石墨烯薄膜原子氧剥蚀行为及电阻特性

目的研究石墨烯薄膜在原子氧空间环境的适应性,为其在航天器上应用提供参考。方法采用刮涂法制备石墨烯薄膜,将石墨烯薄膜材料及石墨烯电阻传感器置于微波源原子氧设备内开展原子氧试验,原子氧剂量分别为3.0×10^20 atoms/cm2和7.5×10^20 atoms/cm^2,研究薄膜表面形貌、结构、成分及电阻性能的变化。结果采用刮涂法可制备氧含量较低的石墨烯薄膜,原子氧剂量为7.5×10^20 atoms/cm^2情况下,石墨烯薄膜的厚度损失为5.3μm,原子氧反应率为7.14×10^-25 atoms/cm^3。原子氧作用后,石墨烯薄膜中碳原子无序程度增大,C—O、—COOH官能团含量降低,C=O官能团含量增加。石墨烯电阻传感器的R0/R比值随原子氧剂量增加线性降低,0.8μm厚度薄膜可探测最大原子氧剂量为5×10^19 atoms/cm^2,增加薄膜厚度有望提高传感器的使用寿命。结论得到了石墨烯薄膜厚度损失、原子氧反应率、微观结构及电阻特性的变化规律,可为石墨烯薄膜的空间应用提供技术支撑。     

常州市裸露地面风蚀扬尘排放清单及分布特征研究

以2014年为基准年,以常州市行政边界为研究区域,利用卫星遥感解译的土地利用类型和裸土面积信息,并通过国土、气象等部门提供的土壤类型、气象因子等相关资料获取本地化因子和参数,估算常州市行政区域内裸露地面土壤扬尘中颗粒物的年排放量。结果表明:常州市裸露地面主要分布在金坛市、溧阳市和武进区,市中心区域最少,裸露土地利用类型主要为农田、滩涂、裸露山体、荒地及未硬化或未绿化的空地等;2014年常州市行政区域内裸露地面风蚀扬尘中TSP、PM 10、PM 2.5的年排放量分别为62.66 t、5.63 t、0.24 t,其中,金坛市土壤起尘量最大,其次为武进区,再次为新北区、溧阳市,市中心区域土壤扬尘最少。     

Bison and cattle grazing management,bare ground coverage,and links to suspended sediment concentrations in grassland streams

This study quantified the impact of bison and cattle grazing management practices on bare ground coverage at the watershed, riparian, and forested riparian scales within the Flint Hills ecoregion in Kansas. We tested for correlations between bare ground coverage and fluvial suspended sediment concentrations during base‐flow and storm‐flow events. We used remotely sensed imagery combined with field surveys to classify ground cover and quantify the presence of bare ground. Base‐flow water samples were collected bi‐monthly during rain‐free periods and 24 h following precipitation events. Storm‐flow water samples were collected on the rising limb of the hydrograph, using single‐stage automatic samplers. Ungrazed treatments contained the lowest coverage of bare ground at the watershed, riparian, and forested riparian scales. Bison treatments contained the highest coverage of bare ground at the watershed scale, while high‐density cattle treatments contained the highest coverage of bare ground at the riparian and forested riparian scales. In bison and cattle‐grazed treatments, a majority of bare ground was located near fence lines, watershed boundaries, and third‐ and fourth‐order stream segments. Inorganic sediment concentrations at base flow were best predicted by riparian bare ground coverage, while storm‐flow sediment concentrations were best predicted by watershed scale bare ground coverage.     

Soil erosion vulnerability under scenarios of climate land-use changes after the development of a large reservoir in a semi-arid area

Climate and land-use/cover changes (LUCC) influence soil erosion vulnerability in the semi-arid region of Alqueva, threatening the reservoir storage capacity and sustainability of the landscape. Considering the effect of these changes in the future, the purpose of this study was to investigate soil erosion scenarios using the Revised Universal Soil Loss Equation (RUSLE) model. A multi-agent system combining Markov cellular automata with multi-criteria evaluation was used to investigate LUCC scenarios according to delineated regional strategies. Forecasting scenarios indicated that the intensive agricultural area as well as the sparse and xerophytic vegetation and rainfall-runoff erosivity would increase, consequently causing the soil erosion to rise from 1.78 Mg ha^?1 to 3.65 Mg ha^?1 by 2100. A backcasting scenario was investigated by considering the application of soil conservation practices that would decrease the soil erosion considerably to an average of 2.27 Mg ha^?1. A decision support system can assist stakeholders in defining restrictive practices and developing conservation plans, contributing to control the reservoir's siltation.     

Carbon Sequestration Function of Check-Dams: A Case Study of the Loess Plateau in China

Check-dams are the most common structures for controlling soil erosion in the Loess Plateau. However, the effect of check-dams on carbon sequestration, along with sediment transport and deposition, has not been assessed over large areas. In this study, we evaluated the carbon sequestration function of check-dams in the Loess Plateau. The results indicate that there were approximately 11 000 check-dams distributed in the Loess Plateau, with an estimate of the amount of sediment of 21 × 10⁹ m³ and a soil organic carbon storage amount of 0.945 Pg. Our study reveals that check-dams in the Loess Plateau not only conserve soil and water but also sequester carbon.     

Detention Outlet Retrofit Improves the Functionality of Existing Detention Basins by Reducing Erosive Flows in Receiving Channels

By discharging excess stormwater at rates that more frequently exceed the critical flow for stream erosion, conventional detention basins often contribute to increased channel instability in urban and suburban systems that can be detrimental to aquatic habitat and water quality, as well as adjacent property and infrastructure. However, these ubiquitous assets, valued at approximately $600,000 per km² in a representative suburban watershed, are ideal candidates to aid in reversing such cycles of channel degradation because improving their functionality would not necessarily require property acquisition or heavy construction. The objective of this research was to develop a simple, cost‐effective device that could be installed in detention basin outlets to reduce the erosive power of the relatively frequent storm events (~ < two‐year recurrence) and provide a passive bypass to maintain flood control performance during infrequent storms (such as the 100‐year recurrence). Results from a pilot installation show that the Detain H₂O device reduced the cumulative sediment transport capacity of the preretrofit condition by greater than 40%, and contributed to reduced flashiness and prolonged baseflows in receiving streams. When scaling the strategy across a watershed, these results suggest that potential gains in water quality and stream channel stability could be achieved at costs that are orders of magnitude less than comparable benefits from newly constructed stormwater control measures.     

模拟降雨径流作用下红壤坡面侵蚀水动力学机制

土壤侵蚀过程受控于侵蚀外营力和土壤抗侵蚀性能,深入理解坡面流水动力学特性及其侵蚀动力是研究土壤侵蚀动力学机制的基础。利用可变坡土槽,通过不同雨强(60、90和120 mm/h)和径流冲刷(10、15和20 L/min)组合模拟试验,研究了第四纪黏土红壤坡面水流的水动力学特征参数及其与土壤侵蚀量间的关系。结果显示:降雨和径流冲刷影响了坡面产流产沙过程和坡面流水力学特性,其中平均流速v、平均水深h、雷诺数Re和水流功率ω均随降雨强度和上方来水流量的增加而增大,相对水深曼宁糙率n/h则减小,其水力学他参数(弗如德数Fr、阻力系数f和水流剪切力τ)变化规律不明显。坡面水流平均速度取值范围为0.21~0.45 m/s,平均水深取值范围为5.6~9.4 mm,在试验条件下红壤坡面侵蚀水流流态大部分均处于"紊流-急流区"。不论从径流角度看或是从泥沙角度分析,由相对水深和曼宁糙率系数两种水动力因子共同组成的复合水动力特征参数-相对水深曼宁糙率,是表征不同上方来水流量和降雨强度条件下第四纪粘土红壤坡面侵蚀特征的水动力参数。     

尾矿库洪水漫顶溃坝演化规律试验研究

为分析尾矿库洪水漫顶溃坝的演化规律,采用物理模型试验方法建立尾矿库漫顶溃坝演化模型。在自主研制的尾矿库溃坝模拟试验平台上,以国内某尾矿库为研究对象,基于非恒定水流泥沙非平衡非饱和冲刷机理,根据模型相似理论和溃决侵蚀模型原理,模拟尾矿库洪水漫顶溃坝过程,建立尾矿库漫顶溃坝演化模型。试验结果表明,尾矿库洪水漫顶溃坝位移与坝体饱和程度有关,坝体浸润线越高,尾矿库溃坝时滑动位移越大,溃口破坏程度取决于溢流对坝体的冲刷侵蚀作用;在该试验条件下,获得尾矿库洪水漫顶溃坝过程中坝体位移、浸润线高度、溃口最大流速和溃口的演化规律。降低坝体浸润线高度、增大安全干滩长度、铺设坝面引流明渠等措施有助于减少尾矿库洪水漫顶溃坝的灾害破坏。     

ABC算法优化SVR的磨损故障预测模型

目的为了提高故障预测的精度,针对支持向量回归SVR(Support vector machine for regression,SVR)参数选择困难的问题,提出一种采用人工蜂群(artificial bee colony,ABC)算法优化支持向量回归(SVR)的故障预测模型(ABC-SVR)。方法该模型先对样本数据进行重构,然后将故障预测误差(适应度)作为优化目标,通过ABC算法寻优找到最优的SVR参数,建立故障预测模型。最后通过实例仿真验证模型的优越性。结果采用ABC算法优化的SVR故障预测模型进行时间序列预测,能够较好地跟踪发动机滑油金属元素浓度的变化过程,并且能够提前2个取样时间预测异常情况的出现。结论 ABC-SVR模型有效解决了SVR参数选择难题,能够更加准确地表现故障变化规律,提高了故障预测精度。     

三种流速下高强钢与微弧氧化钛电偶腐蚀研究

目的研究三种流速下微弧氧化钛和高强钢的电偶腐蚀行为。方法在面积比为1:1情况下进行1,3,7 m/s流速下的电化学测试和电偶腐蚀试验研究。结果随着流速的增大,偶合电流、总腐蚀速率和电偶腐蚀速率增大。当流速为7 m/s时,高强钢总腐蚀速率和电偶腐蚀速率分别达到8.64 mm/a和0.39 mm/a,与静态相比分别增大146倍和15.6倍,与1 m/s流速下相比分别增大8.6倍和5倍。结论在面积比为1:1时,冲刷腐蚀速率远大于电偶腐蚀速率。