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Yifei Chen 한국콘텐츠학회 2021 ICCC International Digital Design Invitation Exhib Vol.2021 No.8

Minimal Rational Curves on Complete Toric Manifolds and Applications

Chen, Yifei,Fu, Baohua,Hwang, Jun-Muk Cambridge University Press 2014 Proceedings of the Edinburgh Mathematical Society Vol.57 No.1

<B>Abstract</B><P>We show that minimal rational components on a complete toric manifold <I>X</I> correspond bijectively to some special primitive collections in the fan defining <I>X</I>, and the associated varieties of minimal rational tangents are linear subspaces. Two applications are given: the first is a classification of <I>n</I>-dimensional toric Fano manifolds with a minimal rational component of degree <I>n</I>, and the second shows that any complete toric manifold satisfying certain combinatorial conditions on the fan has the target rigidity property.</P>

Study of Harmonic Suppression of Ship Electric Propulsion Systems

Yifei Wang,Youxin Yuan,Jing Chen 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.5

This paper studies the harmonic characteristics of ship electric propulsion systems and their treatment methods. It also adopts effective measures to suppress and prevent ship power systems from affecting ship operation due to the serious damage caused by harmonics. Firstly, the harmonic characteristics of a ship electric propulsion system are reviewed and discussed. Secondly, aiming at problems such as resonant frequency and filter characteristics variations, resonance point migration, and unstable filtering performances in conventional passive filters, a method for fully tuning of a passive dynamic tunable filter (PDTF) is proposed to realize harmonic suppression. Thirdly, to address the problems of the uncontrollable inductance L of traditional air gap iron core reactors and the harmonics of power electronic impedance converters (PEICs), this paper proposes an electromagnetic coupling reactor with impedance transformation and harmonic suppression characteristics (ECRITHS), with the internal filter (IF) designed to suppress the harmonics generated by PEICs. The ECRITHS is characterized by both harmonic suppression and impedance change. Fourthly, the ECRITHS is investigated. This investigation includes the harmonic suppression characteristics and impedance transformation characteristics of the ECRITHS at the fundamental frequency, which shows the good performance of the ECRITHS. Simulation and experimental evaluations of the PDTF are carried out. Multiple PDTFs can be configured to realize multi-order simultaneous dynamic filtering, and can effectively eliminate the current harmonics of ship electric propulsion systems. This is done to reduce the total harmonic distortion (THD) of the supply currents to well below the 5% limit imposed by the IEEE-519 standard. The PDTF also can eliminate harmonic currents in different geographic places by using a low voltage distribution system. Finally, a detailed discussion is presented, with challenges and future implications discussed. The research results are intended to effectively eliminate the harmonics of ship electric power propulsion systems and to improve the power quality of ship power systems. This is of theoretical and practical significance for improving the power quality and power savings of ship power systems.

A Distributed Adaptive Mixed Self-/Event-triggered Formation Control Approach for Multiple Stratospheric Airships with Relative State Constraints and Input Delay

Yifei Zhang,Ming Zhu,Tian Chen,Zewei Zheng 제어·로봇·시스템학회 2023 International Journal of Control, Automation, and Vol.21 No.1

This paper investigates the distributed formation control problem of multiple stratospheric airships in three-dimensional space with several practical problems, such as relative state constraints, input delay, input saturation and disturbances. An adaptive mixed self-/event-triggered formation control scheme is proposed by combining backstepping control, an adaptation technique and a mixed self-/event-triggered control mechanism. First, a novel relative-error-constraint virtual control law is designed based on the barrier Lyapunov function, which is processed into the desired velocity and angular velocity as the input of the next-step designed controller. Then, an adaptive controller is designed based on a designed adaptive law that is utilized to eliminate the influence of external disturbances, input saturation and input delay. In addition, a mixed self-/event-triggered mechanism is designed in the whole system, involving a self-triggered mechanism in the virtual control law and an event-triggered mechanism in the adaptive controller. All signals in the closed-loop system are proven to be semiglobal, uniform and ultimately bounded, and Zeno behavior is proven to be excluded. Finally, the effectiveness of the proposed method is verified through simulations.

Study of Harmonic Suppression of Ship Electric Propulsion Systems

Wang, Yifei,Yuan, Youxin,Chen, Jing The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.5

This paper studies the harmonic characteristics of ship electric propulsion systems and their treatment methods. It also adopts effective measures to suppress and prevent ship power systems from affecting ship operation due to the serious damage caused by harmonics. Firstly, the harmonic characteristics of a ship electric propulsion system are reviewed and discussed. Secondly, aiming at problems such as resonant frequency and filter characteristics variations, resonance point migration, and unstable filtering performances in conventional passive filters, a method for fully tuning of a passive dynamic tunable filter (PDTF) is proposed to realize harmonic suppression. Thirdly, to address the problems of the uncontrollable inductance L of traditional air gap iron core reactors and the harmonics of power electronic impedance converters (PEICs), this paper proposes an electromagnetic coupling reactor with impedance transformation and harmonic suppression characteristics (ECRITHS), with the internal filter (IF) designed to suppress the harmonics generated by PEICs. The ECRITHS is characterized by both harmonic suppression and impedance change. Fourthly, the ECRITHS is investigated. This investigation includes the harmonic suppression characteristics and impedance transformation characteristics of the ECRITHS at the fundamental frequency, which shows the good performance of the ECRITHS. Simulation and experimental evaluations of the PDTF are carried out. Multiple PDTFs can be configured to realize multi-order simultaneous dynamic filtering, and can effectively eliminate the current harmonics of ship electric propulsion systems. This is done to reduce the total harmonic distortion (THD) of the supply currents to well below the 5% limit imposed by the IEEE-519 standard. The PDTF also can eliminate harmonic currents in different geographic places by using a low voltage distribution system. Finally, a detailed discussion is presented, with challenges and future implications discussed. The research results are intended to effectively eliminate the harmonics of ship electric power propulsion systems and to improve the power quality of ship power systems. This is of theoretical and practical significance for improving the power quality and power savings of ship power systems.

Electrokinetic techniques, their enhancement techniques and composite techniques with other processes for persistent organic pollutants remediation in soil: A review

Yuxin Chen,Dan Zhi,Yaoyu Zhou,Anqi Huang,Shikang Wu,Bin Yao,Yifei Tang,Chaoran Sun 한국공업화학회 2021 Journal of Industrial and Engineering Chemistry Vol.97 No.-

Persistent organic pollutants (POPs) in soil have caused widespread concern, which is necessary to developefficientand greentechnologies.Electrokinetic (EK)remediationtechnology,theirenhancementtechniquesand composite techniques with other processes have shown broad application prospects in thefield of soilPOPs remediation. In this paper, the progressof EK remediation technology in the remediation of POPs in soilin recent years is reviewed. It can be seen that some technologies need to be further studied and evaluated,and it is inappropriate to simplycompare them.The effectoffield remediation is boundto be affected byfieldconditions,andthefinal datawill be differentfromthelaboratory data. Some emerging technologies,such asadvanced oxidation technology and nanotechnology, demonstrated high POPs removal rates when coupledwith EK remediation technology. This paper provides some insights into the future development of thetechnology and provides reference for the selection of technology in practical application.

Human Amnion-Derived Mesenchymal Stem Cells Protect Human Bone Marrow Mesenchymal Stem Cells against Oxidative Stress-Mediated Dysfunction via ERK1/2 MAPK Signaling

Ning Chen,Yuli Wang,Junchi Ma,Yifei Du,Jing Miao 한국분자세포생물학회 2016 Molecules and cells Vol.39 No.3

Epidemiological evidence suggests that bone is especial-ly sensitive to oxidative stress, causing bone loss in the elderly. Previous studies indicated that human amnion-derived mesenchymal stem cells (HAMSCs), obtained from human amniotic membranes, exerted osteoprotective effects in vivo. However, the potential of HAMSCs as seed cells against oxidative stress-mediated dysfunction is unknown. In this study, we systemically investigated their antioxidative and osteogenic effects in vitro. Here, we demonstrated that HAMSCs significantly promoted the proliferation and osteoblastic differentiation of H2O2-induced human bone marrow mesenchymal stem cells (HBMSCs), and down-regulated the reactive oxygen species (ROS) level. Further, our results suggest that activation of the ERK1/2 MAPK signal transduction pathway is essential for both HAMSCs-mediated osteogenic and protective effects against oxidative stress-induced dysfunction in HBMSCs. U0126, a highly selective inhibitor of extracellular ERK1/2 MAPK signaling, significantly suppressed the antioxidative and osteogenic effects in HAMSCs. In conclusion, by modulating HBMSCs, HAMSCs show a strong potential in treating oxidative stress- mediated bone deficiency.

Deep Local Multi-level Feature Aggregation Based High-speed Train Image Matching

Jun-Liang Chen,Xiang Li,Yifei Wei,Xiao-jun Wang 한국인터넷정보학회 2022 KSII Transactions on Internet and Information Syst Vol.16 No.5

At present, the main method of high-speed train chassis detection is using computer vision technology to extract keypoints from two related chassis images firstly, then matching these keypoints to find the pixel-level correspondence between these two images, finally, detection and other steps are performed. The quality and accuracy of image matching are very important for subsequent defect detection. Current traditional matching methods are difficult to meet the actual requirements for the generalization of complex scenes such as weather, illumination, and seasonal changes. Therefore, it is of great significance to study the high-speed train image matching method based on deep learning. This paper establishes a high-speed train chassis image matching dataset, including random perspective changes and optical distortion, to simulate the changes in the actual working environment of the high-speed rail system as much as possible. This work designs a convolutional neural network to intensively extract keypoints, so as to alleviate the problems of current methods. With multi-level features, on the one hand, the network restores low-level details, thereby improving the localization accuracy of keypoints, on the other hand, the network can generate robust keypoint descriptors. Detailed experiments show the huge improvement of the proposed network over traditional methods.

Apparatus for producing a 168Er Bose–Einstein condensate

Seo Bojeong,Chen Ziting,Huang Mingchen,Parit Mithilesh K.,He Yifei,Chen Peng,Jo Gyu-Boong 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.82 No.9

We report on the experimental realization of Bose–Einstein condensate (BEC) of 168Er atoms with tunable s-wave and dipolar interactions in a newly developed apparatus. Here, we describe an efcient method for trapping slow Er atoms in a narrow linewidth magneto-optical trap. After evaporative cooling in a crossed optical dipole trap, we achieve a spin-polarized condensate of > 2.5 × 104 atoms at the temperature of T ≃ 50 nK. The efcient preparation of ultracold erbium bosons ofers new possibilities for studying many-body physics with dipolar interactions.

Study on the Mechanical Properties of Functional Graphene/Polyethylene Composites by Molecular Dynamics Simulation

Yuanyuan Qin,Yifei Wang,Jin Liu,Fengfeng Chen,Aiying Yao,Zhanchun Chen,Fu Junyu 한국고분자학회 2022 Macromolecular Research Vol.30 No.12

The mechanical properties of functionalized graphene/polyethylene (f- GRA/PE) composites and graphene/polyethylene (GRA/PE) composites were studied based on the crystallized models with the molecular dynamics simulation in this paper. The effects of GRA and f-GRA with different mass fractions on the mechanical properties of polyethylene were considered. The results showed that the adsorption capacity of polyethylene molecular chains of f-GRA is stronger, the compatibility of f-GRA/PE system is higher with decreasing the interface distance, and the dynamic property of molecular chain is weaker with reducing the radius of gyration of f-GRA/ PE. Furthermore, the reduction of mechanical energy consumption results in the increase of wear resistance of the system, which is more obvious when the mass fraction of f-GRA increases. Finally, the influence of different tensile rates on the composite system was studied. It was found that during the tensile process, the ability of the composite material to resist deformation in the stretching direction is enhanced, and the functionalized graphene inhibits the movement of the molecular chain due to the adsorption force, which improves the yield stress of the f-GRA/PE composite material, thereby increasing the tensile strength. Tensile rate has a certain effect on mechanical properties, and elastic modulus and yield stress increase with the increase of strain rate.