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Non-destructive photoacoustic imaging of metal surface defects
Jeon, Seungwan,Kim, Jeesu,Yun, Jong Pil,Kim, Chulhong IOP 2016 Journal of optics Vol.18 No.11
<P>The detection of metal surface defects is important in achieving the goals of product quality enhancement and manufacturing cost reduction. Identifying the defects with visual inspection is difficult, inaccurate, and time-consuming. Thus, several inspection methods using line cameras, magnetic field, and ultrasound have been proposed. However, identifying small defects on metal surfaces remains a challenge. To deal with this problem, we propose the use of photoacoustic imaging (PAI) as a new non-destructive imaging tool to detect metal surface defects. We successfully visualized two types of cracks (i.e., unclassified and seam cracks) in metal plate samples using PAI. In addition, we successfully extracted cracked edges from height-encoded photoacoustic maximum amplitude projection images using the Laplacian of Gaussian filtering method, and then, quantified the detected edges for a statistical analysis. We concluded that PAI can be useful in detecting metal surface defects reducing the defect rate and manufacturing cost during metal production.</P>
A Novel 2-D Synthetic Aperture Focusing Technique for Acoustic-Resolution Photoacoustic Microscopy
Jeon, Seungwan,Park, Jihoon,Managuli, Ravi,Kim, Chulhong IEEE 2019 IEEE transactions on medical imaging Vol.38 No.1
<P>Acoustic-resolution photoacoustic microscopy (AR-PAM) is a promising technology for vascular or tumor-targeted molecular imaging. Unique advantages of AR-PM are its non-invasive, non-ionizing real-time, and deeper imaging depth. AR-PAM typically uses an ultrasound transducer with a high acoustic numerical aperture (NA) to enable deeper imaging depth. While high NA achieves good lateral resolution in the focal plane but significantly degrades the lateral resolution in the out-of-focus region. Synthetic aperture focusing technique (SAFT) has been introduced to overcome this out-of-focus degradation by synthesizing the correlated signals. Several 2-D SAFTs have been also reported to improve degraded resolution in all directions. However, the resolution enhancement of the previously reported 2-D SAFTs are suboptimal and are not equivalent to the 1-D SAFT performance under an ideal condition with the sample orientation perpendicular to the synthetic aperture direction. In this paper, we present a new 2-D SAFT called 2-D directional SAFT that improves the lateral resolution significantly and we compare our results against 1-D SAFT under ideal condition. We applied this algorithm to phantom and <I>in vivo</I> images to show the improvement in image quality. We also implement this algorithm in a graphical processing unit to achieve high performance to show the practicality of implementing this new algorithm in a system.</P>
희박 예혼합 메탄-공기 혼합기의 연소 및 배기 배출물 특성: 균질급기
조승완(Seungwan Cho),최승환(Seunghwan Choi),곽철우(Chulwoo Kwark),전충환(Chungwhan Jeon),장영준(GYoungjuen Chang) 한국자동차공학회 2003 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
A Cylindrical constant volume combustion chamber was used to investigate the combustion and exhaust characteristics of a homogeneous charge methane-air mixture under various overall charge pressures, excess air ratios and ignition times. Combustion pressure development measured by piezoelectric pressure transduce and exhaust emissions measured by 2-valve gas chromatography were used to investigate the effects of initial pressures, excess air ratios and ignition times on the combustion characteristics.<br/> It was found that the combustion duration, flame speed and burning velocity had good characteristics under the conditions of an excess air ratio of 1.1, an overall charge pressure of 0.15 MPa and an ignition time of 300 ms in the present study. And the CO,In this paper, the effects of ethanol blended gasoline on emissions and their catalytic conversion efficiencies characteristics were investigated in a electronic fuel injection gasoline engine. The results showed that the increase of ethanol concentration in the blended fuels brings about the reduction of THC and CO₂ emissions from the gasoline engine were improved. THC emissions were drastically reduced by up to thirty percent. And brake specific fuel consumption was increased, but brake specific energy consumption could be improved. However, unburned ethanol and acetaldehyde emissions increased. The conversion efficiency of pt/Rh based three-way catalysts and the the effect of ethanol on CO and NOx emissions were investigated by the change of engine's speed, load and air/fuel ratio. Furthermore, the effect of ethanol blended fuel on the reduction of THC, CO and NOx emissions at idle speed. concentration was proportional to the ignition time and overall charge pressure, the 0₂, concentration was proportional to the excess air ratio, and the UHC concentration was inversely proportional to the ignition time and overall charge pressure.<br/>
Hong, Seungwan,Park, Sangho,Park, Lee Won,Jeon, Minseo,Chang, Hangbae North-Holland 2018 Future generations computer systems Vol.82 No.-
<P><B>Abstract</B></P> <P>In the Internet of Things (IoT) era, a variety of devices that accumulate a range of data and electronic information are connected to the internet. This information is intelligently processed to create new services. As a result, the range of security risks is expanded, and the risk of compromise of electronic information is increasing. To combat this risk, research and investments in electronic information security technology is steadily increasing, and various security systems are being steadily developed. However, since electronic information security technology suitable for the IoT environment is not classified, many security systems perform redundant functions. The use of redundant security systems not only wastes costs in terms of security management, but also inefficiently performs security operations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A classification of electronic information security in IoT environment is proposed. </LI> <LI> Based on the constructed classification, a meta analysis of S. Korea was conducted. </LI> <LI> Using the results, ideal security management to each classification can be practiced. </LI> </UL> </P>
조승완(Seungwan Cho),최승환(Seunghwan Choi),전충환(Chunghwan Jeon),장영준(Youngjune Chang) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
A cylindrical constant volume combustion chamber is used to investigate the combustion radical characteristics of homogeneous charge methane-air mixture under various excess air ratios. An optical fiber bundle is used to measure the emissions of CH* and C*₂ radicals in this research is map the mixture uniformity in the combustion chamber at 5㎜ apart from center position. The experimental results show that there exist a relationship between the intensity ratio(ICH*/IC*₂) and the excess air ratio.
정적연소실내 예연소실 설계인자 및 스월 강도에 따른 연소특성에 관한 실험적 연구
전충환(Chunghwan Jeon),양인규(Ingyu Yang),김현규(Hyunkyu Kim),송주헌(Juhun Song),장영준(Youngjune Chang),조승완(Seungwan Cho) 한국자동차공학회 2010 한국자동차공학회 부문종합 학술대회 Vol.2010 No.5
Natural gas is a promising alternative fuel to meet strict engine emission regulations in many countries. The development of natural gas engines requires low emissions along with the demand for better fuel consumption and increased power ratings. In this study, a cylindrical Constant Volume Combustion Chamber(CVCC) was used to investigate the combustion characteristics under different swirl intensity and equivalence ratio. The maximum combustion pressure and mass fraction of burned gas was evaluated in particular by the orifice diameter, volume ratio of pre-chamber, equivalence ratio and swirl intensity. This result could provide combustion characteristics with variation of swirl intensity.
분위기 압력에 따른 커먼레일 시스템의 비증발 디젤 분무특성에 관한 실험적 연구
전충환(Chunghwan Jeon),정정훈(Jeonghoon Jeong),김현규(Hyunkyu Kim),송주헌(Juhun Song),장영준(Youngjune Jang),조승완(Seungwan Cho) 한국자동차공학회 2010 한국자동차공학회 부문종합 학술대회 Vol.2010 No.5
It is very important to understand the spray characteristics and fuel injection conditions in direct injection diesel engine because the emission gas compositions from diesel engines are related to spray formation processes. The objective of the papers is the characteristics of the macroscopic behaviour of diesel sprays. In this study, the characteristics of diesel spray has been studied using a shadowgraph and laser scattering. The spray characteristics such as spray tip penetration and spray cone angle studied at various injection pressure and ambient pressure.