Novel TiC-based composites with enhanced mechanical properties

Novel TiC-based composites were synthesized by reactive hot-pressing at 1800 °C for 1 h with ZrB₂ addition as a sintering aid for the first time. The effects of ZrB₂ contents on the phase composition, microstructure evolution, and mechanical properties were reported. Based on the reaction and solid solution coupling effects between ZrB₂ and TiC, the product ZrC may be partially or completely dissolved into the TiC matrix, and then phase separation within the miscibility gap is observed to form lamellar nanostructured ZrC-rich (Zr, Ti)C. The TiC-10 mol.% ZrB₂ (starting batch composition) exhibits good comprehensive mechanical properties of hardness 27.7 ± 1.3 GPa, flexural strength 659 ± 48 MPa, and fracture toughness of 6.5 ± 0.6 MPa m^1/2, respectively, which reach or exceed most TiC-based composites using ceramics as sintering aids in the previous reports.     

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.     

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.     

An unsafe behaviour formation mechanism based on risk perception

It is commonly acknowledged that human behaviour is implicated in most safety problems. However, research on the formation mechanism of unsafe behaviour remains incomplete. Risk perception is one of the fundamental issues in risk research, and individual risk perception can be identified as a critical antecedent of human behaviour. This study attempts to construct and test a theoretical model to reveal the formation mechanism of unsafe behaviour based on risk perception. First, to lay a solid foundation for the developed new mechanism, several key concepts about risk perception and unsafe behaviour were explained. Second, the formation mechanism of biases in individual risk perception was developed based on psychological distance theory, and the biases in risk perception were subsequently classified. Lastly, an unsafe behaviour formation mechanism was put forward based on risk perception as an explanatory variable. This study is novel in that it uses psychological distance to explore the formation of biases in individual risk perception. Further, the presented work provides a new approach to understanding and explaining the formation mechanism of human unsafe behaviour.     

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.     

界面聚合聚酰胺纳滤膜渗透选择性能优化的研究进展

纳滤因其分离效率高、操作压力低、环境友好等优点，在废水处理、海水淡化和工业分离纯化等众多领域有着重要的应用。界面聚合法制备的聚酰胺（PA）纳滤膜是最为常用的纳滤膜种类之一。然而界面聚合反应速度快，如何通过调控界面聚合过程，优化纳滤膜选择分离层的结构从而提高渗透选择性，以满足不同领域对纳滤膜需求仍是亟需解决的问题。本文从影响界面聚合单体扩散因素的角度出发，综述了近年来PA纳滤膜渗透选择性能优化的研究进展，包括新型PA纳滤膜、纳米材料/PA混合基质膜及超薄PA纳滤膜3个方面，探讨了选择分离层结构调控与纳滤膜渗透选择性能优化的关系，最后指出目前界面聚合制备高渗透选择性PA纳滤膜在规模化、稳定性及可控性存在的问题，并对未来界面聚合纳滤膜在微观结构和聚合过程调控方面的研究进行了展望。     

Flame Retardancy and Mechanical Properties of Bio‐Based Furan Epoxy Resins with High Crosslink Density

This work outlines an interesting approach to bioepoxy resins from sustainable 2,5‐bis((oxiran‐2‐ylmethoxy)methyl)furan (BOF). The 3,3′‐diamino diphenyl‐sulfone (33DDS) and 4,4′‐diamino diphenyl‐sulfone (44DDS) are employed as hardeners. For comparison, petro‐based networks from diglycidyl ether of bisphenol A (DGEBA) are developed as well. The systematic analyses suggest that the BOF/DDS networks show higher crosslink densities and mechanical properties than DGEBA/DDS thermosets. Remarkably, an attractive multilayer tubular microstructure is fabricated in the BOF/44DDS thermosets, and it greatly enhances the mechanical performance. Apart from that, BOF/DDS composites exhibit excellent flame retardancy. Especially, for BOF/44DDS, the self‐extinguishment happens in 7 s. The fire retardant mechanism confirms that a low heat release rate and heat release capacity as well as a compact char layer occur in the pyrolysis of BOF/DDS. Thus, the BOF/DDS exhibits superior performance over its DGEBA counterparts and meets a wide variety of requirements in engineering.     

Densification,mechanical and thermal properties of ZrC1 − x ceramics fabricated by two-step reactive hot pressing of ZrC and ZrH2 powders

Densification behavior, mechanical and thermal properties of ZrC_1 ? x ceramics with various C/Zr ratios of 0.6–1.0 have been investigated by two-step reactive hot pressing of ZrC and ZrH₂ powders at 30 MPa and 1500–2100 °C. The two-step reactive hot pressed ZrC_1 ? x ceramic has a higher relative density (> 95.3%) than that (91.9%) of stoichiometric ZrC sintered at 2100 °C. A cubic Zr₂C-type ordered phase forms in the ZrC_1 ? x sample obtained at a ZrC/ZrH₂ molar ratio of 0.6 at a relatively low temperature of 1100 °C. The decrease in C/Zr ratio is beneficial to densification of ZrC_1 ? x ceramic, however, excess grain growth occurs after sintering above densification temperature. The elastic modulus and Vickers hardness decrease with decreasing the C/Zr ratio. With decreasing the C/Zr ratio, both thermal conductivity and specific heat decrease due to the enhanced scattering of conducting phonons and electrons by carbon vacancies.     

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。     

Visualizations of Mercury Methylation and Dynamic Transformations by In Vivo Imaging

Visualization of Hg(II) and MeHg in their native contexts is significant for examining mercury poisoning, while it is challenging because of indistinguishable fluorescent (FL) signals during FL imaging. Herein, visualizations of mercury methylation and dynamic transformations of Hg(II) and MeHg are achieved in living biological systems. Well distinguishable FL responses (blue emission for Hg(II), yellow emission for MeHg) are obtained by a double‐response FL probe (DPAHB) without any interference. As demonstrated by experimental and computational studies, the distinguishable signals are attributed to selective binding with DPAHB and different inhibition of excited‐state proton transfer. Through control tests for live‐dead markers, mercury methylation is demonstrated to be employed in living biological systems. Therefore, the methylation and dynamic transformations of both ions are monitored in zebrafish by imaging, and these results are confirmed by traditional high‐performance liquid chromatography‐based methods. The methylation of Hg(II) to MeHg, dynamic transformations and final accumulations of both species in zebrafish tissues are visualized successfully. This method is also convenient for fast evaluation of detoxification reagents. This is the first visualization of in vivo mercury methylation and dynamic transformation of both species and is effective for studying pathological processes in their native contexts.