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毛乌素沙地东南缘樟子松(Pinus sylvestris var.mongolica)人工林土壤粒度特征 被引量:6
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作者 杨军怀 董治宝 +4 位作者 南维鸽 宋绍鹏 肖南 刘生权 孟小强 《中国沙漠》 CSCD 北大核心 2018年第4期815-822,共8页
为探讨毛乌素沙地东南缘樟子松(Pinus sylvestris var.mongolica)人工林下土壤粒度特征,以陕西省榆林市横山区、榆阳区和神木市樟子松人工林0~200cm土层为对象,测定土壤粒度组成,分析土壤粒度参数。结果表明:(1)毛乌素东南缘樟子松人工... 为探讨毛乌素沙地东南缘樟子松(Pinus sylvestris var.mongolica)人工林下土壤粒度特征,以陕西省榆林市横山区、榆阳区和神木市樟子松人工林0~200cm土层为对象,测定土壤粒度组成,分析土壤粒度参数。结果表明:(1)毛乌素东南缘樟子松人工林土壤机械组成主要为细砂(34.73%~44.57%)和中砂(40.63%~50.28%),粗粉砂含量(0.27%~1.34%)最低。(2)平均粒度介于细砂和中砂(1.81~2.20Φ),分选系数较好至中等(0.63~0.76),偏度近对称至正偏(0.03~0.13),峰度中等(0.94~1.07)。(3)空间上,0~200cm土层平均粒径自东北向西南逐渐变细且差异显著,分选系数、偏度和峰度在0~60cm内无规律,60~200cm土层有规律,即自东北向西南分选变差、细粒物质增加、粒度频率曲线变窄,但变化不显著。深度上,各参数无统一变化规律,但0~30cm土层比30~60cm平均粒径小,分选变差,细粒物质增加,粒度频率曲线变窄。(4)樟子松林和土壤间的相互作用在0~30cm较其他深度显著。 展开更多
关键词 毛乌素沙地 樟子松(Pinus SYLVESTRIS var.mongolica)人工林 粒度
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General Lyapunov Stability and Its Application to Time-Varying Convex Optimization
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作者 zhibao song Ping Li 《IEEE/CAA Journal of Automatica Sinica》 SCIE EI CSCD 2024年第11期2316-2326,共11页
In this article, a general Lyapunov stability theory of nonlinear systems is put forward and it contains asymptotic/finite-time/fast finite-time/fixed-time stability. Especially, a more accurate estimate of the settli... In this article, a general Lyapunov stability theory of nonlinear systems is put forward and it contains asymptotic/finite-time/fast finite-time/fixed-time stability. Especially, a more accurate estimate of the settling-time function is exhibited for fixedtime stability, and it is still extraneous to the initial conditions.This can be applied to obtain less conservative convergence time of the practical systems without the information of the initial conditions. As an application, the given fixed-time stability theorem is used to resolve time-varying(TV) convex optimization problem.By the Newton's method, two classes of new dynamical systems are constructed to guarantee that the solution of the dynamic system can track to the optimal trajectory of the unconstrained and equality constrained TV convex optimization problems in fixed time, respectively. Without the exact knowledge of the time derivative of the cost function gradient, a fixed-time dynamical non-smooth system is established to overcome the issue of robust TV convex optimization. Two examples are provided to illustrate the effectiveness of the proposed TV convex optimization algorithms. Subsequently, the fixed-time stability theory is extended to the theories of predefined-time/practical predefined-time stability whose bound of convergence time can be arbitrarily given in advance, without tuning the system parameters. Under which, TV convex optimization problem is solved. The previous two examples are used to demonstrate the validity of the predefined-time TV convex optimization algorithms. 展开更多
关键词 Fixed-time stability nonlinear system predefined-time stability time-varying(TV)convex optimization
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新型冠状病毒肺炎疫情下小儿外科诊疗工作建议 被引量:3
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作者 朱天琦 何大维 +9 位作者 詹江华 陈亚军 杨星海 段栩飞 吕志宝 董岿然 俞松 张利兵 唐维兵 冯杰雄 《中华小儿外科杂志》 CSCD 北大核心 2020年第4期289-292,共4页
2019年12月底我国首次报道新型冠状病毒肺炎(COVID-19)。根据国家卫健委制定的指南建议以及国内外最新发表的研究文献,本"专家意见"起草COVID-19疫情背景下小儿外科诊疗防控工作建议,着重于推荐COVID-19疫情期间,小儿外科临... 2019年12月底我国首次报道新型冠状病毒肺炎(COVID-19)。根据国家卫健委制定的指南建议以及国内外最新发表的研究文献,本"专家意见"起草COVID-19疫情背景下小儿外科诊疗防控工作建议,着重于推荐COVID-19疫情期间,小儿外科临床工作中的各级预防和控制措施,适用于国内外各级儿童医院和小儿外科机构的临床实践和医疗防护。 展开更多
关键词 小儿外科 诊疗工作 外科诊疗 新型冠状病毒 儿童医院 临床实践 防控工作 肺炎
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Catalytic transfer hydrogenation of levulinate ester intoγ-valerolactone over ternary Cu/ZnO/Al2O3 catalyst 被引量:2
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作者 Chuntao Zhang zhibao Huo +4 位作者 Dezhang Ren Zhiyuan song Yunjie Liu Fangming Jin Wanning Zhou 《Journal of Energy Chemistry》 SCIE EI CAS CSCD 2019年第5期189-197,共9页
An effective catalytic transfer hydrogenation (CTH) process of bio-based levulinate esters into γ-valerolactone (GVL) was explored over ternary Cu/ZnO/Al2O3 catalyst which was prepared by coprecipitation method and c... An effective catalytic transfer hydrogenation (CTH) process of bio-based levulinate esters into γ-valerolactone (GVL) was explored over ternary Cu/ZnO/Al2O3 catalyst which was prepared by coprecipitation method and could be sustainably used. As a result, quantitative conversion of ethyl levulinate (EL) and 99.0% yield of GVL were obtained in the CTH process using i-PrOH as hydrogen donor. The Cu/ZnO/Al2O3 catalyst with high-surface-area could be reused at least four times without the loss of catalytic activity. Furthermore, the structure and properties of Cu/ZnO/Al2O3 catalyst was characterized through XRD, BET, SEM, TEM and H2-TPR. Also, the influence of different support oxides and calcination temperatures was investigated. 展开更多
关键词 Bio-based COMPOUNDS Cu/ZnO/Al2O3 TRANSFER HYDROGENATION γ-valerolactone Green process
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飞机电缆雷电间接效应的耦合特性仿真研究 被引量:7
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作者 靳嘉嘉 司晓亮 +4 位作者 汪友华 仇善良 王森 李志宝 张松 《电工技术》 2018年第1期20-23,共4页
为降低雷电间接效应危害,提高飞行安全性,针对雷电对机身内部电缆雷电感应耦合的影响,采用基于有限元积分与传输线矩阵法的电磁仿真软件CST对飞机内部电缆进行雷电流脉冲仿真研究,分析在雷电流分量A作用下不同布局电缆感应电压和感应电... 为降低雷电间接效应危害,提高飞行安全性,针对雷电对机身内部电缆雷电感应耦合的影响,采用基于有限元积分与传输线矩阵法的电磁仿真软件CST对飞机内部电缆进行雷电流脉冲仿真研究,分析在雷电流分量A作用下不同布局电缆感应电压和感应电流耦合情况。仿真结果表明,内部电缆感应电压和感应电流受电缆布局影响较大,且非屏蔽电缆和屏蔽电缆上的感应电压具有明显差异,随着飞机内部非屏蔽电缆与机身蒙皮间距离的增大,非屏蔽电缆感应电压呈线性增长。 展开更多
关键词 雷电 间接效应 电磁仿真 电磁耦合
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A field investigation of wind erosion in the farming–pastoral ecotone of northern China using a portable wind tunnel: a case study in Yanchi County 被引量:1
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作者 nan ling dong zhibao +5 位作者 xiao weiqiang li chao xiao nan song shaopeng xiao fengjun du lingtong 《Journal of Arid Land》 SCIE CSCD 2018年第1期27-38,共12页
The farming-pastoral ecotone in northern China is an extremely fr@e ecological zone where wind erosion of cropland and rangeland is easy to occur. In this study, using a portable wind tunnel as a wind simulator, we co... The farming-pastoral ecotone in northern China is an extremely fr@e ecological zone where wind erosion of cropland and rangeland is easy to occur. In this study, using a portable wind tunnel as a wind simulator, we conducted field simulated wind erosion experiments combined with laboratory analysis to investigate wind erosion of soils in trampled rangeland, non-tilled cropland and tilled cropland in Yanchi County, China. The results showed that compared with rangeland, the cropland had a higher soil water holding capacity and lower soil bulk density. The wind erosion rate of trampled rangeland was much higher than those of non-tilled cropland and tilled cropland. For cropland, the wind erosion rate of the soil after tilling was surprisingly less than that of the soil before tilling. With increasing of wind speed, the volume mean diameter of the eroded sediment collected by the trough in the wind tunnel generally increased while the clay and silt content decreased for all soils. The temporal variation in wind erosion of the trampled rangeland indicated that particle entrainment and dust emission decreased exponentially with erosion time through the successive wind erosion events due to the exhaustion of erodible particles. 展开更多
关键词 wind erosion rate wind tunnel eroded sediment soil particle size CROPLAND RANGELAND semi-arid region
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