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The evolution of the experimental frequency width of symmetric modes of an aluminum plate is studied as a function of the angle of incidence below the first critical angle. It is found that the frequency width predicted by resonant scattering theory, corrected for the directivity of emitter and receiver, generally explains the experimental frequency width well. However, large discrepancies remain for the frequency width of the S1 mode at angles of incidence larger than 9°. It is demonstrated that these are caused by not taking into account the complex nature of the slowness of the plate mode. This suggests that there is a need for a theory that models the interaction of a beam of ultrasound, bounded in space and time, with an elastic plate. [Copyright &y& Elsevier]

Polymer-tethered colloidal particles (aka "particle brush materials") have attracted interest as a platform for innovative material technologies and as a model system to elucidate glass formation in complex structured media. In this contribution, Brillouin light scattering is used to sequentially evaluate the role of brush architecture on the dynamical properties of brush particles in both the individual and assembled (film) state. In the former state, the analysis reveals that brush-brush interactions as well as global chain relaxation sensitively depend on grafting density; i.e., more polymer-like behavior is observed in sparse brush systems. This is interpreted to be a consequence of more extensive chain entanglement. In contrast, the local relaxation of films does not depend on grafting density. The results highlight that relaxation processes in particle brush-based materials span a wider range of time and length scales as compared to linear chain polymers. Differentiation between relaxation on local and global scale is necessary to reveal the influence of molecular structure and connectivity on the aging behavior of these complex systems. [ABSTRACT FROM AUTHOR]

The plot of the transmission coefficient moduli cannot be used to analyze all the resonances of layered structures because of the overlapping of the resonances. A method using the scattering matrix eigenvalues is presented. It allows, first, to annihilate the overlapping and to recover the resonance positions and half-widths and second, to divide in two independent sets most of the resonances involved in symmetric structures as well as in nonsymmetric ones. Comparisons between the results provided by the method and those coming from the poles of the transmission coefficient agree. In many cases, the transition terms constitute a generalization of the transmission coefficients. [ABSTRACT FROM AUTHOR]