4,434 research outputs found
Triggering waves in nonlinear lattices: Quest for anharmonic phonons and corresponding mean free paths
Guided by a stylized experiment we develop a self-consistent anharmonic
phonon concept for nonlinear lattices which allows for explicit
"visualization." The idea uses a small external driving force which excites the
front particles in a nonlinear lattice slab and subsequently one monitors the
excited wave evolution using molecular dynamics simulations. This allows for a
simultaneous, direct determination of the existence of the phonon mean free
path with its corresponding anharmonic phonon wavenumber as a function of
temperature. The concept for the mean free path is very distinct from known
prior approaches: the latter evaluate the mean free path only indirectly, via
using both, a scale for the phonon relaxation time and yet another one for the
phonon velocity. Notably, the concept here is neither limited to small lattice
nonlinearities nor to small frequencies. The scheme is tested for three
strongly nonlinear lattices of timely current interest which either exhibit
normal or anomalous heat transport
Directional far-field response of a spherical nanoantenna
We study the directional far-field response of a spherical nanoantenna via engineering the plasmonic nanosphere's distance, size, and material. A unified pattern synthesis approach based on the T-matrix method and the particle swarm optimization is proposed for the directional beamforming of the nanoantenna. The angular response of the directional nanoantenna is very sensitive to the material change but is immunized to the random error of the spatial position of each particle. The physical origin of the high directionality is attributed to the coherent near-field distribution with large correlation length. This work provides the fundamental theory and physics for future nanoantenna design. © 2011 Optical Society of America.published_or_final_versio
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