Subwavelength position sensing using nonlinear feedback and wave chaos

We demonstrate a position-sensing technique that relies on the inherent sensitivity of chaos, where we illuminate a subwavelength object with a complex structured radio-frequency field generated using wave chaos and a nonlinear feedback loop. We operate the system in a quasi-periodic state and analyze changes in the frequency content of the scalar voltage signal in the feedback loop. This allows us to extract the object's position with a one-dimensional resolution of ~\lambda/10,000 and a two-dimensional resolution of ~\lambda/300, where \lambda\ is the shortest wavelength of the illuminating source.Comment: 4 pages, 4 figure

Logarithmic periodicities in the bifurcations of type-I intermittent chaos

The critical relations for statistical properties on saddle-node bifurcations are shown to display undulating fine structure, in addition to their known smooth dependence on the control parameter. A piecewise linear map with the type-I intermittency is studied and a log-periodic dependence is numerically obtained for the average time between laminar events, the Lyapunov exponent and attractor moments. The origin of the oscillations is built in the natural probabilistic measure of the map and can be traced back to the existence of logarithmically distributed discrete values of the control parameter giving Markov partition. Reinjection and noise effect dependences are discussed and indications are given on how the oscillations are potentially applicable to complement predictions made with the usual critical exponents, taken from data in critical phenomena.Comment: 4 pages, 6 figures, accepted for publication in PRL (2004

Efeito de porta-enxertos na produção de castanha de um clone de cajueiro-anão precoce.

O objetivo deste trabalho foi avaliar,a partir de um pomar comercial, o efeito de três porta-enxertos na produção de castanha do clone do cajueiro anão precoce.bitstream/CNPAT-2010/5360/1/Ct-045.pd

Boolean Chaos

We observe deterministic chaos in a simple network of electronic logic gates that are not regulated by a clocking signal. The resulting power spectrum is ultra-wide-band, extending from dc to beyond 2 GHz. The observed behavior is reproduced qualitatively using an autonomously updating Boolean model with signal propagation times that depend on the recent history of the gates and filtering of pulses of short duration, whose presence is confirmed experimentally. Electronic Boolean chaos may find application as an ultra-wide-band source of radio wavesComment: 10 pages and 4 figur

Efeito da adubação nitrogenada e do pastejo sobre a frequência de espécies invasoras em ambientes de pastagem cultivada.

Altas doses de nitrogênio e manejo do pastejo mais intensivo tendem a diminuir a freqüência de espécies invasoras, pelo favorecimento do crescimento da espécie principal e efeito do pastejo sobre a presença de espécies invasoras de potencial forrageiro

Matemática, Literatura & Aulas

A aprendizagem da Matemática não ocorre por mera transmissão de saberes do professor para os alunos. A ideia de que o conhecimento pode passar linearmente de uma cabeça – daquele que sabe – para outra(s) cabeça(s) – para aqueles que querem saber –, pelas palavras ditas e escritas, não tem qualquer correspondência com a realidade. A aprendizagem é um processo adaptativo, simultaneamente individual e coletivo, baseado na ação e na reflexão, no qual a comunicação tem um papel fundamental, na medida que permite estabelecer ligação entre as pessoas