Ternary Mn＋1AXn phases with layered hexagonal structures, as candidate materials used for next-generation nuclear reactors, have shown great potential in tolerating radiation damage due to their unique combination of...Ternary Mn＋1AXn phases with layered hexagonal structures, as candidate materials used for next-generation nuclear reactors, have shown great potential in tolerating radiation damage due to their unique combination of ceramic and metallic properties. However, Mn＋1AXn materials behave differently in amorphization when exposed to energetic neutron and ion irradiations in experiment. We first analyze the irradiation tolerances of different Mn＋1AXn（MAX） phases in terms of electronic structure, including the density of states（DOS） and charge density map. Then a new method based on the Bader analysis with the first-principle calculation is used to estimate the stabilities of MAX phases under irradiation. Our calculations show that the substitution of Cr/V/Ta/Nb by Ti and Si/Ge/Ga by Al can increase the ionicities of the bonds,thus strengthening the radiation tolerance. It is also shown that there is no obvious difference in radiation tolerance between Mn＋1ACn and Mn＋1ANn due to the similar charge transfer values of C and N atoms. In addition, the improved radiation tolerance from Ti3AlC2 to Ti2AlC （Ti3AlC2 and Ti2AlC have the same chemical elements）, can be understood in terms of the increased Al/TiC layer ratio. Criteria based on the quantified charge transfer can be further used to explore other Mn＋1AXn phases with respect to their radiation tolerance, playing a critical role in choosing appropriate MAX phases before they are subjected to irradiation in experimental test for future nuclear reactors.展开更多
AIM: To reduce astigmatism, increase corneal volume and improve visual acuity. METHODS: A retrospective, single-surgeon, singlecenter, clinic-based study of a surgical procedure on twenty-four eyes of fourteen patient...AIM: To reduce astigmatism, increase corneal volume and improve visual acuity. METHODS: A retrospective, single-surgeon, singlecenter, clinic-based study of a surgical procedure on twenty-four eyes of fourteen patients diagnosed with stage Ⅲ or stage Ⅳ keratoconus. Paired arcuate keratotomy coupled with modified circular keratotomy was performed at a single center by a single surgeon as an outpatient procedure with local anaesthetic in a minor surgery room. Modified circular keratotomy was performed 7 mm from the pupillary center with depth of incision ranging between 70% and 90% of corneal thickness. Arcuate keratotomy was performed 2.5 mm from the pupillary center with the depth of incision at 90% of corneal thickness. Angular length of the arcs ranged between 60° and 120° depending on the astigmatic power of the cornea. RESULTS: Astigmatism decreased in 87.5% of the 24 treated eyes, increased in 8.33% and did not change in 4.17%. Corneal volume increased in 91.66% of the 24 eyes and decreased in 8.34%. Visual acuity improved in 100% of the eyes; there was a mean improvement of 59% from preoperative visual acuity, 8.34% of the treated eyes reaching a visual acuity of 1.0(20/20) with correction. No complications occurred during orafter surgery. No suturing was performed and there was no rupturing at incision sites. There was statistical significance difference between pre.sph against post.sph(P = 0.001). Also between pre.cyl against post.cyl(P = 0.005), there was no significance difference between pre.axis against post.axis(P = 0.05).CONCLUSION: Paired arcuate keratotomy coupled with modified circular keratotomy should be considered as an intervention before performing keratoplasty.展开更多
To reduce the greenhouse effect caused by the surgery of nitrogen-oxides concentration in the atmosphere and develop a future energy carrier of renewables,it is very critical to develop more efficient,controllable,and...To reduce the greenhouse effect caused by the surgery of nitrogen-oxides concentration in the atmosphere and develop a future energy carrier of renewables,it is very critical to develop more efficient,controllable,and highly sensitive catalytic materials.In our work,we proposed that nitric oxide(NO),as a supplement to N_(2) for the synthesis of ammonia,which is equipped with a lower barrier.And the study highlighted the potential of CeO_(2)(111)nanosheets with La doping and oxygen vacancy(OV)as a high-performance,controllable material for NO capture at the site of Vo site,and separation the process of hydrogenation.We also reported that the E_(ads) of-1.12 eV with horizontal adsorption and the Bader charge of N increasing of 0.53|e|and O increasing of 0.17|e|at the most active site of reduction-OV predicted.It is worth noting thatΔG of NORR(NO reduction reaction)shows good performance(thermodynamically spontaneous reaction)to synthesize ammonia and water at room temperature in the theoretical calculation.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.91226202 and 91426304)
文摘Ternary Mn＋1AXn phases with layered hexagonal structures, as candidate materials used for next-generation nuclear reactors, have shown great potential in tolerating radiation damage due to their unique combination of ceramic and metallic properties. However, Mn＋1AXn materials behave differently in amorphization when exposed to energetic neutron and ion irradiations in experiment. We first analyze the irradiation tolerances of different Mn＋1AXn（MAX） phases in terms of electronic structure, including the density of states（DOS） and charge density map. Then a new method based on the Bader analysis with the first-principle calculation is used to estimate the stabilities of MAX phases under irradiation. Our calculations show that the substitution of Cr/V/Ta/Nb by Ti and Si/Ge/Ga by Al can increase the ionicities of the bonds,thus strengthening the radiation tolerance. It is also shown that there is no obvious difference in radiation tolerance between Mn＋1ACn and Mn＋1ANn due to the similar charge transfer values of C and N atoms. In addition, the improved radiation tolerance from Ti3AlC2 to Ti2AlC （Ti3AlC2 and Ti2AlC have the same chemical elements）, can be understood in terms of the increased Al/TiC layer ratio. Criteria based on the quantified charge transfer can be further used to explore other Mn＋1AXn phases with respect to their radiation tolerance, playing a critical role in choosing appropriate MAX phases before they are subjected to irradiation in experimental test for future nuclear reactors.
文摘AIM: To reduce astigmatism, increase corneal volume and improve visual acuity. METHODS: A retrospective, single-surgeon, singlecenter, clinic-based study of a surgical procedure on twenty-four eyes of fourteen patients diagnosed with stage Ⅲ or stage Ⅳ keratoconus. Paired arcuate keratotomy coupled with modified circular keratotomy was performed at a single center by a single surgeon as an outpatient procedure with local anaesthetic in a minor surgery room. Modified circular keratotomy was performed 7 mm from the pupillary center with depth of incision ranging between 70% and 90% of corneal thickness. Arcuate keratotomy was performed 2.5 mm from the pupillary center with the depth of incision at 90% of corneal thickness. Angular length of the arcs ranged between 60° and 120° depending on the astigmatic power of the cornea. RESULTS: Astigmatism decreased in 87.5% of the 24 treated eyes, increased in 8.33% and did not change in 4.17%. Corneal volume increased in 91.66% of the 24 eyes and decreased in 8.34%. Visual acuity improved in 100% of the eyes; there was a mean improvement of 59% from preoperative visual acuity, 8.34% of the treated eyes reaching a visual acuity of 1.0(20/20) with correction. No complications occurred during orafter surgery. No suturing was performed and there was no rupturing at incision sites. There was statistical significance difference between pre.sph against post.sph(P = 0.001). Also between pre.cyl against post.cyl(P = 0.005), there was no significance difference between pre.axis against post.axis(P = 0.05).CONCLUSION: Paired arcuate keratotomy coupled with modified circular keratotomy should be considered as an intervention before performing keratoplasty.
基金funded by the Natural Science Foundation of China(No.21603109)the Henan Joint Fund of the National Natural Science Foundation of China(No.U1404216)+1 种基金the Scientific Research Program Funded by Shaanxi Provincial Education Department(No.20JK0676)the Special Fund of Tianshui Normal University,China(No.CXJ2020-08)。
文摘To reduce the greenhouse effect caused by the surgery of nitrogen-oxides concentration in the atmosphere and develop a future energy carrier of renewables,it is very critical to develop more efficient,controllable,and highly sensitive catalytic materials.In our work,we proposed that nitric oxide(NO),as a supplement to N_(2) for the synthesis of ammonia,which is equipped with a lower barrier.And the study highlighted the potential of CeO_(2)(111)nanosheets with La doping and oxygen vacancy(OV)as a high-performance,controllable material for NO capture at the site of Vo site,and separation the process of hydrogenation.We also reported that the E_(ads) of-1.12 eV with horizontal adsorption and the Bader charge of N increasing of 0.53|e|and O increasing of 0.17|e|at the most active site of reduction-OV predicted.It is worth noting thatΔG of NORR(NO reduction reaction)shows good performance(thermodynamically spontaneous reaction)to synthesize ammonia and water at room temperature in the theoretical calculation.
