Influence of thermal runaway in styrene–acrylonitrile bulk copolymerization revealed by computational fluid dynamics modeling

The computational fluid dynamics (CFD) and kinetic-based moment methods coupled approach is adopted to simulate the bulk copolymerization of styrene–acrylonitrile (SAN) in a stirred tank reactor. Numerical simulations are carried out to investigate the impacts of impeller speed, monomer ratio, initiator ratio, and initial reaction temperature on the copolymerization process and product properties. Particularly, the Chaos theory is selected as a criterion for evaluating the occurrence of the thermal runaway. The Flory's and Stockmayer's distributions are employed to calculate chain length distribution and copolymer composition distribution of copolymer. The simulation results highlight that the appearance of thermal runaway can be postponed by properly increasing the rotation speed, decreasing the initiator loadings, initial acrylonitrile contents and initial reactor temperature. Furthermore, significant differences exist in the product properties that predicted by the ideal and non-ideal models, which demonstrates that the temperature heterogeneity plays a crucial role in SAN copolymerization. This study could offer references for the safe operation and design of polymerization processes.     

N-乙氧基羰基-N,N',N'-三甲基胍高效液相色谱分析方法研究

N-乙氧基羰基-N,N',N'-三甲基胍(简称:三甲基胍)是合成高选择性森林除草剂环嗪酮的主要中间体,国内未见高效液相色谱检测方法的报道,我们采用反相高效液相色谱法对三甲基胍进行了定量分析研究,流动相为:V(水)︰V(乙腈)=90︰10,使用ODSC18为填料的不锈钢柱及具可变波长的紫外检测器.本方法的变异系数为0.19％,标准偏差为0.15,平均回收率为99.56％,经优化后的检测方法简捷、准确,能满足工业化产品定量检测需要.     

Coherent energy projection of modulated signals from a sparse array

In this article, coherent energy projection is generalized to modulated signals, enabling the precise delivery of energy to a specific target area. The system and mathematical model are established to characterize the far‐field energy interference from a randomized sparse transmitting array. By using the method of transmitting delay pre‐compensation and spatial coherent combination, the coherent energy of the modulated signals increases significantly after demodulation at the receiving end. The coherent energy scape is presented to describe the spatial distribution of projected energy in the target area, rather than the commonly used performance metric of front‐end energy analysis. Then the simulations set out to examine the spatial grating lobes and potential for expanding the focal spot using multi‐foci accumulation. We also employ the particle swarm optimization to find the optimum distribution of foci to match the focal spot with the desired target area and energy level. Analysis and numerical results are provided to demonstrate the correctness of the theoretical results and effectiveness of the proposed coherent energy projection method.     

天津市近代机场的规划和建设研究

分析近代天津历次近代城市规划中机场布局思想的演进历程，采用比较研究方法剖析天津近代各类机场设计方案的异同及其各自特征，并总结了天津近代机场场面规制及其跑道形制在不同时期的演进规律，还从规划编制体例角度论证了天津近代机场规划及其实例应用。     

Anderson Acceleration for Nonconvex ADMM Based on Douglas-Rachford Splitting

The alternating direction multiplier method (ADMM) is widely used in computer graphics for solving optimization problems that can be nonsmooth and nonconvex. It converges quickly to an approximate solution, but can take a long time to converge to a solution of high-accuracy. Previously, Anderson acceleration has been applied to ADMM, by treating it as a fixed-point iteration for the concatenation of the dual variables and a subset of the primal variables. In this paper, we note that the equivalence between ADMM and Douglas-Rachford splitting reveals that ADMM is in fact a fixed-point iteration in a lower-dimensional space. By applying Anderson acceleration to such lower-dimensional fixed-point iteration, we obtain a more effective approach for accelerating ADMM. We analyze the convergence of the proposed acceleration method on nonconvex problems, and verify its effectiveness on a variety of computer graphics including geometry processing and physical simulation.     

Ta含量对NiCoCrAlY涂层性能的影响

采用真空雾化的方法制备了Ta含量为0、2%及5%的NiCoCrAlYTa合金粉末,利用超音速火焰喷涂制备了三种涂层,研究了Ta对合金粉末微观组织及物相的影响,绘制了1050℃条件下涂层的高温氧化动力学曲线,研究了500h氧化试验后涂层组织和β相的分布,初步探讨了Ta元素对改善涂层抗氧化性能的作用机理。研究结果表明:Ta通过提高MCrAlY体系抗氧化元素的溶质浓度,促进了氧化膜的形成,随着Ta含量的增加,涂层的内氧化程度降低,涂层抗氧化性能提高。但含Ta涂层在长时间氧化条件下会生成CrTaO_4、AlTaO_4等尖晶石类氧化物,且Ta的氧化物PBR值较大,对涂层的抗热震性能不利。     

多氢酸酸化反应特征及动力学

利用自制多氢酸液XS-1进行静态岩粉溶蚀与岩心流动实验,通过SEM、ICP等实验考察了多氢酸的缓速性与预防二次沉淀性能,并研究了多氢酸与岩心反应动力学特性。结果表明,XS-1多氢酸液具有良好的缓速与预防二次沉淀性能,反应后残酸的极限浓度为0.296 1 mol/L,酸液有效作用时间为6~7 h。在该多氢酸体系下岩心渗透率提高至4.15倍,在此条件下以酸岩反应动力学参数模型建立动力学方程,反应速率比同条件下普通酸液小,进一步证明多氢酸具有一定的缓速性。     

In situ Raman spectroscopic study towards the growth and excellent HER catalysis of Ni/Ni(OH)2 heterostructure

The electrochemical water splitting to produce H₂ in high efficiency with earth-abundant-metal catalysts remains a challenge. Here, we describe a simple “cyclic voltammetry + ageing” protocol at room temperature to activate Ni electrode (AC-Ni/NF) for hydrogen evolution reaction (HER), by which Ni/Ni(OH)₂ heterostructure is formed at the surface. In situ Raman spectroscopy reveals the gradual growth of Ni/Ni(OH)₂ heterostructure during the first 30 min of the aging treatment and combined with polarization measurements, it suggests a positive relation between the Ni/Ni(OH)₂ amount and HER performance of the electrode. The obtained AC-Ni/NF catalyst, with plentiful Ni–Ni(OH)₂ interfaces, exhibits remarkable performance towards HER, with the low overpotential of only 30 mV at a H₂-evolving current density of 10 mA/cm² and 153 mV at 100 mA/cm², as well as a small Tafel slope of 46.8 mV/dec in 1 M KOH electrolyte at ambient temperature. The excellent HER performance of the AC-Ni/NF could be maintained for at least 24 h without obvious decay. Ex situ experiments and in situ electrochemical-Raman spectroscopy along with density functional theory (DFT) calculations reveal that Ni/Ni(OH)₂ heterostructure, although partially reduced, can still persist during HER catalysis and it is the Ni–Ni(OH)₂ interface reducing the energy barrier of H1 adsorption thus promoting the HER performance.     

Super‐Tough,Self‐Healing Polyurethane Based on Diels‐Alder Bonds and Dynamic Zinc–Ligand Interactions

Self‐healing polymer materials have attracted extensive attention and have been explored due to their ability of crack repairing in materials. This paper aims to develop a novel polyurethane‐based material with high self‐healing efficiency and excellent mechanical properties under 80 °C on the basis of reversible Diels–Alder bonds as well as zinc–ligand structure (DA‐ZN‐PU). By integrating DA bonds and zinc–ligand structure, as‐prepared DA‐ZN‐PU samples reach the maximum tensile strength as much as 28.45 MPa. After self‐healing, the tensile strength is 25.85 MPa, leading to the high self‐healing efficiency of 90.8%. In addition, by introducing carbonyl iron powder (CIP), a new polyurethane containing carbonyl iron powder (DA‐ZN‐CIP‐PU) can be achieved, exhibiting microwave‐assisted self‐healing property. And the self‐healing efficiency can be reached to 92.6% in 3 min. Due to high self‐healing efficiency and excellent mechanical properties of the prepared novel polyurethane, it has application attributes in crack repair of functional composite materials.