Palladium-based catalysts have long been considered the benchmark for methane combustion;however,the authentic phase of catalytic active sites remains a subject of ongoing debate.Additionally,challenges like water-poi...Palladium-based catalysts have long been considered the benchmark for methane combustion;however,the authentic phase of catalytic active sites remains a subject of ongoing debate.Additionally,challenges like water-poisoning and long-term stability need to be addressed to advance catalyst performance.Herein,we investigate Pd on Co_(3)O_(4) nanorods as a highly effective catalyst for catalytic oxidation of methane,demonstrating long-term stability and water tolerance during a 100-h continuous operation at 350℃.Comprehensive characterizations reveal the presence of an active Pd-oxygen vacancy(Ov)-cobalt interface in Pd/Co_(3)O_(4),which effectively adsorbs molecular O_(2).The absorbed oxygen species on this interface are activated and directly participate in methane combustion.Moreover,near-ambient pressure X-ray photoelectron spectroscopy demonstrates that Pd nanoparticles undergo a rapid phase transition and predominantly remain in the metallic state during the reaction.This behavior is attributed to the electronic metal-support interaction between Pd and Co_(3)O_(4).Furthermore,in situ Fourier transformed infrared spectrum reveals that under reaction conditions,HCO3*species are formed initially and subsequently transformed into formate species,indicating that the formate pathway is the dominant mechanism for CH_(4) oxidation.展开更多
针对当前主流增强现实显示设备中的光学组合器存在的光效低,或系统复杂,或不便携带等问题,提出了直投式视网膜投影增强现实近眼显示光学系统的设计方案。光学系统自像面至物面之间依次包括视网膜投影透镜、平行光像源和补偿透镜组三个...针对当前主流增强现实显示设备中的光学组合器存在的光效低,或系统复杂,或不便携带等问题,提出了直投式视网膜投影增强现实近眼显示光学系统的设计方案。光学系统自像面至物面之间依次包括视网膜投影透镜、平行光像源和补偿透镜组三个部分。在仿真过程中,使用玻璃平板替代平行光像源,视网膜投影透镜选择双胶合透镜作为初始结构进行仿真和优化,在设计和仿真补偿透镜组时引入偶次非球面进行设计,同时仿真过程中使用人眼模型进行辅助优化,以模拟实际应用情况。最后,光学系统中的平行光像源使用激光光源及相关光学器件,并使用几何透镜搭建了该光学系统的实物样机以验证系统的显示效果。经过仿真和优化,所设计的光学系统工作在486~656 nm波段,对平行的像源光线进行成像时,点列图均方根(Root Mean Square,RMS)半径为9.59μm,在截止频率处的调制传递函数(Modulation Transfer Function,MTF)大于0.8;加入补偿透镜组后,整个系统对环境光成像时,在0°、3.75°和7.5°的三个半视场的点列图RMS半径分别为3.28μm、4.44μm和5.36μm,且全视场在截止频率处的MTF大于0.6,所设计的光学系统对显示像源和环境光的功率衰减分别在10%以下及30%以下。该系统可实现视网膜投影成像同时对环境光进行补偿,所搭建的样机可实现增强现实显示效果,系统有好的成像质量、高光效和结构简单等优点。展开更多
文摘Palladium-based catalysts have long been considered the benchmark for methane combustion;however,the authentic phase of catalytic active sites remains a subject of ongoing debate.Additionally,challenges like water-poisoning and long-term stability need to be addressed to advance catalyst performance.Herein,we investigate Pd on Co_(3)O_(4) nanorods as a highly effective catalyst for catalytic oxidation of methane,demonstrating long-term stability and water tolerance during a 100-h continuous operation at 350℃.Comprehensive characterizations reveal the presence of an active Pd-oxygen vacancy(Ov)-cobalt interface in Pd/Co_(3)O_(4),which effectively adsorbs molecular O_(2).The absorbed oxygen species on this interface are activated and directly participate in methane combustion.Moreover,near-ambient pressure X-ray photoelectron spectroscopy demonstrates that Pd nanoparticles undergo a rapid phase transition and predominantly remain in the metallic state during the reaction.This behavior is attributed to the electronic metal-support interaction between Pd and Co_(3)O_(4).Furthermore,in situ Fourier transformed infrared spectrum reveals that under reaction conditions,HCO3*species are formed initially and subsequently transformed into formate species,indicating that the formate pathway is the dominant mechanism for CH_(4) oxidation.
文摘针对当前主流增强现实显示设备中的光学组合器存在的光效低,或系统复杂,或不便携带等问题,提出了直投式视网膜投影增强现实近眼显示光学系统的设计方案。光学系统自像面至物面之间依次包括视网膜投影透镜、平行光像源和补偿透镜组三个部分。在仿真过程中,使用玻璃平板替代平行光像源,视网膜投影透镜选择双胶合透镜作为初始结构进行仿真和优化,在设计和仿真补偿透镜组时引入偶次非球面进行设计,同时仿真过程中使用人眼模型进行辅助优化,以模拟实际应用情况。最后,光学系统中的平行光像源使用激光光源及相关光学器件,并使用几何透镜搭建了该光学系统的实物样机以验证系统的显示效果。经过仿真和优化,所设计的光学系统工作在486~656 nm波段,对平行的像源光线进行成像时,点列图均方根(Root Mean Square,RMS)半径为9.59μm,在截止频率处的调制传递函数(Modulation Transfer Function,MTF)大于0.8;加入补偿透镜组后,整个系统对环境光成像时,在0°、3.75°和7.5°的三个半视场的点列图RMS半径分别为3.28μm、4.44μm和5.36μm,且全视场在截止频率处的MTF大于0.6,所设计的光学系统对显示像源和环境光的功率衰减分别在10%以下及30%以下。该系统可实现视网膜投影成像同时对环境光进行补偿,所搭建的样机可实现增强现实显示效果,系统有好的成像质量、高光效和结构简单等优点。
