The competition between different magnetic structures in hole-doped Fe-pnicitides is explored based on an extended five-orbital Hubbard model including long-range Coulomb interactions.Our results show that the stabili...The competition between different magnetic structures in hole-doped Fe-pnicitides is explored based on an extended five-orbital Hubbard model including long-range Coulomb interactions.Our results show that the stabilized magnetic structure evolves with increasing hole doping level.Namely,the stripe antiferromagnetic phase dominates at zero doping,while magnetic structures with more antiferromagnetic linking numbers such as the staggered tetramer,staggered trimer,and staggered dimer phases become energetically favorable as the hole density increases.At a certain doping level,energy degeneracy of different magnetic structures appears,indicating strong magnetic frustration and magnetic fluctuations in the system.We suggest that the magnetic competition induced by the hole doping may explain the fast decrease of the Neel temperature TNand the moderately suppressed magnetic moment in the hole doped Fe-pnicitides.Moreover,our results show a sign reversal of the kinetic energy anisotropy as the magnetic ground state evolves,which may be the mechanism behind the puzzling sign reversal of the in-plane resistivity anisotropy in hole-doped Fe-pnicitides.展开更多
Objective: To assess the efficacy and safety of extracorporeal shock wave lithotripsy or pneumatic ureteroscopic lithotripsy for lower ureteral stones therapy, we sought to identify and summarize randomized controlled...Objective: To assess the efficacy and safety of extracorporeal shock wave lithotripsy or pneumatic ureteroscopic lithotripsy for lower ureteral stones therapy, we sought to identify and summarize randomized controlled trials that were used to treat distal ureteral stone. Methods: Eligible studies were identified from electronic databases. Database search, quality assessment, and data extraction were performed by two reviewers independently. Our primary outcome was the stone-free rate. Secondary outcomes were the fragmentation rate, complications and the rate of re-treatment and secondary procedures. The results were assessed by Review Manager 5.0. Publication bias was evaluated by Stata 11.0. Results: 13 trials were included. Meta-analysis of pooled data showed that pneumatic ureteroscopic lithotripsy demonstrated a significant advantage over extracorporeal shock wave lithotripsy (OR = 0.14, 95% CI [0.09, 0.23], P < 0.00001) in the stone-free rate;the extracorporeal shock wave lithotripsy had statistical disadvantages over pneumatic ureteroscopic lithotripsy in the fragmentation rate of ureteral stones (OR = 0.14, 95% CI [0.05, 0.39], P = 0.0002);and the rate of re-treatment and secondary procedure was lower in pneumatic ureteroscopic lithotripsy than in extracorporeal shock wave lithotripsy (OR = 5.37, 95% CI [2.61, 11.07], P < 0.00001). Our pooled results showed that there was no statistical difference between extracorporeal shock wave lithotripsy and pneumatic ureteroscopic lithotripsy in hematuresis, ureteral stricture and urosepsis or fever. Finally extracorporeal shock wave lithotripsy had a higher incidence of colic pain than pneumatic ureteroscopic lithotripsy. Conclusion: The present meta-analysis suggested that pneumatic ureteroscopic lithotripsy had large advantages over extracorporeal shock wave lithotripsy in the treatment of lower ureteral stones.展开更多
Although lead-based perovskite solar cells have achieved more than 25%power conversion efficiency,the toxicity of lead and instability are still urgent problems faced in industrial application.Lead-free halide double ...Although lead-based perovskite solar cells have achieved more than 25%power conversion efficiency,the toxicity of lead and instability are still urgent problems faced in industrial application.Lead-free halide double perovskite(DP)materials are promising candidates to resolve these issues.Based on the density functional theory,we explore the geometric stability,thermodynamic stability,mechanical stability,electronic structures,and optical properties of theCs_(2)B 0BiI_(6)(B 0=Li,Na and K)DP materials.By analyzing the tolerance factor and octahedral factor,we find the geometric stabilities ofCs_(2)NaBiI_(6) andCs_(2)KBiI_(6) DPs are better thanCs_(2)LiBiI_(6).By calculating the total energy,formation energy and decomposition energy,we propose that the most favorable structure ofCs_(2)B 0BiI_(6) is the orthorhombic phase,andCs_(2)LiBiI_(6) is less stable relative to the other two counterparts from an energetic viewpoint.Mechanical stability evaluations reveal that the orthorhombicCs_(2)LiBiI_(6) material is less stable relative to the isostructuralCs_(2)NaBiI_(6) andCs_(2)KBiI_(6) DPs.The mechanical property calculations indicate that theCs_(2)B 0BiI_(6) DPs possess good ductility,which can be used as flexible materials.Electronic structures and optical property calculations show that the orthorhombicCs_(2)B 0BiI_(6) DPs have suitable band gap values,weaker exciton binding energies,and excellent optical absorption performance in the visible-light range.Based on the above comprehensive assessments,we can conclude that the orthorhombic Cs_(2)NaBiI_(6) and Cs_(2)KBiI_(6) DPs with good stability are promising candidates for solar cell applications.展开更多
Based on first-principles simulations,we revisit the crystal structures,electronic structures,and structural stability of the layered transition metal dichalcogenides(TMDCs)NbS2,and shed more light on the crucial role...Based on first-principles simulations,we revisit the crystal structures,electronic structures,and structural stability of the layered transition metal dichalcogenides(TMDCs)NbS2,and shed more light on the crucial roles of the van der Waals(vdW)interactions.Theoretically calculated results imply that the vdW corrections are important to reproduce the layered crystal structure,which is significant to correctly describe the electronic structure of NbS2.More interestingly,under hydrostatic pressure or tensile strain in ab plane,an isostructural phase transition from two-dimensional layered structure to three-dimensional bulk in the I4/mmm phase has been uncovered.The abnormal structural transition is closely related to the electronic structure instability and interlayer bonding effects.The interlayer Nb-S distances collapse and the interlayer vdW interactions disappear,concomitant with new covalent bond emerging and increasing coordination number.Present work highlights the significance of the vdW interactions,and provides new insights on the unconventional structural transitions in NbS2,which will attract wide audience working in the hectic field of TMDCs.展开更多
Branched CdTe nanocrystals with zinc blende structure were directly synthesized in the early growth stage at a high initial concentration of cadmium precursor and a high molar ratio of Cd precursor to Te precuesor. Ac...Branched CdTe nanocrystals with zinc blende structure were directly synthesized in the early growth stage at a high initial concentration of cadmium precursor and a high molar ratio of Cd precursor to Te precuesor. Activation of the cadmium precursor by octadecylamine was found to be critical for the formation of branched CdTe nanocrystals. Furthermore, these as-prepared CdTe nanocrystals can evolve into nearly monodisperse dots through Ostwald ripening and still keep strong photoluminescence. These results manifest a new route to synthesize branch- and dot-shaped CdTe nanocrystals with zinc blende structure.展开更多
A new bismuth-based halide double perovskite Cs_(2)KBiCl_(6) was isolated successfully through solid-state reactions and investigated using X-ray and neutron diffraction.Rather than an ordered structure,the crystal st...A new bismuth-based halide double perovskite Cs_(2)KBiCl_(6) was isolated successfully through solid-state reactions and investigated using X-ray and neutron diffraction.Rather than an ordered structure,the crystal structure consists of shifted Cs,K,Bi,and Cl sites from the ideal positions with fractional occupancy in compensation,leading to variable local coordination of Cs^(+)ions,as revealed by^(133)Cs solid-state nuclear magnetic resonance spectroscopy.Cs_(2)KBiCl_(6) displays volume hysteresis at 5-298 K range upon heating and cooling.The Cs_(2)KBiCl_(6) has a direct bandgap of 3.35(2)eV and red-shift luminescence of around 600 nm upon Mn doping compared with the Na analogue.The stabilization of disordered structure in Cs_(2)KBiCl_(6) is related to two factors including the large-sized K^(+)cation which prefers to coordinate with more than six Cl^(-),and the Bi^(3+)with 6s^(2) lone pair which has a preference for a local asymmetric environment.These findings could have general application and help to understand the structure and property of halide perovskites.展开更多
基金the Guangxi Natural Science Foundation,China(Grant Nos.2022GXNSFAA035560and GuikeAD20159009)the Scientific Research Foundation of Guilin University of Technology(Grant No.GLUTQD2017009)。
文摘The competition between different magnetic structures in hole-doped Fe-pnicitides is explored based on an extended five-orbital Hubbard model including long-range Coulomb interactions.Our results show that the stabilized magnetic structure evolves with increasing hole doping level.Namely,the stripe antiferromagnetic phase dominates at zero doping,while magnetic structures with more antiferromagnetic linking numbers such as the staggered tetramer,staggered trimer,and staggered dimer phases become energetically favorable as the hole density increases.At a certain doping level,energy degeneracy of different magnetic structures appears,indicating strong magnetic frustration and magnetic fluctuations in the system.We suggest that the magnetic competition induced by the hole doping may explain the fast decrease of the Neel temperature TNand the moderately suppressed magnetic moment in the hole doped Fe-pnicitides.Moreover,our results show a sign reversal of the kinetic energy anisotropy as the magnetic ground state evolves,which may be the mechanism behind the puzzling sign reversal of the in-plane resistivity anisotropy in hole-doped Fe-pnicitides.
文摘Objective: To assess the efficacy and safety of extracorporeal shock wave lithotripsy or pneumatic ureteroscopic lithotripsy for lower ureteral stones therapy, we sought to identify and summarize randomized controlled trials that were used to treat distal ureteral stone. Methods: Eligible studies were identified from electronic databases. Database search, quality assessment, and data extraction were performed by two reviewers independently. Our primary outcome was the stone-free rate. Secondary outcomes were the fragmentation rate, complications and the rate of re-treatment and secondary procedures. The results were assessed by Review Manager 5.0. Publication bias was evaluated by Stata 11.0. Results: 13 trials were included. Meta-analysis of pooled data showed that pneumatic ureteroscopic lithotripsy demonstrated a significant advantage over extracorporeal shock wave lithotripsy (OR = 0.14, 95% CI [0.09, 0.23], P < 0.00001) in the stone-free rate;the extracorporeal shock wave lithotripsy had statistical disadvantages over pneumatic ureteroscopic lithotripsy in the fragmentation rate of ureteral stones (OR = 0.14, 95% CI [0.05, 0.39], P = 0.0002);and the rate of re-treatment and secondary procedure was lower in pneumatic ureteroscopic lithotripsy than in extracorporeal shock wave lithotripsy (OR = 5.37, 95% CI [2.61, 11.07], P < 0.00001). Our pooled results showed that there was no statistical difference between extracorporeal shock wave lithotripsy and pneumatic ureteroscopic lithotripsy in hematuresis, ureteral stricture and urosepsis or fever. Finally extracorporeal shock wave lithotripsy had a higher incidence of colic pain than pneumatic ureteroscopic lithotripsy. Conclusion: The present meta-analysis suggested that pneumatic ureteroscopic lithotripsy had large advantages over extracorporeal shock wave lithotripsy in the treatment of lower ureteral stones.
基金supported by the National Natural Science Foundation of China(Grant No.11864008)Guangxi Natural Science Foundation,China(Grant Nos.2018GXNSFAA138185,2018AD19200,and 2019GXNSFGA245006).
文摘Although lead-based perovskite solar cells have achieved more than 25%power conversion efficiency,the toxicity of lead and instability are still urgent problems faced in industrial application.Lead-free halide double perovskite(DP)materials are promising candidates to resolve these issues.Based on the density functional theory,we explore the geometric stability,thermodynamic stability,mechanical stability,electronic structures,and optical properties of theCs_(2)B 0BiI_(6)(B 0=Li,Na and K)DP materials.By analyzing the tolerance factor and octahedral factor,we find the geometric stabilities ofCs_(2)NaBiI_(6) andCs_(2)KBiI_(6) DPs are better thanCs_(2)LiBiI_(6).By calculating the total energy,formation energy and decomposition energy,we propose that the most favorable structure ofCs_(2)B 0BiI_(6) is the orthorhombic phase,andCs_(2)LiBiI_(6) is less stable relative to the other two counterparts from an energetic viewpoint.Mechanical stability evaluations reveal that the orthorhombicCs_(2)LiBiI_(6) material is less stable relative to the isostructuralCs_(2)NaBiI_(6) andCs_(2)KBiI_(6) DPs.The mechanical property calculations indicate that theCs_(2)B 0BiI_(6) DPs possess good ductility,which can be used as flexible materials.Electronic structures and optical property calculations show that the orthorhombicCs_(2)B 0BiI_(6) DPs have suitable band gap values,weaker exciton binding energies,and excellent optical absorption performance in the visible-light range.Based on the above comprehensive assessments,we can conclude that the orthorhombic Cs_(2)NaBiI_(6) and Cs_(2)KBiI_(6) DPs with good stability are promising candidates for solar cell applications.
基金Project supported by the National Natural Science Foundation of China(Grant No.11864008)Guangxi Natural Science Foundation,China(Grant Nos.2018GXNSFAA138185 and 2018AD19200)High performance computational resources provided by LvLiang Cloud Computing Center of China and National Supercomputer Center on TianHe-2 are gratefully acknowledged.
文摘Based on first-principles simulations,we revisit the crystal structures,electronic structures,and structural stability of the layered transition metal dichalcogenides(TMDCs)NbS2,and shed more light on the crucial roles of the van der Waals(vdW)interactions.Theoretically calculated results imply that the vdW corrections are important to reproduce the layered crystal structure,which is significant to correctly describe the electronic structure of NbS2.More interestingly,under hydrostatic pressure or tensile strain in ab plane,an isostructural phase transition from two-dimensional layered structure to three-dimensional bulk in the I4/mmm phase has been uncovered.The abnormal structural transition is closely related to the electronic structure instability and interlayer bonding effects.The interlayer Nb-S distances collapse and the interlayer vdW interactions disappear,concomitant with new covalent bond emerging and increasing coordination number.Present work highlights the significance of the vdW interactions,and provides new insights on the unconventional structural transitions in NbS2,which will attract wide audience working in the hectic field of TMDCs.
基金Supported by the National Natural Science Foundation of China(No.20771035)
文摘Branched CdTe nanocrystals with zinc blende structure were directly synthesized in the early growth stage at a high initial concentration of cadmium precursor and a high molar ratio of Cd precursor to Te precuesor. Activation of the cadmium precursor by octadecylamine was found to be critical for the formation of branched CdTe nanocrystals. Furthermore, these as-prepared CdTe nanocrystals can evolve into nearly monodisperse dots through Ostwald ripening and still keep strong photoluminescence. These results manifest a new route to synthesize branch- and dot-shaped CdTe nanocrystals with zinc blende structure.
基金the National Science Foundation of China(Nos.22090043 and 22161014)Guangxi Natural Science Foundation(Nos.2019GXNSFGA245006 and 2020GXNSFAA297220)the Foundation of Guilin University of Technology(No.GUTQDJJ2018115)for the financial support。
文摘A new bismuth-based halide double perovskite Cs_(2)KBiCl_(6) was isolated successfully through solid-state reactions and investigated using X-ray and neutron diffraction.Rather than an ordered structure,the crystal structure consists of shifted Cs,K,Bi,and Cl sites from the ideal positions with fractional occupancy in compensation,leading to variable local coordination of Cs^(+)ions,as revealed by^(133)Cs solid-state nuclear magnetic resonance spectroscopy.Cs_(2)KBiCl_(6) displays volume hysteresis at 5-298 K range upon heating and cooling.The Cs_(2)KBiCl_(6) has a direct bandgap of 3.35(2)eV and red-shift luminescence of around 600 nm upon Mn doping compared with the Na analogue.The stabilization of disordered structure in Cs_(2)KBiCl_(6) is related to two factors including the large-sized K^(+)cation which prefers to coordinate with more than six Cl^(-),and the Bi^(3+)with 6s^(2) lone pair which has a preference for a local asymmetric environment.These findings could have general application and help to understand the structure and property of halide perovskites.
