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A grand master of seismology and mentoring

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Earthquake Science 2022年第1期35卷 61-62页

作者： zhongwen zhan Seismological Laboratory California Institute of TechnologyPasadenaCA 91125USA

I joined Don Helmberger’s group in the summer of 2008,after getting a Master’s degree in China from Sidao Ni,another graduate student of Don’s.I was very excited,because Don has a giant academic family tree and I thought I would become Don’s last student,which is quite an honor in the Chinese culture,so-called the“final apprentice”.I was wrong!Don had another seven students after me and the final apprentice honor went to Voon-Hui *** Don’s long career,he had scores of students,many of whom are now big names in academia,especially in the United States and in China,because Don mentored a number of Chinese students.

关键词： has quite excited

Stationary phase approximation in the ambient noise method revisited

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Earthquake Science 2010年第5期23卷 425-431页

作者： zhongwen zhan Sidao Ni Mengcheng National Geophysical Observatory School of Earth and Space Sciences University of Science and Technology of China Hefei 230026 China Key Laboratory of Dynamic Geodesy Institute of Geodesy and Geophysics Chinese Academy of Sciences Wuhan 430077 China

The method of extracting Green＇s function between stations from cross correlation has proven to be effective theoretically and experimentally. It has been widely applied to surface wave tomography of the crust and upmost mantle. However, there are still controversies about why this method works. Snieder employed stationary phase approximation in evaluating contribution to cross correlation function from scatterers in the whole space, and concluded that it is the constructive interference of waves emitted by the scatterers near the receiver line that leads to the emergence of Green＇s function. His derivation demonstrates that cross correlation function is just the convolution of noise power spectrum and the Green＇s function. However, his derivation ignores influence from the two stationary points at infinities, therefore it may fail when attenuation is absent. In order to obtain accurate noise-correlation function due to scatters over the whole space, we compute the total contribution with numerical integration in polar coordinates. Our numerical computation of cross correlation function indicates that the incomplete stationary phase approximation introduces remarkable errors to the cross correlation function, in both amplitude and phase, when the frequency is low with reasonable quality factor Q. Our results argue that the dis- tance between stations has to be beyond several wavelengths in order to reduce the influence of this inaccuracy on the applications of ambient noise method, and only the station pairs whose distances are above several （〉5） wavelengths can be used.

关键词： ambient seismic noise stationary phase approximation Green's function

Estimated Green's function extracted from superconducting gravimeters and seismometers

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Earthquake Science 2011年第2期24卷 143-150页

作者： Xiangfang Zeng zhongwen zhan Yong Zheng Mengcheng National Geophysical Observatory School of Earth and Space Sciences University of Science and Technology of China China Seismological Laboratory California Institute of Technology Pasadena CA 91125 USA 3 CAS Key Laboratory of Dynamical Geodesy Institute of Geodesy and Geophysics Wuhan 430077 China CAS Key Laboratory of Dynamical Geodesy Institute of Geodesy and Geophysics Wuha'n 430077 China

Estimated Green’s function （EGF） between stations has been extracted from ambient seismic noise, direct surface wave and coda waves. It is also confirmed by laboratory experiments on ultrasonics and theoretical derivations assuming diffusive wave field, equi-partition of modes or random sources on an enclosed surface. This method provides a new approach to study the crust and mantle structure at regional scale, continental scale and global scale. Following the achievements with seismometer records, the records of infrasonic station, hydrophone and microphone were also used to obtain the EGFs of different wave fields. Since superconducting gravimeter is a better long period instrument than regular seismometer, EGF at longer period is expected to be obtained with the cross correlation of gravity data. In this paper, we will show the EGFs extracted by cross-correlations between the superconducting gravimeters and the seismometers. Both the travel times and dispersion curves obtained from different data types are consistent. The result shows that it is possible to retrieve the deep structure by the cross correlation of gravity data.

关键词： superconducting gravimeter noise cross-correlation estimated Green’s function

Comparison of ground truth location of earthquake from InSAR and from ambient seismic noise: A case study of the 1998 zhangbei earthquake

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Earthquake Science 2011年第2期24卷 239-247页

作者： Jun Xie Xiangfang Zeng Weiwen Chen zhongwen zhan CAS Key Laboratory of Geodynamical Laboratory Institute of Geodesy and Geophysics Wuhan 430077 China Mengcheng National Geophysical Observatory School of Earth and Space Sciences University of Science and Technology of China Hefei 230026 China Seismological Laboratory California Institute of Technology Pasadena CA 91125 USA

Because ambient seismic noise provides estimated Green’s function （EGF） between two sites with high accuracy, Rayleigh wave propagation along the path connecting the two sites is well resolved. Therefore, earthquakes which are close to one seismic station can be well located with calibration extracting from EGF. We test two algorithms in locating the 1998 zhangbei earthquake, one algorithm is waveform-based, and the other is traveltime-based. We first compute EGF between station ZHB （a station about 40 km away from the epicenter） and five IC/IRIS stations. With the waveform-based approach, we calculate 1D synthetic single-force Green’s functions between ZHB and other four stations, and obtain traveltime corrections by correlating synthetic Green’s functions with EGFs in period band of 10–30 s. Then we locate the earthquake by minimizing the differential travel times between observed earthquake waveform and the 1D synthetic earthquake waveforms computed with focal mechanism provided by Global CMT after traveltime correction from EGFs. This waveform-based approach yields a location which error is about 13 km away from the location observed with InSAR. With the traveltime-based approach, we begin with measuring group velocity from EGFs as well as group arrival time on observed earthquake waveforms, and then locate the earthquake by minimizing the difference between observed group arrival time and arrival time measured on EGFs. This traveltime-based approach yields accuracy of 3 km, Therefore it is feasible to achieve GT5 （ground truth location with accuracy 5 km） with ambient seismic noises. The less accuracy of the waveform-based approach was mainly caused by uncertainty of focal mechanism.

关键词： ambient seismic noise estimated Green’s function ground truth location Rayleigh wave

Rapid Phase Ambiguity Elimination Methods for DOA Estimator via Hybrid Massive MIMO Receive Array

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Chinese Journal of Electronics 2024年第1期33卷 175-184页

作者： Xichao zhan zhongwen SUN Feng SHU Yiwen CHEN Xin CHENG Yuanyuan WU Qi zhanG Yifan LI Peng zhanG School of Information and Communication Engineering Hainan University School of Electronic and Optical Engineering Nanjing University of Science and Technology

For a sub-connected hybrid multiple-input multiple-output(MIMO) receiver with K subarrays and N antennas, there exists a challenging problem of how to rapidly remove phase ambiguity in only single time-slot. A direction of arrival(DOA) estimator of maximizing received power(Max-RP) is proposed to find the maximum value of K-subarray output powers, where each subarray is in charge of one sector, and the center angle of the sector corresponding to the maximum output is the estimated true DOA. To make an enhancement on precision, Max-RP plus quadratic interpolation(Max-RP-QI) method is designed. In the proposed Max-RP-QI, a quadratic interpolation scheme is adopted to interpolate the three DOA values corresponding to the largest three receive powers of *** achieve the Cramer Rao lower bound, a Root-MUSIC plus Max-RP-QI scheme is developed. Simulation results show that the proposed three methods eliminate the phase ambiguity during one time-slot and also show low computational complexities. The proposed Root-MUSIC plus Max-RP-QI scheme can reach the Cramer Rao lower bound,and the proposed Max-RP and Max-RP-QI are still some performance losses 2–4 d B compared to the Cramer Rao lower bound.

关键词： Phased arrays Interpolation Wireless sensor networks Direction-of-arrival estimation Simulation Receiving antennas Massive MIMO

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大型柔性航天器动力学与振动控制研究进展

力学学报 2019年第1期51卷 1-13页

作者：曹登庆白坤朝丁虎周徐斌潘忠文陈立群詹世革哈尔滨工业大学航天学院哈尔滨150001 国家自然科学基金委员会数理科学部北京100085 上海大学上海应用数学和力学研究所上海200072 上海卫星工程研究所上海2011095 北京宇航系统工程研究所北京100076 哈尔滨工业大学深圳校区理学院广东深圳518055

随着航天重大工程的逐步实施,航天器正朝着超高速、超大尺度、多功能的方向发展,其面临的发射和运行环境也更加恶劣.航天器发射过程中的振动及其主/被动控制、在轨运行中大型柔性航天器动力学建模与动态响应分析、结构振动与飞行器姿态... 详细信息

随着航天重大工程的逐步实施,航天器正朝着超高速、超大尺度、多功能的方向发展,其面临的发射和运行环境也更加恶劣.航天器发射过程中的振动及其主/被动控制、在轨运行中大型柔性航天器动力学建模与动态响应分析、结构振动与飞行器姿态的混合控制等问题越来越复杂且难于处理;航天器结构的大型化和柔性化(如大阵面天线和太阳翼等)也对其地面试验和半实物仿真提出了挑战.本文着重介绍大型柔性航天器涉及到的动力学与振动控制问题,包括航天器发射过程中的整星隔振,大型柔性结构动力学建模与振动响应分析,大型柔性航天器的结构振动与姿轨控耦合动力学及其混合控制等.提炼出航天动力学与控制领域中亟待解决的若干基础科学问题,包括:多刚柔体系统动力学建模与模型降阶(涉及大变形柔性体动力学建模、多求解器合作仿真、模型降阶、组合结构动力学建模的解析方法等);复杂结构状态空间模型构建方法与能控性(涉及状态空间模型构建的理论与实验方法、复杂结构振动控制系统的能观性与能控性等);航天器姿态运动与大型柔性结构振动的混合控制律设计(涉及姿态机动与结构振动的鲁棒混合控制、执行机构与压电控制器的协同控制等).

关键词：大型柔性航天器空间结构非线性动力学振动控制姿轨控多体系统动力学

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非油炸胡萝卜脆片的开发研究

美食研究 2016年第3期33卷 26-28页

作者：汤纯孟静陈胜姝谢静张文烨曹仲文扬州大学旅游烹饪学院江苏扬州225127

通过冷冻与微波光波干燥相结合的技术制作胡萝卜脆片,利用正交试验与方差分析确定出制作胡萝卜脆片的最佳条件组合:50%微波+50%光波、冷冻温度为-18℃、小苏打浓度为0.36 mol/L,此方法加工的非油炸胡萝卜脆片感官效果最好。

关键词：胡萝卜光波微波交替加热比例:食品加工