Clay minerals can experience strong tensile and compressive forces in extreme environments such as the deep sea and subsurface.Moreover,the presence of water films greatly affects the mechanical properties of clay.To ...Clay minerals can experience strong tensile and compressive forces in extreme environments such as the deep sea and subsurface.Moreover,the presence of water films greatly affects the mechanical properties of clay.To explore these properties,we use a molecular dynamics(MD)simulation method to study axial mechanical behavior and failure mechanisms of hydrated kaolinite.Two types of deformation are applied to kaolinite examples with varying water film thicknesses:stretching along the transverse(x)direction,and compression along the longitudinal(z)direction.The ultimate strengths of hydrated kaolinite with different water film thicknesses range from 8.12%to 27.53%(for stretching along the x-direction)and from 15.71%to 26.02%(for compression along the z-direction)less than those of dehydrated kaolinite.Additionally,we find that hydrated kaolinite is more prone to tensile than compressive failure under high stress.When stretched along the x-direction,the diffusion of water molecules results in unstable tensile properties.When compressed along the z-direction,water films weaken the compressive strength of the system and lead to greater compressive deformation,but also delay the time at which the system fails.Furthermore,we investigated the failure mechanisms of hydrated kaolinite through analysis of interaction energies.The tensile failure along the x-direction is caused by the breaking of the covalent bonds in the clay mineral sheet.On the other hand,the compressive failure along the z-direction is due to the crushing of the internal structure of the clay mineral sheet.展开更多
Phase matching or quasi-phase matching(QPM)is of significant importance to the conversion efficiency of second harmonic generation(SHG)in artificial nonlinear crystals like lithium niobate(LN)crystal or microstructure...Phase matching or quasi-phase matching(QPM)is of significant importance to the conversion efficiency of second harmonic generation(SHG)in artificial nonlinear crystals like lithium niobate(LN)crystal or microstructured nonlinear crystals like periodic-poled lithium niobate(PPLN)crystals.In this paper,we propose and show that the incident angle of pump laser light can be harnessed as an alternative versatile tool to engineer QPM for high-efficiency SHG in a PPLN crystal,in addition to conventional means of period adjusting or temperature tuning.A rigorous model is established and analytical solution of the nonlinear conversion efficiency under the small and large signal approximation theory is obtained at different incident angles.The variation of phase mismatching and walk-off length with incident angle or incident wavelength are also explored.Numerical simulations for a PPLN crystal with first order QPM structure are used to confirm our theoretical predictions based on the exact analytical solution of the general large-signal theory.The results show that the narrow-band tunable SHG output covers a range of 532 nm–552.8 nm at the ideal incident angle from 0°to 90°.This theoretical scheme,fully considering the reflection and transmission at the air-crystal interface,would offer an efficient theoretical system to evaluate the nonlinear frequency conversion and help to obtain the maximum SHG conversion efficiency by selecting an optimum incident wavelength and incident angle in a specially designed PPLN crystal,which would be very helpful for the design of tunable narrow-band pulse nanosecond,picosecond,and femtosecond laser devices via PPLN and other microstructured LN crystals.展开更多
地球科学的研究成果通常记录在技术报告、期刊论文、书籍等文献中,但许多详细的地球科学报告未被使用,这为信息提取提供了机遇。为此,我们提出了一种名为GMNER(Geological Minerals named entity recognize,MNER)的深度神经网络模型,用...地球科学的研究成果通常记录在技术报告、期刊论文、书籍等文献中,但许多详细的地球科学报告未被使用,这为信息提取提供了机遇。为此,我们提出了一种名为GMNER(Geological Minerals named entity recognize,MNER)的深度神经网络模型,用于识别和提取矿物类型、地质构造、岩石与地质时间等关键信息。与传统方法不同,本次采用了大规模预训练模型BERT(Bidirectional Encoder Representations from Transformers,BERT)和深度神经网络来捕捉上下文信息,并结合条件随机场(Conditional random field,CRF)以获得准确结果。实验结果表明,MNER模型在中文地质文献中表现出色,平均精确度为0.8984,平均召回率0.9227,平均F1分数0.9104。研究不仅为自动矿物信息提取提供了新途径,也有望促进矿产资源管理和可持续利用。展开更多
紫精材料在外界刺激(如光、热、电)下会表现出灵敏的变色行为,在光学开关和分子传感识别中具有良好的潜在应用前景.通过一步反应合成了4-氟苯乙酮双取代紫精衍生物(VioF_(2)·2Cl).氟苯乙酮取代基的引入扩大了其共轭体系,起到稳定...紫精材料在外界刺激(如光、热、电)下会表现出灵敏的变色行为,在光学开关和分子传感识别中具有良好的潜在应用前景.通过一步反应合成了4-氟苯乙酮双取代紫精衍生物(VioF_(2)·2Cl).氟苯乙酮取代基的引入扩大了其共轭体系,起到稳定自由基的作用,使着色更稳定持久.VioF_(2)·2Cl在紫外(ultraviolet,UV)灯的照射下可以快速地从白色转变为浅黄色直至黄绿色,显示出了灵敏的光致变色行为.变色后晶体中的VioF_(2)^(2+)分子间具有更短的π···π^(*)作用距离,能够促进光致电子转移(photoinduced electron transfer,PET)过程的发生,并且起到稳定紫精阳离子自由基的作用,使其能够在氧气环境下持续变色3 d而不被氧化褪色.这种新型的紫精衍生物表现出了更为灵敏的光致变色性能及自由基着色稳定性,在光致变色材料领域具有良好的潜在应用可能.展开更多
基金supported by the National Natural Science Foundation of China(No.52009149)the Guangdong Basic and Applied Basic Research Foundation(No.2021A1515012612),China。
文摘Clay minerals can experience strong tensile and compressive forces in extreme environments such as the deep sea and subsurface.Moreover,the presence of water films greatly affects the mechanical properties of clay.To explore these properties,we use a molecular dynamics(MD)simulation method to study axial mechanical behavior and failure mechanisms of hydrated kaolinite.Two types of deformation are applied to kaolinite examples with varying water film thicknesses:stretching along the transverse(x)direction,and compression along the longitudinal(z)direction.The ultimate strengths of hydrated kaolinite with different water film thicknesses range from 8.12%to 27.53%(for stretching along the x-direction)and from 15.71%to 26.02%(for compression along the z-direction)less than those of dehydrated kaolinite.Additionally,we find that hydrated kaolinite is more prone to tensile than compressive failure under high stress.When stretched along the x-direction,the diffusion of water molecules results in unstable tensile properties.When compressed along the z-direction,water films weaken the compressive strength of the system and lead to greater compressive deformation,but also delay the time at which the system fails.Furthermore,we investigated the failure mechanisms of hydrated kaolinite through analysis of interaction energies.The tensile failure along the x-direction is caused by the breaking of the covalent bonds in the clay mineral sheet.On the other hand,the compressive failure along the z-direction is due to the crushing of the internal structure of the clay mineral sheet.
基金Project supported by the National Natural Science Foundation of China(Grant No.11974119)the Science and Technology Project of Guangdong Province,China(Grant No.2020B010190001)+2 种基金the Guangdong Innovative and Entrepreneurial Research Team Program(Grant No.2016ZT06C594)the National Key Research and Development Program of China(Grant Nos.2018YFA,0306200,and 2019YFB2203500)the Science and Technology Program of Guangzhou City(Grant No.2023A04J1309).
文摘Phase matching or quasi-phase matching(QPM)is of significant importance to the conversion efficiency of second harmonic generation(SHG)in artificial nonlinear crystals like lithium niobate(LN)crystal or microstructured nonlinear crystals like periodic-poled lithium niobate(PPLN)crystals.In this paper,we propose and show that the incident angle of pump laser light can be harnessed as an alternative versatile tool to engineer QPM for high-efficiency SHG in a PPLN crystal,in addition to conventional means of period adjusting or temperature tuning.A rigorous model is established and analytical solution of the nonlinear conversion efficiency under the small and large signal approximation theory is obtained at different incident angles.The variation of phase mismatching and walk-off length with incident angle or incident wavelength are also explored.Numerical simulations for a PPLN crystal with first order QPM structure are used to confirm our theoretical predictions based on the exact analytical solution of the general large-signal theory.The results show that the narrow-band tunable SHG output covers a range of 532 nm–552.8 nm at the ideal incident angle from 0°to 90°.This theoretical scheme,fully considering the reflection and transmission at the air-crystal interface,would offer an efficient theoretical system to evaluate the nonlinear frequency conversion and help to obtain the maximum SHG conversion efficiency by selecting an optimum incident wavelength and incident angle in a specially designed PPLN crystal,which would be very helpful for the design of tunable narrow-band pulse nanosecond,picosecond,and femtosecond laser devices via PPLN and other microstructured LN crystals.
文摘地球科学的研究成果通常记录在技术报告、期刊论文、书籍等文献中,但许多详细的地球科学报告未被使用,这为信息提取提供了机遇。为此,我们提出了一种名为GMNER(Geological Minerals named entity recognize,MNER)的深度神经网络模型,用于识别和提取矿物类型、地质构造、岩石与地质时间等关键信息。与传统方法不同,本次采用了大规模预训练模型BERT(Bidirectional Encoder Representations from Transformers,BERT)和深度神经网络来捕捉上下文信息,并结合条件随机场(Conditional random field,CRF)以获得准确结果。实验结果表明,MNER模型在中文地质文献中表现出色,平均精确度为0.8984,平均召回率0.9227,平均F1分数0.9104。研究不仅为自动矿物信息提取提供了新途径,也有望促进矿产资源管理和可持续利用。
文摘紫精材料在外界刺激(如光、热、电)下会表现出灵敏的变色行为,在光学开关和分子传感识别中具有良好的潜在应用前景.通过一步反应合成了4-氟苯乙酮双取代紫精衍生物(VioF_(2)·2Cl).氟苯乙酮取代基的引入扩大了其共轭体系,起到稳定自由基的作用,使着色更稳定持久.VioF_(2)·2Cl在紫外(ultraviolet,UV)灯的照射下可以快速地从白色转变为浅黄色直至黄绿色,显示出了灵敏的光致变色行为.变色后晶体中的VioF_(2)^(2+)分子间具有更短的π···π^(*)作用距离,能够促进光致电子转移(photoinduced electron transfer,PET)过程的发生,并且起到稳定紫精阳离子自由基的作用,使其能够在氧气环境下持续变色3 d而不被氧化褪色.这种新型的紫精衍生物表现出了更为灵敏的光致变色性能及自由基着色稳定性,在光致变色材料领域具有良好的潜在应用可能.
