Current studies have shown that the spatial‐temporal graph convolutional network (ST‐GCN) is effective for skeleton‐based action recognition. However, for the existing ST‐GCN‐based methods, their ...temporal kernel size is usually fixed over all layers, which makes them cannot fully exploit the temporal dependency between discontinuous frames and different sequence lengths. Besides, most of these methods use average pooling to obtain global graph feature from vertex features, resulting in losing much fine‐grained information for action classification. To address these issues, in this work, the authors propose a novel spatial attentive and temporal dilated graph convolutional network (SATD‐GCN). It contains two important components, that is, a spatial attention pooling module (SAP) and a temporal dilated graph convolution module (TDGC). Specifically, the SAP module can select the human body joints which are beneficial for action recognition by a self‐attention mechanism and alleviates the influence of data redundancy and noise. The TDGC module can effectively extract the temporal features at different time scales, which is useful to improve the temporal perception field and enhance the robustness of the model to different motion speed and sequence length. Importantly, both the SAP module and the TDGC module can be easily integrated into the ST‐GCN‐based models, and significantly improve their performance. Extensive experiments on two large‐scale benchmark datasets, that is, NTU‐RGB + D and Kinetics‐Skeleton, demonstrate that the authors’ method achieves the state‐of‐the‐art performance for skeleton‐based action recognition.
We report an effective surface-enhanced Raman scattering (SERS) substrate enabled by synthesis of gold nanobipyramids (Au NBPs) in a microfluidic chip. Improved seed-mediated method was implemented ...for consecutive synthesis of Au NBPs in an S-shaped micromixer. Under precise control of flow rates of reactants, Au NBPs with various morphologies can be prepared in microchannels to serve as effective SERS substrates. With the assistance of this substrate, Raman signals of rhodamine 6G (R6G) probe molecules were significantly enhanced with high sensitivity and reproducibility, the dependence between SERS spectra and Au NBPs morphologies was investigated. Owing to the control mechanism involved in the reaction process in microchannels, these flexible, stable and high-performance SERS substrates can have potential application in diverse fields, particularly in biosensing areas.
We report a microfluidic chip designed and fabricated for the consecutive synthesis of gold nanobipyramids (Au NBPs) with controllable morphology. The seed-mediated method is employed to synthesize ...Au NBPs in an S-shaped micromixer. Under sufficient mixing and precise flow rate control of various reactants during microfluidic synthesis, Au NBPs with various aspect ratios can be obtained through this microfluidic platform. The dependence of reactant concentration on the morphology of synthesized Au NBPs is studied by changing the flow rate of silver nitrate (AgNO
3
), ascorbic acid (AA) and gold seed in microchannel respectively, analytical simulation is performed to validate the control mechanism during Au NBPs synthesis in a microchannel.
We prepare metal films with various thicknesses on liquid substrates by thermal evaporation and investigate the annealing effect on these films. Gold films deposited on a silicone oil surface consist ...of a large number of branched aggregates, which contains plenty of gold nanoparticles. This characteristic morphology is mainly attributed to the isotropic and free-sustained liquid substrate. Thermal annealing results in the reintegration of nanoparticles; thus, the surface morphology and microstructure of gold films change significantly. The dependence of annealing conditions on the surface-enhanced Raman scattering performance of gold films is studied, in which gold films show favorable Raman activity when annealed at certain annealing temperature and the experimental results are verified by simulation analysis. The study on the optimal annealing temperature of surface-enhanced Raman scattering substrate will pave the way for the potential application of films deposited on liquid surfaces in microfluidics and enhanced Raman detection.
During the operation of gas insulated switchgear (GIS) and gas insulated line (GIL), the conducting bar generates joule heat, and a non-uniform distribution of temperature forms in the bulk of the ...insulators. As the load varies, the temperature distribution changes, and it has an influence on the bulk conductivity of the insulators. Moreover, the surface charge accumulation can be affected. In order to clarify this, a surface charge measurement system which could achieve temperature control was constructed, and a model insulator with truncated cone type was employed, as well as two types of high-voltage electrodes, i.e. plate and needle electrodes. It is found that both polarities of charges existed on the insulator surface when a dc high voltage was applied to the plate or needle electrode, and homo-charge density was much higher than that of hetero-one. As for the plate electrode, homo-charges resulted from micro-discharges, while generated by corona in the case with needle electrode. As temperature increased, homo-charge density decreased, kept unchanged and increased for three cases, respectively, i.e. when dc voltage was applied to the plate electrode, and when voltage of 3 and 20 kV was applied to the needle electrode. Moreover, a simulation model involving multi-physics was established, which included heat conduction in solid and transient field changing from the initial capacitive to stationary resistive field distribution. It is proved that the electric conduction of the insulator bulk contributed to the accumulation of hetero-charges, and temperature could enhance this. Besides, when temperature increased, the corona inception voltage reduced, and hence the homo-charge density increased. Due to the effect of neutralization and the differences in the sensitivity of corona with different intensity to temperature, the tendency of homo-charge density changing with temperature for the three cases showed distinct in the experiments.
Four typical types of artificial defects are designed in conducting the decomposition experiments of SF6 gas to obtain and understand the decomposition characteristics of SF6 gas-insulated medium ...under different types of negative DC partial discharge (DC-PD), and use the obtained decomposition characteristics of SF6 in diagnosing the type and severity of insulation fault in DC SF6 gas-insulated equipment. Experimental results show that the negative DC partial discharges caused by the four defects decompose the SF6 gas and generate five stable decomposed components, namely, CF4, CO2, SO2F2, SOF2, and SO2. The concentration, effective formation rate, and concentration ratio of SF6 decomposed components can be associated with the PD types. Furthermore, back propagation neural network algorithm is used to recognize the PD types. The recognition results show that compared with the concentrations of SF6 decomposed components, their concentration ratios are more suitable as the characteristic quantities for PD recognition, and using those concentration ratios in recognizing the PD types can obtain a good effect.
Surface-enhanced Raman scattering (SERS) substrates were prepared by depositing Ag atoms on liquid surfaces via thermal evaporation at room temperature. These free-sustained substrates result in the ...formation of uniform Ag films, in which ramified Ag aggregates consist of substantial Ag nanoclusters with narrow gaps of several nanometers in between. SERS spectra of rhodamine 6G were investigated for this substrate to evaluate the SERS performance of this characteristic film morphology, and the results indicated that the SERS intensity from the closely-packed Ag nanostructures and small intervals were significantly enhanced. The dependence of SERS enhancement on the film thickness, nanoparticle size, and gap width was studied. An analytical model was proposed to simulate the electric field distribution during SERS detection, and the results validated the experimental observations.
•A theoretical model that describes the growth mechanism of various Zn nanocrystals on liquid substrates is proposed.•The specific growth behavior is mainly attributed to the isotropic substrates and ...the deviation of seed crystal in the initial growth stage.•Growth mechanism of various nanocrystals is investigated, and the dependence of crystal length and growth rate is discussed.
We present a theoretical model describing the growth of low-dimensional nanocrystals with various shapes on liquid surfaces. The characteristic aggregation of deposited atoms is primarily resulted from the property of isotropic and free-sustained substrates. In the subsequent growth process, the atoms diffuse along preferential growth direction after they meet and then the low-dimensional nanocrystal forms gradually. The variety of nanocrystal morphology is attributed to the deviation of seed crystal size or growth direction in the initial stage caused by inhomogeneous deposition conditions. The dependence of nanocrystal length and growth rate during the growth process was discussed, and the results are in good agreement with the experimental findings.
We report a facile approach for the wettability control of copper (Cu) films grown on a silicone oil surface by thermal evaporation. Characteristic aggregation of deposited Cu atoms was obtained due ...to the isotropic and free-sustained liquid substrates. Through the fine adjustment of deposition parameters in the growth process, Cu films with controlled morphology from ramified aggregates to continuous films can be prepared. Accompanied with the evolution of morphology, water wettability was effectively reduced and the hydrophilic-to-hydrophobic transition can be achieved. The relationship between the wettability and microstructure of Cu films was investigated. These films with characteristic morphology and controlled wettability may open lots of application avenues in the development of devices with modified surface properties.
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