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Performance Improvement of Satellite Navigation System Using Inter-satellite Distance Information
Moonseok Choi,Jongsun Ahn,Sangkyung Sung,Jaegyu Jang,Young Jae Lee 한국항공우주학회 2018 International Journal of Aeronautical and Space Sc Vol.19 No.2
A satellite navigation system calculates the position of a user using measurement values from a satellite, receiver, and broadcast ephemeris, which provides position information about the navigation satellite. However, in scenarios where it is difficult to secure sufficient satellite visibility, such as in a downtown area, the position accuracy of a global navigation satellite system is reduced. This study proposes a navigation algorithm for improving the accuracy of navigation using a measurement value in addition to the existing pseudorange measurement. A user who cannot secure a sufficient navigation visibility uses a standalone scheme that depends exclusively on the pseudorange measurement to estimate the position. The proposed method uses a position estimation algorithm that uses the measured value of the distance between satellites and geometric relation between users to construct a measurement equation, and combines this with the existing pseudorange measurement equation. The results obtained from static and dynamic experiments verify the superior performance of the proposed navigation algorithm.
Disorder-mediated enhancement of fiber numerical aperture.
Choi, Youngwoon,Yoon, Changhyeong,Kim, Moonseok,Yang, Juhee,Choi, Wonshik Optical Society of America 2013 Optics letters Vol.38 No.13
<P>The numerical aperture (NA) of a multimode optical fiber sets the limit of the information transport capacity along the spatial degree of freedom. In this Letter, we report that the application of a highly disordered medium can overcome the capacity limit set by the fiber NA. Specifically, we coated the input surface of a multimode fiber with a disordered medium made of ZnO nanoparticles and transported a wide-field image through the fiber with a spatial resolution beyond the diffraction limit given by the fiber NA. This was made possible because multiple scatterings induced by the disordered medium physically increased the NA of the entire system. Our study will lead to enhancing the spatial resolution of fiber-based endoscopic imaging and also improving the information transport capacity in optical communications.</P>
Performance Improvement of Satellite Navigation System Using Inter-satellite Distance Information
Choi, Moonseok,Ahn, Jongsun,Sung, Sangkyung,Jang, Jaegyu,Lee, Young Jae The Korean Society for Aeronautical Space Sciences 2018 International Journal of Aeronautical and Space Sc Vol.19 No.2
A satellite navigation system calculates the position of a user using measurement values from a satellite, receiver, and broadcast ephemeris, which provides position information about the navigation satellite. However, in scenarios where it is difficult to secure sufficient satellite visibility, such as in a downtown area, the position accuracy of a global navigation satellite system is reduced. This study proposes a navigation algorithm for improving the accuracy of navigation using a measurement value in addition to the existing pseudorange measurement. A user who cannot secure a sufficient navigation visibility uses a standalone scheme that depends exclusively on the pseudorange measurement to estimate the position. The proposed method uses a position estimation algorithm that uses the measured value of the distance between satellites and geometric relation between users to construct a measurement equation, and combines this with the existing pseudorange measurement equation. The results obtained from static and dynamic experiments verify the superior performance of the proposed navigation algorithm.
High-speed synthetic aperture microscopy for live cell imaging.
Kim, Moonseok,Choi, Youngwoon,Fang-Yen, Christopher,Sung, Yongjin,Dasari, Ramachandra R,Feld, Michael S,Choi, Wonshik Optical Society of America 2011 Optics letters Vol.36 No.2
<P>We present a high-speed synthetic aperture microscopy for quantitative phase imaging of live biological cells. We measure 361 complex amplitude images of an object with various directions of illumination covering an NA of 0.8 in less than one-thirteenth of a second and then combine the images with a phase-referencing method to create a synthesized phase image. Because of the increased depth selectivity, artifacts from diffraction that are typically present in coherent imaging are significantly suppressed, and lateral resolution of phase imaging is improved. We use the instrument to demonstrate high-quality phase imaging of live cells, both static and dynamic, and thickness measurements of a nanoscale cholesterol helical ribbon.</P>
Optical Imaging With the Use of a Scattering Lens
Youngwoon Choi,Changhyeong Yoon,Moonseok Kim,Wonjun Choi,Wonshik Choi IEEE 2014 IEEE journal of selected topics in quantum electro Vol.20 No.2
<P>“Turbidity” caused by multiple light scattering distorts the propagation of waves, and thus undermines optical imaging. For example, translucent biological tissues exhibiting optical turbidity have posed limitations on the imaging depth and energy transmission. Here, we introduce a novel method called turbid lens imaging (TLI) that records a transmission matrix of a scattering medium charactering the input-output response of the medium. The knowledge of this transmission matrix allows one to find an incident wave out of the distorted transmitted wave. Therefore, it converts the highly complex medium into a useful imaging optics. We demonstrate that the image distortion by a scattering medium can be eliminated by the use of the transmission matrix and a clean object image can be retrieved as a result. We extend TLI for imaging through a multimode optical fiber, which is also a scattering medium, and demonstrate an endoscopic imaging by using a single multimode optical fiber itself as a lens. In addition, we show that TLI removes the pixelation artifact in using an image fiber bundle and improve spatial resolution. Our method of making use of multiple light scattering will lay a foundation for advance optical bioimaging methods.</P>
Radiator 입출구 위치가 방열성능에 미치는 영향분석
최문석(Moonseok Choi),정순안(Sunan Jeong),정성우(Seongwoo Jeong),전길웅(Gil Woong Jun) 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11
The radiators are used for cooling the internal combustion engine of automobiles. And the radiators operate by passing a liquid coolant through the engine block, where it is heated, then through the radiator itself where it loses heat to the atmosphere. The conventional radiators have at least two spigots for coolant circulation. The inlet spigot location is recommended at the very highest point of radiator and outlet spigot at the very lowest point of it. Two spigots are located diagonally. In this study, the prototype radiator, which has 3 inlet and 3 outlet spigots, was manufactured for verifying the heat performance effect by testing. As the test result, the maximum heat rejection variation is 1.4%. This value variation can be considered as it is acceptable experimental error range. Therefore, this study shows the inlet and outlet spigot position is not effect on radiator heat performance.