SSZ-13分子筛上甲醇转化过程中甲氧基物种的生成与活性研究

本文使用固体核磁共振（NMR）技术研究了SSZ-13分子筛上甲醇制烯烃反应过程中表面甲氧基物种的生成以及反应活性.通过二维¹³C-²⁷Al HMQC NMR方法确证了甲醇在分子筛骨架Brønsted酸位上生成的甲氧基物种,以及在Lewis酸位上生成的另外一种表面甲氧基物种.¹³C NMR结合气相色谱-质谱（GC-MS）实验结果表明,这两种甲氧基物种在甲醇制烯烃反应中均具有较高的反应活性,既可以导致烃池物种的生成,也可以参与烃池反应生成碳氢化合物.     

Numerical simulation of two droplets impacting upon a dynamic liquid film

The impact of droplets on the liquid film is widely involved in industrial and agricultural fields. In recent years, plenty of works are limited to dry walls or stationary liquid films, and the research of multi-droplet impact dynamic films is not sufficient. Based on this, this paper employs a coupled level set and volume of fluid (CLSVOF) method to numerically simulate two-droplet impingement on a dynamic liquid film. In our work, the dynamic film thickness, horizontal central distance between the droplets, droplets' initial impact speed, and simultaneously the flow velocity of the moving film are analyzed. The evolution phenomenon and mechanism caused by the collision are analyzed in detail. We find that within a certain period of time, the droplet spacing does not affect the peripheral crown height; when the droplet spacing decreases or the initial impact velocity increases, the height of the peripheral crown increases at the beginning, and then, because the crown splashed under Rayleigh-Plateau instability, this results in the reduction of the crown height. At the same time, it is found that when the initial impact velocity increases, the angle between the upstream peripheral jet and the dynamic film becomes larger. The more obvious the horizontal movement characteristics, the more restrained the crown height; the spread length increases with the increase of the dynamic film speed, droplet spacing and the initial impact velocity. When the liquid film is thicker, more fluid enters the crown, due to the crown being unstable, the surface tension is not enough to overcome the weight of the rim at the end of the crown, resulting in droplets falling off.     

Near-zero thermal expansion in β-CuZnV2O7 in a large temperature range

We report a new type of near-zero thermal expansion material β-CuZnV₂O₇ in a large temperature range from 173 K to 673 K. It belongs to a monoclinic structure (C2/c space group) in the whole temperature range. No structural phase transition is observed at atmospheric pressure based on the x-ray diffraction and Raman experiment. The high-pressure Raman experiment demonstrates that two structural phase transitions exist at 0.94 GPa and 6.53 GPa, respectively. The mechanism of negative thermal expansion in β-CuZnV₂O₇ is interpreted by the variations of the angles between atoms intuitively and the phonon anharmonicity intrinsically resorting to the negative Grüneisen parameter.     

Dynamics and intermittent stochastic stabilization of a rumor spreading model with guidance mechanism in heterogeneous network

We propose a novel rumor propagation model with guidance mechanism in heterogeneous complex networks. Firstly, the sharp threshold of rumor propagation, global stability of the information-equilibrium and information-prevailing-equilibrium under R₀ <1 and R₀> 1 is carried out by Lyapunov method and LaSalle's invariant principle. Next, we design an aperiodically intermittent stochastic stabilization method to suppress the rumor propagation. By using the Itô formula and exponential martingale inequality, the expression of the minimum control intensity is calculated. This method can effectively stabilize the rumor propagation by choosing a suitable perturb intensity and a perturb time ratio, while minimizing the control cost. Finally, numerical examples are given to illustrate the analysis and method of the paper.     

Contract-based scheme for computational resource allocation in cloud-assisted parked vehicular edge computing

Having shown promising performance with high flexibility and efficiency in vehicular edge computing (VEC) network, the parked vehicles (PVs) received an increasing number of attentions in recent years. However, PVs’ residual battery power restricts their running time. In addition, there is still no alternate resource pool for the PVs to cope with the emergencies in the previous VEC framework. To alleviate these problems, we model a cloud-assisted parked vehicular edge computing (PVEC) framework, in which the PVs are classified based on their residual battery power. PVs corporate with the cloud servers (CSs) for the computational resources provision. In addition, we formulate the utilities of the service provider (SP) and PVs and design a contract-based resource allocation problem for the maximization of the SP’s utility. Considering that it is intractable to solve the optimization problem directly, the primal problem is simplified and decoupled into two sub-problems. To design the optimal contracts, we solve the sub-problems by Lagrangian multiplier method and dual function. Simulation results prove that the utilities of PVs can reach to the maximum when they choose the contract corresponding to their types. In addition, the simulation results illustrate the superiority of proposed scheme over previous schemes in improving the utilities of the SP and social welfare.     

飞秒激光-等离子体相互作用中快电子能量分布

 采用不同量程的电子谱仪与LiF热释光探测器相配合,测量了飞秒激光 等离子体相互作用中产生的快电子能量分布。结果显示快电子能量分布的一致性和多个重要特征与国外同类实验和计算机模拟结果相似。快电子能谱在低能处产生凹陷是由于冷电子的回流产生的;几种加速机制共同作用是能谱在100~350 keV范围内出现平台的原因;快电子的有效温度较好地满足共振吸收的温度定标律是由于反射激光加速与共振吸收机制均是通过朗道阻尼或波破对电子进行加速的。     

金属蒸汽中的激光维持爆震波

 应用我们发展的一个激光与金属蒸汽相互作用的简化物理模型对激光维持爆震波的点火激励、传播规律作了数值研究并取得了较好的结果。计算得到的LSD波阈值与激光脉宽的关系表现出典型的幂规律I_th∝τ^-1/2。此外，还得到了一些关于LSD波屏蔽效应的有益结果。在LSD波充分发展的阶段，LSD波阵面的光学厚度可达5~10的量级，这表明LSD波具有很强的屏蔽作用。     

叠氮化铅的等离子体电子作用机理初探

本文分析了装有不同药剂的半导体桥（Semiconductor Bridge,SCB）火工品的电流信号,结合叠氮化铅（Lead Azide,LA）的铅核反应机理,探索性地分析了等离子体中电子对药剂分解反应的影响.表明SCB等离子体中的电子可能直接参与铅核的生成反应,使Pb²⁺/Pb⁰转化变得容易,实现6.89μs的发火.     

高维广义蔡氏电路中的快慢动力学行为及其分岔分析

讨论了四阶广义蔡氏电路在两时间尺度下的动力学行为. 由数值模拟得到了系统在不同参数条件下的周期簇发解和混沌吸引子. 通过引入快慢分析法,从分岔的角度,以周期解为例, 对系统动力学行为产生的机理及其演化规律进行了理论分析和解释, 其结论与数值计算的结果基本符合.     

Pb-Mg-Al合金腐蚀机理的电子理论研究

为了了解Pb-Mg-Al合金腐蚀的物理本质, 本文采用基于第一性原理的赝势平面波方法系统地计算了Pb-Mg-Al合金中各物相的结合能、费米能级和局域态密度等电子结构参数, 分析了合金的电化学腐蚀机理. 计算结果表明：Pb-Mg-Al合金中各主要组成物相稳定性大小关系为 Mg₁₇Al₁₂>Mg₂Pb>Mg;Mg,Mg₂Pb和Mg₁₇Al₁₂的费米能级存在E_f(Mg)>E_f(Mg₂Pb)>E_f(Mg₁₇Al₁₂)的关系, 说明Mg最容易失去电子, Mg₂Pb次之, Mg₁₇Al₁₂最难;局域态密度表明, 在同样的外界条件下, 体系中Mg相和Mg₂Pb相对于Mg₁₇Al₁₂均处于不稳定的状态, 容易失去电子, 即容易发生腐蚀. Pb-Mg-Al合金体系中不同物相的费米能级差构成了电化学腐蚀的电动势, 导致电子从费米能级高的Mg相和Mg₂Pb相流向费米能级低的Mg₁₇Al₁₂相, 使Pb-Mg-Al合金发生腐蚀.