Adaptive Fixed-Time Control of Strict-Feedback High-Order Nonlinear Systems

This paper examines the adaptive control of high-order nonlinear systems with strict-feedback form. An adaptive fixed-time control scheme is designed for nonlinear systems with unknown uncertainties. In the design process of a backstepping controller, the Lyapunov function, an effective controller, and adaptive law are constructed. Combined with the fixed-time Lyapunov stability criterion, it is proved that the proposed control scheme can ensure the stability of the error system in finite time, and the convergence time is independent of the initial condition. Finally, simulation results verify the effectiveness of the proposed control strategy.

Lyapunov stability of competitive cells dynamics in tumor mechanobiology

Poromechanics plays a key role in modelling hard and soft tissue behaviours, by providing a thermodynamic framework in which chemo-mechanical mutual interactions among fluid and solid constituents can be consistently rooted, at different scale levels. In this context, how different biological species (including cells, extra-cellular components and chemical metabolites) interplay within complex environments is studied for characterizing the mechanobiology of tumor growth, governed by intratumoral residual stresses that initiate mechanotransductive processes deregulating normal tissue homeostasis and leading to tissue remodelling. Despite the coupling between tumor poroelasticity and interspecific competitive dynamics has recently highlighted how microscopic cells and environment interactions influence growth-associated stresses and tumor pathophysiology, the nonlinear interlacing among biochemical factors and mechanics somehow hindered the possibility of gaining qualitative insights into cells dynamics. Motivated by this, in the present work we recover the linear poroelasticity in order to benefit of a reduced complexity, so first deriving the well-known Lyapunov stability criterion from the thermodynamic dissipation principle and then analysing the stability of the mechanical competition among cells fighting for common space and resources during cancer growth and invasion. At the end, the linear poroelastic model enriched by interspecific dynamics is also exploited to show how growth anisotropy can alter the stress field in spherical tumor masses, by thus indirectly affecting cell mechano-sensing. GraphicAbstract

Discontinuous Control and Stability Analysis of Step-Down DC-DC Voltage Converters

Step down DC-DC converters are power electronic circuits, which mainly used to convert voltage from a level to a lower level. In this paper, a discontinuous controller is proposed as a control method in order to control Step-Down DC-DC converters. A Lyapunov stability criterion is used to mathematically prove the ability of the proposed controller to give the desired voltage. Simulationsl1 are performedl1 in MATLABl1 software. The simulationl1 resultsl1 are presentedl1 for changesl1 in referencel1 voltagel1 and inputl1 voltagel1 as well as stepl1 loadl1 variations. The resultsl1 showl1 the goodl1 performancel1 of the proposedl1 discontinuousl1 controller.

Smooth Trajectory Planning for Autonomous Leader-Follower Robots

Path planning is a key factor that determines how well a robotic vehicle performs in executing automated formations and maneuvers as in multi-vehicle platooning and self- organizing leader following with safe and graceful movements. Many types of path- planning schemes have been employed in the autonomous robotics and driving systems. In this paper, we will focus on the application of a smooth path-planning (SPP) algorithm that produces simple-to-implement robotic maneuvers. The algorithm is derived from using a well-established Lyapunov stability criterion and a clever dynamical control synthesis. We show that the SPP can be adapted to many autonomous guidance scenarios. Simulations show that the SPP resulted in autonomous behaviors similar to that parallel those of human or animal actions. The paper presents results using Matlab simulations as well as Gazebo animation. The results will provide a foundation for an implementation of SPP on actual robotic vehicles.

Hot Forming Optimization of ZK30 Magnesium Alloy

The modeling of the forming of materials at high homologous temperatures allows obtaining optimum forming parameters, reduced costs and improving final properties of the finished product. In this work, the behavior of the ZK30 Magnesium alloy was characterized by means of compression tests at temperatures 300 to 450oC and strain rates between 0.1 and 8.7 s-1. Using data from these tests, the parameters of the Garofalo equation are calculated. In addition, by means of the second Lyapunov stability criterion, the optimum temperature at a given temperature is determined which should minimize the appearance of deformation bands and cracks during hot working. This temperature was found to be 641 K (368oC) at 8.7 s-1.

Adaptive Fuzzy Command Filtered Control for Chua’s Chaotic System

In this paper, we propose the command filtered adaptive fuzzy backstepping control (AFBC) approach for Chua’s chaotic system with external disturbance. Based on two proposed first-order command filters, the convergence of tracking errors as well as the problem of “explosion of complexity” in traditional backstepping design procedure is solved. In the command filtered AFBC design, we do not need to calculate the complicated partial derivatives of the virtual control inputs. Fuzzy logic systems (FLSs) are used to identify the system uncertainties in real time. Based on Lyapunov stability criterion, the proposed controller can guarantee that all signals in the closed-loop system keep bounded, and the tracking errors converge to a small region eventually. Finally, simulation studies have been provided to verify the effectiveness of the proposed method.