Understanding the factors affecting COVID-19 mortality in Italy: Does a relationship exist with a sharp increase in Intensive Care Unit admissions?

Background: The present study aims to explore if a relationship exists between the immediate sharp increase in Intensive Care Unit (ICU) admissions and the mortality rates in Italy. Methods: Official epidemiological data on COVID-19 were employed. The forward lagged (0, 3, 7, 14 days) daily variations in the number of deaths according to the number of days after the outbreak started and the daily increases in ICU admissions were estimated. Results: A direct relationship between the sharp increase of ICU admissions and mortality rates has been shown. Furthermore, the analysis of the forward lagged daily variations in the number of deaths showed that an increase in the daily number of ICU admissions resulted in significantly higher mortality after 3, 7, and 14 days. The most pronounced effect was detected after 7 days, with 250 deaths (95% C.I. 108.1-392.8) for the highest increase in the ICU admissions -from 100 to 200- Conclusions: These results would serve as a warning for the scientific community and the health care decision-makers to prevent a quick and out-of-control saturation of the ICU beds in case of a relapse of the COVID-19 outbreak.

Nonlinear robust control of large-scale system with input saturation

The article studies control algorithms of multiply connected system for dynamic plants with control saturation and nonlinear cross-connections. The authors of the article offer a decentralized control law based on the hyperstability criterion. They also use this law to constuct the MIMO servo system with input saturation. To illustrate the capability of the proposed decentralized robust control system the authors use an inverted pendulums connected by a spring.

Disturbance estimator-based switching function for discrete-time sliding mode control systems with control saturation

In this paper, a new disturbance estimator-based switching function (SF) is presented dedicated to discrete-time sliding mode control (DSMC) systems with disturbances and control saturation (CS). This SF is featured by an ( n+1)th-order disturbance estimator, which utilizes n+1 past disturbance terms to attain accurate disturbance rejection. Moreover, an auxiliary state is integrated into the SF to address the CS problem. One uniqueness of the developed method is that it is capable of achieving the ideal quasi-sliding mode and produces a zero-convergence error of the SF under the influence of disturbances and CS, which is rarely realized in DSMC methods. In addition, system states dynamics is rigorously analysed adopting the Lyapunov technique. The feasibility and virtue of the designed results are verified by a numerical example.

Input-constrained chaos synchronization of horizontal platform systems via a model predictive controller

Horizontal platform systems are mechanical systems that can exhibit both periodic and chaotic behaviour. Various control techniques have been developed to solve their chaos synchronization. However, the avoidance of control saturation is rarely considered in existing control techniques. In this paper, a model predictive controller is developed to address the input-constrained chaos synchronization of horizontal platform systems. To meet the requirements of computational efficiency, the highly efficient symplectic pseudospectral method is taken as the core solver of the model predictive controller. Two methods to impose the terminal boundary condition are considered. And two indices, i.e., the approximate synchronization time and the synchronization-consumed energy, are proposed to evaluate the synchronization performance. Numerical simulations demonstrate that the developed model predictive controller can achieve faster synchronization while owns better robustness under various kinds of external disturbances when compared to several feedback controllers.

Stability boundary analysis of highly flexible aircraft with control saturation and structural flexibility

In this work, a method has been presented to analyze the influence of control saturation and structural flexibility on the stable radius of highly flexible aircraft. A dynamic model of aircraft is constructed followed by the analysis of kinetic characteristics. In this paper, the closed-loop stability boundary of highly flexible aircraft with open-loop instability is studied. The amplitude limit and bandwidth limit of the control signal are considered in the closed-loop stability boundary calculation. Our analysis shows that the boundary is related to the left eigenvector corresponding to the unstable poles and the amplitude constraint of the control signals. Stability of the boundary of feedback control system further reduces the limitation of the bandwidth of actuators. Focused on the phugoid instability of highly flexible aircraft, computational formulation of the closed-loop stable boundary is achieved. The Monte Carlo analysis has been employed to validate the stable region, under the LQR controller. Both the theory and simulations have nice correlations with each other which verify the stability of the closed-loop system, restricted by the open-loop system, and the influence of control signal bandwidth constraints.

Adaptive Saturated Neural Network Tracking Control of Spacecraft: Theory and Experimentation

An adaptive saturated neural network (NN) controller is developed for 6 degree-of-freedom (6DOF) spacecraft tracking, and its hardware-in-the-loop experimental validation is tested on the ground-based test facility. To overcome the dynamics uncertainties and prevent the large control saturation caused by the large tracking error at the beginning operation, a saturated radial basis function neural network (RBFNN) is introduced in the controller design, where the approximate error is counteracted by an adaptive continuous robust term. In addition, an auxiliary dynamical system is employed to compensate for the control saturation. It is proved that the ultimate boundedness of the closed-loop system is achieved. Besides, the proposed controller is implemented into a testbed facility to show the final operational reliability via hardware-in-the-loop experiments, where the experimental scenario describes that the simulator is tracking a planar trajectory while synchronizing its attitude with the desired angle. Experimental results illustrate that the proposed controller ensures that the simulator can track a preassigned trajectory with robustness to unknown inertial parameters and disturbances.