We investigate the dynamics of parity-and time-reversal（PT） symmetric two-energy-level atoms in the presence of two optical and one radio-frequency fields. The strength and relative phase of fields can drive the sys...We investigate the dynamics of parity-and time-reversal（PT） symmetric two-energy-level atoms in the presence of two optical and one radio-frequency fields. The strength and relative phase of fields can drive the system from the unbroken to the broken PT symmetric regions. Compared with the Hermitian model, Rabi-type oscillation is still observed, and the oscillation characteristics are also adjusted by the strength and relative phase in the region of the unbroken symmetry. At the exception point, the oscillation breaks down. To better understand the underlying properties we study the effective Bloch dynamics and find that the emergence of the PT components of the fixed points is the feature of the PT symmetry breaking and the projections in the x–y plane can be controlled with high flexibility compared with the standard two-level system with the PT symmetry. It helps to study the dynamic behavior of the complex PT symmetric model.展开更多
Cost-effective electrocatalysts for the hydrogen evolution reaction （HER） play a key role in the field of renewable energy. Although tremendous efforts have been devoted to the search of alternative materials, Pt/C ...Cost-effective electrocatalysts for the hydrogen evolution reaction （HER） play a key role in the field of renewable energy. Although tremendous efforts have been devoted to the search of alternative materials, Pt/C is still the most efficient electrocatalyst for the HER. Nevertheless, decreasing the loading of Pt in the designed eletrocatalysts is of significance. However, with low Pt loading, it is challenging to maintain excellent catalytic performance. Herein, a new catalyst （Pt/NPC） was prepared by dispersing Pt nanoparticles （PtNPs） with an average diameter of 1.8 nm over a three-dimensional （3D） carbon network co-doped with N and P. Because of the high electronegativity of the N and P dopants, PtNPs were uniformly dispersed on the carbon network via high electronic affinity between Pt and carbon, affording a Pt/NPC catalyst; Pt/NPC exhibited superior HER activity, attributed to the down-shift of the Pt d-band caused by the donation of charge from N and P to Pt. The results show that Pt/NPC with an ultralow Pt loading of 1.82 wt.% exhibits excellent HER performance, which corresponds to a HER mass activity 20.6-fold greater than that observed for commercial 20% Pt/C at an overpotential of 20 mV vs. RHE.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 11104171,11404199,11574187 and 11604188the Youth Science Foundation of Shanxi Province of China under Grant No 2012021003-1the Natural Science Foundation for Youths of Shanxi Province under Grant Nos 201601D201027 and 1331KSC
文摘We investigate the dynamics of parity-and time-reversal（PT） symmetric two-energy-level atoms in the presence of two optical and one radio-frequency fields. The strength and relative phase of fields can drive the system from the unbroken to the broken PT symmetric regions. Compared with the Hermitian model, Rabi-type oscillation is still observed, and the oscillation characteristics are also adjusted by the strength and relative phase in the region of the unbroken symmetry. At the exception point, the oscillation breaks down. To better understand the underlying properties we study the effective Bloch dynamics and find that the emergence of the PT components of the fixed points is the feature of the PT symmetry breaking and the projections in the x–y plane can be controlled with high flexibility compared with the standard two-level system with the PT symmetry. It helps to study the dynamic behavior of the complex PT symmetric model.
基金Acknowledgements This work was financially supported by National Natural Science Foundation of China （No. 21425103） and Natural Science Foundation of Jiangsu Province （No. SBK201341397）.
文摘Cost-effective electrocatalysts for the hydrogen evolution reaction （HER） play a key role in the field of renewable energy. Although tremendous efforts have been devoted to the search of alternative materials, Pt/C is still the most efficient electrocatalyst for the HER. Nevertheless, decreasing the loading of Pt in the designed eletrocatalysts is of significance. However, with low Pt loading, it is challenging to maintain excellent catalytic performance. Herein, a new catalyst （Pt/NPC） was prepared by dispersing Pt nanoparticles （PtNPs） with an average diameter of 1.8 nm over a three-dimensional （3D） carbon network co-doped with N and P. Because of the high electronegativity of the N and P dopants, PtNPs were uniformly dispersed on the carbon network via high electronic affinity between Pt and carbon, affording a Pt/NPC catalyst; Pt/NPC exhibited superior HER activity, attributed to the down-shift of the Pt d-band caused by the donation of charge from N and P to Pt. The results show that Pt/NPC with an ultralow Pt loading of 1.82 wt.% exhibits excellent HER performance, which corresponds to a HER mass activity 20.6-fold greater than that observed for commercial 20% Pt/C at an overpotential of 20 mV vs. RHE.
