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排序方式: 共有113条查询结果,搜索用时 15 毫秒
21.
构造运动强烈、不断发生强震的云南地壳,可能经常有部分区域处于不稳定状态,外力也正是在此基础上才得以对地震活动显示出明显的调制效应。1988年11月6日澜沧—耿马7.6级、7.2级大地震前的大量观测资料表明,云南地区,特别是澜沧—耿马附近地区又再次出现了类似1970年通海7.7级、1974年大关7.1级和1976年龙陵7.4级大地震之前,曾发生过的那种地表涝旱剧变和大气压力巨涨落现象。这种震前的外部异常扰动具有很强的重复性,在对应地震上也显示了很强的应验性,故其很有可能在云南未来7级大地震的监视预报中发挥作用。 相似文献
22.
福建闽江水口库区飘浮植物覆盖对水体环境的影响 总被引:18,自引:0,他引:18
为了探索城市富营养化湖泊生态修复技术,2000年9月在南京市莫愁湖物理生态工程试验区内,开展了隔离外源污染、覆盖底泥和种植水生植物对湖泊水质平均水平和水体脉动强度影响的比较研究.试验结果表明,通过围隔隔离外源污染可在较短时间内迅速改善湖泊TN的平均水平,但难以提高湖泊生态系统的稳定性;通过覆盖底泥控制内源污染难以改善湖泊水质的平均水平,并且难以提高湖泊生态系统的稳定程度;种植水生植物不仅能够全面改善湖泊水质的平均水平,而且可以提高湖泊生态系统的稳定性.此外,富营养化湖泊中,藻类生长与湖水营养盐浓度并不存在正相关的关系.因此,对城市湖泊富营养化的防治,在控制外源污染降低营养盐浓度的同时,应恢复湖泊原有的以水生高等植物为主的生态系统. 相似文献
23.
24.
A theoretical and an experimental investigation was carried out, where a carbon fibre corrugated circular cylinder was tested to destuction under external hydrostatic pressure. The theoretical investigation was via the finite element method, where the structure was modelled with several orthotropic axisymmetric thin-walled shell elements. The experimental observations were aided with strategically placed strain gauges. Comparison between theory and experiment showed that the experimentally observed buckling pressure was a little lower than the theoretical prediction. This may have been due to the fact that the model had slight initial geometrical imperfections in the circumferenential direction. 相似文献
25.
Reducing large-scale deforestation in commodity frontiers remains a key challenge for climate change mitigation and the conservation of biodiversity. Public and private anti-deforestation policies have been shown to effectively reduce forest loss, but the conditions under which such policies get adopted are rarely examined. Here we propose a set of conditions that we expect to be associated with the adoption of effective anti-deforestation policies in commodity frontiers. We then examine whether these conditions have influenced policy adoption in South America’s major soy-and-cattle frontiers: the Brazilian Amazon, the Cerrado, the Chaco, the Chiquitano, and Paraguay’s Atlantic Forest. By collating empirical data from diverse sources, including literature review, extensive expert interviews, and analysis of primary and secondary data, we show that the Cerrado, the Chaco, and the Chiquitano differ from the Brazilian Amazon in multiple ways that might have inhibited adoptions of effective anti-deforestation instruments. These conditions include: a higher importance of the agricultural sector within the respective countries, lower carbon stocks and species richness, higher prevalence of private land tenure, and higher baseline compliance with forest reserve regulations on private lands. We also observe that the adoption of the most effective private anti-deforestation instrument, commodity moratoria, may respond to similar conditions as those influencing the adoption of public instruments. Incentivizing public and private actors to adopt effective anti-deforestation policies in the Cerrado, Chaco, and the Chiquitano will likely be more challenging than it has been in the Brazilian Amazon. 相似文献
26.
Carl T. F. Ross Andrew P. F. Little Leonidas Chasapides Jeff Banks Daniele Attanasio 《Ocean Engineering》2004,31(2):239-252
The paper reports on the buckling of three ring-stiffened prolate domes under external hydrostatic pressure. The study was partly theoretical and partly experimental, where in the case of the latter, the finite element was used. Comparison between experiment and theory was good. The effect of ring stiffening the domes was to increase their buckling resistances by factors varying from 4.43 to 5.72. 相似文献
27.
C. T. F. Ross Bak Hock Huat Tay Boon Chei Chai Min Chong M. D. A. Mackney 《Ocean Engineering》2003,30(5):691-705
The paper reports on a theoretical and an experimental investigation into six GRP hemi-ellipsoidal dome shells, which were tested to destruction under external hydrostatic pressure. All six domes were of oblate shape and of three different aspect ratios. Each aspect ratio consisted of two dome shells, one made from two layers of glass fibre and one made from three layers of glass fibre. The theoretical analysis was via the finite element method where a non-linear theory was used which allowed for both geometrical and material non-linearity. Comparison between theory and experiment was good. 相似文献
28.
Behaviour of Coupled Modes in a Simple Nonlinear Air-Sea Interaction ModelLiChongyinandLiaoQinghai(LASG,InstituteofAtmospheri... 相似文献
29.
Jean-François Royer Daniel Cariolle Fabrice Chauvin Michel Déqué Hervé Douville Rong-Ming Hu Serge Planton Annie Rascol Jean-Louis Ricard David Salas Y Melia Florence Sevault Pascal Simon Samuel Somot Sophie Tyteca Laurent Terray Sophie Valcke 《Comptes Rendus Geoscience》2002,334(3):147-154
Two climate simulations of 150 years, performed with a coupled ocean/sea-ice/atmosphere model including stratospheric ozone, respectively with and without heterogeneous chemistry, simulate the tropospheric warming associated with an increase of the greenhouse effect of carbon dioxide and other trace gases since 1950 and their impact on sea–ice extent, as well as the stratospheric cooling and its impact on ozone concentration. The scenario with heterogeneous chemistry reproduces the formation of the ozone hole over the South Pole from the 1970s and its deepening until the present time, and shows that the ozone hole should progressively fill during the coming decades. To cite this article: J.-F. Royer et al., C. R. Geoscience 334 (2002) 147–154. 相似文献
30.
Aaron Kingsbury 《Geoforum》2006,37(4):596-609
Business associations (BAs) represent a widely prevalent institution contingent upon a plethora of regional and industrial contexts around the world. Although their role in local development is rarely highlighted this paper argues that analysis of the structure and strategies of BAs reveals important insights into the problematic nature of external economies, typically based on the willingness of highly independent small firms to share and possibly fund some common service(s). BAs illustrate cooperative behaviour and their fragmentation indicates limits to cooperation and thereby to the contested nature of this particular external economy. Conceptually, the paper interprets BAs as institutional expressions of local cooperation and theorizes their strategy and structure in terms of a ‘logic of exchange’ model. This model defines the relationships between BAs, their members (organizational domains) and governments in terms of the logics of ‘membership’ and ‘influence’ that help understand the opportunities afforded and tensions imposed by the rationale and dynamics of cooperation. Empirically, the paper examines the formation and performance of BAs in the restructuring of the Okanagan’s wine industry that was stimulated by the Free Trade Agreement (FTA) between the US and Canada in 1989 and the North American Free Trade Agreement (NAFTA) of 1991. In the Okanagan wine industry, a newly formed BA was vital in helping firms overcome the crisis generated by free trade. However, subsequent fragmentation that arose out of member disenchantment with logics of influence and membership, indicated limits to local cooperation that may constitute a significant diseconomy in a future crisis. 相似文献