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Nonlinear behavior of Tb_4O_7-modified ZnO-Pr_6O_(11)-based ceramics with high breakdown field

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Journal of Rare Earths 2013年第3期31卷 276-280页

作者： choon-woo nahm Semiconductor Ceramics Laboratory Department of Electrical EngineeringDongeui UniversityBusan 614-714Korea

The effect of Tb407 on electrical behavior of the ZnO-Pr6Oll-based varistor ceramics was investigated. Microstructural analysis indicated that the addition of Tb407 decreased average grain size from 3.6 to 3.2 and increased the sintered density from 5.58 to 5.68 g/cm3. As the amount ofTb407 increased, the breakdown field increased from 9393 to 12437 V/cm and the nonlinear coefficient increased from 50 to 65. The varistor ceramics added with 0.5 mol.% in the amount of Tb407 exhibited an excellent stability by exhibiting 0. 1% in the variation rate of the breakdown field, 0% in the variation rate of the nonlinear coefficient, and 8.8% in the variation rate of the leakage current density for DC-accelerated aging stress of 0.85 E1 mA/115 ℃/24 h.

关键词： doping ZnO breakdown field electrical properties varistor ceramics rare earths

Contrast evaluation methods for natural color images in display systems: within- and cross-content evaluations

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Journal of Zhejiang University-Science C(Computers and Electronics) 2011年第11期12卷 897-909页

作者： choon-woo KIM School of Information and Communication Engineering Inha University

Contrast evaluation can be used as a criterion to evaluate performance of contrast enhancement algorithms and to compare contrast capability of display systems. This paper deals with contrast evaluation models for natural color images. Two separate models are defined for within- and cross-content evaluations. The former is to differentiate the perceived contrast of the images with the same content. The latter is to discriminate the differences in contrast among the images with different contents. Perception mechanisms are quite different for within- and cross-content evaluations. Local contrast plays an important role in within-content evaluation. In contrast, global contrast dominates the contrast perception for cross-content evaluation. Results of human visual experiments show that the proposed evaluation models outperform previous methods for both within- and cross-content evaluations.

关键词： Contrast evaluation Global contrast Local contrast Within content Cross content Statistical significance

New separation algorithm for touching grain kernels based on contour segments and ellipse fitting

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Journal of Zhejiang University-Science C(Computers and Electronics) 2011年第1期12卷 54-61页

作者： Lei YAN Cheol-woo PARK Sang-Ryong LEE choon-Young LEE School of Mechanical Engineering Kyungpook National University Daegu 702-701 Korea School of Technology Beijing Forestry University Beijing 100083 China

A new separation algorithm based on contour segments and ellipse fitting is proposed to separate the ellipse-like touching grain kernels in digital *** image is filtered and converted into a binary image *** the contour of touching grain kernels is extracted and divided into contour segments (CS) with the concave points on *** next step is to merge the contour segments,which is the main contribution of this *** distance measurement (DM) and deviation error measurement (DEM) are proposed to test whether the contour segments pertain to the same kernel or *** they pass the measurement and judgment,they are merged as a new *** with these newly merged contour segments,the ellipses are fitted as the representative ellipses for touching *** verify the proposed algorithm,six different kinds of Korean grains were *** results showed that the proposed method is efficient and accurate for the separation of the touching grain kernels.

关键词： Separation algorithm Touching grains Contour segments Ellipse fitting

Structural considerations in friction welding of hybrid Al_2O_3-reinforced aluminum composites

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Transactions of Nonferrous Metals Society of China 2011年第A01期21卷 42-46页

作者： In-Duck PARK choon-Tae LEE Hyun-Soo KIM woo-Jin CHOI Myung-Chang KANG Busan Metropolitan City Hall Fundamental Industries Division 2001 Jungang-ro Yeonje-gu Busan 611-735 Korea Department of Automotive & Mechanical Engineering Silla University Research & Development Center Sam-Ho precision 1256-1 Daejeo2-dong Gangseo-gu Busan 618-807 Korea National Core Research Center for Hybrid Materials Solution Pusan National University

Comparative studies on the relationship between the welding parameters and joining efficiency in the friction welding of hybrid Al203-reinforced aluminum composites were conducted. Metal matrix composites （MMCs） with 37% （volume fraction） aluminum particle were joined by friction welding. The results show that the effects of the rotation speed on the reduction rate of particle size are greater than those of the upset pressure, and the area of the MMC weld zone decreases as the joining efficiency increases, while it is considered that the joining efficiency does not increase as the reduction rate of particle size decreases. During the macro-examination of the bonding interlace, a gray discolored region was observed on the bonding interface, and the center of the region was dark gray. After the micro-examination of the bonding interface, base metal made some second particulate formed by condensed alumina particulate but discoloration part distributed minute alumina particulate without second particulate. Consequently, it was also observed that rotational speed of 3 000 r/min and upset pressure of 63.6 MPa showed a very ***.

关键词： friction welding hybrid aluminum composite bonding interface joining efficiency metal matrix composite

Heterostructures in two-dimensional colloidal metal chalcogenides:Synthetic fundamentals and applications

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Nano Research 2019年第8期12卷 1750-1769页

作者： Yuho Min Eunmi Im Geon-Tae Hwang Jong-woo Kim Cheol-woo Ahn Jong-Jin Choi Byung-Dong Hahn Joon-Hwan Choi woon-Ha Yoon Dong-Soo Park Dong choon Hyun Geon Dae Moon Functional Ceramics Department Powder & Ceramics DivisionKorea Institute of Materials Science (KIMS)ChangwonGyeongnam51508Republic of Korea Department of Polymer Science and Engineering Kyungpook National UniversityDaegu41566Republic of Korea Dongrtam Regional Division Korea Institute of Industrial TechnologyBusan46938Republic of Korea

As a new class of two-dimensional materials, two-dimensional (2D) heterostructures constructed from metal chalcogenides (MCs) have been gaining tremendous attention due to their unprecedented physical and chemical phenomena, mainly originated from their distinct structural features such as composition, architecture type, spatial arrangement of each component, crystal structure, exposed facet and interface, dimensionality in their heterostructures. Towards the realization of practical applications, synthetic approaches need a rational design with a variety of architecture types including laterally-combined, vertically-aligned, and conformally-coated 2D MC heterostructures. Among various synthetic routes, solution-based synthesis is thought of as an alternative to fabrication through high-cost setups since it can control those structural features in a cheap fashion. This review presents recent progress on solution-based synthesis to produce various 2D MC heterostructures with a focus on the synthetic fundamentals in terms of thermodynamic and kinetic aspects related to the growth mechanism. Four different synthetic approaches are reviewed: seeded growth, cation exchange reaction, colloidal atomic layer deposition, direct synthesis including one-step process and modified electrochemical method. We also provide some representative applications of 2D MC heterostructures and their hybrid composites in various fields including optoelectronics, thermoelectrics, catalysis, and battery. Finally, we offer an insight into challenges and future directions in a synthetic improvement of 2D MC heterostructures.

关键词： metal chalcogenide heterostructure anisotropic nanomaterials two-dimensional (2D) nanomaterials solution-based synthesis

Air Traffic Volume and Air Traffic Control Human Errors

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Journal of Transportation Technologies 2011年第3期1卷 47-53页

作者： woo-choon Moon Kwang-Eui Yoo Youn-Chul Choi 不详

Navigable airspaces are becoming more crowded with increasing air traffic, and the number of accidents caused by human errors is increasing. The main objective of this paper is to evaluate the relationship between air traffic volume and human error in air traffic control (ATC). First, the paper identifies categories and elements of ATC human error through a review of existing literature, and a study through interviews and surveys of ATC safety experts. And then the paper presents the results of an experiment conducted on 52 air traffic controllers sampled from the Korean ATC organization to find out if there is any relationship between traffic volume and air traffic controller human errors. An analysis of the experiment clearly showed that several types of ATC human error are influenced by traffic volume. We hope that the paper will make its contribution to aviation safety by providing a realistic basis for securing proper manpower and facility in accordance with the level of air traffic volume.

关键词： ATC Human Error Air traffic volume Workload

AC Scheduling Based on Thermodynamics of Indoor for On-Campus Small Data

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Journal of Power and Energy Engineering 2015年第4期3卷 282-288页

作者： Hyun Duck Choi Soon woo Rhee choon Ki Ahn Myo Taeg Lim School of Electrical Engineering Korea University Seoul Republic of Korea

This paper proposes a new day-ahead control scheme of an air conditioning (AC) based on thermodynamic model of indoor-temperature. The thermodynamic model of indoor-temperature can be achieved by modified first-order thermal dynamic equation. For the practical verification of proposed model, we implemented the home energy management system (HEMS) in the laboratory and used real experiment data sets. The proposed model can be represented by a state-space model of indoor-temperature and its parameters are obtained by least square algorithm. Through the proposed thermodynamic model, indoor-temperature can be predicted closely, and a behavior pattern of AC can also be achieved. This research involves the experimental verification of the proposed approach and communication architecture between the aggregator and a system user in a laboratory environment.

关键词： Home Energy Management System (HEMS) Least-Square Convex Optimization Demand Response (DR) Air-Conditioning (AC)

Potential risk factors for nonalcoholic steatohepatitis related to pancreatic secretions following pancreaticoduodenectomy

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World Journal of Gastroenterology 2011年第32期17卷 3716-3723页

作者： Sun choon Song Seong Ho Choi Dong wook Choi Jin Seok Heo woo Seok Kim Min Jung Kim Department of Surgery Samsung Medical Center Sungkyunkwan University School of Medicine

AIM: To identify risk factors for nonalcoholic steatohepatitis following pancreaticoduodenectomy, with a focus on factors related to pancreatic secretions. METHODS: The medical records of 228 patients who had a pancreaticoduodenectomy over a 16-mo period were reviewed retrospectively. The 193 patients who did not have fatty liver disease preoperatively were included in the final analysis. Hepatic steatosis was diagnosed using the differences between splenic and hepatic attenuation and liver-to-spleen attenuation as measured by non-enhanced computed tomography. RESULTS: Fifteen patients (7.8%) who showed postoperative hepatic fatty changes were assigned to Group A, and the remaining patients were assigned to Group B. Patient demographics, preoperative laboratory findings (including levels of C-peptide, glucagon, insulin and glucose tolerance test results), operation types, and final pathological findings did not differ significantly between the two groups; however, the frequency of pancreatic fistula (P = 0.020) and the method of pancreatic duct stenting (P = 0.005) showed significant differences between the groups. A multivari- ate analysis identified pancreatic fistula (HR = 3.332, P = 0.037) and external pancreatic duct stenting (HR = 4.530, P = 0.017) as independent risk factors for the development of postoperative steatohepatitis. CONCLUSION: Pancreatic fistula and external pancreatic duct stenting were identified as independent risk factors for the development of steatohepatitis following pancreaticoduodenectomy.

关键词： Nonalcoholic fatty liver diseases Nonalcoholic steatohepatitis Pancreatic duct stenting Pancreatic fistula Pancreatic surgery

Natural Variation in OsPRR37 Regulates Heading Date and Contributes to Rice Cultivation at a Wide Range of Latitudes

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Molecular Plant 2013年第6期6卷 1877-1888页

作者： Bon-Hyuk Koo Soo-Cheul Yoo Joon-woo Park choon-Tak Kwon Byoung-Doo Lee Gynheung An Zhanying Zhang linjie Li Zichao Li Nam-Chon Paek Department of Plant Science Plant Genomics and Breeding Institute and Research Institute for Agriculture and Life Sciences Seoul National UniversitySeoul 151-921 Korea Department of Plant Systems Biotech and Crop Biotech Institute Kyung Hee University Yongin 446-701 Korea Key Lab of Crop Heterosis and Utilization of Ministry of Education and Beijing Key Lab of Crop Genetic Improvement China Agriculture UniversityBeijing 100193 China Institute of Green Bio Science and Technology Seoul National University Pyeongchang 232-916 Korea

Heading date and photoperiod sensitivity are fundamental traits that determine rice adaptation to a wide range of geographic environments. By quantitative trait locus （QTL） mapping and candidate gene analysis using whole- genome re-sequencing, we found that Oryza sativa Pseudo-Response Regulator37 （OsPRR37; hereafter PRR37） is respon- sible for the Early heading7-2 （EH7-2）/Heading date2 （Hd2） QTL which was identified from a cross of late-heading rice ＇Milyang23 （M23）＇ and early-heading rice ＇H143＇. H143 contains a missense mutation of an invariantly conserved amino acid in the CCT （CONSTANS, CO-like, and TOC1） domain of PRR37 protein. In the world rice collection, different types of nonfunctional PRR37 alleles were found in many European and Asian rice cultivars. Notably, the japonica varieties harboring nonfunctional alleles of both Ghd7/Hd4 and PRR37/Hd2 flower extremely early under natural long-day condi- tions, and are adapted to the northernmost regions of rice cultivation, up to 53~ N latitude. Genetic analysis revealed that the effects of PRR37 and Ghd7 alleles on heading date are additive, and PRR37 down-regulates Hd3a expression to suppress flowering under long-day conditions. Our results demonstrate that natural variations in PRR37/Hd2 and GhdT/ Hd4 have contributed to the expansion of rice cultivation to temperate and cooler regions.

关键词： rice heading date quantitative trait locus natural variation Ghd7 OsPRR37.