http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
An Embedding of Multiple Edge-Disjoint Hamiltonian Cycles on Enhanced Pyramid Graphs
장정환 한국정보처리학회 2011 Journal of information processing systems Vol.7 No.1
The enhanced pyramid graph was recently proposed as an interconnection network model in parallel processing for maximizing regularity in pyramid networks. We prove that there are two edge-disjoint Hamiltonian cycles in the enhanced pyramid networks. This investigation demonstrates its superior property in edge fault tolerance. This result is optimal in the sense that the minimum degree of the graph is only four.
Effect of Hardness of the Piston Ring Coating on the Wear Characteristics of Rubbing Surfaces
장정환,문영훈,주병돈,이재호 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.6
In marine engines, the wear between the piston-ring face and the cylinder liner is an extremely unpredictable and hard-to-reproduce phenomenon that significantly decreases engine performance. This study investigates the characteristics of wear arising between both hard and soft piston-ring coatings and the running surface of the cylinder liner. A detailed tribological analysis using a Pin-on-Disk (POD) testing machine compares the wear rate and the friction coefficient between piston-ring coatings and the cylinder liner for various test parameters, such as test temperature, roughness of the liner, and lubrication. The experimental results show that the wear rate and the friction coefficient of soft coatings were higher than those of hard coatings. The wear rate and the friction coefficient were also found to be influenced by test temperature, due to the lubrication effect of the wear-protective oxidized layers that developed at elevated temperatures. The surface roughness of the cylinder liner on the wear rate strongly influenced the soft coating but was much less apparent for the hard coating. The morphological features of the scuffed cylinder liner revealed that a harder piston-ring coating enhances scuffing of the cylinder liner. In marine engines, the wear between the piston-ring face and the cylinder liner is an extremely unpredictable and hard-to-reproduce phenomenon that significantly decreases engine performance. This study investigates the characteristics of wear arising between both hard and soft piston-ring coatings and the running surface of the cylinder liner. A detailed tribological analysis using a Pin-on-Disk (POD) testing machine compares the wear rate and the friction coefficient between piston-ring coatings and the cylinder liner for various test parameters, such as test temperature, roughness of the liner, and lubrication. The experimental results show that the wear rate and the friction coefficient of soft coatings were higher than those of hard coatings. The wear rate and the friction coefficient were also found to be influenced by test temperature, due to the lubrication effect of the wear-protective oxidized layers that developed at elevated temperatures. The surface roughness of the cylinder liner on the wear rate strongly influenced the soft coating but was much less apparent for the hard coating. The morphological features of the scuffed cylinder liner revealed that a harder piston-ring coating enhances scuffing of the cylinder liner.
Characterization of Deposited Layer Fabricated by Direct Laser Melting Process
장정환,Byeong Don Joo,Chester J. Van Tyne,문영훈 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.3
Deposition dimensions are important in the final applications of products made by direct laser melting (DLM). This investigation used a 200 W fiber laser to produce single-line beads from stainless steel 316L powder using a variety of different energy distributions. To investigate the deposited layer, deposition width, height, penetration depth, and side surface roughness were measured. In order to validate the effectiveness of the two main process parameters (laser power and scan rate), multi-layered beads were fabricated by the sequential layering of single lines. It was found that with an increase in linear energy density, the wetting angle was reduced, and the average roughness was also increased with linear energy density. An equation that predicts the deposition height for a multi-layered bead is proposed and experimentally validated in this study. For deposited layer applications, the material properties of the deposited layer, such as contact angle, interfacial contact resistance, and flexural strength are estimated. The rougher deposited layers show higher contact angle and interfacial contact resistance. The flexural strength of the DLM fabricated specimen is above 250 MPa.
삼각측량법과 최소자승법을 활용한 실내 위치 결정의 산포 감소 방안에 관한 연구
장정환,이두용,장청윤,이창호 대한안전경영과학회 2011 대한안전경영과학회 학술대회논문집 Vol.2011 No.2
본 논문에서는 위치기반서비스의 핵심기능을 담당하는 측위기술 중 흔히 사용되고 있는 삼각측량법과 최소자승법을 보정한 방법을 이용하여 객체의 위치를 결정하는 알고리즘의 산포를 감소시키는 방안을 연구하였다. 두 측위 방법에서 사용되는 거리값은 모두 동일한 보정과 필터링 과정을 적용하였으며, 프로그램 구현 후 실내에서 테스트를 실시하였다. 프로그램은 LabView 2010으로 구현하였고, 각각의 알고리즘을 모듈화하여 필터링 적용 전후 및 개선효과를 비교하기 쉽도록 구성하였다. 일반적인 환경에서 실험한 결과 삼각측량이 최소자승법보다 더 좋은 정확도를 보여주었고, 필터링 과정을 거칠수록 정확도가 향상되는 것을 확인하였다.
장정환,성영은 한국공업화학회 2020 한국공업화학회 연구논문 초록집 Vol.2020 No.-
Due to excessive use of fossil fuels, concentration of carbon dioxide in the atmosphere has risen steadily, and it results in environmental issues like greenhouse effect and sea-level rising. To control these issues, various approaches have been studied and electrochemical carbon dioxide reduction reaction emerges as solution by converting carbon dioxide into feedstocks. It not only reduces carbon dioxide emission, but also stores intermittent renewable energy into stable products. Among diverse electrocatalysts, only copper metal can produce multi-electron(>2) products like methane, ethylene, ethanol, etc. Also, recent studies report that copper-doped ceria shows high methane selectivity by oxygen vacancies around Cu sites. So, we synthesized bct phase ceria and doped dispersed Cu single atoms by wet impregnation. The Cu-doped ceria produced methane from carbon dioxide, and it was annealed under argon atmosphere to remove ligands surrounding it.