• Korean Journal of Optics and Photonics
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• 제29권4호
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• pp.166-172
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• 2018

In this paper, we propose a new method to predict a mirror's surface deformation due to the stress of moisture release by a coating in the environment of outer space. We measured the surface deformation of circular samples 50 mm in diameter and 1.03 mm thick, using an interferometer. The results were analyzed using Zernike fringe polynomials. The coating stress caused by moisture release was calculated to be 152.7 MPa. This value was applied to an analytic model of a 1.25 mm thickness sample mirror, confirming that the change of surface deformation could be predicted within the standard deviation of the measurement result ($78.9{\pm}5.9nm$). Using this methodology, we predicted the surface deformation of 600 mm hyperbolic mirror for the Compact Advanced Satellite, which will be launched in 2019. The result is only $2.005{\mu}m$ of focal shift, leading to 2.3% degradation of modulation transfer function (MTF) at the Nyquist frequency, which satisfies the requirement.

• Publications of The Korean Astronomical Society
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• 제30권2호
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• pp.645-647
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• 2015

We have initiated a Very Long Baseline Interferometer (VLBI) monitoring project of 36 methanol maser sources at 6.7 GHz using the Japanese VLBI Network (JVN) and East-Asian VLBI Network (EAVN), starting in August 2010. The purpose of this project is to systematically reveal 3-dimensional (3-D) kine-matics of rotating disks around forming high-mass protostars. As an initial result, we present proper mo- tion detections for two methanol maser sources showing an elliptical spatial morphology, G 002.53+00.19 and G 006.79-00.25, which could be the best candidates associated with the disk. The detected proper motions indicate a simple rotation in G 002.53+00.19 and rotation with expansion in G 006.79-00.25, respectively, on the basis of disk model fits with rotating and expanding components. The expanding motions might be caused by the magnetic-centrifugal wind on the disk.

• The Journal of Korean Academy of Prosthodontics
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• 제41권6호
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• pp.699-713
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• 2003

Statement of problem. Titanium is the most important material for biomedical and dental implants because of their high corrosion resistance and good biocompatibility. These beneficial properties are due to a protective passive oxide film that spontaneously forms on the surface. Purpose. The purpose of this study was to evaluate the responses of osteoblast-like cells on different surface treatments on Ti discs. Material and Methods. Group 1 represented the machined surface with no treatment. Group 2 surfaces were sandblasted with $50{\mu}m\;Al_2O_3$ under $5kgf/cm^2$ of pressure. Groups 3 and 4 were sandblasted under the same conditions. The samples were treated on a titanium oxide surface with reactive sputter depositioning and thermal oxidation at $600^{\circ}C$ (Group 3) and $800^{\circ}C$ (Group 4) for one hour in an oxygen environment. The chemical composition and microtopography were analyzed by XRD, XPS, SEM and optical interferometer. The stability of $TiO_2$ layer was studied by petentiodynamic curve. To evaluate cell response, osteoblast extracted from femoral bone marrow of young adult rat were cultured for cell attachment, proliferation and morphology on each titanium discs. Results and Conclusion. The results were as follows : 1. Surface roughness values were, from the lowest to the highest, machined group, $800^{\circ}C$ thermal oxidation group, $600^{\circ}C$ thermal oxidation group and blasted group. The Ra value of blasted group was significantly higher than that of $800^{\circ}C$ thermal oxidation group (P=0.003), which was not different from that of $600^{\circ}C$ thermal oxidation group (P<0.05). 2. The degree of cell attachment was highest in the $600^{\circ}C$ thermal oxidation group after four and eight hours (P<0.05), but after 24 hours, there was no difference among the groups (P>0.05). 3. The level of cell proliferation showed no difference among the groups after one day, three days, and seven days (P>0.05). 4. The morphology and arrangement of the cells varied with surface roughness of the discs.

• Korean Journal of Optics and Photonics
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• 제20권5호
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• pp.272-275
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• 2009

In order to enhance the background noise filtering performance of the white light interferometry(WLI), we demonstrate the noise filtering performance of preprocessing of the measured fringe signals. The WLI was realized through a mirau interferometer which was equipped with a green LED. When measuring large-height and rough surface objects, the illumination optics are considered the numerical aperture(NA) and the depth of focus(DOF). In this case, the limited NA of the illumination optics has a considerable impact on the interference fringe. Therefore, we propose a preprocessing method that uses the intensity difference between the measured intensity and the moving average intensity. The performance is demonstrated by measuring an array of metal solder balls fabricated on printed circuit board(PCB). The proposed method reduces the noise pixels by 15 percent.

• Journal of Space Technology and Applications
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• 제1권2호
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• pp.199-216
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• 2021

In 2020, the solar and space environment division at the Korea Space Science Society surveyed the status of data archives in solar physics, magnetosphere, and ionosphere/upper atmosphere in Korea to promote broader utilization of the data and research collaboration. The survey includes ground- and satellite-based instruments and developing models by research institutes and universities in Korea. Based on the survey results, this study reports the status of the ground-based instruments, data products in the ionosphere and upper atmosphere, and documentation of them. The ground-based instruments operated by the Korea Polar Research Institute and Korea Astronomy and Space Science Institute include ionosonde, Fabry-Perot interferometer in Arctic Dasan stations, Antarctic King Sejong/Jang Bogo stations, and an all-sky camera, VHF radar in Korea. We also provide information on total electron content and scintillation observations derived from the Global Navigation Satellite System (GNSS) station networks in Korea. All data are available via the webpage, FTP, or by request. Information on ionospheric data and models is available at http://ksss.or.kr. We hope that this report will increase data accessibility and encourage the research community to engage in the establishment of a new Space Science Data Ecosystem, which supports archiving, searching, analyzing, and sharing the data with diverse communities, including educators, industries, and the public as wells as the research scientist.

• The Journal of Korean Academy of Prosthodontics
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• 제47권4호
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• pp.376-384
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• 2009

Purpose: The purpose of this study was to evaluate the response of osteoblast-like cells to Ca-P coated surface obtained via Ion beam-assisted deposition (IBAD) method and Sol-Gel process on anodized surface by cellular proliferation and differentiation. Material and methods: The surface of a commercially pure titanium (Grade IV) discs with dimension of 10mm diameter and 2 mm thickness was modified by anodic oxidation under a constant voltage of 300 V. The experimental groups were coated with Ca-P by the IBAD method and Sol-Gel process on anodized surface. The surface roughness (Ra) of specimens was measured by optical interferometer and each surface was examined by SEM. To evaluate cell response, MG63 cells were cultured and cell proliferation, ALP activity and the ability of cell differentiation were examined. Also, cell morphology was examined by SEM. The significant of each group was verified by Kruskal-Wallis Test ($\alpha$=.05). Results: The Ra value of Ca-P coated surface by IBAD method was significantly higher than Ca-P coated surface by Sol-gel process (P < .05). The level of cell proliferation and ALP activity was higher in Ca-P coated surface by IBAD method (P<.05). The expression of ALP showed higher level expression in Ca-P coated surface by IBAD method. Cells grown on Ca-P coated surface by IBAD method were uniformly distributed and developed a very close layer. Conclusion: These experiments showed better performances of Ca-P coated surface by IBAD method with respect to Ca-P coated surface by Sol-gel process. Ca-P coated surface by IBAD method appear to give rise more mature osteoblast characteristics and might result in increased bone growth and bone-implant contact.

• Korean Journal of Optics and Photonics
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• 제28권3호
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• pp.108-115
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• 2017

We report the assembly procedure and performance evaluation of a visible and near-infrared spectrometer in the wavelength region of 400-900 nm, which is later to be combined with fore-optics (a telescope) to form a f/2.5 imaging spectrometer with a field of view of ${\pm}7.68^{\circ}$. The detector at the final image plane is a $640{\times}480$ charge-coupled device with a $24{\mu}m$ pixel size. The spectrometer is in an Offner relay configuration consisting of two concentric, spherical mirrors, the secondary of which is replaced by a convex grating mirror. A double-pass test method with an interferometer is often applied in the assembly process of precision optics, but was excluded from our study due to a large residual wavefront error (WFE) in optical design of 210 nm ($0.35{\lambda}$ at 600 nm) root-mean-square (RMS). This results in a single-path test method with a Shack-Hartmann sensor. The final assembly was tested to have a RMS WFE increase of less than 90 nm over the entire field of view, a keystone of 0.08 pixels, a smile of 1.13 pixels and a spectral resolution of 4.32 nm. During the procedure, we confirmed the validity of using a Shack-Hartmann wavefront sensor to monitor alignment in the assembly of an Offner-like spectrometer.