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Jangsik In,Yoonsung Han,Sunghoon Kim,Jaechul Shim,Jongill Hong 한국자기학회 2006 Journal of Magnetics Vol.11 No.3
We successfully enhanced the performance of a spin valve by inserting an ultra-thin layer of partially oxidized Fe in the pinned and free layers. With the exchange bias field kept large, the spin valve reached a GMR of 12%, which corresponded to a 55% increase in GMR when we compared it with that of spin valves without any inserted layer. The layer of partially oxidized Fe was more effective for improving the properties of the spin valve than the layer of partially oxidized Co??Fe₁?. Considering all the results, we can contribute the significant improvement to the combined effect of the modified local electronic structures at the Fe impurities and the enhanced spin-dependent reflections at the α-Fe₂O₃ phase in the magnetic layer.
Jangsik Yoo,Jongsun Ahn,Young Jae Lee,Sangkyung Sung 대한전기학회 2012 Journal of Electrical Engineering & Technology Vol.7 No.5
Fault detection and isolation (FDI) algorithms provide fault monitoring methods in GPS measurement to isolate abnormal signals from the GPS satellites or the acquired signal in receiver. In order to monitor the occurred faults, FDI generates test statistics and decides the case that is beyond a designed threshold as a fault. For such problem of fault detection and isolation, this paper presents and evaluates position domain integrity monitoring methods by formulating various pseudorange prediction methods and investigating the resulting test statistics. In particular, precise measurements like carrier phase and Doppler rate are employed under the assumption of fault free carrier signal. The presented position domain algorithm contains the following process; first a common pseudorange prediction formula is defined with the proposed variations in pseudorange differential update. Next, a threshold computation is proposed with the test statistics distribution considering the elevation angle. Then, by examining the test statistics, fault detection and isolation is done for each satellite channel. To verify the performance, simulations using the presented fault detection methods are done for an ideal and real fault case, respectively.
Effects of a Au-Cu Back Layer on the Properties of Spin Valves
Jangsik In,Sanghoon Kim,Jaeyong Kang,Ajay Tiwari,Jongill Hong 한국자기학회 2007 Journal of Magnetics Vol.12 No.3
We have studied the effect of Au-Cu back layer system ~10 A thick on the properties of a spin valve. The back layers were Cu, Au, co-sputtered CuxAu1-x, laminated [Au/Cu]n and bi-layer [Au/Cu]. When Au was added to the Cu, the resistance of the spin valve abruptly increased most likely due to impurity scattering. The GMR values were not increased significantly for all the structures. In the case of co-sputtered CuxAu1-x, the changes in the resistance, ?R, was increased at a composition of ~Au0.5Cu0.5. This increase in ?R is due to increase in the resistance and not from the enhanced spin-dependent scattering. The structural analyses showed that the orthorhombic Au0.5Cu0.5 was formed in the back layer instead of the face-centered tetragonal Au0.5Cu0.5 as we expected. Thermal annealing over 400℃ may be required to have face-centered tetragonal in the 10 A thick ultra-thin film. In the case of a laminated or bi-layered back layer, the properties of the spin valve were improved, which may be attributed to the increase in the mean free path of conduction electrons.
커먼레일시스템의 비증발 디젤 분무에서 분사율과 주변기체의 압력에 따른 주변기체 유입
공장식(Jangsik Kong),강진석(Jinsuk Kang),배충식(Choongsik Bae) 한국자동차공학회 2003 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Entrainment of ambient gas is a crucial characteristics of transient diesel spray. Recently, it was found that the mass flow rate of ambient gas into transient diesel spray increased with the distance from the nozzle, i.e., axial momentum flow rate of entrained gas increased along spray axis. This tendency is different from the turbulent jet whose momentum flow rate is independent from axial positions.<br/> To understand more detailed spray behaviors, it is necessary to quantify the entrainment characteristics of transient diesel sprays under realistic injection and ambient conditions In this study, measured was the entrained velocity of ambient gas into a diesel spray with LDV (Laser Doppler Velocimetry) technlmique. Non-evaporating transient diesel sprays from a common-rail injection system with triangular injection rate profile were observed. The effects of ambient gas density and nozzle hole geometry were assessed with entrainment coefficient.<br/> There appeared a region where entrainment coefficients were remaining almost constant after onset of entrainment while iIjection rates were changing The effect of common-rail pressure, which altered the slope of injection rate curve, was hardly noticed at this region. Entrainment coefficient increased with ambient gas density, that is, the effect of ambient gas density on entrainment of transient diesel spray is larger than that of turbulent jet whose entrainment coefficient remains constant.<br/> Non-dimensional distance was defined to reflect the effect of nozzle hole diameter and ambient gas density together. Mean value of entrnainment coefficient was found to increase with non-dimensional distance from the nozzle.<br/>
Kong, Jangsik,Bae, Choongsik Professional Engineering Publishing Ltd 2015 Proceedings of the Institution of Mechanical Engin Vol. No.
<P>This experimental study investigates the effect of a conical nozzle orifice on the combustion and emissions of an optically accessible single-cylinder diesel engine equipped with a high-pressure common-rail injection system. In-cylinder pressure analysis and emission measurements were conducted to investigate the combustion and emission characteristics. Direct imaging visualization was used to characterize the combustion process. The engine was operated at an indicated mean effective pressure of 0.5 MPa, an engine speed of 1200 r/min and injection pressures of 30 MPa, 80 MPa and 120 MPa. The results showed that overall combustion occurred more quickly when a conical nozzle orifice was used than with a cylindrical nozzle orifice. The ignition delay of the conical nozzle orifice was shorter than that of the cylindrical nozzle orifice. The conical nozzle orifice also showed a lower peak heat release rate and a larger diffusion burn proportion during the combustion process. In terms of emissions, the conical nozzle orifice emitted lower smoke emissions and produced higher nitrogen oxide and hydrocarbon emissions. Direct combustion imaging confirmed that the conical nozzle orifice had a shorter ignition delay and a larger proportion of diffusion combustion. Moreover, its flame intensity was higher than that from the cylindrical nozzle orifice owing to its improved atomization and prolonged diffusion combustion.</P>
저급 프로세서에 적용 가능한 무인기용 GPS/INS 고장검출 알고리즘 구현
유장식(Jangsik Yoo),안종선(Jongsun Ahn),성상경(Sangkyung Sung),이영재(Young Jae Lee),천세범(Sebum Chun) 한국항공우주학회 2010 韓國航空宇宙學會誌 Vol.38 No.8
GPS/INS 통합시스템의 고장검출에는 카이제곱 분포 기반의 알고리즘이 일반적으로 사용된다. 본 논문에서는 기존의 RAIM (Receiver Autonomous Integrity Monitor)과 카이제곱 분포 기반의 알고리즘을 결합하여 무인기용 저급 프로세서에 적용하기 위해 단순화시킨 GPS/INS 고장검출 알고리즘을 제안한다. 제안한 알고리즘의 검중을 위해 고장모델을 사용하여 그 결과를 나타내었다. In the CPS/INS integrated system fault detection, algorithm based on a chi-square distribution is commonly used. In this paper, it has been proposed simplified CPS/INS fault detection algorithm that is combined conventional RAIM (Receiver Autonomous Integrity Monitor) and algorithm based on chi-square distribution for UAV using row-grade processor. It use a fault model to verify the proposed algorithm and produced the result.
분사기공형상이 HSDI 디젤 엔진의 성능과 배기에 미치는 영향
공장식(Jangsik Kong),국상훈(Sanghoon Kook),이승원(Seungwon Lee),최욱(Wook Choi),배충식(Choongsik Bae) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
In the study, the influence of nozzle hole geometry, rail pressure and injection timing on combustion was analyzed in an optical access single-cylinder diesel engine equipped with a high pressure common-rail injection system. The K factor represents the taper ratio of the nozzle hole of the injector. The injection rate showed that tapered nozzle hole with bigger K factor result in a higher injection speed. A tapered nozzle produced some favorable results; a greater heat release and decreased THC (Total Hydrocarbon) and PM (Particulate Matter), despite an increase in NOx (Nitrogen Oxides) level.
[디젤엔진부문] 분사기공형상이 디젤 분무특성에 미치는 영향
공장식(Jangsik Kong),유준(Jun Yu),배충식(Choongsik Bae) 한국자동차공학회 2001 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2001 No.11_1
Spray characteristics of fuel injection system is one of the most important factors in combustion and emission control, especially in HSDJ (High Speed Direct Injection) diesel engine where interval between burning and evaporation of atomized fuel is relatively short. An investigation into spray characteristics obtained from different geometric hole shapes of VCO (Valve Covered Orifice) nozzles was performed. General spray characteristics were evaluated as a function of factor representing the taper ratio of the injector hole of the injector using spray images frozen by a CCD camera incorporating a strobo light Macroscopic spray visualization showed that tapered nozzle hole with higher K factor resulted in faster penetration, especially at lower ambient pressure, and smaller spray angle.