• 한국소음진동공학회논문집
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• 제17권2호
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• pp.168-176
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• 2007

The mixture sound speed in bubbly fluids is highly dispersive due to differences of the density and compressibility between bubbles and fluids. The dispersion range in bubbly fluids expands to a higher frequency than the resonance frequency of an air bubble. A theoretical model was developed to compute the reduction of radiation noise that is generated by a force applied on an infinite flat plate using a bubble layer as a compliant baffle. For evaluating the effectiveness of a bubble layer in reducing the structure-borne noise of an infinite elastic plate, the noise reduction levels for various parameters such as the thickness of bubble layers, the volume fractions and the distribution types of bubbly fluids are calculated numerically. The noise reduction effect of an air bubble layer on an infinite flat plate is considerable level and similar to the tendency of dispersion of bubbly fluids. It is recommended that the thickness of a bubble layer should be increased with keeping an appropriate volume fraction of an air bubble for the most effective reduction of the radiation noise.

• 한국자동차공학회논문집
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• 제12권5호
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• pp.58-65
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• 2004

A cylindrical constant volume combustion chamber was used to investigate the combustion characteristics of stratified methane-air mixture under several initial charge conditions in the author's previous reports. The results showed that the improvement of thermal efficiency and reduction of heat loss was realized simultaneously by using 2-stage injection method. This paper deals with the reason why the stratified combustion has showed better combustion rate through the measurement and analysis of chemiluminescence of C $H^{*}$ and $C_{2}$$^{*}$ radicals. An optic fiber bundle is used to measure the local emission of C $H^{*}$ and $C_{2}$$^{*}$ radicals to map the relationship between the excess air ratio and local radical intensity ratio in the combustion vessel at 5 mm apart form the geometric center. The results show that there exist a relationship between the intensity ratio and the air-fuel ratio. It is revealed that the improvement of combustion rate in a lean-stratified mixture is realized through the 2-stage injection method. method.

• 한국환경과학회지
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• 제8권1호
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• pp.33-43
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• 1999

This paper aims to describe the characteristics of air pollution using air pollutants concentration and meteorological data observed at Kimhae from December 1996 to November, 1997. The results are as follows : The concentration distribution of sulfur dioxide($SO_2$), carbon monoxide(CO), particulate matter(PM-10), and nitrogen dioxide($NO_2$) is high during the late fall and winter and low during the summer, but ozone concentration is low during the winter season and high during summer season except Jangma period and these distributions appear to be closely connected with insolation and the number of clear day. Diurnal variation of concentrations for sulfur dioxide, particulate matter, and carbon monoxide are high during the rush hours and nighttime and low during the daytime and these variations are distinct toward the winter season. And diurnal variation of nitrogen dioxide concentration has also same pattern and these patterns are closely related to the increasing traffic volume at rush hours. Diurnal variation of ozone concentration is generally increase for daytime and decrease for the late afternoon and are closely related to the insolation and photochemical reaction. The 24 hour average concentrations of air pollutant observed at Kimhae represented a positive correlation and a negative correlation for $O_3$ and also a negative correlation for the meteorological elements such as wind speed and cloud cover.

• 한국분무공학회지
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• 제9권4호
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• pp.17-23
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• 2004

Spray characteristics of a twin-hole air shrouded nonle designed for gasoline injectors was investigated by using laser diffraction particle analyzer (LDPA) and tomography reconstruction- A confined spray chamber which is optically accessible through a pair of glass windows was made to simulate the fuel injection condition in intake manifold of gasoline engine. The measurement was applied to the twin hole injector with and without an air shroud. It demonstrates that for the case with an air shroud, fine atomization is achieved and there exists a large number of fine droplets between the region of the main spray streams, which conforms with the spray visualization. The drop size distribution was investigated as a function of elapse time after fuel injection. The distribution was greatly affected by the measurement position from the injector exit. Also, the spatially resolved spray volume fraction and Sauter Mean Diameter (SMD) from line-of-sight data of the LDPA are tomographically reconstructed by Convolution Fourier transformation under the steady injection condition.

• 한국환경보건학회지
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• 제25권3호
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• pp.51-57
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• 1999

This study was carried out to investigate the concentrations of Ni, Cr and Cu, to analyze the correlations among those, and between concentrations and traffic volumes by type of car in roadside ambient air at Chongro-, Chungkechon- and Kangnam terminal- area in Seoul from October 1st to October 31st in 1997. The results were as follows ; 1. The means of concentrations of Ni in roadside ambient air were 34.1, 25.1 and 23.6 ng/m$^3$ at Chungkechon, Kangnam terminal and Chongro area, respectively. The highest concentrations of Ni by time were 26.8 in the evening, 45.5 in the evening and 49.4 ng/m$^3$ in the forenoon at Chongro, Chungkechon and Kangnam terminal area, respectively. 2. The means of concentrations of Cr in road side ambient air were 97.7, 80.1 and 70.9 ng/m$^3$ at Chong, Chungkechon and Kangnam terminal area, respectively. The highest concentrations of Cu by time were 205.3 in the evening, 114.4 in the evening and 92.3 ng/m$^3$ in the forenoon at Chongro, Chungkechon and Kangnam terminal area, respectively. 4. The tendencies of concentrations of Ni and Cr by time were similar to each other. Especially, at Kangnam terminal area, correlation coefficients between concentrations of Ni and Cr and the traffic volume of bus were high(r=0.997,0.975). 5. The tendency of concentration of Cu and the traffic volume of passenger car at each area were high(r=0.832, 0.968) 6. Correlation coefficients between Cu and Zn, and between Ni and Cr were 0.762 and 0.842, respectively. This means that the possibility of co-existence of Cu-Zn or Ni-Cr is very high.

• 설비공학논문집
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• 제21권3호
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• pp.186-192
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• 2009

In this study it is intended to review the moving characteristics of smoke by performing visualization for calculation of the optimal smoke exhaust air volume in case a fire occurs in tunnels where transverse ventilation is applied, and to obtain basic data necessary for design of the smoke exhaust systems by deriving optimal smoke exhaust operational conditions under various conditions. As a result of this study, if it was assumed 0 critical velocity in the tunnel, the smoke exhaust air volume was limited within 250 meter in the road-tunnel disaster prevention indicator and the exhaust efficiency was from 55.1% to 95.8% in the result of this study. In case of oversized exhaust ports, the generated smoke is more than the case of uniform exhaust. When the critical velocity in the tunnel is 1.75 m/s and 2.5 m/s, the optimal smoke exhaust air volume has to be more than $173\;m^3/s$, $236\;m^3/s$ for the distance of the moving smoke which can limit the distance to 250 m.

• 한국대기환경학회지
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• 제2권3호
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• pp.11-18
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• 1986

In order to evaluate the state of the environmental pollution by vehicle exhaust in Seoul area the correlation between lead in air and leaves of roadside trees has been investigated during August in 1985. The dust in the atmosphere was collected by high volume air sampler to measure the concentration of lead. On the other hand, lead as a pollution indicator was extracted from the leaves of roadside trees (Ginkgo biloba, Salix pseudo/lasiogyne, platanus occidentalis) by conventional method and their concentrations were determined. The following results were obtained : 1. Lead concentrations in the leaves of roadside trees varied with trees, for example, the average concentrations of lead in each of the leaves of Ginkgo biloba, Salix pseudo/lasiogyne and Platanus occidentalis were 20.66 ppm, 9.37 ppm, and 10.58 ppm, respectively. 2. The dust sampled along heavily traveled highways showed that lead content tended to increase with traffic volume. 3. The correlation coefficients between lead correlation in air and leaves of Gingo biloba, Salix pseudo/lasiogyne, and Platanus orientalis were 0.80, 0.85, and 0.87, respectively.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2012년도 춘계학술발표대회 논문집
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• pp.376-381
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• 2012

Natural gas is converted in to LNG by chilling and liquefying the gas to the temperature of $-162^{\circ}C$, when liquefied, the volume of natural gas is reduced to 1/600th of its standard volume. This gives LNG the advantage in transportation. The pressure dorp of the cascade liquefaction cycle was investigated and simulated using HYSYS software. The simulation results showed that the pressure drop in the LNG heat exchanger is set to 50 kPa considering the increase in the compressor work of cryogenic cascade liquefaction cycle.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.181-183
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• 2004

Conventional VVVF control voltage-fed inverter of blower induction motor has advantage that very speedy response characteristics for air-harmonic. But there have bad power factor on input orient have its large volume and high error ratio over 80%. And there are very expensive by reason of using the capacitor input rectifier. In this paper, It could make the smoothing capacitor-less inverter for air-blower motor by using the instantaneous compensation PWM controller. This inverter system has small volume and value compare with the conventional VVVF control inverter for blower induction motor for air-harmonic equipment.

• 대한의용생체공학회:의공학회지
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• 제32권3호
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• pp.251-256
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• 2011

Virtual colonoscopy is favored over conventional colonoscopy because its non-invasive procedure can avoid complications that may happen in a conventional approach and because it can cleanse colon electronically instead of uncomfortable conventional colon cleansing. Electronic Colon Cleansing(ECC) has to deal with not only removing tagged fecal material but also recovering Partial Volume Effect(PVE) due to tagging material. This paper proposes an ECC method restoring inherent natural PVE while previous approaches focused only on reducing PVE due to tagged fecal material. The proposed method reduces PVE using 3-dimensional adaptive density correction and then replaces tagged fecal material into air. Next, it generates natural PVE for the replaced air adjacent to soft tissue and finally makes smooth transition of gray values for soft tissue adjacent to the replaced air. The proposed method applied to eleven patient data, and showed promising results.