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Numerical Simulation of 2D Supersonic Magnetohydrodynamic Channel and Study on Hall Effect

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Chinese Journal of Aeronautics 2011年第2期24卷 136-144页

作者： ZHENG xiaomei LU Haoyu xu Dajun CAI Guobiao School of Astronautics Beihang University Beij'ing 100191 China

In this research effort,numerical simulation of two-dimensional magnetohydrodynamic（MHD） channel is performed and Hall effect is *** computational model consists of the Navier-Stokes（N-S） equations coupled with electrical-magnetic source terms,Maxwell equations and the generalized Ohm＇s *** conditions for the electrical potential equation considering Hall effect are *** start with,the MHD channel with single-pair electrodes is studied and flow of the electric current is in accordance with physical *** the MHD channel with five-pair electrodes is numerically *** results show that the electrical current concentrates on the downstream of the anode and the upstream of the cathode due to Hall effect,and the flow field becomes *** the current value of the magnetic interaction parameter,the electrical-magnetic force affects the flow remarkably,decreasing the outlet Mach number and increasing the outlet pressure;what＇s more,the flow structure in the channel becomes extremely *** of MHD channels with continual electrodes and segmented electrodes are *** results show that performance of the MHD channel with segmented electrodes is better than that with continual electrodes with the increase of Hall parameter.

关键词： hypersonic vehicles scramjet magnetohydrodynamics Hall effect numerical simulation

DES-Fe3O4 composite for rapid extraction of residual plant growth regulators in edible vegetable oil

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Chinese Chemical Letters 2019年第6期30卷 1182-1185页

作者： Ting Tan xiaomei xu Yiqun Wan State Key Laboratory of Food Science and Technology Nanchang University Nanchang 330047 China Center of Analysis and Testing Nanchang University Nanchang 330031 China School of Chemistry Nanchang University Nanchang 330031 China

A rapid DES-Fe3O4 microextraction coupled with liquid chromatography method was ingeniously developed for simultaneous control of five typical plant growth regulators in a planting cycle including indole-3-acetic acid, abscisic acid, thidiazuron, 1-naphthylacetic acid and forchlorfenuron. The experiments were carried out with one type of carboxylic acid-assisted deep eutectic solvent (nChCl:nacetic acid=1:3) as extractant, coupled with ultrasonic wave extraction for 30 min at bath temperature at 50 ℃. Under the optimum conditions, good extraction performances of linearities for five plant growth regulators were achieved separately in the range of 0.10–50 mg/L of indole-3-acetic acid, 0.06–50 mg/L of abscisic acid, 0.20–50 mg/L of thidiazuron, 0.50–50 mg/L of 1-naphthylacetic acid and 0.06–50 mg/L of forchlorfenuron and recoveries were ranged from 70.4%to 102.2%. Meanwhile, Fe3O4 was preferentially combined with DES in the oil matrix, the advantage of which was pointed to rapid and efficient separation of targeted plant growth regulators from complicated oil matrix. The proposed approach achieved satisfied results and met the monitoring requirements of plant growth regulators control in edible vegetable oil samples.

关键词： DES-Fe3O4 composite Deep eutectic solvent Rapid separation Plant growth regulators Edible vegetable oil

Fractional Fourier domain hopped communication method based on chirp modulation for underwater acoustic channels

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Journal of Systems Engineering and Electronics 2017年第3期28卷 449-456页

作者： Xingbin Tu xiaomei xu Zheguang Zou Liangliang Yang Jianming Wu College of Ocean and Earth Science Xiamen UniversityXiamen 361102China Key Laboratory of Underwater Acoustic Communication and Marine Information Technology Ministry of EducationXiamen 361005China

To improve the data rate of underwater acoustic frequency-hopped communications, frequency hopping is applied to different orders of fractional Fourier domain (FrFD), to enable non-intrusive, bandwidth-limited acoustic communications. An FrFD frequency-hopped communication method based on chirp modulation, namely multiple chirp shift keying-FrFD hopping (MCSK-FrFDH), is proposed for underwater acoustic channels. Validated by both simulations and experimental results, this method can reach a bandwidth efficiency twice more than conventional frequency-hopped methods with the same data rate and anti-multipath capability, suggesting that the proposed method achieves a better performance than the traditional frequency hopped communication in underwater acoustic communication channels. Results also show that in practical scenarios, the MCSK-FrFDH system with longer symbol length performs better at the low signal-to-noise ratio (SNR), while the system with larger frequency sweeping range performs better at a high SNR.

关键词： underwater acoustic communication fractional Fourier domain (FrFD) frequency hopping chirp signal

QMCR:A Q-Learning-Based Multi-Hop Cooperative Routing Protocol for Underwater Acoustic Sensor Networks

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China Communications 2021年第8期18卷 224-236页

作者： Yougan Chen Kaitong Zheng Xing Fang Lei Wan xiaomei xu Key Laboratory of Underwater Acoustic Communication and Marine Information Technology(Xiamen University) Ministry of EducationXiamen 361005China Shenzhen Research Institute of Xiamen University Shenzhen 518000China Dongshan Swire Marine Station College of Ocean and Earth SciencesXiamen UniversityXiamen 361102China School of Information Technology Illinois State UniversityNormalIL 61790USA School of Informatics Xiamen UniversityXiamen 361005China

Routing plays a critical role in data transmission for underwater acoustic sensor networks(UWSNs)in the internet of underwater things(IoUT).Traditional routing methods suffer from high end-toend delay,limited bandwidth,and high energy *** the development of artificial intelligence and machine learning algorithms,many researchers apply these new methods to improve the quality of *** this paper,we propose a Qlearning-based multi-hop cooperative routing protocol(QMCR)for *** protocol can automatically choose nodes with the maximum Q-value as forwarders based on distance ***,we combine cooperative communications with Q-learning algorithm to reduce network energy consumption and improve communication *** results show that the running time of the QMCR is less than one-tenth of that of the artificial fish-swarm algorithm(AFSA),while the routing energy consumption is kept at the same *** to the extremely fast speed of the algorithm,the QMCR is a promising method of routing design for UWSNs,especially for the case that it suffers from the extreme dynamic underwater acoustic channels in the real ocean environment.

关键词： Q-learning algorithm routing internet of underwater things underwater acoustic communication multi-hop cooperative communication

Spatial information recognizing of ocean eddies based on virtual force field and its application

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Acta Oceanologica Sinica 2007年第4期26卷 44-52页

作者： LI Ce DU Yunyan SU Fenzhen YANG xiaomei xu Jun State Key Laboratory of Resources and Environment Information System Institute of Geographic Science and Natural Resources Chinese Academy of Sciences Beijing 100101 China

A new approach to detecting ocean eddies automatically from remote sensing imageries based on the ocean eddy＇s eigen-pattern in remote sensing imagery and ＂force field-based shape extracting method＂ is proposed. First, the analysis on extracting eddies＇ edges from remote sensing imagery using conventional edge detection arithmetic operators is performed and returns digitized vector edge data as a result. Second, attraction forces and fusion forces between edge curves were analyzed and calculated based on the vector eddy edges. Thirdly, the virtual significant spatial patterns of eddy were detected automatically using iterative repetition followed by optimized rule. Finally, the spatial form auto-detection of different types of ocean eddies was done using satellite images. The study verified that this is an effective way to identify and detect the ocean eddy with a complex form.

关键词： ocean eddy spatial pattern recognizing force field detection

Electrochemical performance of La_(1-x)Sr_xCuO_(3-δ)-Sm_(0.15)Ce_(0.85)O_(1.925) composite cathodes in IT-SOFCs

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Rare Metals 2006年第Z1期25卷 256-260页

作者： ZHENG Minzhang XIN Hua LIU xiaomei LIU Qian xu Dan SU Wenhui Department of Physics Jilin University Changchun 130023 China College of Tele Communications Engineering Jilin University Changchun 130023 China Department of Physics Jilin University Changchun 130023 China Department of Physics Jilin University Changchun 130023 China 　 Department of Physics Jilin University Changchun 130023 China

The cathode material La1-xSrxCuO3-δ(x=0.15, 0.2, 0.3, 0.4) was synthesized by a sol-gel method. X-ray diffraction reveals that a single phase of perovskite is formed. The investigation of the electrical properties suggests that La0.7Sr0.3CuO3-δ has the highest electrical conductivity. La0.7Sr0.3CuO3-δ powder was mixed with different amount SDC (Sm0.15Ce0.85O1.925) powder (5wt.%-30wt.%) as composite cathodes. Electrochemical properties of the composite cathodes were researched further. Investigation suggests that the addition of appropriate amount SDC to La0.7Sr0.3CuO3-δ can improve the electrochemical properties and obtain better cathodic performance. Using La0.7Sr0.3CuO3-δ-SDC composite materials as a cathode based on SDC electrolyte, higher current density and power density at intermediate temperatures can be obtained.

关键词： SOFC Composite Cathode La1-xSrxCuO3-δ SDC

A Cooperative Security Monitoring Mechanism Aided by Optimal Multiple Slave Cluster Heads for UASNs

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China Communications 2023年第5期20卷 148-169页

作者： Yougan Chen Wei Wang Xiang Sun Yi Tao Zhenwen Liu xiaomei xu Key Laboratory of Underwater Acoustic Communication and Marine Information Technology Xiamen UniversityXiamen 361005China Shenzhen Research Institute of Xiamen University Shenzhen 518000China Dongshan Swire Marine Station College of Ocean and Earth SciencesXiamen UniversityXiamen 361102China State Key Laboratory of Robotics Shenyang Institute of AutomationChinese Academy of SciencesShenyang 110016China Department of Electrical and Computer Engineering University of New MexicoAlbuquerqueNM 87131USA College of Harbour and Coastal Engineering Jimei UniversityXiamen 361021China

As each cluster head(CH)sensor node is used to aggregate,fuse,and forward data from different sensor nodes in an underwater acoustic sensor network(UASN),guaranteeing the data security in a CH is very *** this paper,a cooperative security monitoring mechanism aided by multiple slave cluster heads(SCHs)is proposed to keep track of the data security of a *** designing a low complexity“equilateral triangle algorithm(ETA)”,the optimal SCHs(named as ETA-based multiple SCHs)are selected from the candidate SCHs so as to improve the dispersion and coverage of SCHs and achieve largescale data security *** addition,by analyzing the entire monitoring process,the close form expression of the probability of the failure attack identification for the SCHs with respect to the probability of attack launched by ordinary nodes is *** simulation results show that the proposed optimal ETA-based multiple SCH cooperation scheme has lower probability of the failure attack identification than that of the existing *** addition,the numerical simulation results are consistent with the theoretical analysis results,thus verifying the effectiveness of the proposed scheme.

关键词： underwater acoustic sensor networks data security cluster head nodes optimal location distribution of multiple slave cluster head nodes

Automatic target recognition method for inverse synthetic aperture sonar imaging

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Chinese Journal of Acoustics 2018年第4期37卷 463-476页

作者： ZHU Zhaotong PENG Shibao xu Jia xu xiaomei The 705th Research Institute CSIC Xi'an 650011 Department of Electronic Engineering Tsinghua University Beijing 100084 School of Information and Electronic Beijing Institute of Technology Beijing 100081 Key Laboratory of Underzvater Acoustic Communication and Marine Information Technology (Xiamen University) Xiamen 361101 School of Ocean and Earth Sciences Xiamen University Xiamen 361101

To address the randomness of target aspect angle and the incompleteness of observed target in inverse synthetic aperture sonar（ISAS） imaging,a method for target recognition is proposed based on topology vector feature（TVF） of multiple highlights. Analysis of the projection relationship from 3 D space to 2 D imaging plane in ISAS indicates that the distance between two highlights in the cross-range scale calibrated image is determined by the distance between the corresponding physical scattering centers. Then, TVFs of different targets, which remain stable in various possibilities of target aspect angle, can be built. K-means clustering technique is used to effectively alleviate effect of the point missing due to incompleteness of the observed target. A nearest neighbor classifier is used to realize the target recognition. The ISAS experimental results using underwater scaled models are provided to demonstrate the effectiveness of the proposed method. A classification rate of 84.0% is reached.

关键词： Automatic target recognition method for inverse synthetic aperture sonar imaging

Dust storms in northern China during the last 500 years

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Science China Earth Sciences 2021年第5期64卷 813-824页

作者： Shuang ZHANG Hai xu Jianghu LAN Yonaton GOLDSMITH Adi TORFSTEIN Guilin ZHANG Jin ZHANG Yunping SONG Kang’en ZHOU Liangcheng TAN Sheng xu xiaomei xu Yehouda ENZEL Institute of Surface-Earth System Science School of Earth System ScienceTianjin UniversityTianjin 300072China State Key Laboratory of Loess and Quaternary Geology Institute of Earth EnvironmentChinese Academy of SciencesXi'an 710061China Institute of Earth Sciences the Hebrew University of JerusalemJerusalem 91904Israel Department of Earth System Science University of CaliforniaIrvineCA 92697USA

The history and mechanisms of dust storms in northern China remain unclear owing to the paucity of reliable longterm,high-resolution geological *** this study,we reconstructed the dust storm history of the last~500 years in northern China,based on sedimentary coarse fraction(>63μm)of a well-dated core from Lake Daihai,Inner *** highresolution data reveal three intervals of frequent dust storms:AD 1520–1580,AD 1610–1720,and AD 1870–*** dust storm events in the Lake Daihai area were broadly synchronous with those inferred from other historical or geological records and generally occurred during cold *** in the intensity of Siberian High and the westerlies modulated by temperature variations are the likely major factors controlling dust storm *** interesting feature is that although the intensities of dust storms have been systematically increased during the recent warming period,a clear decreasing trend within this period is *** recent increase in average dust storm intensity may be ascribed to an increase in particle supply resulting from a rapid increase in human activity,whereas the weakening trend was likely caused by decreases in average wind speed resulting from the recent global warming.

关键词： Dust storm Lake Daihai Temperature Wind speed Human activity