• 천문학회지
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• 제17권1호
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• pp.37-49
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• 1984

UBV photoelectric observations were carried out for bright stars in M67 and the masses of clump stars and giant stars were derived in M67 and the other old open clusters, NGC 188, NGC 2420, NGC 2506 and IC 4651. The mean mass of clump stars in the five clusters ranges $m=0.5{\sim}1.0m_{\odot}$, and its ratio to the mean mass of giant stars is about 0.83. The number ratio of blue stragglers to the stars brighter than the turn-off of main sequence increases with cluster age whereas that of clump stars decreases with age. These results imply that the clump stars and blue stragglers are at the phase of horizontal branch evolution.

• 한국통신학회논문지
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• 제34권5A호
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• pp.421-428
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• 2009

Inter-cell coordination has been an emerging issue for mitigating inter-cell interference in broadband wireless access networks such as IEEE802.16 and 3GPP LTE (Long Term Evolution). This paper proposes uplink/downlink hybrid inter-cell coordination patterns for a TDD (Time Division Duplex)/MC-CDMA (Multi-Carrier Code Division Multiple Access) system. For the performance analysis, closed forms of inter-cell interferences are derived when uplink and downlink transmissions coexist over a multi-cell environment. In the analysis, we find an optimal ratio of downlink transmit powers of BSs (Base Stations) based on the target outage probability and the performance according to ratios of uplink/downlink transmit powers of MSs (Mobile Stations)/BSs is explored. Our numerical results show that interference mitigation utilizing the characteristics of the uplink and downlink power ratio is very effective in improving system performance in terms of QoS.

• Smart Structures and Systems
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• 제1권2호
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• pp.217-233
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• 2005

Elastic and electromagnetic waves can be used to gather important information about particulate materials. To facilitate smart geophysical characterization of particulate materials, their fundamental properties are discussed and experimental procedures are presented for both elastic and electromagnetic waves. The first application is related to the characterization of particulate materials using shear waves, concentrating on changes in effective stress during consolidation, multi-phase phenomena with relation to capillarity, and microscale characteristics of particles. The second application involves electromagnetic waves, focusing on stratigraphy detection in layered soils, estimation of void ratio and its spatial distribution, and conduction in unsaturated soils. Experimental results suggest that shear waves allow studying particle contact phenomena and the evolution of interparticle forces, while electromagnetic waves give insight into the characteristics of the fluid phase and its spatial distribution.

• 천문학논총
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• 제30권2호
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• pp.385-387
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• 2015

Stellar mass is an important parameter of galaxies. We estimate the dynamical mass of an elliptical galaxy by its velocity dispersion and effective radius using the Hernquist model in the framework of MOdified Newtonian Dynamics (MOND). MOND is an alternative theory to the dark matter paradigm. In MOND the dynamical mass is the same as the baryonic mass or luminous mass, and in elliptical galaxies most of the baryons reside in stars. We select elliptical galaxies between redshift 0.05 and 0.5 from the main galaxy sample and the luminous red galaxy sample in the Sloan Digital Sky Survey. We find that the stellar mass-to-light ratio at different redshift epochs can be fitted by a gamma distribution, and its mean is smaller at smaller redshifts.

• 천문학회보
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• 제45권1호
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• pp.58.2-58.2
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• 2020

We present a method for determining the abundance ratio of nitrogen to iron ([N/Fe]) from low-resolution (R~2000) stellar spectra from large spectroscopic surveys such as Sloan Digital Sky Survey (SDSS) and Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). The basic idea of the method is to match a grid of synthetic spectra with an observed spectrum in the CN band region around 3883 Å. To calibrate our estimate of [N/Fe], we make use of the giants observed in Apache Point Observatory Galaxy Evolution Experiment (APOGEE), which are also observed in the SDSS. This method will be applied to the Galactic halo stars to determine [N/Fe], and the measured nitrogen abundance ratios will be used to investigate the C-N anti-correlation, which is observed in globular clusters, to trace their origin with their kinematic properties.

• 천문학회보
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• 제45권1호
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• pp.63.1-63.1
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• 2020

We investigate the effect of recent star formation (RSF) on the α-elements-to-iron ratio ([α/Fe]) estimation for galaxies. Measuring galactic [α/Fe] is a powerful tool to pinpointing the timescale of chemical evolution and star formation. Our working hypothesis is that, with increasing stellar surface temperature, absorption equivalent width (EW) of α-elements decreases faster than that of Fe-peak elements, and thus RSF will lower the line ratio of EW(α)/EW(Fe). Moreover, young stars outshine, effectively lowering EW(α)/EW(Fe) of integrated light of RSF galaxies. Here we test our hypothesis using SDSS (optical spectrophotometric), GALEX (UV photometric) and IllustrisTNG datasets, and show that, if RSF is not considered thoroughly, EW(α)/EW(Fe) lowered by RSF can be routinely misinterpreted as low [α/Fe]. We discuss possible implications of the result in the context of the conventional [α/Fe]-mass relation of galaxies.

• 한국환경보건학회지
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• 제22권4호
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• pp.82-90
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• 1996

This study was performed to find the optimum mixing ratio of paper waste in composting of mixture of swine feces and newspaper. Using the experimental setting of aeration rate which was found in the experiment carried out priorly, and moisture contents reported in other literature, just the initial C:N ratios were differentiated by mixing different amount of newspaper with the same amount of swine feces. This study was carried out by operating 4 experimental cornposting reactors of bench scale for 3 weeks. The followings are the conclusions that were derived from this study. 1. During composting reaction, the C:N ratio of each cornposter was decreased. Degree of decrease was in order of run 3, run 2, run 4, and run 1 of which initial C:N ratio was 30, 25, 35, and 20 respectively. All of the final composts were found to be completed composting reaction. 2. Ash contents of each reactor increased rapidly in order of run 3, run 2, run 4, and run 1. The absolute values of quadratic effect coefficients of each second order regression function was 0.059, 0.038, 0.032, and 0.030 respectively. Ash contents evolution trend had a linear correlation with the C:N ratio trend. (r=-0.96932, p<0.05) 3. The range of highest temperatures reached during composting was 47.2-53.5$\circ$C. Those were not significantly different from one another. Thermophilic temperatures were maintained in the range of 48-108 hours. 4. Contents of heavy metal detected in the final compost were lower than those of Korean and European standards. 5. Concentration range of Nitrogen in the final compost was 1.11-2.27%, and that of phosphorus was 8.40-10.70 mg/kg. 6. The optimum C:N ratio which has been proposed without the consideration of types of bulking agents should be re-examined. Biodegradabilities of each bulking agents was thought to be important factor when determining the optimum initial C:N ratio for cornposting.

• 대한전자공학회논문지TC
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• 제47권1호
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• pp.10-18
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• 2010

Polar transmitter는 현재 GSM (Global System for Mobile Communications), EDGE (Enhanced Data Rates for GSM Evolution), GPRS (General Packet Radio Service) 등과 같은 협대역 통신 방식에만 주로 적용되고 있다. 본 논문에서는 polar transmitter를 OFDM (Orthogonal Frequency Division Multiplexing)과 같은 광대역 통신방식에 적용하기 위해 OFDM 통신 시스템이 가지고 있는 높은 PAPR (Peak-to-Average Power Ratio)을 감소시킬 수 있는 windowed-sinc 함수 기반의 PAPR 감소기법을 제안한다. 이 방법은 기존의 피크 윈도잉 (peak windowing) 기법에서 매우 인접한 여러 개의 피크들 또는 주변 신호에 비해 상대적으로 큰 피크에 의해 발생하는 과도한 신호 왜곡 효과를 완화시킨다. 다양한 윈도우 형태와 길이를 적용하여 비트오율 (Bit Error Rate; BER)과 오차 벡터 크기 (Error Vector Magnitude; EVM)를 측정한 결과, 제안된 기법은 기존의 피크 윈도잉 기법과 유사한 스펙트럼 성능을 가지면서 비트오율의 향상 및 PAPR 감소 성능이 우수함을 나타내었다.

• 전자공학회논문지
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• 제50권4호
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• pp.9-16
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• 2013

LTE (long term evolution) 및 LTE-A (LTE-Advanced) 시스템에서는 폐회로 기반의 다중 안테나 기술이 적용되었으며, 최대 비 전송 방식 (maximum ratio transmission, MRT) 보다 성능은 감소되지만, 동 이득 (equal gain) 특성을 유지할 수 있는 동 이득 전송 (equal gain transmission, EGT) 코드북을 채택하고 있다. 본 논문에서는 LTE 및 LTE-A 시스템에서 사용되는 코드북보다 성능을 향상시킬 수 있는 차분 코드북을 제안한다. 특히 동 이득 특성을 그대로 유지하면서 LTE 시스템의 코드북 요구조건을 모두 만족시키는 코드북을 제안한다. 코드북을 구성하는 코드워드들의 인자들 (elements)이 8-PSK(phase-shift keying) 성운 (constellation) 만을 사용하므로, 선부호화 및 복호 시 계산량이 낮아지는 LTE 코드북의 장점을 그대로 유지할 수 있다. 동 이득 성질은 특히 상향 링크에서 첨두 전력 대 평균 전력비 (PAPR)에 상당한 영향을 미치므로 매우 중요하다. 본 논문에서는 각 송신 안테나에 동 이득을 유지하는 성질을 이용한 새로운 차분 코드북을 제안하고, 동작원리를 회전 로크 구조로 설명한다. 컴퓨터 시뮬레이션을 통한 성능 분석에서, 동일한 피드백 비트 수를 갖는 같은 크기의 코드북에서 제안하는 차분 코드북은 기존 LTE 코드북보다 최소 0.9dB 성능 향상을 보인다.

• 전자공학회논문지D
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• 제36D2호
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• pp.41-47
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• 1999

본 논문에서는 플라즈마 건식 식각 공정을 모의 실험하기 위하여 셀 제거 방법을 적용하여 개발한 시뮬레이터의 성능을 보고한다. 마스크의 기하학적 형상에 의한 그림자 효과(shadow effect)를 고려하기 위한 알고리즘과, 오차의 누적을 막기 위한 알고리즘을 새로이 적용하였다. 입사하는 이온의 분포를 계산하기 위해서 해석적 모델과 몬테 카를로 방법을 모두 적용하였다. 또한 사용자가 유닉스(UNIX) 환경에서 공정 조건을 편리하게 입력할 수 있도록 그래픽 사용자 환경(graphic user interface, GUI)을 개발하였다. 개발된 3D-SURFILER(SURface proFILER)의 성능을 검증하기 위한 콘택 홀(contact hol) 구조의 시뮬레이션에서 셀의 수를 36,000($30{\times}40{\times}30$)으로 설정하여 시뮬레이션하였을 때 SUN ULTRA 1 시스템에서 약 10Mbyte의 메모리가 사용되었으며, 시뮬레이션 시간을 20분이었다. 종횡비(aspect ratio)가 1.57인 콘택 홀 구조에서 반응성 이온 식각(reactive ion etching, RIE)을 시뮬레이션하였으며, 이온의 증속 식각의 정도를 나타내는 손상 계수의 변화와 압력이 600mTorr일 때의 이온의 입사 분포에 의한 토포그래픽(topography) 진화를 시뮬레이션하였다.