• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.35 no.6
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• pp.591-598
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• 2017

This study is for coordinates analysis(geocentric and rectangular coordinate) of Korean geodetic VLBI which has been operated by NGII (National Geographic Information Institute) in Republic of Korea since 2014. The purpose of this study is a fundamental research to determine the Korean geodetic datum. The VLBI data recorded from September 29th 2014 to July 31th 2017, total approximately a hundred of VLBI databases, is used to calculate daily positions and position rates. The VLBI coordinates are based on ITRF(2000,2005,2008,2014) with epochs of the first Korean VLBI observation date(September 29th 2014) and Korean Geodetic Datum(January 1st 2002). And as a results of VLBI observation, Korean VLBI coordinate movement velocity of 3.1cm/yr in the direction of $112.4^{\circ}$.

• The Journal of the Korea institute of electronic communication sciences
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• v.12 no.1
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• pp.75-84
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• 2017

It becomes more and more more important for the storage that supports high speed recording and stable access from network environment. As one field of basic science which produces massive astronomical data, VLBI(: Very Long Baseline Interferometer) is now demanding more data writing performance and which is directly related to astronomical observation with high resolution and sensitivity. But most of existing storage are cloud model based for the high throughput of general IT, finance, and administrative service, and therefore it not the best choice for recording of big stream data. Therefore, in this study, we design storage system optimized for high performance of I/O and concurrency. To solve this problem, we implement packet read and writing module through the use of libpcap and pf_ring API on the multi core CPU environment, and build a scalable storage based on software RAID(: Redundant Array of Inexpensive Disks) for the efficient process of incoming data from external network.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.6
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• pp.1159-1168
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• 2020

In the past, control and monitor of a large number of instruments is a specialized area, which requires an expensive dedicated module to implement. However, with the recent development of embedded technology, various products capable of performing M&C (Monitor and Control) have been released, and the scope of application is expanding. Accordingly, it is possible to more easily build a small M&C environment than before. In this paper, we discussed a method to replace the M&C of the VLBI system, which had to be implemented through a specialized hardware product, with an inexpensive general imbeded technology. Memory based data transmission, reception and storage is a technology that is already generalized not only in VLBI but also in the network field, and more effective M&C can be implemented when some items of Ethernet are optimized for the VLBI (Very Long Baseline Interferometer) system environment. In this paper, we discuss in depth the design and implementation for the multidrop based IoT architecture.

• Journal of Astronomy and Space Sciences
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• v.21 no.1
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• pp.29-38
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• 2004

A ultra low noise Q-band HEMT receiver for VLBI has been developed using a local oscillator with a very high phase stability. The performance of receiver was verified by comparison with receivers which were developed at the other countries. The receiver noise temperature shows 65 K in the frequency ragne from 42 ㎓ to 44 ㎓, less than 100 K from 39 ㎓ to 46 ㎓, respectively. A receiver noise temperature at SiO major line of 43㎓ which will be mainly observed by using this receiver has been optimized.

• Journal of The Korean Astronomical Society
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• v.55 no.6
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• pp.207-213
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• 2022

The Seoul Radio Astronomy Observatory (SRAO) operates a 6.1-meter radio telescope on the Gwanak campus of Seoul National University. We present the efforts to reform SRAO to a Very Long Baseline Interferometry (VLBI) station, motivated by recent achievements by millimeter interferometer networks such as Event Horizon Telescope, East Asia VLBI Network, and Korean VLBI Network (KVN). For this goal, we installed a receiver that had been used in the Combined Array for Research in Millimeter-wave Astronomy and a digital backend, including an H-maser clock. The existing hardware and software were also revised, which had been dedicated only to single-dish operations. After several years of preparations and test observations in 1 and 3-millimeter bands, a fringe was successfully detected toward 3C 84 in 86 GHz in June 2022 for a baseline between SRAO and KVN Ulsan station separated by 300 km. Thanks to the dual frequency operation of the receiver, the VLBI observations will soon be extended to the 1 mm band and verify the frequency phase referencing technique between 1 and 3-millimeter bands.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.111-111
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• 2014

Intensity interferometry, based on the Hanbury Brown--Twiss effect, is a simple and inexpensive method for optical interferometry at microarcsecond angular resolutions. Motivated by recent technical developments, we argue that the sensitivity of large modern intensity interferometers can be improved by factors up to approximately 25,000, corresponding to 11 photometric magnitudes, compared to the pioneering Narrabri Stellar Interferometer of the 1970s when resolving. Our approach, based on spectrally resolved light, permits the construction of large optical interferometers at the cost of (very) long-baseline radio interferometers. Realistic intensity interferometers are able to spatially resolve main-sequence O-type stars in the Magellanic Clouds. Multi-channel intensity interferometers can address a wide variety of science cases: (i) linear radii, effective temperatures, and luminosities of stars; (ii) mass-radius relationships of compact stellar remnants; (iii) stellar rotation; (iv) stellar convection and the interaction of stellar photospheres and magnetic fields; (v) the structure and evolution of multiple stars; (vi) direct measurements of interstellar distances; (vii) the physics of gas accretion onto supermassive black holes; and (viii) calibration of amplitude interferometers by providing a sample of calibrator stars.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.38 no.6
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• pp.717-723
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• 2020

Determination of local tie vectors between the space geodetic techniques such as VLBI (Very Long Baseline Interferometer), SLR (Satellite Laser Ranging), DORIS (Doppler Orbit determination and Radiopositioning Integrated on Satellite), GNSS (Global Navigation Satellite System) is essential for combination of ITRF (International Terrestrial Reference Frame). Therefore, it is required to compute IVP (Invariant Point) position of each space geodetic technique with high accuracy. In this study, we have computed Sejong VLBI IVP position by using updated mathematical model for adjustment computation so that the improvement on efficiency and reliability in computation are obtained. The measurements used for this study are the coordinates of reflective targets on the VLBI antenna and their accuracies are set to 1.5 mm for each component. The results show that the position of VLBI IVP together with its standard deviation is successfully estimated when they are compared with those of the results from previous study. However, it is notable that additional terrestrial surveying should be performed so that realistic measurement errors are incorporated in the adjustment computation process.

• Journal of The Korean Astronomical Society
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• v.47 no.6
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• pp.235-253
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• 2014

Intensity interferometry, based on the Hanbury Brown-Twiss effect, is a simple and inexpensive method for optical interferometry at microarcsecond angular resolutions; its use in astronomy was abandoned in the 1970s because of low sensitivity. Motivated by recent technical developments, we argue that the sensitivity of large modern intensity interferometers can be improved by factors up to approximately 25 000, corresponding to 11 photometric magnitudes, compared to the pioneering Narrabri Stellar Interferometer. This is made possible by (i) using avalanche photodiodes (APD) as light detectors, (ii) distributing the light received from the source over multiple independent spectral channels, and (iii) use of arrays composed of multiple large light collectors. Our approach permits the construction of large (with baselines ranging from few kilometers to intercontinental distances) optical interferometers at the cost of (very) long-baseline radio interferometers. Realistic intensity interferometer designs are able to achieve limiting R-band magnitudes as good as $m_R{\approx}14$, sufficient for spatially resolved observations of main-sequence O-type stars in the Magellanic Clouds. Multi-channel intensity interferometers can address a wide variety of science cases: (i) linear radii, effective temperatures, and luminosities of stars, via direct measurements of stellar angular sizes; (ii) mass-radius relationships of compact stellar remnants, via direct measurements of the angular sizes of white dwarfs; (iii) stellar rotation, via observations of rotation flattening and surface gravity darkening; (iv) stellar convection and the interaction of stellar photospheres and magnetic fields, via observations of dark and bright starspots; (v) the structure and evolution of multiple stars, via mapping of the companion stars and of accretion flows in interacting binaries; (vi) direct measurements of interstellar distances, derived from angular diameters of stars or via the interferometric Baade-Wesselink method; (vii) the physics of gas accretion onto supermassive black holes, via resolved observations of the central engines of luminous active galactic nuclei; and (viii) calibration of amplitude interferometers by providing a sample of calibrator stars.

• Journal of the Institute of Convergence Signal Processing
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• v.12 no.4
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• pp.333-340
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• 2011

KJJVC(Korea-Japan Joint VLBI Correlator) was installed at the KJCC(Korea-Japan Correlation Center) and has been operated by KASI(Korea Astronomy and Space Science Institute) from 2009. KJNC is able to correlate the VLBI observed data through KVN(Korean VLBI Network), VERA(VLBI Exploration of Radio Astrometry), and JVN(Japanese VLBI Network) and its joint network array. And it is used exclusively as computer in order to process the observed data for the scientific purpose KJJVC used the VSI(VLBI Standard Interface) as the VLBI international standard at the data input-output specification between each component. Especially, for correlating the observed data, the data is transmitted with 1024Mbps speed between Mark5B high-speed playback and RVDB(Raw VLBI Data Buffer). The EMI(Electromagnetic lnterference), which is occurred by data transmission with high-speed, cause the data loss and the loss occurrence is frequently often for long transmission cable. Finally it will be caused the data recognition error by decreasing the voltage level of digital data signal. In this paper, in order to minimize the data loss by measuring the EMI noise level in transmission of the VSI specification, the 3 methods such as 1) RC filtering method, 2) lmpedance matching using Microstrip line, and 3) Signal buffering method using Differential line driver, were proposed. To verify the effectiveness of each proposed method, the performance evaluation was conducted by implementing and simulations for each method. Each proposed method was effectively confirmed as the high-speed data transmission of the VSI specification.

• Proceedings of the Technology Innovation Conference
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• 1997.12a
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• pp.159-176
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• 1997

This paper deals with demand surveys for big science and technology research facilities and equipments to advance national S'||'&'||'T research infrastructure. We perform surveys thrice based on applied Delphi method on the future demand of big S'||'&'||'T research facilities and equipments among Korean scientists and engineers. We employ the concept of big S'||'&'||'T research facilities and equipments as follows: \circled1 The operating size of it is equivalent to that of an institute or research center, and/or \circled2 The users in various disciplines are many, and/or \circled3 The application areas or spill-over effects are large, and/or \circled4 The scale and scope of research objects is equivalent to that of mega science area such as earth.oceanography.space, and/or \circled5 The expenses for installing and operating it are to be supported by government, and/or \circled5 The facilities are expected as necessary for international joint research, and/or \circled7 It is necessary for promoting creative basic science and developing creative technology. We ask the respondents to answer the following questionnaire: - How to prioritize the equipments according to the degree of importance\ulcorner $\square$ Promotion of basic science and mega science, the development of the technologies to enhance the public welfare, the competitiveness of industrial technologies, the job creation for the S'||'&'||'T personnel, and international cooperation. - Who should be in charge of acquisition and operation of the equipments\ulcorner $\square$ Industry, Government Research Institutes, Academy, ERC and SRC. - When shall we acquire the equipment\ulcorner $\square$ Within 2000, 2002, 2007, 2012, and 2017. - How shall we acquire the equipments\ulcorner $\square$ International Joint Development, Domestic Development, Acquisition from Overseas, - How much will the equipment generate spill-over effects to national competitiveness\ulcorner $\square$ Promotion of basic science, contribution to the economy, supply of S'||'&'||'T personnel, and international cooperation. We suggest the following equipments as prioritized candidates after consulting the officers from MOST, MOE, MIC, MOEN and experts from KBSI and STEPI:(table omitted) where, #1, Korea Advanced Liquid Metal Reactor, #2. 800 MHz Superconduction Fourier-Transform Nuclear Magnetic Resonance Spectrometer, #3. Ion Accelerator, #4. Seismic Test Facility, #5. Transonic Wind Tunnel, #6. Radio Telescope for Very Long Baseline Interferometer, #7. 3000t Universal(or Large Structure) Testing Machine, #8. Compost Facility or Plasma Pyrolysis Facility.