Computer simulation of microstructures evolution for three-high cross-rolling of hollow steels
Based on the rigid-plastic finite element method (FEM), an investigation on three-high cross-rolling of hollow steels was carried out in this study. The numerical model coupled thermal, mechanical and microstructural phenomena, in which some empirical recrystallization mode were obtained using the Gleeble-3500 thermomechanical simulator. The distributions of different field-variables, including temperature, strain and grain size, were obtained by FEM simulation. After different mandrel diameters were calculated, the investigation obtained the effect of microstructures evolution and compared the grain size between no mandrel and different mandrel diameters.
Numerical simulation of deformation and microstructures evolution for hexagon hollow steels rolling
To explore the methods for improving the mechanical properties and increasing the service life, deeply analyses were carried out on the forming process of hexagon hollow steels. This paper established the three-dimensional model, calculated the strain field, stress field, temperature field by Rigid-plastic FEM, built up the microstructure evolution model based on physical metallurgy theories for the rolling process of hollow steels. The variation of average grain size with rolling velocity was obtained.
Recent progress in engineering near-infrared persistent luminescence nanoprobes for time-resolved biosensing/bioimaging
Persistent luminescence nanoprobes (PLNPs) can remain luminescent after ceasing excitation. Due to the ultra-long decay time of persistent luminescence (PersL), autofluorescence interference can be efficiently eliminated by collecting PersL signal after autofluorescence decays completely, thus the imaging contrast and sensing sensitivity can be significantly improved. Since near-infrared (NIR) light shows reduced scattering and absorption coefficient in penetrating biological organs or tissues, near-infrared persistent luminescence nanoprobes (NIR PLNPs) possess deep tissue penetration and offer a bright prospect in the areas of in vivo biosensing/bioimaging. In this review, we firstly summarize the design of different types of NIR PLNPs for biosensing/bioimaging, such as transition metal ions-doped NIR PLNPs, lanthanide ions-doped NIR PLNPs, organic molecules-based NIR PLNPs, and semiconducting polymer self-assembled NIR PLNPs. Notably, organic molecules-based NIR PLNPs and semiconductor self-assembled NIR PLNPs, for the first time, were introduced to the review of PLNPs. Secondly, the effects of different types of charge carriers on NIR PersL and luminescence decay of NIR PLNPs are significantly emphasized so as to build up an in-depth understanding of their luminescence mechanism. It includes the regulation of valence band and conduction band of different host materials, alteration of defect types, depth and concentration changes caused by ion doping, effective radiation transitions and energy transfer generated by different luminescence centers. Given the design and potential of NIR PLNPs as long-lived luminescent materials, the current challenges and future perspective in this rapidly growing field are also discussed.