• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1B
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• pp.1-9
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• 2009

In this paper, we propose an enhanced handoff support scheme based on network-based mobility management protocol, Proxy Mobile IPv6 (PMIPv6), which is actively standardized by the IETF NETLMM working group. By utilizing the dynamic virtual hierarchy network architecture between mobile access gateways (MAGs), the proposed scheme can support network scalability and reliability to wireless access network. In addition, we propose pre-authentication process based on the policy store (PS) to support a fast and seamless handoff. We evaluate the performance of the proposed scheme in terms of handoff delay and end-to-end delay thru computer simulation. Thru, various computer simulation results, we verified the superior performance of the proposed scheme by comparing with the results of other schemes.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.56.1-56.1
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• 2013

We have carried out follow-up observations of transiting extrasolar planets using small- to medium-sized reflectors located in Korea. Using the 0.60m telescope stationed at CbNUO (Chungbuk National University Observatory) we have achieved a photometric precision of 1.48 milli-magnitudes (root-mean-square scatter of data) of a HAT-P-09b (transit duration of 3.43 hrs) transit light curve (transit depth ~ 1.3%) with V=12.3 mag for the host star. We expect a photometric precision of 1.0 - 1.2 milli-magnitude for brighter targets (V ~ 10 - 11 mag). The transit technique and its application will be outlined. The results of test observations will be presented and the defocus technique will be discussed.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.38.3-38.3
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• 2019

We present newly discovered dwarf galaxy candidates in deep wide-field images of NGC 1291 obtained with KMTNet. We identify 15 dwarf galaxy candidates by visual inspection within the virial radius of NGC 1291. Using imaging simulations, we demonstrate that our imaging data is complete up to 26 mag arcsec^-2 or -10 abs.mag with > 70% of the completeness rate. We also apply automated detection method to find the dwarfs. However, the completeness and the reliability are relatively low compared to the visual inspection. We find that structural and photometric properties of dwarf candidates such as effective radius, central surface brightness, Sérsic index, and absolute magnitude appear to be consistent with those of known dwarf galaxies in nearby groups and clusters, except for color. NGC 1291, residing in a relatively isolated environment, tends to accompany bluer dwarf galaxies (≃0.58) than those in denser environment. It shows that the quenching of dwarfs is susceptible to the environment.

• Journal of the Korean Institute of Navigation
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• v.23 no.3
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• pp.29-34
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• 1999

In this paper, an X-band power amplifier using GaAs FET was designed and fabricated, which is to be used as SART transmitter sweeping at the frequency range of 9.2 GHz~9.5 GHz. The amplifier is consist of two stages using ATF-46101 FET of Hewllett-Packard. Finally, the amplifier using microstrip line matching solution shows that MAG is 23 dB at the center frequency of 9.35 GHz.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.145-146
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• 1996

We have estimated a metal abundance of [Fe/H]= -0.04 $\pm$ 0.05 dex, a reddening of E(B- V)= 0.28 mag, an age of 1.1 $\pm$ 0.1 Gyr, and a distance of 2.5 $\pm$ 0.2 kpc for NGC 1245 using the Washington filter system.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.147-148
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• 1996

We have estimated a metal abundance of [Fe/H]= -0.48 $\pm$ 0.14 dex, a reddening of E(B- V)= 0.30 mag, an age of 2.0 $\pm$ 0.4 Gyr, and a distance of 7.9 $\pm$ 0.8 kpc for Tombaugh 2 using the Washington filter system.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.123-124
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• 1996

Snapshots of eight SA and standard fields from low to high galactic latitudes were made using the KPNO 0.9m 2K $\times$ 2K CCD with a limiting magnitude from 19 to 22.5. The purpose of this study is to determine the vertical distribution of stars with respect to Galactic latitude and z-distance in comparison with the model simulation between intermediate population to the 'thick disk' component of scale height of a few kpc. Comparison of the preliminary results between observed and model simulation for 3 of the S fields shows good agreement both in V-mag and B- V color distributions. A bimodal distribution in B- V at high galactic latitude seems to be represented by a halo and 'thick disk' dwarf in the blue and by a normal disk dwarf population in the red.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.83.1-83.1
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• 2010

Recent observations of Sloan Digital Sky Survey (SDSS) for the ugriz filters have provided the largest and the most homogeneous photometric database. Especially, the ugriz systems have been used in many telescopes, such as SDSS, CFHT, and Gemini, and will be applied next generation large telescopes. In addition, many stellar evolution models, like as PADOVA, BaSTI and DSEP, have introduced theoretical isochrones in ugriz system, to apply the isochrones into the photometry of stars in globular clusters. In this study, we transformed Yonsei-Yale($Y^2$) isochrones to ugriz photometric system and fit the isochrones to the (g-r, r), (g-i, r), and (r-i, r) CMDs of 13 globular clusters (Chun et al. 2009, Clem et al. 2008, An et al. 2008). We found that the derived ages from $Y^2$-isochrones are 1~3Gyr younger and the estimated distance moduli are 0.3mag larger than the values inferred from the other isochrones in r-band. Also, the E(B-V) are 0.02~0.04mag less than those estimated from the other models. The ages of each globular cluster estimated from $Y^2$-isochrones are 12~14Gyr and distance moduli show good agreement with previous studies. From this result, we confirmed the availability of the $Y^2$-isochrones in gri filters. However, it is a problem which will improve that E(B-V) values obtained from $Y^2$-isochrones are too small. Finally, the result of this study is expected to be used research of globular cluster in ugirz photometric system.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.6
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• pp.383-389
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• 2001

We report on the design, fabrication, and characterization of 0.35${\mu}{\textrm}{m}$-gate AIGaAs/InGaAs PHEMTs for millimeter-wane applications. The epi-wafer structures were designed using ATLAS for optimum DC and AC characteristics, 0.351m-gate AIGaAs/rnGaAs PHEMTs having different gate widths and number of fingers were fabricated using electron beam lithography Dependence of RF characteristics of PHEMT on gate finger with and number of gate fingers have been investigated. PHEMT haying two 0.35$\times$60${\mu}{\textrm}{m}$$^2$ gate fingers showed the knee voltage, pinch-off voltage, drain saturation current density, and maximum transconductance of 1.2V, -1.5V, 275㎃/mm, and 260.17㎳/mm, respectively. The PHEMT showed fT(equation omitted)(current gain cut-off frequency) of 45㎓ and fmax(maximum oscillation frequency) of 100㎓. S$_{21}$ and MAG of the PHEMT were 3.6dB and 11.15dB, respectively, at 35㎓

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.79.2-79.2
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• 2019

We introduce Maemi Dual Field Telescope System (MDFTS) which is newly installed at Kyung Hee Astronomical Observatory (KHAO). MDFTS consists of two telescope tubes (40cm and 10cm), whose observing fields are aligned with different field of view, 15' x 11' and 83' x 63' respectively. We present the specification of instruments (telescope, mount, camera, and filter system) and the observation environment of KHAO. We expect that MDFTS can be used for transient survey e.g. Intensive Monitoring Survey of Nearby Galaxies (IMSNG). Based on observations conducted so far, the limiting magnitude of 40cm telescope in B-band is B_lim ~ 16 mag at 5-σ detection with 150 seconds total integration time under dark and clear observing condition. Also the integrated observing software for MDFTS, KAOS40 is now under developing.