Multilayer perceptron adaptive dynamic control of mobile robots : experimental validation

This paper presents experimental results acquired from the implementation of an adaptive control scheme for nonholonomic mobile robots, which was recently proposed by the same authors and tested only by simulations. The control system comprises a trajectory tracking kinematic controller, which generates the reference wheel velocities, and a cascade dynamic controller, which estimates the robot's uncertain nonlinear dynamic functions in real-time via a multilayer perceptron neural network. In this manner precise velocity tracking is attained, even in the presence of unknown and/or time-varying dynamics. The experimental mobile robot, designed and built for the purpose of this research, is also presented in this paper.peer-reviewe

Is there a governance failure in corporatised Australian Government Business Enterprises? Evidence from their Chief Executive Officers’ compensation.

Over the last three decades, governments have commercialised and corporatised many of their government business enterprises (GBEs) without privatising them under New Public Management (NPM) policy, which requires them to act as a corporate sector entity. These GBEs have independent boards that are responsible for the corporate governance of these entities, including the hiring of chief executive officers (CEOs) and determining their compensation. We examine the association between pay and performance for CEOs of GBEs and find that the levels and changes in CEO compensation are not associated with GBE performance despite being the explicit intent of NPM and regulatory policy. We suggest that this corporate governance failure could be due to the composition of the GBE boards. Our evidence shows that only 11.29% of directors appointed have public listed company experience with the balance of director appointments, being either senior public servants or political appointments who may lack the motivation or have any incentive to closely monitor CEO compensation. Accordingly, we suggest some possible policy changes to both the determination of CEO compensation and the composition of GBE boards

Dual adaptive dynamic control of mobile robots using neural networks

This paper proposes two novel dual adaptive neural control schemes for the dynamic control of nonholonomic mobile robots. The two schemes are developed in discrete time, and the robot's nonlinear dynamic functions are assumed to be unknown. Gaussian radial basis function and sigmoidal multilayer perceptron neural networks are used for function approximation. In each scheme, the unknown network parameters are estimated stochastically in real time, and no preliminary offline neural network training is used. In contrast to other adaptive techniques hitherto proposed in the literature on mobile robots, the dual control laws presented in this paper do not rely on the heuristic certainty equivalence property but account for the uncertainty in the estimates. This results in a major improvement in tracking performance, despite the plant uncertainty and unmodeled dynamics. Monte Carlo simulation and statistical hypothesis testing are used to illustrate the effectiveness of the two proposed stochastic controllers as applied to the trajectory-tracking problem of a differentially driven wheeled mobile robot.peer-reviewe

Unscented transform-based dual adaptive control of nonlinear MIMO systems

The paper proposes a multilayer perceptron neural network controller for dual adaptive control of a class of stochastic MIMO nonlinear systems subject to functional uncertainty. The neural network parameters are adjusted in real-time using the Unscented Kalman filter algorithm and no pre-operational training phase is required. Dual adaptive control aims to strike a compromise between the two control characteristics of caution and probing, leading to an improved overall performance. The system is evaluated through numerical simulations and Monte Carlo analysis. The resulting performance of the dual adaptive controller is not only consistently superior to non-dual adaptive control schemes, but also surpasses the performance of similar controllers that are based on Extended Kalman filter estimators. This reflects the enhanced accuracy of the Unscented Kalman filter estimator, despite being a local estimation method. In addition, unlike use of other estimators, the proposed approach neither requires the computation of complex Jacobian matrices as part of the design, nor the evaluation of such matrices in real-time. This renders the proposed controller inherently amenable and practical for real-time implementation.peer-reviewe

Multilayer perceptron functional adaptive control for trajectory tracking of wheeled mobile robots

Sigmoidal multilayer perceptron neural networks are proposed to effect functional adaptive control for handling the trajectory tracking problem in a nonholonomic wheeled mobile robot. The scheme is developed in discrete time and the multilayer perceptron neural networks are used for the estimation of the robot’s nonlinear kinematic functions, which are assumed to be unknown. On-line weight tuning is achieved by employing the extended Kalman filter algorithm based on a specifically formulated multiple-input, multiple-output, stochastic model for the trajectory error dynamics of the mobile base. The estimated functions are then used on a certainty equivalence basis in the control law proposed in (Corradini et al., 2003) for trajectory tracking. The performance of the system is analyzed and compared by simulation.peer-reviewe

The 25th Mediterranean Conference on Control and Automation

The 25th Mediterranean Conference on Control and Automation (MED 2017) was held on July 3-6, 2017 on the island of Malta. The first MED took place in 1993 in Chania, Greece, and a complete list of the locations of later MED conferences is available at www.med-control.org. The 2017 edition was held for the first time in Malta, at the University of Malta Valletta Campus. The campus is a 17th century baroque building endowed with striking historical frescoes, portraits, and architectural features that is also well equipped with modern conference facilities. The conference was organized under the auspices of the Mediterranean Control Association (MCA) and the technical cosponsorship of the IEEE Control Systems Society and the IEEE Robotics and Automation Society.peer-reviewe

Multilayer perceptron dual adaptive control for mobile robots

This paper presents a novel dual adaptive dynamic controller for trajectory tracking of nonholonomic wheeled mobile robots. The controller is developed in discrete-time and the robot's nonlinear dynamic functions are assumed to be unknown. A sigmoidal multilayer perceptron neural network is employed for function approximation, and its weights are estimated stochastically in real-time. In contrast to adaptive certainty equivalence controllers hitherto published for mobile robots, the proposed control law takes into consideration the estimates' uncertainty, thereby leading to improved tracking performance. The proposed method is verified by realistic simulations and Monte Carlo analysis.non peer-reviewe

Hospital mortality among major trauma victims admitted on weekends and evenings: a cohort study

Article deposited according to publisher policy posted on SHERPA/RoMEO, 14/09/2010.YesFunding provided by the Open Access Authors Fund

CCL3L1 Copy Number Variation and Susceptibility to HIV-1 Infection: A Meta-Analysis

Background: Although several studies have investigated whether CCL3L1 copy number variation (CNV) influences the risk of HIV-1 infection, there are still no clear conclusions. Therefore, we performed a meta-analysis using two models to generate a more robust estimate of the association between CCL3L1 CNV and susceptibility to HIV-1 infection. Methods: We divided the cases and controls into two parts as individuals with CCL3L1 gene copy number (GCN) above the population specific median copy number (PMN) and individuals with CCL3L1 GCN below PMN, respectively. Odds ratios (ORs) with 95 % confidence intervals (95 % CIs) were given for the main analysis. We also conducted stratified analyses by ethnicity, age group and sample size. Relevant literatures were searched through PubMed and ISI Web of Knowledge up t