In skeleton-based action recognition, the approaches based on graph convolutional networks(GCN) have achieved remarkable performance by modeling spatial-temporal graphs to explore the physical dependencies between body joints. However, these methods mostly apply hierarchical GCNs to aggregate wider-range neighborhood information, which makes joint features be weakened during long diffusion. In this paper, we design a multi-scale mixed dense graph convolutional network (MMDGCN) to overcome both shortcomings. We propose a dense graph convolution operation to enhance the local context information of joints, and then the spatial and temporal attention modules with a larger receptive field are introduced to help the model strengthen the discriminative features to adaptively refine the intermediate feature maps. We also design a multi-scale mixed temporal convolution module, which provides a flexible temporal graph through the combination of different scale convolution kernels. Extensive experiments on the three real-world datasets (NTU-RGB+D, NTU-RGB+D120 and Kinetics) demonstrate that the performance of the proposed MMDGCN in skeleton-based action recognition.INDEX TERMS dense graph convolution, spatial and temporal attention module, multi-scale mixed temporal convolution, skeleton-based action recognition
A conformal log-periodic balloon antenna operating at the very high frequency (VHF) band is presented in this paper. The antenna consists of eight conformal bowtie-dipole elements cross-fed by a parallel-strip transmission line and is then attached to the surface of a cylindrical balloon. After a detailed comparative analysis of the radiation performance of conformal strip-dipole and bowtie-dipole, a conformal log-periodic bowtie-dipole balloon antenna is designed. Simulated results show that its operating bandwidth ranges from 60 MHz to 233 MHz with the voltage standing wave ratio (VSWR) less than 2 and a good end-fire radiation pattern of 5 dBi average gain. Measured results of a full-scale prototype fabricated with aluminum foils and a polyvinyl chloride balloon are in good agreement with simulated ones, which demonstrates the balloon antenna's potential applications in VHF communication systems.
Index Terms-Balloon antenna, bowtie-dipole, conformal antenna, log-periodic antenna, very high frequency (VHF)0018-926X (c)
We herein report a linear polarizer based on a 2D array of substrate integrated waveguide cavities, which can convert an arbitrary linearly polarized (LP) incident wave into an outgoing LP wave in a specified polarization direction with constant transmittance. Two orthogonal slots etched on the front surface of the cavity are utilized to couple a wave of arbitrary polarization into the cavity, while another slot on the back side helps to couple the field out along a desired polarization direction. Microwave experiments are performed as a proof of concept. The proposed polarizer exhibits very good performance with stable transmittance as 50% and a polarization extinction ratio over 45 dB. The new polarizer is potentially useful in novel polarization-selective devices that are immune to the polarization direction of an incident plane wave.
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