Impact cratering: The South American record—Part 2     

《Chemie der Erde / Geochemistry》2019,79(2):191-220

In the first part of this review of the impact record of South America, we have presented an up-to-date introduction to impact processes and to the criteria to identify/confirm an impact structure and related deposits, as well as a comprehensive examination of Brazilian impact structures. The current paper complements the previous one, by reviewing the impact record of other countries of South America and providing current information on a number of proposed impact structures. Here, we also review those structures that have already been discarded as not being formed by meteorite impact. In addition, current information on impact-related deposits is presented, focusing on impact glasses and tektites known from this continent, as well as on the rare K–Pg boundary occurrences revealed to date and on reports of possible large airbursts. We expect that this article will not only provide systematic and up-to-date information on the subject, but also encourage members of the South American geoscientific community to be aware of the importance of impact cratering and make use of the criteria and tools to identify impact structures and impact deposits, thus potentially contributing to expansion and improvement of the South American impact record.  相似文献   

On the rocking–sliding instability of rigid blocks under ground excitation: Some new findings     

《Soil Dynamics and Earthquake Engineering》2015

Rocking (overturning) instability analyses of rigid blocks based on the assumption that the friction between the block and the ground is sufficiently large to exclude the effect of sliding, are reconsidered by including the effect in question. Both modes of overturning instability – without impact and after one impact – are thoroughly discussed in connection with small sliding, whose value depends on the values of kinetic (dry) friction coefficient and the external frequency excitation. Using an energy approach the analytical derivation of the nonlinear differential equations of motion of free-standing rigid blocks under one-sine ground pulse including the effect of sliding, are comprehensively established. The serious difficulties in solving this problem on one hand the change of the kinetic friction coefficient during the motion and on the other hand the reliable evaluation of the actual friction effect when rocking is included, are effectively confronted. This is achieved through a reliable approximation of an equivalent (reduced) coefficient assuming that the major part of friction takes place from the initiation of motion and terminates shortly after the onset of rocking. In cases of slender blocks closed form solutions for overturning due to simultaneous rocking–sliding without or after one impact, are conveniently derived. Among other findings, it was explored that the single block in question for small values of the external frequency (long periods of excitation) the sliding effect is beneficial (stabilizing the block), while for large values of external frequency this effect is detrimental (destabilizing the block).  相似文献   

吉林省重大暴雨过程影响损失评估模型的建立     

袭祝香  纪玲玲  张硕 《气象与环境学报》2014,30(5):141-145

利用1961-2012年吉林省逐日降水资料、暴雨灾情资料、逐年GDP和人口资料采用灰色关联度分析方法建立重大暴雨过程指数及灾损指数,利用相关分析法对重大暴雨过程造成损失的影响因素进行探讨,采用多元回归法建立重大暴雨过程影响损失评估模型,并进行拟合和试评估检验。结果表明：吉林省重大暴雨过程造成的损失与前7 d雨量及重大暴雨过程指数相关显著;利用前7 d雨量和重大暴雨过程指数建立的影响损失评估模型拟合和试评估效果均较好,可在实际业务中应用;由于在重大暴雨过程发生前,评估因子就可获得,因此,可以对其灾害损失进行定量预评估,在实际业务中指导意义较大。  相似文献   

沈阳大气成分观测站站址环境特征分析          下载免费PDF全文

张云海  王扬锋  马雁军 《气象与环境学报》2008,24(4):31-35

根据沈阳地理位置、地形特点和区域环境及气候环境等,对沈阳大气成分站所处站址环境进行探讨。并利用2004—2006年逐时气象观测数据对周围地物影响以及周围大气污染源对观测数据可能产生的影响进行了分析。结果表明:沈阳大气成分站的站址设置基本符合建站要求,颗粒物和黑炭浓度的观测数据可以反映出沈阳地区大气环境特征与大气成分变化情况。  相似文献   

Addressing the impacts of large-scale land investments: Re-engaging with livelihood research     

《Geoforum》2017

What started as a media-driven hype about the global land rush has developed into a well-established academic debate on land governance and an important domain for policy intervention. Research over the past decade has deepened our understanding of how land, water and forests, which were once considered to be local assets and the sources of livelihoods, are transformed into global goods and the focus of capital investments. We are now clearly aware that such transformation generates significant impacts on the livelihood security of vulnerable groups. In response to this, a variety of policy interventions have been devised to minimize the negative impacts (‘do not harm’) and create new opportunities (‘do good’). Yet, it is still unclear how actual policy implementations play out on the ground, what the real impacts are at the local level and whether these interventions help people to improve their livelihoods. In this paper, we present an overview of the existing intervention approaches and their theoretical underpinnings, and discuss how to optimize the developmental outcomes. We argue that the once popular livelihood research framework should be revised and then incorporated more robustly in the existing intervention approaches, as it could help investors and governmental actors to engage in making their investments more relevant to local development.  相似文献   

Expansion of round gobies in a non-navigable river system     

《Limnologica》2017

A number of Ponto-Caspian Gobiid species have greatly increased their geographical ranges over recent decades. Most expansion studies to date, however, have focused on navigable waterways. In this study, we present a summary of six-years (2008–2013) monitoring of round goby Neogobius melanostomus expansion along two connected non-navigable rivers. Contiguous range expansion was observed in both rivers, with dispersal rate ranging from 1.2 to 3.2 km/year. Gobies at newly invaded sites ranged from 20 to 117 mm, with both juveniles and adult fish observed. Though the data did not allow us to see any consistent pattern in the first years after detection, there was some evidence for a shift to a female-biased, juvenile-dominated population over time. While the abundance of non-native tubenose goby Proterorhinus semilunaris appeared to be negatively influenced by round goby establishment, diversity of nearshore native fish showed no evidence of dramatic decline attributable to round goby.  相似文献