Recent studies have revealed the extraordinary performance of zirconium oxide in propane dehydrogenation,which is attributed to the excellent reactivity of the coordinatively unsaturated zirconium sites(Zr_(cus))aroun...Recent studies have revealed the extraordinary performance of zirconium oxide in propane dehydrogenation,which is attributed to the excellent reactivity of the coordinatively unsaturated zirconium sites(Zr_(cus))around the oxygen vacancies.The origin of the enhanced catalytic activity of ZrO_(2)with defective tetrahedral Zr sites was examined by direct comparison with its pristine counterpart in the current study.Electronic-structure analysis revealed that electrons from oxygen removal were localized within vacancies on the defective surface,which directly attacked the C-H bond in propane.The involvement of localized electrons activates the C-H bond via back-donation to the antibonding orbital on the defective surface;conversely,charge is transferred from propane to the pristine surfaces.The barrier for the first C-H bond activation is clearly significantly reduced on the defective surfaces compared to that on the pristine surfaces,which verifies the superior activity of Zr_(cus).Notably,however,the desorption of both propene and hydrogen molecules from Zr_(cus)is more difficult due to strong binding.The calculated turnover frequency(TOF)for propene formation demonstrates that the pristine surfaces exhibit better catalytic performance at lower temperatures,whereas the defective surfaces have a larger TOF at high temperatures.However,the rate-determining step and reaction order on the defective surface differ from those on the pristine surface,which corroborates that the catalysts follow different mechanisms.A further optimization strategy was proposed to address the remaining bottlenecks in propane dehydrogenation on zirconium oxide.展开更多
A new method based on cross-spectrum estimation for the verification and validation of computer simulation models is expounded in accordance with the characteristics of missile systems. The new method can expose the d...A new method based on cross-spectrum estimation for the verification and validation of computer simulation models is expounded in accordance with the characteristics of missile systems. The new method can expose the differences between two time processes in several aspects and can also give quantitative analysis results about the statistical consistence between them. An application to an actual anti-tank missile system simulation is presented and the calculated results confirm the effectiveness of the method. The approach can also be employed to verify the simulation models of other dynamic systems.展开更多
文摘Recent studies have revealed the extraordinary performance of zirconium oxide in propane dehydrogenation,which is attributed to the excellent reactivity of the coordinatively unsaturated zirconium sites(Zr_(cus))around the oxygen vacancies.The origin of the enhanced catalytic activity of ZrO_(2)with defective tetrahedral Zr sites was examined by direct comparison with its pristine counterpart in the current study.Electronic-structure analysis revealed that electrons from oxygen removal were localized within vacancies on the defective surface,which directly attacked the C-H bond in propane.The involvement of localized electrons activates the C-H bond via back-donation to the antibonding orbital on the defective surface;conversely,charge is transferred from propane to the pristine surfaces.The barrier for the first C-H bond activation is clearly significantly reduced on the defective surfaces compared to that on the pristine surfaces,which verifies the superior activity of Zr_(cus).Notably,however,the desorption of both propene and hydrogen molecules from Zr_(cus)is more difficult due to strong binding.The calculated turnover frequency(TOF)for propene formation demonstrates that the pristine surfaces exhibit better catalytic performance at lower temperatures,whereas the defective surfaces have a larger TOF at high temperatures.However,the rate-determining step and reaction order on the defective surface differ from those on the pristine surface,which corroborates that the catalysts follow different mechanisms.A further optimization strategy was proposed to address the remaining bottlenecks in propane dehydrogenation on zirconium oxide.
文摘大规模MIMO系统中,相对于其他基于信道矩阵分解的波束成形算法,如迫零、最小均方误差算法等,匹配滤波(Matched filter,MF)具有复杂度极低的优点,从而成为一种极具实用潜力的波束成形算法。鉴于此,本文推导了基站采用MF波束成形算法时,用户端信干噪比(Signal-to-interferenceand-noise ratio,SINR)的近似概率密度函数(Probability density function,PDF)。该函数对于推导与分析系统性能,如和速率、中断概率等至关重要。仿真表明:当基站天线数趋于大规模时,SINR公式的PDF曲线趋近于通过纯仿真得到的PDF曲线。
文摘A new method based on cross-spectrum estimation for the verification and validation of computer simulation models is expounded in accordance with the characteristics of missile systems. The new method can expose the differences between two time processes in several aspects and can also give quantitative analysis results about the statistical consistence between them. An application to an actual anti-tank missile system simulation is presented and the calculated results confirm the effectiveness of the method. The approach can also be employed to verify the simulation models of other dynamic systems.
基金supported by the National Natural Science Foundation of China(Nos.21173096 and21203071)the China Postdoctoral Science Foundation(No.2013M541288)the China Postdoctoral Science Special Foundation(No.2015T80297)~~
文摘基于密度泛函理论计算分析了2种Eosin Y-Ti O2(101)吸附构型下的几何结构、电子结构及电荷转移性质.结果表明,Eosin Y以H构型吸附在Ti O2(101)表面时的体系总能量比B构型的高59.7 k J/mol;Eosin Y以B构型吸附在Ti O2(101)表面时比以H构型吸附时的吸附能更高.因此,B吸附构型更易形成.此外,还对电子注入动力学进行了模拟并对界面间的电荷转移进行了Bader定量分析.结果显示,与吸附H构型相比,B构型下的电子注入过程更迅速也更完全.
