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POINT SPREAD FUNCTION OF THE SOFT X-RAY TELESCOPE ABOARD YOHKOH
SHIN JUNHO,SAKURAI TAKASHI The Korean Astronomical Society 2003 Journal of The Korean Astronomical Society Vol.36 No.suppl1
Pre-launch calibration data have been analyzed for evaluating the point spread function (PSF) of Yohkoh Soft X-ray Telescope (SXT). Especially, it is found crucial that the effect of undersampling should be treated properly. The best fit solution of the SXT PSF, which is modeled by an elliptical Moffat function, has been derived by the comparison with the ground experiment data. In order to examine the off-axis variation of the SXT PSF, we need to define in advance the location of the optical axis on the CCD. According to the previous studies, the off-axis variation of effective area (the vignetting function) may be approximated either by two non-concentric cones or by a cone with some flat distortions. There have been, however, no fully approved representations for the SXT vignetting effect. The effect of the shift of the optical axis from the geometrical center of the telescope is investigated by numerical simulation. It is revealed from our study that the full width at half maximum (FWHM) of the SXT PSF stays nearly constant within an error bound over the central area of the CCD where the solar disk is located.
Shin Junho 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.78 No.11
Distribution of a high-stability clock signal is an important topic for many applications. Recently, optical frequency comb transfer through outdoor atmosphere has become a valuable tool for the clock distribution due to its versatility. To extend the benefits of comb-based open-air clock distribution, one-way radiofrequency (RF) transfer with a single optical frequency comb is an attractive approach due to its simplicity and broad application span. Here, we transfer an L-band RF signal across 820-m-scale outdoor beam path with a single optical frequency comb. We measured the absolute phase noise of the transferred RF signal, and analyzed it with Kolmogorov’s f −8/3 power law and Taylor’s hypothesis of frozen turbulence. We also show that the residual-phase noise of the transferred RF signal can be suppressed to the femtosecond regime by a delay-locked loop. Our results may benefit remote ranging at km-range, inter-building clock distribution, and optical communication through aerial drones.
A Novel Primary-Side Regulation Technique for Active-Clamp Forward Converter
Junho Shin,Jong-Won Shin 전력전자학회 2023 ICPE(ISPE)논문집 Vol.2023 No.-
This paper proposes a novel primary-side regulation method of an active-clamp forward converter (ACFW) without using tertiary winding. The proposed method offers the tight regulation of output voltage under load fluctuations. The output voltage is estimated by sensing input voltage, input current, and clamp capacitor voltage. A control loop in the primary side is designed by analyzing the effect of the parasitic components to compensate the error of the estimated output voltage. The proposed method does not require any signal isolation or additional winding of transformer to simplify its implementation. The effectiveness of proposed method is verified by experiment by 100-kHz 200-W prototype ACFW.