A Modified Capacitor Current Feedback Active Damping Approach for Grid Connected Converters with an LCL Filter

Zhiqiang Wan,Jian Xiong,Ji Lei,Chen Chen,Kai Zhang 전력전자학회 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.5

Capacitor current feedback active damping is extensively used in grid-connected converters with an LCL filter. However, systems tends to become unstable when the digital control delay is taken into account, especially in low switching frequencies. This paper discusses this issue by deriving a discrete model with a digital control delay and by presenting the stable region of an active damping loop from high to low switching frequencies. In order to overcome the disadvantage of capacitor current feedback active damping, this paper proposes a modified approach using grid current and converter current for feedback. This can expand the stable region and provide sufficient active damping whether in high or low switching frequencies. By applying the modified approach, the active damping loop can be simplified from fourth-order into second-order, and the design of the grid current loop can be simplified. The modified approach can work well when the grid impedance varies. Both the active damping performance and the dynamic performance of the current loop are verified by simulations and experimental results.

Fabrication and Characterization of Vertically Aligned ZnO Nanorod Arrays via Inverted Monolayer Colloidal Crystals Mask

Cheng Chen,Taotao Ding,Zhiqiang Qi,Wei Zhang,Jun Zhang,Juan Xu,Jingwen Chen,Jiangnan Dai,Changqing Chen 대한금속·재료학회 2018 ELECTRONIC MATERIALS LETTERS Vol.14 No.4

The periodically ordered ZnO nanorod (NR) arrays have been successfully synthesized via a hydrothermal approach on thesilicon substrates by templating of the TiO2ring deriving from the polystyrene (PS) nanosphere monolayer colloidal crystals(MCC). With the inverted MCC mask, sol–gel-derived ZnO seeds could serve as the periodic nucleation positions for thesite-specific growth of ZnO NRs. The large-scale patterned arrays of single ZnO NR with good side-orientation can be readilyproduced. According to the experimental results, the as-integrated ZnO NR arrays showed an excellent crystal quality andoptical property, very suitable for optoelectronic applications such as stimulated emitters and ZnO photonic crystal devices.

Occurrence, evolution, and functions of DNA phosphorothioate epigenetics in bacteria

Tong, Tong,Chen, Si,Wang, Lianrong,Tang, You,Ryu, Jae Yong,Jiang, Susu,Wu, Xiaolin,Chen, Chao,Luo, Jie,Deng, Zixin,Li, Zhiqiang,Lee, Sang Yup,Chen, Shi National Academy of Sciences 2018 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.115 No.13

<P><B>Significance</B></P><P>Phosphorothioate (PT) modification of the DNA sugar-phosphate backbone is an important microbial epigenetic modification governed by DndABCDE, which together with DndFGH, constitutes a restriction-modification system. We show that up to 45% of 1,349 identified bacterial <I>dnd</I> systems exhibit the form of solitary <I>dndABCDE</I> without the restriction counterparts of <I>dndFGH</I>. The combination of epigenomics, transcriptome analysis, and metabolomics suggests that in addition to providing a genetic barrier against invasive DNA, PT modification is a versatile player involved in the epigenetic control of gene expression and the maintenance of cellular redox homeostasis. This finding provides evolutionary and functional insights into this unusual epigenetic modification. Our results imply that PT systems might evolve similar to other epigenetic modification systems with multiple cellular functions.</P><P>The chemical diversity of physiological DNA modifications has expanded with the identification of phosphorothioate (PT) modification in which the nonbridging oxygen in the sugar-phosphate backbone of DNA is replaced by sulfur. Together with DndFGH as cognate restriction enzymes, DNA PT modification, which is catalyzed by the DndABCDE proteins, functions as a bacterial restriction-modification (R-M) system that protects cells against invading foreign DNA. However, the occurrence of <I>dnd</I> systems across a large number of bacterial genomes and their functions other than R-M are poorly understood. Here, a genomic survey revealed the prevalence of bacterial <I>dnd</I> systems: 1,349 bacterial <I>dnd</I> systems were observed to occur sporadically across diverse phylogenetic groups, and nearly half of these occur in the form of a solitary <I>dndBCDE</I> gene cluster that lacks the <I>dndFGH</I> restriction counterparts. A phylogenetic analysis of 734 complete PT R-M pairs revealed the coevolution of M and R components, despite the observation that several PT R-M pairs appeared to be assembled from M and R parts acquired from distantly related organisms. Concurrent epigenomic analysis, transcriptome analysis, and metabolome characterization showed that a solitary PT modification contributed to the overall cellular redox state, the loss of which perturbed the cellular redox balance and induced <I>Pseudomonas fluorescens</I> to reconfigure its metabolism to fend off oxidative stress. An in vitro transcriptional assay revealed altered transcriptional efficiency in the presence of PT DNA modification, implicating its function in epigenetic regulation. These data suggest the versatility of PT in addition to its involvement in R-M protection.</P>

A Secret Sharing Scheme Based on AES

Jie Cui,Lei Chen,Yiming Zhang,Zhiqiang Xie,Hong Zhong 보안공학연구지원센터 2014 International Journal of Security and Its Applicat Vol.8 No.6

In order to solve the key setting difficulty and the key security problem in the file encryption, key distributed storage technology may be a proper choice to help improve the safety of the key. In the paper, a novel secret sharing scheme is proposed by AES encryption algorithm for file confidentiality, dynamic key generation mechanism to generate keys, multi-secret-sharing ideas on key pre-treatment, using Shamir threshold scheme for secret dispersed storage. Finally, a few tests are carried out and the test results suggest that the efficiency of the whole scheme is good.

Permissions based Automatic Android Malware Repair using Long Short Term Memory

Zhiqiang Wu(오지강),Xin Chen(천신),Scott Uk-Jin Lee(이욱진) 한국컴퓨터정보학회 2019 한국컴퓨터정보학회 학술발표논문집 Vol.27 No.1

Simulation and Test of Gear Pump Flow Pulsation

Chen Zongbin,Lv Zhiqiang,Xu Rongwu,Liao Jian 한국유체기계학회 2018 International journal of fluid machinery and syste Vol.11 No.3

Flow pulsation is the inherent properties of volumetric hydraulic pump, the direct noise source of hydraulic system. Simulating the internal gear pumps’ flow pulsation based on the mathematical model is difficult, so a new simulation method was adopted in this article. The chamber of the pump is divided into four Control Volumes (CVs), whose effective volumes change along with the rotation of the gears. The CVs take in fluid from suction port and squeeze fluid out at the outlet port. According the CVs connection relationship, the pump simulation model was established in AMESim. To verify the simulation results, flow pulsation experiment was conducted and experiment data show that simulation model is correct and the accuracy is up to 95%. Results prove that the modeling method and experiment test are effective. Thus the evaluation of flow pulsation from simulation to testing was established, which shown great significance to evaluate and develop the pump’s vibration and noise.

Revitalization and Re-cultivation of Vegetation in Karst Region Through Animal

Zhiqiang Lai,Xian-feng Yi,Na Yao,Xiao-Yan Cai,Yongliang Liang,Shize Qin,Yuanrong Chen,Shangmin Qin,M. Pogaonik 한국초지조사료학회 2009 한국초지조사료학회 학술대회논문집 Vol.2009 No.08

From 2002 to 2007, two different systems (shrubs and grasses) were established to raise appropriate ruminants for the purpose of improving biological diversity and fragile ecological environment in the karst-areas through grazing. The objective was to find out a novel way to promote the application of ecological restoration and reconstruction, and the agricultural economy could develop in sustainable way in the karst areas in Guangxi and similar areas in Southwest China.

Damage and failure characterization of 7075 aluminum alloy hot stamping

Zhiqiang Zhang,Yuejie Cui,Qing-Min Chen 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.1

7000 series high strength aluminum alloys are increasingly used in manufacturing automobile body parts to meet the more stringent demands for automobile lightweight. Hot stamping of 7000 series high strength aluminum alloys is a complex thermal-mechanical coupling process and precise simulation is needed to predict material fracture. To obtain damage model of 7075 aluminum alloy in hot stamping, five different stress triaxiality specimens were designed. The fracture strain, critical strain and average stress triaxiality of different specimens were obtained by the hybrid finite element simulation and experiment (FE-EXP) method. GISSMO model of 7075 aluminum alloy at 400 °C was established. Compared with the experimental results of U-shaped part hot stamping under different lubrication conditions, the calibrated GISSMO model was demonstrated to predict the damage behavior of 7075 aluminum alloy during high temperature deformation accurately.

A Coupling Method of Response Surfaces (CRSM) for Cutting Parameters Optimization in Machining Titanium Alloy under Minimum Quantity Lubrication (MQL) Condition

Zhiqiang Liu,Ming Chen,Jinyang Xu,Shu Han 한국정밀공학회 2013 International Journal of Precision Engineering and Vol. No.

This paper presents a new flexible method referring to coupling response surface methodology (CRSM) to acquire optimum cutting parameters in machining of difficult-to-cut titanium alloy under minimum quantity lubrication (MQL) condition. Cutting speed, feed rate and depth of cut are designed as three factors by using the Taguchi method, which are also subject to several constraints including processing efficiency, cutting force and surface quality. In addition, turning experiments of titanium alloy were performed in order to set up the model based on Taguchi experimental design and multiple regression method. ANOVA was carried out to prove the adequacy of the developed mathematical model and the influences of cutting parameters on constraints were also observed. The results indicated that the feed rate was the dominant factor affecting surface roughness and cutting forces, which were minimized when the feed rate and depth of cut were set to the lowest level, while cutting speed was set to the highest level. Moreover, the predicted values obtained by CRSM were in good agreement with the experimental values, which indicated that CRSM was an effective method to determine optimum cutting conditions for machining process under MQL condition.

Small Double-Stranded RNA Mediates the Anti-Cancer Effects of p21WAF1/ClP1 Transcriptional Activation in a Human Glioma Cell Line

Zhiqiang Dong,Yamei Dang,Yirong Chen 연세대학교의과대학 2014 Yonsei medical journal Vol.55 No.2

Purpose: This study was conducted to investigate the small double-stranded RNA (dsRNA) mediated anti-tumor effects of p21WAF1/ClP1 (p21) transcriptional activation in vitro in the human glioma SHG-44 cell line. Materials and Methods: Human glioma SHG-44 cells were transfected with dsRNA using LipofectAMINE 2000 transfection reagent. Real-time PCR and Western blot analysis were conducted to detect p21 and survivin mRNA and protein levels, respectively. Cell proliferation was examined by MTT assay. Cell cycle distribution and apoptosis were detected by flow-cytometric analysis. Results: We found that dsRNA targeting p21 promoter (dsP21) significantly induced the expression of p21 at transcription and protein levels,and reduced the expression of survivin. AS well, dsP21 transcription significantlyinhibited human glioma SHG-44 cell proliferation. Analysis of cell cycle distributionrevealed that dsP21 transfection increased accumulation of cells in the G0/G1 phase and reduced accumulation of cells in the S phase. Further analysis revealed that dsP21 transcription led to an increase in both early and late stages of apoptosis in human glioma SHG-44 cells. Conclusion: In the present study, P21 activation by RNA-induced gene activation (RNAa) induced anti-tumor activity in vitro in a humanglioma SHG-44 cell line. The results suggested that RNAa could be used for human glioma treatment by targeted activation of tumor suppressor genes.