• 한국대기환경학회지
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• 제19권1호
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• pp.13-23
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• 2003

A local wind model and a three dimensional local environmental model including advection, diffusion, deposition. and photochemical reactions were performed at Gwangyang Bay, Korea, to predict air flow and air pollutants concentrations. A large grid was used, and nesting method was employed for small grid calculation. From the meterological module simulation, we were able to reproduce local wind characteristics such as sea/land winds and mountain/valley winds simulation at Gwangyang Bay. In addition, the concentration module showed high concentration regions at Yosu industrial complex, Gwangyang steel company. and Container anchor. It was also seen that air pollutants were dispersed by sea/land winds. A comparison between the measurement and the prediction of sulfur dioxide and nitric oxide, which are relatively low-reacted pollutants, was performed. However, the measured nitrogen dioxide and ozone concentrations were higher than the simulated ones. Particularly, ozone concentration between 8 a..m. and 8 p.m. agreed well, but the measured ozone during the rest of time were generally higher.

• 한국산업보건학회지
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• 제28권3호
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• pp.273-282
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• 2018

Objectives: Dustiness of nanomaterials is considered as exposure index of essential material. Research on dustiness of nanomaterial is needed to control exposure in workplaces. Method: Dustiness measurement using vortex shaker were installed in the laboratory. Nanomaterials, 1 g, was put in the glass test tube and shaked using vortex shaker. Aerosol dispersed was measured using scanning mobility particle sizer(SMPS) and optical particle counter(OPC). Mass concentration using PVC filter and cassette was measured and TEM grid sampling was conducted. Total particle concentration and size distribution were calculated. Image and chemical composition of particles in the air were observed using transmission electron microscopy and energy dispersive X-ray spectrometer. Eleven different test nanomaterials were used in the study. Results: Rank of mass concentration and particle number concentration were coincided in most cases. Rank of nanomateirals with low concentration were not coincided. Two types of fumed silica had the highest mass concentration and particle number concentration. Indium tin oxide, a mixture of indium oxide and tin oxide, had high mass concentration and particle number concentration. Indium oxide had very low mass concentration and particle number concentration. Agglomeration of nanoparticles in the air were observed in TEM analysis and size distribution. In this study, mass concentration and particle number concentration were coincided and two index can be used together. The range of dustiness in particle number concentration were too wide to measure in one method. Conclusion: Particle number concentration ranged from low concentration to high concentration depend on type of nanomaterial, and varied by preparation and amount of nanomaterial used. Further study is needed to measure dustiness of all nanomaterial as one reference method.

• 설비공학논문집
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• 제11권4호
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• pp.549-559
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• 1999

An experimental study was peformed to measure the viscosity of microencapsulated PCM slurries as the functions of its concentration and temperature, and also influence to its fluid dynamics. For the viscosity measurement, a rotary type viscometer, which was equipped with temperature control system, was adopted. The slurry was mixed with water and Sodium Lauryl Sulphate as a surfactant by which its suspended particles were dispersed well without the segregation of particles during the experiment. The viscosity was increased as the concentration of MicroPCM particle added. The surfactant increased 5% of the viscosity over the working fluid without particles. Experiments were proceeded by changing parameters such as PCM particles'concentration as well as the temperature of working fluid. As a result, a model to the functions of temperature for the working fluid and its particle concentration is proposed. The proposed model, for which its standard deviation shows 0.8068, is agreed well with the reference's data. The pressure drop was measured by U-tube manometer, and then the friction factor was obtained. It was noted that the pressure drop was not influenced by the state of PCM phase, that is solid or liquid in its core materials at their same concentration. On the other hand, it was described that the pressure drop of the slurry was much increased over the working fluid without particles. A friction factor was placed on a straight line in all working fluids of the laminar flow regardless of existing particles as we expected.

• 한국전기전자재료학회논문지
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• 제29권4호
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• pp.199-204
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• 2016

This paper was proposed floating island power MOSFET for lowering on state resistance and the proposed device was maintained 600 V breakdown voltage. The electrical field distribution of floating island power MOSFET was dispersed to floating island between P-base and N-drift. Therefore, we designed higher doping concentration of drift region than doping concentration of planar type power MOSFET. And so we obtain the lower on resistance than on resistance of planar type power MOSFET. We needed the higher doping concentration of floating island than doping concentration of drift region and needed width and depth of floating island for formation of floating island region. We obtained the optimal parameters. The depth of floating island was $32{\mu}m$. The doping concentration of floating island was $5{\times}1,012cm^2$. And the width of floating island was $3{\mu}m$. As a result of designing the floating island power MOSFET, we obtained 723 V breakdown voltage and $0.108{\Omega}cm^2$ on resistance. When we compared to planar power MOSFET, the on resistance was lowered 24.5% than its of planar power MOSFET. The proposed device will be used to electrical vehicle and renewable industry.

• 한국대기환경학회지
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• 제15권6호
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• pp.757-765
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• 1999

Lagrangian particle dispersion model(LPDM) is an effective tool to calculate the dispersion from a point source since it dose not induce numerical diffusion errors in solving the pollutant dispersion equation. Fictitious particles are released to the atmosphere from the emission source and they are then transported by the mean velocity and diffused by the turbulent eddy motion in the LPDM. The concentration distribution from the dispersed particles in the calculation domain are finally estimated by applying a particle count method or a Gaussian kernel method. The two methods for calculating concentration profiles were compared each other and tested against the analytic solution and the tracer experiment to find the strength and weakness of each method and to choose computationally time saving method for the LPDM. The calculated concentrations from the particle count method was heavily dependent on the number of the particles released at the emission source. It requires lots fo particle emission to reach the converged concentration field. And resulting concentrations were also dependent on the size of numerical grid. The concentration field by the Gaussian kernel method, however, converged with a low particle emission rate at the source and was in good agreement with the analytic solution and the tracer experiment. The results showed that Gaussian kernel method was more effective method to calculate the concentrations in the LPDM.

• Safety and Health at Work
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• 제1권1호
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• pp.98-101
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• 2010

This study explored the health hazard of those exposed to methylene chloride by assessing its atmospheric concentration when a tear gas mixture was aerially dispersed. The concentration of methylene chloride ranged from 311.1-980.3 ppm (geometric mean, 555.8 ppm), 30 seconds after the dispersion started. However, the concentration fell rapidly to below 10 ppm after dispersion was completed. The concentration during the dispersion did not surpass the National Institute for Occupational Safety and Health 'immediately dangerous to life or health' value of 2,300 ppm, but did exceed the American Conference of Governmental Industrial Hygienists excursion limit of 250 ppm. Since methylene chloride is highly volatile (vapor pressure, 349 mmHg at $20^{\circ}C$), the post-dispersion atmospheric concentration can rise instantaneously. Moreover, the o-chlorobenzylidenemalononitrile formulation of tear gas (CS gas) is an acute upper respiratory tract irritant. Therefore, tear gas mixtures should be handled with delicate care.

• 한국해양환경ㆍ에너지학회지
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• 제8권3호
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• pp.134-139
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• 2005

본 연구에서는 조간대에서 유출된 기름의 표착 및 침투과정을 파악하고, 침투된 기름의 해수 침투차단 여부를 검토하는 것을 목적으로 하여 모의 조간대를 이용하여 연구를 수행하였다. 표착된 기름의 침투깊이는 분산유가 가장 낮았으며, 풍화유 그리고 원유의 순서로 깊어지는 경향을 나타냈다. 그리고 기름의 침투는 표착된 기름의 양에 의해 좌우되는 것을 알 수 있었으며, 유출된 기름의 침투는 첫번째 조석에서 거의 대부분 결정되며 그이후에는 거의 변화가 없었다. 침투된 기름은 토양 표층으로부터 2 cm 부분이 가장 농도가 높음을 알았다. 기름의 침투량의 증가와 더불어 해수의 침투량이 감소하였으며, 분산유보다는 원유나 풍화유가 보다 많은 양의 해수를 차단하였다. 따라서 해수의 침투량의 차단이라는 관점에서 볼 때 연안 조간대에서 표착유의 저서생물에 대한 피해는 풍화유나 원유가 분산유보다 클것으로 사료된다.

• 한국균학회지
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• 제23권1호통권72호
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• pp.71-79
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• 1995

Rhizopus oryzae의 카드뮴 적응 및 해독기작과 이에 관련된 세포내 생리 생화학적 변화를 조사하였다. R. oryzae는 카드뮴 첨가농도가 증가함에 따라 거의 비례적으로 잠복기가 길어졌다. 카드뮴의 해독에 관련하는 system은 카드뮴 첨가 배양시에만 적응기 중에 특이하게 유도, 생성되어져 카드뮴 결합단백질의 성격을 지닐 것으로 추정되는 2종류의 단백질과 동일한 시기, 조건하에서 유의하게 증가되는 무기인산중합체 pool에 의하여 1차적으로 운용되어질 것으로 사료되며, 2차적, 보완적 system은 ACPase의 derepression 그리고 phosphatidyl serine의 합성증가 등의 방법을 통하여 운용될 것으로 생각된다. 또한 총지질화합물의 조성변화 등과 같은 다양한 생리 생화학적 물질대사 경로의 변화를 일으켰다. 이러한 변화의 총화로 크게는 형태적 변화까지 일어나 카드뮴 적응 및 해독에 필요한 성장형태로서 여러 가지 산물 생성에 유리한 dispersed filamentous type을 취하였다.

• 반도체디스플레이기술학회지
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• 제22권1호
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• pp.83-87
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• 2023

Y₂SiO₅ Powder based on silicon and yttrium is well known as powder phosphors due to their excellent sustainability and efficiency. A new electroluminescence device was fabricated with Y₂SiO₅:Eu³⁺ powder phosphors though a simple screen printing method. The powder-dispersed electroluminescence device consisted of the Y₂SiO₅:Eu³⁺ powder-dispersed phosphor layer and BaTiO₃-dispersed dielectric layer. The annealing temperature of the phosphor for the best powder electroluminescence performance was optimized to high temperature in ambient atmosphere though a solid-state reaction. The Eu³⁺ concentration for the best device performance was also investigated and furthermore, the thermal dependence of the electroluminescence intensity was investigated at the operating voltage at 100℃, which is the Curie temperature of the BaTiO₃ layer. And the intensity was exponentially increased with voltage and increased linearly with frequency.

• 한국기계가공학회지
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• 제20권11호
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• pp.24-29
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• 2021

In this study, the electrical and mechanical properties of carbon polymer composites, which have been gradually increasing in use in various fields, were investigated, and environment-friendly carbon nanofiber/waterborne polyurethane composites were prepared. Carbon nanofibers (diameter = approximately 100-300 mm) were synthesized using a relatively simple CVD process, obtaining a carbon material for application in ultrathin planar heating films and EMP shielding films in the future. The carbon nanofiber was dispersed, and mixed with water-dispersible polyurethane using a dispersing aid. According to the carbon nanofiber mass ratio, 20%-60% polyurethane/carbon nanofiber composites were manufactured. At a concentration of approximately 20%, the percolation threshold was determined, and at a concentration of approximately 50%, an electrical conductivity greater than 0.1 S/cm was determined. Moreover, a sample having a concentration of up to 60% was evaluated to further understand the mechanical properties. It was observed that as the concentration of the carbon nanofibers increased, the elongation decreased.