南秦岭小茅岭复式岩体地球化学特征及其构造意义

南秦岭北缘小茅岭复式岩体主要由宋家屋场基性辉绿(辉长)岩,迷魂阵、磨沟峡和叶家湾中性-偏酸性闪长岩组成,形成于新元古代早期870~840 Ma。岩石地球化学研究显示,宋家屋场基性岩属亚碱性系列岩石,富集轻稀土元素及大离子亲石元素,Nb、Ta、Ti、P等具有弱的负异常,Zr、Hf等高场强元素的含量较高,Zr/Y、Ta/Yb比值较高,Zr/Nb比值较低,与岛弧玄武岩的地球化学特征相似,在构造环境判别图解中投于火山弧岩石区域,一些元素的富集特征可能来源于受俯冲块体流体交代的岩石圈地幔。迷魂阵、磨沟峡及叶家湾闪长岩体均属准铝质亚碱性系列岩石,具有岛弧火成岩的地球化学特征。Sr-Nd-Hf同位素地球化学分析显示,宋家屋场岩体主要来自亏损地幔源区,磨沟峡和叶家湾岩体主要为新生基性下地壳的部分熔融,而迷魂阵岩体主要为古老地壳物质的部分熔融。上述特征表明小茅岭复式岩体各组成部分可能形成于870~840 Ma俯冲相关的岛弧构造背景,俯冲块体脱水形成的流体交代上覆地幔楔,这种地幔部分熔融形成了宋家屋场角闪辉绿(辉长)岩,由于基性岩浆的加热,诱发新生基性下地壳及原古老地壳物质部分熔融,岩浆上升、侵位,形成磨沟峡、叶家湾及迷魂阵岩体。结合陡岭地区~850–780 Ma变质作用及岩浆事件相关报导,在南秦岭北缘小茅岭—陡岭隆起带上,新元古代早期存在一期构造-岩浆-变质事件,该事件的区域大地构造属性则有待进一步研究。     

湖北宜昌重要地质遗迹资源特征及发展模式探讨

本文系统总结了湖北宜昌地区省级及省级以上地质遗迹资源,认为该地区地质遗迹分布规律主要可概括为两个方面,一是受控于地形和河流的综合作用,以各类地貌景观遗迹为特点;二是各个地质时代地层剖面齐全,古生物化石产地聚集。其中可归类为世界级地质遗迹点为5个,均以“古生物化石”为核心,分别为三峡地区埃迪卡拉生物群、长阳寒武纪清江生物群、黄花场中奥陶统大坪阶“金钉子”、王家湾上奥陶统赫南特阶“金钉子”和远安三叠系南漳—远安动物群。立足于此,文中首次详细总结了这些地质遗迹点的化石代表、科学及科普意义,并从地质遗迹自身保护和应用方式、地质遗迹载体、地学研学、地质文化的传播和文创科普产品5个方面对古生物地质遗迹资源的发展模式进行了详细探讨,从而为宜昌地区全域地质遗迹开发和旅游提供新思路。     

Influence of grain size gradation of sand impurities on strength behaviour of cement-treated clay

In nature, soils are often composed of varying amounts of clay, silt and sand. Variation of the percentage of these compositions can affect the final strength of the soils when stabilised with cement. In this study, focus was placed on clayey soils with different gradation of sand impurities up to 40% in mass. An extensive study of such clayey soils treated with cement was investigated. For the results, it is noted that water:cement ratio was a major influence of strength development of cement-treated clayey soils. In contrast, the soil:cement ratio was found to have minor effects on the strength development. The presence of sand impurities has a significant reduction on the strength development of the cement-treated clayey soil mixture due to more free water available for hydration. The use of free-water:cement ratio is adopted which was shown to be capable of adjusting for such change in amount of free water and water holding capacity of the clay which is determined with Atterberg’s liquid limit tests. The effects of gradation (fine, coarse and well-graded) of the sand impurities were found to affect strength development minimally, owing to similarities in their liquid limits when mixed with clay. Ordinary Portland cement (OPC)-treated clayey soils produced a more rapid gain in strength but lower final strength at 28 days of curing as compared with Portland blast furnace cement (PBFC). This is found to be persistent for different gradation of sand impurities. A linear correlation can be established based on the log of the unconfined compressive strengths developed at different curing age, with slopes of these linear trends found to be similar for PBFC and OPC-treated clayey soil specimens. Finally, a strength prediction model comprising of these findings is developed. The parameters adopted in this model coincide with values proposed by past studies, thereby validating the robustness of the model. The practical benefits from this study offer a quality control scheme to forecast long-term performance of cement-treated clayey soils as well as optimise cement dosage in cement stabilisation to produce a more cost-effective and less environmental-invasive usage of the technology in geotechnical applications.

     

Size distribution of free particles in soils: a geometric modelling approach

Acta Geotechnica - Suffusion is a typical form of internal erosion for gravel soils in which fine particles are detached by seepage and transport by water through pores. The prediction of erodible...     

Understanding the dynamical-microphysical-electrical processes associated with severe thunderstorms over the Beijing metropolitan region

The Dynamical-microphysical-electrical Processes in Severe Thunderstorms and Lightning Hazards(STORM973)project conducted coordinated comprehensive field observations of thunderstorms in the Beijing metropolitan region(BMR)during the warm season from 2014 to 2018.The aim of the project was to understand how dynamical,microphysical and electrical processes interact in severe thunderstorms in the BMR,and how to assimilate lightning data in numerical weather prediction models to improve severe thunderstorm forecasts.The platforms used in the field campaign included the Beijing Lightning Network(BLNET,consisting of 16 stations),2 X-band dual linear polarimetric Doppler radars,and 4 laser raindrop spectrometers.The collaboration also made use of the China Meteorological Administration’s mesoscale meteorological observation network in the Beijing-Tianjin-Hebei region.Although diverse thunderstorm types were documented,it was found that squall lines and multicell storms were the two major categories of severe thunderstorms with frequent lightning activity and extreme rainfall or unexpected local short-duration heavy rainfall resulting in inundations in the central urban area,influenced by the terrain and environmental conditions.The flash density maximums were found in eastern Changping District,central and eastern Shunyi District,and the central urban area of Beijing,suggesting that the urban heat island effect has a crucial role in the intensification of thunderstorms over Beijing.In addition,the flash rate associated with super thunderstorms can reach hundreds of flashes per minute in the central city regions.The super(5%of the total),strong(35%),and weak(60%)thunderstorms contributed about 37%,56%,and 7%to the total flashes in the BMR,respectively.Owing to the close connection between lightning activity and the thermodynamic and microphysical characteristics of the thunderstorms,the lightning flash rate can be used as an indicator of severe weather events,such as hail and short-duration heavy rainfall.Lightning data can also be assimilated into numerical weather prediction models to help improve the forecasting of severe convection and precipitation at the cloud-resolved scale,through adjusting or correcting the thermodynamic and microphysical parameters of the model.     

池养条件下军曹鱼早期发育阶段的生长和摄食

研究了军曹鱼(Rachycentron canadum)早期阶段的生长和摄食特性。结果表明:1~29日龄间,全长与日龄之间呈指数函数相关:y=3.6922e0.0995x(R=0.9913);体重与日龄间呈指数函数相关:y=0.0002e0.276x(R=0.9830);体重与全长之间为幂函数相关:y=5×10-6x2.786(R=0.9957);口径与日龄的关系为直线函数关系:y=0.1034x-0.0044(R=0.9939)。鱼苗早期阶段的生长速度存在显著性差异。军曹鱼早期鱼苗在3~6日龄时主要摄食原生动物、单轮幼虫和轮虫;7~12日龄时主要摄食桡足类无节幼体;13日龄以后主要摄食桡足类成体。仔、稚鱼阶段,军曹鱼的摄食活动呈现明显的昼夜节律,其饱满度指数均在12时前后出现最高峰,日摄食率分别为57.36%和14.78%。     

中国省域广播电视业发展水平的空间计量研究

以2008~2014年中国31个省域的统计数据为基础,采用空间计量经济学方法对中国广播电视业发展水平的空间格局及其影响因素进行测算与分析。研究发现,中国省域广播电视业发展水平最高的集聚分布于东部沿海地区,部分东部地区和中部地区发展一般,西北、西南地区发展水平较低,总体呈现从东向西递减的梯度变化,但全国整体发展水平呈现显著上升趋势。经济发展水平、消费需求、财政投入和信息技术水平与中国广播电视产业呈现正相关,而产业结构与广播电视产业呈现负相关,且各省地理空间的邻接上未表现出溢出效应。     

Improved Priority‐Flood method for depression filling by redundant calculation optimization in local micro‐relief areas

Depression filling is a critical step in distributed hydrological modeling using digital elevation models (DEMs). The traditional Priority‐Flood (PF) approach is widely used due to its relatively high efficiency when dealing with a small‐sized DEM. However, it seems inadequate and inefficient when dealing with large high‐resolution DEMs. In this work, we examined the relationship between the PF algorithm calculation process and the topographical characteristics of depressions, and found significant redundant calculations in the local micro‐relief areas in the conventional PF algorithm. As such calculations require more time when dealing with large DEMs, we thus propose a new variant of the PF algorithm, wherein redundant points and calculations are recognized and eliminated based on the local micro‐relief water‐flow characteristics of the depression‐filling process. In addition, depressions and flatlands were optimally processed by a quick queue to improve the efficiency of the process. The proposed method was applied and validated in eight case areas using the Shuttle Radar Topography Mission digital elevation model (SRTM‐DEM) with 1 arc‐second resolution. These selected areas have different data sizes. A comparative analysis among the proposed method, the Wang and Liu‐based PF, the improved Barnes‐based PF, the improved Zhou‐based PF, and the Planchon and Darboux (P&D) algorithms was conducted to evaluate the accuracy and efficiency of the proposed algorithm. The results showed that the proposed algorithm is 43.2% (maximum) faster than Wang and Liu's variant of the PF method, with an average of 31.8%. In addition, the proposed algorithm achieved similar performance to the improved Zhou‐based PF algorithm, though our algorithm has the advantage of being simpler. The optimal strategies using the proposed algorithm can be employed in various landforms with high efficiency. The proposed method can also achieve good depression filling, even with large amounts of DEM data.     

Preliminary results of 4-D water vapor tomography in the troposphere using GPS

Slant-path water vapor amounts (SWV) from a station to all the GPS (Global Positioning System) satellites in view can be estimated by using a ground-based GPS receiver. In this paper, a tomographic method was utilized to retrieve the local horizontal and vertical structure of water vapor over a local GPS receiver network using SWV amounts as observables in the tomography. The method of obtaining SWV using ground-based GPS is described first, and then the theory of tomography using GPS is presented. A water vapor tomography experiment was made using a small GPS network in the Beijing region. The tomographic results were analyzed in two ways: (1) a pure GPS method, i.e., only using GPS observables as input to the tomography; (2) combining GPS observables with vertical constraints or a priori information, which come from average radiosonde measurements over three days. It is shown that the vertical structure of water vapor is well resolved with a priori information. Comparisons of profiles between radiosondes and GPS show that the RMS error of the tomography is about 1–2mm. It is demonstrated that the tomography can monitor the evolution of tropospheric water vapor in space and time. The vertical resolution of the tomography is tested with layer thicknesses of 600 m, 800 m and 1000 m. Comparisons with radiosondes show that the result from a resolution of 800m is slightly better than results from the other two resolutions in the experiment. Water vapor amounts recreated from the tomography field agree well with precipitable water vapor (PWV) calculated using GPS delays. Hourly tomographic results are also shown using the resolution of 800 m. Water vapor characteristics under the background of heavy rainfall development are analyzed using these tomographic results. The water vapor spatio-temporal structures derived from the GPS network show a great potential in the investigation of weather disasters.     

Numerical modeling of hyperpycnal flows in an idealized river mouth

Numerical experiments in an idealized river mouth are conducted using a three-dimensional hydrodynamics model (EFDC model) to examine the impacts of suspended sediment concentration (SSC), settling velocity of sediment and tidal mixing on the formation and maintenance of estuarine hyperpycnal flows. The standard experiment presents an illustrative view of hyperpycnal flows that carry high-concentrated sediment and low-salinity water in the bottom layer (>1.0 m in thickness) along the subaqueous slope. The structure and intra-tidal variation of the simulated hyperpycnal flows are quite similar to those previously observed off the Huanghe (Yellow River) mouth. Results from the three control experiments show that SSC of river effluents is the most important parameter to the formation of hyperpycnal flows. High SSC will increase the bulk density of river effluents and thus offset the density difference between freshwater and seawater. Low SSC of river effluents will produce a surface river plume, as commonly observed in most large estuaries. Both the settling velocity of sediment particles and the tidal mixing play an important role in maintaining the hyperpycnal flows. Increasing settling velocity enhances the deposition of sediment from the hyperpycnal layer and thus accelerates the attenuation of hyperpycnal flows, whereas increasing tidal mixing destroys the stratification of water column and therefore makes the hyperpycnal flows less evident. Our results from numerical experiments are of importance to understand the initiation and maintenance of hyperpycnal flows in estuaries and provide a reference to the rapidly decaying hyperpycnal flows off the Huanghe river mouth due to climatic and anthropogenic forcing over the past several decades.