一次人工触发闪电上行正先导的传输特征

利用山东一次人工触发闪电的高速摄像和30 m, 60 m和480 m的同步电场测量, 清晰显示了人工触发闪电上行正先导的传输特征.上行正先导头部光强相对较强, 二维发展速度变化波动较大并呈现明显不规则性,表明上行正先导发展具有明显的梯级特征. 在先导开始阶段从340 m到705 m高度之间上行正先导平均发展速度为9.8×10⁴ m/s,起始速度是 3.8×10⁴ m/s,局部速度总体上随高度呈现增加趋势.电场变化在近距离产生有规律的梯级状 变化,记录到的28个梯级相邻梯级间隔变化从14 μs 到 39 μs,几何平均值为25.1 μs. 估计的先导梯级长度分布在0.9 m到3.7 m,几何平均值为1.7 m.先导电场变化由慢的正向梯级状变化和 脉冲变化组成,结合光学和电场变化测量结果,得出正先导头部通道发生弯曲可使其电场变化的梯级特征减弱 或消失;正负先导梯级形成机制可能类似,均由其先导头部前端的双向流光发展而来.     

雷暴电场对宇宙射线次级粒子μ 子的影响研究

西藏羊八井宇宙射线观测站的中子监测器主要探测宇宙射线次级粒子中能量在500 MeV—20 GeV的核子成分和少量的负μ子成分. 本文分析了2008—2010年观测站附近发生的62次雷暴期间中子监测器和大气平均电场仪的同步观测资料, 发现27次雷暴期间中子监测器计数率发生明显变化, 显著性S>5σ, 其中13次变化显著, 显著性S>10σ . 显著性S>10σ的13次个例信号变化百分比与地面电场场强幅值之间存在大体一致的变化趋势, 而显著性在5σ <S<10σ之间的14次个例信号变化百分比与地面电场场强幅值之间不存在相似的变化趋势. 较强雷暴当顶时中子监测器计数率变化一般不明显, 而中子监测器计数率变化明显的个例则多发生于雷暴云不当顶, 但探测器仍处于雷暴云下部正电荷层的控制范围之内时, 或者当顶雷暴处于形成或消散阶段. Dorman等把雷暴期间中子监测器计数率的变化归因于雷暴云内电场对宇宙射线次级粒子μ子的作用, 并建立了雷暴期间中子监测器计数率变化与雷暴地面电场相关联的理论. 本文分析发现雷暴期间羊八井中子监测器计数率变化与地面电场场强之间相关性较小或者没有相关性, 不支持Dorman的理论.     

Tris‐amidoximate uranyl complexes via η2 binding mode coordinated in aqueous solution shown by X‐ray absorption spectroscopy and density functional theory methods

The present study sheds some light on the long‐standing debate concerning the coordination properties between uranyl ions and the amidoxime ligand, which is a key ingredient for achieving efficient extraction of uranium. Using X‐ray absorption fine structure combined with theoretical simulation methods, the binding mode and bonding nature of a uranyl–amidoxime complex in aqueous solution were determined for the first time. The results show that in a highly concentrated amidoxime solution the preferred binding mode between UO₂²⁺ and the amidoxime ligand is η² coordination with tris‐amidoximate species. In such a uranyl–amidoximate complex with η² binding motif, strong covalent interaction and orbital hybridization between U 5f/6d and (N, O) 2p should be responsible for the excellent binding ability of the amidoximate ligand to uranyl. The study was performed directly in aqueous solution to avoid the possible binding mode differences caused by crystallization of a single‐crystal sample. This work also is an example of the simultaneous study of local structure and electronic structure in solution systems using combined diagnostic tools.     

Full Dissolution of the Whole Lithium Sulfide Family (Li2S8 to Li2S) in a Safe Eutectic Solvent for Rechargeable Lithium–Sulfur Batteries

The lithium–sulfur battery is an attractive option for next‐generation energy storage owing to its much higher theoretical energy density than state‐of‐the‐art lithium‐ion batteries. However, the massive volume changes of the sulfur cathode and the uncontrollable deposition of Li₂S₂/Li₂S significantly deteriorate cycling life and increase voltage polarization. To address these challenges, we develop an ?‐caprolactam/acetamide based eutectic‐solvent electrolyte, which can dissolve all lithium polysulfides and lithium sulfide (Li₂S₈–Li₂S). With this new electrolyte, high specific capacity (1360 mAh g^?1) and reasonable cycling stability are achieved. Moreover, in contrast to conventional ether electrolyte with a low flash point (ca. 2 °C), such low‐cost eutectic‐solvent‐based electrolyte is difficult to ignite, and thus can dramatically enhance battery safety. This research provides a new approach to improving lithium–sulfur batteries in aspects of both safety and performance.     

Self-assembled vesicles prepared from amphiphilic cyclodextrins as drug carriers

Controlled self-assembly of amphiphilic cyclodextrin is always a challenging topic in the field of supramolecular chemistry, since it provides the spontaneous generation of well-defined aggregation with functional host sites with great potential applications in drug-carrier systems. β-Cyclodextrin modified with an anthraquinone moiety (1) was successfully synthesized. In the aqueous solution, 1 was found able to self-assemble into vesicles, which was characterized in detail by TEM, SEM, EFM, and DLS. The formation mechanism of the vesicles was suggested based on the 2D ROESY and UV-vis results, and further verified by the MD simulation. Subsequently, the stimuli response property of the vesicles, including to Cu(2+) and H(+), was also studied. The vesicles can efficiently load Paclitaxel inside the membrane with functional macrocyclic cavities available, which can further carry small molecules, such as ferrocene. The vesicles loading with Paclitaxel have remarkable anticancer effects. This work will provide new strategy in drug-carrier systems and tumor treatment methods.     

Microwave‐Induced In Situ Synthesis of Zn2GeO4/N‐Doped Graphene Nanocomposites and Their Lithium‐Storage Properties

Zn₂GeO₄/N‐doped graphene nanocomposites have been synthesized through a fast microwave‐assisted route on a large scale. The resulting nanohybrids are comprised of Zn₂GeO₄ nanorods that are well‐embedded in N‐doped graphene sheets by in situ reducing and doping. Importantly, the N‐doped graphene sheets serve as elastic networks to disperse and electrically wire together the Zn₂GeO₄ nanorods, thereby effectively relieving the volume‐expansion/contraction and aggregation of the nanoparticles during charge and discharge processes. We demonstrate that an electrode that is made of the as‐formed Zn₂GeO₄/N‐doped graphene nanocomposite exhibits high capacity (1463 mAh g^?1 at a current density of 100 mA g^?1), good cyclability, and excellent rate capability (531 mAh g^?1 at a current density of 3200 mA g^?1). Its superior lithium‐storage performance could be related to a synergistic effect of the unique nanostructured hybrid, in which the Zn₂GeO₄ nanorods are well‐stabilized by the high electronic conduction and flexibility of N‐doped graphene sheets. This work offers an effective strategy for the fabrication of functionalized ternary‐oxide‐based composites as high‐performance electrode materials that involve structural conversion and transformation.     

Electrocatalytic Synthesis of Nylon-6 Precursor at Almost 100 % Yield

Synthesis of cyclohexanone oxime via the cyclohexanone-hydroxylamine process is widespread in the caprolactam industry, which is an upstream industry for nylon-6 production. However, there are two shortcomings in this process, harsh reaction conditions and the potential danger posed by explosive hydroxylamine. In this study, we presented a direct electrosynthesis of cyclohexanone oxime using nitrogen oxides and cyclohexanone, which eliminated the usage of hydroxylamine and demonstrated a green production of caprolactam. With the Fe electrocatalysts, a production rate of 55.9 g h⁻¹ g_cat⁻¹ can be achieved in a flow cell with almost 100 % yield of cyclohexanone oxime. The high efficiency was attributed to their ability of accumulating adsorbed hydroxylamine and cyclohexanone. This study provides a theoretical basis for electrocatalyst design for C−N coupling reactions and illuminates the tantalizing possibility to upgrade the caprolactam industry towards safety and sustainability.     

层板复合材料的疲劳剩余刚度统计分布模型

在分析现有关于层板复合材料疲劳剩余刚度衰退模型的基础上，根据层板复合材料在疲劳载荷作用下刚度衰退变化的现象，研究了疲劳载荷对层板复合材料刚度衰退的影响，建立了一个新的、更为合理的用于描述层板复合材料在常幅疲劳载荷作用下的刚度衰退模型，导出了剩余刚度统计分布的表达式，给出了确定模型参数的方法。为验证该模型，设计了几组测试实验，并利用试验结果对模型参数进行了估计。利用该统计分布模型，可以预报层板复合材料在给定应力水平的疲劳载荷作用下循环指定周次时剩余刚度的统计分布。实验数据表明，理论预报和实验结果符合得是很好的。     

Natural convection heat transfer at reduced pressures

This paper experimentally studies the natural convection heat transfer characteristics on horizontal and vertical plates at pressures lower than atmospheric value. Eight different pressures ranging from 10Pa to 101.325kPa, and three heating loads were used in the experiments. It is found that natural convection heat transfer characteristics at reduced pressures are independent of the plate arrangements and present different behaviors in two pressure ranges, 10Pa < p < 1000Pa and p > 1000Pa. The experimental heat transfer results are correlated into a non-dimensional equation to help the thermal design of stratosphere aircrafts and airborne equipment.