• 한국대기환경학회지
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• 제23권2호
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• pp.225-241
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• 2007

A closed flux chamber system was used for measuring major greenhouse gas (GHG) emission from tideland and/or wetland soils in estuarine area at Saemankum, Kunsan in southwestern Korea during from months of February to June 2006. Hourly averaged GHG soil emissions were measured two to three times a day during the ebb tide hours only. Site soils were analyzed for soil parameters (temperature, pH, total organic contents, N and C contents in soil) in the laboratory. Soil GHG fluxes were calculated based on the GHG concentration rate of change measured inside a closed chamber The analysis of GHG was conducted by using a Gas Chromatography (equipped with ECD/FID) at laboratory. Changes of daily, monthly GHGs' fluxes were examined. The relationships between the GHG emissions and soil chemical contents were also scrutinized with respect to gas production and consumption mechanism in the soil. Soil pH was pH $7.47{\pm}0.49$ in average over the experimental period. Organic matter contents in sample soil was $6.64{\pm}4.98\;g/kg$, and it shows relatively lower contents than those in agricultural soils in Kunsan area. Resulting from the soil chemistry data, soil nitrogen contents seem to affect GHG emission from the tidal land surface. The tidal soil was found to be either source or sink for the major GHG during the experimental periods. The annual average of $CH_{4}\;and\;CO_{2}$ fluxes were $0.13{\pm}0.86\;mg\;m^{-2}h^{-1}\;and\;5.83{\pm}138.73\;mg\;m^{-2}h^{-1}$, respectively, which will be as a source of these gases. However, $N_{2}O$ emission showed in negative flux, and the value was $-0.02{\pm}0.66\;mg\;m^{-2}h^{-1}$, and it implies tidal land surface act as a sink of $N_{2}O$. Over the experimental period, the absolute values of gas fluxes increased with soil temperature in general. Averages of the ambient gas concentration were $86.8{\pm}6.\;ppm$ in $CO_{2},\;1.63{\pm}0.34\;ppm\;in\;CH_{4},\;and\;0.59{\pm}0.15\;ppm\;in\;N_{2}O$, respectively. Generally, under the presence of gas emission from agricultural soils, decrease of gas emission will be observed as increase in ambient gas concentration. We, however, could not found significant correlation between the ambient concentrations and their emissions over the experimental period. There was no GHG compensation points existed in tide flat soil.

• 한국전기전자재료학회논문지
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• 제27권4호
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• pp.257-261
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• 2014

Carbon nanotubes (CNT) has the excellent physical characteristics in the sensor, medicine, manufacturing and energy fields, and it has been studied in those fields for the several years. We fabricated the NOx gas sensors of MOS-FET type using the MWCNT. The fabricated sensor was used to detect the NOx gas for the variation of $V_{gs}$ (gate-source voltage) with the ambient temperature. The gas sensor absorbed the NOx gas molecules showed the decrease of resistance, and the sensitivity of sensor was reduced by the NOx gas molecules accumulated on the MWCNT surface. Furthermore, when the voltage ($V_{gs}$) was applied to the gas sensor, the term of the decrease in resistance was increased. On the other hand, the sensor sensitivity for the injection of NOx gas was the highest value at the ambient temperature of $40^{\circ}C$. We also obtained the adsorption energy ($40^{\circ}C$) using the Arrhenius plots by the reduction of resistance due to the $V_{gs}$ voltage variations. As a result, we obtained that the adsorption energy also was increased with the increasement of the applied $V_{gs}$ voltages.

• 대한전자공학회논문지
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• 제25권4호
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• pp.407-416
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• 1988

Thick film city gas sensors were fabricated using \ulcornerFe2O3 and \ulcorner-Fe2O3 as raw materials. Their electrical properties and sensitivity characteristics were investigated and the surface conditions for various firing temperatures were analyzed. The fabricated devices exhibited high sensitivity to butane gas(75~80% n 1, 000ppm butane ambient). Also they showed good selectivity and long-term stability. A city gas alarm system using fabricated sensors was made for the practical application.

• Bulletin of the Korean Chemical Society
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• 제35권10호
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• pp.2995-3000
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• 2014

A sensitive concentration method utilising modified gas-purge microsyringe extraction (GP-MSE) was developed. Concentration (reduction in volume) to a microlitre volume was achieved. PAHs were utilised as semivolatile analytes to optimise the various parameters that affect the concentration efficiency. The injection rate and temperature were the key factors that affected the concentration efficiency. An efficient concentration (75.0-96.1%) of PAHs was obtained under the optimised conditions. The method exhibited good reproducibility (RSD values that ranged from 1.5 to 9.0%). The GP-MSE concentration method enhances the volume reduction (concentration factor), leading to a low method detection limit ($0.5-15ngL^{-1}$). Furthermore, this method offers the advantage of small-volume sampling, enabling even the detection of diurnal hourly changes in the concentration of PAHs in ambient air. Utilising this method in combination with GC-MS, the diurnal hourly flux of PAHs from the gas phase of ambient air was measured. Indeed, the proposed technique is a simple, fast, low-cost and environmentally friendly.

• 한국지하수토양환경학회지:지하수토양환경
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• 제14권6호
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• pp.87-94
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• 2009

대수층에 존재하는 휘발성 오염물질을 제거하는 새로운 공법으로서 Surfactant-enhanced air sparging(SEAS)은 지하수의 표면장력을 감소함으로써 지하수 폭기효율의 증대를 도모한다. 그러나 SEAS기술도 기본적으로 오염물질의 휘발에 의한 물질이동에 의존함으로써 휘발성이 낮은 오염물질의 제거에는 매우 제한적이다. 본 연구는 승온된 조건에서 SEAS기술을 준휘발성 물질인 n-decane에 대하여 적용함으로써 SEAS기술의 확장여부를 시험하였다. 지하수 폭기실험은 내경 5 cm, 길이 80 cm의 1차원 토양(모래)컬럼을 사용하여 실시하였다. 실험은 총 3회 실시하였으며, 상온에서 증류수로 포화된 조건에서 1회, 상온($23^{\circ}C$)에서 음이온계 계면활성제(sodium dodecylbenzene sulfonate, SDBS) 수용액으로 포화된 조건에서 1회(상온 SEAS), 그리고 승온상태($73^{\circ}C$)에서 SDBS수용액으로 포화된 조건에서 1회(승온 SEAS) 실시하였다. 계면활성제가 적용된 경우의 폭기에 의한 공기포화율(57%)은 증류수로 포화된 조건의 공기포화율(10%)보다 높게 측정되었다. 승온 및 상온조건에서의 공기포화율은 거의 차이가 없었으나 n-decane의 제거속도는 현저한 차이를 나타내었다. 토양유출 가스에 포함된 n-decane의 농도는 상온조건에 비하여 승온조건에서 10배 이상 높았으며, 따라서 제거속도도 10배 이상의 차이를 나타내었다. 본 연구 결과에 따라 상온에서 휘발성이 낮으나 수 십도의 온도상승으로 증기압이 획기적으로 늘어날 수 있는 준휘발성 물질에 대하여 SEAS 기술이 효과적으로 응용될 수 있을 것으로 보인다.

• 반도체디스플레이기술학회지
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• 제7권3호
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• pp.51-54
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• 2008

In this study, we investigated variations in undoped ZnO thin film properties with working pressure, $O_2$/Ar ratio, and annealing ambient. Higher vacuum pressure during deposition was observed to bring about slower growth rate resulting in samples with better crystallinity as well as hole generation efficiency through formation of shallower oxygen interstitial. Given that $O_2$/Ar ratio is greater than unity, O provided from the ambient to ZnO during annealing was found to preferably situate at interstitial sites. When He was used for the second annealing, significant changes were not observed. On the other hand, O ambient caused increased density of oxygen interstitial, thereby making the film more intrinsic-like high resistivity ZnO.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 추계학술대회 논문집
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• pp.117-120
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• 1999

The relationship between the DC degradation characteristics of the ZnO varistor and the ambient sintering-process is investigated in this study. ZnO varistors made of Matsuoka's composition were fabricated by standard ceramic techniques. The ambient sintering-process is performed at the extraordinary electrical-furnace which is equipped with the vacuum system. The Gas of sintering process was oxygen, nitrogen, argon, air respectively. The microstructure of ZnO varistors be made use of SEM equipment. The condition of DC degradation tests were conducted at $115\pm2^{\circ}C$ for periods up to 13 h. Current-voltage analysis is used to determine nonlinear coefficients($\alpha$). Resistance-frequency and capacitance-frequency analysis are accomplished to the understanding of electrical properties as DC degradation test. From above analysis, it is found that the ZnO varistor sintered in oxygen atmosphere showed superior properties at the DC degradation test.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2006년도 제32회 KOSCO SYMPOSIUM 논문집
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• pp.79-85
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• 2006

In this study, to increase the mixing between flue gas and reducing agent, new shapes of $NH_3$ ejection nozzles are designed and experimentally and numerically tested. The nozzles have six holes perpendicular to the ambient flue gas flow and the tilting angle between direction of ambient flow and the hole axis is varied. To evaluate the mixing efficiency of the proposed nozzles, numerical and experimental tests are applied to several flow conditions comparing with single hole nozzle, which is commonly used in conventional SCR process. From the results the nozzle with tilted multi-holes has the large region of high turbulent intensity compared with conventional single hole nozzle. This is originated from the high vorticity near the upstream of the jet flow issuing from the hole. The high turbulent intensity and vorticity magnitude lead to enhanced mixing between flue gas and reducing agent. Hence, the most suitable moral ratio between NOx and reducing agent for the catalytic reaction can be obtained on behalf of the intensified scalar mixing within shorter physical mixing length.

• 한국입자에어로졸학회지
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• 제6권4호
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• pp.151-164
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• 2010

Inorganic ions and water are major components of ambient fine particles. Water content in fine particles is mainly determined by ambient meteorological conditions and the concentrations of hygroscopic species such as inorganic ions. Thus, to reduce fine particle mass concentration, it is important to accurately estimate the relationship between water content and the concentration of ions in fine particles. Water content in fine particles in Seoul are estimated by using a gas/particle equilibrium model to understand the characteristics of fine particle mass concentration. In addition, sensitivity of fine particle mass concentration to the changes of particulate ionic species (sulfate, nitrate, and ammonium) is estimated. It was found that water content in Seoul is mostly determined by the concentrations of the hygroscopic ionic species, especially, sulfate and ammonium, and ambient relative humidity.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.125.2-125.2
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• 2015

The evolution of oxidation states of vanadium is monitored with ambient pressure X-ray photoemission spectroscopy. As the pressure of oxygen gas and surface temperature change, the formations of various oxidation states of vanadium are observed on the surface. Under 100mTorr of the oxygen gas pressure and 523K of sample temperature, VO2 and V2O5 are formed on the surface. The temperature-dependent resistance measurement on grown sample shows a clear metal-insulator transition near 350K. In addition, the measurement of Raman spectroscopy displays the structural change from monoclinic to rutile structures across the phase transition temperature.