Intelligent control of a single-link flexible manipulator using sliding modes and artificial neural networks

This letter presents a new intelligent control scheme for the accurate trajectory tracking of flexible link manipulators. The proposed approach is mainly based on a sliding mode controller for underactuated systems with an embedded artificial neural network to deal with modelling inaccuracies. The adopted neural network only needs a single input and one hidden layer, which drastically reduces the computational complexity of the control law and allows its implementation in low-power microcontrollers. Online learning, rather than supervised offline training, is chosen to allow the weights of the neural network to be adjusted in real time during the tracking. Therefore, the resulting controller is able to cope with the underactuating issues and to adapt itself by learning from experience, which grants the capacity to deal with plant dynamics properly. The boundedness and convergence properties of the tracking error are proved by evoking Barbalat's lemma in a Lyapunov-like stability analysis. Experimental results obtained with a small single-link flexible manipulator show the efficacy of the proposed control scheme, even in the presence of a high level of uncertainty and noisy signals

High prevalence of hepatitis B virus and low vaccine response in children and adolescents in Northeastern Brazil

Children have an increased likelihood of becoming carriers of the chronic hepatitis B virus. A total of 1,381 children and adolescents were assessed in five municipalities of Maranhao State, Brazil, for detection of anti-HBc, HBsAg and anti-HBs serologic markers and sociodemographic and behavioral features. Among those who were HBsAg negative and anti-HBc negative, the proportion of anti-HBs positives was calculated after the individuals had completed the vaccination schedule. The robust variance of the Poisson’s regression model was used in order to have adjusted tables and calculate the prevalence ratio. Multivariate analysis was performed to identify the factors associated with the prevalence of anti-HBc with or without HBsAg and the vaccine response. It was observed that 163 children were anti-HBc positive and nine individuals were HBsAg positive. The factors associated with the infection were: municipality of residence (residing in Morros municipality or Humberto de Campos municipality), residence in a rural area, aged between 13 and 15 years old, and illicit drug use. The percentage of individuals who were anti-HBc negative and received all three doses of the vaccine was 48.5%. Among these, only 276 (38.9%) had antibodies at protective concentrations. In an adjusted analysis, Morros municipality presented an increased positivity of vaccine response (p < 0.001), and the age ranging between 6 and 10 years old presented a reduced frequency of response. This study reveals a high prevalence of current and past HBV infection within the targeted age group which, in addition to the low vaccination coverage and serological responses, raises concerns about the management of prevention measures, especially the quality of vaccination in these locations