• KSBB Journal
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• 제13권6호
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• pp.644-648
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• 1998

In the production of a low cost bacterial insecticide, it is important to produce a high spore concentration using low price substrates. Experiments were carried out to investigate the effects of the addition of mineral salts and glucose, and of dissolved oxygen concentration on the cell growth and spore formation of Bacillus thuringiensis var aizawai using a cheap wheat and soybean meal in the batch culture. The maximum viable cell number was 1.2${\times}$109 CFU/mL at 12 hr culture and spore yield was 54.2% at 74 hr culture using an industrial medium containing 20 g/L wheat meal and 30 g/L soybean meal under 1.0 vvm aeration and 200 rpm agitation. The cell growth and the spore formation were not enhanced by the addition of mineral salts in industrial medium, whereas th addition of 10g/L glucose decreased the cell growth and spore formation. We could obtain a maximum viable cell number of 2.2${\times}$109 CFU/mL and spore number of 1.9${\times}$109 CFU/mL at the dissolved oxygen concentration of 60% of saturation. The spore concentration was enhanced approximately by 2 times as compared to the dissolved oxygen concentration of 50%. In the bench-scale culture, the maximum viable cell and spore number were 2.5${\times}$109 CFU/mL, and 2.2${\times}$109 CFU/mL, respectively under 1.0 vvm aeration and 400 rpm agitation. The spore yield was 88% based on the maximum viable cell number. As a result, it was confirmed that the production of high spore concentration could be obtained by a bench-scale culture using an industrial medium.

• 한국안전학회지
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• 제19권1호
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• pp.137-140
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• 2004

최근 산업현장에서는 제품의 품질과 성능을 향상시키기 위해 나노 기술로 나아가는 추세에 있으며, 이러한 연구들로 인해 많은 화학제품의 원료들이 더욱 미세한 상태로 가공 및 취급되어지고 있다. 이에 분진의 특성상 그 위험성이 따라 증가하고 있으므로, 분진폭발의 발생을 예방하기 위해 분진운의 발화온도와 폭발한계산소농도 등을 찾아내는 것은 매우 중요한 일이다. 따라서 본 연구에서는 현재 국내에서 생산되고 있는 Hydroxy Propyl Methyl Cellulose (HPMC)을 가지고 실험을 하였으며, 생산 및 취급과정에서 뜨거운 표면으로부터 발생될 수 있는 화재 및 폭발을 예방하고자, Godbert-Greenwald Furnace장치로 실험하였다. 그 결과 분진 입자의 크기가 작아짐으로서 발화온도는 낮아지는 경향을 나타내었으며, 분진입자의 크기가 45${\mu}m$에서 HPMC 분진운의 최소발화온도는 364$^{\circ}C$로 나타났으며, 폭발한계산소 농도는 11%로 나타났다.

• 한국물환경학회지
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• 제37권2호
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• pp.92-102
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• 2021

In this study, the distribution characteristics according to the type of BOD and the effect of nitrogenous oxygen demand (NOD) and algal oxygen demand on BOD in three streams (Bokhacheon, Byeongseongcheon, and Gulpocheon) were evaluated. Although the BOD and NOD concentrations demonstrated a difference in the three streams, the carbonaceous BOD(CBOD)/BOD ratio was 0.75 (p=0.053, one-way ANOVA), and there was no significant difference in the three streams (r2≥0.92, p<0.0001). The NOD concentration of the Bokhacheon with high NH3-N was 1.7±1.3 mg/L, which was the highest among the three streams and showed a significant correlation with BOD. Seasonal variations in NOD in the three streams did not show a significant correlation with changes in NH3-N concentration (r2<0.28, p≥0.1789), and there was no significant difference in NOD even though NH3-N concentration in Gulpocheon was about twice that of Byeongseongcheon (p=0.870, one way ANOVA). The particulate CBOD(PCBOD)/CBOD ratio of the three streams was 0.55~0.64, and about 60% of the biodegradable organic matter was present in the particulate form. When the Chl.a concentration in the stream was more than 7 ㎍/L, the PCBOD tended to increase with the Chl.a concentration (r2=0.61, p=0.003). In the three streams, particulate NOD accounted for 81% of NOD; however, despite the large variation in NH3-N concentration (0.075~3.182 mg/L), there was no significant difference in soluble NOD(SNOD) concentration that ranged from 0.1 to 0.3 mg/L. In this study, the low contribution rate of SNOD to NOD is considered as a result of the removal of nitrifying bacteria along with the particles during the filtration process.

• 조명전기설비학회논문지
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• 제16권6호
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• pp.95-101
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• 2002

고농도의 오존발생에 영향을 주는 많은 변수들이 존재한다. 이러한 변수들은 오존발생장치 설계시 매우 중요한 요소가 되고 설계전에 반드시 고려되어야 할 것들이다. 오존발생장치 설계 후에도 고농도 오존발생에 크게 영향을 주는 주변변수들이 있다. 본 연구에서는 오존발생에 영향을 주는 많은 주변변수들중에서 입력산소가스의 유량과 여기에 첨가되는 첨가가스가 고농도의 오존발생에 미치는 영향을 조사하였다. 결과적으로, 입력산소가스의 유량을0.75[LPM］～2.00[LPM］으로 변화시키면서 오존농도를 측정한 결과 1.25［LPM］에서 71145［ppm］의 최대오존발생량을 보여주었다. 입력산소가스에 첨가되는 질소가스의 유량을 0.0［vol%］～6.4［vol%］으로 변화시켜가면서 발생되는 오존농도를 측정한 결과 첨가되는 질소가스량이 0.8［vol%］인 경우 최대 73135［ppm]의 오존을 얻을 수 있었다. 이것은 순수산소만을 입력가스로 사용했을 때보다 최대오존발생량이 3［%］가량 증가한 결과이다. 입력산소가스에 첨가되는 아르곤가스의 유량을 0.0[vol%］～6.4[vol％］으로 변화시켜가면서 발생되는 오존농도를 측정한 결과 첨가되는 아르곤가스량이 0.8［vol%］인 경우 최대 67288［ppm］의 오존을 얻을 수 있었다.

• Safety and Health at Work
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• 제6권1호
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• pp.18-24
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• 2015

Background: In 2006, three farmers died at the bottom of an agricultural shallow well where the atmosphere contained only 6% oxygen. This study aimed to document the variability of levels of oxygen and selected hazardous gases in the atmosphere of wells, and to identify ambient conditions associated with the low-oxygen situation. Methods: A cross-sectional survey, conducted in June 2007 and July 2007, measured the levels of oxygen, carbon monoxide, hydrogen sulfide, and explosive gas (percentage of lower explosive limit) at different depths of the atmosphere inside 253 wells in Kamphaengphet and Phitsanulok provinces. Ambient conditions and well use by farmers were recorded. Carbon dioxide was measured in a subset of wells. Variables independently associated with low-oxygen condition (<19.5%) were identified using multivariate logistic regression. Results: One in five agricultural shallow wells had a low-oxygen status, with oxygen concentration decreasing with increasing depth within the well. The deepest-depth oxygen reading ranged from 0.0% to 20.9%. Low levels of other hazardous gases were detected in a small number of wells. The low-oxygen status was independently associated with the depth of the atmosphere column to the water surface [odds ratio (OR) = 13.5 for 8-11 m vs. <6 m], depth of water (OR = 0.17 for 3-<8 m vs. 0-1 m), well cover (OR = 3.95), time elapsed since the last rainfall (OR = 7.44 for >2 days vs. <1 day), and location of well in sandy soil (OR = 3.72). Among 11 wells tested, carbon dioxide was detected in high concentration (>25,000 ppm) in seven wells with a low oxygen level. Conclusion: Oxygen concentrations in the wells vary widely even within a small area and decrease with increasing depth.

• 한국농공학회논문집
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• 제57권4호
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• pp.31-38
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• 2015

This study aims to assess the effectiveness of limestone, zeolite, and crushed concrete as capping material to block the release of heavy metals (As, Cu, Cr, Ni, and Pb) and reduce the sediment oxygen demand. The efficiency of limestone, zeolite, and crushed concrete was evaluated in a reactor in which a 1-cm thick layer of capping materials was placed on the sediments collected from Inchon north harbor. Dissolved oxygen concentration and heavy metal concentration in seawater above the uncapped sediments and capping material were monitored for 17 days. The sediment oxygen demand was in the following increasing order: crushed concrete ($288.37mg/m^2{\cdot}d$) < zeolite ($428.96mg/m^2{\cdot}d$) < limestone ($904.53mg/m^2{\cdot}d$) < uncapped ($981.34mg/m^2{\cdot}d$). The capping materials could reduce the sediment oxygen demand by blocking the release of biochemical matters consuming dissolved oxygen in seawater. It was also shown that zeolite and crushed concrete could effectively block the release of Cu, Ni, and Pb but those were not effective for the interruption of As and Cr release from marine contaminated sediments.

• 환경위생공학
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• 제18권4호
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• pp.64-69
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• 2003

Recently, Indoor air quality(IAQ) in workplace, residential environments and office has been concern of people, scientists and related the public. The oxygen in air was very important and essential element in every aspect of life. This study was performed on a questionnaire survey of 400 people about their awareness of indoor air quality, oxygen generators and measured of oxygen concentration in indoor environment. The results obtained were as follows; As respondents are having their 90% of daytime indoors a day, and 80% of them can feel indoor air pollutions degrees directly by particle matters. The control of most important problems of IAQ was the poor ventilation. We know that 22% of the respondents was recognized the oxgen generator. And for the installation of indoor pollution control equipment, 20% of all respondents installed oxygen generators because almost respondents was not satified the trust of ability purified indoor air pollutants. In the experimental results, it was found that the oxygen concentration of sampling sites were in the range of 20~23.5%. Therefore, it was recommended that the government related IAQ was suggested the guideline and control of oxygen generators. Finally, it appeared that the oxygen generators using indoor environment can be applied to new technology for cleaning of indoor air.

• Transactions on Electrical and Electronic Materials
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• 제15권6호
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• pp.315-319
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• 2014

In this paper, we investigate visible light stress instability in radio frequency (RF) sputtered a-IGZO thin film transistors (TFTs). The oxygen flow rate differs during deposition to control the concentration of oxygen vacancies, which is confirmed via RT PL. A negative shift is observed in the threshold voltage ($V_{TH}$) under illumination with/without the gate bias, and the amount of shift in $V_{TH}$ is proportional to the concentration of oxygen vacancies. This can be explained to be consistent with the ionization oxygen vacancy model where the instability in $V_{TH}$ under illumination is caused by the increase in the channel conductivity by electrons that are photo-generated from oxygen vacancies, and it is maintained after the illumination is removed due to the negative-U center properties.

• 한국결정성장학회지
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• 제4권3호
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• pp.210-222
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• 1994

축방향의 균일한 자장이 Czochralski 도가니에 가하여졌을 때의 유동장, 온도장 및 산소의 농도장이 수치적으로 연구되었다.Czochralski 유동장과 농도장에 작용하는 부력, thermocapillarity, 원심력, 자성력, 산소의 확산계수, 산소의 segregation coefficient, SiO형태의 evaporation, 도가니벽의 ablation 등이 고려되었다. 회전방향으로의 대칭성으로부터 자오면에서의 속도성분과 회전방향의 속도성분, 온도, 전류의 흐름 등이 먼저 정상상태에 도달하였다고 가정하고 초기에 일정한 산소의 농도가 주어진 상황에서 비정상 상태의 산소의 농도장이 해석되었다. Czochralski 유동장에서의 대류와 확산에 의한 산소의 전달현상이 파악되었으며 결정성장 표면으로 흡수되는 산소의 농도가 연구되었다.

• Corrosion Science and Technology
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• 제2권4호
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• pp.178-182
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• 2003

Slow Strain Rate Tests (SSRT) were carried out to investigate the effect of environmental factors on the Stress Corrosion Cracking (SCC) susceptibility of 3.5NiCrMoV steels used in discs for Low-Pressure (LP) steam turbines in electric power generating plants. The influences of dissolved oxygen on the stress corrosion cracking of turbine steel were studied, For this purpose, specimens were strained at variously oxygenated conditions at $150^{\circ}C$ in pure water. When the specimen was strained with $1{\times}10^{-7}s^{-1}$ at $150^{\circ}C$ in pure water, increasing concentration of dissolved oxygen decreased the elongation and the UTS. The corrosion potential and the corrosion rare increased as the amounts of dissolved oxygen increased. The increase of the SCC susceptibility of the turbine steel in a highly dissolved oxygen environment is due to the non protectiveness of the oxide layer on the turbine steel surface and the increase of the corrosion current. These results clearly indicate that oxygen concentration increases Stress Corrosion Cracking susceptibility in turbine steel at $150^{\circ}C$.