• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2013.04a
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• pp.116-116
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• 2013

마그네슘은 스마트폰, 전자기기 케이스, 내화벽돌과 아크용접봉 제조시의 첨가물 등으로 사용되고 있는데, 최근에는 재활용을 위한 마그네슘 용해로를 취급하거나 가공하는 사업장이 증가하고 있어 사고위험성이 높아지고 있다. 금속분을 취급하는 사업장에서의 금속분진은 저장이나 축적 등과 같이 주로 퇴적물로서 존재한다. 퇴적분진의 발화온도는 퇴적물 형상과 두께, 입경, 분위기 가스의 유속, 산소농도, 부유분진의 농도, 퇴적밀도, 수분 등의 많은 영향인자가 관여하기 때문에 이론적 예측이 힘들고 실험적인 측정에 의존할 수 밖에 없는 것이 현실이다. 본 연구에서는 연소성이 높고 화재폭발사고사례가 많은 마그네슘(Mg) 분진을 사용하여 승온속도 변화에 따른 열분해특성을 조사하였다. 퇴적분진의 열적특성을 조사하기 위하여 METTLER TOLEDO의 TGA/DSC1를 사용하였으며, Mg 시료의 평균입경은 38, $142{\mu}m$이다. 입경 $38{\mu}m$의 Mg 시료의 열중량분석 결과, 중량증가는 $400{\sim}500^{\circ}C$의 범위에서 시작되며 $550^{\circ}C$에서 급격하게 중량이 증가하고 있으며, 증량증가개시온도(Temperature of weight gain)는 $460^{\circ}C$에서 시작하여 $900{\sim}950^{\circ}C$ 범위에서 중량 증가 포화값에 도달하였다. 입경 $142{\mu}m$의 Mg에 대하여 공기중 승온속도를 5, 10, $20^{\circ}C/min$으로 변화시키면서 실온에서 $900^{\circ}C$까지 가열 시키는 경우의 시료의 중량 변화에 따른 열분해 특성은 승온속도가 증가할수록 2단계의 S자 곡선은 완만하게 상승을 나타내며 중량증가개시온도가 높아지는 경향을 보이고 있다. 중량증가개시온도가 승온속도에 따라 변화하는 결과를 나타내고는 있지만, 시료량의 증가에 따른 영향을 열중량분석 실험방법의 제약으로 인하여 확인할 수 가 없었다. 그러나 만일 시료량이 크게 증가하는 경우에는 동일한 승온조건에서 중량증가 개시온도는 낮아질 가능성이 있다. 중량증가는 시료의 산화반응에 의한 것이므로 시료량의 증가는 시료 내부에의 열의 축적을 용이하게 하여 보다 낮은 온도에서도 산화반응이 충분히 일어나는 조건이 형성되기 때문이다. 승온속도가 증가할수록 산화 반응한 괴상형태의 연소입자가 크게 증가하고 있는 것을 알 수 있다. 승온속도에 따른 중량개시온도 곡선을 보면 [그림 24]와 같으며 승온속도 5, 10, $20^{\circ}C/min$의 증가에 따라 중량개시온도는 각각 490, 510, $530^{\circ}C$가 얻어졌으며 승온속도의 증가에 따라 중량개시온도가 증가하는 경향을 보이고 있다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.6
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• pp.154-160
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• 2020

This study analyzed the fire intensity according to the zones classification between traditional market stores using FDS software. Modeling was conducted for the Seomoon traditional market district 4 at Daegu, which places combustibles, such as textiles and clothing near the passageway. The first ignition point assumed a short circuit fire situation at the fourth store combustible. The analysis was conducted under similar conditions as the fire situation in 2016. When there was no section wall, the fire spread rapidly through radiation in all directions from the fire-origin point. After 600 seconds, the mall was burnt to the ground. When section walls were present, however, the fire could be restricted inside the compartment. The first intensity of the two analysis conditions was predicted from the total heat energy from 200 seconds (X₁) to 600 seconds (X₂), where the heat generation rate began to increase rapidly. As a result of installing section walls near the fire point, heat energy generation of approximately 11.12 MW (55.68 %) was delayed. Further analysis of smoke control, according to the section wall arrangement and re-installation facilities, will be needed to study the characteristics of fire in traditional markets comprehensively.

• Journal of the Korean Institute of Gas
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• v.19 no.5
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• pp.75-80
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• 2015

Aluminum dusts, from micro to nano-scale, are widely used in various applications such as propulsion and pyrotechnic compounds because of high burning rate. In this study, the pyrolysis hazard of aluminum dusts with different median size (sized by 70 nm, 100 nm, $6{\mu}m$, $15{\mu}m$) were investigated experimentally. The thermal decomposition characteristics of aluminum dusts with the variation of heating rate were investigated using TGA (Thermo gravimetric analysis) and was estimated the minimum ignition temperature from temperature of weight gain in nano and micro-sized aluminum dusts with different diameter. In the same condition of heating rate, the temperature of weight gain in aluminum dust layers increased with increasing of particle size and increased with increasing of heating rates in air. From the results, it was estimated that the pyrolysis hazard of aluminum dusts decrease with increasing of mean diameter.

• Korean Chemical Engineering Research
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• v.51 no.1
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• pp.121-126
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• 2013

The objective of this research is to predict the TG curve of blends of bituminous coal and sub-bituminous coal during devolatilization. TSL (Thermal Shock Large) TGA was used for Experiments, and Coats-redfern method was used for reaction order calculation. Based on reaction order, sum method was verified to be suitable for a single coal, then, prediction and comparison of TG curve of coal blends was conducted using both of WSM (Weight Sum Method) and MWSM (Modified Weight Sum Method), where the latter was developed in this research. The presented experiment results and WSM & MWSM were showed to be reasonable using linear least square method. MWSM performed more accurately than WSM for the case that TG curve had different slopes and the case that sharp weight loss happened due to release of volatile matter. The results showed that it's possible to predict the thermal behavior of coal blends during devolatilization based on the thermal behavior of single coals.

• Fire Science and Engineering
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• v.30 no.3
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• pp.104-109
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• 2016

Candle fires do not occur frequently, but can easily result in death. In this study, the thermal characteristics of candles and conditions and debris of candle fires were investigated to determine the causes of candle fires. The rates of decrease in weight of 10 candles were measured and found to be between 2.6 g/h and 6.7 g/h. Most candle fires are caused by the ignitiong of combustible materials close to them. The temperature near a candle ranges from about $200^{\circ}C$ to $400^{\circ}C$ at a distance of 1 cm and low ignition temperature materials such as papers can easily catch fire. The melting temperature of candles ranges between $50^{\circ}C$ and $70^{\circ}C$ and their major chemical components are fatty acids and normal hydrocarbons (over C20). Using pretreatment conditions involving the use of activated charcoal strips at $150^{\circ}C$ for 16 hours, the fire debris including candle residues were analyzed using a Gas-chromatograph/Mass-spectrometer (GC/MS).

• Phonetics and Speech Sciences
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• v.4 no.3
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• pp.143-149
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• 2012

The purpose of this study is to investigate the speech rate of an esophageal speech group that is capable of vocalization after surgery. The subjects in this experiment were 10 male esophageal speakers and 10 male laryngeal speakers. Each group read a reading passage that was recorded by a DAT recorder (Rolando, EDIROL R-09). These records were analyzed by using CSL (Computerized Speech Lab, model 4150). The results were as follows: (1) the overall speech rate of esophageal speech was 2.50 SPS (syllable per second) while the overall speech rate of laryngeal speech was 4.23 SPS. (2) The articulatory rate of esophageal speech was 3.14 SPS (syllable per second) while the articulatory rate of laryngeal speech was 4.75 SPS. Speech rates as well as articulatory rates of esophageal speech were significantly lower than laryngeal speech. These differences between the two groups may be due to reduced efficiency of airflows across the pharyngeal-esophageal segment for esophageal speakers when compared to airflow through the glottis for laryngeal speakers. These results would provide a guideline in speech rates for esophageal speakers in clinical settings.

• Annual Conference on Human and Language Technology
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• 2018.10a
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• pp.210-214
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• 2018

본 논문에서는 한국어 대화 엔진에서의 문장 분류 방법에 대해서 소개한다. 문장 분류시 말뭉치에서 관찰되지 않은 표현들을 포함한 입력 발화를 처리하기 위하여, 태깅되지 않은 뉴스 데이터로부터 일반적인 단어 의미 벡터들이 훈련 및 성능 평가되었고, 이를 문장 분류기에 적용하였다. 또한, 실 서비스에 적용 가능한 빠른 분류 속도를 유지함과 동시에 문제에 특화된 의미 벡터들을 학습하기 위하여, 기존에 사용되던 캐릭터 기반 의미 벡터 대신 도메인 특화 단어 의미 벡터의 사용이 제안되었다. 실험 결과, 자체 구축된 테스트 말뭉치에 대하여 본 논문에서 제안된 시스템은 문장 단위 정확률 96.88, 문장당 평균 실행 시간 12.68 msec을 기록하였다.

• Phonetics and Speech Sciences
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• v.9 no.1
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• pp.27-39
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• 2017

This paper deals with how speech rate in Korean is affected by the sociolinguistic factors such as region, gender and generation. Speech rate was quantified as articulation rate (excluding physical pauses) and speaking rate (including physical pauses), both expressed as the number of syllables per second (sps). Other acoustic measures such as pause frequency and duration were also examined. Four hundred twelve subjects were chosen from Korean Standard Speech Database considering their age, gender and region. The result shows that generation has a significant effect on both speaking rate and articulation rate. Younger speakers produce their speech with significantly faster speaking rate and articulation rate than older speakers. Mean duration of total pause interval and the total number of pause of older speakers are also significantly different to those of younger speakers. Gender has a significant effect only on articulation rate, which means male speakers' speech rate is characterized by faster articulation rate, longer and more frequent pauses. Finally, region has no effect both on speaking and articulation rates.

• Phonetics and Speech Sciences
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• v.6 no.4
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• pp.79-90
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• 2014

An intonation curve stylization was used for an acoustical analysis of English speech. For the analysis, acoustical feature values were extracted from 1,848 utterances produced with normal and fast speech rate by 28 (12 women and 16 men) native speakers of English. Men are found to speak faster than women at normal speech rate but no difference is found between genders at fast speech rate. Analysis of pitch point features has it that fast speech has greater Pt (pitch point movement time), Pr (pitch point pitch range), and Pd (pitch point distance) but smaller Ps (pitch point slope) than normal speech. Men show greater Pt, Pr, and Pd than women. Analysis of sentence level features reveals that fast speech has smaller Sr (sentence level pitch range), Sd (sentence duration), and Max (maximum pitch) but greater Ss (sentence slope) than normal speech. Women show greater Sr, Ss, Sp (pitch difference between the first pitch point and the last), Sd, MaxNr (normalized Max), and MinNr (normalized Min) than men. As speech rate increases, women speak with greater Ss and Sr than men.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.2
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• pp.389-396
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• 1994

It is very important to clarify the ignition and flame propagation processes of methanol fuel in the Spark-ignition engine. High speed Schlieren photography and pressure trace analyses were used to study on combustion characteristics of methanol fuel in a constant volume chamber. Methanol-air mixtures equivalence rations from lean limit to 1.4 were ignited at initial pressure (0.1, 0.3, 0.5 MPa), temperature (313 343, 373 K) and ignition energy (40, 180 mJ). As the result of this study, we verified the characteristics such as ignition delay, effective thermal efficiency, flame propagation velocity, lean limit, ignitability and combustion duration. Obatained results are as follows. (1) The time to 10% reach of maximum pressure was 40-50% of the total combustion duration for this experimental condition hardly affected by equivalence ratio. (2) The Effective thermal efficiency, as calculated from maximum pressure was the highest when the mixture was slightly lean $({\phi} 0.8-0.9)$ and maximum pressure was the highest when the mixiture was slightly rich $({\phi} 1.2-1.2).$