Sponges boring into precious corals: an overview with description of a new species of Alectona (Demospongiae, Alectonidae) and a worldwide identification key for the genus     

Barbara Calcinai  Carlo Cerrano  Nozomu Iwasaki  & Giorgio Bavestrello 《Marine Ecology》2008,29(2):273-279

Precious corals represent peculiar substrata for several species of boring sponges that exploit their carbonatic scleraxis, strongly decreasing their commercial value. Here we describe a new species of the genus Alectona from Japan recorded in a colony of Paracorallium japonicum (Kishinouye, 1903). The spicular complement of the new species consists of diactinal spicules covered by mushroom-like tubercles, often modified into styloid forms, and fusiform amphiasters with two or sometimes four verticils, each generally made up of six short tubercled rays. A complete survey of the literature on boring sponges recorded in precious corals in the Mediterranean Sea and Pacific Ocean indicates that the species of the family Alectonidae are the most strictly associated to this kind of substratum. Their world distribution, in fact, partially or totally overlap that of their coral hosts.  相似文献   

全断面隧道掘进机护盾受力监测及卡机预警     

刘泉声  彭星新  黄兴  雷广峰  魏莱  刘鹤 《岩土力学》2018,39(9):3406-3414

全断面隧道掘进机(简称TBM)在穿越深部软弱地层时围岩收敛变形较大,围岩容易挤压护盾,导致TBM卡机,影响TBM正常掘进。通过分析TBM卡机灾害孕育过程,得到了预测TBM卡机的重要条件：一是围岩变形量大于预留的空间,二是额定推力不能克服摩擦阻力。为了监测实际工程TBM卡机状态,提出了一种监测护盾变形的方案以及护盾受力的计算方法,可通过监测得到的变形估算护盾的受力,进而计算出护盾受到的摩擦阻力,得到TBM卡机的状态。根据TBM受到的摩擦阻力、TBM正常掘进时所需推力和TBM额定推力之间的关系,将TBM卡机状态分为4个等级,即无卡机、轻微卡机、卡机和严重卡机,并提出了对应的处理措施。结合TBM卡机条件以及护盾受力监测方案,提出了TBM卡机灾害预警流程。在兰州水源地输水隧洞工程中应用了该监测方案和卡机灾害预警流程,应用结果表明,预测的卡机状态与TBM实际状态基本一致,说明该方法具有一定的可靠性,对指导TBM隧道施工具有重要意义。  相似文献   

TBM滚刀破岩的广义粒子动力学数值模拟     

翟淑芳  周小平  毕靖 《岩土力学》2018,39(7):2699-2707

提出了一种新的无网格数值模拟计算方法--广义粒子动力学法(GPD),并在GPD算法中引入了粒子损伤理论。运用GPD方法,建立了TBM单滚刀、双滚刀作用下的完整岩体破岩模型,成功模拟了TBM滚刀破岩过程。通过与数值模拟结果及室内试验结果的对比分析,验证了GPD法模拟TBM滚刀破岩过程的有效性。同时,运用GPD方法建立了含节理岩体及高围压条件下岩体的TBM滚刀破岩模型,研究了节理及围压条件下TBM滚动破岩过程。得到了节理对TBM滚刀破岩效率的影响,既可能是促进作用又可能是抑制作用,高围压对TBM滚刀破岩过程中裂纹的起裂及扩展和破岩深度有较大的影响。  相似文献   

Is contract farming an inclusive alternative to land grabbing? The case of potato contract farming in Maharashtra,India     

《Geoforum》2017

In the recent explosion of attention given to the land grabbing phenomenon, contract farming has been identified as a potentially inclusive alternative for smallholders to outright acquisition of farm land by agri-business capital. This paper responds to these claims by resituating contract farming as an equally important form of land control. The focus of the paper is a case study of potato contract farming in Maharashtra, India. While there is ‘nothing new’ about contract farming as a mode of agriculture production in India, its influence on patterns of agrarian change is poorly understood. Adopting an agrarian political economy-informed livelihoods approach, the paper argues that rather than an inclusive alternative to land grabbing, contract farming in the study site represents another way that capital is coming to control land in rural India, with just as important implications for agrarian livelihoods. While some individual households have improved their livelihoods through participation, the contract scheme acts to reinforce already existing patterns of inequality. In particular, the unequal power relations between firm and farmer skew the capture of benefits towards the firm, and render participating households vulnerable to indebtedness and loss of autonomy over land and livelihood decisions.  相似文献   

Privatization,financialization and ocean grabbing in New Brunswick herring fisheries and salmon aquaculture     

《Marine Policy》2017

The growing literature on individual transferable quotas (ITQs) and on intensive salmon aquaculture and its negative impacts on the environment and other users of related marine space has been little connected to the developing literature on financialization and to the literature on ocean grabbing within fisheries. This paper seeks to address this gap through a case study of the recent history of herring fisheries and intensive aquaculture in New Brunswick, Canada, exploring how specific neoliberal processes – including privatization and marketization (in herring fleet ITQs and aquaculture lease systems), (re)regulation, financialization and globalization – have interacted to support the reshaping of regional fisheries from mixed small-scale, family-based, petty commodity fisheries towards vertically-integrated, corporate, financialized fisheries characterized by ocean grabbing.  相似文献   

沪-蓉高速铁路跨越汉江特大桥桩孔施工技术   总被引：2，自引：0，他引：2       下载免费PDF全文

杨宗仁  史学伟 《探矿工程》2010,37(2):47-50

介绍了沪-蓉高速铁路武汉蔡家湾特大桥岩溶区域钻孔施工工艺、施工设备的选择,施工技术参数的确定,以及岩溶地层钻孔施工常见事故的处理及预防。  相似文献   

非开挖导向钻进轨迹的三维模拟与调控设计   总被引：1，自引：1，他引：0       下载免费PDF全文

乌效鸣  高辉杜峰 《探矿工程》2001,(5):45-46,49

应用空间解析方法和计算机三维图形技术,科学地模拟非开挖导向钻井时钻头在地下的立体坐标位置、倾角、面向角和运行路线,准确、快捷地调控非开挖导向钻井的钻孔设计轨迹。  相似文献   

冲击反循环钻进工艺在滑坡治理工程中的应用     

黄恒杰  殷关虎  苏力才 《南方国土资源》2001,14(2):67-70

大口径钻孔灌注桩的入岩问题 ,历来是广西基础施工中的一大难题。最近 ,广西第一地质工程地质施工公司引进了冲击反循环钻进方法用于滑坡治理工作 ,取得重大突破。文章结合工程实例着重介绍该方法的钻进原理、成孔工艺、技术参数选择、事故的预防和处理以及技术经济指标的对照和分析等 ,可供基础施工的同行们借鉴。  相似文献   

坑内单管水力反循环取心钻探技术研究     

陈礼干 《矿产与地质》2001,15(4):284-289

阐明了坑内水力反循环连续取心钻进的原理以及该工艺所具有优点、缺陷及相应的工艺措施。提出了该工艺规程参数的计算原理及计算方法。  相似文献   

Using the Entropy of Curves to Segment a Time or Spatial Series   总被引：1，自引：0，他引：1  

A. Denis  F. Crémoux 《Mathematical Geology》2002,34(8):899-914

The concept of the thermodynamics of curves is used to analyze change in the variability of time or spatial series. More specifically, the entropy of a curve makes it possible to divide a nonstationary random field, because of a change in variance, into subdomains where data are said to be stationary. It is demonstrated that for time and spatial series the entropy of a curve is the slope of the cumulative sum of absolute differences. Numerical simulations show the efficiency of this tool. It can be shown that the presence of a linear or quadratic trend is without effect on the localization of the stationary subdomains. A practical case is studied with data collected from a tunnel boring machine where several parameters are recorded. This analysis can bring more information on the mechanical behavior of the different geological formations and explain or justify unplanned delays.  相似文献