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BiFeO3 Thickness Dependence of the Exchange Bias in Polycrystalline BiFeO3/NiFe Bilayers
Xiaobo Xue,Biao You,Wenbing Rui,Wei Zhang,Jun Du,Xueyong Yuan,Qingyu Xu 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
A clear exchange bias has been observed at room temperature in a series of BiFeO3(t)/NiFe(3.6nm) bilayers, in which the BiFeO3 layers are single-phase polycrystalline with t varied from 8 nmto 240 nm. With increasing t, both the exchange bias field (HE) and the coercivity (HC) increasesharply and approach maxima when t is about 40 nm, which is close to one half the spin cycloidalmodulation period (64 nm) of the bulk BiFeO3 material. The oscillatory variations of HE and HCwith the BiFeO3 layer thickness suggest that the cycloidal spin structure may exist in polycrystallineBiFeO3 thin films. The angular dependence of the exchange bias exhibits collinear unidirectionaland uniaxial anisotropies in the present BiFeO3/NiFe bilayers.
Optical and acoustic metamaterials: superlens, negative refractive index and invisibility cloak
Wong, Zi Jing,Wang, Yuan,O’Brien, Kevin,Rho, Junsuk,Yin, Xiaobo,Zhang, Shuang,Fang, Nicholas,Yen, Ta-Jen,Zhang, Xiang IOP 2017 Journal of optics Vol.19 No.8
<P>Metamaterials are artificially engineered materials that exhibit novel properties beyond natural materials. By carefully designing the subwavelength unit cell structures, unique effective properties that do not exist in nature can be attained. Our metamaterial research aims to develop new subwavelength structures with unique physics and experimentally demonstrate unprecedented properties. Here we review our research efforts in optical and acoustic metamaterials in the past 15 years which may lead to exciting applications in communications, sensing and imaging.</P>
Jing Li,Jian Wu,Xiguo Yuan,Xiaobo Li,Liefu Ai 제어·로봇·시스템학회 2017 International Journal of Control, Automation, and Vol.15 No.1
This paper considers the problem of the global finite-time stabilization for the high-order nonlinear systemswith unknown control directions. Due to the uncertainty of control directions, the paper analyzes all possibleconditions of the directions. The Lyapunov-based logic switching rule ensures that we can find the correct controldirections. The adaptive switching controller with a switching parameter which is to be tuned online guarantees thatthe derivative of Lyapunov function is less than a negative definite function and the closed-loop system is globallyfinite-time stable. The effectiveness of the proposed method is illustrated by an example.
Wang Wenjie,Han Zhenhua,Pei Jin,Pavesi Giorgio,Gong Xiaobo,Yuan Shouqi 한국CDE학회 2023 Journal of computational design and engineering Vol.10 No.1
To reduce the energy consumption of large centrifugal pumps, modified heuristic intelligent algorithms are used to directly optimize the diffuser of centrifugal pumps. Considering the hydraulic efficiency under the design condition as the optimization target, in this study, 14 geometric parameters such as the inlet diameter, outlet diameter, and leading and trailing vane angles of the diffuser are selected as design variables, and the modified particle swam optimization and gravitational search algorithm are used to directly search for optimization in the design space. The performance and loss of internal entropy production of the different models before and after optimization are compared and analyzed in detail. The results show that the global optimization ability of the modified algorithm is improved. The diffuser model changes from cylindrical to twisted, the vane wrap angle increases, and the thickness of the leading edge decreases. Under the design condition, the efficiency of modified particle swarm optimization algorithm solution is increased by 2.75% and modified gravitational search algorithm solution by 2.21%, while the power remains unchanged. Furthermore, the optimization solution has the largest lift efficiency improvement under part-load conditions. After optimization, the unstable flow in the model is improved and internal entropy production loss is reduced significantly. The interior of the diffuser is dominated by turbulent entropy production and direct entropy production under different operating conditions, and the wall entropy production accounts for the smallest proportion.
Liang Rundong,Zhao Xiuwen,Hu Guichao,Yue Weiwei,Yuan Xiaobo,Ren Junfeng 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.77 No.7
InSe-based van der Walls heterostructures (vdWHs) have attracted research interests recently because of their particular properties. In this work, the electronic structure and the optical properties of Mn-doped InSe/WSe2 vdWHs are investigated by using first-principles calculations. Mn doping in InSe/WSe2 vdWHs induces an increase in the system's band gap. The optical properties of the vdWHs are also studied, and the absorption intensity of Mn-doped InSe/WSe2 is found to be enhanced in the near-infrared and ultraviolet regions. In addition, built-in electric fields are generated in InSe/WSe2 and Mn-doped InSe/WSe2, which can inhibit recombination of photogenerated electron-hole pairs. This work predicates the feasibility of enhancing the optical properties in InSe/WSe2 vdWHs by introducing dopants, which extends the applications of InSe materials in the field of optoelectronics.