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Yuming Qi,Tengwu He,Miaolin Feng 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.7
Adding nanotwins to a metal could be a way to effectively improve its strength without suppressing its tensile ductility, whichsuggests that their unique nanostructure may alter microstructure evolution and deformation mechanisms. In this work, weperform a molecular dynamics-based tension simulation of two-dimension (2D) polycrystalline copper (Cu) with embeddednanotwins under uniaxial stress conditions. The results of MD-simulation reveal that the spacing of the twin boundarieshad a significant effect on the mechanical properties of nanotwinned materials. Specifically, an irregular relationship isfound between the twin boundary spacing ( DT ) and the strength of the material. It exhibits that the peak stress reached amaximum at DT = 12.5 nm and decreased thereafter with increasing average DT . However, flow stress reaches a maximumat a critical value of DT = 7 nm. According to the analysis of microstructure evolution, the presence of nanotwins hinder themotion of partial dislocations and stacking faults, and the stress-concentrated region leads to the transition from coherenttwin boundaries to incoherency. The stress-concentrated region locates in the step of incoherent would release the intrinsicstacking faults responsible for the formation of hierarchical contraction nanotwins stacking faults which efficiently improvesthe strength of Cu. In addition, as the tension proceeds, some samples begin to display the secondary twinning. This workwill be helpful for further investigation the nucleation and evolution of 2D nanotwinned metals and for formulating effectivestrength criteria for 2D nanotwinned metals.
Synergistic Effect of Copper and Cobalt in Cu-Co-O Composite Nanocatalyst for Catalytic Ozonation
Yuming Dong,Lina Wu,Guangli Wang,Hui Zhao,Pingping Jiang,Cuiyun Feng 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.11
A novel Cu-Co-O composite nanocatalyst was designed and prepared for the ozonation of phenol. A synergistic effect of copper and cobalt was observed over the Cu-Co-O composite nanocatalyst, which showed higher activity than either copper or cobalt oxide alone. In addition, the Cu-Co-O composite revealed good activity in a wide initial pH range (4.11-8.05) of water. The fine dispersion of cobalt on the surface of copper oxide boosted the interaction between catalyst and ozone, and the surface Lewis acid sites on the Cu-Co-O composite were determined as the active sites. The Raman spectroscopy also proved that the Cu-Co-O composite was quite sensitive to the ozone. The trivalent cobalt in the Cu-Co-O composite was proposed as the valid state.
Synergistic Effect of Copper and Cobalt in Cu-Co-O Composite Nanocatalyst for Catalytic Ozonation
Dong, Yuming,Wu, Lina,Wang, Guangli,Zhao, Hui,Jiang, Pingping,Feng, Cuiyun Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.11
A novel Cu-Co-O composite nanocatalyst was designed and prepared for the ozonation of phenol. A synergistic effect of copper and cobalt was observed over the Cu-Co-O composite nanocatalyst, which showed higher activity than either copper or cobalt oxide alone. In addition, the Cu-Co-O composite revealed good activity in a wide initial pH range (4.11-8.05) of water. The fine dispersion of cobalt on the surface of copper oxide boosted the interaction between catalyst and ozone, and the surface Lewis acid sites on the Cu-Co-O composite were determined as the active sites. The Raman spectroscopy also proved that the Cu-Co-O composite was quite sensitive to the ozone. The trivalent cobalt in the Cu-Co-O composite was proposed as the valid state.
Observer Design for A Class of Uncertain State-Delayed Nonlinear Systems
Junwei Lu,Chunmei Feng,Shengyuan Xu,Yuming Chu 대한전기학회 2006 International Journal of Control, Automation, and Vol.4 No.4
This paper deals with the observer design problem for a class of state-delayed nonlinear systems with or without time-varying norm-bounded parameter uncertainty. The nonlinearities under consideration are assumed to satisfy the global Lipschitz conditions and appear in both the state and measured output equations. The problem we address is the design of a nonlinear observer such that the resulting error system is globally asymptotically stable. For the case when there is no parameter uncertainty, a sufficient condition for the solvability of this problem is derived in terms of linear matrix inequalities and the explicit formula of a desired observer is given. Based on this, the robust observer design problem for the case when parameter uncertainties appear is considered and the solvability condition is also given. Both of the solvability conditions obtained in this paper are delay-dependent. A numerical example is provided to demonstrate the applicability of the proposed approach.
Molecular dynamics simulation of primary irradiation damage in Ti-6Al-4V alloys
Tengwu He,Xipeng Li,Yuming Qi,Min Zhao,Miaolin Feng Korean Nuclear Society 2024 Nuclear Engineering and Technology Vol.56 No.4
Displacement cascade behaviors of Ti-6Al-4V alloys are investigated using molecular dynamics (MD) simulation. The embedded atom method (EAM) potential including Ti, Al and V elements is modified by adding Ziegler-Biersack-Littmark (ZBL) potential to describe the short-range interaction among different atoms. The time evolution of displacement cascades at the atomic scale is quantitatively evaluated with the energy of primary knock-on atom (PKA) ranging from 0.5 keV to 15 keV, and that for pure Ti is also computed as a comparison. The effects of temperature and incident direction of PKA are studied in detail. The results show that the temperature reduces the number of surviving Frenkel pairs (FPs), and the incident direction of PKA shows little correlation with them. Furthermore, the increasing temperature promotes the point defects to form clusters but reduces the number of defects due to the accelerated recombination of vacancies and interstitial atoms at relatively high temperature. The cluster fractions of interstitials and vacancies both increase with the PKA energy, whereas the increase of interstitial cluster is slightly larger due to their higher mobility. Compared to pure Ti, the presence of Al and V is beneficial to the formation of interstitial clusters and indirectly hinders the production of vacancy clusters.
Light-induced negative differential resistance effect in a resistive switching memory device
Xiaojun Wang,Yuanyang Wang,Ming Feng,Kaiyue Wang,Pinbo Bai,Yuming Tian 한국물리학회 2020 Current Applied Physics Vol.20 No.3
The negative differential resistance (NDR) effect was observed in a Pt/BiFeO3/TiO2/BiFeO3/Pt memory cell by using light-illumination as extra stimulation. Further, the coexistence appearances and gradually becomes obvious when the device is exposed to light-illumination, which display an excellent stability and reversibility of the coexistence of NDR and resistive switching (RS) at room temperature. Through analysis of the physical conduction mechanism, it is expected that a large number of photo-generated charge carriers are induced under light-illumination on the surface and interface of the heterojunction is responsible for the appearance of this coexistence phenomenon. Importantly, the NDR effect is strengthened by the competition transfer of charge carrier in the polarized electric field under light-illumination. This work shows that the coexistence of lightmodulated NDR and RS can deeply explore the potential applications of light-controlled multifunctional devices.