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The design of global fixed-time observer for a category of lower-triangular nonlinear systems is reported in this brief. Under a wild condition that admits the Holder continuous conditions as a special case, a constructive algorithm of global fixed-time observer design is proposed by virtue of non-recursive combining bi-limit homogeneous technique. Rigorous stability analysis as well as robustness with respect to exogenous disturbances is provided to show the proposed observer ensuring global fixed-time convergent performance of the estimation error dynamics. Simulation results of an example of MEMS mirror with the nonlinear viscous damping dissipative load are given to confirm the effectiveness of the proposed algorithm.

Supported single-atom catalysts (SACs) have received a lot of attention due to their super-high atom utilization and outstanding catalytic performance. However, the instability of the supported transition-metal (TM) atoms hampers their widespread applications. Exploration of an appropriate substrate to stabilize the supported single atom is crucial for the future implementation of SACs. In recent years, two-dimensional materials have been proposed as possible substrates due to their large specific surface areas, but their chemically inert surfaces are difficult to stabilize TM atoms without defecting or doping. Herein, by means of systematic first-principles calculations, we demonstrate that the defect-free MoS2 monolayer in the unconventional phase (1T') can effectively immobilize single TM atoms owing to its unique electrophilic property as compared to the conventional 2H phase. As a prototype probe, we investigated oxygen reduction reaction (ORR) catalyzed by a total of 21 single TM atoms stabilized on 1T'-MoS2 and successfully screened out two candidates, Cu and Pd@1T'-MoS2, which have a low overpotential of 0.41 and 0.32 V respectively, outperforming most of the previously reported ORR catalysts. Furthermore, we reveal that the adsorption energy of the ORR intermediate, *OH, provides an excellent descriptor to assess the ORR activity, which is further determined by the d-band center of the supported TM adatoms, thus being a great advantage for future design of stable and high-performance SACs.

The global fixed-time stabilization of a class of perturbed planar nonlinear systems using output feedback is addressed in this brief. Under a generalized Lipschitz continuous condition, a constructive controller design of global output feedback is proposed based on a continuous fixed-time observer. The bi-limit homogeneity technique is employed to show global fixed-time stability of the closed-loop system. Simulation of a MEMS mirror model illustrates the appealing performance of the proposed method.

Sensitive detection of nucleolin (NCL) is of great significance for the early diagnosis of cancer. In this work, as a new type of two-dimensional (2D) transition metal dichalcogenides (TMDCs), TaS2 nanoflakes (NFs) were precisely constructed by atomic layer deposition (ALD) on carbon fiber paper (CFP) with high specific surface area. In situ observation showed that the nucleation and growth of TaS2 nanoflakes were precisely controlled by the number of ALD cycles, thereby regulating their electrochemical properties. The electrochemical performance of TaS2NFs was observed in depth, and compared with that of traditional 2D TMDCs. Due to the high surface area and conductivity, anodic/cathodic current of ∼1570 μA of TaS2NFs/CFP can be obtained. Subsequently, an electrochemical biosensor based on ALD-constructed TaS2NFs/CFP for cancer-related NCL detection was fabricated. Due to the excellent electrochemical performance of TaS2NFs/CFP, ultrasensitive detection of NCL in the linear range of 0.1 pM–10 nM with a detection limit of 0.034 pM was achieved.

The fixed-time stabilization problem is addressed in this paper for a kind of nonholonomic systems in chained form with unmatched uncertainties and time-varying output constraints. A novel tan-type barrier Lyapunov function is introduced to deal with time-varying output constraints. Under the unified framework of the considered system with and without output constraints, a state feedback controller is designed with the aid of adding a power integrator technique and switching control strategy. It is shown that the suggested controller ensures the states of closed-loop system to zero in a given fixed time without disobeying the constraints. Finally, simulation results are given to confirm the efficacy of the presented control scheme.

A sliding mode robust control law based on Hamilton-Jacobi Inequality (HJI) theory and a disturbance observer is proposed for a wire-driven parallel robot (WDPR) used in a wind- tunnel test. First, the wire-driven parallel robot is described, and its kinematics model established. Second, according to the uncertainty, external disturbance, and redundant drive of the system, the dynamic model of the end-effector and drive system, and the overall dynamic model of the system are established. Hamilton-Jacobi Inequality theory and the designed disturbance observer are applied to the designed sliding mode robust control law, and the anti-interference ability of the WDPR is verified. The stability of the closed-loop system is analyzed by Lyapunov's second method, and the results show that the closed-loop system tends to be asymptotically stable. Finally, taking the dynamic trajectory simulation of compound motion and six-degree-of-freedom motion as examples, the designed sliding mode robust control law is verified by simulation, and the contrastive simulation analysis shows that the disturbance observer can effectively reduce the switching gain, thus effectively reducing chattering and improving the control accuracy of the system. The simulation results show that the designed sliding mode robust control law can effectively suppress the influence of external disturbance on the control error. The control input and the length of the wire change in a certain range. They also prove that the pose error is small, and the control accuracy is high. All of the foundings lay a theoretical foundation and technical support for the practical application of the prototype in a wind-tunnel test.

The control quality of servo system requires not only stability, speed, and accuracy, but also strong anti-jamming ability. The permanent magnet synchronous motor (PMSM) is a multivariable and strongly coupled time-varying nonlinear system. It will be subject to different degrees of external interference. According to the advantages and limitations of fractional-order PID (FOPID) controller and active disturbance rejection control (ADRC), the fractional-order calculus concept is integrated into ADRC. In this paper, a control strategy of position servo system based on fractional-order extended state observer (FOESO) is proposed. The FOESO and fractional-order control law are designed to form a fractional-order active disturbance rejection control (FOADRC). The FOADRC controller is applied to the position loop control of the servo system. Through the experiment and performance analysis, it is proved that the FOESO can well observe the internal and external disturbances of the system, and the FOADRC has a good control effect in the position servo system.

The negative electron affinity InGaAs photocathode is an important part of the infrared vacuum detector. The article focuses on the adsorption of residual gas in the preparation of InGaAs photocathodes. The impact of the adsorbates on the generation of negative electron affinity was calculated and discussed. Models of InGaAs surface with residual gas were built and the work function, charge transfer, dipole and the formation energy have been analyzed based on the first principles. The dipole from the surface to the residual gas molecule was generated by the charge transfer. The surface work function went up followed. The biggest increment came up to 0.410 eV, which is caused by the adsorption of CO2. The photoelectrons escape was restrained. As a result, three chemical cleaning methods were proposed to clean the InGaAs surface. It is found that oxide is more stable to be wiped off than the other residual gas molecule. So a further treatment needs to be raised.

Although MoS

This article considers global stabilization problem for a kind of uncertain high-order nonlinear systems (HONSs). Two distinct characteristics of this study are that the considered system possesses the input-quantized actuator, and the prescribed time convergence of the system states is wanted. To address these, a novel state-scaling transformation (SST) is firstly introduced to convert the aboriginal prescribed-time stabilization (PTS) to the asymptotic stabilization of the transformed one. Then, under the new framework of equivalent transformation, a quantized state feedback controller that achieves of the performance requirements is developed with the aid of the technique of adding a power integrator (API). Finally, simulation results of a liquid-level system are provided to confirm the efficacy of the proposed approach.

Supported single-atom catalysts (SACs) have received a lot of attention due to their super-high atom utilization and outstanding catalytic performance. However, the instability of the supported transition-metal (TM) atoms hampers their widespread applications. Exploration of an appropriate substrate to stabilize the supported single atom is crucial for the future implementation of SACs. In recent years, two-dimensional materials have been proposed as possible substrates due to their large specific surface areas, but their chemically inert surfaces are difficult to stabilize TM atoms without defecting or doping. Herein, by means of systematic first-principles calculations, we demonstrate that the defect-free MoS

Although it suffers from a heavy dependence on the noble platinum catalyst, the electrochemical hydrogen evolution reaction (HER) is one of the most promising methods for the production of hydrogen. After numerous efforts, it is found that MoS

This paper addresses the problem of fixed-time stabilization of chained-form nonholonomic systems with time-varying state constraints. A nonlinear mapping is introduced to transform the state-constrained system into a new system without state constraints. Then, by employing switching control and backstepping techniques, a state feedback controller is successfully constructed to guarantee that the states of the closed-loop system are regulated to zero for any given fixed time without violation of the constraints.

A fractional-order active disturbance rejection control strategy is presented to realize precise trajectory tracking and point-to-point positioning performances of a newly designed linear motor. Structure characteristics and working mechanism of the new linear motor are analyzed. Reference acceleration feedforward, extended state observer, tracking differentiator, and fractional-order proportional derivative algorithm are combined to achieve high-precision trajectory tracking and point-to-point positioning performances. Different simulations and experiments are compared, and results illustrate that the proposed method performs well in spite of parameter variations and external disturbances. Consequently, precision trajectory tracking and point-to-point positioning performances of the novel linear motor have been obtained.

Nonholonomic constraint is widespread in many aerospace applications such as space robots, artificial satellites, aircrafts etc. In this paper, the problem of global prescribed-time stabilization is addressed for a category of uncertain nonholonomic constraint systems (namely, nonholonomic systems for short) with actuator dead-zones. To deal with the obstacle that the presence of input dead-zone nonlinearities renders the traditional discontinuous feedback control technique inapplicable to nonholonomic systems, a novel switching-based state-scaling transformation (switching-based-SST) is introduced. This transformation can change the original predefined-time stabilization into the asymptotic stabilization of the transformed one. Under such new framework, a state feedback controller that achieves the prescribed-time convergence performance is developed by using the recursive idea. Finally, a practical application to a unicycle-type mobile robot is presented to confirm the validity of the proposed method.

A novel 6-degree-of-freedom (6-DOF) parallel robot driven by six novel linear motors is designed and controlled in this paper. Detailed structures of linear motors are illustrated. A control strategy based on kinematics of the 6-DOF parallel robot is used, and six linear motors are controlled to track their own desired trajectories under a designed fractional-order active disturbance rejection controller (FOADRC). Compared with the normal ADRC, two desired trajectories and three different working situations of a linear motor are simulated to show good performances of the FOADRC. Experimental results show that six linear motors can track their own desired trajectories accurately under payloads and disturbances, and the novel 6-DOF parallel robot can be controlled well.

A fractional-order modified active disturbance rejection controller is presented to realize precise point-to-point positioning control driven by a novel linear motor. Working principle and dynamic model of the novel linear motor are demonstrated. Reference acceleration feedforward, tracking differentiator, extended state observer, and fractional order proportional derivative controller are combined to achieve high point-to-point positioning accuracy. Simulation results and experimental validation are compared to illustrate that the proposed fractional-order modified active disturbance rejection controller is robust to external disturbances and parameter variations, and high point-to-point positioning performances of the novel linear motor for different desired positions have been obtained.

This paper addresses the problem of fixed-time stabilization of chained-form systems with state constraints. A nonlinear mapping is first introduced to transform the state-constrained system into a new system without state constraints. Then, by employing backstepping and switching control techniques, a state feedback controller is successfully constructed to guarantee that the states of the closed-loop system are regulated to zero for any given fixed time without violation of the constraints.

Modeling human operator's dynamic plays a very important role in the manual closed-loop control system, and it is an active research area for several decades. Based on the characteristics of human brain and behaviour, a new kind of fractional order mathematical model for human operator in SISO systems is proposed. Compared with the traditional models based on the commonly used quasi-linear transfer function method or the optimal control theory method, the proposed fractional order model has simple structure with only few parameters, and each parameter has explicit physical meanings. The actual data and experiment results with the second-order controlled element illustrate the effectiveness of the proposed method., Comment: 9 pages, 21 figures

The top surface of the distant robot framework sub-framework is worked in resource examination and upkeep tasks, oil is an alternate sort of gas and petrochemical modern robot arrangements. The framework which is industrially accessible from altered arrangement organizations, have been inspected. For thickness estimations, the vision camera framework (most automated frameworks, visual investigation framework, attractive or electromagnetic, the more significant part of these mechanical frameworks, a framework that executes various restricted examination innovation. Digital physical framework is improved by consolidating the gadget's capacities to be associated with one another by utilizing data innovation and robotization arrangements, information and physical components, and a remote sensor organization, filling in the industry 4.0 to ever-changing today it has become a term. This article uses a portable robot with a Wireless Sensor Network (WSN) to check the identification and observing framework. When an odd occasion happens, the odd occasion happens because to set the caution to the majority of sensor hubs in precisely the business climate, it can happen. Structure incorporates the self-ruling robot (operator) as a part of the remote sensor organization; the portable robot will move to the location position for examination. The reason is to build up a moderately ease, another processing plant with the position and observing capacities inside the extent of a dependable. This manner, it might be anyplace, including the mind-boggling occasion of preparing and replication.

The flexible clamping component is used to support the stator of linear ultrasonic motors (LUM). It distinctly improves the vibration characteristics of the motor and simplifies the structure, nevertheless brings the mechanical drift phenomenon. In order to improve the positional accuracy and structural stability of the V-shaped LUM, this paper studies the mechanical drift mechanism of the LUM with clamping component. Mechanical model of the motor with flexible clamp which occur mechanical drift is established, and the mechanism as well as control methods are analyzed. Based on the model, the mechanical drift experiments of clamping components with different stiffness are carried out. The experimental results show that the mechanical drift is obvious when the stiffness of the two flexible clamps are different, while the mechanical drift hardly occur when using the clamping components with tremendous tangential stiffness. Therefore, a kind of straight beam clamping LUM is proposed. The research indicate that the new motor has little mechanical drift, better running performance and higher structural stability, which can be used in the precision positioning of the mechanical devices.

Trajectory tracking control based on fractional calculus of a new linear motor is presented and experiments are verified in this paper. Design details and principle analyses of the new motor are exhibited. Fractional calculus is used to improve the tracking performance, and the motion controller is composed of a fractional-order proportional-derivative controller, a first-order and a second-order extended state observer. The proposed method is compared with an active disturbance rejection controller, and simulations and experiments are performed to verify the effectiveness. Good trajectory tracking performance of the new linear motor has been realized in spite of parameter variations and external disturbances.