Mosaic structure ZrC-SiC coatings were fabricated on low-density, porous C/C composites via thermal evaporation and an in-situ method. ZrC was packed in a typical lamellar mode, and the mosaic structure was formed by ...Mosaic structure ZrC-SiC coatings were fabricated on low-density, porous C/C composites via thermal evaporation and an in-situ method. ZrC was packed in a typical lamellar mode, and the mosaic structure was formed by the deposition of Zr and Si atoms on the shallow surface of the porous C/C composites.Ablation analysis showed that the defects in the coatings originate from the boundary between the ZrC and holes created by the consumption of SiC at 2500℃. After ablation for 200 s at 3000℃, a dense ZrO2 layer formed on the coating surface, and the defects were sealed owing to the continuous supply of ablative components. The mass and line ablation rates of the Zr C-SiC coatings were-0.46 ± 0.15 mg cm^-2·s^-1 and-1.00± 0.04 μm s^-1, respectively.展开更多
The mosaic structure in a Ni-based single-crystal superalloy is simulated by molecular dynamics using a potential employed in a modified analytic embedded atom method. From the calculated results we find that a closed...The mosaic structure in a Ni-based single-crystal superalloy is simulated by molecular dynamics using a potential employed in a modified analytic embedded atom method. From the calculated results we find that a closed threedimensional misfit dislocation network, with index of （011）{100} and the side length of the mesh 89.6A, is formed around a cuboidal γ′ precipitate. Comparing the simulation results of the different mosaic models, we find that the side length of the mesh only depends on the lattice parameters of the γ and γ′ phases as well as the γ/γ′ interface direction, but is independent of the size and number of the cuboidal γ′ precipitate. The density of dislocations is inversely proportional to the size of the cuboidal γ′ precipitate, i.e. the amount of the dislocation is proportional to the total area of the γ/γ′ interface, which may be used to explain the relation between the amount of the fine γ′ particles and the creep rupture life of the superalloy. In addition, the closed three-dimensional networks assembled with the misfit dislocations can play a significant role in improving the mechanical properties of superalloys.展开更多
We focus on a modified version of the non-Hermitian Aubry-Andre-Harper(AAH)model,which has garnered significant attention due to its ability to investigate localization phenomena,metal-insulator transitions,and topolo...We focus on a modified version of the non-Hermitian Aubry-Andre-Harper(AAH)model,which has garnered significant attention due to its ability to investigate localization phenomena,metal-insulator transitions,and topological phase transitions.We have made two key modifications to the non-Hermitian AAH model:First,we introduce a mosaic structure that allows for the mixing of localized and extended states,resulting in the appearance of mobility edges,which is a feature that is not present in the original non-Hermitian AAH model.In the insulating phase,leveraging Fields Medal winner Avila's global theory,our work derives a theoretical description of the localization length,a crucial parameter previously unavailable in the non-Hermitian AAH model,and obtains the exact expression for mobility edges.We studied the variation of the energy spectrum with the amplitude and quantitatively determined the topological phase transition point within the spectrum.Furthermore,we introduced an asymmetric parameter g and calculated its corresponding localization length,the location of mobility edges,as well as the precise expressions for its extended and localized states.By quantitatively calculating the Lyapunov exponent of dual models,our work reveals an interesting fact about the robustness of localized states:within an appropriate relationship between g and the coupling potential strength,the localized states exhibit similar characteristics to those in the mosaic non-Hermitian AAH model.Our work offers a more complete and nuanced understanding of localization phenomena in disordered non-Hermitian systems,paving the way for further research in this promising field.展开更多
This paper investigates the major structural parameters, such as crystal quality and strain state of （001）-oriented GaN thin films grown on sapphire substrates by metalorganic chemical vapour deposition, using an in...This paper investigates the major structural parameters, such as crystal quality and strain state of （001）-oriented GaN thin films grown on sapphire substrates by metalorganic chemical vapour deposition, using an in-plane grazing incidence x-ray diffraction technique. The results are analysed and compared with a complementary out-of-plane x- ray diffraction technique. The twist of the GaN mosaic structure is determined through the direct grazing incidence t of （100） reflection which agrees well with the result obtained by extrapolation method. The method for directly determining the in-plane lattice parameters of the GaN layers is also presented. Combined with the biaxial strain model, it derives the lattice parameters corresponding to fully relaxed GaN films. The GaN epilayers show an increasing residual compressive stress with increasing layer thickness when the two dimensional growth stage is established, reaching to a maximum level of-0.89 GPa.展开更多
An approach based on depth-sensitive skew-angle x-ray diffraction （SAXRD） is presented for approximately evalu- ating the depth-dependent mosaic tilt and twist in wurtzite c-plane GaN epilayers. It is found that （...An approach based on depth-sensitive skew-angle x-ray diffraction （SAXRD） is presented for approximately evalu- ating the depth-dependent mosaic tilt and twist in wurtzite c-plane GaN epilayers. It is found that （103） plane and （101） plane, among the lattice planes not perpendicular to the sample surface, are the best choices to measure the depth profiles of tilt and twist for a GaN epilayer with a thickness of less than 2 μm according to the diffraction geometry of SAXRD. As an illustration, the depth-sensitive （103）/（101） ω-scans of a 1.4-μm GaN film grown by metal-organic chemical vapor deposition on sapphire substrate are measured and analyzed to show the feasibility of this approach.展开更多
In searching for more bioactive compounds, phytochemical investigations on the acetone extract of the leaves ofNicotiana tabacurn resulted in the isolation of two new sesquiterpenes, nicosesquiterpene A and B （1 and ...In searching for more bioactive compounds, phytochemical investigations on the acetone extract of the leaves ofNicotiana tabacurn resulted in the isolation of two new sesquiterpenes, nicosesquiterpene A and B （1 and 2）, along with four known sesquiterpene derivatives （3-6）. Structural elucidation of I and 2 was performed by spectral methods, such as HRMS, IR, UV, 1D and 2D NMR spectroscopy. Compounds 1 and 2 are the first naturally occurring pterosin-type sesquiterpene bearing an isopropyl moiety. Compounds 1-6 were also evaluated for their anti-tobacco mosaic virus （anti-TMV） activity. The results showed that compounds 1 and 2 exhibited high anti-TMV activity with inhibition rates of 36.7% and 45.6%, respectively, which is higher than that of positive control. The other compounds also showed potential activity with inhibition rates in the range of 22.7%-29.2%.展开更多
A commercial epi-ready(201)β-Ga_(2)O_(3) wafer was investigated upon diamond sawing into pieces measuring 2.5×3 mm^(2).The defect structure and crystallinity in the cut samples has been studied by X-ray diffract...A commercial epi-ready(201)β-Ga_(2)O_(3) wafer was investigated upon diamond sawing into pieces measuring 2.5×3 mm^(2).The defect structure and crystallinity in the cut samples has been studied by X-ray diffraction and a selective wet etching technique.The density of defects was estimated from the average value of etch pits calculated,including near-edge regions,and was obtained close to 109 cm^(-2).Blocks with lattice orientation deviated by angles of 1-3 arcmin,as well as non-stoichiometric fractions with a relative strain about(1.0-1.5)×10^(-4)in the[201]direction,were found.Crystal perfection was shown to decrease significantly towards the cutting lines of the samples.To reduce the number of structural defects and increase the crystal perfection of the samples via increasing defect motion mobility,the thermal annealing was employed.Polygonization and formation of a mosaic structure coupled with dislocation wall appearance upon 3 h of annealing at 1100℃ was observed.The fractions characterized by non-stoichiometry phases and the block deviation disappeared.The annealing for 11 h improved the homogeneity and perfection in the crystals.The average density of the etch pits dropped down significantly to 8×10^(6) cm^(-2).展开更多
A major earthquake occurrence zone means a place where M ≥6 events have occurred since the Holocene and similar shocks may happen again in the future. The dynamic context of the major earthquake occurrence zones in C...A major earthquake occurrence zone means a place where M ≥6 events have occurred since the Holocene and similar shocks may happen again in the future. The dynamic context of the major earthquake occurrence zones in China is primarily associated with the NNE-directed push of the India plate, next with the westward subduction of the Pacific plate. The Chinese mainland is a grand mosaic structure of many crust blocks bounded by faults and sutures. When it is suffered from boundary stresses, deformation takes place along these faults or sutures while the block interiors remain relatively stable or intact. Since the Quaternary, for example, left slip on the Xianshuihe-Xiaojiang fault zone in southwestern China has produced a number of fault-depression basins in extensional areas during periods Q1 and Q2. In the Q3, the change of stress orientation and enhancement of tectonic movement made faults of varied trends link each other, and continued to be active till present day, producing active fanlt zones in this region. Usually major earthquakes occur at some special locations on these active fault zones. During these events, in the epicenter areas experience intensive deformation character- ized by large-amplitude rise and fall of neighboring sections, generation of horst-graben systems and dammed rivers. The studies on palaeoearthquakes suggest that major shocks of close magnitudes often repeated for several times at a same place. By comparison of the Chi-Chi, Taiwan event in 1999 and Yuza, Yunnan event in 1955, including contours of accelerations and intensities, destruction of buildings, and in contrast to the Xigeda formation in southwestern China, a sandwich model is established to account for the mechanism of deformation caused by major earthquakes. This model consists of three layers, i.e. the two walls of a fault and the ruptured zone intercalated between them. This ruptured zone is just the loci where stress is built up and released, and serves as a channel for seismic waves.展开更多
Developing cost-effective electrocatalysts with high activity and stability especially at high current density is of great significance for the large-scale commercial application of electrochemical water splitting to ...Developing cost-effective electrocatalysts with high activity and stability especially at high current density is of great significance for the large-scale commercial application of electrochemical water splitting to hydrogen production but still remains challenging.Herein,we report an effective confinement pyrolysis strategy to fabricate embedded ruthenium-cobalt nanoclusters supported on N-doped porous two-dimensional carbon nanosheets(RuCo@CN).Markedly,the embedded structure can effectively prevent the migration,agglomeration,and leaching of nanoparticles,thus endowing the RuCo@CN catalyst with high stability.To be exact,high stability with up to 650 h can be achieved at high current density(-500 and-1000 mA·cm^(-2)).Besides,the RuCo@CN catalysts also exhibit highly reactive with low overpotentials of only 11mV at-10 mA·cm^(-2).Density functional theory calculations reveal that the introduction of cobalt reduces the decomposition barrier of H_(2)O for RuCo@CN alloy,thus promoting hydrogen evolution reaction.展开更多
基金supported by National Science Foundation of China (No. 51405522)the self-fund of State Key Laboratory for Powder Metallurgy (PM-CSU-2015-03)
文摘Mosaic structure ZrC-SiC coatings were fabricated on low-density, porous C/C composites via thermal evaporation and an in-situ method. ZrC was packed in a typical lamellar mode, and the mosaic structure was formed by the deposition of Zr and Si atoms on the shallow surface of the porous C/C composites.Ablation analysis showed that the defects in the coatings originate from the boundary between the ZrC and holes created by the consumption of SiC at 2500℃. After ablation for 200 s at 3000℃, a dense ZrO2 layer formed on the coating surface, and the defects were sealed owing to the continuous supply of ablative components. The mass and line ablation rates of the Zr C-SiC coatings were-0.46 ± 0.15 mg cm^-2·s^-1 and-1.00± 0.04 μm s^-1, respectively.
基金Project supported by the State Key Development Program for Basic Research of China （Grant No G2000067102） and the National Natural Science Foundation of China （Grant No 90101004）.
文摘The mosaic structure in a Ni-based single-crystal superalloy is simulated by molecular dynamics using a potential employed in a modified analytic embedded atom method. From the calculated results we find that a closed threedimensional misfit dislocation network, with index of （011）{100} and the side length of the mesh 89.6A, is formed around a cuboidal γ′ precipitate. Comparing the simulation results of the different mosaic models, we find that the side length of the mesh only depends on the lattice parameters of the γ and γ′ phases as well as the γ/γ′ interface direction, but is independent of the size and number of the cuboidal γ′ precipitate. The density of dislocations is inversely proportional to the size of the cuboidal γ′ precipitate, i.e. the amount of the dislocation is proportional to the total area of the γ/γ′ interface, which may be used to explain the relation between the amount of the fine γ′ particles and the creep rupture life of the superalloy. In addition, the closed three-dimensional networks assembled with the misfit dislocations can play a significant role in improving the mechanical properties of superalloys.
基金Project supported by the National Natural Science Foundation of China(Grant No.12301218)。
文摘We focus on a modified version of the non-Hermitian Aubry-Andre-Harper(AAH)model,which has garnered significant attention due to its ability to investigate localization phenomena,metal-insulator transitions,and topological phase transitions.We have made two key modifications to the non-Hermitian AAH model:First,we introduce a mosaic structure that allows for the mixing of localized and extended states,resulting in the appearance of mobility edges,which is a feature that is not present in the original non-Hermitian AAH model.In the insulating phase,leveraging Fields Medal winner Avila's global theory,our work derives a theoretical description of the localization length,a crucial parameter previously unavailable in the non-Hermitian AAH model,and obtains the exact expression for mobility edges.We studied the variation of the energy spectrum with the amplitude and quantitatively determined the topological phase transition point within the spectrum.Furthermore,we introduced an asymmetric parameter g and calculated its corresponding localization length,the location of mobility edges,as well as the precise expressions for its extended and localized states.By quantitatively calculating the Lyapunov exponent of dual models,our work reveals an interesting fact about the robustness of localized states:within an appropriate relationship between g and the coupling potential strength,the localized states exhibit similar characteristics to those in the mosaic non-Hermitian AAH model.Our work offers a more complete and nuanced understanding of localization phenomena in disordered non-Hermitian systems,paving the way for further research in this promising field.
基金supported by the National Natural Science Foundation of China (Grant Nos. 60506001,60776047,60976045 and 60836003)the National Basic Research Programme of China (Grant No. 2007CB936700)the National Science Foundation for Distinguished Young Scholars,China (Grant No. 60925017)
文摘This paper investigates the major structural parameters, such as crystal quality and strain state of （001）-oriented GaN thin films grown on sapphire substrates by metalorganic chemical vapour deposition, using an in-plane grazing incidence x-ray diffraction technique. The results are analysed and compared with a complementary out-of-plane x- ray diffraction technique. The twist of the GaN mosaic structure is determined through the direct grazing incidence t of （100） reflection which agrees well with the result obtained by extrapolation method. The method for directly determining the in-plane lattice parameters of the GaN layers is also presented. Combined with the biaxial strain model, it derives the lattice parameters corresponding to fully relaxed GaN films. The GaN epilayers show an increasing residual compressive stress with increasing layer thickness when the two dimensional growth stage is established, reaching to a maximum level of-0.89 GPa.
基金supported by the Young Scientists Fund of the National Natural Science Foundation of China(Grant Nos.61306017 and 61204006)the Key Program of the National Natural Science Foundation of China(Grant No.61334002)the Fundamental Research Funds for the Central Universities of China(Grant Nos.K5051225016 and K5051325020)
文摘An approach based on depth-sensitive skew-angle x-ray diffraction （SAXRD） is presented for approximately evalu- ating the depth-dependent mosaic tilt and twist in wurtzite c-plane GaN epilayers. It is found that （103） plane and （101） plane, among the lattice planes not perpendicular to the sample surface, are the best choices to measure the depth profiles of tilt and twist for a GaN epilayer with a thickness of less than 2 μm according to the diffraction geometry of SAXRD. As an illustration, the depth-sensitive （103）/（101） ω-scans of a 1.4-μm GaN film grown by metal-organic chemical vapor deposition on sapphire substrate are measured and analyzed to show the feasibility of this approach.
基金supported by the National Natural Science Foundation of China (Nos. 31360081 and 31400303)the Basic Research Foundation of Yunnan Province (Nos. 2014FB163 and 2014FD078)the Product Research Foundation of China Tobacco Yunnan Industrial Co., Ltd. (No. 2014CP01)
文摘In searching for more bioactive compounds, phytochemical investigations on the acetone extract of the leaves ofNicotiana tabacurn resulted in the isolation of two new sesquiterpenes, nicosesquiterpene A and B （1 and 2）, along with four known sesquiterpene derivatives （3-6）. Structural elucidation of I and 2 was performed by spectral methods, such as HRMS, IR, UV, 1D and 2D NMR spectroscopy. Compounds 1 and 2 are the first naturally occurring pterosin-type sesquiterpene bearing an isopropyl moiety. Compounds 1-6 were also evaluated for their anti-tobacco mosaic virus （anti-TMV） activity. The results showed that compounds 1 and 2 exhibited high anti-TMV activity with inhibition rates of 36.7% and 45.6%, respectively, which is higher than that of positive control. The other compounds also showed potential activity with inhibition rates in the range of 22.7%-29.2%.
基金funded by the Russian Science Foundation,project#23-29-10196。
文摘A commercial epi-ready(201)β-Ga_(2)O_(3) wafer was investigated upon diamond sawing into pieces measuring 2.5×3 mm^(2).The defect structure and crystallinity in the cut samples has been studied by X-ray diffraction and a selective wet etching technique.The density of defects was estimated from the average value of etch pits calculated,including near-edge regions,and was obtained close to 109 cm^(-2).Blocks with lattice orientation deviated by angles of 1-3 arcmin,as well as non-stoichiometric fractions with a relative strain about(1.0-1.5)×10^(-4)in the[201]direction,were found.Crystal perfection was shown to decrease significantly towards the cutting lines of the samples.To reduce the number of structural defects and increase the crystal perfection of the samples via increasing defect motion mobility,the thermal annealing was employed.Polygonization and formation of a mosaic structure coupled with dislocation wall appearance upon 3 h of annealing at 1100℃ was observed.The fractions characterized by non-stoichiometry phases and the block deviation disappeared.The annealing for 11 h improved the homogeneity and perfection in the crystals.The average density of the etch pits dropped down significantly to 8×10^(6) cm^(-2).
文摘A major earthquake occurrence zone means a place where M ≥6 events have occurred since the Holocene and similar shocks may happen again in the future. The dynamic context of the major earthquake occurrence zones in China is primarily associated with the NNE-directed push of the India plate, next with the westward subduction of the Pacific plate. The Chinese mainland is a grand mosaic structure of many crust blocks bounded by faults and sutures. When it is suffered from boundary stresses, deformation takes place along these faults or sutures while the block interiors remain relatively stable or intact. Since the Quaternary, for example, left slip on the Xianshuihe-Xiaojiang fault zone in southwestern China has produced a number of fault-depression basins in extensional areas during periods Q1 and Q2. In the Q3, the change of stress orientation and enhancement of tectonic movement made faults of varied trends link each other, and continued to be active till present day, producing active fanlt zones in this region. Usually major earthquakes occur at some special locations on these active fault zones. During these events, in the epicenter areas experience intensive deformation character- ized by large-amplitude rise and fall of neighboring sections, generation of horst-graben systems and dammed rivers. The studies on palaeoearthquakes suggest that major shocks of close magnitudes often repeated for several times at a same place. By comparison of the Chi-Chi, Taiwan event in 1999 and Yuza, Yunnan event in 1955, including contours of accelerations and intensities, destruction of buildings, and in contrast to the Xigeda formation in southwestern China, a sandwich model is established to account for the mechanism of deformation caused by major earthquakes. This model consists of three layers, i.e. the two walls of a fault and the ruptured zone intercalated between them. This ruptured zone is just the loci where stress is built up and released, and serves as a channel for seismic waves.
基金financially supported by the Fundamental Research Funds for the Central Universities (No.D5000220257,D5000220443)the National Natural Science Foundation of China (No.22002120)+2 种基金the Natural Science Foundation of Chongqing,China (No.cstc2020jcyj-msxm X0750)the Guangdong Basic and Applied Basic Research Foundation (No.2019A1515110507)the Key Research and Development Program of Shaanxi (No.2023-YBGY-322)。
文摘Developing cost-effective electrocatalysts with high activity and stability especially at high current density is of great significance for the large-scale commercial application of electrochemical water splitting to hydrogen production but still remains challenging.Herein,we report an effective confinement pyrolysis strategy to fabricate embedded ruthenium-cobalt nanoclusters supported on N-doped porous two-dimensional carbon nanosheets(RuCo@CN).Markedly,the embedded structure can effectively prevent the migration,agglomeration,and leaching of nanoparticles,thus endowing the RuCo@CN catalyst with high stability.To be exact,high stability with up to 650 h can be achieved at high current density(-500 and-1000 mA·cm^(-2)).Besides,the RuCo@CN catalysts also exhibit highly reactive with low overpotentials of only 11mV at-10 mA·cm^(-2).Density functional theory calculations reveal that the introduction of cobalt reduces the decomposition barrier of H_(2)O for RuCo@CN alloy,thus promoting hydrogen evolution reaction.
