Remarks on the Sommerfeld effect characterization in the wavelet domain

In many applications in engineering, a mechanical system operates in the nonstationary regime, either partially of fully, creating the possibility to generate nonlinearities in them. Great efforts have been made to better understand and characterize these phenomena. One of several methods that are being used for the processing of signals of a nonstationary nature, as well as for the characterization of nonlinearities in mechanical systems, is the wavelet transform. A particular phenomenon that is seen in systems operating in the nonstationary regime is the Sommerfeld effect, which occurs due to the nonlinear interaction between a nonideal energy source and a mechanical system. This phenomenon can lead to high amplitudes of vibration for the system that in turn can cause damage in it. Therefore, this work presents an application of the continuous wavelet transform and the wavelet packet transform for the characterization of the Sommerfeld effect in mechanical systems where only the time response is at hand. Experimental procedures were performed where a nonideal energy source (an unbalanced DC motor) was used to excite (a) a portal frame and (b) a three-story shear-building. The results showed the effectiveness and the potential of the methods proposed.

ENTANGLEMENT AND AUTOCORRELATION FUNCTION IN SEMICONDUCTOR MICROCAVITIES

The autocorrelation function of the light emitted by a microcavity containing a semiconductor quantum well in the nonstationary regime is investigated. An analytical expression in the weak pumping and strong coupling regime is derived. Furthermore, it is shown that the initial entangled state can be deduced from the nonstationary autocorrelation function.