The development of formic acid dehydrogenation materials with high activity and low cost is key to realizing hydrogen energy utilization.Herein,we describe a specific low-loading strategy to construct a high-activity ...The development of formic acid dehydrogenation materials with high activity and low cost is key to realizing hydrogen energy utilization.Herein,we describe a specific low-loading strategy to construct a high-activity Co atom site catalyst for this reaction.Under optimal conditions,the formic acid dehydrogenation performance of Co─Fe dual-atom catalyst(turnover frequency of 2,446.8 h^(−1),hydrogen production rate of 1,015,306.1 mL gCo^(−1)h^(−1))was 300 times greater than that of commercial 5%Pd/C.High-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure spectra,combined with theoretical calculations,confirm that the presence of different active sites(Co single-atom,Co-Co dual-atom,Co─Fe dual-atom)in catalysts is the key factor affecting their catalytic activity.These findings provide a strong scientific basis for the development of single-atom and dual-atom catalysts.展开更多
High-speed and precision positioning are fundamental requirements for high-acceleration low-load mechanisms in integrated circuit （IC） packaging equipment. In this paper, we derive the transient nonlinear dynamicres...High-speed and precision positioning are fundamental requirements for high-acceleration low-load mechanisms in integrated circuit （IC） packaging equipment. In this paper, we derive the transient nonlinear dynamicresponse equations of high-acceleration mechanisms, which reveal that stiffness, frequency, damping, and driving frequency are the primary factors. Therefore, we propose a new structural optimization and velocity-planning method for the precision positioning of a high-acceleration mechanism based on optimal spatial and temporal distribution of inertial energy. For structural optimization, we first reviewed the commonly flexible multibody dynamic optimization using equivalent static loads method （ESLM）, and then we selected the modified ESLM for optimal spatial distribution of inertial energy; hence, not only the stiffness but also the inertia and frequency of the real modal shapes are considered. For velocity planning, we developed a new velocity-planning method based on nonlinear dynamic-response optimization with varying motion conditions. Our method was verified on a high-acceleration die bonder. The amplitude of residual vibration could be decreased by more than 20% via structural optimization and the positioning time could be reduced by more than 40% via asymmetric variable velocity planning. This method provides an effective theoretical support for the precision positioning of high-acceleration low-load mechanisms.展开更多
Gasoline compression ignition(GCI)has been considered as a promising combustion concept to yield ultralow NOX and soot emissions while maintaining high thermal efficiency.However,how to improve the low-load performanc...Gasoline compression ignition(GCI)has been considered as a promising combustion concept to yield ultralow NOX and soot emissions while maintaining high thermal efficiency.However,how to improve the low-load performance becomes an urgent issue to be solved.In this paper,a GCI engine model was built to investigate the effects of internal EGR(i-EGR)and pre-injection on in-cylinder temperature,spatial concentration of mixture and OH radical,combustion and emission characteristics,and the control strategy for improving the combustion performance was further explored.The results showed an obvious expansion of the zone with an equivalence ratio between 0.8∼1.2 is realized by higher pre-injection ratios,and the s decreases with the increase of pre-injection ratio,but increases with the increase of i-EGR ratio.The high overlap among the equivalentmixture zone,the hightemperature zone,and the OH radical-rich zone can be achieved by higher i-EGR ratio coupled with higher preinjection ratio.By increasing the pre-injection ratio,the combustion efficiency increases first and then decreases,also achieves the peak value with a pre-injection ratio of 60%and is unaffected by i-EGR.The emissions of CO,HC,NOX,and soot can also be reduced to low levels by the combination of higher i-EGR ratios and a pre-injection ratio of 60%.展开更多
随着风电在电力系统中占比的逐年攀升,传统机组单独承担调频任务已难以适应其需求变化。因此,风电需具备与传统电源协同调节系统频率的能力。首先,基于风电调频的快速性和火电调频的持久性,设计了一种以火电为主、风电为辅的联合一次调...随着风电在电力系统中占比的逐年攀升,传统机组单独承担调频任务已难以适应其需求变化。因此,风电需具备与传统电源协同调节系统频率的能力。首先,基于风电调频的快速性和火电调频的持久性,设计了一种以火电为主、风电为辅的联合一次调频控制策略。其次,充分考虑风电场内各机组的运行差异,提出一种基于裕度因子的功率分配策略,有效挖掘各机组的调频能力并确保其安全运行。同时,提出一种针对风电场内风机分组运行的持久备用功率再分配策略。该策略预先安排少数风电机组以低减载率的超速模式运行,当调频风机退出频率支撑后,减载风机将根据调频风机的转速,采用一种基于转速反比例因子的差异化能量分配策略,以有效弥补调频风机退出后的能量缺额,缓解频率二次跌落(secondary frequency drop,SFD)。仿真结果表明,所提策略能够实现风火联合参与一次调频,在保证经济性和可靠性的前提下,充分发掘风电调频性能,有效改善电力系统频率响应特性。展开更多
基金supported by the National Natural Science Foundation of China(21603054,31671930)the Natural Science Foundation of Hebei Province(B2016204136,B2016204131)+3 种基金the Young Top-notch Talents Foundation of Hebei Provincial Universities(BJ2016027)the Innovation and entrepreneurship training program for college students of Hebei Agricultural University(s202010086046,2019085)the Scientific Research Development Fund project of Hebei Agricultural University(JY2020028)the Innovation and entrepreneurship training program for college students of Hebei Agricultural University(2025019,2025198).
文摘The development of formic acid dehydrogenation materials with high activity and low cost is key to realizing hydrogen energy utilization.Herein,we describe a specific low-loading strategy to construct a high-activity Co atom site catalyst for this reaction.Under optimal conditions,the formic acid dehydrogenation performance of Co─Fe dual-atom catalyst(turnover frequency of 2,446.8 h^(−1),hydrogen production rate of 1,015,306.1 mL gCo^(−1)h^(−1))was 300 times greater than that of commercial 5%Pd/C.High-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure spectra,combined with theoretical calculations,confirm that the presence of different active sites(Co single-atom,Co-Co dual-atom,Co─Fe dual-atom)in catalysts is the key factor affecting their catalytic activity.These findings provide a strong scientific basis for the development of single-atom and dual-atom catalysts.
基金supported by the National Key Basic Research Program of China (2011CB013104)National Natural Science Foundation of China (U1134004)+2 种基金Guangdong Provincial Natural Science Foundation (2015A030312008)Science and Technology Program of Guangzhou (201510010281)Guangdong Provincial Science and Technology Plan (2013B010402014)
文摘High-speed and precision positioning are fundamental requirements for high-acceleration low-load mechanisms in integrated circuit （IC） packaging equipment. In this paper, we derive the transient nonlinear dynamicresponse equations of high-acceleration mechanisms, which reveal that stiffness, frequency, damping, and driving frequency are the primary factors. Therefore, we propose a new structural optimization and velocity-planning method for the precision positioning of a high-acceleration mechanism based on optimal spatial and temporal distribution of inertial energy. For structural optimization, we first reviewed the commonly flexible multibody dynamic optimization using equivalent static loads method （ESLM）, and then we selected the modified ESLM for optimal spatial distribution of inertial energy; hence, not only the stiffness but also the inertia and frequency of the real modal shapes are considered. For velocity planning, we developed a new velocity-planning method based on nonlinear dynamic-response optimization with varying motion conditions. Our method was verified on a high-acceleration die bonder. The amplitude of residual vibration could be decreased by more than 20% via structural optimization and the positioning time could be reduced by more than 40% via asymmetric variable velocity planning. This method provides an effective theoretical support for the precision positioning of high-acceleration low-load mechanisms.
基金sponsored by the projects of National Natural Science Foundation of China (Grant Nos.51806127 and 52075307)Key Research and Development Program of Shandong Province (Grant No.2019GHZ016).
文摘Gasoline compression ignition(GCI)has been considered as a promising combustion concept to yield ultralow NOX and soot emissions while maintaining high thermal efficiency.However,how to improve the low-load performance becomes an urgent issue to be solved.In this paper,a GCI engine model was built to investigate the effects of internal EGR(i-EGR)and pre-injection on in-cylinder temperature,spatial concentration of mixture and OH radical,combustion and emission characteristics,and the control strategy for improving the combustion performance was further explored.The results showed an obvious expansion of the zone with an equivalence ratio between 0.8∼1.2 is realized by higher pre-injection ratios,and the s decreases with the increase of pre-injection ratio,but increases with the increase of i-EGR ratio.The high overlap among the equivalentmixture zone,the hightemperature zone,and the OH radical-rich zone can be achieved by higher i-EGR ratio coupled with higher preinjection ratio.By increasing the pre-injection ratio,the combustion efficiency increases first and then decreases,also achieves the peak value with a pre-injection ratio of 60%and is unaffected by i-EGR.The emissions of CO,HC,NOX,and soot can also be reduced to low levels by the combination of higher i-EGR ratios and a pre-injection ratio of 60%.
文摘随着风电在电力系统中占比的逐年攀升,传统机组单独承担调频任务已难以适应其需求变化。因此,风电需具备与传统电源协同调节系统频率的能力。首先,基于风电调频的快速性和火电调频的持久性,设计了一种以火电为主、风电为辅的联合一次调频控制策略。其次,充分考虑风电场内各机组的运行差异,提出一种基于裕度因子的功率分配策略,有效挖掘各机组的调频能力并确保其安全运行。同时,提出一种针对风电场内风机分组运行的持久备用功率再分配策略。该策略预先安排少数风电机组以低减载率的超速模式运行,当调频风机退出频率支撑后,减载风机将根据调频风机的转速,采用一种基于转速反比例因子的差异化能量分配策略,以有效弥补调频风机退出后的能量缺额,缓解频率二次跌落(secondary frequency drop,SFD)。仿真结果表明,所提策略能够实现风火联合参与一次调频,在保证经济性和可靠性的前提下,充分发掘风电调频性能,有效改善电力系统频率响应特性。
