Secondary Voltage Control for Reactive Power Sharing in an Islanded Microgrid

Qian Guo,Hongyan Wu,Liaoyuan Lin,Zhihong Bai,Hao Ma 전력전자학회 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.1

Owing to mismatched feeder impedances in an islanded microgrid, the conventional droop control method typically results in errors in reactive power sharing among distributed generation (DG) units. In this study, an improved droop control strategy based on secondary voltage control is proposed to enhance the reactive power sharing accuracy in an islanded microgrid. In a DG local controller, an integral term is introduced into the voltage droop function, in which the voltage compensation signal from the secondary voltage control is utilized as the common reactive power reference for each DG unit. Therefore, accurate reactive power sharing can be realized without any power information exchange among DG units or between DG units and the central controller. Meanwhile, the voltage deviation in the microgrid common bus is removed. Communication in the proposed strategy is simple to implement because the information of the voltage compensation signal is broadcasted from the central controller to each DG unit. The reactive power sharing accuracy is also not sensitive to time-delay mismatch in the communication channels. Simulation and experimental results are provided to validate the effectiveness of the proposed method.

Distributed Secondary Voltage Control of Islanded Microgrids with Event-Triggered Scheme

Guo, Qian,Cai, Hui,Wang, Ying,Chen, Weimin The Korean Institute of Power Electronics 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.6

In this study, the distributed secondary voltage control of islanded microgrids with multi-agent consensus algorithm is investigated. As an alternative to a time-triggered approach, an event-triggered scheme is proposed to reduce the communication load among inverter-based distributed generators (DGs). The proposed aperiodic control scheme reduced unnecessary utilization of limited network bandwidth without degrading control performance. By properly establishing a distributed triggering condition in DG local controller, each inverter is only required to send voltage information when its own event occurs. The compensation of voltage amplitude deviation can be realized, and redundant data exchange related to fixed high sampling rate can be avoided. Therefore, an efficient use of communication infrastructure can be realized, particularly when the system is operating in steady state. The effectiveness of the proposed scheme is verified by simulations on a microgrid test system.

Experimental Study of Large-amplitude Wavefront Correction in Free-space Coherent Optical Communication

Qian Guo,Shuang Cheng,Xizheng Ke 한국광학회 2021 Current Optics and Photonics Vol.5 No.6

In a free-space coherent optical communication system, wavefront distortion is frequently beyond the correction range of the adaptive-optics system after the laser has propagated through the atmospheric turbulence. A method of residual wavefront correction is proposed, to improve the quality of coherent optical communication in free space. The relationship between the wavefront phase expanded by Zernike polynomials and the mixing efficiency is derived analytically. The influence of Zernike-polynomial distortion on the bit-error rate (BER) of a phase-modulation system is analyzed. From the theoretical analysis, the BER of the system changes periodically, due to the periodic extension of wavefront distortion. Experimental results show that the BER after correction is reduced from 10 −1 to 10 −4 ; however, when the closed-loop control algorithm with residual correction is used, the experimental results show that the BER is reduced from 10 −1 to 10 −7 .

Predictors and Dynamic Nomogram to Determine the Individual Risk of Malignant Brain Edema After Endovascular Thrombectomy in Acute Ischemic Stroke

Qian-mei Jiang,Shuai Yu,Xiaofeng Dong,Huai-shun Wang,Jie Hou,Zhi-chao Huang,Zhi-liang Guo,Shou-jiang You,Guo-dong Xiao 대한신경과학회 2022 Journal of Clinical Neurology Vol.18 No.3

Background and Purpose This study aimed to construct an optimal dynamic nomogram for predicting malignant brain edema (MBE) in acute ischemic stroke (AIS) patients after endovascular thrombectomy (ET). Methods We enrolled AIS patients after ET from May 2017 to April 2021. MBE was defined as a midline shift of >5 mm at the septum pellucidum or pineal gland based on follow-up computed tomography within 5 days after ET. Multivariate logistic regression and LASSO (least absolute shrinkage and selection operator) regression were used to construct the nomogram. The area under the receiver operating characteristic curve (AUC) and decisioncurve analysis were used to compare our nomogram with two previous risk models for predicting brain edema after ET. Results MBE developed in 72 (21.9%) of the 329 eligible patients. Our dynamic web-based nomogram (https://successful.shinyapps.io/DynNomapp/) consisted of five parameters: basal cistern effacement, postoperative National Institutes of Health Stroke Scale (NIHSS) score, brain atrophy, hypoattenuation area, and stroke etiology. The nomogram showed good discrimination ability, with a C-index (Harrell’s concordance index) of 0.925 (95% confidence interval=0.890–0.961), and good calibration (Hosmer-Lemeshow test, p=0.386). All variables had variance inflation factors of <1.5 and tolerances of >0.7, suggesting no significant collinearity among them. The AUC of our nomogram (0.925) was superior to those of Xiang-liang Chen and colleagues (0.843) and Ming-yang Du and colleagues (0.728). Conclusions Our web-based dynamic nomogram reliably predicted the risk of MBE in AIS patients after ET, and hence is worthy of further evaluation.

Protective effects of blueberry drink on cognitive impairment induced by chronic mild stress in adult rats

Qian Guo,Young-Nam Kim,Bog-Hieu Lee 대한지역사회영양학회 2017 Nutrition Research and Practice Vol.11 No.1

BACKGROUND/OBJECTIVES: Stress-induced cognitive impairment is related to the suppression of hippocampal neurogenesis that results from an increase of oxidative stress. Therefore, the aim of this study was to investigate the effects of administration of a blueberry drink, having a high antioxidant power, on the cognitive performance of adult rats exposed to chronic mild stress. MATERIALS/METHODS: Twelve-week-old male Sprague-Dawley rats (n = 48) were randomly divided into four groups: control (CO), stress (ST), control + 5% blueberry drink (CO + B), and stress + 5% blueberry drink (ST + B). After eight weeks, the cognitive performance was assessed using a multiple T-maze water test. Levels of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and ascorbic acid were measured in the brain, and catecholamine concentrations were measured in plasma. RESULTS: The brain weights of the rats from the ST and ST + B groups were significantly lower than those of the rats from the CO and CO + B groups. The cognitive performance of the ST group was impaired when compared to that of the CO group. This impairment was significantly improved by the blueberry drink supplementation (P < 0.05). The brain SOD and CAT concentrations were not influenced by the stress or by the blueberry drink. However, the brain levels of GPx and ascorbic acid were significantly lower in the ST group than those in the CO group and were increased by the blueberry drink supplementation. The plasma catecholamine concentrations were affected by chronic mild stress and by the blueberry drink. The plasma norepinephrine and dopamine concentrations were decreased by the chronic stress and improved by the blueberry drink supplementation. The plasma epinephrine level was only influenced by the stress. CONCLUSION: These findings suggest that the blueberry drink may protect against the cognitive impairment induced by chronic mild stress.

Rational quartic Said-Ball Conics

Qian-Qian Hu,Guo-Jin Wang (사)한국CDE학회 2007 한국CAD/CAM학회 국제학술발표 논문집 Vol.2007 No.8

Highly Efficient Shoot Regeneration from Cotyledonary Nodes of Vegetable Soybean

Qian-Qian Liu,Gang Chen,Jun-Yi Gai,Yue-Lin Zhu,Li-Fei Yang,Guo-Ping Wei,Cong Wang 한국원예학회 2010 원예과학기술지 Vol.28 No.2

풋콩(Glycine max (L.) Merrill) 6개 품종의 자엽절 절편체로부터 thidiazuron(TDZ)과 NAA 농도를 달리한 배지에서 신초의 효율적인 재분화를 조사한 후, 가장 효과가 좋은 생장조절물질 조합으로 배지 종류, 접종방법 및 품종별 신초 재분화율을 조사하였다. 또한 절편체를 배지에 수직 또는 수평으로 치상하는 방법과 B5, 1/2 B5, MS, 1/2 MS, MSB(MS salts + B5 organics) 등의 5가지 기본 배지에 관하여 시험하였다. B5 배지에 1㎎?L<SUP>-1</SUP> TDZ, 0.05㎎?L<SUP>-1</SUP> NAA, 5㎎?L<SUP>-1</SUP> AgNO₃를 첨가한 처리에서 6개 품종의 신초 재분화율이 55.3-88.9%로 높았다. ‘L?ling No. 1’의 경우 수직으로 치상하는 것이 수평으로 치상하는 것보다 신초 재분화율이 37.5% 더 높았다. 따라서 풋콩은 TDZ를 처리한 B5 배지에 자엽절을 수직으로 치상할 때 신초 재분화율이 높았다. To establish a highly efficient system for shoot regeneration in vegetable soybean (Glycine max (L.) Merrill), explants were obtained from six genotypes and adventitious shoots were regenerated from cotyledonary nodes cultured on medium supplemented with different concentrations of N-phenyl-N′-1, 2, 3-thiadiazol-5-ylurea (thidiazuron TDZ) and 1-naphthylacetic acid (NAA). The most effective combination of plant growth regulators was selected first and then the effects of medium types, inoculation methods and genotypic differences on shoot regeneration were studied. The explants were inserted either vertically or horizontally into the medium and five basal media, including B5, ½ B5, MS, ½ MS, and MSB (MS salts and B5 organics), were tested. The shoot regeneration frequency of the six genotypes ranged from 53.5% to 88.9% and three of them reached 88.9%, 87.5% and 83.3%, respectively, on B5 medium supplemented with 1 ㎎?L<SUP>-1</SUP> TDZ, 0.05 ㎎?L<SUP>-1</SUP> NAA, and 5 ㎎?L<SUP>-1</SUP> AgNO₃. The shoot regeneration frequency of explants cultured on B5 medium was significantly higher than that of the other four basal media. The vertically inserted explants were found to yield a higher shoot regeneration frequency than that of horizontally inserted ones; the maximum difference of regenerating percentages between the two methods was 37.5%. In summary, TDZ was an efficient plant growth regulator for shoot induction. B5 medium and vertically inserted explants promoted shoot regeneration. We believe this highly efficient shoot regeneration system will provide foundation for the further transgenic studies in vegetable soybean.

Preparation and Characterization of Acid and Pepsin-soluble Collagens from Scales of Croceine and Redlip Croakers

Qian-Qian Wu,Tao Li,Bin Wang,Guo-Fang Ding 한국식품과학회 2015 Food Science and Biotechnology Vol.24 No.6

Acid-soluble (ASC) and pepsin-soluble collagen (PSC) from scales of croceine croaker (ASCPC and PSC-PC) and redlip croaker (ASC-PP and PSC-PP) were prepared with yields of 0.37±0.08% (ASCPC), 1.09±0.23% (PSC-PC), 0.42±0.09% (ASC-PP), and 1.14±0.30% (PSC-PP) (dry scale basis). Gly (347.1- 359.8 residues/1,000 residues) was the major amino acid. Contents of imino acid were between 189.4 and 192.9 residues/1,000 residues in all 4 collagens. ASC-PC and ASC-PP were type I collagens. Differences in subunit components between ASC and PSC were observed. Denaturation temperature values of ASC-PC, ASC-PP, PSC-PC, and PSC-PP were 30.7, 30.1, 27.5, and 26.6℃, respectively. All 4 collagens were soluble at pH 1-4. Values declined when NaCl concentrations exceeded 2%. Freeze-dried collagens showed loose, fibrous, and porous structures. The 4 scale collagens can be alternatives to collagen from terrestrial animals for applications in functional food, cosmetic, and biomedical industries.

The effects of a summer reading program for migrant children in migrant schools: First-year results from a randomized experiment

Qian Guo,Young-Suk Grace Kim,Yan Liu,Yan Peng,WENKAI SUN,Yijie Wang,Li Yang 서울대학교 교육연구소 2021 Asia Pacific Education Review Vol.22 No.1

Thanks to urbanization, some developing countries have a large migrant population. Academic performance of migrant children is usually far from satisfactory, much to the concern of educators and legislators. Meanwhile, research has attested to the importance of reading skill development by the end of third grade for later academic achievement. Against this background, we evaluated the effects of providing self-selected, developmentally appropriate books on the reading performance and summer reading amount of students in migrant schools in China, employing a randomized controlled trial. The intervention program improved rising second-graders’ word reading scores and summer reading amount. It proved particularly beneficial to low-performing children and children from disadvantaged families. The findings have implications for improving the academic achievement of migrant children in migrant schools in China and similar developing countries, especially where parental support may not be expected for the academic development of children.

Nano-Rheology of Single Unentangled Polymeric Lubricant Films

Guo, Qian,Chung, Pil Seung,Jhon, Myung S.,Choi, Hyoung Jin WILEY-VCH Verlag 2008 Macromolecular theory and simulations Vol.17 No.9

<P>Rheology and tribology become more and more critical issues in order to satisfy the harsh requirements for ultra-small head/media spacing HDDs. In this communication, MD simulations with a bead/spring model were employed to examine the nano-rheological response of nonfunctional and functional PFPEs by analyzing the shear viscosity of nanoscale PFPE films and the relaxation processes as a function of wall interaction/separation and endgroup functionality. Our simulation results indicate that thin PFPE films show more solid-like behavior, especially under high shear rate. The film deformation and shear viscosity change by tuning the film thickness and the endgroup functionality was discussed in conjunction with the relaxation processes.</P><P> <img src='wiley_img/10221344-2008-17-9-MATS200800048-gra001.gif' alt='wiley_img/10221344-2008-17-9-MATS200800048-gra001'> </P>