Superhard F-carbon predicted by ab initio particle-swarm optimization methodology

A simple (5 + 6 + 7)-sp(3) carbon (denoted as F-carbon) with eight atoms per unit cell predicted by a newly developed ab initio particle-swarm optimization methodology on crystal structure prediction is proposed. F-carbon can be seen as the reconstruction of AA-stacked or 3R-graphite, and is energetically more stable than 2H-graphite beyond 13.9 GPa. Band structure and hardness calculations indicate that F-carbon is a transparent superhard carbon with a gap of 4.55 eV at 15 GPa and a hardness of 93.9 GPa at zero pressure. Compared with the previously proposed Bct-, M- and W-carbons, the simulative x-ray diffraction pattern of F-carbon also well matches the superhard intermediate phase of the experimentally cold-compressed graphite. The possible transition route and energy barrier were observed using the variable cell nudged elastic band method. Our simulations show that the cold compression of graphite can produce some reversible metastable carbons (e.g. M- and F-carbons) with energy barriers close to diamond or lonsdaleite.     

茂金属催化剂的负载化

茂金属催化剂是继齐格勒-纳塔催化剂之后的新一代烯烃聚合催化剂,与多活性中心催化剂相比,这种单一活性中心类型的催化剂具有聚合活性较高、聚合物分子量分布较窄等特点。其中,负载化是茂金属催化剂实用化的重要课题,它克服了均相催化体系中聚合物形貌不可控的缺点,降低了助催化剂的用量。近些年来茂金属负载化的研究仍很活跃。本文总结了近十年来茂金属负载化的研究进展,主要对载体的形貌、载体的改性处理、茂金属催化剂的负载方法和负载化茂金属催化剂的应用进行了评述并展望了茂金属催化剂负载化的发展趋势。     

Effect of DC bias on microstructural rearrangement of a-SiN:H films on PET substrate

Hydrogenated amorphous silicon nitride (a-SiN:H) films were deposited on flexible polyethylene terephthalate substrates at temperature as low as 100 °C by hot-wire chemical vapor deposition using SiH₄, H₂ and NH₃ precursors. Field emission scanning emission microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy and small angle X-ray scattering were employed to study structural and microstructural properties of a-SiN:H films. The rms surface roughness increased with increase of positive bias to substrate. Intermediate range order, porosity and interface inhomogeneity in amorphous of a-SiN:H films evaluated by acoustic and optical phonon of silicon network, Guinier plot and correlated length from Raman and SAXS characterizations. The fractal behavior of a-SiN:H domains approached the perfect symmetry and the intermediate range order of a-SiN:H films deteriorate with increase of the positive substrate bias. Both correlation length and void size of the a-SiN:H amorphous domain increased with increase of the substrate bias from 0 to +200 V.     

(硫杂)杯[4]芳烃缩氨基(硫)脲(桥联)衍生物的合成

对叔丁基(硫杂)杯[4]芳烃-1,3-二醛基衍生物4a和4b与苯基氨基硫脲进行“1＋2”缩合反应, 合成了杯[4]芳烃缩氨基硫脲衍生物5a和5b, 产率为84%和85%. 化合物4a和4b与1,6-己基双氨基脲发生“1＋1”缩合反应, 合成了杯[4]芳烃双缩氨基脲桥联衍生物6a和6b, 产率为83%和80%. 新化合物的结构与构象经元素分析、质谱、核磁共振谱等表征证实.     

非旋转钝锥高超声速双平面拍摄风洞自由飞试验

在高超声速下(6 马赫) 开展了双平面拍摄风洞自由飞试验,对非旋转钝锥在小攻角下的运动特性和圆锥摆动问题进行了研究. 试验结果表明,虽然只预置了攻角而无侧滑角,模型仍然全部出现了圆锥摆动,且在观察窗范围内侧滑角幅值均大于攻角幅值. 模型角运动虽均处于小于10° 的小攻角和小侧滑角状态,但阻尼力矩项呈现较为明显的非线性,而静力矩项的非线性较弱,近似为线性. 5 组实验中,有1 组模型的角运动可能趋于极限平面运动或者是攻角幅值较小的极限圆锥运动,另外4 组试验模型角运动显示出了趋于极限圆锥运动的趋势. 尾端盖对模型的角运动影响不明显,而尾部对称布置的片条状凸起物对整个角运动幅值变化的稳定性存在明显影响,有凸起物的两组模型角运动幅值波动明显较小.      

不确定混沌系统的反同步与参数辨识

针对一类混沌系统,提出了一种系统的混沌反同步设计方案,基于该方案,设计一种自适应控制方法,实现了参数不确定系统的混沌反同步和未知参数的辨识.数值模拟结果表明了提出方法的有效性.     

利用单驱动变量实现一类分数阶混沌系统的修正投影同步

通过设计一个合适的响应系统,提出了一种修正投影同步方案,该方法通过传递一个驱动变量实现了一类分数阶混沌系统的修正投影同步,由于只需在驱动系统和响应系统之间传递一个驱动变量,具有较高的实用价值,最后以分数阶统一混沌系统为例进行了数值仿真,理论和数值仿真表明了该方法的有效性.     

Synthesis of Chiral Aldehyde Catalysts by Pd‐Catalyzed Atroposelective C−H Naphthylation

Chiral aldehyde catalysis opens new avenues for the activation of simple amines. However, the lack of easy access to structurally diverse chiral aldehyde catalysts has hampered the development of this cutting‐edge field. Herein, we report a Pd‐catalyzed atroposelective C?H naphthylation with 7‐oxabenzonorbornadienes for the preparation of axially chiral biaryls with excellent enantioselectivities (up to >99 % ee). This reaction is scalable and robust, which serves as a key step to provide a rapid access to axially chiral aldehyde catalysts through a three‐step C?H functionalization sequence. These chiral aldehydes exhibit better activities and enantioselectivities than the previously reported organocatalysts in the asymmetric activation of glycine derived amides and dipeptides. Moreover, preliminary investigation also discloses that the aldehyde catalyst can effectively override the intrinsic facial selectivity of chiral dipeptide substrates, showcasing the strong chiral induction ability of this type of novel aldehyde catalysts.     

Approaching the Lithiation Limit of MoS2 While Maintaining Its Layered Crystalline Structure to Improve Lithium Storage

MoS₂ holds great promise as high‐rate electrode for lithium‐ion batteries since its large interlayer can allow fast lithium diffusion in 3.0–1.0 V. However, the low theoretical capacity (167 mAh g^?1) limits its wide application. Here, by fine tuning the lithiation depth of MoS₂, we demonstrate that its parent layered structure can be preserved with expanded interlayers while cycling in 3.0–0.6 V. The deeper lithiation and maintained crystalline structure endows commercially micrometer‐sized MoS₂ with a capacity of 232 mAh g^?1 at 0.05 A g^?1 and circa 92 % capacity retention after 1000 cycles at 1.0 A g^?1. Moreover, the enlarged interlayers enable MoS₂ to release a capacity of 165 mAh g^?1 at 5.0 A g^?1, which is double the capacity obtained under 3.0–1.0 V at the same rate. Our strategy of controlling the lithiation depth of MoS₂ to avoid fracture ushers in new possibilities to enhance the lithium storage of layered transition‐metal dichalcogenides.     

A UoI-Optimal Policy for Timely Status Updates with Resource Constraint

Timely status updates are critical in remote control systems such as autonomous driving and the industrial Internet of Things, where timeliness requirements are usually context dependent. Accordingly, the Urgency of Information (UoI) has been proposed beyond the well-known Age of Information (AoI) by further including context-aware weights which indicate whether the monitored process is in an emergency. However, the optimal updating and scheduling strategies in terms of UoI remain open. In this paper, we propose a UoI-optimal updating policy for timely status information with resource constraint. We first formulate the problem in a constrained Markov decision process and prove that the UoI-optimal policy has a threshold structure. When the context-aware weights are known, we propose a numerical method based on linear programming. When the weights are unknown, we further design a reinforcement learning (RL)-based scheduling policy. The simulation reveals that the threshold of the UoI-optimal policy increases as the resource constraint tightens. In addition, the UoI-optimal policy outperforms the AoI-optimal policy in terms of average squared estimation error, and the proposed RL-based updating policy achieves a near-optimal performance without the advanced knowledge of the system model.