• 말소리와 음성과학
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• 제7권3호
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• pp.45-53
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• 2015

The current study investigated CVCC syllables in spontaneous American English speech to find out whether such syllables are produced as phonological units with a string of segments, showing a hierarchical structure. Transcribed data from the Buckeye Speech Corpus was used for the analysis in this study. The result of the current study showed that the constituents within a CVCC syllable as a phonological unit may have phonetic variations (namely, the final coda may undergo deletion). First, voiceless alveolar stops were the most frequently deleted when they occurred as the second final coda consonants of a CVCC syllable; this deletion may be an intermediate process on the way from the abstract form CVCC (with the rime VCC) to the actual pronunciation CVC (with the rime VC), a production strategy employed by some individual speakers. Second, in the internal structure of the rime, the proportion of deletion of the final coda consonant depended on the frequency of the word rather than on the position of postvocalic consonants on the sonority hierarchy. Finally, the segment following the consonant cluster proved to have an effect on the reduction of that cluster; more precisely, the following contrast was observed between obstruents and non-obstruents, reflecting the effect of sonority: when the segment following the consonant cluster was an obstruent, the proportion of deletion of the final coda consonant was increased. Among these results, the effect of word frequency played a critical role for promoting the deletion of the second coda consonant for clusters in CVCC syllables in spontaneous speech. The current study implies that the structure of syllables as phonological units can vary depending on individual speakers' lexical representation.

• Journal of Microbiology and Biotechnology
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• 제20권4호
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• pp.789-797
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• 2010

The limited information on differential gene expression in the different serotypes of Actinobacillus pleuropneumoniae has significantly hampered the research on the pathogenic mechanisms of this organism and the development of multivalent vaccines against A. pleuropneumoniae infection. To compare the gene expressions in the A. pleuropneumoniae strains CVCC259 (serotype 1) and CVCC261 (serotype 3), we screened the differentially expressed genes in the two strains by performing representational difference analysis (RDA). Northern blot analyses were used to confirm the results of RDA. We identified 22 differentially expressed genes in the CVCC259 strain and 20 differentially expressed genes in the CVCC261 strain, and these genes were classified into 11 groups: (1) genes encoding APX toxins; (2) genes encoding transferrin-binding protein; (3) genes involved in lipopolysaccharide (LPS) biosynthesis; (4) genes encoding autotransporter adhesin; (5) genes involved in metabolism; (6) genes involved in the ATP-binding cassette (ABC) transporter system; (7) genes encoding molecular chaperones; (8) genes involved in bacterial transcription and nucleic acid metabolism; (9) a gene encoding protease; (10) genes encoding lipoprotein/membrane protein; and (11) genes encoding various hypothetical proteins. This is the first report on the systematic application of RDA for the analysis of differential gene expression in A. pleuropneumoniae serotypes 1 and 3. The determination of these differentially expressed genes will serve as an indicator for future research on the pathogenic mechanisms of A. pleuropneumoniae and the development of a multivalent vaccine against A. pleuropneumoniae infection.

• 한국분무공학회지
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• 제10권2호
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• pp.41-47
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• 2005

Exhaust gas emissions from internal combustion engines are one of the major sources of air pollution. And. it is extremely difficult to increase gasoline engine efficiency and to reduce NOx and PM(particulate matter) simultaneously in diesel combustion. This paper offers some basic concepts to overcome the above problems. To solve the problems, a recommended technique is CAI(controlled auto-ignition) combustion. In this paper. internal EGR(exhaust gas recirculation) effect is suggested to realize CAI combustion. An experimental study was carried out to achieve CAI combustion using homogeneous premixed gas mixture in the constant volume combustion chamber(CVCC). A flame trap was used to simulate internal EGR effect and to increase flame propagation speed in the CVCC. Flame propagation photos and pressure signals were acquired to verify internal EGR effect. Flame trap creates high speed burned gas jet. It achieves higher flame propagation speed due to the effect of geometry and burned gas jet.

• 에너지공학
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• 제13권4호
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• pp.311-318
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• 2004

본 연구에서는 정적연소실을 이용하여 차량용 대체연료로써 메란 및 수소첨가 메탄의 연소특성을 수소첨가율, 점화위치 및 점화방법에 따라 고찰하였다. 그 결과, 중심점화이고 수소를 첨가하지 많은 순수 메탄의 화염전파과정은 타원형으로 전파하나 수소첨가율이 증가함에 따라 화염면상에 매우 규칙적인 세포구조를 가진 불안정한 타원형화염으로 천이되었고 연소속도도 증가하였다. 또한, 벽면 및 0.5R 점화이고 수소를 첨가하지 않은 순수 메탄의 화염전파과정은 불안정한 타원형으로 전파하고 있었지만, 수소첨가율이 증가함에 따라 연소중기에 불안정한 타원형에서 평면형으로 천이 됐다가 연소말기에는 화염면 선단이 움푹 패인 매우 불규칙한 세포구조를 갖는 패기형으로 변화되었으며 연소속도도 증가하였다 한편, 세 가지 점화위치 모두에 있어서 MSCDI와 CDI사용에 따른 화염전파형태는 외견상 큰 차이는 없었지만, 동일시간에 MSCDI장치의 화염면적은 CDI의 화염면적보다 약간 더 크게 나타났다.

• 한국분무공학회지
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• 제18권4호
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• pp.188-195
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• 2013

An investigation on spray characteristics of fuels which diesel and di-methyl ether (DME) with change of injection pressure used the multi-injection in constant volume combustion chamber (CVCC). Diesel was already used famous fuel which we could use. DME showed similar features with diesel like as cetane number, auto-ignition temperature. High cetane number of diesel and DME could make possible to compression ignition. DME showed different atomization from diesel due to evaporating pressures and boiling points. Experiments were carried out in CVCC equipped with Delphi solenoid 6-hole type injector and the spray characteristics of diesel and DME were tested the various pre and pilot injection. Terms of injections and a number of injections in multi-injection has been controlled. Experiments were performed in 2 types that 1500 rpm, 2000 rpm and under the condition of injection ranging from 100 bar to 500 bar. From the results of this experiment diesel showed longer spray penetration than DME. That result showed different of atomization speed DME and diesel. Result of high injection pressure condition showed similar spray characteristics diesel and DME. After this investigation, new conditions and experiments using laser light to go forward and add the fuels like as the biodiesel and diesel and DME blend.

• 한국분무공학회지
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• 제19권4호
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• pp.188-196
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• 2014

The spray and combustion characteristics of n-dodecane fuel were investigated in a CVCC (constant volume combustion chamber). The selection of ambient conditions for the spray followed ECN (engine combustion network) guidelines, which simulates the ambient condition of diesel engines at start of fuel injection. ECN is a collaboration network whose main objective is to establish an internet library of well-documented experiments that are appropriate for model validation and the advancement of scientific understanding of combustion at conditions specific to engines. Therefore repeatability of the experiments with high accuracy was important. The ambient temperature was varied from 750 to 930 K while the density was fixed at around $23kg/m^3$. The injection pressure of the fuel was varied from 500 to 1500 bar. The spray was injected in both non-reacting ($O_2$ concentration of 0%) and reacting conditions ($O_2$ concentration of 15%) to examine the spray and the combustion characteristics. Direct imaging with Mie Scattering was used to obtain the liquid penetration length. Shadowgraph was implemented to observe vapor length and lift-off length at non-reacting and reacting conditions, respectively. Pressure data was analyzed to determine the ignition delay with respect to the spray and ambient conditions.

• 에너지공학
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• 제12권2호
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• pp.124-130
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• 2003

본 연구에서는 정적연소실을 이용하여 차량용 대체연료로써 메탄 및 수소첨가 메탄의 연소특성을 수소첨가율, 점화위치 및 점화방법에 따라 고찰하였다. 그 결과 연소효율, 최고연소압력 등과 같은 연소특성을 악화시키지 않고 희박 혼합기 조건하에서도 MSCDI 장치 사용에 의해 전 연소시간과 NO 농도를 저감시킬 수 있었다. 또한, 수소를 천연가스의 주 성분인 메탄에 혼합함에 따라 전 연소시간은 순수 메탄만을 사용할 때에 비해 단축되었으며, 이와 동시에 연소촉진율도 순수 메탄만을 사용하였을 때에 비해 상당히 향상되었다.

• 한국분무공학회지
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• 제20권1호
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• pp.43-52
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• 2015

Experimental study was conducted to investigate the effects of ultra-high injection pressure and nozzle hole diameter on diesel flow and spray characteristics. Electronically controlled ultra-high pressure fuel injection system was made to supply the fuel of ultra-high pressure consistently. Three injection pressures, 80, 160, and 250MPa were applied. Four type of injectors with identical eight nozzle holes were used. The four injectors have nozzle hole diameters of 115, 105, 95, and $85{\mu}m$ respectively. Injection quantity and rate were measured to investigate flow characteristics according to injection pressures and nozzle hole diameters. Mie-scattering and shadowgraph were performed to visualize liquid and vapor phases of diesel spray in a constant volume combustion chamber (CVCC). Ambient conditions of high pressure and high temperature in a diesel engine were simulated by using CVCC.

• 한국자동차공학회논문집
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• 제13권2호
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• pp.22-28
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• 2005

Exhaust gas emissions from internal combustion engines are one of the major sources of air pollution. And, it is extremely difficult to increase gasoline engine efficiency and to reduce $NO_X$ and PM(particulate matter) simultaneously in diesel combustion. This paper offers some basic concepts to overcome the above problems. To solve the problems, a recommended technique is CAI(controlled auto-ignition) combustion. In this paper, a flame trap was used to simulate internal EGR(exhaust gas recirculation) effect. An experimental study was carried out to find combustion characteristics using homogeneous premixed gas mixture in the constant volume combustion chamber(CVCC). Flame propagation photos and pressure signals were acquired to verify the flame trap effect. The flame trap creates high speed burned gas jet. It achieves higher flame propagation speed and more stable combustion due to the effect of geometry and burned gas jet.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 2010년도 춘계학술 발표회
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• pp.59-63
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• 2010

토치 점화 장치의 연소 특성을 파악하기 위하여 7개의 각기 다른 토치 점화 장치를 설계하였다. 토치 점화장치의 오리피스 직경에 따른 특성을 파악하기 위하여, 토치 점화 장치의 체적과 높이는 고정하고, 오리피스 직경을 4mm에서 16mm까지 2mm씩 증가시키며 실험하였다. 초기 화염 생성 및 전파는 질량 연소율과 연소 촉진율로 분석하였다. 질량 연소율과 연소 촉진율을 계산하기 위하여 정적 연소실 내의 평균 압력을 측정하였다. 또한 shadow graph법을 이용하여, 초기 화염 생성과 화염 전파과정 전 영역을 가시화하였다. 토치 점화 장치를 사용한 경우에는 일반적인 스파크 점화와 비교하여 질량 연소율의 기울기가 증가하였고, 연소 촉진율도 개선된것을 확인하였다. 또한 가시화된 이미지를 확인한 결과 토치 점화 장치를 사용하면 초기 화염 발달 단계에서 화염이 난류 화염으로 천이되어 연소가 촉진된것을 확인하였다.