A efficient time-domain algorithm, based on the spatial pulse response approach, is proposed for the determination of the acoustic fields radiated by means of acoustical sources. The computations are performed by the discrete representation array modelling (DREAM) procedure, specially adapted to study the planar and arbitrarily structured multielement transducer arrays. DREAM, based on the discrete representation computational concept, acts as the generator of the array velocity potential impulse response, and thus, does not require any analytical solutions prior to the computations. The computations are valid for all field regions and may be performed for any excitation form. Apart from the classic case of rigid baffle conditions, the free and soft planar baffle also can be considered. The use of the time-domain solution for causal Green's function for lossy media enables the wideband absorption effects to be modeled. The accuracy of computations depends on temporal and spatial discretization and can be obtained as required. The quantitative rules, which determine the required discretizations to be predicted, are proposed. The computational examples show that DREAM allows the different and various transducers to be modeled. Its possibilities are illustrated by computations for the multielement transducers, including the beam-steered, amplitude-weighted sonar array, the focusing annular transducer, and the diverging and converging cylindrical array.

By using the spectral moments method, we calculate the infrared spectra of chiral and achiral single-walled carbon nanotubes (SWCNTs) of different diameters and lengths. We show that the number of the infrared modes, their frequencies, and intensities depend on the length and chirality of the nanotubes. Furthermore, the dependence of the infrared spectrum as a function of the size of the SWCNT bundle is analyzed. These predictions are useful to interpret the experimental infrared spectra of SWCNTs.

We report on minimum energy calculations, using a convenient Lennard-Jones expression of the van der Waals intermolecular potential, to derive the optimum configurations of C 60 molecules inside single wall carbon nanotubes. Depending on the diameter of the nanotube, C 60 molecules were found to form linear or zigzag chains inside the nanotubes. In the following, we use the spectral moments method, together with a bond-polarizability model, to calculate the nonresonant Raman spectrum for infinitely long isolated C 60 peapods. We present the evolution of the Raman spectrum as a function of the diameter and chirality of the nanotube. The changes of the Raman spectrum as a function of the configuration of the C 60 molecules inside the nanotubes are identified. On the other hand, the effect of the filling factor on the Raman spectrum is analyzed. These predictions are useful to interpret the experimental Raman spectra of fullerene peapods.

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