Rock slope stability evaluation in static and seismic conditions for left bank of Jinsha River Bridge along Lijiang-Xamgyi'nyilha railway, China

Jinsha River Bridge is located along the Lijiang-Xamgyi＇nyilha railway on the southeastern Tibet plateau; it is an area with a high prevalence of earthquakes. The bridge abutments were designed to be constructed in river bank slopes, where rocks are controlled by two sets of joint planes that significantly influence the stability of the left bank slope. According to the engineering-geological conditions and the characteristics of discontinuities, strength properties of the rock mass were obtained based on Barton model and direct shear test. Numerical analyses were performed using FLAC3D software to examine the slope＇s response to seismic loading. Then in order to evaluate the damage trends of the rock mass under the different loading conditions, a calculation model based on the geological parameters and slope stability was simulated and analyzed using the discrete element numerical simulation program UDEC （Universal Dis- tinct Element Code）, and the effect of degradation of discontinuities on the slope stability was investigated. The results show that the destruction of rock mass under the gravity, bridge foundation, and seismic load are mainly concentrated within 30 m depth of slope, and the slope under loading may slide along joint planes. In addition, the dynamic analysis by amplification of the input loading indicates that instability occurs to the bank slope at a height of about 200 m, and rock blocks will fail under seismic load. Therefore, to prevent the slope from deformation under the engineering loading and strong earthquakes, the bridge foundation should be strengthened.

中国中亚热带常绿阔叶林群落木本植物多样性比较

常绿阔叶林是我国亚热带的地带性植被类型,也是我国最重要的植被类型之一。常绿阔叶林植被型下各种群落类型的物种组成、结构、动态等特征已有大量研究,本研究基于浙江的天童和古田山、湖南的八大公山以及云南的珠江源、雕翎山和鸡足山6个大型常绿阔叶林动态监测样地的调查数据,对其木本植物的物种组成、区系成分、生长型类型百分比、种–面积关系进行了综合比较,以期进一步了解中国中亚热带常绿阔叶林在东、中、西部地区的物种多样性差异。结果显示:(1)中国中亚热带中部的八大公山样地物种的科、属、种丰富度最高,其次为东部的天童和古田山样地,而西部的珠江源、雕翎山和鸡足山样地的丰富度最低,相同植被类型样地的物种组成相似性最高,东、中、西部的常绿阔叶林植被的物种组成存在显著的差异;(2)东部样地木本植物的科、属均以热带区系为主,尤其泛热带分布的科、属最多,而中、西部样地虽然以热带科为主,但以温带属居多,北温带分布属最多;(3)东、中部3个样地木本植物以乔木成分为主,天童、古田山和八大公山样地乔木种比例分别是57.4%、51.6%和55.9%,西部样地灌木(珠江源、雕翎山和鸡足山样地分别是56.9%、54.2%、48.5%)成分均高于乔木(43.1%、41.7%、42.7%),中部样地木本植物落叶种(59.2%)占比远高于常绿种(40.8%),东、西部样地则是常绿种比例高于落叶种,天童、古田山、珠江源、雕翎山、鸡足山样地常绿种比例分别是51.3%、59.1%、62.7%、69.8%、58.3%;(4)八大公山和雕翎山样地的常绿种(分别有97种和67种)和落叶种(141种,29种)在数量上差距最大,雕翎山和珠江源样地的常绿种(69.8%,62.7%)和落叶种(30.2%,37.3%)在比例上差距最大。上述研究结果反映了中国中亚热带典型常绿阔叶林、山地常绿落叶阔叶混交林、半湿润常绿阔叶林的群落物种组成、物种多样性和群落结构的差异,为指示中亚热带常绿阔叶林植被从东到西的物种周转特征和植被变化规律提供了科学依据。

中国亚热带4个森林动态监测样地无人机可见光遥感影像数据集

常绿阔叶林是我国亚热带地区的地带性植被类型。由于亚热带森林植物群落垂直结构复杂、林冠郁闭度高,对常绿阔叶林冠层的研究尚缺乏高质量的监测数据。本数据集包含浙江天童山、浙江百山祖、广东车八岭、广东鼎湖山4个大于20 ha的森林动态监测样地2014年8月或2016年9月采集的无人机可见光遥感影像。本数据集是通过将无人机影像、地面控制点和地面调查数据相结合而获得的。每个样地的数据集包括4个文件:~5 cm空间分辨率的正射影像图和数字表面模型、1 m空间分辨率的森林冠层高度数据和正射影像质量报告。本数据集可为常绿阔叶林的林冠生态学、生物多样性、生态系统功能等研究提供数据支撑。

中国植被图(1:1000000)现实性更新

植被图是生物多样性保护、生态学研究、植被管理与恢复和国家决策的重要辅助信息源.我国上一代植被图,即中国植被图(1:1000000),是由逾250位生态学家组成的团队自20世纪80年代花了20多年完成的.但是,随着过去30多年间的快速发展,我国的植被分布与植被类型发生了剧烈的变化,对上一代植被图进行现实性更新已成为迫在眉睫的需求.本文使用了一种"众源采集-变化检测-遥感分类-专家审核"的策略尝试对中国植被图(1:1000000)进行现实性更新.本研究共收集了203024条地面调查数据,并有50余位植被生态学家参与到专家审核的工作中.更新后的植被图包含12个植被型组、55个植被(亚)型和866个(亚)群系类别,精度在植被型组、植被(亚)型和(亚)群系水平上分别为64.8%,61%和40%.与上一代植被图相比,过去30多年间的人类活动和气候变化导致了我国约330万km^2植被类型发生了变化.更新后的植被图将会有助于理解和管理我国的陆地生态系统.

Reduced Graphene Oxide/Carbon Nanofiber Based Composite Fabrics with Spider Web‑like Structure for Microwave Absorbing Applications

Composite fabrics with excellent microwave absorbing performance are highly desired.Herein,reduced graphene oxide/carbon nanofiber(rGO/CNF)based composite fabrics with spider web-like structure were successfully synthesized by electrostatic spinning technique.The spider web-like structure in the composite fabrics provides a connected network for efficient conductive loss of microwave energies.Magnetic loss benefits from the deposited nickel nanoparticles(Ni NPs)anchored in the carbon nanofibers.Meanwhile,the deposited thin polypyrrole(PPy)layers on the conductive network acts as a protective layer for Ni NPs as well as provides abundant interfaces for dissipating electromagnetic energies,which endow the composite fabrics stable microwave absorbing performance.Due to the synergistic effect of microwave absorb-ing mechanism,the maximum reflection loss(RL_(max))of the composite fabric at 6.72 GHz is-46.15 dB,and the effective absorption bandwidth(EAB)is as wide as 8.63 GHz(from 9.37 to 18 GHz).What's more,favorable mechanical and heat insulation properties of the composite fabrics reveal its multifunctional advantages.This rGO/CNF based composite fabric demonstrates a new direction for multifunctional and flexible microwave absorbing materials(MAMs).

Relative contributions of biotic and abiotic factors to the spatial variation of litter stock in a mature subtropical forest

Aims Dead plant material(i.e.litter)is the major source of soil organic matter and thus plays a fundamental role in regulating soil carbon cycling in global forest ecosystems.The storage of litter is jointly determined by its production from plants and decomposition in a given environment.However,only few studies have explored the relative importance of en-vironmental(i.e.abiotic)and plant(i.e.biotic)factors in driving the spa-tial variation of litter mass.The objective of this study is to quantify the relative contributions of biotic and abiotic factors in affecting the spatial variation of aboveground litter stock in a mature subtropical forest.Methods The aboveground litter mass was sampled in 187 grids of a 20-hm forest dynamics plot in a subtropical broad-leave forest in eastern China.The contributions of environmental variables,topographical and species variables on litter stocks were quantified by the boosted regression tree analysis.Important Findings The mean aboveground litter stock was 367.5 g m^(−2) in the Tiantong dynamics forest plot across all the 187 grids.The litter stock ranged from 109.2 to 831.3 g m^(−2) and showed a large spatial variation with the coefficient of variance as 40.8%.The boosted regression tree analysis showed that slope elevation and soil moisture were the most influential variables on the spatial variation of litter stock.The relatively influence of abiotic factors(environmental and topographical factors)was 71.4%,which is larger than biotic factors(28.6%).Overall,these findings sug-gest that abiotic factors play a more important role than plants in driving the spatial variation of aboveground litter stock in the subtropical forest.Given that the global carbon-cycle models have been aiming to refine from the hundred kilometers to sub-kilometer scale,this study highlights the urgency of a better understanding of the spatial variation of litter stock on the fine scale.

Evaluation of potential failure of rock slope at the left abutment of Jinsha River Bridge by model test and numerical method

Jinsha River Bridge is located on Tiger Leaping Gorge town,China.The left bank slope composes of moderately thick layer of slate overlain by schistose basalt,and where rocks are controlled by two sets of joint planes.To evaluate the stability of the rock slope under bridge foundation,model test and calculation model based on the geological parameters and the slope stability was simulated and analyzed using Universal Distinct Element Code(UDEC)and Finite Element Mehod(FEM).According to model test,failure mainly initiated at the toe with shear movement along the joint planes,eventually resulting in the sliding along the slope surface and formation of tension crack at the crest of the model.This result coincide with the UDEC model,which shows that slope surface will produce loosening damage and slipping expected along the joint planes under different loading conditions.Moreover,the result of FEM analysis indicates that the rock mass under the main pier has potential shear failure region.So,the bridge foundation should be strengthened to prevent the slope failure under external forces.

Recent progress in colloidal quantum dot photovoltaics

The development of photovoltaic devices, solar cells, plays a key role in renewable energy sources. Semiconductor colloidal quantum dots （CQDs）, including lead chacolgenide CQDs that have tunable electronic bandgaps from infrared to visible, serve as good candidates to harvest the broad spectrum of sunlight. CQDs can be processed from solution, allowing them to be deposited in a roll-to-roll printing process compatible with low-cost fabrication of large area solar panels. Enhanced multiexciton generation process in CQD, compared with bulk semiconductors, enables the potential of exceeding Shockley-Queisser limit in CQD photovoltaics. For these advantages, CQDs photovoltaics attract great attention in academics, and extensive research works accelerate the development of CQD based solar cells. The record efficiency of CQD solar cells increased from 5.1% in 2011 to 9.9% in 2015. The improvement relies on optimized material processing, device architecture and various efforts to improve carrier collection efficiency. In this review, we have summarized the progress of CQD photovoltaics in year 2012 and after. Here we focused on the theoretical and experimental works that improve the understanding of the device physics in CQD solar cells, which may guide the development of CQD photovoltaics within the research community.