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| 1 | A Stable Q Compensated Reverse Time Migration Method Based on Excitation Amplitude Imaging Condition显示文摘The stability and efficiency,especially the stability,are generally concerned issues in Q compensated reverse time migration(Q-RTM).The instability occurs because of the exponentially boosted high frequency ambient noise during the forward or backward seismic wavefield propagation.The regularization and low-pass filtering methods are two effective strategies to control the instability of the wave propagation in Q-RTM.However,the regularization parameters are determined experimentally,and the wavefield cannot be recovered accurately.The low-pass filtering method cannot balance the selection of cutoff frequency for varying Q values,and may damage the effective signals,especially when the signal-to-noise ratio(SNR)of the seismic data is low,the Q-RTM will be a highly unstable process.In order to achieve the purpose of stability,the selection of cutoff frequency will be small enough,which can cause great damage to the effective high frequency signals.In this paper,we present a sta-ble Q-RTM algorithm based on the excitation amplitude imaging condition,which can compensate both the amplitude attenuation and phase dispersion.Unlike the existing Q-RTM algorithms enlarging the amplitude,the exponentially attenuated seismic wavefield will be used during both the forward and backward wavefield propagation of Q-RTM.Therefore,the new Q-RTM algorithm is relative stable,even for the low SNR seismic data.In order to show the accuracy and stability of our stable Q-RTM algorithm clearly,an example based on Graben model will be illustrated.Then,a realistic BP gas chimney model further demonstrates that the proposed method enjoys good stability and anti-noise performance compared with the traditional Q-RTM with amplitude amplification.Compare the Q-RTM images of these two models to the reference images obtained by the acoustic RTM with acoustic seismic data,the new Q-RTM results match the reference images quite well.The proposed method is also tested using a field seismic data,the result shows the effectiveness of our proposed method. | Qingqing Li Li-Yun Fu Weijia Sun Wei Wei Wanting Hou | 2020 | Communications in Computational Physics2020，28，6： | 0 |
| 2 | Spin-Modulated Oxygen Electrocatalysis显示文摘The electrocatalysis reactions involving oxygen,such as oxygen evolution reaction(OER)and oxygen reduction reaction(ORR),play a critical role in energy storage/conversion applications,e.g.,fuel cells,metal-air batteries,and electrochemical water splitting.The high kinetic energy barrier of the OER/ORR is highly associated with the spin state interconversion between singlet OH^(−)/H_(2)O and triplet O_(2),which is influenced by the spin state and magnetism of catalysts.This Review summarizes recent progress and advances in understanding spin/magnetism-related effects in oxygen electrocatalysis to develop spin theory.It is demonstrated that the spin states(low,intermediate,and high spin)of magnetic transition metal catalysts(TMCs)can directly affect the reaction barriers of OER/ORR by tailoring the bonding of oxygen intermediates with TMCs.Besides,the spin states of TMCs can build a spin-selective channel to filter the electron spins required for the single/triplet interconversion of O species during OER/ORR.In this Review,we introduced many approaches to modulating spin state,for instance,altering the crystal field,oxidation state of active-site ions,and the morphology of TMCs.What’s more,a magnetic field can drive the spin flip of magnetic ions to achieve the spin alignment(↑↑)(i.e.,facilitating spin polarization),which will strengthen the spin selectivity for accelerating the filtration and transfer of the spins with the same direction for the generation and conversion of triplet ↑O=O↑.Importantly,the origin of magnetic field enhancement on OER/ORR are deeply discussed,which provides a great vision for the magnetism-assisted catalysis.Finally,the challenges and perspectives for future development of spin/magnetism catalysis are presented.This Review is expected to highlight the significance of spin/magnetism theory in breaking the bottleneck of electrocatalysis field and promote the development of high-efficientcy electrocatalysts for practical applications. | Zhi Fang Wanting Zhao Tong Shen Daping Qiu Yucheng Lv Xinmei Hou Yanglong Hou | 2023 | Precision Chemistry2023，1，7： | 0 |
| 3 | Extremum of a time-inhomogeneous branching random walk显示文摘Consider a time-inhomogeneous branching random walk, generated by the point process Ln which composed by two independent parts: ‘branching’offspring Xn with the mean 1+B(1+n)−β for β∈(0,1) and ‘displacement’ ξn with a drift A(1+n)^(−2α) for α∈(0,1/2), where the ‘branching’ process is supercritical for B>0 but ‘asymptotically critical’ and the drift of the ‘displacement’ ξn is strictly positive or negative for |A|>0 but ‘asymptotically’ goes to zero as time goes to infinity. We find that the limit behavior of the minimal (or maximal) position of the branching random walk is sensitive to the ‘asymptotical’ parameter β and α. | Wanting HOU Xiaoyue ZHANG Wenming HONG | 2021 | Frontiers of Mathematics in China2021，16，2： | 0 |
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