• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2008년도 춘계학술대회 논문집
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• pp.70-73
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• 2008

Grounding impedance depends on the frequency of current flowing into a grounding system. Especially, the lightning gives a broad frequency spectrum from low frequency up to 1 MHz. So the grounding impedance related to high frequency current like lightning should be measured with high frequency source. In this paper, we described the grounding impedances of deeply-driven ground rods of 10 ${\sim}$ 48 m long with respect to the frequency of injected currents and the feed point. For the experiments, we used the wideband power amplifier which can produce sinusoidal voltages with the frequency ranges of DC ${\sim}$ 250 MHz. As a result, the longer the ground rod is, the lower the ground resistance is. However the grounding impedance of deeply-driven ground rod in the range of higher frequency is significantly increased. As a consequence, it is important to evaluate the high frequency performance of grounding systems for lightning protection.

• 한국진공학회지
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• 제5권1호
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• pp.73-76
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• 1996

We have prepared hydrogenated amophous silicon (a-si : H) films with superlattice structure by hydrogen radical anneling(HRA) technique. We have studied the preparation of a-Si :H films by HRA and the optical & electronic characteristics. Optical band gap and the hydrogen contents in the a Si : H film is decreased as HRA time increased. We first report a -Si : H film prepared by periodicdeposition of a-Si : H layer and HRA have the superlattice structure using TEM . After 1 hour light soaking on the a-Si :H film prepared by HRA, there are no difference in the temperatre dependence of dark conductivity and the conductivity activation energy. An excellent stability for light in a-Si :H films by HRA can be explained using the long-range structural relaxation of the amorphous network and the propertiesof light -induced defects(LID) proposed by Fritzsche.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 1999년도 추계종합학술대회
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• pp.331-335
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• 1999

LAN, WAN 및 VBR 트래픽 특성에 관한 최근의 실험적 연구들은 기존의 Poisson 가정에 의한 모델들이 네트워크 트래픽의 장기간 의존성 및 self-similar 특성들을 과소평가 함으로써, 실제 트래픽의 특성을 제대로 나타낼 수 없다는 것을 지적해 왔다. 본 본문에서는 실시간 운영중인 Ethernet 트래픽을 측정하여, 통계학적인 접근법들을 통해 이러한 self-similar 특성들에 대해 평가하였다. 그리고 exactly self-similar 모델링인 Pareto-like ON/OFF 소스 모델링에 의한 트래픽과 기존의 Poisson 모델링을 비교 분석함으로써, self-similar 트래픽이 실제의 Ethernet 트래픽 특성을 잘 반영한다는 것을 보였다.

• 한국통신학회논문지
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• 제33권1B호
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• pp.17-24
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• 2008

The effect of the variable packet size on the LRD characteristic of the MMPP traffic model is investigated. When we generate packet traffic for the performance evaluation of IP packet network, MMPP model can be used to generate packet interarrival time. And a random length of packet size from a certain distribution can be assigned to each packet. However, there is a possibility that the variable packet size might change the LRD characteristic of the original MMPP model. In this study, we investigate this possibility. For this purpose the 'refined traffic' is defined, where packet arrival time is generated according to the MMPP model and a random packet length from a specific distribution is assigned to each generated packet. Hurst parameter of the refined traffic is estimated and compared with the original Hurst parameter, which is the input parameter of the MMPP model. We also investigate the effect of the packet size distribution on the queueing performance of the MMPP traffic model and the relationship between the Hurst parameter and queueing performance.

• 대한화학회지
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• 제28권6호
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• pp.361-365
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• 1984

공명 진동${\to}$진동 에너지 이동 과정, $H^{79}Br$(v = 1) + $H^{81}Br$(v = 0) ${\to}$ $H^{79}Br$(v = 0) + $H^{81}Br$(v = 1) + ${\Delta}E\;=\;0.38 cm^{-1}$에 대해 long-lived 충돌모형을 적용하여 에너지 이동 확률을 200 - 800K 범위에서 계산하였다. 계산된 확률은 온도가 상승함에 따라 감소하며 온도 의존성은 P ${\propto}\;T^{-1.8}$이었다. 또한 계산된 확률은 다른 이론들로부터 계산한 확률들 보다 알려져 있는 실험치와 더 잘 일치하였다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제53권8호
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• pp.426-432
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• 2004

This paper presents a systematic approach of measurement, modeling and analysis of grounding system impedance in the field of lightning protection system and intelligent power equipments. The measurement and analysis system of ground impedance is based on a computer aided technique. The magnitude and phase of ground impedance were determined by the novel measurement and analysis using the revised fall-of-potential method. The ground impedances of the ground rod of 50 m long are considerably dependent on the frequency. The ground impedance is mainly resistive in the frequency range of 3-20 kHz. At higher frequencies, the reactive components of the ground impedances are no longer negligible and the inductance of the ground rod was found to be the core factor deciding the ground impedance. Although the steady-state ground resistance of the ground rod of 50 m was less than that of the ground rod of 10 m, the ground impedances of the ground rod of 50 m over the frequency range of more than 60 kHz were much greater than those of the ground rod of 10 m. Furthermore, the equivalent circuit model based on the measured data was proposed. and the calculated results were in approximately agreement with the measured data.

• 대기
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• 제25권1호
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• pp.141-148
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• 2015

Recently increased anthropogenic aerosols change the radiative energy balance and affect human life. The management of air quality requires monitoring both the local emissions and transported pollutants. In order to estimate the quantitative contribution of long-range transport from remote sources on aerosol concentrations in Seoul, the airmasses were classified into five types with respect to their pathways. When airmass came from west over strong emission regions in China, high concentrations of $PM_{10}$, $PM_{2.5}$, black carbon (BC), organic carbon (OC), and elemental carbon (EC) were found, even higher than those for the stagnated airmass. High OC concentrations were found when airmass came from north while BC, EC, and $PM_{2.5}$ concentrations were lower than those of the stagnated airmasses. During dust events, the $PM_{2.5}$ and $PM_{10}$ concentrations increased significantly while carbonaceous aerosol concentrations did not increased. The temporal variations of aerosol concentrations in Seoul were affected by the seasonal variations of airmass pathways. The high $PM_{2.5}$ concentrations over $100{\mu}g\;m^{-3}$ appeared most frequently when the airmasses came from west.

• 한국대기환경학회지
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• 제13권6호
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• pp.451-461
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• 1997

The soil NO flux measurements in Korea were made from 17 May 1997 to 16 June 1997 on grass land at Kunsan National University in southwestern Korea by using flow-through chamber technique. The experiment was conducted in an effort to determine the role of natural emissions of NO on rural atmospheric photochemistry, and to understand the soil NO emission mechanism with respect to soil parameters. Soil NO fluxes were measured every minutes and averaged in every 15 minutes as well as soil temperature. Soil samples were analyzed for $NO_3^-, NH_4^+$, and moisture in soil. Soil nitrate was not detected in most times, and total N-containing was limited in site soils. There was a optimum range of soil moisture and temperature for soil NO flux. The overall average of soil NO emission rates were found to be 1.30 $\pm 0.92 ngNm^{-2}s^{-1}$ (n=1219), and ranged from 0.01 ngNm^{-2}s^{-1}$ to 5.62 ngNm^{-2}s^{-1}$. Diurnal variation of soil NO emission was typical, which was in higher level during daytime, and was in lower level over the night. NO flux showed a strong soil temperature dependence $(r^2=0.78)$, but not with soil moisture and soil N-containing during this experimental period; NO fluxes increased exponentially as soil temperature increased. In order to assure the relevant relationship between soil NO flux and the soil parameters, long-term soil flux measurement on different types of land use should be planned and conducted continuously.

• 한국정보통신학회논문지
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• 제6권3호
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• pp.416-420
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• 2002

네트워크 트래픽의 연구 동향은 LAN, WAN 및 VBR 비디오 트래픽이 통계학적으로 자기 유사과정에 의해 더욱 더 잘 모델링화 된다는 사실을 입증하고 있다. 이것은 기존의 단기간 의존성만을 고려한 포아손 과정에 비해 다른 이론적 특성을 가진다. 즉 광범위한 시계열상에서 aggregation의 정도가 변하더라도 통계학적으로 동일한 특성을 지니게 된다는 것이다. 본 논문에서는 이러한 자기유사과정을 갖는 데이터를 실시간 운영중인 네트워크로부터 측정하여 트래픽을 모델링하고, 비교분석하므로서 다양한 데이터를 지원하는 초고속 네트워크의 성능분석에 적용할 수 있으리라 여겨진다.

• 한국정보통신학회논문지
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• 제6권4호
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• pp.574-581
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• 2002

기존의 큐잉분석은 네트워크 용량설계 및 성능 예측시 상당히 유용하지만, 실제의 경우 큐잉 분석으로부터 예측된 결과는 실제 관측된 성능과는 상당히 다르다. 또한 LAM, WAN 및 VBR 트래픽 특성에 관한 최근의 실험적 연구들은 기존의 Poisson 가정에 의한 모델들이 네트워크 트래픽의 장기간 의존성 및 self-similar 특성을 과소평가 함으로써, 실제 트래픽의 특성을 제대로 나타낼 수 없다는 것을 지적해 왔다. 본 논문에서는 exactly self-similar 모델링인 Pareto-like ON/OFF 소스 모델링에 의한 트래픽과 기존의 Poisson 모델링에 의한 트래픽을 비교 분석함으로써, self-similar 트래픽이 실제의 Ethernet 트래픽 특성을 잘 반영한다는 것을 보임으로써 최적화된 ATM 네트워크 설계 및 성능분석을 이루고자 한다.