14,673 research outputs found
Generation of Sound Bullets with a Nonlinear Acoustic Lens
Acoustic lenses are employed in a variety of applications, from biomedical
imaging and surgery, to defense systems, but their performance is limited by
their linear operational envelope and complexity. Here we show a dramatic
focusing effect and the generation of large amplitude, compact acoustic pulses
(sound bullets) in solid and fluid media, enabled by a tunable, highly
nonlinear acoustic lens. The lens consists of ordered arrays of granular
chains. The amplitude, size and location of the sound bullets can be controlled
by varying static pre-compression on the chains. We support our findings with
theory, numerical simulations, and corroborate the results experimentally with
photoelasticity measurements. Our nonlinear lens makes possible a qualitatively
new way of generating high-energy acoustic pulses, enabling, for example,
surgical control of acoustic energy.Comment: 19 pages, 7 figures, includes supplementary informatio
ISTA-Net: Interpretable Optimization-Inspired Deep Network for Image Compressive Sensing
With the aim of developing a fast yet accurate algorithm for compressive
sensing (CS) reconstruction of natural images, we combine in this paper the
merits of two existing categories of CS methods: the structure insights of
traditional optimization-based methods and the speed of recent network-based
ones. Specifically, we propose a novel structured deep network, dubbed
ISTA-Net, which is inspired by the Iterative Shrinkage-Thresholding Algorithm
(ISTA) for optimizing a general norm CS reconstruction model. To cast
ISTA into deep network form, we develop an effective strategy to solve the
proximal mapping associated with the sparsity-inducing regularizer using
nonlinear transforms. All the parameters in ISTA-Net (\eg nonlinear transforms,
shrinkage thresholds, step sizes, etc.) are learned end-to-end, rather than
being hand-crafted. Moreover, considering that the residuals of natural images
are more compressible, an enhanced version of ISTA-Net in the residual domain,
dubbed {ISTA-Net}, is derived to further improve CS reconstruction.
Extensive CS experiments demonstrate that the proposed ISTA-Nets outperform
existing state-of-the-art optimization-based and network-based CS methods by
large margins, while maintaining fast computational speed. Our source codes are
available: \textsl{http://jianzhang.tech/projects/ISTA-Net}.Comment: 10 pages, 6 figures, 4 Tables. To appear in CVPR 201
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