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          • KCI등재SCOPUS

            Pilot Sequence Assignment for Spatially Correlated Massive MIMO Circumstances

            Pengxiang,Li,Yuehong,Gao,Zhidu,Li,Dacheng,Yang 한국인터넷정보학회 2019 KSII Transactions on Internet and Information Syst Vol.13 No.1

            For massive multiple-input multiple-output (MIMO) circumstances with time division duplex (TDD) protocol, pilot contamination becomes one of main system performance bottlenecks. This paper proposes an uplink pilot sequence assignment to alleviate this problem for spatially correlated massive MIMO circumstances. Firstly, a single-cell TDD massive MIMO model with multiple terminals in the cell is established. Then a spatial correlation between two channel response vectors is established by the large-scale fading variables and the angle of arrival (AOA) span with an infinite number of base station (BS) antennas. With this spatially correlated channel model, the expression for the achievable system capacity is derived. To optimize the achievable system capacity, a problem regarding uplink pilot assignment is proposed. In view of the exponential complexity of the exhaustive search approach, a pilot assignment algorithm corresponding to the distinct channel AOA intervals is proposed to approach the optimization solution. In addition, simulation results prove that the main pilot assignment algorithm in this paper can obtain a noticeable performance gain with limited BS antennas.

          • KCI등재SCOPUS

            Possible coexistence of Harmonia axyridis Pallas (Coleoptera: Coccinellidae) and Diaeretiella rapae M'Intosh (Hymenoptera: Braconidae) in the biological control of Lipaphis erysimi (Homoptera: Aphididae)

            Pengxiang,Wu,Muhammad,Haseeb,Chang,Liu,Shuo,Yan,Jing,Xu,Runzhi,Zhang 한국응용곤충학회 2019 Journal of Asia-Pacific Entomology Vol.22 No.1

            To study the interactions between the aphidophagous predator Harmonia axyridis Pallas (Coleoptera: Coccinellidae) and the specialist aphid parasitoid Diaeretiella rapae M'Intosh (Hymenoptera: Braconidae) in the biological control of mustard aphid, Lipaphis erysimi (Homoptera: Aphididae), the prey discrimination by H. axyridis among unparasitized, non-mummified parasitized and mummified aphids was examined under laboratory conditions. Prey/host selections were also tested by offering L. erysimi at various developmental stages to assess the possibility of coexistence between the two species, so the prey preference of H. axyridis when D. rapae parasitize aphids, and the host preference of D. rapae when H. axyridis interfered with the parasitization were detected. We found that H. axyridis could discriminate against mummies rather than non-mummified parasitized aphids. The ladybug showed a significantly positive preference for adult prey when D. rapae turned aphids into mummies, while D. rapae tended to parasitize younger nymphal aphids when H. axyridis was introduced. The present study suggests the prey discrimination against mummies by H. axyridis, and indicates that H. axyridis and D. rapae can avoid resource competition by attacking different and non-overlapping developmental stages of aphid. Thus, H. axyridis and D. rapae can potentially coexist and establish a stable ecosystem in the biological control of L. erysimi.

          • KCI등재SCOPUS

            Control Method of Self-Frequency Recovery and Active Power Sharing for an Isolated Microgrid Based on VSGs

            Pengxiang,Xing,Fan,Ma,Chunzheng,Tian,Changqing,Xu,Lili,Wang 대한전기학회 2019 Journal of Electrical Engineering & Technology Vol.14 No.1

            The concept of virtual synchronous generator (VSG) is emerging as an attractive solution for renewable energies to enhance the microgrid inertia and damping property by emulating the essential behaviors of conventional synchronous generators. However, in the isolated microgrid based on VSGs, there will be a frequency deviation when the power demand varies because of the droop characteristic of the VSG in active power–frequency regulation. In this paper, a control method for VSGs to implement self-frequency recovery and active power sharing in isolated microgrid is proposed. With this method, the VSGs regulate their power baseline values over multiple iterations through local-feedback of the frequency deviation until the microgrid frequency restores to normal value, and simultaneously share the power demand variation according to the ratio of their power baseline values. Compared to the previous studies, the proposed method can eliminate the output power and frequency oscillations in secondary control, and additionally, reduce the dependence of the microgrid on communication system, which is beneficial to enhance the robustness of the microgrid operation. Simulation results proved the proposed method to be effective.

          • SCIESCOPUSKCI등재

            Pilot Sequence Assignment for Spatially Correlated Massive MIMO Circumstances

            Li,,Pengxiang,Gao,,Yuehong,Li,,Zhidu,Yang,,Dacheng Korean Society for Internet Information 2019 KSII Transactions on Internet and Information Syst Vol.13 No.1

            For massive multiple-input multiple-output (MIMO) circumstances with time division duplex (TDD) protocol, pilot contamination becomes one of main system performance bottlenecks. This paper proposes an uplink pilot sequence assignment to alleviate this problem for spatially correlated massive MIMO circumstances. Firstly, a single-cell TDD massive MIMO model with multiple terminals in the cell is established. Then a spatial correlation between two channel response vectors is established by the large-scale fading variables and the angle of arrival (AOA) span with an infinite number of base station (BS) antennas. With this spatially correlated channel model, the expression for the achievable system capacity is derived. To optimize the achievable system capacity, a problem regarding uplink pilot assignment is proposed. In view of the exponential complexity of the exhaustive search approach, a pilot assignment algorithm corresponding to the distinct channel AOA intervals is proposed to approach the optimization solution. In addition, simulation results prove that the main pilot assignment algorithm in this paper can obtain a noticeable performance gain with limited BS antennas.

          • KCI등재

            Influence mechanism of the compositions in coal-fired flue gas on Hg0 oxidation over commercial SCR catalyst

            Jian,Mei,Pengxiang,Sun,Xin,Xiao,Qi,Zhang,Hui,Zhao,Yongfu,Guo,Shijian,Yang 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.75 No.-

            Optimizing the performance of commercial SCR catalyst (i.e., V2O5–WO3/TiO2) for Hg0 oxidationremained stagnant as the influence mechanism of the compositions offlue gas on Hg0 oxidation wasunclear. In this work, the mechanism of Hg0 oxidation and the influence mechanism of the compositionsofflue gas on Hg0 oxidation over V2O5–WO3/TiO2 were investigated. The reaction orders of Hg0 oxidationover V2O5–WO3/TiO2 in regard to both the concentrations of Hg0 and HCl in gas phase wereapproximately 0. Hence, Hg0 oxidation over V2O5–WO3/TiO2 primarily followed the Langmuir–Hinshelwood mechanism, and the elementary reactions of Hg0 oxidation primarily involved the physicaladsorption of Hg0, the formation of Cl* radial, and the reaction of physically adsorbed Hg0 and Cl* radial. SO2, NO, H2O, and NH3 not only restrained the Cl* radial formation but also disturbed the reaction ofphysically adsorbed Hg0 and Cl* radial. Meanwhile, the physical adsorption of Hg0 was restrained by bothH2O and NH3. Hence, Hg0 oxidation over V2O5–WO3/TiO2 was obviously restrained when SO2, NO, H2O,and NH3 were present influe gas.

          • The Design and Realization of a Popular Science Long Corridor Based on 3D Stereo Technology

            Aiying,Mao,Pengxiang,Gao,Airu,Mao,Yuanyuan,Song,Jinxia,Yu 보안공학연구지원센터 2016 International Journal of Multimedia and Ubiquitous Vol.11 No.6

            Through the design and technical realization of a popular science long corridor based on 3D stereo technology, three hot applications of 3D technology including 3D folding technology, 3D holographic imaging technology and 3D printing technology were introduced in the paper. The three techniques as a whole in the popular science long corridor display the method to decrease the realization cost of the popular science long corridor. The interactive part of the two-dimensional animation was added into the popular science long corridor to reflect truly the effect of the computer technology integrating application.

          • KCI등재SCOPUS

            HYDRAULIC RETARDERS FOR HEAVY VEHICLES: ANALYSIS OF FLUID MECHANICS AND COMPUTATIONAL FLUID DYNAMICS ON BRAKING TORQUE AND TEMPERATURE RISE

            Hongpeng,Zheng,Yulong,Lei,Pengxiang,Song 한국자동차공학회 2017 International journal of automotive technology Vol.18 No.3

            Hydraulic retarders are auxiliary braking devices that reduce the velocity of a vehicle, particularly when a vehicle is driven downhill. Such velocity reduction could reduce the potential risk caused by brake failure caused by the service brake working for a long time and the temperature of the brake shoe becomes extremely high. This paper introduces the construction of the hydraulic retarder and proposes two mathematical models for the hydraulic retarder. The first mathematical model is deduced by using fluid mechanics, which is used to analyze the mechanism of how braking torque is produced and the key factors that can influence the value of the braking torque. The second mathematical model is deduced by using thermodynamics, which is used to quantify the heat produced by the hydraulic retarder. This research emphasizes that the flow rate and the average velocity of the working fluid in the working chamber mainly determine the braking torque of the hydraulic retarder. The flow rate into and out of the working chamber determines the temperature rise of the working fluid. Computational fluid dynamics (CFD) simulations are conducted with the Reynolds-averaged Navier-Stokes (RANS) and Shear Stress Transport (SST) turbulent models. Experiments are carried out to justify the two mathematical models and the CFD simulations. The results show that the mathematical models are capable of describing the force analysis and energy conversion of the hydraulic retarder and SST is more accurate for CFD simulation and the error is within 6 %.

          • KCI등재SCOPUS

            Strategy for the Seamless Mode Transfer of an Inverter in a Master–Slave Control Independent Microgrid

            Yi,Wang,Hanhong,Jiang,Pengxiang,Xing 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.1

            To enable a master–slave control independent microgrid system (MSCIMGS) to supply electricity continuously, the microgrid inverter should perform mode transfer between grid-connected and islanding operations. Transient oscillations should be reduced during transfer to effectively conduct a seamless mode transfer. This study uses a typical MSCIMGS as an example and improves the mode transfer strategy in three aspects: (1) adopts a status-tracking algorithm to improve the switching strategy of the outer loop, (2) uses the voltage magnitude and phase pre-synchronization algorithm to reduce transient shock at the time of grid connection, and (3) applies the hybrid-sensitivity H∞ robust controller instead of the current inner loop to improve the robustness of the controller. Simulations and experiments show that the proposed strategy is more practical than the traditional proportional–derivative control mode transfer and effective in reducing voltage and current oscillations during the transfer period.

          • A Novel Interleaved Non-Isolated Switched-Capacitor Network High Step-Up DC/DC Converter

            Xinying,Li,Yan,Zhang,Pengxiang,Zeng,Jinshui,Zhang,Jinjun,Liu 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

            This paper introduces a novel interleaved non-isolated high step-up DC/DC converter with switchedcapacitor network. Due to interleaved structure and switched-capacitor network, the proposed converter has the advantage of low input current ripple, high step-up voltage conversion ratio and low voltage stress for all the switches and diodes which means lower voltage level semiconductors and high efficiency. After a detailed comparison with other recent existing topologies, it is clear that the proposed converter has a lower comprehensive cost, higher voltage conversion ratio, and lower output voltage ripple than other converters. The operation principle, steady-state analysis, parameter design for this converter are presented. Finally, experiment results are also presented to demonstrate the effectiveness of the proposed converter.

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