Single crystals subjected to shock compression exhibit responses with distinct two-wave structures for certain crystal orientations.However,little is known to date regarding how the shock response depends on crystal o...Single crystals subjected to shock compression exhibit responses with distinct two-wave structures for certain crystal orientations.However,little is known to date regarding how the shock response depends on crystal orientation,and especially why the two-wave structure depends on the crystal orientation.In this work,molecular dynamics simulations of shock compressions in copper single crystals are performed to investigate the orientation dependence of shock responses and the corresponding deformation mechanisms.Four copper single crystals with[001],[011],[012],and[123]crystal orientations along the depth direction are investigated.The[011],[012],and[123]crystal orientations of copper single crystals show distinct two-wave structures in their shock responses,while such a two-wave structure in the shock response is not seen for those orientations having a[001]crystal orientation.The potential causes are analyzed by considering the propagation velocities of both elastic and plastic waves.We develop a technique for identifying twin structures in face-centered cubic crystals and this technique can effectively identify the twin structure.The morphology of shock-induced defects(e.g.,dislocations and twins)shows the significant dependence of crystal orientation and the mechanisms behind these are discussed in detail.Finally,the Johnson-Cook constitutive model describing dynamic deformations at high temperatures and high strain rates is used to analyze the relationships between the shock responses and microscopic defects.The predictions of the Johnson-Cook constitutive model are consistent with the results of the molecular dynamics simulations.展开更多
There is an increasing demand for advanced optical imaging techniques that can detect and resolve nanosize objects at a spatial resolution below the optical diffraction limit, especially in three-dimensional (3D) ce...There is an increasing demand for advanced optical imaging techniques that can detect and resolve nanosize objects at a spatial resolution below the optical diffraction limit, especially in three-dimensional (3D) cellular environments. In this study, using a polarization-activated localization scheme based on the orientation-dependent properties of anisotropic plasmonic metal nanoparticles (MNPs), "photoswitchable" imaging of single gold nanorods (AuNRs) was accomplished not only in two dimensions but also in three dimensions. Moreover, the Rayleigh scattering background arising from the congested subcellular structures was efficiently suppressed. Thus, we obtained the 3D distributions of both the position and the orientation of the AuNRs inside the cells and investigated their intemalization kinetics. To our knowledge, this is the first demonstration of the confocal-like 3D imaging of non-fluorescence nanoparticles with a high resolution and almost zero background. This technique is easy to implement and should greatly facilitate MNP studies and applications in biomedicine and biology.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.11972165,and 11502085)the Japan Society for the Promotion of Science(Grant No.P18067)the Fundamental Research Funds for the Central Universities of China(Grant No.2016YXMS097)。
文摘Single crystals subjected to shock compression exhibit responses with distinct two-wave structures for certain crystal orientations.However,little is known to date regarding how the shock response depends on crystal orientation,and especially why the two-wave structure depends on the crystal orientation.In this work,molecular dynamics simulations of shock compressions in copper single crystals are performed to investigate the orientation dependence of shock responses and the corresponding deformation mechanisms.Four copper single crystals with[001],[011],[012],and[123]crystal orientations along the depth direction are investigated.The[011],[012],and[123]crystal orientations of copper single crystals show distinct two-wave structures in their shock responses,while such a two-wave structure in the shock response is not seen for those orientations having a[001]crystal orientation.The potential causes are analyzed by considering the propagation velocities of both elastic and plastic waves.We develop a technique for identifying twin structures in face-centered cubic crystals and this technique can effectively identify the twin structure.The morphology of shock-induced defects(e.g.,dislocations and twins)shows the significant dependence of crystal orientation and the mechanisms behind these are discussed in detail.Finally,the Johnson-Cook constitutive model describing dynamic deformations at high temperatures and high strain rates is used to analyze the relationships between the shock responses and microscopic defects.The predictions of the Johnson-Cook constitutive model are consistent with the results of the molecular dynamics simulations.
基金Acknowledgements This work was supported by the National Natural Sdence Foundation of China (Nos. 91027037, 21127009, 21425519 and 21221003), Hunan University 985 fund, Tsinghua University Startup fund, the Natural Science Foundation of Zhejiang Province (No. LY16B050006) and Wenzhou Medical University Setup fund (No. QTJ15022).
文摘There is an increasing demand for advanced optical imaging techniques that can detect and resolve nanosize objects at a spatial resolution below the optical diffraction limit, especially in three-dimensional (3D) cellular environments. In this study, using a polarization-activated localization scheme based on the orientation-dependent properties of anisotropic plasmonic metal nanoparticles (MNPs), "photoswitchable" imaging of single gold nanorods (AuNRs) was accomplished not only in two dimensions but also in three dimensions. Moreover, the Rayleigh scattering background arising from the congested subcellular structures was efficiently suppressed. Thus, we obtained the 3D distributions of both the position and the orientation of the AuNRs inside the cells and investigated their intemalization kinetics. To our knowledge, this is the first demonstration of the confocal-like 3D imaging of non-fluorescence nanoparticles with a high resolution and almost zero background. This technique is easy to implement and should greatly facilitate MNP studies and applications in biomedicine and biology.