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Zhao, Pengcheng,Liu, Zijing,Yu, Tao,Xie, Jinsen,Chen, Zhenping,Shen, Chong Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.12
Small Modular Reactors (SMRs) are attracting wide attention due to their outstanding performance, extensive studies have been carried out for lead-based fast reactors (LFRs) that cooled with Lead or Lead-bismuth (LBE), and small modular natural circulation LFR is one of the promising candidates for SMRs and LFRs development. One of the challenges for the design small modular natural circulation LFR is to master the natural circulation thermal-hydraulic performance in the reactor primary circuit, while the natural circulation characteristics is a coupled thermal-hydraulic problem of the core thermal power, the primary loop layout and the operating state of secondary cooling system etc. Thus, accurate predicting the natural circulation LFRs thermal-hydraulic features are highly required for conducting reactor operating condition evaluate and Thermal hydraulic design optimization. In this study, a thermal-hydraulic analysis code is developed for small modular natural circulation LFRs, which is based on several mathematical models for natural circulation originally. A small modular natural circulation LBE cooled fast reactor named URANUS developed by Korea is chosen to assess the code's capability. Comparisons are performed to demonstrate the accuracy of the code by the calculation results of MARS, and the key thermal-hydraulic parameters agree fairly well with the MARS ones. As a typical application case, steady-state analyses were conducted to have an assessment of thermal-hydraulic behavior under nominal condition, and several parameters affecting natural circulation were evaluated. What's more, two characteristics parameters that used to analyze natural circulation LFRs natural circulation capacity were established. The analyses show that the core thermal power, thermal center difference and flow resistance is the main factors affecting the reactor natural circulation. Improving the core thermal power, increasing the thermal center difference and decreasing the flow resistance can significantly increase the reactor mass flow rate. Characteristics parameters can be used to quickly evaluate the natural circulation capacity of natural circulation LFR under normal operating conditions.
A New Ambiguity Elimination Method for BSS Block Signals in Time Domain
Wei Zhao,Fengshan Wang,Yuehong Shen,Yuanyuan Wu,Zhigang Yuan,Pengcheng Xu,Pengcheng Xu,Yimin Wei,Wei Jian 보안공학연구지원센터 2015 International Journal of Signal Processing, Image Vol.8 No.11
This paper deals with the ambiguity problem of blind source separation (BSS) in the case where continuously received mixture signals are split in time and processed block by block. Due to the inherent permutation and scaling ambiguities of BSS, tying the separated components at each adjacent time blocks doesn’t recover the original source signals correctly in general. Inspired by the Permutation Method of reconstructing source signal blocks in time domain, a new ambiguity elimination approach is proposed in this paper. This method aims to concatenate the separated components in adjacent blocks by artificially setting contrast blocks for each adjacent time blocks. The core idea of this method is to utilize the associativity between components recovered from contrast blocks and corresponding adjacent blocks. Compared with Permutation Method, the main advantage of this new method consists in the fact that it is much more efficient in terms of separation quality and computational speed. Besides, a tradeoff can be adjusted between separation quality and computational speed by choosing different length of contrast blocks. Real-life experiments are performed to validate the performance of this method on the wireless communication system with two transmitting and receiving antennas.
Effect of welding residual stress on operating stress of nuclear turbine low pressure rotor
Tan Long,Zhao Liangyin,Zhao Pengcheng,Wang Lulu,Pan Jiajing,Zhao Xiuxiu 한국원자력학회 2020 Nuclear Engineering and Technology Vol.52 No.8
The purpose of this study is to investigate the effect of welding residual stress on operating stress in designing a nuclear turbine welded rotor. A two-dimensional axisymmetric finite element model is employed to calculate the residual stress before and after post weld heat treatment (PWHT), and then the superposition of residual stress after PWHT and operating stress at normal speed and overspeed were discussed. The investigated results show that operating stress can be affected significantly by welding residual stress, and the distribution trend of superposition stress at the weld area is mainly determined by welding residual stress. The superposition of residual stress and operating stress is linear superposition, and the hoop stress distribution of superposition stress is similar with the distribution of residual stress. With the increasing overspeed, the distribution pattern of the hoop superimposed stress remains almost unchanged, while the stress level increases
Pengcheng Han,Xiaoqiong He,Zhiqin Zhao,Haolun Yu,Yi Wang,Xu Peng,Zeliang Shu 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.1
This study proposes a new modulation strategy to deal with unbalanced output voltage that is based on three-levelneutral-point-clamped cascaded rectifiers. The fundament idea is to reallocate the value of the voltage levels generated by each ofthe modules on the basis of space vector pulse width modulation. This proposed modulation strategy can reduce the switchingfrequency while maintaining the mutual-module voltage balance. First, an analysis of unbalanced output voltage is reflected. Then a new modulation strategy is introduced in detail. Internal module capacitor voltages are balanced by the selection ofredundant vectors. Moreover, the voltage balance ability is calculated. Finally, the feasibility of this modulation strategy isverified through experimental results.
Zhao Jingyi,Li Bingyan,Ren Yongxia,Liang Tiansong,Wang Juan,Zhai Suna,Zhang Xiqian,Zhou Pengcheng,Zhang Xiangxian,Pan Yuanyuan,Gao Fangfang,Zhang Sulan,Li Liming,Yang Yongqiang,Deng Xiaoyu,Li Xiaole,C 생화학분자생물학회 2021 Experimental and molecular medicine Vol.53 No.-
Compelling evidence has indicated the vital role of lysine-specific demethylase 4 A (KDM4A), hypoxia-inducible factor-1α (HIF1α) and the mechanistic target of rapamycin (mTOR) signaling pathway in nasopharyngeal carcinoma (NPC). Therefore, we aimed to investigate whether KDM4A affects NPC progression by regulating the HIF1α/DDIT4/mTOR signaling pathway. First, NPC and adjacent tissue samples were collected, and KDM4A protein expression was examined by immunohistochemistry. Then, the interactions among KDM4A, HIF1α and DDIT4 were assessed. Gain- and loss-of-function approaches were used to alter KDM4A, HIF1α and DDIT4 expression in NPC cells. The mechanism of KDM4A in NPC was evaluated both in vivo and in vitro via RT-qPCR, Western blot analysis, MTT assay, Transwell assay, flow cytometry and tumor formation experiments. KDM4A, HIF1α, and DDIT4 were highly expressed in NPC tissues and cells. Mechanistically, KDM4A inhibited the enrichment of histone H3 lysine 9 trimethylation (H3K9me3) in the HIF1α promoter region and thus inhibited the methylation of HIF1α to promote HIF1α expression, thus upregulating DDIT4 and activating the mTOR signaling pathway. Overexpression of KDM4A, HIF1α, or DDIT4 or activation of the mTOR signaling pathway promoted SUNE1 cell proliferation, migration, and invasion but inhibited apoptosis. KDM4A silencing blocked the mTOR signaling pathway by inhibiting the HIF1α/DDIT4 axis to inhibit the growth of SUNE1 cells in vivo. Collectively, KDM4A silencing could inhibit NPC progression by blocking the activation of the HIF1α/DDIT4/mTOR signaling pathway by increasing H3K9me3, highlighting a promising therapeutic target for NPC.
Han, Pengcheng,He, Xiaoqiong,Zhao, Zhiqin,Yu, Haolun,Wang, Yi,Peng, Xu,Shu, Zeliang The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.1
This study proposes a new modulation strategy to deal with unbalanced output voltage that is based on three-level neutral-point-clamped cascaded rectifiers. The fundament idea is to reallocate the value of the voltage levels generated by each of the modules on the basis of space vector pulse width modulation. This proposed modulation strategy can reduce the switching frequency while maintaining the mutual-module voltage balance. First, an analysis of unbalanced output voltage is reflected. Then a new modulation strategy is introduced in detail. Internal module capacitor voltages are balanced by the selection of redundant vectors. Moreover, the voltage balance ability is calculated. Finally, the feasibility of this modulation strategy is verified through experimental results.
Rapid Structural Improvement of CVD-Grown Multi-Walled Carbon Nanotubes by Drastic Thermite Reaction
Jiang Zhao,Jing Chen,Pengcheng Zhang,Haofeng Yu,Jie Chen 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2015 NANO Vol.10 No.8
Multi-walled carbon nanotubes (MWCNTs) produced by chemical vapor deposition (CVD) are the most common commercial products at extremely low price in the market. However, due to the inherent drawbacks of CVD surroundings at temperature below ~ 1000℃, CVD-grown nanotubes usually have very disordered structure, resulting in most of their properties being much below expectations. Herein, we present a simple and energy-efficient method for improving rapidly the structure of CVD-grown MWCNTs via a drastic thermite reaction process. Direct observations from scan electron microscope (SEM) and transmission electron microscope (TEM) images, decrease of ID/IG ratios in Raman spectra, increase of the starting oxidation temperatures observed in thermogravimetric analysis (TGA), decrease of the volumetric electrical resistivity and decrease of the turn-on electric fields from 3.64 to 2.88 V/µm in field emission measurements suggest that the graphitization of MWCNTs can be effectively enhanced and the structure of nanotubes becomes more ordered after the drastic thermite reaction process.
Wei Zhao,Zhi-Gang Yuan,Yue-hong Shen,Yufan Cao,Yimin Wei,Pengcheng Xu,Wei Jian 한국전자통신연구원 2015 ETRI Journal Vol.37 No.4
This paper deals with the problem of blind source separation (BSS), where observed signals are a mixture of delayed sources. In reference to a previous work, when the delay time is small such that the first-order Taylor approximation holds, delayed observations are transformed into an instantaneous mixture of original sources and their derivatives, for which an extended second-order blind identification (SOBI) approach is used to recover sources. Inspired by the results of this previous work, we propose to generalize its first-order Taylor approximation to suit higher-order approximations in the case of a large delay time based on a similar version of its extended SOBI. Compared to SOBI and its extended version for a first-order Taylor approximation, our method is more efficient in terms of separation quality when the delay time is large. Simulation results verify the performance of our approach under different time delays and signal-to-noise ratio conditions, respectively.