主要对机器学习中深度学习内应用较广、效果较好的一种Attention注意力机制的相关知识进行了总结。首先从背景、原理、分类、比较、应用场景等方面入手,参考了多篇文献;背景方面,介绍了深度学习、自然语言处理(natural language process...主要对机器学习中深度学习内应用较广、效果较好的一种Attention注意力机制的相关知识进行了总结。首先从背景、原理、分类、比较、应用场景等方面入手,参考了多篇文献;背景方面,介绍了深度学习、自然语言处理(natural language processing,NLP)的相关技术的研究现状,并明确了Attention在其中的定位;原理方面,由于self-attention的优越性和广泛应用,主要对self-attention进行了阐述;最后对不同的Attention类别进行了整理,依据不同的分类标准,划分了6大类别,并分别对其进行介绍。此外,将经典的卷积神经网络(convolutional neural network,CNN)、循环神经网络(recurrent neural network,RNN)与Attention机制进行对比,进一步明确了Attention在当前的深度学习中的地位,最后对应用场景进行了简要的介绍。展开更多
Raman spectroscopy has been widely used to identify the physical properties of carbon nanotubes(CNTs),and to assess their functionalization as well as orientation.Recently,Raman spectroscopy has become a powerful tool...Raman spectroscopy has been widely used to identify the physical properties of carbon nanotubes(CNTs),and to assess their functionalization as well as orientation.Recently,Raman spectroscopy has become a powerful tool to characterize the interfacial properties between CNTs and polymer matrices.This review provides an overview of micro-Raman spectroscopy of CNTs and its application in studying CNT reinforced polymer composites.Based on the specific Raman band shifts relating to the mechanical deformation of CNTs,Raman scattering can be used to evaluate the interactions between the CNTs and the surrounding polymer in the composites,and to detect the phase transitions of the polymer,and investigate the local stress state as well as the Young's modulus of the CNTs.Moreover,we also review the current progress of Raman spectroscopy in various CNT macroarchitectures(such as films,fibers as well as composite fibers).The microscale structural deformation of CNT macroarchitectures and strain transfer factors from macroscale architectures to microscale structures are inferred.Based on an in situ Raman-tensile test,we further predict the Young's modulus of the CNT macroarchitectures and reveal the dominating factors affecting the mechanical performances of the CNT macroarchitectures.展开更多
In this study, the size distribution of atmospheric aerosol in Beijing was monitored by the scanning mobility particle sizer spectrometer and the optical particle sizer. The size of particles in atmospheric aerosol wa...In this study, the size distribution of atmospheric aerosol in Beijing was monitored by the scanning mobility particle sizer spectrometer and the optical particle sizer. The size of particles in atmospheric aerosol was primarily distributed in the range of less than 1 pm. It showed different changes with the mass concentrations of particulate matters with an aerodynamic diameter of 〈2.5 pm （PM2.5） for different sizes of fine particles. The amount of ultrafine particles （less than about 60 nm） decreased while the larger ones （〉60 nm） increased along with the mass concentration of PM2.5 in atmospheric aerosol. This was be- cause of the formation of the secondary atmospheric aerosol. The polylactic acid （PLA） nanofibers were prepared for filtering the aerosol by electrospinning. PLA nanofiber mats were used as the middle layer to design the composite filter membranes. Atmospheric aerosol was used as dust source in the filtration test. The results showed that the filtration efficiency of the com- posite filter media increased along with the thickness of nanofiber mats, which was controlled by the collection time during electrospinning. Filtration efficiency can be improved obviously by compositing with a thin layer of nanofibers.展开更多
基金supported by the National Natural Science Foundation of China (20874023,10874177)the National Key Basic Research Program of China (2007CB936803)the Knowledge Innovation Project of Chinese Academy of Sciences (KJCX2-YW-M01)
文摘Raman spectroscopy has been widely used to identify the physical properties of carbon nanotubes(CNTs),and to assess their functionalization as well as orientation.Recently,Raman spectroscopy has become a powerful tool to characterize the interfacial properties between CNTs and polymer matrices.This review provides an overview of micro-Raman spectroscopy of CNTs and its application in studying CNT reinforced polymer composites.Based on the specific Raman band shifts relating to the mechanical deformation of CNTs,Raman scattering can be used to evaluate the interactions between the CNTs and the surrounding polymer in the composites,and to detect the phase transitions of the polymer,and investigate the local stress state as well as the Young's modulus of the CNTs.Moreover,we also review the current progress of Raman spectroscopy in various CNT macroarchitectures(such as films,fibers as well as composite fibers).The microscale structural deformation of CNT macroarchitectures and strain transfer factors from macroscale architectures to microscale structures are inferred.Based on an in situ Raman-tensile test,we further predict the Young's modulus of the CNT macroarchitectures and reveal the dominating factors affecting the mechanical performances of the CNT macroarchitectures.
文摘In this study, the size distribution of atmospheric aerosol in Beijing was monitored by the scanning mobility particle sizer spectrometer and the optical particle sizer. The size of particles in atmospheric aerosol was primarily distributed in the range of less than 1 pm. It showed different changes with the mass concentrations of particulate matters with an aerodynamic diameter of 〈2.5 pm （PM2.5） for different sizes of fine particles. The amount of ultrafine particles （less than about 60 nm） decreased while the larger ones （〉60 nm） increased along with the mass concentration of PM2.5 in atmospheric aerosol. This was be- cause of the formation of the secondary atmospheric aerosol. The polylactic acid （PLA） nanofibers were prepared for filtering the aerosol by electrospinning. PLA nanofiber mats were used as the middle layer to design the composite filter membranes. Atmospheric aerosol was used as dust source in the filtration test. The results showed that the filtration efficiency of the com- posite filter media increased along with the thickness of nanofiber mats, which was controlled by the collection time during electrospinning. Filtration efficiency can be improved obviously by compositing with a thin layer of nanofibers.
