场次暴雨条件下濂水流域水沙关系探究

为探究场次暴雨条件下流域的水沙关系,该研究以赣南濂水流域为对象,基于1965—2020年的水文气象数据和土地利用数据,运用聚类分析、判别分析和Spearman相关分析等,在场次暴雨条件下,分析不同洪水类型、不同时段下的水沙特征及水沙关系,并对水沙滞回关系进行探究。结果表明：流域120场暴雨洪水划分为3种类型,发生频率由高到低依次为：Ⅲ型（短历时、小径流、低洪峰）、Ⅰ型（长历时、中径流、中洪峰）、Ⅱ型（中历时、大径流、高洪峰）。整个研究期划分的5个时段中,1996-2005年、2006-2020年的输沙特征值增幅较大,且单位径流的输沙能力大幅上升。不同洪水类型下的各水沙环路曲线比例差异较大;在不同时段下,逆时针型、“8”字型曲线分别在1996-2005年、2006-2020年的比例最高分别为4.30%、55.6%,这与流域内果园大面积开发导致的沙源位置及数量的改变有着密切关系。研究成果可为流域的水沙管理及调控提供科学依据。     

Validation of water sorption‐based clay prediction models for calcareous soils

Soil particle size distribution (PSD), particularly the active clay fraction, mediates soil engineering, agronomic and environmental functions. The tedious and costly nature of traditional methods of determining PSD prompted the development of water sorption‐based models for determining the clay fraction. The applicability of such models to semi‐arid soils with significant amounts of calcium carbonate and/or gypsum is unknown. The objective of this study was to validate three water sorption‐based clay prediction models for 30 calcareous soils from Iran and identify the effect of CaCO₃ on prediction accuracy. The soils had clay content ranging from 9 to 61% and CaCO₃ from 24 to 97%. The three water sorption models considered showed a reasonably fair prediction of the clay content from water sorption at 28% relative humidity (RMSE and ME values ranging from 10.6 to 12.1 and −8.1 to −4.2, respectively). The model that considers hysteresis had better prediction accuracy than the other two that do not. Moreover, the prediction errors of all three models arose from under‐prediction of the clay content. The amount of hygroscopic water scaled by clay content decreased with increasing CaCO₃ content. The low organic carbon content of the soils and the low fraction of low‐activity clay minerals like kaolinite suggested that the clay content under‐predictions were due to large CaCO₃ contents. Thus, for such water‐sorption based models to work accurately for calcareous soils, a correction factor that considers the reduction of water content due to large CaCO₃ content should be included.     

不同添加剂对土壤中乙草胺吸附／解吸的影响

采用批处理恒温振荡法,利用气相色谱一质谱联用仪研究了人工添加不同吸附物质对土壤中乙草胺的吸附／解吸作用。结果表明,人工添加不同吸附物质对土壤中乙草胺的吸附强度和吸附容量不同,不同的添加剂对土壤中乙草胺的吸附／解吸作用均呈现明显的非线性关系,可用Freundlich模型描述。并且随着土壤中添加量的增大,吸附强度增大、吸附容量增大、所得吸附等温线的非线性也逐步增大;另外,添加剂对乙草胺的解吸迟滞作用也随添加剂含量的增高而更加明显。但是不同添加剂对土壤中乙草胺的吸附能力有明显差异,其中煤粉的吸附能力最大,其次是壳聚糖,沸石最小。     

基于J—A模型磁滞回线仿真及有效性研究

分析变压器、发电机等铣芯设备的暂态行为时,常用分段线性化的磁化曲线代替磁滞回线,但这种方法存在计算误差和震荡问题。分析J-A磁滞回线模型的基本原理,用等式变彤方法推导出逆J—A模型,分析其计算稳定性差的可能原因。根据已有参数,应用J—A模型对实际磁性材料的动态磁滞回线进行仿真分析,研究结果表明,涡流损耗对磁滞回线的影响较大。     

Mechanical Response Characteristics of the Earth Pressure Cell in Sand

Sand is a typical particle structure. The effective stress and corresponding deformation are both determined by the particle characteristics of the medium skeleton, and the changeable condition of the particles will further affect the mechanical response of the earth pressure cell in the test process. To correctly measure the earth pressure value, micromechanical method was applied to analyse the force chain formed by the particles contact under loading unloading condition, and the transferring process, the force strain curve and relationship between the cell mechanical response and the ideal response curve were analyzed in detail, which verified the above mechanical response model based on Particle Flow Code (PFC) method. According to the structural characteristics of the sand and above numerical model, the loading condition, porosity, friction coefficient between the particles and stiffness of the earth pressure cell affecting mechanical response of the earth pressure cell were deeply investigated, the numerical results indicated that there were obvious hysteresis and strain irreversibility for the response curve, and the measured value was sensitive to the above factors. Therefore, research on the force chain structure and corresponding evolution law brings forward a scientific base and new research means for understanding its micromechanical characteristics, and different factors influencing the earth pressure cell are also important for cell calibration and practical monitoring to get more correct earth pressure value.     

椭圆钴纳米环磁化动力学研究

利用Monte-Carlo方法模拟了不同偏心率、不同厚度的椭圆钴纳米环的磁特性.模拟结果表明：当系统的偏心率较小时,厚度越大的椭圆钴纳米环的涡旋态（＂vortex＂态）越稳定,此系统的磁滞回线保持圆形纳米环的主要特征;系统的偏心率较大时,系统的磁特性与圆形纳米环有较大差别,涡旋态的稳定性与厚度并无明显关联;对椭圆钴纳米环的自旋组态分析发现,椭圆系统在极化态（＂onion＂态）与涡旋态之间出现了更多的亚稳态.     

浸渍杉木吸湿滞后研究

[目的]对浸渍杉木的吸湿和解吸特性进行研究,旨在为浸渍木材加工过程中的木材尺寸变化提供参考依据。[方法]根据Hailwood-Horrobin吸附模型,拟合出20℃和30℃浸渍杉木与杉木对比材的吸湿及解吸曲线并进行对比。[结果]在温度相同的条件下,相比杉木对比材,相对湿度对浸渍杉木吸湿和解吸过程影响较小;浸渍杉木的等温吸湿曲线与解吸曲线均低于杉木对比材。[结论]浸渍杉木存在吸湿滞后现象。在同样的大气环境下,浸渍杉木达到稳定的过程要快于杉木对比材,但浸渍杉木的吸湿滞后差值要小于杉木对比材的差值。     

Effect of soil physical and chemical properties on the sorption-desorption hysteresis of the diketonitrile metabolite of isoxaflutole

Isoxaflutole, [4-(2-methanesulfonyl-4-trifluoromethylbenzoyl)-5-cyclopropyl isoxazole] is a relatively new pre-emergence herbicide which undergoes rapid conversion to a diketonitrile metabolite in soil. The half-life of isoxaflutole is very short but the half-life of diketonitrile is much longer and hence, diketonitrile remains for a extended period of time in soil. Sorption-desorption studies were conducted with five soils varying in physical and chemical properties. The batch equilibration technique was used for the sorption experiments, while completely mixed batch reactor systems with the decant and refill method was used for the desorption experiments. Four subsequent desorptions were examined after the sorption process in each soil with an equilibration period of seven days. An apparent sorption-desorption hysteresis was observed in all five soils. Organic matter content and the clay content of the soils were the two determining factors for hysteresis. In soils with high organic matter content, the sorption-desorption hysteresis was mainly governed by organic matter content, but in soils with low organic matter clay content played an important role. With the exception of the Chelsea soil, which had a very high organic matter content (57.4%), all other soils exhibited a high correlation between the clay content and hysteresis index (HI) values calculated at 0.75 ( r ² = 0.960), 25 ( r ² = 0.934) and 150 mg L⁻¹ ( r ² = 0.928). In conclusion, the potential for leaching through soil and crop injury due to isoxaflutole and its metabolite would decrease as soil organic matter and clay content increases.     

基于两阶段纯追踪模型的农用车辆路径跟踪算法研究

针对车辆自身加工、装配误差及轮胎侧滑等因素导致理论转向运动模型与实际转向运动模型不一致的情况,基于最小二乘法对车辆进行了转向运动模型辨识,得到了不同设定线速度下的转向运动模型。同时,为解决常规纯追踪算法计算得出的部分控制量无法使车辆转向系统作出响应,造成路径跟踪精度下降问题,提出了一种考虑横向偏差和横偏角的两阶段纯追踪算法,并针对两个阶段的切换提出了设置过渡区滞后切换策略。模拟环境S形路径跟踪实验表明,在行驶速度为0.6 m/s时,固定前视距离的纯追踪算法平均横向偏差为0.523 8 m,两阶段纯追踪算法为0.361 6 m,其跟踪精度提高30.9%,较固定前视距离的纯追踪算法具有更好的路径跟踪性能。采用滞后切换策略将两阶段的切换跳变率从2.18%减至1.16%,抑制效果提升46.8%。