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Xu, Hongtao,Wu, Changjin,Xiahou, Zhao,Jung, Ranju,Li, Ying,Liu, Chunli Springer US 2017 Nanoscale research letters Vol.12 No.1
<P>Five percent of Fe-doped ZnO (ZnO:Fe) thin films were deposited on Pt/TiO<SUB>2</SUB>/SiO<SUB>2</SUB>/Si substrates by a spin-coating method. The films were annealed without (ZnO:Fe-0T) and with a pulsed magnetic field of 4 T (ZnO:Fe-4TP) to investigate the magnetic annealing effect on the resistance switching (RS) behavior of the Pt/ZnO:Fe/Pt structures. Compared with the ZnO:Fe-0T film, the ZnO:Fe-4TP film showed improved RS performance regarding the stability of the set voltage and the resistance of the high resistance state. Transmission electron microscopy and X-ray photoelectron spectroscopy analyses revealed that the ZnO:Fe-4TP film contains more uniform grains and a higher density of oxygen vacancies, which promote the easier formation of conducting filaments along similar paths and the stability of switching parameters. These results suggest that external magnetic fields can be used to prepare magnetic oxide thin films with improved resistance switching performance for memory device applications.</P>
JUN WAN,Hongtao Wu,Rui Ma,Liang'an Zhang 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.3
A general method is presented for the inverse kinematics resolution of redundant manipulators with joint limits. The success of avoiding joint angular position limits of the original clamping weighted least-norm method is ascribable to the strength of the repulsive potential field function. However, the repulsive potential field function may lead to excessive joint angular velocities that can exceed the corresponding limits. We propose an improved clamping weighted least-norm method that adds an elastic field function into the original method for the sake of sustaining the constraints of joint angular velocity limits. Moreover, for hierarchical task-level construction, the priority of avoiding joint angular velocity limits is lower than that of avoiding joint angular position limits. To adequately illustrate the effectiveness of the proposed method, case studies were performed in comparison with other methods in singular configurations of a redundant manipulator.
Fengyu Xu,Xingsong Wang,Hongtao Wu 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.3
A nondestructive testing technique based on magnetic flux leakage is presented to inspect automatically the stay cables with large diameters of a cable-stayed bridge. Using the proposed inspection method, an online nondestructive testing (NDT) modular sensor is developed. The wreath-like sensor is composed of several sensor units that embrace the cable at equal angles. Each sensor unit consists of two permanent magnets and a hall sensor to detect the magnetic flux density. The modular sensor can be installed conveniently on cables with various diameters by increasing the number of sensor units and adjusting the relative distances between adjacent sensor units. Results of the experiments performed on a man-made cable with faults prove that the proposed sensor can inspect the status signals of the inner wires of the cables. To filter the interfering signals, three processing algorithms are discussed, including the moving average method,improved detrending algorithm, and signal processing based on a digital filter. Results show that the developed NDT sensor carried by a cable inspection robot can move along the cable and monitor the state of the stay cables.
A review of the transmission tower-line system performance under typhoon in wind tunnel test
Xianying Li,Yu Yao,Hongtao Wu,Biao Zhao,Bin Chen,Tao Yi 한국풍공학회 2019 Wind and Structures, An International Journal (WAS Vol.29 No.2
As a regenerated turbulent wind field process, wind tunnel test has proven to be a promising approach for investigating the transmission tower-line system (TTLS) performance in view of experimental scaled models design, simulation techniques of wind field, and wind induced responses subjected to typhoon. However, the challenges still remain in using various wind tunnels to regenerate turbulent wind field with considerable progress having been made in recent years. This review paper provides an overview of the state-of-the-art of the wind tunnel based on active or passive controlled simulation techniques. Specific attention and critical assessment have been given to: (a) the design of experimental scaled models, (b) the simulation techniques of wind field, and (c) the responses of TTLS subjected to typhoon in wind tunnel. This review concludes with the research challenges and recommendations for future research direction.
Yao Li,XiaoLong Yang,Hongtao Wu,Bai Chen 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.1
A six-axis vibration isolation system is essential to high-precision space systems for attenuating vibrations on precise instruments. The kinematic optimal design is researched for the space six-axis vibration isolator via Stewart mechanism. Jacobian matrix is the basis of the kinematic performance index. However, the conventional Jacobian matrix is not usually dimensionally homogeneous due to the inhomogeneous physical units, caused by the different mathematical representations of the rotation and translation. In this paper, we propose a dual quaternion approach to derive the dimensionally homogeneous Jacobian matrix of a general six-axis parallel mechanism. Two quaternions are used to parameterize the rotation and translation of the platform. The dimensionally scaling factor for the generalized Jacobian matrix is defined as the ratio of the norms of the two quaternions. The dimensionally homogenous Jacobian matrix is then obtained and applied to the optimal design of the six-axis vibration isolator. The performance index of isotropy is considered to make the isolator minimum kinematic coupling in its working configuration.
Fractional order viscoelasticity in characterization for atrial tissue
Jing Jin Shen,Cheng Gang Li,Hongtao Wu,Masoud Kalantari 한국유변학회 2013 Korea-Australia rheology journal Vol.25 No.2
Atrial tissue due to its solid-like and fluid-like constituents shows highly viscoelastic properties. Up to now, the distribution pattern of muscle fiber in heart is not well established, and it is hard to establish the constitutive model for atrial tissue completely based on the microstructure level. Consider the equivalence between the fractional viscoelasticity and the fractal spring-dashpot model, a generalized fractional order Maxwell model is proposed to model the porcine atrial tissue in the phenomenological sense. This model has a simple expression and intuitively physical meanings. The constitutive parameters in the model are estimated in the complex domain by a genetic algorithm. Final results illustrate the proposed model gets a well agreement with the experimental data.
A New Model-free Robust Adaptive Control of Cable-driven Robots
Yaoyao Wang,Lufang Liu,Mingxing Yuan,Qingxun Di,Bai Chen,Hongtao Wu 제어·로봇·시스템학회 2021 International Journal of Control, Automation, and Vol.19 No.9
For high performance control of cable-driven robots, a new model-free robust adaptive control is proposed using adaptive proportional-integral-derivative nonsingular fast terminal sliding mode (PID-NFTSM) in this paper. The designed control scheme has three elements, which are time-delay estimation (TDE) and a new PIDNFTSM manifold and a combined adaptive reaching law. The TDE element is applied to achieve the lumped system dynamics and hence founds a practical model-free structure. Meanwhile, a new PID-NFTSM manifold is designed to inherit the advantages of the NFTSM and high-order SM (HOSM) and integral SM (ISM) controls. Because of this design, the PID-NFTSM manifold can effectively ensure the non-singularity and high comprehensive control performance. Then, by combining the fast-TSM-type reaching law and a constant speed one with adaptive gain, we design a new combined adaptive reaching law for performance reinforcement. Benefiting from above three parts, our proposed control is model-free, highly precise and strongly robust. Stability is analyzed using Lyapunov theory. The effectiveness of our control is proved by comparative simulation studies. For high performance control of cable-driven robots, a new model-free robust adaptive control is proposed using adaptive proportional-integral-derivative nonsingular fast terminal sliding mode (PID-NFTSM) in this paper. The designed control scheme has three elements, which are time-delay estimation (TDE) and a new PIDNFTSM manifold and a combined adaptive reaching law. The TDE element is applied to achieve the lumped system dynamics and hence founds a practical model-free structure. Meanwhile, a new PID-NFTSM manifold is designed to inherit the advantages of the NFTSM and high-order SM (HOSM) and integral SM (ISM) controls. Because of this design, the PID-NFTSM manifold can effectively ensure the non-singularity and high comprehensive control performance. Then, by combining the fast-TSM-type reaching law and a constant speed one with adaptive gain, we design a new combined adaptive reaching law for performance reinforcement. Benefiting from above three parts, our proposed control is model-free, highly precise and strongly robust. Stability is analyzed using Lyapunov theory. The effectiveness of our control is proved by comparative simulation studies.