• 대한전기학회:학술대회논문집
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• 대한전기학회 1993년도 하계학술대회 논문집 A
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• pp.54-56
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• 1993

A systematic procedure for determining the elements of system state matrix is suggested. The interrelation of submatrices of the system matrix is investigated. Each element or each block can be represented in algebraic form. These results can be applied in the eigenvalue sensitivity analysis with respect to the changes in controller parameters.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 B
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• pp.990-992
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• 2002

30kW electrical power conversion system is delveloped for the variable speed wind turbine system. In the wind energy conversion system(WECS) a synchronous generator with field current excitation converts the mechanical energy into electrical energy. As the voltage and frequency of generator output vary according to the wind speed, a dc/dc boosting chopper is utilized to maintain constant dc link voltage. Grid connection type PWM inverter supply currents into the utility line by regulating the dc link voltage. The active power is controlled by q-axis current which the reactive power can be controlled by d-axis current reference change. The phase angle of utility voltage is detected using s/w PLL(Phased Locked Loop) in d-q synchronous reference frame. This scheme gives a low cost power solution for variable speed WECS.

• 한국재료학회지
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• 제24권11호
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• pp.604-609
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• 2014

The thermoelectric power and dc conductivity of $La_{2/3+x}TiO_{3-{\delta}}$ (x = 0, 0.13) were investigated. The thermoelectric power was negative between 80K and 300K. The measured thermoelectric power of x = 0.13 increased linearly with increased temperatures and was represented by $S_0+BT$. The x = 0 sample exhibited insulating behavior, while the x = 0.13 sample showed metallic behavior. The electric resistivity of x = 0.13 had a linear temperature dependence at high temperatures and a T3/2 dependence below about 100K. On the other hand, the electric resistivity of x = 0 has a linear relation between $ln{\rho}/T$ and 1/T in the range of 200 to 300K, and the activation energy for small polaron hopping was 0.23 eV. The temperature dependence of thermoelectric power and the resistivity of x = 0 suggests that the charge carriers responsible for conduction are strongly localized. This temperature dependence indicates that the charge carrier (x = 0) is an adiabatic small polaron. These experimental results are interpreted in terms of spin (x = 0.13) and small polaron (x = 0) hopping of almost localized Ti 3d electrons.

• 천문학회보
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• 제40권2호
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• pp.42.1-42.1
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• 2015

We model the Spectral Energy Distribution (SED) of Class 0 protostar L1527 IRS using a radiative transfer code RADMC-3D. In addition to the photometry data from literatures, we include the Herschel/PACS data which well covers the far-infrared SED peak of L1527 IRS, providing precise constraints to the density structure and other physical properties of its circumstellar envelope. Previously, Tobin et al. (2013) presented a dust continuum modeling results using a rotating and infalling envelope (Terebey and Shu, & Cassen 1984 ; TSC envelope), which originally describes a power-law density profile (${\rho}{\propto}r-{\alpha}$) with the power-law index (${\alpha}$) of 1.5. However, we find that Herschel/PACS data are better fitted with a shallower power-law density profile. This smaller power-law might be attributed to a inner envelope. Thus, we fit the SED of L1527 IRS with a Bonnor-Ebert sphere, which is a combination of the inner flat-topped and the outer power-law (${\alpha}=2$) density profiles. This Bonnor-Ebert sphere is often used to explain the density profile of prestellar cores, which is considered the earliest stages of star formation. The well-fitted SED with a Bonnor-Ebert sphere suggests that L1527 IRS might have collapsed from a Bonnor-Ebert sphere rather than a singular isothermal sphere.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 추계학술대회 논문집 학회본부 A
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• pp.214-216
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• 2000

This paper presents an comparative study on the effect of STATCOM and UPFC to the power system static analysis. The effect of STATCOM can be analyzed with PSS/E program which is generally used in power system analysis, while UPFC model for static analysis is not provided yet. Thus, UPFC is equivalently represented as a synchronous condenser and load, while the active and reactive power of the specific transmission line and the voltage of the bus is controlled appropriately. This procedure is implemented by IPLAN which is an external macro program of PSS/E. The simulation results show that UPFC is more effective to control the bus voltage than STATCOM, because UPFC can control not only the bus voltage where the parallel inverter is installed but also the active and reactive power flow in the transmission line where the series inverter is installed.

• 한국전자파학회논문지
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• 제12권2호
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• pp.251-256
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• 2001

부분대역 잡음 간섭이 존재하는 Rayleigh fading 전송 채널에서 , MSK 변조방식을 사용하는 hybrid DS/SFH 확산 스펙트럼 시스템의 성능을 분석한다. 비트오율 성능을 수신기에서의 평균 신호 대 잡은 $E_{b}/N_{0}(SNR)$와 신호 대 간섭 비 $E_{b}/N_{J}(SJR)$, 그리고 다양한 채널 파라메터의 함수로 유도한다. 그 결과 집접파 대 간접파의 전력비인 Rician factor K 가 클수록 최악의 BER 성능을 일으키는 것은 부분 대역 간섭이지만, 간접 파만이 존재하는 Rayleigh fading 채널(K=0) 에서는 전 대역 간섭($\rho$=1)이다. 시스템의 성능이 K에 따라서 많은 변화를 보이는데, K=10인 Rician fading 채널에서 $10^{-2}$의 동일한 BER을 얻기 위해 AWGN 채널보다 1.9dB 정도의 SNR을 더 필요로 하지만, K=0인 Rayleigh fading 채널보다 5dB 정도의 SNR이득을 갖는다.

• Bulletin of the Korean Chemical Society
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• 제29권4호
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• pp.790-794
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• 2008

Nucleophilic addition reaction of benzenethiols (PhSH) to 1-(2-nitrovinyl) benzenes ($\beta$ NS) in the presence of triethylamine (TEA) has been studied in acetonitrile at 25 ${^{\circ}C}$. The rate is first order with respect to [PhSH], [TEA] and [$\beta$ NS]. The reaction is found to proceed with the formation of ion-pair between benzenethiol and TEA. A suitable mechanism with the formation of an adduct between ion-pair and substrate in a slow step followed by its rearrangement to 1,2-addition product in a fast step has been proposed and corresponding rate law derived. From the rate law, the rate constants for the interaction between ion-pair and $\beta$NS have been evaluated. Interestingly, in both para-substituted substrates and benzenethiols the rate increases with the electron-withdrawing power of the substituents. The positive sign of $\rho_x$ in benzenethiols has been explained. The magnitude of cross-interaction constant, $\rho_{xy}$ is small (0.08). The magnitude of the Hammett $\rho_x$ values is higher than that of the Bronsted, $\beta_x$ values for benzenethiols. The kinetic isotope effect, $k_H/k_D$, is found to be greater than unity. A suitable transition state with simultaneous formation of $C_\beta$ -H and $B_\alpha$ -S bonds involving the ion-pair and $\beta$NS in a single concerted step has been proposed to account for these observations.

• 디지털콘텐츠학회 논문지
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• 제8권4호
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• pp.491-497
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• 2007

무선 홈 응용을 실현하는데 있어서 근거리 네트워킹 기술의 중요성은 증가하고 있다. 예를 들어, 블루투스와 IEEE 802.11b 표준은 무선 홈 응용 구축을 위한 가장 일반적으로 사용되고 있는 기술들이다. 하지만 두 표준은 동일한 무허가 ISM(Industrial, Scientific, Medical) 무선 스펙트럼 대역을 공유하기 때문에 심각한 간섭을 피할 수 없으며, 두 기술을 사용하는 이종 디바이스가 아주 근접하여 있을 경우에 시스템 성능은 심각하게 손상을 받는다. 본 논문에서 연구한 가우시안 FSK 블루투스 시스템은 전자기기 사이의 무선 연결성을 위한 근거리 무선통신 기술의 표준이다. 본 논문에서는 가우시안 FSK 블루투스 시스템에서 동일채널간섭의 영향을 분석하였다. 본 연구에서 사용한 성능 평가 요소는 무선 채널에서의 SIR, 간섭 지수 $\rho$, 그리고 BER 등이며 이를 기반으로 성능을 평가하였다. 가우시안 FSK 블루투스 시스템의 성능 평가에서 다양한 소스로 부터의 동일채널간섭의 영향은 IGA(Impulsive Gaussian Approximation) 방식을 이용하여 분석하였고 다양한 채널상태를 나타내기 위하여 Eb/No, $\rho$와 SIR 값에 따라서 블루투스 시스템의 성능을 분석하여 결과 그래프에 나타내었다.

• 한국산학기술학회논문지
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• 제8권3호
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• pp.444-453
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• 2007

최근에 전기 아-크로의 보급과 그 운전으로 전력계통에 전압플리커 및 유효전력변동과 같은 전력품질상의 문제가 발생될 가능성이 높은 것으로 보고되고 있다. 이 문제를 해결할 수 있는 방법에는 대표적으로 무효전력보상방법이 있는데, 이것은 유효전력변동의 전력품질문제해결에는 한계가 있다. 따라서, 본 논문에서는 이의 해결책으로서 X/R 비율에 근거한 유효전력보상 개념과 그 최적앨고리즘을 제안하여 이의 타당성을 모델링과 시뮬레이션을 통하여 검증하였다.

• 천문학회보
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• 제41권2호
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• pp.31.3-32
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• 2016

We present the radial variations of the scale heights and the vertical velocity dispersions in a sample of nearby edge-on galaxies using BIMA/CARMA $^{12}CO$ ($J=1{\rightarrow}0$), VLA/EVLA HI, and Spitzer $3.6{\mu}m$ data. Both the disk thicknesses and the velocity dispersions of gas and stars vary with radius, contrary to assumptions of previous studies. We investigate how the interstellar gas pressure and the gravitational instability parameter differ from values derived assuming constant velocity dispersions and scale heights. Using the measurement of the disk thicknesses and the derived radial profiles of gas and stars, we estimate the corresponding volume densities. The gravitational instability parameter Q follows a fairly uniform profile with radius and is ${\geq}1$ across the star-forming disk. The star formation law has a slope that is significantly different from those found in more face-on galaxy studies. The midplane gas pressure appears to roughly hold a power-law correlation with the midplane volume density ratio (${\rho}_{H2}/{\rho}_{HI}$).