• Journal of Communications and Networks
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• 제5권3호
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• pp.187-196
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• 2003

We consider the use of error control coding in direct sequence-code-division multiple access (OS-COMA) systems that employ multiuser detection (MUO) and space diversity. The relative performance gain between Reed-Solomon (RS) code and convolutional code (CC) is well known in [1] for the single user, additive white Gaussian noise (AWGN) channel. In this case, RS codes outperform CC's at high signal-to-noise ratios. We find that this is not the case for the multiuser interference channel mentioned above. For useful error rates, we find that soft-decision CC's to be uniformly better than RS codes when used with DS-COMA modulation in multiuser space-time channels. In our development, we use the Gaussian approximation on the interference to determine performance error bounds for systems with low number of users. Then, we check their accuracy in error rate estimation via system's simulation. These performance bounds will in turn allow us to consider a large number of users where we can estimate the gain in user-capacity due to channel coding. Lastly, the use of turbo codes is considered where it is shown that they offer a coding gain of 2.5 dB relative to soft-decision CC.

• 천문학논총
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• 제27권4호
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• pp.201-207
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• 2012

Following the first Public Release of the AKARI Point Source catalogues, we have worked on the production of a new far-infrared All-Sky Diffuse mapping product. In this paper we report first results from the All Sky diffuse maps that will shortly be released to the community, based on analysis of data from the Far Infrared Surveyor ($65{\mu}m-160{\mu}m$) instrument. These data are likely to have a strong impact on studies of extended structures, and the diffuse ISM.

• 천문학회보
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• 제43권1호
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• pp.41.2-41.2
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• 2018

EL CVn-type eclipsing binaries are composed of a massive A-type main-sequence primary star and a hotter B-type secondary one. These are worthy of particular attention because the secondary stars are rare objects to be extremely low-mass white dwarf precursors (ELM proto-WD) with the mass of ${\leq}0.2M_{\odot}$, evolving to higher effective temperatures and higher surface gravities. A few of them were discovered to show multi-periodic pulsations in one or both components. We monitored one of these rare and interesting objects, J0247-25 (=1SWASP J024743.37-251549.2), at two KMTNet sites of SAAO in South Africa and SSO in Australia. The observations were performed with the KMTNet 1.6m telescopes and pre-science 4K CCD cameras during the system test run from July to November 2014. Using the photometric data obtained for a total of 23 nights, we constructed well-defined eclipsing light curves in B/V-bands and derived absolute parameters (mass and radius, etc.) of each binary component. After subtracting model eclipsing curves from the data, we detected seven frequencies with 33~53 cycles per day (c/d) and identified them to be Delta Sct-type pulsations originated from the A-type primary component. Five frequencies were turned out to be excited by rotational splitting of non-radial pressure modes, enabled us to investigate rotational properties. We could not detect any frequency higher than 100 c/d, implying that pulsation amplitudes of the proto-WD secondary decrease greatly.

• 대한수학회지
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• 제33권2호
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• pp.309-318
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• 1996

The Gross Laplacian $\Delta_G$ was introduced by Groww for a function defined on an abstract Wiener space (H,B) [1,7]. Suppose $\varphi$ is a twice H-differentiable function defined on B such that $\varphi"(x)$ is a trace class operator of H for every x \in B.in B.

• 천문학회지
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• 제29권spc1호
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• pp.235-236
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• 1996

Using a phenomenological model for the accretion onto the magnetic white dwarf, we calclliated some optical line profiles from the magnetosphere of such systems. Line profiles of these systems seem to be produced in the magnetosphere of the compact star due to the reemission of X-ray produced near the stellar surface. Some results of our new calculation and the analysis of these results will be presented. Our results show that the model used here can reproduce the observed optical line profiles and open the possiblity to determine the parameters of individual systems.

• 정보보호학회지
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• 제19권5호
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• pp.68-72
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• 2009

최근 들어 기학급수적으로 증가하는 방송 및 통신 시스템으로 인해 무선 주파수 자원의 고갈 문제가 심각하게 대두되고 있다. 이와 같은 주파수 고갈과 비효율적인 주파수 사용 문제를 해결하기 위해 유휴 주파수를 합리적으로 이용하기 위한 인지무선(Cognitive radio) 기술이 많은 관심을 받고 있다. 본 고에서는 TV 주파수 대역 내 유휴자원(White space)을 대상으로 주파수 공유 기술인 인지무선 기술을 적용하기 위해 현재 표준화가 진행 중인 IEEE 802.22 WRAN을 중심으로 인지 무선네트워크를 위한 보안 표준화 현황을 살펴본다.

• 천문학논총
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• 제32권1호
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• pp.11-15
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• 2017

We present the AKARI far-infrared (FIR) all-sky maps and describe its characteristics, calibration accuracy and scientific capabilities. The AKARI FIR survey has covered 97% of the whole sky in four photometric bands, which cover continuously 50-180 micron with band central wavelengths of 65, 90, 140, and 160 microns. The data have been publicly released in 2014 (Doi et al., 2015) with improved data quality that have been achieved since the last internal data release (Doi et al., 2012). The accuracy of the absolute intensity is ${\leq}10%$ for the brighter regions. Quantitative analysis of the relative intensity accuracy and its dependence upon spatial scan numbers has been carried out. The data for the first time reveal the whole sky distribution of interstellar matter with arcminute-scale spatial resolutions at the peak of dust continuum emission, enabling us to investigate large-scale distribution of interstellar medium in great detail. The filamentary structure covering the whole sky is well traced by the all-sky maps. We describe advantages of the AKARI FIR all-sky maps for the study of interstellar matter comparing to other observational data.

• 천문학회보
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• 제36권2호
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• pp.155.1-155.1
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• 2011

The Korea Astronomy and Space Science Institute (KASI) and the Department of Astronomy at the University of Texas at Austin (UT) are developing a near infrared wide-band high resolution spectrograph, IGRINS (Immersion Grating Infrared Spectrograph). The white-pupil design of the instrument optics uses 7 cryogenic mirrors including 3 aspherical off-axis collimators and 4 flat fold mirrors. Two of the 3 collimators are H- and K-band pupil transfer mirrors and they are designed as compensators for the system alignment in each channel. Therefore, their mount design will be one of the most sensitive parts in the IGRINS optomechanical system. The other flat fold mirrors are designed within the limited area. Each of those includes the features of 3 axial hard points and 2 radial hard points with one spring plunger in order for the proper deflection of the mirror. The design work will include the computer-aided 3D modeling and finite element analysis (FEA) to optimize the structural stability and the thermal behavior of the mount models. The mount body will also include a tip-tilt and translation adjustment mechanism to be used as the alignment compensators.

• Journal of Astronomy and Space Sciences
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• 제2권1호
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• pp.7-18
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• 1985

Accretion rate가 $M=10^{16}g/sec$ 와 $M=10^{18}g/sec$인 경우의 정상상태의 Accretion disk의 모델들을 만들었다. 중심에 있는 별은 백색왜성으로 가정하고 질량은 $1M_\odot$이고 반경은 $10^9cm$로 보았다. 이 모델을 왜신성인 Z cha와 Z Cam에 응용하였다.

• International Journal of Aeronautical and Space Sciences
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• 제11권2호
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• pp.118-125
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• 2010

This paper describes a mid-course guidance strategy based on the earliest intercept geometry (EIG) guidance. An analytical solution and performance validation will be addressed for generalized mid-course guidance problems in area air-defence in order to improve reachability and performance. The EIG is generated for a wide range of possible manoeuvres of the challenging missile based on the guidance algorithm using differential geometry concepts. The main idea is that a mid-course guidance law can defend the area as long as it assures that the depending area and objects are always within the defended area defined by EIG. The velocity of Intercept Point in EIG is analytically derived to control the Intercept Geometry and the defended area. The proposed method can be applied in deciding a missile launch window and launch point for the launch phase.