• 한국안전학회지
• /
• 제21권4호
• /
• pp.7-12
• /
• 2006

Recently, the application of transverse ventilation system with oversized exhaust ports has been increased in bidirectional road tunnel in order to improve smoke exhaust ability. Therefore, in this study, for decision of the optimal smoke exhaust rates in the transverse ventilation system, several standards of nations are compared and numerical simulations with variations of exhaust flow rates are carried out in terms of smoke spread distance by FDS ver. 3.1. As results, in the case of no internal longitudinal air velocity in tunnel, the smoke exhaust rate of $80m^{3}/s$ (the smoke generation rate at HRR of 20MW) is sufficient enough to limit the smoke spread within 250m in 6 minutes after the fire. However, in the case of the internal longitudinal air velocity at 2.5m/s, the smoke exhaust rate should be increased $130m^{3}/s$.

• 한국항행학회논문지
• /
• 제3권2호
• /
• pp.167-173
• /
• 1999

본 논문에서는 적응 sidelobe canceller에 Howells-Applebaum과 DMI 알고리즘을 적용하여 수렴속도와 간섭제거 성능을 알아보았다. Applebaum 알고리즘은 계산상의 간단함으로 많이 이용되어지지만 수렴속도가 느리고 eigenvalue spread에 영향을 받는다. 반면에 DMI는 Applebaum 알고리즘에 비해 빠른 수렴속도를 보이나 계산 및 구현이 복잡하다. 빠른 수렴속도와 우수한 간섭제거성능을 요구하는 적응 SLC(sidelobe canceller)에 이 두 알고리즘을 적용하여 성능 및 계산의 복잡성을 비교해 보고 적응 SLC에 DMI 알고리즘이 더 적합함을 보인다.

• The Journal of Asian Finance, Economics and Business
• /
• 제7권11호
• /
• pp.45-53
• /
• 2020

Past literatures have not studied the impact of real-world events or information on the return and volatility of virtual currencies, particularly on the COVID-19 event, day-of-the-week effect, daily high-low price spreads and information flow rate. The study uses the ARMA-GARCH model to capture Bitcoin's return and conditional volatility, and explores the impact of information flow rate on conditional volatility in the Bitcoin market based on the Mixture Distribution Hypothesis (Clark, 1973). There were 3,064 samples collected during the period from 1^st of January 2012 to 20^th April, 2020. Empirical results show that in the Bitcoin market, a daily high-low price spread has a significant inverse relationship for daily return, and information flow rate has a significant positive relationship for condition volatility. The study supports a significant negative relationship between information asymmetry and daily return, and there is a significant positive relationship between daily trading volume and condition volatility. When Bitcoin trades on Saturday & Sunday, there is a significant reverse relationship for conditional volatility and there exists a day-of-the-week volatility effect. Under the impact of COVID-19 event, Bitcoin's condition volatility has increased significantly, indicating the risk of price changes. Finally, the Bitcoin's return has no impact on COVID-19 events and holidays (Saturday & Sunday).

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2014년도 제49회 KOSCO SYMPOSIUM 초록집
• /
• pp.187-190
• /
• 2014

An experimental study on downwardly and upwardly spreading flames over slanted electrical wire, which is insulated by Polyethylene(PE), was conducted with applied AC electric field. The result showed that downwardly and upwardly spreading flames with angle of inclination leaned toward burnt side and unburned side, respectively. With applied AC electric fields, size of downwardly spreading flame decreased slightly and that of upwardly spreading flame increased significantly. Flame spread rate showed various trends in terms of inclination, applied voltage and frequency.

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2014년도 제49회 KOSCO SYMPOSIUM 초록집
• /
• pp.363-365
• /
• 2014

An experimental study on effect of AC electric field on upwardly spreading flame over electrical wire, which is insulated by Polyethylene(PE), was conducted. The result showed that upwardly spreading flame leaned toward unburned side with angle of inclination. With applied electric field, size of upwardly spreading flame increased significantly. Flame spread rate showed various trends with inclination, applied voltage and frequency.

• Journal of Communications and Networks
• /
• 제8권2호
• /
• pp.220-227
• /
• 2006

In this paper, we present a novel approach to analyze the throughput of direct-sequence spread spectrum multiple access (DS/SSMA) unslotted ALOHA system. In the unslotted system, the departure rate of interfering transmissions is proportional to the number of current interferers that can be regarded as the system state. In order to model this state-dependency, we introduce a two-dimensional state transition model that describes the state transition of the system. This model provides a more rigorous analysis tool for the DS/SSMA unslotted ALOHA systems with both fixed and variable packet lengths. Numerical results reveal that this analysis yields an accurate system performance that coincides with the simulation results. Throughout the analysis we have discovered that the state-dependency of the departure rate causes interference averaging effect in the unslotted system and that this effect yields a higher throughput for the unslotted system than for the slotted system when supported by a strong channel coding.

• 전자공학회논문지A
• /
• 제33A권11호
• /
• pp.19-31
• /
• 1996

Spread spectrum method gurantees good performance in digital communication system under multi-path interference and jamming signals. The purpose of this paper is to develop the wireless modem using DS/SS techinque. The transceiver consists of a spread spectrum DQPSK transmitter and a mtching receiver. The system operates with the chipping rate set to 4 Mcps and the number of chips/symbol at 64, making the data rate 62.5 Kbps using QPSK modilation. The receiver section uses a digital matched filter for fast acquisition of burst signals and uses the comparing the BER of proposed system iwth that of narrow bnd system under various additive white gaussian noises. It is showen that the proposed sysem has better performance than narrow band system. When jamming signals is added to the suggested DS/SS system, we also show that the experimental performance (BER) of the suggested wireless modem is almost same as theroretical performance.

• 한국통신학회논문지
• /
• 제19권5호
• /
• pp.939-951
• /
• 1994

최소 평균 제곱(least mean squares) 알고리듬에 기반을 둔 적응 동화기의 수렴속도는 입력신호의 공분산 행렬에 의해 결정된다. 공분산 행렬의 고유값 spread가 1에 가까울때 수렴속도는 매우 빠르다. 본 논문에서는 LMS 기반 적응 동화기의 빠른 수렴을 위해 통계적으로 주어진 채널에 적합한 변형된 기준신호를 제안하였다. 이론적인 분석과 모의실험을 통해 LMS 기반 적응 동화기의 빠른 수렴을 얻는데 이 변형 방법이 효과적임을 알 수 있었다.

• Journal of Communications and Networks
• /
• 제14권2호
• /
• pp.206-212
• /
• 2012

In this paper, in order to effectively apply unitary space-time modulation to the direct-sequence spread-spectrum multiple-access (DSSS-MA) networks, we propose a low-rate, noncoherent, unitary, and space-time modulated DSSS system supporting any number of transmit antennas based on Walsh matrices. The proposed scheme simultaneously performs bandwidth spreading and space-time coding and outperforms those using high-rate, conventional unitary space-time constellations. Furthermore, the proposed scheme allows for a simple detector structure based on fast Walsh transforms.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2018년도 추계 학술논문 발표대회
• /
• pp.61-62
• /
• 2018

On this Study, it conducts the Standards investigation about air leakage of Buildings for performance improvement of Smoke control in Fire. In domestic standards, it is incomplete the Criteria standards of air leakage. Therefore it is considered that won't limit the smoke spread due to stack effect. But in the case of the United States, it conducts the Hot smoke air-Leakage test and it consider that can prevent the Smoke Spread in Compartment.