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This paper proposes an event-based adaptive tracking control scheme for the n-link robotic systems in the presence of unknown backlash-like hysteresis (BLH) and deferred position constraints. By combining a transformation error with an asymmetric Lyapunov function, the devised control tactic achieves that the position constraints of robotic systems are not violated after user pre-specified time. In contrast to the results of robotic systems with position constraints, this paper removes a common assumption condition generated by the conventional barrier Lyapunov function method. Then, the adverse effect of unknown BLH can be offset by the Nussbaum function. Meanwhile, an event-triggered mechanism is designed to economize on the network bandwidth resources. Finally, based on the Lyapunov theory, an event-based adaptive tracking control tactic is proposed to ensure that all the signals of robotic systems are bounded under unknown BLH and deferred position constraints. Some simulation results proof that the devised control scheme is valid.

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This article is concerned with the dynamic event-triggered-based adaptive output-feedback tracking control problem of nonlinear multiagent systems with time-varying input delay. By utilizing the approximation capability of neural network (NN), a low-gain nonlinear observer is first established to estimate the immeasurable states. To mitigate the effect of time-varying input delay, an auxiliary system with communication information is designed to generate the compensation signals. Then, a distributed adaptive composite NN dynamic surface control (DSC) strategy is proposed to acquire the satisfactory tracking accuracy, where the filter errors are compensated by the introduced serial-parallel estimation model. Moreover, an effective switching dynamic event-triggered mechanism is developed to determine the communication instants and reduce the update frequency of the controller. It is proven that the consensus tracking error converges to a residual set of the origin. Finally, simulation results are presented to demonstrate the effectiveness of the proposed composite NN DSC scheme.

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This article investigates the adaptive performance guaranteed tracking control problem for multiagent systems (MASs) with power integrators and measurement sensitivity. Different from the structural characteristics of existing results, the dynamic of each agent is a power exponential function. A method called adding a power integrator technique is introduced to guarantee that the consensus is achieved of the MASs with power integrators. Different from existing prescribed performance tracking control results for MASs, a new performance guaranteed control approach is proposed in this article, which can guarantee that the relative position error between neighboring agents can converge into the prescribed boundary within preassigned finite time. By utilizing the Nussbaum gain technique and neural networks, a novel control scheme is proposed to solve the unknown measurement sensitivity on the sensor, which successfully relaxes the restrictive condition that the unknown measurement sensitivity must be within a specific range. Based on the Lyapunov functional method, it is proven that the relative position error between neighboring agents can converge into the prescribed boundary within preassigned finite time. Finally, a simulation example is proposed to verify the availability of the control strategy.

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This article investigates the quantized adaptive finite-time bipartite tracking control problem for high-order stochastic pure-feedback nonlinear multiagent systems with sensor faults and Prandtl-Ishlinskii (PI) hysteresis. Different from the existing finite-time control results, the nonlinearity of each agent is totally unknown in this article. To overcome the difficulties caused by asymmetric hysteresis quantization and PI hysteresis, a new distributed control method is proposed by adopting the adaptive compensation technique without estimating the lower bounds of parameters. Radial basis function neural networks are employed to estimate unknown nonlinear functions and solve the problem of algebraic loop caused by the pure-feedback nonlinear systems. Then, an adaptive neural-network compensation control approach is proposed to tackle the problem of sensor faults. The problem of the "explosion of complexity" caused by repeated differentiations of the virtual controller is solved by using the dynamic surface control technique. Based on the Lyapunov stability theorem, it is proved that all signals of the closed-loop systems are semiglobal practical finite-time stable in probability, and the bipartite tracking control performance is achieved. Finally, the effectiveness of the proposed control strategy is verified by some simulation results.

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This article focuses on the containment control problem for nonlinear multiagent systems (MASs) with unknown disturbance and prescribed performance in the presence of dead-zone output. The fuzzy-logic systems (FLSs) are used to approximate the unknown nonlinear function, and a nonlinear disturbance observer is used to estimate unknown external disturbances. Meanwhile, a new distributed containment control scheme is developed by utilizing the adaptive compensation technique without assumption of the boundary value of unknown disturbance. Furthermore, a Nussbaum function is utilized to cope with the unknown control coefficient, which is caused by the nonlinearity in the output mechanism. Moreover, a second-order tracking differentiator (TD) is introduced to avoid the repeated differentiation of the virtual controller. The outputs of the followers converge to the convex hull spanned by the multiple dynamic leaders. It is shown that all the signals are semiglobally uniformly ultimately bounded (SGUUB), and the local neighborhood containment errors can converge into the prescribed boundary. Finally, the effectiveness of the approach proposed in this article is illustrated by simulation results.

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N-maleoylchitosan (NMCS) is a biocompatible derivative of chitosan, but its solubility in water is dependent on the degree of maleoyl substitution. In this study, the NMCS sample with a maleoyl substitution degree of 70% was synthesized by the reaction of maleic anhydride and the amino groups of chitosan. The resulting NMCS can be ready to dissolve in water over a wide pH range (from 2 to 9). The aggregation behavior of NMCS in aqueous media was studied by steady-state fluorescence spectroscopy, viscometric, field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The critical aggregation concentration (CAC) of NMCS in water is found to be 0.05-0.06mg/mL. With increasing NMCS concentration to approximately 0.5mg/mL, which is 10 times of the CAC, NMCS molecules self-assemble to fiber-like aggregates with an averaged diameter of approximately 2.5microm and length of more than 100microm. The driving force for the aggregation is attributed to the hydrophobic interaction as evident from isothermal titration calorimetry (ITC) study. These fiber-like aggregates might have potential applications in tissue engineering scaffold.

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An interfacial free radical polymerization method was developed to fabricate polysaccharide nanocapsules, in which poor water-soluble drug of felodipine could be effectively encapsulated with good stability during storage. Exemplified by the preparation of felodipine-loaded N-maleoylchitosan (NMCS) nanocapsules, a felodipine/chloroform mixture was dispersed in NMCS aqueous solution with the aid of a nonionic surface active agent. After charging initiator, the vinylated groups of NMCS were polymerized on the oil-water interface. As a result, felodipine was loaded into NMCS nanocapsule. The morphology and the size distribution of synthesized nanocapsules were characterized by field emission scanning electron microscopy (FESEM) and dynamic light scattering (DLS) techniques. The quantitative drug loading and sustained release behavior were investigated. The encapsulation efficiency and drug loading content were found to be strongly dependent on the feed felodipine concentration. The release dynamics showed strong correlation with the degree of maleoyl substitution and the feed NMCS concentration during the course of nanocapsules preparation.

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A novel simple method was developed to successfully synthesize biocompatible N-carboxyethylchitosan (NCECS) with a substitution degree of approx. 41% using the Michael addition reaction. The NCECS structure was characterized by Fourier transform infra-red spectrometry (FT-IR), (1)H-NMR, elemental analysis, X-ray diffraction spectrometry (XRD) and thermogravimetric analysis (TGA). The physicochemical properties of NCECS in solution are found to be strongly dependent on the pH value. In the pH range of 5.0-5.5, NCECS aggregates in dilute aqueous solution as evident by steady-state fluorescence spectroscopy and viscosimetry. The aggregated NCECS shows a spheric morphology from the atomic force microscopy (AFM) study. The possible aggregation mechanism was discussed.

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Biocompatible and polymerizable natural macromolecules have been found to provide great advantages in the preparation of hydrogels, which have wide applications in the fields of tissue engineering and polymeric drug delivery systems. To develop a new biocompatible polymerizable chitosan derivative, N-maleic acyl-chitosan (NMCS) was synthesized in this study. This novel biomaterial was designed from the N-acylation of chitosan with maleic anhydride introducing functional carboxyl and vinylated (--C[double bond]C--) groups. The structure of NMCS was characterized by FTIR, (1)H NMR, element analysis, and X-ray diffraction (XRD). NMCS can be dissolved into water because of its decreased crystallinity compared with chitosan. The NMCS's multiporous and microgel morphology was revealed by transmission electron microscope (TEM). Crosslinked hydrogel films can be successfully obtain through the macromolecular polymerization of NMCS. Subsequently, 3T3 fibroblasts were cultured onto the surface of the polymerized NMCS (P-NMCS) films to examine the capability of cell attachment and proliferation. Results from the cell culture demonstrate that P-NMCS films provide significant improvement in cell attachment and proliferation over unmodified chitosan. The improved P-NMCS cytocompatibility is expected to provide substantial contributions to tissue engineering in the future.

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