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Parameters Analysis and Operational Area Calculations of VSG Applied to Distribution Networks

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CSEE Journal of Power and Energy Systems 2023年第6期9卷 2214-2223页

作者： Zhipeng Lyu Xiaotong Gong Linxu liu lan liu State Grid Shanghai Energy Interconnect Research Institute Shanghai 200120China Shanghai University of Electric Power Shanghai 200090China China Electric Power Research Institute Beijing 100192China

Virtual synchronous generator(VSG)technology is an effective way to realize coordinated energy supply of active distribution networks and comprehensive energy at *** paper starts from the two perspectives of grid-connected operational modes and island operational *** on the mathematical model of VSG,referring to existing grid standards,comprehensively considering its active and reactive-power loop stability and dynamic performance,the influencing factors of the related control parameters K,Dq,J,Dp are *** selection range for K,Dq,J,Dp is proposed,which ensures stability and robustness in grid-connected and island operational *** this paper,this method can be used as a reference for control strategy research and practical engineering applications of ***,effects of parameter selection on stability and dynamic performance of active and reactive-power loops are analyzed by using the zero-pole map and Bode diagram,and feasibility of the scheme is verified by PSCAD/EMTDC.

关键词： Active-power loop grid-connected island operation modes parameters design reactive-power loop stability analyzes virtual synchronous generator

Decoding the secret of species coexistence: a perspective from soil fungi

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Science China(Life Sciences) 2020年第1期63卷 169-170页

作者： lan liu Jian Zhang Zhejiang Tiantong Forest Ecosystem National Observation and Research Station School of Ecological and Environmental SciencesEast China Normal UniversityShanghai 200241China Shanghai Institute of Pollution Control and Ecological Security Shanghai 200092China

"What determines species diversity"was listed as one of the25 highlighted and extremely challenging questions in the journal Science on its 125^(th)anniversary(Pennisi,2005).Why are there so many species in the world?How do these species coexist in one community?Ecologists and evolutionary biologists have struggled with these questions for centuries.A leading explanation,particularly in tropical forests,is Janzen-Connell hypothesis(Janzen,1970;Connell,1971),which suggests that local abundance of seeds and seedlings is negatively affected by conspecific neighbors through accu・mulation of host-specific natural enemies(conspecific negative density dependence,CNDD).

关键词： soil listed journal

Adaptive Multiscale Method for Two-dimensional Nanoscale Adhesive Contacts

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Chinese Journal of Mechanical Engineering 2013年第3期26卷 606-612页

作者： TONG Ruiting liu Geng liu lan WU Liyan School of Mechanical Engineering Northwestern Polytechnical University

There are two separate traditional approaches to model contact problems: continuum and atomistic theory. Continuum theory is successfully used in many domains, but when the scale of the model comes to nanometer, continuum approximation meets challenges. Atomistic theory can catch the detailed behaviors of an individual atom by using molecular dynamics (MD) or quantum mechanics, although accurately, it is usually time-consuming. A multiscale method coupled MD and finite element (FE) is presented. To mesh the FE region automatically, an adaptive method based on the strain energy gradient is introduced to the multiscale method to constitute an adaptive multiscale method. Utilizing the proposed method, adhesive contacts between a rigid cylinder and an elastic substrate are studied, and the results are compared with full MD simulations. The process of FE meshes refinement shows that adaptive multiscale method can make FE mesh generation more flexible. Comparison of the displacements of boundary atoms in the overlap region with the results from full MD simulations indicates that adaptive multiscale method can transfer displacements effectively. Displacements of atoms and FE nodes on the center line of the multiscale model agree well with that of atoms in full MD simulations, which shows the continuity in the overlap region. Furthermore, the Von Mises stress contours and contact force distributions in the contact region are almost same as full MD simulations. The method presented combines multiscale method and adaptive technique, and can provide a more effective way to multiscale method and to the investigation on nanoscale contact problems.

关键词： adaptive multiscale method adhesive contact

Analysis of the 3' ends of tRNA as the cause of insertion sites of foreign DNA in Prochlorococcus

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Journal of Zhejiang University-Science B(Biomedicine & Biotechnology) 2010年第9期11卷 708-718页

作者： Hai-lan liu Jun ZHU Institute of Bioinformaties College of Agriculture and Biotechnology Zhejiang University Hangzhou 310029 China Institute of Maize Research College of Agriculture Sichuan Agricultural University Ya'an 625014 China

The purpose of this study was to investigate the characteristics of transfer RNA(tRNA) responsible for the association between tRNA genes and genes of apparently foreign origin(genomic islands) in five high-light adapted Prochlorococcus *** bidirectional best BLASTP(basic local alignment search tool for proteins) search and the conservation of gene order against each other were utilized to identify genomic islands,and 7 genomic islands were found to be immediately adjacent to tRNAs in Prochlorococcus marinus AS9601,11 in *** MIT9515,8 in *** MED4,6 in *** MIT9301,and 6 in *** *** Carlo simulation showed that tRNA genes are hotspots for the integration of genomic islands in Prochlorococcus *** tRNA genes associated with genomic islands showed the following characteristics:(1) the association was biased towards a specific subset of all iso-accepting tRNA genes;(2) the codon usages of genes within genomic islands appear to be unrelated to the codons recognized by associated tRNAs;and,(3) the majority of the 3' ends of associated tRNAs lack CCA *** findings contradict previous hypotheses concerning the molecular basis for the frequent use of tRNA as the insertion site for foreign genetic *** analysis of a genomic island associated with a tRNA-Asn gene in *** MIT9301 suggests that foreign genetic material is inserted into the host genomes by means of site-specific recombination,with the 3' end of the tRNA as the target,and during the process,a direct repeat of the 3' end sequence of a boundary tRNA(namely,a scar from the process of insertion) is formed elsewhere in the genomic *** the analysis of the sequences of these targets,it can be concluded that a region characterized by both high GC content and a palindromic structure is the preferred insertion site.

关键词： Genomic islands Prochlorococcus Transfer RNA(tRNA) Palindromic structure Codon usage

Evaluation of Slow Light Periodic Signals Considering the Distortion in EDF

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Chinese Physics Letters 2014年第3期31卷 82-85页

作者： WANG WU Chong-Qing WANG Zhi liu Guo-Dong liu lan-lan SUN Zhen-Chao Institute of Optical Information and Key Lab of Luminescence and Optical Information Technology Beijing Jiaotong University Beijing 100044

Based on the fundamental harmonic phase delay, a new definition of fundamental harmonic fractional delay （FHFD） is proposed to evaluate slow light with the consideration of signal distortion, to eliminate the dependence on the choice of the reference point. By solving the rate equation of erbium-doped fiber （EDF）, it is shown that the slow light always accompanies the signal distortion when the periodic signal propagates in EDF, and FHFD depends on the signal distortion, as well as the average input power, the modulation depth and the length of EDF. The results of simulations and experiments indicate that the definition of FHFD is reasonable and effective to evaluate the slow light of periodic signals.

关键词： FIBERS RESEARCH SEMICONDUCTOR doping ERBIUM SLOW light PHYSICS research

LF-CNN:Deep Learning-Guided Small Sample Target Detection for Remote Sensing Classification

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Computer Modeling in Engineering & Sciences 2022年第4期131卷 429-444页

作者： Chengfan Li lan liu Junjuan Zhao Xuefeng liu School of Computer Engineering and Science Shanghai UniversityShanghai200444China Key Laboratory for Digital land and Resources of Jiangxi Province East China University of TechnologyNanchang330013China School of Electronic and Electrical Engineering Shanghai University of Engineering ScienceShanghai201620China School of Communication&Information Engineering Shanghai UniversityShanghai200444China

Target detection of small samples with a complex background is always difficult in the classification of remote sensing *** propose a new small sample target detection method combining local features and a convolutional neural network(LF-CNN)with the aim of detecting small numbers of unevenly distributed ground object targets in remote sensing *** k-nearest neighbor method is used to construct the local neighborhood of each point and the local neighborhoods of the features are extracted one by one from the convolution *** the local features are aggregated by maximum pooling to obtain global feature *** classification probability of each category is then calculated and classified using the scaled expected linear units function and the full connection *** experimental results show that the proposed LF-CNN method has a high accuracy of target detection and classification for hyperspectral imager remote sensing data under the condition of small *** drawbacks in both time and complexity,the proposed LF-CNN method can more effectively integrate the local features of ground object samples and improve the accuracy of target identification and detection in small samples of remote sensing images than traditional target detection methods.

关键词： Small samples local features convolutional neural network(CNN) k-nearest neighbor(KNN) target detection

Properties of the high-mass star forming region IRAS 22475+5939

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Research in Astronomy and Astrophysics 2012年第7期12卷 845-856页

作者： Xiao-lan liu Jun-Jie Wang National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China Graduate University of Chinese Academy of Sciences Beijing 100049 China

IRAS 22475＋5939 has been we can still discover new characteristics well studied by previous astronomers, but about it, using the first observations of the lines from CO J=2-1, 13C0 J=2-1 and 13CO J=3-2 by the KOSMA 3m telescope. The mapping of the intensity ratio of 13CO J=3-2 and 13CO J=2-1 shows that the distribution of the temperature has two peaks, neither of which coincide with the IRAS 22475＋5939 source or the center of the HII region, but rather are located at the edge of the HII region. Overlays of the Spitzer IRAC 8 p.m with CO contours indicate that they are associated with each other and that the strongest polycyclic aro- matic hydrocarbon （PAH） emission is at the IRAS 22475＋5939 source position. The IRAS LRS spectrum at 7μm-23 μm and the PHT-s spectrum at 2μm-12μm of the IRAS 22475＋5939 source also exhibit strong PAH emission characteristics in the main PAH bands： The diversity of the PAH family should be responsible for the plateaus in the PAH emission in the PHT-s and IRAS-LRS spectra. Analysis and mod- eling in the infrared bands suggest that IRAS 22475＋5939 is more likely to be a class I young stellar object. Where this is the case, the star is likely to have a tempera- ture of Tefr-9995.8K, mass-15.34Mo, luminosity -1.54×104 L- and age 1.54-104 yr. The model shows that circumstellar disc emission is important for wavelengths between 1 and 10μm, otherwise, the envelope fluctuates for A 〉 10μm. Bipolar outflow is confirmed in the molecular cloud, and the excited star of the HII region could be the driving source of the outflow. High resolution is required fm better results.

关键词： ISM: jets and outflow -- ISM: molecular -- ISM: kinematical and dy-namics -- star formation

On the Period Variation of the W UMa-type Contact Binary V502 Ophiuchi

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Chinese Journal of Astronomy and Astrophysics 2006年第3期6卷 331-337页

作者： Qing-Yao liu Yu-lan Yang National Astronomical Observatories/Yunnan Observatory Chinese Academy of Sciences Kunming 650011

The variation in the orbital period of the W UMa type contact binary V502 Oph is analyzed. The orbital period exhibits a wavelike variation with a periodicity of 23.0 years and an amplitude of AP = 1.24 ×10^-5 days superimposed on secular decrease of dP/dt = 1.68× 10^-7 day per year. The long-term decrease may be accompanied by the contraction of the secondary at a rate of 83 m per year and a mass transfer rate from the primary to the secondary of 4.28×10^-8M· per year. The short-term oscillation may be explained by the presence of a third component. Orbital elements of the third body and its possible mass are presented.

关键词： stars: contact binary - period change - star: individual: V502 Oph

Direct Numerical Simulation of Particle Dispersion in the Flow Around a Circular Cylinder

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Journal of Thermal Science 2004年第4期13卷 344-349页

作者： lan liu Feng Ji Jianren Fan Kefa Cen Inst. of Thermal Power Eng. Zhejiang Univ. Hangzhou 310027 China

The major objective of the paper is to use direct numerical simulation method to get the dispersion patterns of different Stokes number particles in cylinder wake at low Reynolds numbers. The gas fluid structure is simulated by a spectral-element method with third-order accuracy. Non-reflecting boundary condition is specified for the outlet downstream boundary. Lagrangian approach is used to trace particle trajectory. The simulation results show factors to be considered to characterize the particle dispersion and find different particle dispersion pattern in a circular cylinder wake and in a plane wake.

关键词： direct numerical simulation wake particle dispersion gas-solid fluid.