901 research outputs found
Frequency Dependent Mechanical Properties of Elastic Metamaterials with Locally Resonant Microstructures
Frequency dependent mechanical properties of elastic metamaterials with locally resonant microstructures were investigated. Due to the dynamic behavior of the microstructures, the mechanical properties of these elastic metamaterials, if represented by effective continuous media, would exhibit frequency dependent characteristics. This phenomenon was studied from the energy propagation point of view. Based on the monatomic mass lattice model, two band gap formation mechanisms were proposed. For each representative element, considering the time period when effective mass velocity increases from zero to maximum, if the kinetic energy requirement is beyond the capability of the external work of external spring, the monatomic lattice type band gap would be generated; if the kinetic energy requirement is negative, the two inner masses interaction type of band gap would be generated. This analytical solution was also verified by FE simulation. Following that, the band gap in diatomic mass-in-mass lattice systems was explained based on the proposed two formation mechanisms, and the passing band between the two band gaps generated by the single negative effective mass in diatomic mass-in-mass lattice systems was eliminated based on the analytical derivation and verified by the tone burst wave propagation using FE simulation. Further, the dynamic behavior of rods made of elastic metamaterials with frequency dependent properties was investigated. Based on the frequency dependent mass density and Young’s modulus for the effective continuum, it was found that the rod natural frequency distribution was changed and no natural resonance frequency in the band gap region of the corresponding metamaterial. Besides, the general wave amplitude transfer function was derived for wave propagation in layered structures, and the final transmitted wave amplitude of the layered metamaterial structure with decreasing density was obtained using Mathematical Induction method. Making use of the frequency dependent properties, the elastic phase-controlling metalayer was also analyzed. It was analytically and numerically demonstrated that, whether a normal incident longitudinal wave can propagate through the interface depends on whether the wave length is larger or shorter than the periodic length of the metalayer element. In addition, since the phase gradients are the same at both sides of metalayer, this type of elastic metalayer may serve as an energy absorption material. Finally, the wave attenuation characteristics of an elastic metamaterial composed of spherical rubber-encased alumina particle inclusions in an epoxy matrix was verified by numerical simulation and coil shaker based vibration test. Moreover, the dynamic behavior of free-free end rod made of the same elastic metamaterial was obtained by piezoelectric patches based vibration tests. It was found that the wave attenuation effect would increase with the number of inner resonators, and the rod natural frequencies would shift ahead when input frequency was close to band gap region
Inner and Inter Label Propagation: Salient Object Detection in the Wild
In this paper, we propose a novel label propagation based method for saliency
detection. A key observation is that saliency in an image can be estimated by
propagating the labels extracted from the most certain background and object
regions. For most natural images, some boundary superpixels serve as the
background labels and the saliency of other superpixels are determined by
ranking their similarities to the boundary labels based on an inner propagation
scheme. For images of complex scenes, we further deploy a 3-cue-center-biased
objectness measure to pick out and propagate foreground labels. A
co-transduction algorithm is devised to fuse both boundary and objectness
labels based on an inter propagation scheme. The compactness criterion decides
whether the incorporation of objectness labels is necessary, thus greatly
enhancing computational efficiency. Results on five benchmark datasets with
pixel-wise accurate annotations show that the proposed method achieves superior
performance compared with the newest state-of-the-arts in terms of different
evaluation metrics.Comment: The full version of the TIP 2015 publicatio
Skeleton Key: Image Captioning by Skeleton-Attribute Decomposition
Recently, there has been a lot of interest in automatically generating
descriptions for an image. Most existing language-model based approaches for
this task learn to generate an image description word by word in its original
word order. However, for humans, it is more natural to locate the objects and
their relationships first, and then elaborate on each object, describing
notable attributes. We present a coarse-to-fine method that decomposes the
original image description into a skeleton sentence and its attributes, and
generates the skeleton sentence and attribute phrases separately. By this
decomposition, our method can generate more accurate and novel descriptions
than the previous state-of-the-art. Experimental results on the MS-COCO and a
larger scale Stock3M datasets show that our algorithm yields consistent
improvements across different evaluation metrics, especially on the SPICE
metric, which has much higher correlation with human ratings than the
conventional metrics. Furthermore, our algorithm can generate descriptions with
varied length, benefiting from the separate control of the skeleton and
attributes. This enables image description generation that better accommodates
user preferences.Comment: Accepted by CVPR 201
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