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This paper considers the problem of fault-tolerant attitude control for a flexible spacecraft subject to input and state constraint. Particularly, a new sliding mode-based attitude control with fixed-time convergent for the flexible spacecraft is developed in which the convergence rate of the system state is improved both far from and at close range of the origin. In contrast to the existing complicated prescribed performance controls (PPC), the proposed PPC possesses a much simpler structure due to the use of a novel constraint concept without employing error transformation. It also introduces a modified prescribed performance function (MPPF) to explicitly determine the settling time. It is rigorously proved that the attitude variable is kept within the predefined constraint boundaries even when the actuator saturation is taken into account. Moreover, the proposed controller is inherently continuous and the chattering is effectively reduced. An adaptive mechanism is developed in which no prior knowledge of the lumped uncertainties is required. Finally, numerical simulations are presented to demonstrate that the proposed controller is able to successfully accomplish attitude control with high attitude pointing accuracy and stability. More specifically, it provides faster convergence (improvement percentage of convergence time (IP_CT) is about 18%) and more accurate control (improvement percentages of MRPs (IP_MRPs) and angular velocity (IP_AV) are about 60% and 80%, respectively) under healthy actuators. Values of IP_CT, IP_CT, and IP_AV are 50%, 99.9% and 99.9% under faulty actuators, respectively.

An adaptive control of MEMS gyroscopes with guaranteed transient and steady-state performance has been presented in Lu and Fei (2016). A performance function characterizing the convergence rate, maximum overshoot and steady-state error is used for the output error transformation, such that stabilizing the transformed system is sufficient to achieve the tracking control of the original system with a priori prescribed performance. The main objective of this comment is to point out a mistake occurred through the paper, resulted in the ineffectiveness of the proposed controller.

Background: Microdialysis (MD) can detect organ-related metabolic changes before they become measurable in plasma through the biochemical parameters. This study aims to evaluate the early detection of metabolic changes during experimental kidney transplantation (KTx). Material and methods: During preparation of 8 donor kidneys, one MD catheter was inserted in the renal cortex and samples were collected. After a 6-hour cold ischemia time (CIT), kidneys were implanted in the 8 recipient pigs. Throughout the warm ischemia time (WIT) and after reperfusion, kidneys were monitored. The interstitial glucose, lactate, pyruvate, glutamate, and glycerol concentrations were evaluated. Results: A significant decline in glucose level was observed at the end of CIT. The lactate level was reduced to the minimum point of 0.35 ± 0.08 mmol/L in CIT. After reperfusion, lactate values raised significantly. During the WIT, the pyruvate level increased, continued until the end of the WIT. For glutamate, a steady increase was noted during explantation, CIT, WIT, and early reperfusion phases. The increase of glycerol value continued in the early postreperfusion, which was then followed by a sharp decline. Conclusion: MD is a fast and simple minimally invasive method for measurement of metabolic substrates in renal parenchyma during KTx. MD offers the option of detecting minor changes of interstitial glucose, lactate, pyruvate, glutamate, and glycerol in every stage of KTx. Through the use of MD, metabolic changes can be continuously monitored during the entire procedure of KTx.

Introduction. The aim of the present study was to evaluate the feasibility of a technique that uses solely the transhiatal approach to create a high intrathoracic esophagogastric anastomosis after laparoscopic transhiatal resection of the distal esophagus. Method. Using a laparoscopic approach, the esophagi of 10 midsized pigs were dissected and transected as high as possible in the thorax, and the anvil of a circular stapler was introduced perorally into the esophageal stump. Through a midline short laparotomy, the circular stapler was inserted into the gastric tube and advanced through the hiatus to be connected with the anvil and create the anastomosis. Results. Development of the technique was completed within the first 6 experiments. The last 4 operations were entirely successful, standardized, and easily reproducible. Conclusion. The technique is feasible in this experimental setting. Further studies are required to establish if there is a clinical role for this technique in esophageal surgery.