Effects of corridor networks on plant species composition and diversity in an intensive agriculture landscape     

Qian Tang  Guofu Liang  Xunling Lu  Shengyan Ding 《中国地理科学(英文版)》2014,24(1):93-103

The development of modern agriculture has resulted in much homogenization of the landscape consisting of large patches of farmland,so small remnant non-crop habitats especially linear corridors play an important role in the conservation of species and the maintenance of ecosystem functions.However,little attention has been paid to the effects of corridors structural characteristics on the plant species restricted to such habitats.In this study,we selected three types of corridors including ditch,hedgerow and road,and ana-lyzed their structural characteristics.The plant species presented in these corridors were investigated,and the species diversity,abun-dance and frequency were estimated.Moreover,spatial arrangements of corridors were classified into different types to discuss whether there were significant effects of corridor network on plant distribution.The results show that three types of corridors have different ef-fects on plant species composition and diversity.The one-one combined corridor networks and total network associated by three corri-dors have more complex structural features than each single type of corridor.However,there is no strong correlation between the corri-dor networks with their plant species.We suggest that carrying out a pointed vegetation survey at corridor intersections to further test the relationships between structural features of corridor and plants is necessary.  相似文献   

Parametric study for optimal design of large piled raft foundations on sand     

《Computers and Geotechnics》2014

In designing piled raft foundations, controlling the total and differential settlements as well as the induced bending moments of the raft is crucial. The majority of piled raft foundations have been designed by placing piles uniformly. In such a design method, the settlements of the piled rafts are likely to be large, which leads to an increase of the pile length and/or number of piles required to reduce the settlements. However, this increase does not satisfy the requirement for economical design. On the basis of a parametric study, this paper contributes a framework for considering an economical design methodology in which piles are placed more densely beneath the column positions when the piled raft is subjected to column loads. The analysis uses PLAXIS 3D software, and the validity of the parametric study is examined through the results of centrifuge model tests conducted by the authors. The study shows that the concentrated pile arrangement method can help to considerably reduce the total and differential settlements as well as the induced bending moments of the raft. Moreover, the effects of parameters, such as pile length, pile number, raft thickness and load types, on the piled raft behavior are investigated. This study can help practicing engineers choose pile and raft parameters in combination with the concentrated pile arrangement method to produce an economical design.  相似文献   

一个新颖的哲学理论：突现论及其在地质上的应用          下载免费PDF全文

张旗 《甘肃地质》2022,(1):1-11

突现论是一个崭新的哲学理论,只有100多年的历史,但是,突现论已经崛起为复杂性系统的核心理论,成为近期哲学领域研究的热点之一。突现论认为,世界是由不同层级（或层次）构成的,不同层次按照事物的复杂程度不断提高划分的。世界基本上有三大层次,从低到高为物理、生命和心灵。突现论有4个特征：1,不同层次性质不同,高层次性质来源于低层次;2,突现具有不可预测的新颖性;3,不可还原性;4,高低层次之间存在因果关系。文中简要介绍了突现论的概念并探讨了突现论在变质岩、岩浆岩、矿床学以及地球演化研究中的可能的应用,希望能够对科学研究的进一步发展有利。  相似文献   

贯入角度对截齿破岩性能与几何排布的影响研究     

肖建成  卢景景  周辉  徐福通  冯春 《岩土力学》2022,43(12):3372-3384

截齿贯入角度是双轮铣槽机布齿系统设计中的关键因素之一。基于连续−非连续单元法（CDEM）,建立截齿不同角度冲击贯入破岩的数值模型,通过断裂能本构模型实现岩体弹性−损伤−断裂的破裂过程,开展截齿有效角度50º～90º区间内的9组冲击贯入破岩模拟,研究贯入角度对截齿破岩性能的影响规律,讨论贯入角度对截齿几何排布的影响,总结布齿系统的截齿几何排布规律。结果表明,当贯入角度从90º降低到50º时,岩体由张拉−拉剪破裂向剪切−拉剪破裂转变,截齿平均贯入力与破碎程度提高,截齿的跃进式侵入特性的显著性减低;贯入角度为75º～90º的第I类截齿与小于55º的第III类截齿在破岩中起辅助作用,贯入角度为55º～75º的第II类截齿可在岩体内部产生范围较大的水平非贯通裂隙,在布齿系统破碎岩体过程中发挥主要作用;2个第II类截齿先后贯入岩体可较好地破碎截线间的岩体,可构成一类基本破岩单元,多个基本破岩单元按照正弦线形式排布,由此形成了一种布齿系统设计方法。研究成果为完善双轮铣槽机布齿系统设计方法,打破国外在双轮铣槽机布齿系统设计方法上的技术壁垒提供了理论基础。  相似文献   

提高连续墙抓斗入岩效率若干问题的探讨          下载免费PDF全文

贾学强  苏伟  丁洪亮  刘永光 《探矿工程》2015,42(10):59-62

越来越多的连续墙工程提出了入岩要求,而现阶段广泛使用的连续墙抓斗入岩效率低下,针对这种状况,以抓斗抓取地层的特点为出发点,对其现阶段在岩石地层抓取效率低下的原因进行分析,然后以岩石破碎学为理论支撑,从抓斗自重、油缸闭合力、斗齿布置规格以及抓取方式等方面着手,提出了若干可用于提高抓斗入岩效率的改进建议。  相似文献   

PDC钻头切削齿布齿设计的新思路          下载免费PDF全文

金永男  陈宗涛  由昌英  段隆臣 《探矿工程》2015,42(5):72-76

切削齿布齿设计是PDC钻头设计的关键。为提高PDC钻头的钻进效率,综合考虑PDC钻头切削齿的设计特点和切削先后顺序等因素,并且通过对PDC钻头单切削齿实验结果进行分析,提出了以冠部轮廓法线为基准的切削齿布齿设计方法。  相似文献   

校院两级管理下的排课软件设计与实现     

肖洪生  陈善雄 《广东海洋大学学报》2005,25(6):65-68

阐述了排课系统的管理层次、操作权限分配、资源管理、网络排课的具体实现过程。本系统较好地解决了多个校区、多个学院之间的分配资源和排课冲突问题。其特点是资源统一管理、分散使用,利用校园网进行教学管理,不受时间、空间的限制。  相似文献   

不同布缆方式锚碇沉管管段运动的数值模拟          下载免费PDF全文

杨璨  王永学  左卫广 《海洋工程》2014,32(1):32-40

通过建立波浪作用下锚碇沉管管段运动的时域数值计算模型,对锚碇沉管的运动响应及锚碇缆受力特性进行了研究。应用集中质量法求解锚碇缆力,应用四阶Runge-Kutta法求解管段时域运动方程,计算了在不同沉深、不同周期、不同波高和不同波向条件下沉管管段的运动幅值和锚碇缆力。数值计算的结果表明:锚碇沉管的锚碇缆对沉管管段的运动起到一定的约束作用,在沉放深度较浅、波浪周期较大时,锚碇缆对沉管管段运动幅度的制约更为明显。通过五种布缆方式的计算与分析,探讨了布缆方式对沉管管段运动响应及锚碇缆受力的影响,并给出了较为合理的布缆方案。  相似文献   

Transport of moderately sorted gravel at low bed shear stresses: The role of fine sediment infiltration          下载免费PDF全文

Emeline Perret  Céline Berni  Benoît Camenen  Albert Herrero  Kamal El Kadi Abderrezzak 《地球表面变化过程与地形》2018,43(7):1416-1430

A reliable estimation of sediment transport in gravel‐bed streams is important for various practical engineering and biological studies (e.g., channel stability design, bed degradation/aggradation, restoration of spawning habitat). In the present work, we report original laboratory experiments investigating the transport of gravel particles at low bed shear stresses. The laboratory tests were conducted under unsteady flow conditions inducing low bed shear stresses, with detailed monitoring of the bed topography using a laser scanner. Effects of bed surface arrangements were documented by testing loose and packed bed configurations. Effects of fine sediments were examined by testing beds with sand, artificial fine sand or cohesive silt infiltrated in the gravel matrix. Analysis of the experimental data revealed that the transport of gravel particles depends upon the bed arrangement, the bed material properties (e.g., size and shape, consolidation index, permeability) and the concentration of fine sediments within the surface layer of moving grains. This concentration is directly related to the distribution of fine particles within the gravel matrix (i.e., bottom‐up infiltration or bridging) and their transport mode (i.e., bedload or suspended load). Compared to loose beds, the mobility of gravel is reduced for packed beds and for beds clogged from the bottom up with cohesive fine sediments; in both cases, the bed shear stress for gravel entrainment increases by about 12%. On the other hand, the mobility of gravel increases significantly (bed shear stress for particle motion decreasing up to 40%) for beds clogged at the surface by non‐cohesive sand particles. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

山东黄河水利工程移民安置规划浅论          下载免费PDF全文

马强 《山东国土资源》2005,21(8):56-59

移民安置关系社会稳定和经济可持续发展。要采取措施,尽快恢复生产,使搬迁居民达到或超过原有生活水平。移民安置规划主要内容包括实物指标调查、农村移民生产措施规划、居民点规划及专项处理规划等。实物指标调查是移民安置规划设计的第一步基础工作。实物数量、现状的标准等是确定移民安置规模和专业项目复建规划的重要依据。移民安置规划是移民规划设计的核心。农村移民生产安置方案的制定和措施的落实是移民安置规划设计的重点,移民生活安置环境容量的分析与移民安置目标的确定则是移民安置规划的关键。  相似文献