Chaos and Unpredictability in the Vibration of an Elasto-Plastic Beam

This contribution discusses the nonlinear dynamics of a pin-ended elasto-plastic beam with both kinematic and isotropic hardening. An iterative numerical procedure based on the operator split technique is developed in order to deal with the nonlinearities in the equations of motion. Free and forced responses for harmonic sinusoidal and square wave excitations are investigated. Numerical simulations present many interesting behaviors such as jump phenomena, sensitivity to initial conditions, chaos and transient chaos. These results indicate that there are practical problems in predicting the response of the beam even when periodic steady state response is expected.

Experimental Vibration Characteristics of a Beam with Nonlinear Support Using Receptance Coupling Analysis

This paper applies the Multi-Harmonic Nonlinear Receptance Coupling Approach (MUHANORCA) (Ferreira 1998) to evaluate the frequency response characteristics of a beam which is clamped at one end and supported at the other end by a nonlinear cubic stiffness joint. In order to apply the substructure coupling technique, the problem was characterised by coupling a clamped linear beam with a nonlinear cubic stiffness joint. The experimental results were obtained by a sinusoidal excitation with a special force control algorithm where the level of the fundamental force is kept constant and the level of the harmonics is kept zero for all the frequencies measured.

Morphological investigation of Toxoplasma gondii in vivo by a multiple beam interference microscope

A recently developed technique, namely multiple beam interference microscopy, has been applied to investigate the morphology of the parasite Toxoplasma gondii for the first time. The interference pattern obtained from the multiple internal reflection of a T. gondii, sandwiched between a glass plate and a cover plate, was focused on the objective of a conventional microscope. Because of the enhance contrast, several details of sub cellular structure and separating compartments are clearly visible. Details reveal the presence of a nucleus, lipid body, dense granule, rhoptry and amylopectin. The wall thickness of the membrane of the lipid body and the amylopectin is of the order of 0.02 µm and can be clearly distinguished with the help of the present technique. The same parasite has also been examined with the help of atomic force microscopy, and because of its thick membrane, the inner structural details were not observed at all. Sub cellular details of T. gondii observed with the present technique have been reported earlier only by low amplification transmission electron microscopy and not by any optical microscopic technique.

Utilização de uma interface do tipo "particle beam" para a obtenção de espectros de massas de compostos pouco voláteis em solução

Due to source contamination and wearing of instrument components problems caused by the direct insertion probe technique, a new way of introduction of low volatile compounds into mass spectrometer was tested. This new scheme comprises the introduction of the low volatile compounds solutions via a six port valve connected to a particle beam interface. Solutions of isatin were injected into this system and the best results were obtained with CH2Cl2, CH3OH and CH3CN. The solution inlet system has shown to be advantageous over the conventional way of direct insertion probe introduction.

Photic driving in the electroencephalogram of children and adolescents: harmonic structure and relation to the resting state

In order to identify latent bioelectrical oscillators, 15 normal subjects (aged 9-17 years, 8 males, 7 females) were subjected to intermittent photic stimulation. The EEG amplitude spectra corresponding to the 11 fixed frequencies of stimulation presented (3-24 Hz) were combined to form "profiles" of the driving reaction in the right occipital area. The driving response varied with frequency, and was demonstrable in 70-100% of cases (using as criterion peak amplitudes 20% larger than those of the neighbors). The strongest responses were observed at the frequency closest to the alpha peak of the resting EEG. A secondary profile maximum was in the theta band. In 10 subjects, this maximum exceeded half the alpha peak (with an average of 72.4% of the alpha peak), while in the resting spectra, theta amplitudes were much lower than the alpha maxima. This responsiveness in theta activity seems to be characteristic of prepubertal and pubertal subjects. The profiles and resting EEG spectra showed a highly significant Pearson's correlation, with the peak in the theta band of the profiles being the main difference observed between them. The correlation coefficient was significantly correlated with the ratio of the maxima in the theta and alpha bands (R = -0.77, P<0.001). The correlation coefficient between profile and resting spectrum may be a useful indicator in screening methods used to reveal latent cerebral oscillators. Profiles for the second and third harmonics were correlated with those of the first harmonic (fundamental frequency), when considering the corresponding EEG frequencies. Peak frequencies in all three profiles were close to those of the individual's background alpha rhythm, and peak amplitudes in higher harmonics were not much lower than those of the fundamental frequency (mean values of 84 and 63%, for second and third harmonics, respectively).