Unusual quadratic dispersion of flexural vibrational mode and red-shift of Raman shift of in-plane mode with increas- ing layer-number are quite common and interesting in low-dimensional materials, but their physical ...Unusual quadratic dispersion of flexural vibrational mode and red-shift of Raman shift of in-plane mode with increas- ing layer-number are quite common and interesting in low-dimensional materials, but their physical origins still remain open questions. Combining ab initio density functional theory calculations with the empirical force-constant model, we study the lattice dynamics of two typical two-dimensional （2D） systems, few-layer h-BN and indium iodide （InI）. We found that the unusual quadratic dispersion of flexural mode frequency on wave vector may be comprehended based on the com- petition between atomic interactions of different neighbors. Long-range interaction plays an essential role in determining the dynamic stability of the 2D systems. The frequency red-shift of in-plane Raman-active mode from monolayer to bulk arises mainly from the reduced long-range interaction due to the increasing screening effect.展开更多
CrI3 in two-dimensional(2D) forms has been attracting much attention lately due to its novel magnetic properties at atomic large scale.The size and edge tuning of electronic and magnetic properties for 2D materials ha...CrI3 in two-dimensional(2D) forms has been attracting much attention lately due to its novel magnetic properties at atomic large scale.The size and edge tuning of electronic and magnetic properties for 2D materials has been a promising way to broaden or even enhance their utility, as the case with nanoribbons/nanotubes in graphene, black phosphorus, and transition metal dichalcogenides.Here we studied the CrI3 nanoribbon(NR) and nanotube(NT) systematically to seek the possible size and edge control of the electronic and magnetic properties.We find that ferromagnetic ordering is stable in all the NR and NT structures of interest.An enhancement of the Curie temperature TC can be expected when the structure goes to NR or NT from its 2D counterpart.The energy difference between the FM and AFM states can be even improved by up to 3–4 times in a zigzag nanoribbon(ZZNR), largely because of the electronic instability arising from a large density of states of iodine-5p orbitals at EF.In NT structures, shrinking the tube size harvests an enhancement of spin moment by up to 4%, due to the reduced crystal-field gap and the re-balance between the spin majority and minority populations.展开更多
Background：PM2.5 （aerodynamic diameter ≤ 2.5 μtm） is a dominant and ubiquitous air pollutant that has become a global concern as PM2.5 exposure has been linked to many adverse health effects including cardiovascu...Background：PM2.5 （aerodynamic diameter ≤ 2.5 μtm） is a dominant and ubiquitous air pollutant that has become a global concern as PM2.5 exposure has been linked to many adverse health effects including cardiovascular and pulmonary diseases.Emerging evidence supports a correlation between increased air PM2.5 levels and skin disorders although reports on the underlying pathophysiological mechanisms are limited.Oxidative stress is the most common mechanism of PM2.5-induced adverse health effects.This study aimed to investigate PM2.5-induced oxidative damage and apoptosis in immortalized human keratinocyte （HaCaT） cells.Methods：HaCaT cells were exposed to 0,25,50,100,or 200 μtg/ml PM2.5 for 24 h.Reactive oxygen species （ROS） generation,lipid peroxidation products,antioxidant activity,DNA damage,apoptotic protein expression,and cell apoptosis were measured.Results：PM2.5 exposure （0-200 μtg/ml） for 24 h resulted in increased ROS levels （arbitrary unit：201.00 ± 19.28,264.50 ± 17.91,305.05 ± 19.57,427.95 ＋ 18.32,and 436.70 ± 17.77） and malondialdehyde production （0.54 ± 0.05 nmol/mg prot,0.61 ± 0.06 nmol/mg prot,0.68 ± 0.05 nmol/mg prot,0.70 ± 0.05 nmol/mg prot,and 0.76 ± 0.05 nmol/mg prot）,diminished superoxide dismutase activity （6.47 ± 0.28 NU/mg prot,5.97 ± 0.30 NU/mg prot,5.15 ± 0.42 NU/mg prot,4.08 ± 0.20 NU/mg prot,and 3.76 ± 0.37 NU/mg prot）,and increased DNA damage and apoptosis in a dose-dependent manner in HaCaT cells.Moreover,cytochrome-c,caspase-3,and caspase-9 expression also increased proportionately with PM2.5 dosing.Conclusion：PM2.5 might elicit oxidative stress and mitochondria-dependent apoptosis that likely manifests as skin irritation and damage.展开更多
基金Project supported by the Major Program of Aerospace Advanced Manufacturing Technology Research Foundation from NSFC and CASC,China(Grant No.U1537204)the National Key Research and Development Program of China(Grant No.2017YFA0206301)the National Natural Science Foundation of China(Grant No.51702146)
文摘Unusual quadratic dispersion of flexural vibrational mode and red-shift of Raman shift of in-plane mode with increas- ing layer-number are quite common and interesting in low-dimensional materials, but their physical origins still remain open questions. Combining ab initio density functional theory calculations with the empirical force-constant model, we study the lattice dynamics of two typical two-dimensional （2D） systems, few-layer h-BN and indium iodide （InI）. We found that the unusual quadratic dispersion of flexural mode frequency on wave vector may be comprehended based on the com- petition between atomic interactions of different neighbors. Long-range interaction plays an essential role in determining the dynamic stability of the 2D systems. The frequency red-shift of in-plane Raman-active mode from monolayer to bulk arises mainly from the reduced long-range interaction due to the increasing screening effect.
基金Project supported by the National Key R&D Program of China(Grant No.2017YFA0206301)the Major Program of Aerospace Advanced Manufacturing Technology Research Foundation NSFC and CASC,China(Grant No.U1537204)
文摘CrI3 in two-dimensional(2D) forms has been attracting much attention lately due to its novel magnetic properties at atomic large scale.The size and edge tuning of electronic and magnetic properties for 2D materials has been a promising way to broaden or even enhance their utility, as the case with nanoribbons/nanotubes in graphene, black phosphorus, and transition metal dichalcogenides.Here we studied the CrI3 nanoribbon(NR) and nanotube(NT) systematically to seek the possible size and edge control of the electronic and magnetic properties.We find that ferromagnetic ordering is stable in all the NR and NT structures of interest.An enhancement of the Curie temperature TC can be expected when the structure goes to NR or NT from its 2D counterpart.The energy difference between the FM and AFM states can be even improved by up to 3–4 times in a zigzag nanoribbon(ZZNR), largely because of the electronic instability arising from a large density of states of iodine-5p orbitals at EF.In NT structures, shrinking the tube size harvests an enhancement of spin moment by up to 4%, due to the reduced crystal-field gap and the re-balance between the spin majority and minority populations.
文摘Background：PM2.5 （aerodynamic diameter ≤ 2.5 μtm） is a dominant and ubiquitous air pollutant that has become a global concern as PM2.5 exposure has been linked to many adverse health effects including cardiovascular and pulmonary diseases.Emerging evidence supports a correlation between increased air PM2.5 levels and skin disorders although reports on the underlying pathophysiological mechanisms are limited.Oxidative stress is the most common mechanism of PM2.5-induced adverse health effects.This study aimed to investigate PM2.5-induced oxidative damage and apoptosis in immortalized human keratinocyte （HaCaT） cells.Methods：HaCaT cells were exposed to 0,25,50,100,or 200 μtg/ml PM2.5 for 24 h.Reactive oxygen species （ROS） generation,lipid peroxidation products,antioxidant activity,DNA damage,apoptotic protein expression,and cell apoptosis were measured.Results：PM2.5 exposure （0-200 μtg/ml） for 24 h resulted in increased ROS levels （arbitrary unit：201.00 ± 19.28,264.50 ± 17.91,305.05 ± 19.57,427.95 ＋ 18.32,and 436.70 ± 17.77） and malondialdehyde production （0.54 ± 0.05 nmol/mg prot,0.61 ± 0.06 nmol/mg prot,0.68 ± 0.05 nmol/mg prot,0.70 ± 0.05 nmol/mg prot,and 0.76 ± 0.05 nmol/mg prot）,diminished superoxide dismutase activity （6.47 ± 0.28 NU/mg prot,5.97 ± 0.30 NU/mg prot,5.15 ± 0.42 NU/mg prot,4.08 ± 0.20 NU/mg prot,and 3.76 ± 0.37 NU/mg prot）,and increased DNA damage and apoptosis in a dose-dependent manner in HaCaT cells.Moreover,cytochrome-c,caspase-3,and caspase-9 expression also increased proportionately with PM2.5 dosing.Conclusion：PM2.5 might elicit oxidative stress and mitochondria-dependent apoptosis that likely manifests as skin irritation and damage.
