• Environmental Engineering Research
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• 제24권1호
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• pp.159-172
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• 2019

To investigate the influence of pollution events on the chemical composition and formation processes of aerosol particles, 24-h integrated size-segregated particulate matter (PM) was collected during the fall season at an urban site of Gwangju, Korea and was used to determine the concentrations of mass, water-soluble organic carbon (WSOC) and ionic species. Furthermore, black carbon (BC) concentrations were observed with an aethalometer. The entire sampling period was classified into four periods, i.e., typical, pollution event I, pollution event II, and an Asian dust event. Stable meteorological conditions (e.g., low wind speed, high surface pressure, and high relative humidity) observed during the two pollution events led to accumulation of aerosol particles and increased formation of secondary organic and inorganic aerosol species, thus causing $PM_{2.5}$ increase. Furthermore, these stable conditions resulted in the predominant condensation or droplet mode size distributions of PM, WSOC, $NO_3{^-}$, and $SO{_4}^{2-}$. However, difference in the accumulation mode size distributions of secondary water-soluble species between pollution events I and II could be attributed to the difference in transport pathways of air masses from high-pollution regions and the formation processes for the secondary chemical species. The average absorption ${\AA}ngstr{\ddot{o}}m$ exponent ($AAE_{370-950}$) for 370-950 nm wavelengths > 1.0 indicates that the BC particles from traffic emissions were likely mixed with light absorbing brown carbon (BrC) from biomass burning (BB) emissions. It was found that light absorption by BrC in the near UV range was affected by both secondary organic aerosol and BB emissions. Overall, the pollution events observed during fall at the study site can be due to the synergy of unfavorable meteorological conditions, enhanced secondary formation, local emissions, and long-range transportation of air masses from upwind polluted areas.

• 한국정보통신학회논문지
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• 제16권4호
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• pp.785-792
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• 2012

본 연구에서는 고속 및 저전력 스위칭 소자 응용을 위하여 n-채널 무접합 및 반전모드 MuGFET 와 p-채널 무접합 및 축적모드 MuGFET의 기판전압에 따른 전류-전압 특성을 측정하고 비교 분석하였다. 기판전압에 따른 문턱전압과 포화 드레인 전류 변화로부터 n-채널 소자에서는 반전모드 소자가 무접합 소자보다 변화량이 크며 p-채널 소자에서는 무접합 소자가 축적모드 소자보다 변화량이 큰 것을 알 수 있었다. 전달컨덕턴스 변화는 n-채널 소자보다 p-채널 소자의 변화량이 큰 것을 알 수 있었다. 그리고 subthreshold swing 특성으로부터 n-채널 소자와 p-채널 무접합 소자는 기판전압 변화에 따라 S값의 변화가 거의 없지만 p-채널 축적모드 소자는 기판전압이 양의 방향으로 증가할 때 S 값이 증가하는 것으로 관측되었다. 기판전압을 이용한 고속 및 저전력 스위칭 소자 응용 측면에서는 n-채널 소자에서는 반전모드 소자가 p-채널 소자에서는 무접합 소자가 더 좋은 특성을 보였다.

• Journal of Microbiology and Biotechnology
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• 제4권2호
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• pp.146-150
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• 1994

Production of poly-$\beta$-hydroxybutyrate (PHB) in fed-batch fermentation was studied. Utilization of carbon for PHB biosynthesis was investigated by using feeding solutions with different ratios of carbon to nitrogen (C/N). It was observed that at a high C/N ratio carbon source was more preferably utilized for PHB accumulation while its consumption for cellular metabolism appeared to be more favored at a low C/N value. A high cell concentration (184 g/l) was achieved when ammonium hydroxide solution was fed to control the pH, which was also utilized as the sole nitrogen source. For the mass production of PHB, two-stage fed-batch operations were carried out where PHB accumulation was observed to be stimulated by switching the ammonium feeding mode to the nitrogen limiting condition. A large amount of PHB (108 g/l) was obtained with cellular content of 80% within 50 hrs of operation.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.389-392
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• 1999

Fatigue is a process of progressive permanent internal structural change in a material subjected to repeitive stresses. These change may be damaging and result in progressive growth of cracks and complete fracture if the stress repetitins are sufficiently large. For structural members subjected to cyclic loads, the continuous and irrecoverable damage processes are taking place. These processes are referred as the cumulative damage processes due to fatigue loading. Moreover, increased use of high strength concrete makes the fatigue problem more important because the cross-section and dead weight are reduced by using high strength concrete. The purpose of this study is to investigate the shear fatigue behavior of reinforced concrete beams according to shear reinforcement ratio and concrete compressive strength under repeated loadings. For this purpose, comprehensive static and fatigue tests of reinforced concrete beams were conducted. The major test variables for the fatigue teats are the concrete strength and the amount of shear reinforcements. The increase of deflections and steel strains according to load repetition has been plotted and analyzed to explore the damage accumulation phenomena of reinforced concrete beams. An analytical model for shear fatigue behavior has been introduced to analyze the damage accumulation under fatigue loads. The failure mode and fatigue lives have been also studied in the present study. The comparisons between analytical results and experimental data show good correlation.

• Tribology and Lubricants
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• 제34권6호
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• pp.292-299
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• 2018

The objective of this research is to investigate the impact of engine oil aging on PM(Particulate Matter), exhaust gases, and DPF. It is widely known that the specification of a lubricant and its consumption in an ICE considerably influences the release of regulated harmful emissions under normal engine operating conditions. Considering DPF clogging phenomena associated with lubricant-derived soot/ash components, a simulated aging mode is designed for DPF to facilitate engine dynamometer testing. A PM/ash accumulation cycle is developed by considering real-world engine operating conditions for the increment of engine oil consumption and natural DPF regeneration for ash accumulation. The test duration for DPF aging is approximately 300 h with high- and low-SAPs engine oils. Detailed engine lubricant properties of new and aged oils are analyzed to evaluate the effect of engine oil degradation on vehicle mileage. Furthermore, physical and chemical analyses are performed using X-CT, ICP, and TGA/DSC to quantify the engine oil contribution on the PM composition. This is achieved by sampling with various filters using specially designed PM sampling equipment. Using high SAPs engine oil causes more PM/ash accumulation compared with low SAPs engine oils and this could accelerate fouling of the EGR in the engine, which results in an increase in harmful exhaust gas emissions. These test results on engine lubricants under operating conditions will assist in the establishment of regulated and unregulated toxic emissions policies and lubricant quality standards.

• 지역연구
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• 제11권1호
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• pp.79-91
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• 1995

As an exit to solve the economic depression of the development countries in the early twentieth century, the 'old international division of labor' developed. The economic crisis(i.e., under-consumption crisis) was due to the absence of the mode of regulation compatible with the extensive regime of accumulation(i.e., "Fordist" regime). The crisis was solved by the state intervention through the creation on institutions in order to increase the level of consumption. Until the late 1960s when "high Fordism" reached(i.e., a harmonious relation between the monopoly mode of regulation and the intensive accumulation of capital), the developed core countries enjoyed a remarkable economic growth. The external market was not a necessity for the economic growth because there were increases in labor productivity and proportional increases in real wages and thus increases in consumption level. In the 1970s, however, the core faced with economic crisis again. Due to the breakdown of the postwar "Fordist" regime of capital accumulation and the post 1973 world depression, the core needed the Third World as a solution for their internal and international economic crisis. Thus the 'new international division of labor'(NIDL) arose. The "Fordist" method of production(i.e., the divisions of production process) led to the territorial division of labor and to the detailed division of labor. The aim of the NIDL is to exploit reserve armies of labor on a world scale and thus to reduce production costs. According to the NIDL model, the Third World countries have been developing by the core countries' investment on mainly labor-intensive industries and thus have been playing an important role in the global economy. And the NIDL theorists argue that multinational corporations have increasingly invested in the Third World nations and contributed to the economic growth in those regions. Tables presented in the paper show that the global trend since the 1970s does not follow the argument exactly as the NIDL theorists predicted. On the contrary, the core countries focus on developing technology, adopting the automation of production process, and trading within the core countries rather than on investing in the periopheral countries. The continuing investment of multinational corporations into the periphery is not because of cheap labor force but because of the market potentials in the regions. Majority of corporations of the core tries to reduce production costs by investing in technological development more intensively and also by changing regional strategies (i.E., investment from metropolitan areas to medium - or small - size cities, focusing on agglomeration economy, boosting regional diversification, etc.) within their own countries. The main purpose of the paper is to review and to criticize the NIDL theory based on some empirical data.IDL theory based on some empirical data.

• 대한기계학회논문집
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• 제16권5호
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• pp.838-848
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• 1992

본 연구에서는 김성호등의 형상모델인 Fig.1(b)에서 전단하중이 작용하는 경 우에 대한, 복합재료의 탄성층 내부(레진층)에 존재하는 중앙균열의 응력확대계수 산 출을 위하여 균열부위를 제외하고는 섬유층과 레진층이 완전히 접착되었다고 가정한 모델을 다음과 같이 설정 하였다. 접착레진을 주로하는 탄성층(resin rich layer)을 중심으로 상하 각1개의 섬유층(fiber rich layer)과 균질한 특성을 갖는 복합재료의 층으로 단순화하였으며, 복합재료는 레진층이나 섬유층에 비하여 무한히 두꺼우므로 반무한체로 이상화 하였다. 선형탄 이론에 의한 혼합경계조건문제(mixed boundary value problem)로 부터 제2종 Fredholm 적분방정식(fredholm integral equation of a second kind)을 유도하였으며 수치해석적인 방법에 의하여 응력확대계수를 구하였다. 또한, 복합재료의 재료물성 및 균열길이, 섬유두께등이 기하학적 변수에 대하여 응력 확대계수를 산출하였다.

• 한국대기환경학회지
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• 제16권2호
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• pp.89-102
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• 2000

A total of 318 particulate sample sets consisting of both fine PM(FPM : dp$\leq$2.5 ${\mu}{\textrm}{m}$) and coarse PM(CPM : 2.5${\mu}{\textrm}{m}$${\mu}{\textrm}{m}$) was collected by a dichotomous sampler in Suwon area from December 1996 to November 1997. The concentration of seven inorganic elements such as pb. Cr, Cd, Cu, Zn Fe and Na were determined from each sample using an AAS. The purpose of the study was to extensively investigate environmental behaviors of particulate matters and to provide air quality management schemes applying various statistical approaches. The mean concentrations of PM10 Results of correlation analyses indicated the existence of strong correlations among inorganic elements PM10 FPM CPM and various meterological variables. Our study also examined the degree of uncertainties whether the particular elements can be assorted into the accumulation mode or the coarse mode in their size distribution. Furthermore the analysis of the pollution rose showed graphically the direction of potential sources of particulate matters. According to statistical analyses of our data quantitative differences appeared in the pollution patterns between weekdays and weekends.

• Journal of Applied Biological Chemistry
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• 제56권2호
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• pp.109-112
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• 2013

Azole fungicides are one of the most wide-spread antifungal compounds in agriculture and pharmaceutical applications. Their major mode of action is the inhibition of ergosterol biosynthesis, giving depletion of ergosterol, precursors and abnormal steroids. However, metabolic consequences of such inhibition, other than steroidal metabolitesare not well established. Comprehensive metabolic profiles of Saccharomyces cerevisiae has been presented in this study. Wild type yeast was treated either with glucose as control or azole fungicide (ketoconazole). Both polar metabolites and lipids were analyzed with gas chromatography-mass spectrometry. Approximately over 180 metabolites were characterized, among which 18 of them were accumulated or depleted by fungicide treatment. Steroid profile gives the most prominent differences, including the accumulation of lanosterol and the depletion of zymosterol and ergosterol. However, the polar metabolite profile was also highly different in pesticide treatment. The concentration of proline and its precursors, glutamate and ornithine were markedly reduced by ketoconazole. Lysine and glycine level was also decreased while the concentrations of serine and homoserine were increased. The overall metabolic profile indicates that azole fungicide treatment induces the depletion of many polar metabolites, which are important in stress response.

• 한국자동차공학회논문집
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• 제18권6호
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• pp.98-104
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• 2010

An experimental investigation was conducted to analyze the effects of EGR ratio on the combustion, exhaust emissions characteristics and size distributions of particulate matter in a single cylinder diesel engine with common-rail injection system fueled with biodiesel derived from soybean. In order to analyze the combustion, exhaust emissions and measurement of size distributions of particulate matter were carried out under various EGR ratio which was varied from 20~60% and the results were compared to those of results without EGR. The experimental results show that ignition delay was extended and maximum value of rate of heat release (ROHR) was decreased according to increasing of EGR ratio. In addition, oxidies of nitrogen ($NO_x$) emissions were reduced but soot emissions were increased under increasing of EGR ratio. However, under higher EGR ratio region, soot was slightly decreased. And then the particulate size distribution shows that high exhaust gas temperature restrain the formation of soluble organic fraction (SOF) which were beyond the accumulation mode (100~300nm) and lead to increase of nuclei mode particles.