“Transgenic treadmill”: Responses to the emergence and spread of glyphosate-resistant johnsongrass in Argentina     

Rosa Binimelis  Walter Pengue  Iliana Monterroso 《Geoforum》2009,40(4):623-3499

The broad-spectrum herbicide glyphosate has become the largest-selling crop-protection product worldwide. The increased use of glyphosate is associated with the appearance of a growing number of tolerant or resistant weeds, with socio-environmental consequences apart from the loss of productivity. In 2002, a glyphosate-resistant biotype of johnsongrass (Sorghum halepense (L.)) appeared in Argentina and now covers at least 10,000 ha. This paper analyzes the driving forces behind the emergence and spread of this weed and also examines management responses and their implications.Preventive strategies against glyphosate-resistant johnsongrass fail because of the institutional setting. Reactive measures, however, transfer the risks to the society and the environment through the introduction of novel genetically modified crops that allow the use of yet more herbicide. This in turn reinforces the emergence of herbicide-resistant weeds, constituting a new phenomenon of intensification, the “transgenic treadmill”.  相似文献   

Application of Greek lignite as an additive for controlling rheological and filtration properties of water–bentonite suspensions at high temperatures: A review     

Vassilios C. Kelessidis  Cassiani Papanicolaou  Antonios Foscolos 《International Journal of Coal Geology》2009,77(3-4):394-400

This review paper presents the results of an extensive study investigating whether addition of 3% w/w Greek lignite to 6.42% w/w water–bentonite suspensions, after being exposed to high temperatures, can prevent gelation and control filtration characteristics. Two different bentonites and eight lignites from different Greek basins have been used while a commercial lignite product has been used as standard. The lignite-free bentonite suspensions heated to 177 °C for 16 h (thermal aging) thicken considerably, increasing the yield stress and the yield point. Fluid consistency and flow behavior indices also change while no significant change is observed for plastic viscosity. Thermal aging of the suspensions results in unacceptably high fluid loss values.Addition of Greek lignite to water–bentonite suspensions, followed by thermal aging, provided the rheological stability of the suspensions by maintaining the low yield stress/point regardless of the type of bentonite. Some of the lignites performed as well as their commercial counterpart. No specific trends for rheological improvement have been identified with respect to various characteristics of lignites such as contents of humic, fulvic acids, humins and other parameters such as specific surface area and cation exchange capacity.Furthermore, addition of lignite in most cases provided very good filtration control of the water–bentonite suspensions after exposure to 177 °C, with some Greek lignites being superior to the commercial product. The same lignite parameters examined for rheological control, were also examined to determine their effect on fluid loss of these suspensions for both bentonites. The content of humic and fulvic acids of two groups of lignites showed weak inverse correlations with the fluid loss volumes for both bentonites, while all other parameters did not seem to directly correlate with the effectiveness of the lignites.  相似文献   

盐分对黏性土的沉积特性与表面电位影响研究     

张彤炜  邓永锋  邓婷婷  王冲 《冰川冻土》2019,41(4):875-883

为了明晰黏土矿物和盐分浓度在沉积过程中所起的作用及物理机制,选取高岭土、膨润土及两者组成的混合土进行粒径分析试验、沉积试验和Zeta电位测试。结果显示,盐分环境下高岭土和膨润土的平均粒径增大,部分黏粒组向粉粒组转化。高岭土在蒸馏水环境下和盐水环境下,最终都形成土-水的稳定分界面,但是絮凝稳定时间在盐分环境下更短。膨润土在蒸馏水环境下处于稳定的分散体系中,在盐水环境下迅速絮凝沉积。混合土在蒸馏水环境下,上部澄清层和下部沉淀层之间存在土颗粒的悬浮层,且该层的高度最终稳定;盐水环境下,混合土则迅速的发生土水分离。随着NaCl浓度增加,膨润土和高岭土的Zeta电位绝对值降低,因此胶粒组的絮凝行为对平均粒径产生影响,进而影响其沉积特性。  相似文献   

考虑黄土结构性和各向异性的修正剑桥模型     

张玉伟  翁效林  宋战平  谢永利 《岩土力学》2019,40(3):1030-1038

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不同砂−膨润土垂直防渗墙填筑土料的掺量研究     

徐浩青  周爱兆  姜朋明  刘顺青  宋苗苗  陈亮 《岩土力学》2019,40(Z1):424-430

土?膨润土垂直防渗墙在美国已广泛应用于城市卫生填埋场中,我国的工程中则应用较少。由国产膨润土与原地层土混合在自重应力作用下固结形成的防渗墙,其渗透性、孔隙和压缩性如何受膨润土掺量的影响,针对该一问题,使用福建标准砂模拟原地层,以3种典型膨润土作为混合料,在各掺量下对砂?膨润土填筑土料开展改进柔性壁渗透试验固结试验,研究不同膨润土掺量对填筑料渗透系数k、孔隙率n与压缩系数av影响。结果表明,膨润土和砂形成防渗墙时存在一个对应最小n和av的最优掺量Copt,当膨润土掺量小于等于Copt时,随着掺量增加,填筑料k下降很快,av缓慢减小;当掺量大于Copt后,随掺量上升,k降低速度趋缓,av快速地升高。理论上,膨润土掺入较少时黏土颗粒仅填充砂粒间的孔隙而不影响砂粒堆积,掺量达到一定程度后膨润土使砂粒彼此分离,悬浮在其中,填筑料的孔隙率随掺量而增大,可能是宏观上造成最优掺量产生的主要原因。  相似文献   

改进的贝叶斯迭代反演方法及其在白云岩致密储层识别的应用     

马琦琦  孙赞东  杨柳鑫 《物探与化探》2019,(2):234-243

由于低孔隙度和低渗透率的白云岩致密油储集层的纵波阻抗与其围岩差异非常小,利用叠后反演技术难以有效预测储层,而可以提取丰富弹性信息的叠前反演是解决此问题的有效手段,但是由于噪声等问题,叠前反演方程有较强的不适定性,笔者在贝叶斯框架下引入了改进的多变量柯西分布和改进的低频约束因子,重新推导了反演方程,获得了新的目标函数,有效地减少了反演的不适定性,从而提高了反演的稳定性,并结合迭代的思想来不断更新反演求解过程中的背景纵横波速度比值,从而增加了反演结果的精度。模型数据测试和实际资料应用都证明了该方法的稳定性和适用性。统计表明,利用提出的反演方法,目的层段内优质储层厚度预测吻合率高达89.75%。因此,此方法对类似硅质致密储层的勘探有重要的借鉴意义。  相似文献   

变性绕极深层水入侵时南极普里兹湾湍流混合特征研究     

胡俊洋  梁楚进  蔺飞龙 《海洋学报》2021,(3):1-12

基于中国第28、29和31次南极科学考察中的CTD数据,利用Thorpe尺度方法计算了普里兹湾及其附近海域湍动能耗散率,分析了其分布特征,并对当地的水团结构进行研究。结果表明,普里兹湾及其附近海域中,前两个航次观测中次表层湍动能耗散率强度在陆架坡折区域达到最大。在水团分布方面,在第28和29航次中均观测到了变性绕极深层水陆架入侵现象,水团分别向上涌升至海表以下100 m和200 m深度,向南均可达到67.5°S处。普里兹湾陆架坡折区域次表层湍动能耗散率强度分布与当地水团结构存在良好对应关系。研究认为变性绕极深层水入侵陆架,会使该深度水体变得不稳定,发生水体交换现象,最终造成该区域湍流混合强度加强。  相似文献   

基于改进引力模型的公园绿地空间可达性及供需平衡分析方法     

赵洋  徐枫  万义良 《地球信息科学学报》2022,24(10):1993-2003

探究高密度城市公园绿地资源空间配置的有效性和供需平衡问题对城市规划和居民生活具有重要意义。已有研究较少从多尺度、多交通出行模式以及结合地图大数据算法的角度对公园绿地可达性进行探究。本文以广州市越秀区为例,利用百度地图多交通出行数据,提出一种结合多类型公园绿地多级可达时间阈值的改进型引力模型,对越秀区公园绿地的空间可达性及其供需平衡特征进行研究。结果表明：① 越秀区各尺度和各类型公园绿地可达性差异显著,城区尺度可达性大体上呈现由北向南逐层递减趋势,街道尺度可达性则表现出明显的“极化”现象,大型公园绿地可达性远高于社区公园和街头游园且在城市整体可达性中占主体地位;② 从空间集聚情况来看,城区尺度公园绿地可达性值呈现明显的空间集聚分布特征,由北向南表现为高值聚类、不显著、低值聚类,街道尺度相比城区尺度高值聚类减少,低值聚类和无统计意义的区域增多;③ 基于供需平衡视角的空间可达性结果显示,公园绿地供给与居民需求在城区尺度和街道尺度分别呈现出整体平衡和局部失衡的现象,局部失衡主要集中在公园绿地资源相对匮乏的街道。  相似文献   

The Kuroshio East of Taiwan and in the East China Sea and the currents East of Ryukyu Islands during early summer of 1996   总被引：6，自引：0，他引：6  

Yaochu Yuan  Arata Kaneko  Jilan Su  Xiaohua Zhu  Yonggang Liu  Noriaki Gohda  Hong Chen 《Journal of Oceanography》1998,54(3):217-226

Using hydrographic data and moored current meter records and the ADCP observed current data during May–June 1996, a modified inverse method is applied to calculate the Kuroshio east of Taiwan and in the East China Sea and the currents east of Ryukyu Islands. There are three branches of the Kuroshio east of Taiwan. The Kuroshio in the East China Sea comes from the main (first) and second branches of the Kuroshio east of Taiwan. The easternmost (third) branch of the Kuroshio flows northeastward to the region east of Ryukyu Islands. The net northward volume transports of the Kuroshio through Section K₂ southeast of Taiwan and Section PN in the East China Sea are 44.4×10⁶ and 27.2×10⁶ m³s⁻¹, respectively. The western boundary current east of Ryukyu Islands comes from the easternmost branch of the Kuroshio east of Taiwan and an anticyclonic recirculating gyre more east, making volume transports of 10 to 15×10⁶ m³s⁻¹. At about 21°N, 127°E southeast of Taiwan, there is a cold eddy which causes branching of the Kuroshio there.  相似文献   

二异氰酸酯与壳聚糖交联产物对金属离子的吸附性能     

安胜姬  张兰英  郑松志  徐景梅 《吉林大学学报(地球科学版)》1999,29(2):2

研究了二异氰酸酯与壳聚糖的交联反应,其产物与壳聚糖相比,酸溶解度由82.04％降到58.08％。DSC曲线表明,交联产物的热稳定性明显提高,对低价重金属离子(Hg  相似文献