Comments, with reply on 'Continuous time relay-controlled model reference adaptive-system' by A. Abdulkareem and R. Nagarajam

An adaptive scheme is shown by the authors of the above paper (ibid. vol. 71, no. 2, pp. 275-276, Feb. 1983) for continuous time model reference adaptive systems (MRAS), where relays replace the usual multipliers in the existing MRAS. The commenter shows an error in the analysis of the hyperstability of the scheme, such that the validity of this configuration becomes an open question.

Texto-coisa, poema-objeto: a políedrica p(r)oesia de Murilo Mendes e Francis Ponge

Pós-graduação em Estudos Literários - FCLAR

Regeneração natural de um fragmento de cerrado degradado com a formação de pastagens de braquiária (Urochloa decumbens (Stapf) R. D. Webster)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

On the question of neutrino spin precession in a magnetic field

Using the Feynman procedure of ordered exponential operators we solve the evolution equations for a two-neutrino system considering arbitrarily varying matter density and magnetic field along the neutrino trajectory. We show that a large geometrical phase velocity suppresses νL→νR transitions unless some stationary trajectory is found along the neutrino path. Concerning the solar neutrino case, if we admit the standard solar model matter distribution, no such trajectory can be found.