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991.
The age and habitat of the Bende fish fossils have remained a matter of controversy with interpretations ranging between the Paleocene Imo Formation and the Eocene Ameki Formation. Outcrop-based sequence stratigraphic analysis presented in this work shows that the Imo and Ameki Formations together include three laterally extensive estuarine central basin/offshore mud rock units that are associated with the 59.7, 58.1, and the 56.8 ma maximum flooding surfaces, respectively. Field evidence and stratigraphic analysis show that the Bende fossil bones are hosted by the mud rock unit containing the 58.1 ma maximum flooding surface, while the Ameke bone fossils are contained within the condensed section associated with the 56.8 ma maximum flooding surface. Apart from highlighting the relevance of sequence stratigraphy in paleobiological interpretations, this study shows that the Bende fish fauna which Arua first assigned to the Eocene Ameki Formation indeed belongs to the Paleocene Imo Formation. 相似文献
992.
文章根据概率图解法原理,利用VB可视化编程技术,完成了概率图筛分软件的研制.并通过该软件对东升庙矿床矿石品位混合总体进行筛分处理,探究其成矿期次信息.已有研究结果表明:一次成矿作用形成的矿床,其矿石品位的累积概率图是一条直线.而东升庙矿床的8条代表性勘探线中4种主要成矿元素TS、An、Pb、Cu品位的累积概率图均为曲线且出现明显拐点,经多次作图检验证实有效拐点数为1,由此得到新的成矿期次信息,揭示该矿床经历了两期成矿作用,即中元古代同沉积-海底喷气矿化期和后生改造矿化期,这对于研究其成矿物质来源和成矿机理具有重要的意义. 相似文献
993.
The Bhavani Shear Zone (BSZ), part of the Palghat-Cauvery shear system of southern India, comprises a number of subparallel
shear zones ranging in width from a few centimetres to tens of metres. These shear zones are characterised by progressive
mylonitisation and shear fabrics corresponding to increasing strain, as documented by grain size reduction, flattening, elongation
and dimensional preferred orientation of constituent minerals (quartz, hornblende, biotite, plagioclase and orthoclase). However,
SEM-EBSD measured crystal preferred orientations (CPO) of these minerals are more complex and indicate interchange of maximum
(X) and intermediate (Y) tectonic axes during different phases of deformation, with the minimum axis (Z) remaining approximately
constant. The tectonic evolution of the BSZ and the disposition of the surrounding Archaean and Pan-African granulites are
interpreted therefore in terms of polyphase deformation involving both dip-slip and strike-slip movement events in a multiply
reactivated setting. SEM-EBSD CPO analysis provides clearer indication of potentially conflicting movement directions that
are otherwise poorly constrained by shear markers and shear sense indicators. 相似文献
994.
人口空间化是实现人口统计数据与其他环境资源空间数据融合分析的有效途径。本文选取夜间灯光数据、道路网数据、水域分布数据、建成区数据、数字高程模型和地形坡度数据作为影响珠江三角洲人口分布的变量因子,利用随机森林模型对珠江三角洲2010年人口数据进行了30 m格网空间化,并将模拟结果与三个公开数据集作精度对比,最后基于随机森林模型的变量因子重要性分析珠江三角洲人口空间分布的影响因素。结果表明:本文模拟整体精度达到82.32%,均优于WorldPop数据集以及中国公里网格人口数据集,接近GPW数据集,而且在人口密度中等区域模拟精度最高;通过对变量因子重要性进行度量,发现夜间灯光强度是珠江三角洲人口分布的最重要指示性指标,到水域的距离、到建成区的距离和路网密度对珠江三角洲人口分布均具有重要作用。利用随机森林模型结合多源信息能够实现高空间分辨率的人口空间化,可为精细化城市管理提供重要数据源,也可为相关政策决策制定提供支持。 相似文献
995.
Under the condition of freeze-thaw cycles, two types of rocks (granite and andesite), used as slope protection for the Qinghai-Tibet
Railway, were tested according to the special climatic conditions in the Tibetan Plateau, and their various damage processes in appearance
were carefully observed. Observation results show that damage of andesite was more serious than that of granite. Using
an acoustic instrument, ultrasonic velocity was tested. The changing trends of velocity with the number of freeze-thaw cycles were
analyzed, and the freeze-thaw cycle damaging the physical and mechanical properties of rocks can be seen. According to the
changing trends of ultrasonic velocity with the number of freeze-thaw cycles, mechanical parameters of rocks, such as dynamic
elasticity modulus, Poisson’s ratio, and dynamic bulk modulus were analyzed. It is found that they all have declining trends as the
number of freeze-thaw cycles increases, and in particular, when the cycle number reaches a certain extent, the Poisson’s ratio of
rocks begins to become negative. 相似文献
996.
Many of the decisions relating to future urban development require information on climate change risks to cities This review
of the academic and “grey” literature provides an overview assessment of the state of the art in the quantification and valuation
of climate risks at the city-scale. We find that whilst a small number of cities, mostly in OECD countries, have derived quantitative
estimates of the costs of climate change risks under alternative scenarios, this form of analysis is in its infancy. The climate
risks most frequently addressed in existing studies are associated with sea-level rise, health and water resources. Other
sectors such as energy, transport, and built infrastructure remain less studied. The review has also undertaken a case study
to examine the progress in two cities—London and New York—which are relatively advanced in the assessment of climate risks
and adaptation. The case studies show that these cities have benefited from stakeholder engagement at an early stage in their
risk assessments. They have also benefited from the development of specific institutional responsibilities for co-ordinating
such research from the outset. This involvement has been critical in creating momentum and obtaining resources for subsequent
in-depth analysis of sectoral impacts and adaptation needs..While low cost climate down-scaling applications would be useful
in future research, the greatest priority is to develop responses that can work within the high future uncertainty of future
climate change, to build resilience and maintain flexibility. This can best be used within the context of established risk
management practices. 相似文献
997.
998.
Maziar Khosravi Seyed Mostafa Siadatmousavi Ross Vennell Vahid Chegini 《Ocean Dynamics》2018,68(2):239-254
Vessel-mounted ADCP measurements were conducted to describe the transverse structure of flow between the two headland tips in Khuran Channel, south of Iran (26° 45′ N), where the highest tidal velocities in spring tides were ~?1.8 m/s. Current profiles were obtained using a 614.4 kHz TRDI WorkHorse Broadband ADCP over nine repetitions of three cross-channel transects during one semidiurnal tidal cycle. The 2.2-km-long transects ran north/south across the channel. A least-square fit to semidiurnal, quarter-diurnal, and sixth diurnal harmonics was used to separate the tidal signals from the observed flow. Spatial gradients showed that the greatest lateral shears and convergences were found over the northern channel and near the northern headland tip due to very sharp bathymetric changes in this area. Contrary to the historical assumption, the across-channel momentum balance in the Khuran Channel was ageostrophic. The current study represents one of the few examples reported where the lateral friction influences the across-channel momentum balance. 相似文献
999.
1000.
Efisio Solazzo Silvana Di Sabatino Noel Aquilina Agnes Dudek Rex Britter 《Boundary-Layer Meteorology》2010,137(3):441-457
The ongoing trend of urbanisation worldwide is leading to a growing requirement for detailed flow and transport parameterisations
to be included within numerical weather prediction (NWP) models. Such models often employ a simple roughness parameterisation
for urban areas, which is not particularly accurate in predicting or assessing the flow and dispersion at street scale. Moreover,
this kind of parameterisation offers too poor a representation of the mechanical and thermal forcing exerted by urban areas
on the larger scale flow. At present, high computational costs and long simulation running times are among the constraints
for the implementation of more detailed urban sub-models within NWP models. To overcome such limitations, a downscaling procedure
from the atmospheric flow at the synoptic scale to the neighbourhood scale and below, is presented in this study. This is
achieved by means of a simple urban model based on a parameterised formulation of the drag exerted by the building on the
airflow. Application of the urban model for estimating spatially-averaged mean wind speed and the urban heat island over a
selected neighbourhood area in Lisbon, Portugal, is presented. The results show the capability of the urban model to provide
more accurate mean wind and temperature profiles. Moreover, the urban model has the advantage of being cost effective, as
it requires small computational resources, and thus is suitable to be adopted in an operational context. The model is simple
enough to be also used to assess how the resolving of urban surface processes may affect those at the larger scales. 相似文献