Effects of Tearing Conditions on the Crack Propagation in a Monolayer Graphene Sheet

The path of crack propagation in a graphene sheet is significant for graphene patterning via the tearing approach. In this study, we evaluate the fracture properties of pre-cracked graphene during the tearing process, with consideration of the effects of the aspect ratio, loading speed, loading direction, and ambient temperatures on the crack propagation in the monolayer sheet. Some remarkable conclusions are drawn based on the molecular dynamic simulation results, i.e., a higher loading speed may result in a complicated path of crack propagation, and the propagation of an armchair crack may be accompanied by sp carbon links at high temperatures. The reason for this is that the stronger thermal vibration reduces the load stress difference near the crack tip and, therefore, the crack tip can pass through the sp link. A crack propagates more easily along the zigzag direction than along the armchair direction. The out-of-plane tearing is more suitable than the in-plane tearing for graphene patterning. The path of crack propagation can be adjusted by changing the loading direction, e.g., a rectangular graphene ribbon can be produced by oblique tearing. This new understanding will benefit the application of graphene patterning via the tearing approach.     

Formation of hierarchical Si3N4 foams by protein-based gelcasting and chemical vapor infiltration

Silicon nitride foams with a hierarchical porous structure was formed by the combination of protein-based gelcasting,chemical vapor infiltration,and in-situ growth of silicon nitride nanowires.The porosity of the foams can be controlled at 76.3-83.8 vol%with an open porosity of 70.2—82.8 vol%.The pore size distribution was presented in three levels:<2μm(voids among grains and cross overlapping of silicon nitride nanowires(SNNWs)),10—50μm(cell windows),and>100μm(cells).The resulted compressive strength of the porous bodies at room temperature can achieve up to 18.0±1.0 MPa(porosity=76.3 vol%)while the corresponding retention rate at 800℃was 58.3%.Gas permeability value was measured to be 5.16(cm³·cm)/(cm²·s·kPa).The good strength,high permeability together with the pore structure in multiple scales enabled the foam materials for microparticle infiltration applications.     

Blue Luminescence of ZnO Nanoparticles Based on Non‐Equilibrium Processes: Defect Origins and Emission Controls

High concentrations of defects are introduced into nanoscale ZnO through non‐equilibrium processes and resultant blue emissions are comprehensively analyzed, focusing on defect origins and broad controls. Some ZnO nanoparticles exhibit very strong blue emissions, the intensity of which first increase and then decrease with annealing. These visible emissions exhibit strong and interesting excitation dependences: 1) the optimal excitation energy for blue emissions is near the bandgap energy, but the effective excitation can obviously be lower, even 420 nm (2.95 eV < E_g = 3.26 eV); in contrast, green emissions can be excited only by energies larger than the bandgap energy; and, 2) there are several fixed emitting wavelengths at 415, 440, 455 and 488 nm in the blue wave band, which exhibit considerable stability in different excitation and annealing conditions. Mechanisms for blue emissions from ZnO are proposed with interstitial‐zinc‐related defect levels as initial states. EPR spectra reveal the predominance of interstitial zinc in as‐prepared samples, and the evolutions of coexisting interstitial zinc and oxygen vacancies with annealing. Furthermore, good controllability of visible emissions is achieved, including the co‐emission of blue and green emissions and peak adjustment from blue to yellow.     

Effect of electrode change on solidification of slag and metal pool profile in electroslag remelting process

A two-dimensional axisymmetric model is established to study the effect of electrode change on the solidification of slag and metal pool profile during electros...     

脚踝康复受力测量电路的设计

通过分析脚踝康复受力间接测量原理,基于MSP430单片机设计出一种脚踝康复受力测量电路,进行了脚踝康复受力测量实验,实验证明脚踝康复受力测量电路实现踝关节康复力和力矩的间接测量,为踝关节安全康复提供了指导性数据,便于患者自主控制康复强度,提高了康复效果。     

Improved ant colony optimization algorithms for determining project critical paths

In project management, a project can be represented as a network in two ways; namely, activity-on-arc (AoA) and activity-on-node (AoN). Two recent papers have shown that ant colony optimization (ACO) could find critical path(s) in projects represented as AoA networks. This paper points out that the number and placement of logical dummy activities associated with AoA-based networks can pose serious problems. To get around the problems, an ACO technique based on AoN networks is then proposed. For comparison, the two existing AoA-based ACO algorithms were reproduced and modified into AoN-based algorithms. Moreover, the proposed ACO algorithm was applied to AoA networks as well. All six algorithms were tested with several benchmark problems. The test results strongly indicate that AoN-based ACO algorithms are more effective and efficient in finding critical paths than AoA-based algorithms.     

变电站防误闭锁系统的应用现状

对防误闭锁方式的优缺点及防误闭锁系统的现状及发展等进行分析研究,提出电力企业的防误操作对策。     

大学英语阅读与写作教学评价量规的制定与应用

评价量规已经成为语言教学评价中一种有效的工具,它有助于帮助教师向学生阐明学习目标和任务,并向学生提供有效的反馈信息.本文着重介绍了大学英语教学中阅读和写作的评价量规的制定,并阐述了在制定量规时应该遵守的原则.