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Marios Sophocleous 《Ground water》2012,50(6):831-839
The water‐level decline of the High Plains/Ogallala aquifer is one of the largest water management concerns in the United States. The economy and livelihood of people living in that vast region depend almost exclusively on water extracted from that aquifer. A debate about its future is ongoing, and questions remain as to how best to conserve the groundwater resource. Maintaining the aquifer will require reductions in pumping and irrigated hectarage and adopting additional conservation measures. Eventually, the agricultural system will have to be based dominantly on the renewable water resources of the region. In effect, this means a limited‐irrigation and/or dry‐farming regime. What Kansas is currently doing to further extend the life of the aquifer is presented here together with additional measures that could be taken. A key management approach to help sustain the aquifer in western Kansas is to divide the aquifer into subunits on which to base localized management decisions. Another recently adopted measure is the establishment of local enhanced management areas, which would allow locally agreed upon specific corrective controls in those areas. History has shown that incentive and voluntary plans alone have not been successful in halting water‐level declines. Thus, limits and timelines need to be set and checks must be in place to enforce strict administration of conservation measures. It is advocated that water laws be reformed and modernized so that “water rights” are constrained by the current availability of water and the preservation of the resource base for future generations. 相似文献
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Three‐dimensional beam–truss model for reinforced concrete walls and slabs – part 2: modeling approach and validation for slabs and coupled walls 
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下载免费PDF全文 A three‐dimensional beam–truss model (BTM) for reinforced concrete (RC) walls that explicitly models flexure–shear interaction and accurately captures diagonal shear failures was presented in the first part of this two‐paper series. This paper extends the BTM to simulate RC slabs and coupled RC walls through slabs and beams. The inclination angle of the diagonal elements for coupled RC walls is determined, accounting for the geometry of the walls and the level of coupling. Two case studies validate the model: (1) a two‐bay slab–column specimen experimentally tested using cyclic static loading and (2) a five‐story coupled T‐wall–beam–slab specimen subjected to biaxial shake table excitation. The numerically computed lateral force–lateral displacement and strain contours are compared with the experimentally measured response and observed damage. The five‐story specimen is characterized by diagonal shear failure at the bottom story of the walls, which is captured by the BTM. The BTM of the five‐story specimen is used to study the effects of coupling on shear demand for lightly reinforced RC coupled walls. The effect of mesh refinement and bar fracture of non‐ductile transverse reinforcement is studied. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Marios Sophocleous 《Hydrogeology Journal》2002,10(2):348-348
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Humic substances exposed to solar light play the role of photosensitizers in aquatic photochemical processes, generating free
radicals during UV and visible light irradiation. During irradiation, high molecular weight structures are destroyed and low
molecular weight constituents are formed. Alterations of the humic acids metal binding capacity due to their photochemical
alterations occur. The present work reports controlled laboratory experimental results on the binding of copper by a certified
purified peat humic acid (PPHA) before and after irradiation in a laboratory scale photoreactor. A reference curve of copper
binding by photochemically unaltered humic acid was experimentally determined as a function of solution pH by potentiometric
titrations. The experimental data series correspond to a pH range from 3 to 8.5, necessary for the simultaneous consideration
of complexation and metal species solubility contribution in the obtained results. From the experimental results, it was apparent
that copper is strongly bound by humic acid even at the acidic range of pH where the percentage of copper bound reached 60
and 95% at pH values of 3.5 and 5.5, respectively. During 12 and 20 days of irradiation experiments, humic acid photoalteration
was experimentally monitored by a size exclusion chromatography system (HPLC-SEC). From the potentiometric titrations of the
irradiated humic acid solutions by a copper selective electrode, it was apparent that the copper binding capacity of photoaltered
humic acid solutions was significantly reduced for pH values up to 6. 相似文献
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从土壤腐殖质分组到分子有机质组学认识土壤有机质本质 总被引：2，自引：0，他引：2
梳理了与土壤生态系统功能相联系的,特别是对固碳减排的土壤有机质本质认识的研究进展及路径,探讨了经典腐殖质学说存在的问题,概述了新近的有机质保护稳定学说及腐殖质组学学说,并追溯了生物标志物有机质分子研究,最后从土壤学的基本理念和理论出发讨论和重新认识土壤有机质的本质及其价值。从形成条件、分离条件和分子鉴定等多方面分析,土壤腐殖质形成和稳定学说越来越显示出局限性;而面向气候变化的碳固定研究可以深入探析土壤有机质的复杂存在状态。越来越认识到土壤有机质是投入土壤的有机物质经不同程度生物利用或降解的产物残留,只是被土壤不同程度地区隔和封闭,本质上仍是分子量变化极大的生命源有机物的集合。因此,可通过生物标志物分子作为靶标在土壤中提取和识别,该技术的发展将孕育萌生土壤有机质分子组学。后者可以用于判读土壤有机质的结构支撑、反应活性和促生功能等方面的本质差别,这些差别可能是由有机分子组成结构及存在状态所决定而不是由有机分子稳定性决定的。从这个概念出发,类似于土壤微生物分子生态,土壤有机质的丰度、组成、结构与功能间的联系可能是土壤有机质本质的核心问题。对这种关系的量化和参数化表征可用以探索土壤有机质永续固定,且可以保持生命活性的土壤有机质的管理策略及技术,并配合土壤的团聚体理论诠释土壤的本质和生态系统功能服务,这将是未来土壤学服务人类可持续发展的理论立足点。 相似文献