This paper studies the active fault-tolerant control (FTC) problem for nonidentical high-order multi-agent systems, in the presence of actuator faults and network disconnections. The follower agents ...are enabled to track the output of a leader agent in faulty cases, by performing output feedback actuator fault compensations and distributed accommodations of network disconnections. In view of nonidentical nonlinearities, a high-gain observer like-protocol and a cooperative FTC controller are presented, with a synchronization condition to govern the global behavior in undirected/directed graphs. To distributively achieve the synchronization condition by updating local controller parameters, two broadcast mechanisms are presented on a spanning tree (for undirected graphs) and a cycle containing all nodes (for directed graphs). To ensure the tolerance to disconnections, the proposed broadcast mechanisms are redesigned by adding redundant information flows on spanning trees (for undirected graphs) and cycles containing all nodes (for directed graphs).
This article studies an optimal dynamic formation problem for heterogeneous affine nonlinear systems. The nonidenticality in agents and the requirement for dynamic spatial reconfiguration make it a ...challenging task to coordinate different types of agents to maintain an optimized formation shape. In an architecture of event-triggered decision and control, this article investigates how to fulfill dynamic formation by distributively optimizing a team cost function. The basic idea is to design a decision unit for each agent to generate an implicit trajectory as a servo signal, based on which a control unit is designed with a displacement-gradient-based law to achieve the desired local solution. Typical heterogeneous characteristics including different nonlinearities and nonidentical dimensions are dealt with in a unified framework. It is shown that with the proposed triggering mechanisms, the optimal dynamic formation problem can be solved by a distributed control law with only intermittent communication. In theory, the properties of convergence of trajectory tracking errors, optimality of the team solution, and Zeno-freeness of event-triggered mechanisms are proved. Two simulation examples are given to verify the proposed method.
This article addresses the decentralized tracking control problem for a class of strong interconnected nonlinear systems with actuator faults. The considered interconnections are allowed to be ...dominated by some bounding functions, which are linear growth in the status of all subsystems. First, an adaptive high-gain technique is introduced to deal with the unknown strong interconnections. Then, a group of fault-tolerant controllers is designed to adaptively compensate for the effects of the actuator failures, in which the controller gain parameters are adjusted online only according to local available information. Furthermore, with the aid of an algebraic graph theory result, it is proved that all signals of the closed-loop system are globally uniformly bounded, and the tracking errors of all subsystems converge to zero asymptotically. The effectiveness of the proposed control algorithm is demonstrated by a numerical simulation.
The development of high-performance memory devices has played a key role in the innovation of modern electronics. Non-volatile memory devices have manifested high capacity and mechanical reliability ...as a mainstream technology; however, their performance has been hampered by low extinction ratio and slow operational speed. Despite substantial efforts to improve these characteristics, typical write times of hundreds of micro- or milliseconds remain a few orders of magnitude longer than that of their volatile counterparts. Here we demonstrate non-volatile, floating-gate memory devices based on van der Waals heterostructures with atomically sharp interfaces between different functional elements, achieving ultrahigh-speed programming/erasing operations in the range of nanoseconds with extinction ratio up to 10
. This enhanced performance enables new device capabilities such as multi-bit storage, thus opening up applications in the realm of modern nanoelectronics and offering future fabrication guidelines for device scale up.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
Abstract
Iron-chalcogenide superconductors have emerged as a promising Majorana platform for topological quantum computation. By combining topological band and superconductivity in a single material, ...they provide significant advantage to realize isolated Majorana zero modes. However, iron-chalcogenide superconductors, especially Fe(Te,Se), suffer from strong inhomogeneity which may hamper their practical application. In addition, some iron-pnictide superconductors have been demonstrated to have topological surface states, yet no Majorana zero mode has been observed inside their vortices, raising a question of universality about this new Majorana platform. In this work, through angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy measurement, we identify Dirac surface states and Majorana zero modes, respectively, for the first time in an iron-pnictide superconductor, CaKFe
4
As
4
. More strikingly, the multiple vortex bound states with integer-quantization sequences can be accurately reproduced by our model calculation, firmly establishing Majorana nature of the zero mode.
This article studies the robust trajectory tracking control problem of a quadrotor unmanned aerial vehicle (UAV). In order to guarantee the desired trajectory tracking performance in the presence of ...external disturbances and model uncertainties, the design process of the quadrotor UAV controller is divided into two steps. First, by decomposing the attitude dynamic system into two serial-connected subsystems, a cascade active disturbance rejection control scheme is applied to the attitude subsystem. Second, by introducing an additional high-gain design parameter, a novel backstepping sliding-mode control scheme for position subsystem is constructed. Moreover, the Lyapunov stability analysis is provided to show that the trajectory tracking error can converge to an arbitrarily small residual set. Numerical results illustrate the effectiveness of the designed control method and its robustness to the external disturbances and model uncertainties. Finally, the proposed method is implemented on a quadrotor UAV to demonstrate its feasibility in practical application.
This paper investigates the global adaptive control problem for a class of general switched uncertain nonlinear systems. By improving the well-known mode-dependent average dwell time (MDADT) method, ...a new adaptive control scheme is established which ensures the global boundedness of all signals in the resulting closed-loop system under a class of switching signals with MDADT property. As an application, the developed control scheme is utilized to solve the adaptive tracking control problem for a class of switched uncertain lower triangular nonlinear systems with unmodeled dynamics. Finally, simulation study is provided for verifying the validity of our results.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This paper studies the diagnosis and compensation for sensor and actuator faults in a quadrotor unmanned aerial vehicle. Without adding sensors or actuators for increased hardware redundancy, an ...observer-based adaptive controller is proposed to estimate and compensate for the faults. First, using a feedback linearization technique, an inner controller is designed to transform the form of the considered quadrotor unmanned aerial vehicle with faults into a nonlinear system with Lipschitz-like nonlinearities and parametric faulty models. Second, the estimations for unmeasurable state and actuator faults are performed in an output-feedback outer controller to compensate for the actuator faults. Third, a nonlinear high-gain observer is designed to provide the information of the state and faults to the outer controller, with the compensations for sensor faults. A Lyapunov-based analysis shows that appropriate choices of the controller parameters can guarantee the exponential convergence of errors in estimation and trajectory tracking under uncertainties and faults. The robustness to the external disturbances is also discussed. Simulations are given to verify the effectiveness of the proposed scheme. The proposed approach is also implemented on a quadrotor unmanned aerial vehicle to show its feasibility in real-time applications.
Most feature-based stereo visual odometry (SVO) approaches estimate the motion of mobile robots by matching and tracking point features along a sequence of stereo images. However, in dynamic scenes ...mainly comprising moving pedestrians, vehicles, etc., there are insufficient robust static point features to enable accurate motion estimation, causing failures when reconstructing robotic motion. In this paper, we proposed DynPL-SVO, a complete dynamic SVO method that integrated united cost functions containing information between matched point features and re-projection errors perpendicular and parallel to the direction of the line features. Additionally, we introduced a dynamic grid algorithm to enhance its performance in dynamic scenes. The stereo camera motion was estimated through Levenberg-Marquard minimization of the re-projection errors of both point and line features. Comprehensive experimental results on KITTI and EuRoC MAV datasets showed that accuracy of the DynPL-SVO was improved by over 20% on average compared to other state-of-the-art SVO systems, especially in dynamic scenes.
The transition metal kagome lattice materials host frustrated, correlated and topological quantum states of matter
. Recently, a new family of vanadium-based kagome metals, AV
Sb
(A = K, Rb or Cs), ...with topological band structures has been discovered
. These layered compounds are nonmagnetic and undergo charge density wave transitions before developing superconductivity at low temperatures
. Here we report the observation of unconventional superconductivity and a pair density wave (PDW) in CsV
Sb
using scanning tunnelling microscope/spectroscopy and Josephson scanning tunnelling spectroscopy. We find that CsV
Sb
exhibits a V-shaped pairing gap Δ ~ 0.5 meV and is a strong-coupling superconductor (2Δ/k
T
~ 5) that coexists with 4a
unidirectional and 2a
× 2a
charge order. Remarkably, we discover a 3Q PDW accompanied by bidirectional 4a
/3 spatial modulations of the superconducting gap, coherence peak and gap depth in the tunnelling conductance. We term this novel quantum state a roton PDW associated with an underlying vortex-antivortex lattice that can account for the observed conductance modulations. Probing the electronic states in the vortex halo in an applied magnetic field, in strong field that suppresses superconductivity and in zero field above T
, reveals that the PDW is a primary state responsible for an emergent pseudogap and intertwined electronic order. Our findings show striking analogies and distinctions to the phenomenology of high-T
cuprate superconductors, and provide groundwork for understanding the microscopic origin of correlated electronic states and superconductivity in vanadium-based kagome metals.
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