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In this article, the fixed‐time adaptive neural tracking control for a class of second‐order uncertain nonlinear systems is investigated. First, a novel fast fixed‐time stable (FTS) autonomous system with the switched nonlinear term is constructed. Compared with the traditional FTS system (FTSS), the state of the proposed fast FTS system has a faster convergence rate for arbitrary initial state. Then, a fixed‐time terminal sliding mode control (FTSMC) scheme is developed based on the novel fast FTSS, and the tracking error of the closed‐loop system is verified to converge to the origin within a fixed time. The proposed FTSMC scheme not only realizes the upper bound of the settling time independent of the initial conditions but also completely avoids the singularity problem by introducing the switching sliding mode surface. Moreover, an adaptive neural FTSMC scheme is developed for the general uncertain nonlinear systems with the help of the approximation capabilities of neural networks (NNs). The feasibility of the presented control strategy is examined by the simulation of a single‐link robot system. [ABSTRACT FROM AUTHOR]

Gas well production involves various stages, including stable, variable, and declining production. However, existing production-capacity equations typically apply only to the stable production stage, limiting their effectiveness in evaluating gas well productivity across all stages. To address this, the material balance equation and Darcy's equation were employed to account for changes in average formation pressure due to pressure drop funnels. The concept of a pressure-conversion skin factor was introduced, and its approximation was developed, leading to the establishment and solution of a full-stage productivity equation. Numerical simulations were then conducted to verify the accuracy and applicability of this equation. The findings are as follows: ① The full-stage productivity equation remains effective even when production rates and pressure are not constant, with the only potential source of inaccuracy being the approximative solution for the pressure conversion-skin factor. ② Numerical simulations demonstrated that the approximate solution closely matched the numerical simulation results for average formation pressure across various production stages and fundamental parameters, showing a consistent trend and high precision. The approximate and independent approximation solutions for absolute open-flow capacity were nearly identical, indicating the full-stage productivity equation's applicability throughout the production of gas wells. ③ Application results revealed that the full-stage productivity equation offers superior accuracy compared to the modified isochronous well test. ④ The approximate solution generally provides slightly higher accuracy, and the independent approximate solution effectively eliminates the influence of gas leakage radius. Therefore, the use of the approximate solution is recommended to calculate the average formation pressure and the independent approximate solution to calculate the absolute open-flow capacity. The full-stage productivity equation developed in this study is not constrained by the production system, making it suitable for productivity evaluation across all stages of gas well production. This has significant implications for the effective development of gas fields. [ABSTRACT FROM AUTHOR]

To prepare biomass-based wood adhesives with good bonding properties and water resistance is still a challenge and meaningful work in the field of the wood industry. Thus in this present study, under low reaction temperature conditions (50°C), sodium periodate was used as an oxidant to treat carbohydrates such as glucose, sucrose and starch to form biomass-derived aldehydes solutions. Then oxidized glucose- hexamethylenediamine (OGLH), oxidized sucrose- hexamethylenediamine (OSUH) and oxidized strarch-hexamethylenediamine (OSTH) resins were prepared via Schiff base reaction from these solutions with hexamethylenediamine. The resins obtained were applied to the preparation of three-layer laboratory plywood. The whole synthesis was a simple process and low energy consumption; meanwhile, OGLH and OSUH resins show excellent bonding performance, allowing them to be able to consider as a substitute for the current widely used urea-formaldehyde (UF) and its modified resin wood adhesives. Furthermore, this study provides a new process reference for the preparation of carbohydrate-based adhesives. [ABSTRACT FROM AUTHOR]