关键词： Two dimensional materials   Chemical structure   Oxygen   Plasma   Defects  

摘要： Bilayer graphene (BG) may achieve better optoelectronic and sensing applications after modification due to its direct induced band gap and better plasma processing stability. Defect engineering based on oxygen plasma treatment has been proved to be an effective method to achieve the modification of graphene. Understanding the formation and evolution of graphene defects, which cannot be observed directly by the experiment, can help achieve more precise and controllable modification of graphene. Here, we investigate the effect of oxygen plasma treatment on the structure and mechanical properties of BG by molecular dynamics simulations. We report two mechanisms of BG destruction by oxygen plasma: direct sputtering and cascade sputtering. When the defects are mainly sp(3) defects, we report that the elastic modulus is strongly related to oxygen density, and it decreases by only about 16% at low oxygen density (3.92 x 10(21) atoms(center dot) cm(-3)). In contrast, the mechanical properties of BG decrease more significantly when vacancy defects are predominant. Based on the formation and evolution of sp3 defects and vacancy defects, we establish the relationship between defect types and the mechanical properties of BG. This study makes it possible to precisely control the graphene structure for optoelectronic and sensing applications.

关键词： Aqueous sulfide oxidation   catalytic oxidation   mechanistic approach   reaction kinetics   Fenton-like reaction  

摘要： In this study, the kinetics and mechanism of the reaction of sulfide oxidation catalyzed by hydrocarbon solution of 3,3 ', 5,5 '-tetra-tert-butyl-stilbenequinone have been deeply investigated. The reaction is of the first order with respect to each of the reagents. The molecular mechanism of catalysis was discussed, in which elemental sulfur was produced at intermediate stages during transformation of sulfide to sulfate. The algebraic equations describing the transition of catalytic reaction from the diffusion region to the kinetic region were established. The formation of strong reactive oxygen species during the catalyst generation not only plays an extremely important role in the oxidation reaction catalyzed by stilbenequinone, but also paves the way for the development of an advanced catalyst system based on the Fenton reaction. A preliminary survey of advanced catalyst system activity based stilbenequinone/Fe (II)/O-2 has been conducted for oxidative degradation of sulfide.

关键词： chemical mechanical polishing   molecular dynamics simulation   diamond   OH radical   graphitization   friction  

摘要： Ultraflat and damage-free single-crystal diamond is a promising material for use in electronic devices such as field-effect transistors. Diamond surfaces are conventionally prepared by the chemical mechanical polishing (CMP) method, although the CMP efficiency remains a critical issue owing to the extremely high hardness of diamond. Recently, OH radicals have been demonstrated to be potentially useful for improving the CMP efficiency for diamond;however, the underlying mechanisms are still elusive. In this work, we applied our previously developed CMP-specialized tight-binding quantum chemical molecular dynamics simulator to comprehensively elucidate the CMP mechanisms of diamond assisted by OH radicals. Our simulation results indicate that the diamond surface is oxidized by reactions with OH radicals and then a concomitant surface reconstruction takes place due to the distorted and unstable nature of the oxidized diamond surface structure. Furthermore, we interestingly reveal that the reconstruction of the diamond surface ultimately leads to two distinct removal mechanisms: (i) gradual atom-by-atom removal through the desorption of gaseous molecules (e.g., CO2 and H2CO3) and (ii) drastic sheet-by-sheet removal through the exfoliation of graphitic ring structures. Hence, we propose that promoting the oxidation-induced graphitization of the diamond surface may provide a route to further improving the CMP efficiency.

关键词： Advanced oxidation processes   Hydrodynamic cavitation   Heterogeneous photo-Fenton reagent   Persulfate reagent   Density functional theory  

摘要： The present study has addressed carbamazepine (CBZ) degradation by hybrid advanced oxidation system of hydrodynamic cavitation (HC) assisted UV/persulfate with composite ZnO/ZnFe2O4 particles. This hybrid system is comprised of several parallel pathways for generation of both center dot OH and SO4 center dot- radicals. 98.13 +/- 1.03% CBZ degradation was obtained at optimum operational conditions: inlet pressure = 9 atm, pH = 4, initial concentration of CBZ = 15 mg/L, UV power = 18 W, Na2S2O8 = 500 mg/L, ZnO/ZnFe2O4 = 500 mg/L. HC alone resulted in 7.70% degradation of CBZ, while the binary HC + Na2S2O8 system resulted in markedly high degradation of 65.73%. Composite ZnO/ZnFe2O4 particles had dual characteristics, viz. photocatalytic activity and a source of Fe2+/Fe3+ ions released through surface leaching. Relative contributions of (OH)-O-center dot and SO4 center dot- radicals to CBZ degradation were identified through permutation-combination of different oxidation systems. Thermodynamic and kinetic behaviors of reactions of CBZ with (OH)-O-center dot and SO4 center dot- radicals were analyzed using density functional theory (DFT) at B3LYP/6-31 g(d) level. Single electron transfer (SET) between CBZ and SO4 center dot- was the primary (and thermodynamically favorable) reaction pathway in initiation of degradation. Degradation intermediates revealed ionization of CBZ through SET before hydroxylation and oxidation - which was corroboration of DFT simulations.

关键词： 南京理工大学   麦吉尔大学   机械系统动力学   阿伯丁大学  

摘要： 为推动机械系统动力学相关的理论、模型、计算、分析、软件、设计、控制、制造、测试和评估等领域的发展,来自南京理工大学、加拿大麦吉尔大学、英国阿伯丁大学、德国锡根大学等10个国家的20所大学共同组织发起常设机械系统动力学国际会议(the Standing International Conference on Mechanical System Dynamics,ICMSD)。

关键词： 上下料机械手   并联机构   运动学分析   动力学方程   仿真验证  

摘要： 为提高集装箱折弯板材上下料的效率,提出一种新型上下料机械手。该机械手采用2-P(Pa)并联机构与抓取机构相结合的结构,实现了折弯工序对板材的快速搬运。文中介绍了集装箱角柱折弯的加工工艺与新型机械手的结构组成,建立了并联机构的位置方程,利用解析法推导出了并联机构的位置正反解、末端执行机构的速度与加速度方程,为动力学分析奠定基础。利用拉格朗日方程建立了机械手的动力学方程并进行了实例仿真验证。验证结果表明:理论驱动力值与仿真驱动力值误差较小,说明所建立的机构运动学模型及动力学模型的正确性,为机械手后续的动载分配优化及系统控制提供了理论指导。

关键词： SiC(CNT)   Al multiphase interfacial micro-zone   Molecular dynamics   Interfacial characteristics   Mechanical deformation   Failure behavior  

摘要： Developing metal matrix composites (MMCs) with hybrid reinforcements becomes a promising approach to balance and improve their strengths and toughness. However, due to complexity of multiphase interfacial microzones and lack of suitable research method, difficulties are still existing in revealing the structure-property relationship of hybrid MMCs. In this work, molecular dynamics simulations are conducted to study microstructural characteristics and mechanical behavior of SiC(CNT)/Al multiphase interfacial micro-zones under uniaxial tensions. Six atomic-scale structural models of SiC/Ni/CNT, SiC/Al, SiC/Ni/CNT(l)/Al, SiC/CNT(l)/Al SiC/Ni/CNT(s)/Al and SiC/CNT(s)/Al (l: long, s: short) interfacial micro-zones are created, respectively. Compared with those of SiC/Al interfacial micro-zone, improved tensile ductility and toughness are achieved in the SiC/Ni/CNT(l)/Al, SiC/CNT(l)/Al, SiC/Ni/CNT(s)/Al and SiC/CNT(s)/Al interfacial micro-zones, where lots of dislocations, larger dislocation densities and continuously increasing equivalent shear strains appear. SiC/Ni/ CNT(l)/Al and SiC/CNT(l)/Al interfacial micro-zones with long CNT clusters could produce large Young's modulus, while those of SiC/Ni/CNT(s)/Al and SiC/CNT(s)/Al interfacial micro-zones are relatively low caused by poorly load-transferring. Tensile fracture of SiC/Al interfacial micro-zone occurs at the SiC/Al interface due to the local concentrations of both dislocations and plastic deformation, while those of SiC/Ni/CNT(l)/Al, SiC/CNT (l)/Al SiC/Ni/CNT(s)/Al and SiC/CNT(s)/Al interfacial micro-zones all happen in the Al matrix close to the bottom ends of CNTs and SiC. From the analysis above, the microstructural characteristics and mechanical behavior of SiC(CNT)/Al multiphase interfacial micro-zones can be brought into light, which would be applied to design and fabricate smart multiphase MMCs.

关键词： Fe-based amorphous–crystalline composite   Nanoindentation   Molecular dynamics simulation   Mechanical property  

摘要： A new Fe-based amorphous–crystalline composite without non-metallic elements, Fe_(55)Cr_(15)Mo_(15)Ni_(10)W_(5), was prepared by melt-spinning. The formation ability and structure information were investigated by X-ray diffractometer(XRD), energy-dispersive spectrometer(EDS) and scanning electron microscope(SEM). The mechanical properties of the amorphous–crystalline composite were investigated by nanoindentation. A molecular dynamics simulation study was performed to simulate the formation of Fe_(55)Cr_(15)Mo_(15)Ni_(10)W_(5) amorphous alloy. The mechanical properties were obtained by compression simulations simultaneously. The results indicate that the Fe_(55)Cr_(15)Mo_(15)Ni_(10)W_(5) ribbon is an amorphous–crystalline composite structure with good ductility, and the hardness of the amorphous–crystalline composite is about 75%higher than that of master ingot. The simulation mechanical properties are in good agreement with the results of nanoindentation at the nanoscale.

关键词： 电机械制动   自抗扰   制动力闭环   内燃机车  

摘要： 本文针对内燃机车空气制动系统体积大,结构复杂,响应时间慢等缺点,将电机械制动系统应用于内燃机车,并将自抗扰控制技术(active disturbance rejection controller,ADRC)运用于制动力闭环控制。结合电流传感器采集到的反馈电流和编码器位置信号,实现了对列车机械摩擦制动力精确调节。最终基于TI公司的TMS320F28335芯片进行软硬件设计,将控制算法集成到电子制动控制单元,完成了电机械制动系统硬件在环测试,验证了控制算法性能。

关键词： Uncertainty analysis   Interval parameters   Surrogate model   Hilbert-Huang transform (HHT)   Local mean decomposition (LMD)   Multibody dynamics  

摘要： Studying multibody dynamic systems, a common way to evaluate the effects of uncertainty parameters is the response surface method, which works by building a polynomial surro -gate model at each time instant through a set of input and corresponding output responses. However, a dynamic response always becomes a more and more complicated function of uncertainty parameters with the increase of time;as a result, the fitted surrogate model often fails to provide an accurate approximation at later time instants. This paper suggests that a dynamic response is composed of several vibration components and one trend com-ponent. Therefore, it is better to decompose the response into its multiple components, and then fit the amplitude and phase of each vibration component, as well as the trend compo-nent, using polynomial functions. By combining the response surface method with signal decomposition techniques, such as Hilbert-Huang transform and local mean decomposi-tion, this study proposes a novel methodology to develop a high-accuracy surrogate model for interval uncertainty analysis. The proposed methodology will degenerate to the con-ventional response surface method when the dynamic response is a trend component. Three mechanical systems-a Duffing oscillator, a single pendulum and a slider-crank model-are used to confirm the effectiveness of the proposed methodology. This method-ology provides a new technical pathway to improve the accuracy of dynamical uncertainty analysis. (c) 2021 Elsevier Ltd. All rights reserved.