Star Formation in the Outskirts of Disk Galaxies     

Annette M.N. Ferguson 《Astrophysics and Space Science》2002,281(1-2):119-122

The far outer regions of galactic disks allow an important probe of both star formation and galaxy formation. I discuss how observations of HII regions in these low gas density, low metallicity environments can shed light on the physical processes which drive galactic star formation. The history of past star formation at large radii, as traced by observations of old and intermediate-age stars, constrains the epoch at which the highest angular momentum regions of disks were in place; first results for the M31 disk suggest this occured a significant (≳ 8 Gyr) time ago. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

Distribution of Methane and Methanogen Populations in the Qilian Mountain Permafrost, Qinghai Province, China     

LIU Haodong  SU Xin  JIAO Lu  PANG Shouji 《《地质学报》英文版》2013,87(Z1):998-998

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Experimental study on bubble pulse features under the combined action of horizontal and vertical walls     

王诗平  初文华  张阿漫 《中国海洋工程》2014,28(3):293-301

The pulse features of a bubble have a close connection with the boundary condition. When a bubble moves near a rigid wall, it will be attracted by the Bjerknes force of the wall, and a jet pointing at the wall will be generated. In real application, the bubble may move under the combined action of walls in different directions when it forms at the corner of a pipe or at the bottom of a dam. The motion of the bubble shows complex and nonlinear characteristics under these conditions. In order to investigate the bubble pulse features near complex walls, a horizontal wall and a vertical wall are put into the experimental water tank synchronously, and an electric circuit with 200 voltages is designed to generate discharge bubbles, and then experimental study on the bubble pulse features under the combined action of horizontal and vertical walls is carried out. The influences of the combined action of two walls on the bubble shape, pulse period, moving trace and inside jet are obtained by changing the distances from bubble center to the two walls. It aims at providing references for the relevant theoretical and numerical research.  相似文献   

静水生长的淡水湖冰微结构的季节变化及其受生长过程的影响   总被引：3，自引：2，他引：1  

黄文峰  李志军  韩红卫  贾青 《冰川冻土》2016,38(3):699-707

冰物理微结构特征控制着冰层基本物理性质。基于多年冬季对东北平原区水库和湖泊冰层生消过程、气象条件,以及冰层晶体、冰内气泡和密度特征的现场观测,分析了淡水湖冰微结构的季节演化和年变化规律及其影响因素。湖冰晶体结构、气泡含量与分布、冰密度具有明显的分层结构,且在冰厚增长期和稳定期内基本维持不变;进入融化期,冰内微结构变化迅速,表现为晶体边界融化、气泡体积扩展和融水迁移。不同年份、不同湖泊冰晶体类型和气泡形态类似,但各类晶体层厚度比例、气泡含量与尺寸存在差异。统计分析显示,晶体和气泡结构与湖冰生长速率关系密切,晶体粒径与生长速率呈正比,水内气体的产生和溶解过程、水体扰动程度的差异影响着气泡含量同生长速率之间的关系。  相似文献   

非对称荷载作用下土体劈裂注浆压力分析   总被引：1，自引：0，他引：1  

张淼  邹金锋  陈嘉祺  李亮  李振存 《岩土力学》2013,34(8):2255-2263

为研究在非对称荷载作用下土体劈裂注浆压力,基于扩孔理论和统一强度准则并考虑非对称荷载的作用,建立基于扩孔理论的劈裂注浆启劈压力分析模型,推导出浆泡周围塑性区土体的应力场、位移场、塑性区半径以及启劈注浆压力的理论解答,并以工程算例进行论证。结果表明,考虑对称荷载作用下的启劈注浆启劈压力较考虑非对称荷载作用下的值要大,对称荷载作用下的分析方法低估了塑性区半径;无论是柱形劈裂还是球形劈裂,当 1时,启劈压力会随着 的增大而增大,塑性半径会随着 的增大而明显减小;当 1时,启劈压力会随着 的增大而减小,而塑性半径的变化是有限的。预先了解土体的初始应力条件对正确的确定劈裂注浆启劈压力至关重要,可为劈裂注浆的设计和施工会提供更加完善的理论依据。  相似文献   

Roles of financial innovation and information technology: Lessons from US sub-prime mortgage crisis and its implications for China     

James H LENZER JR  Simon Xiaobin ZHAO 《中国地理科学(英文版)》2012,22(3):343-355

The mortgage loan has evolved from a local lending instrument into a major global security and its role is unparallel to other financial instruments in the process of financial globalization.This paper explains how technology and financial innovation transformed the mortgage loan from a local security into a premier global security traded worldwide.It examines the fundamental flaws of this process and why it does not work in regards to mortgage lending and the re-securitization products that were created through financial innovation.The findings show that regulation was unable to keep pace with financial innovation,which created an environment where actors in the financial service sector were able to behave geographically irresponsibly by using information asymmetries to their advantage by participating in moral hazard activities and engaging in other immoral and unethical business practices that were centered around localized geography,which ultimately contributed to the global financial crisis.It also examines the roll of financial innovation in regard to the Lehman Brothers Mini-Bond in Hong and its role as a driving force behind China’s newly emerging shadow banking sector.It concludes with a policy recommendation and its implication for China’s continued economic development.  相似文献   

气氡观测中的恒流鼓泡式脱气-集气装置研制与应用   总被引：1，自引：0，他引：1  

邱永平 《内陆地震》2014,(4):335-340

利用20 cm不锈钢高压锅作为集气室,在锅的两边上、下分别打一个进出水孔,用15 mm不锈钢管道件连接,把进水口制作成高于锅内液面,出水口与锅内液面为同一水平面,形成一高一低,一小一大两个相对稳定的动态水平液面,在进水管中引入气泵输出气体,使集气室内进水同时进行自动连续鼓泡,把水中气体脱出,在输气管中接入玻璃转子流量计控制气体流量,进行恒流鼓泡。并应用于小流量冷水井气氡观测,效果显著。  相似文献   

晴空热对流泡的风廓线雷达探测研究   总被引：2，自引：1，他引：1  

何平  马颖  阮征  王迎春  李长河  曹晓彦 《气象学报》2010,68(2):264-269

文中将风廓线雷达和无线电-声探测系统探测资料用于边界层晴空热对流探测研究.结合探测事例分析了晴空热对流的演变过程和热对流对上层空气的加热效应.在热对流初期,对流高度逐渐抬高,伴有较强上升速度的热对流泡逐渐升高的现象.在热对流旺盛期,热泡合并现象明显,不论是上升还是下沉气流瞬时速度都可以超过1 m/s,可以在约2 km的高度范围内形成一致的上升或下沉运动,并形成闭合环流、周期约1 h.在热对流消退期,对流高度逐渐降低,上升运动变得相对和缓并维持较长时间.在热对流过程中,热泡运动造成气层温度的起伏,热泡与周围温度差可以达到2-4℃.探测结果表明风廓线雷达具有很高的灵敏度,可以探测到晴空热对流泡.并且,风廓线雷达资料具有很高的时间和高度分辨率,可以精细刻画热对流泡的时空分布和演变,配合无线电-声探测系统还可以精确探测热泡温度分布及其对周围温度垂直分布的影响.通过对晴空热对流风廓线雷达探测资料的初步分析,在一定程度上拓展和加深了对热对流泡和边界层热对流运动特征的了解.借助风廓线雷达探测可有效改善低层大气探测,有利于开展低层大气动力与热力过程的数值研究,对于中尺度模式、降水预报的改进等具有重要参考作用.  相似文献   

西班牙的房地产泡沫:城市化与城市建设     

Onofre Rullan  SòniaVives-Miró  JesúsM.GonzálezPérez  尹子潇  顾朝林  陈明玉 《地理研究》2016,35(7):1383-1396

聚焦于西班牙1996-2007年间的房地产泡沫,此次危机与西班牙前两次经历的地产泡沫有着相似的背景条件：将住房建设作为利好投机性投资。但几次泡沫供给结构却不同：此次住房供给主要为分散式,不同于以往的集中供应;旅游地产大量出现;房屋拥有型社会形成。作者认为供给结构的改变并非危机的主要原因,并提出了造成房地产泡沫的四个关键要素：符合一定条件的土地、土地规划的配合、充足的资金与可获得的土地所有权。结论是：政策的制定直接影响土地利用、发展规划、金融系统与个人资产、造成住房由使用品变为投机投资的对象、银行体系信用缺乏保障,最终导致了住房库存量陡增,大量房屋拆除事件与失业率攀升等经济和社会方面的不良影响。  相似文献   

The “easy restriction” syndrome drive local fish stocks to extinction: The case of the management of Swedish coastal populations     

《Marine Policy》2017

Spatially sensitive management built on detailed biological and socio-economic knowledge is required to establish sound fishing regulations and to avoid extinction of small coastal populations of fish and shellfish. Highly productive isolated populations of several commercial species have historically inhabited the Swedish west coast, but during the past century these populations have been depleted by fisheries and with no sign of recovery. Since 1999 several fisheries regulations and different stakeholder co-management initiatives have flourished along the Swedish coast of the Skagerrak. They aimed to facilitate the recovery of collapsed local stocks but the established regulations failed to identify and restrict the main sources of mortality acting on local stocks and they have thus been ineffective to promote the recovery. Furthermore, regulations have operated on the weakest among stakeholders (e.g.. recreational fishers), which have minor influence over management, and the restrictions have been imposed without providing any data which supported the choice (i.e. the “easy restriction” syndrome). In line with the general “spirit” of recent Swedish fishery management, we conclude that managers, without the disapproval of Swedish scientists, have circumvented limitations which should address the largest mortality factor, i.e. the commercial fishery. The regulations presently in place, have been politically uncontroversial and easy to implement, but have been highly unsuccessful. We therefore suggest that stakeholders, including politicians, should start focusing on more effective and science-based management and less on what is politically attractive if Swedish citizens shall have a chance to witness the recovery of their once flourishing coastal populations.  相似文献