Variable neural networks for adaptive control of nonlinear systems

This paper is concerned with the adaptive control of continuous-time nonlinear dynamical systems using neural networks. A novel neural network architecture, referred to as a variable neural network, is proposed and shown to be useful in approximating the unknown nonlinearities of dynamical systems. In the variable neural networks, the number of basis functions can be either increased or decreased with time, according to specified design strategies, so that the network will not overfit or underfit the data set. Based on the Gaussian radial basis function (GRBF) variable neural network, an adaptive control scheme is presented. The location of the centers and the determination of the widths of the GRBFs in the variable neural network are analyzed to make a compromise between orthogonality and smoothness. The weight-adaptive laws developed using the Lyapunov synthesis approach guarantee the stability of the overall control scheme, even in the presence of modeling error(s). The tracking errors converge to the required accuracy through the adaptive control algorithm derived by combining the variable neural network and Lyapunov synthesis techniques. The operation of an adaptive control scheme using the variable neural network is demonstrated using two simulated example

Avaliação da aplicação exógena de poliaminas no crescimento de calos de mangabeira (Hancornia speciosa Gomes) Evaluation of exogenous application of polyamines on callus growth of mangaba tree (Hancornia speciosa Gomes)

Este trabalho teve como objetivo estudar o efeito das poliaminas espermidina e espermina no crescimento de calos Hancornia speciosa Gomes. Calos com 0,5 cm de diâmetro foram inoculados em meio Murashige & Skoog (1962) (MS) a 50% + 100 mg L-1 de caseína hidrolisada + 200 mg L-1 de levedura de cerveja, variando os tratamentos:A: 1 mmol de espermina + 2 mg L-1 de 2,4-D (ácido 2,4 diclorofenoxiacético) + 0,5 mg L-1 de NAA (ácido naftalenoacético); B: 1 mmol de espermidina + 2 mg L-1 de 2,4-D + 0,5 mg L-1 de NAA; C: 2 mg L-1 de 2,4-D + 0,5 mg L-1 de NAA. Não houve influência das poliaminas no crescimento dos calos. observou-se, nos calos tratados com espermidina, maior concentração celular de putrescina (582,37 µg g mf-1) aos 60 dias, maior teor de espermidina (502,54 µg g mf-1) e espermina (868,53 µg g mf-1) aos 40 dias de cultivo, quando se aplicou a própria poliamina. Conclui-se que a aplicação exógena de poliaminas em Hancornia speciosa não proporciona aumento no crescimento de calos. A oxidação promovida por longos períodos de cultivo in vitro induz aumento nos níveis de putrescina.<br>The effect of polyamines spermine and spermidine in the calluses growth of Hancornia speciosa Gomes was studied. Calluses with 0.5 cm diameter were inoculated in Murashige & Skoog (1962) (MS) medium 50% + hidrolizated casein 100 mg L-1 + yeast 200 mg L-1, according to the treatments: A: spermine 1 mmol + 2.4-D 2 mg L-1 + NAA 0.5 mg L-1, B: spermidine 1 mmol + 2.4-D 2 mg L-1 + NAA 0.5 mg L-1, C: 2.4-D 2 mg L-1 + NAA 0.5 mg L-1. There was not polyamine influence in the calluses growth. It was observed in the treated calluses with spermidine larger cellular putrescine concentration (582.37 µg g mf-1) at 60 days, larger spermidine concentration (502.54 µg g mf-1) and spermine (868.53 µg g mf-1) at 40 days of cultivation, when the own polyamine was applied. It was concluded that the exogenous polyamine application in Hancornia speciosa does not provide an increase in the calluses growth. The oxidation promoted by long periods of in vitro cultivation induces an increase in the putrescine levels