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461.
Arnold L. O'brien 《Environmental management》1988,12(5):627-636
In New England, patterns of glacial deposition strongly influence wetland occurrence and function. Many wetlands are associated with permeable deposits and owe their existence to groundwater discharge. Whether developed on deposits of high or low permeability, wetlands are often associated with streams and appear to play an important role in controlling and modifying streamflow. Evidence is cited showing that some wetlands operate to lessen flood peaks, and may have the seasonal effect of increasing spring discharges and depressing low flows. Wetlands overlying permeable deposits may be associated with important aquifers where they can produce slight modifications in water quality and head distribution within the aquifer. Impacts to wetlands undoubtedly will affect these functions, but the precise nature of the effect is difficult to predict. This is especially true of incremental impacts to wetlands, which may, for example, produce a change in streamflow disproportionate to wetland area in the drainage basin, i.e., a nonlinear effect as defined by Preston and Bedford (1988). Additional research is needed before hydrologic function can be reliably correlated with physical properties of wetlands and landscapes.A model is proposed to structure future research and explore relationships between hydrologic function and physical properties of wetlands and landscapes. The model considers (1) the nature of the underlying deposits (geologic type), (2) location in the drainage basin (topographic position), (3) relationship to the principal zone of saturation (hydrologic position), and (4) hydrologic character of the organic deposit. 相似文献
462.
Marie Maud Bear Delphine Mallarde Valérie Langlois Solo Randriamahefa Odile Bouvet Philippe Guerin 《Journal of Polymers and the Environment》1999,7(4):179-184
Sixteen Pseudomonas strains have been tested with a view to developing medium-chain length polyhydroxyalkanoates. Four strains were selected and it is shown that their ability for producing three different polyesters with variable properties was dependent on the strains and substrates. Otherwise, Pseudomonas oleovorans was grown on a mixture of sodium octanoate and undecenoate salts at a 90/10 mol/mol ratio. The corresponding copolymer, bearing lateral double bonds, was chemically modified in the carboxy group. Finally, the ability to tailor-make functional bacterial polyesters aimed at temporary therapeutic applications is demonstrated. 相似文献
463.
液相法芒硝制碱中苛化废渣的利用 总被引:2,自引:0,他引:2
研究了用液相法芒硝制碱的苛化废渣制取轻质CaCO3的工艺及用轻质CaCO3填充母料对聚乙烯进行改性。试验结果表明,本研究所制取的轻质CaCO3的质量符合GB4794-84一级品规格,用其制成母料对低密度聚乙烯填充改性,不仅可消除苛化废渣对环境的污染,降低聚乙烯制品的生产成本,而且可在制品的拉伸强度、断裂伸长率和冲击强度降低不多的情况下,提高制品的硬度、弹性模量、热稳定性及耐蠕变性。 相似文献
464.
Mohamed El Esawey Caitlin Sowers Joy Sengupta Raoul Jain 《Traffic injury prevention》2019,20(2):220-225
Objective: The objective of this study was to evaluate the safety effectiveness of cable barrier systems installation on rural highway sections in British Columbia, Canada.Methods: Data on police-attended serious collisions (injury?+?fatality) on a number of rural highway sections in British Columbia, Canada, were used in the analysis. An empirical Bayes (EB) approach was employed to ensure that the evaluation results were reliable and to account for the regression to the mean artifact. Safety performance functions (SPFs) were developed using data collected at similar sites. For both median cable barrier (MCB) and roadside cable barrier (RCB) sections, the evaluation was undertaken using all serious collisions, truck serious collisions, and off-road serious collisions.Results: For MCB sections, the evaluation results showed statistically significant reductions of 21.7, 53.8, and 34.8% in all serious collisions, truck serious collisions, and off-road left (ORL) combined with head-on (HO) serious collisions. For RCB sections, statistically significant reductions of 74.7, 100, and 100% were found in all serious collisions, truck serious collisions, and off-road right (ORR) serious collisions, respectively. The impact of the after period on the evaluation results was explored. It was found that the changes in safety become more stable using an after period of 2–5 years.Conclusions: Cable barriers were successful in reducing the frequency of serious collisions on provincial highways in British Columbia. 相似文献
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以建筑废弃物粉煤灰砖为吸附材料,经硫酸和盐酸改性研究了粉煤灰砖块粉末(fly ash brick powder,简称FABP)对水体中磷的净化效果,并探究了酸改性种类、投加量、接触时间、p H对磷去除率的影响。结果表明:酸改性后的FABP比表面积显著增大,且表面变得粗糙。硫酸改性粉煤灰砖块粉末(sulfuric acid modified fly ash brick powder,简称S-FABP)对水体中磷有良好的去除效果,当投加量为3.0g时磷去除率达到98.5%,且反应初始的5 min内磷的去除率达92.7%。分析S-FABP去除磷的机理为沉淀反应和吸附反应协同作用的结果,在酸性和碱性条件下有不同的沉淀反应发生。根据Langmuir和Freundlich方程拟合结果,S-FABP对水中磷的吸附等温模型符合Langmuir模型,理论饱和吸附量为7.69 mg/g。 相似文献
468.
为获得最佳瓦斯抽采效果,研究不同钻孔孔径与塑性区范围及抽采效果之间关系,基于弹塑性理论,采用Comsol软件模拟嘉禾矿2254底板巷上穿层钻孔周围煤体塑性区范围分布,修正塑性区半径理论推导公式,得到抽采钻孔混合流量、纯流量和浓度,分析钻孔周围煤体不同塑性区范围下瓦斯抽采效果。结果表明:钻孔孔径越大,塑性区范围越大,抽采钻孔卸压范围越大;若不考虑其他因素,钻孔孔径越大,瓦斯抽采效果越好;通过对比塑性区半径模拟值与计算值,修正塑性区半径公式,该公式适用于浦溪煤矿;随钻孔塑性区范围增加,钻孔瓦斯抽采流量逐渐增加,但瓦斯流量相对钻孔塑性区半径差变化率先增大后减小。研究结果可为提高矿井瓦斯抽采效果提供理论参考。 相似文献
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分别采用NaCl、KCl和CaCl2对黑龙江省某市天然沸石进行改性,考察了pH值、氨氮初始浓度以及温度对改性沸石交换性能的影响,并对改性沸石的交换动力学进行了研究.结果表明,NaCl和KCl改性对沸石原矿交换容量有不同程度提高,而KCl改性后容量有所降低.pH、NH4 初始浓度以及温度对交换性能有明显影响,pH 6.0附近沸石交换容量最大;NH4 初始浓度越高,反应速度越快,相同初始浓度下,钾型沸石交换速度较快,而沸石原矿交换速度最慢.采用Langmuir型离子交换等温线进行非线性回归的结果显示,低温有利于交换反应的进行.溶液中NH4 在改性沸石上的离子交换反应可采用Vermeulen模型描述,沸石原矿拟合相关系数较差.改性沸石多次再生后,其交换容量均有所降低. 相似文献