:1
Lorke Andreas Umlauf Lars Jonas Tobias Wüest Alfred 《Environmental Fluid Mechanics》2002,2(4):291-313
This paper focuses on the impact of an oscillating low-speed current on the structure and dynamics of the bottom-boundary layer (BBL) in a small stratified basin. A set of high-resolution current profile measurements in combination with temperature-microstructure measurements were collected during a complete cycle of the internal oscillation (`seiching') in the BBL of Lake Alpnach, Switzerland. It was found that even a relatively long seiching period of 24 hours significantly changed the form of the near-bottom current profiles as well as the dynamics of the turbulent dissipation rate compared to the steady-state law-of-the-wall. A logarithmic fit to the measured current profiles starting at a distance of 0.5 m above the sediment led to inconsistent estimates of both friction velocity and roughness length. Moreover, a phase lag between the current and the turbulent dissipation of 1.5 hours and a persistent maximum in the current profile at a height of 2.5 to 3 m above the sediment were observed. The experimental findings were compared to the results of a k- turbulence model and showed good agreement in general. Specifically, the inconsistent logarithmic fitting results and the observed phase lag were reproduced well by the model. 相似文献
726.
Christian Damgaard 《Environmental and Ecological Statistics》2006,13(2):229-236
A methodology for estimating environmental thresholds of binary presence–absence data is presented where the level of the
threshold is parameterised. Presence–absence data is fitted to three complementary different models: an independent null-model,
a monotonically increasing or decreasing model, and an optimum model. The range of the three models is strictly between zero
and one and the models are therefore well suited for modelling presence probabilities. The results of the three models may
be combined by using Bayesian model selection methodologies. The proposed methodology is exemplified on observed binary presence–absence
data of Bauera rubioides along an elevation gradient.
Received: May 2005 / Revised: July 2005
An erratum to this article is available at. 相似文献
727.
目的 掌握聚醚推进剂在温度循环与应变耦合作用下的老化机理.方法 开展65~75℃温度循环和3%预应变耦合作用下的老化试验,针对不同老化时间的聚醚推进剂,分析抗拉强度、伸长率等力学性能的变化规律,以及表面微观损伤、分子官能团、反应热等微观损伤演变情况,综合推断聚醚推进剂宏观-微观关联老化机理.结果 随着老化时间延长,最大抗拉强度波动下降,最大伸长率先增大、后减小;高氯酸铵和聚醚粘合剂的分解峰温均向低温方向移动,位于1410 cm?1的高氯酸铵吸收峰增强,而位于1565、1725 cm?1的聚醚粘合剂中氨基甲酸酯、酰胺基团吸收峰下降;嵌在聚醚粘合剂内部的高氯酸铵逐渐暴露,且部分高氯酸铵颗粒与周围界面明显分离,并出现小孔洞.结论 在长期温度循环和预应变作用下,聚醚推进剂分子主链中酰胺基团的C—N键由于分子间结合力较弱而分解断链,破坏了分子主链网状交联结构,使得分散其中的AP粒子逐渐露出表面,并呈现部分断裂损伤特征,引起抗拉强度下降. 相似文献
728.
主要介绍了磨削时工件表面产生局部高温的主要原因,磨削高温对淬火工件表面质量的影响,以及在加工时为了避免局部高温应采取的一些必要措施。提出了预淬火工件表面局部高温的方法。 相似文献
729.
用杂铜电解生产铜粉时,电解液的温度一般可控制在20 ̄60℃。本文介绍了在30℃较低温度和600 ̄1200A/m^2的较低电流密度下,用杂铜电解生产铜粉的试验过程。试验结果表明:低温和低铜离子浓度对生产细粒铜粉有利,而料低电流密度在保证铜粉粒度的情况下,对节约电能有利。 相似文献
730.
根据非稳定热传导基本方程式积分得到离散化方程式,编写出计算程序,利用计算机求出复合板在热处理过程中各结点随时间而变化的温度,绘出等温线,以研究复合板经升温固化处理后的理想冷却方法. 相似文献