四川省植被覆盖时空演变及未来变化趋势分析

四川省地处长江上游,是长江流域重要的生态屏障;解析该区域植被覆盖的时空演变特征,对长江上游的生态环境修护与治理具有重要意义。基于长时间序列的MODIS NDVI数据,解析2000~2016年间四川省植被的空间分布格局与时间变化特征;采用趋势分析法和Hurst指数,预测未来植被的变化趋势及持续性。结果表明:(1)四川省NDVI多年平均值为0.50,植被覆盖整体上呈现川东高于川西的空间分布特征;(2)2000~2016年间,四川省的NDVI值在0.48至0.53之间波动,整体呈上升趋势,增长率为0.002 5/a;(3)植被覆盖度在未来变化将呈现改善大于退化的趋势;植被持续性改善的面积大于持续性退化的面积。     

External validity and factor structure of individual and group workload ratings

Work teams experience workload from the group dynamics in addition to the usual sources of individual workload. This study had three objectives: to assess the responsiveness of new rating scales for group workload (GWL), investigate their component structure, and determine if changes in workload occur as the team matures. Participants (360 individuals, 44 groups) engaged in an emergency response (ER) simulation in the form of a board game; team size, game difficulty (one versus two opponents), and time constraints were varied. ER teams rated workload after each of two sessions using the NASA Task Load Index (TLX) and GWL. GWL was most responsive to larger task demands and reflected changes in coordination demand over time. Components reflected mixtures of TLX and GWL scales and suggested that self-organising processes were operating.     

不同苯乙烯工艺技术经济分析及建议

通过对国内外苯乙烯市场供需趋势的梳理,针对4种苯乙烯主要生产工艺,重点从原料可获性、产品质量、能耗物耗以及成本竞争力等方面对不同工艺主要技术经济指标进行了对比分析,并提出了行业可持续发展的有关建议。     

基于街景地图数据的北京市东城区 街道绿色空间正义评估研究

绿色空间正义是城市空间正义的典型代表，意为在人群中公平分配维护绿色空间的责任和享有绿色空间的权益。根据其定义，以北京市东城区为例，从责任和权益2个角度着眼，一方面基于百度街景地图数据提炼街道空间绿视率的空间分布特点，表征街道绿色空间的客观可感知水平；另一方面将街道绿视率和实时人口热力叠加，探讨街道绿色空间的实际被感知程度，从而完成对北京市东城区街道绿色空间维护和享有情况的评估。发现邻近使用者维护街道绿色空间的责任对绿化客观可感知水平的重要性，以及合理的道路断面设计对同时提升街道空间活力和绿视率即绿化实际被感知程度的有效性。由此总结出2点街道绿色空间规划设计建议，即明晰权责边界并保证公共权益优先级，以及加强落地性设计导则中对绿色空间正义问题的关注，并对未来研究提出展望。     

氮气对复采工作面遗煤复燃的防治效能

为探究不同体积分数N₂对复采工作面遗煤复燃过程的防治效果，采用自主研发的程序升温试验装置，对煤样分别通入体积分数为10%、20%、30%和40%的N₂，以氧化反应过程中耗氧速率V_O2、一氧化碳产生率V_CO和表观活化能E的变化情况来反映煤自燃的发展程度。试验表明:不同体积分数的N₂对煤氧化升温过程均具有抑制作用，相比于煤在纯空气条件下的氧化自燃，通入的N₂体积分数越大，煤初次自燃和二次氧化升温过程的V_O2和V_CO更低、E更高，说明通入的氮气体积分数越大，对煤氧化升温过程的抑制效率越好。其中，在煤初次自燃阶段，当N2体积分数C_N2≥20%时抑制效果更佳；在煤二次氧化复燃阶段，当N₂体积分数C_N2≥40%时抑制效果更佳。     

煤与高岭石表面性质对凝聚过程的影响机制

煤泥水中含大量高岭石等黏土矿物，为其絮凝沉降带来较大的困难。为明确矿物性质对凝聚过程的影响机制，在应用扩展的DLVO理论计算煤和高岭石颗粒间作用力的基础上，采用聚焦光束反射测量仪监测了CaCl2用量为4.50 mmol/L时20 g/L的煤和高岭石的悬浮液在60, 100和150 r/min的搅拌转速下的凝聚过程。结果表明，颗粒间的静电作用力在颗粒表面间距2?200 nm范围内起主导作用，高岭石的电负性较大，在凝聚过程中更难发生靠近和碰撞；较高的转速可为颗粒提供较大的动量，有利于提高碰撞频率，缩短完成凝聚所需时间，实验条件下，煤和高岭石的凝聚时间分别由74和123 s缩短至47和89 s。疏水性作用力在颗粒表面间距小于2 nm的范围内起主导作用，决定了颗粒的黏附效率；煤因强疏水性，在碰撞后更易黏附，且能抵抗更高的流体剪切作用，可由19.32 μm凝聚形成100 μm的大凝聚体，而高岭石则因其亲水性难以得到较大粒度的凝聚体，均小于30 μm。     

Analysis of acoustic Doppler current profiler mean velocity measurements in shallow flows

Acoustic Doppler current profilers (ADCPs) are commonly used instruments for measurement of natural streamflow and flow in manmade channels. Velocities measured in a profile by the instrument are used to estimate the discharge in a channel. A Teledyne RD Instruments StreamPro ADCP was used to measure the mean velocity simultaneously with a laser Doppler anemometer (LDA) in a laboratory flume. An average of 3.9% under-prediction of the mean velocity measured by the ADCP occurred when compared to the measurements of the LDA. Moreover, this study shows that the sampling duration of the measurements significantly impacts the mean point velocities measured by up to 50%.     

In-situ deflectometic measurement of transparent optics in precision robotic polishing

In the ultra-precision manufacturing of large optics, industrial robots have the potential to become an intelligent and economical choice of surface polishing. However, the transport of the workpieces between the polishing platform and the measurement instrument seriously limits the manufacturing efficiency. Therefore, an in-situ measurement system based on the monoscopic deflectometry is developed to determine the form quality of the optical lenses during rough polishing. Stray light reflected from the lower surface of transparent lenses may degrade the measuring quality, thus an effective absolute phase retrieval algorithm is developed to decouple the superposed fringes associated with the upper and lower surfaces. Then, the form of the upper surface under polishing can be reconstructed to guide the subsequent polishing. Experimental results demonstrate that the accuracy of the method is comparable to that of the coordinate measuring machine, consequently the manufacturing efficiency and reliability of large optical workpieces can be greatly improved.     

并联机器人末端轨迹测量系统设计

针对机器人末端轨迹检测问题，提出了一种基于拉线传感器的并联机器人末端轨迹追踪系统。该方案采用拉线式位移传感器与角度传感器作为数据采集端，经数据采集卡传递给计算机进行数据处理，实现末端轨迹测量。最后，设计试验样机并基于 Ｃ＃ ＷｉｎＦｏｒｍ 模块编写数据处理模块，从而实现仿真结果与实际相互印证的目标。     

Investigation of the residual stress in UO2-Mo composites via a neutron diffraction method

UO₂-Mo composites with a core-shell structure have been considered candidates for the thermal conductivity (TC)-enhanced UO₂ pellets and have demonstrated commercial potential for use in novel high-level safety reactors. Nevertheless, UO₂-Mo composites tend to form micro-cracks that are caused by the presence of residual stress (RS) during manufacturing. In this work, neutron diffraction measurements were employed to analyse the RS in UO₂-Mo core-shell structured composites fabricated by spark plasma sintering (SPS) for the first time. It was found that in the UO₂-Mo composites, the RS state present in the UO₂ matrix was tensile in nature. The RS in the UO₂ matrix increased with increaseing Mo content. There was a maximum value of 148 ± 15 MPa in the UO₂-10 vol% Mo composite. The micro-cracks produced in the high-Mo content composites were explained by the results of the neutron diffraction measurements. These results could provide significant guidance for the manufacturing and improvement of the operational performance of UO₂-Mo composites as next-generation fuels.