Cassini图像中受散射光影响的7颗土星近环内卫星的天体测量

卡西尼号探测器携带了光学成像科学子系统(ISS: Imaging Science Subsystem), 在2004--2017年间拍摄了一些土星内卫星的图像. 部分图像中土星内卫星非常靠近土星环, 观测对象受土星环散射光影响导致测量精度差, 甚至无法测量. 由此提出一种适用于这类图像的背景消除算法, 可对受土星光环散射光影响的土星内卫星进行测量. 归算了7颗近环内卫星(土卫十(Janus)、土卫十一(Epimetheus)、土卫十五(Atlas)、土卫十六(Prometheus)、土卫十七(Pandora)、土卫三十二(Methone)和土卫四十九(Anthe))的70张ISS图像, 并与不消除散射光的方法进行了比较. 结果显示, 该方法至少可以提高43%的精度. 和喷气推进实验室的土星卫星历表\lk SAT415相比, 测量得到的赤经和赤纬方向的残差均值分别为0.72km和2.26km, 标准差分别为10.99km和11.36km.     

半潮堤前的反射形态与时均流速场分析

采用模型试验和数值模拟研究了不同水深工况下半潮堤前的反射形态及时均流速场。基于Hilbert变换建立了叠合波的时频分离技术,同时获取了入射波和反射波的波面过程及相位关系,通过试验数据证明其适用于不同反射程度的波浪信号分析。不同水深工况下,半潮堤前形成了部分立波系统,腹点和节点分别以四分之一波长的偶数倍和奇数倍交替增加。半潮堤前底床水质点水平速度包络图与波面包络图相差四分之一周期的相位,水平速度的极大值和极小值分别出现在波面包络图的节点和腹点,意味着节点处易形成冲刷,腹点处易形成淤积。3种工况的周期平均速度场均在迎浪基床上方的堤脚处存在一个小型环流系统,可能引起局部冲刷,此处需加强防护。淹没工况下,半潮堤前的周期平均速度场形成一个大型环流系统,表层水流向堤后,中下层水流向海侧,意味着底床悬起的泥沙很可能向离岸方向流失。     

耕地复种指数遥感监测研究进展

复种指数是进行粮食估产、耕地集约利用评价、农业生态系统模拟等的关键参数,及时、准确地提取复种指数对于粮食安全、土地管理和生态环境安全具有重要意义。在传统的研究中,复种指数主要来源于地面统计数据。使用统计数据来计算复种指数虽然过程简单,但是计算结果存在信息滞后、无法体现统计单元内部的空间异质性、精度低等不足。遥感技术因具有大范围、高时效、低成本等优点而被用于耕地复种指数监测,已有学者对耕地复种指数的遥感监测开展了大量工作。本文以复种指数遥感提取的关键环节为主线,对1997—2020年国内外相关研究进行综述：首先,梳理了已有研究中的监测方法、高质量时间序列遥感数据获取方法及提取结果精度验证方法,并对不同方法的优缺点进行了总结;其次,对已有研究中存在的不足进行了探讨,并提出未来研究的侧重点：① 开展已有监测方法的对比和分析;② 加强地形复杂地区、小农尺度的监测力度;③ 提高遥感数据时空分辨率及处理效率;④ 对提取结果进行多尺度验证。     

气候变化和人类活动影响下澧水流域径流及其不同组分的变化简

目前径流变化相关研究较少涉及径流的不同组分。利用湖南省澧水流域4个水文站点长序列观测资料,不仅分析了2007-2011年相对于1985年以前径流总量及其历时曲线的变化,也分析了地表径流和基流及其历时曲线的变化。与1985年以前比,流域年降雨量保持不变,最显著的变化为森林覆盖率的增加和大量水库的修建。这些人类活动没有造成年径流总量、年基流量和年地表径流量的显著变化,但在日时间尺度上对径流过程产生了重要影响。地表径流和地下径流对人类活动存在差异性响应,2007年以后地表径流在洪峰期流量变小而其他时段变大,而地下径流汇水受人类活动影响较小,基流流量除枯水期外与1985年以前基本一致。本文所揭示的规律可能在中国南方具有一定的代表性。     

Combined effects of light intensity and NH^＋4-enrichment on growth,pigmentation, and photosynthetic performance of Ulva prolifera （Chlorophyta）

The aim of this study was to investigate the effects of light intensity and enhanced nitrogen supply on the growth and photosynthesis of the green-tide macroalga, Ulva prolifera. Thalli of U. prolifera were grown in natural or NH 4 +-enriched seawater under two different light intensities for 7 days, and then the growth rate, pigmentation, and photosynthetic performance of the thalli were evaluated. The results show that the relative growth rate(RGR) was markedly higher under the high light level than under the low light level. Enrichment with NH 4 + enhanced the RGR under high light intensity, but did not affect RGR under low light intensity. In low light conditions, NH 4 +-enrichment resulted in a marked decrease in the maximal photosynthetic rate( P m) and the maximum carbon fixation rate( V max), but it did not affect the half saturation constant for carbon( K 0.5) or the ratio of V max to K 0.5, which reflects the carbon acquisition efficiency. In high light conditions, P m, K 0.5, and the dark respiration rate( R d) increased under NH 4 + enrichment, but V max and the V max / K 0.5 ratio decreased. Regardless of the light intensity, NH 4 +-enrichment did not affect the apparent photosynthetic efficiency( α), which refl ects the ability of the alga to use light energy at low light levels. Under both low and high light intensities, the chlorophyll a(Chl a), chlorophyll b(Chl b), and carotenoids(Car) contents in thalli were higher in NH 4 +-enriched than in natural seawater, except that there was a decrease in the Chl b content of thalli in NH 4 +-enriched seawater under low light intensity. Therefore, NH 4 + enrichment improved the growth and photosynthetic performance of U. prolifera under high light intensity, but not under low light intensity. We discuss the possible mechanisms underlying these physiological responses.     

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一次台风暴雨过程的水汽特征分析

对2014年7月18-19日桂东南受1409号台风＂威马逊＂影响,出现一次降雨强度大、影响范围广、降雨时间长的暴雨过程进行水汽特征分析,得出和验证了有利于出现强降水的大尺度环流背景下,充分的水汽供应是暴雨形成的基本条件之一,水汽通量场反映了水汽源源不断向桂东南输送,水汽通量散度进一步反映有大量的水汽往桂东南输送。     

Experimental investigation on shear strength and permeability of a deeply dewatered sewage sludge for use in landfill covers

This paper presents an experimental study on a deeply dewatered sewage sludge produced by using a new technique of membrane filter press. The experiments involve measurements of sludge composition, basic physical properties, shear strength, water permeability, and leaching toxicity. The measurements of shear strength and permeability were also performed on the sludge specimens soaked in a low acid leachate or distilled water for 1 and 2 months. This is to investigate the influence of chemical change in pore fluid as a result of rainfall infiltration or leachate seepage at landfills. Comparison tests were also carried out on silty clay that is commonly used for landfill cover material. The experimental results show that the deeply dewatered sludge contains 66 % organic content and 85 % water content (dry mass basis). The undrained shear strength of the sludge is >25 kPa even after 2-month soaking in the leachate and distilled water, meeting the requirement of the Chinese standard [CJ/T249-2007, Disposal of sludge from municipal wastewater treatment plant: sludge quality for co-landfilling. Ministry of Building and Construction, P.R. China (in Chinese), 2007]. The measured cohesion and friction angle for the sludge are >20 kPa and 22.3°, respectively. The soaking of sludge specimens in either leachate or distilled water resulted in an increase in frictional angle by several degrees. The water permeability for the sludge ranges from 0.68 × 10^?8 to 1.3 × 10^?8 cm/s, and permeability after 2-month soaking is less than the minimum requirement for the barrier layer of landfill covers (i.e., 1.0 × 10^?7 cm/s). The concentrations of heavy metals leaching from the dewatered sludge are lower than the limit values of leaching toxicity for the wastewater discharge standard of China. The experimental results indicate that deeply dewatered sludge can be used as an alternative material for the barrier layer of landfill covers.     

Non-Darcian flow toward a larger-diameter partially penetrating well in a confined aquifer

In this study, non-Darcian flow to a larger-diameter partially penetrating well in a confined aquifer was investigated. The flow in the horizontal direction was assumed to be non-Darcian and described by the Izbash equation, and the flow in the vertical direction was assumed to be Darcian. A linearization procedure was used to approximate the nonlinear governing equation. The Laplace transform associated with the finite cosine Fourier transform was used to solve such non-Darcian flow model. Both the drawdowns inside the well and in the aquifer were analyzed under different conditions. The results indicated that the drawdowns inside the well were generally the same at early times under different conditions, and the features of the drawdowns inside the well at late times were similar to those of the drawdowns in the aquifer. The drawdown in the aquifer for the non-Darcian flow case was larger at early times and smaller at late times than their counterparts of Darcian flow case. The drawdowns for a partially penetrating well were the same as those of a fully penetrating well at early times, and were larger than those for a fully penetrating well at late times. A longer well screen resulted in a smaller drawdown in the aquifer at late times. A larger power index n in the Izbash equation resulted in a larger drawdown in the aquifer at early times and led to a smaller drawdown in the aquifer at late times. A larger well radius led to a smaller drawdown at early times, but it had little impact on the drawdown at late times. The wellbore storage effect disappears earlier when n is larger.     

国际经济地理学研究的知识图谱分析

基于Web of Science核心数据库收录的1982－2020年7 260篇期刊论文及其参考文献,借助CiteSpace绘制国际经济地理学的知识图谱,梳理该领域的知识基础、研究热点和研究前沿。结果发现：1）知识基础的演进轨迹遵循了新区域主义——制度、社会、文化、演化转向的时序变化,21世纪以来,关系、演化经济地理学下的经典文献成为主要的知识来源。2）研究热点突出,创新和增长始终是研究核心,近年来韧性、全球生产网络、金融地理、全球城市、不平等、企业家精神等成为新的研究热点。3）研究前沿具有较强的问题导向,主要基于西方发达国家的产业发展实践。4）研究空间呈现英美主导的两级格局,大部分国家仍处于边缘地带。5）国际经济地理学呈现明显的数字转向、可持续转型趋势,新冠疫情对学科走向也有一定影响。借鉴国际研究经验,中国经济地理学应加强理论创新并提出具有中国实践特色的理论体系,同时推动多学科之间的交叉融合并加强从社会学视角解读社会经济活动的地理学意义。