• 한국물환경학회지
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• 제37권4호
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• pp.286-295
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• 2021

The removal efficiency of road-deposited sediment (SDR) by road sweeping was analyzed by performing particle size analysis before and after road sweeping at four highways during May to December 2019. The SDR accounted for the largest proportion in the range of 250 to 850 ㎛ and the degree of its proportion had an effect on the particle size distribution curve. The particle size distribution of the collected sediments showed a similar distribution at all sites. Below 75 ㎛, the removal efficiency of SDR showed a constant value around 40%, but above 75 ㎛, it increased as the particle size increased. The removal efficiency was 82-90% (average 86%) for gravel, 66-93% (average 79%) for coarse sand, 35-92% (average 64%) for fine sand, 29-69% (average 44%) for very fine sand, 19-58% (average 40%) for silt loading, 10-59% (average 40%) for TSP, 13-57% (average 40%) for PM10, and 15-61% (average 38%) for PM2.5. SDR removal efficiency showed an average of 69% for the four highways. It was found that if the amount of SDR was less than 100 g/m², it was affected by the road surface condition and had a large regional deviation. As such, the amount of SDR and the removal efficiency increased. The fine particles, which have relatively low removal efficiency, contained a large amount of pollutants, which is an important factor in water and air pollution. Therefore, various measures to improve the removal efficiency of fine particles in SDR by road sweeping are needed.

• 대한토목학회논문집
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• 제28권4A호
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• pp.573-580
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• 2008

본 연구에서는 초고성능 콘크리트(Ultra High Performance Concrete, UHPC)에서 석영질 충전재의 입자크기가 콘크리트 성능에 미치는 영향을 평가하였다. 본 연구에서 고려한 충전재의 입경은 각각 2, 4, 8, 14, $26{\mu}m$이며, 평가항목으로는 굳지 않은 상태에서의 유동성과 압축강도, 극한변형률, 탄성계수 및 휨강도를 평가하였다. 또한 UHPC의 역학적 특성과 미세구조의 관계를 규명하기 위해 XRD, MIP 시험을 수행하였다. 실험을 통해 충전재의 입자크기가 작을수록 유동성 및 강도특성이 향상됨을 알 수 있었다. MIP 분석을 통해 충전재 입자크기가 작을수록 공극률이 감소하고, 따라서 UHPC의 강도가 증가함을 알 수 있었다. 그리고 XRD 분석을 통해 UHPC에서 충전재 입자크기에 따른 화학적 반응의 변화는 거의 없는 것으로 나타났다.

• Korean Chemical Engineering Research
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• 제51권5호
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• pp.602-608
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• 2013

$CO_2$를 포집, 수송, 저장하는 기술에 있어서 경제적이고 친환경적 혁신기술로 주목받고 있는 가스 하이드레이트 이용기술의 연구가 활발히 진행되고 있다. 본 연구에서는 가스 하이드레이트를 이용한 $CO_2$ 수송/저장기술의 핵심이 되는 자기보존효과(self-preservation effect)가 발현하는지를 확인하고자 하였다. 특히 $CO_2$ 하이드레이트 입자의 직경에 대한 효과 정도를 실험적으로 살펴보았다. 밀리미터, 마이크론, 그리고 나노 크기의 각각 다른 직경을 갖는 세 종류 $CO_2$ 하이드레이트 샘플을 준비하였고, 3주간 $-15{\sim}-30^{\circ}C$의 온도 및 대기압 조건에서 각각의 샘플 무게 변화를 측정하였다. 실험연구 결과 $CO_2$ 하이드레이트의 자기보존효과를 최대한 얻기 위해서는 온도는 가능한 낮아야 하며, 샘플의 직경 크기가 클수록 좋고, 샘플은 치밀한 구조로 조직되어 높은 밀도를 갖는 방식으로 제조하는 것이 매우 향상된 결과를 얻을 수 있음을 확인하였다.

• 한국분말재료학회지
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• 제31권2호
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• pp.132-136
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• 2024

This study investigated the effects of revolution speed and ball size in planetary milling on the microstructure and dehydrogenation behavior of TiH₂ powder. The particle size analysis showed that the large particles present in the raw powder were effectively refined as the revolution speed increased, and when milled at 500 rpm, the median particle size was 1.47 ㎛. Milling with a mixture of balls of two or three sizes was more effective in refining the raw powder than milling with balls of a single size. A mixture of 3 mm and 5 mm diameter balls was the optimal condition for particle refinement, and the measured median particle size was 0.71 ㎛. The dependence of particle size on revolution speed and ball size was explained by changes in input energy and the number of contact points of the balls. In the milled powder, the endothermic peak measured using differential thermal analysis was observed at a relatively low temperature. This finding was interpreted as the activation of a dehydrogenation reaction, mainly due to the increase in the specific surface area and the concentration of lattice defects.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 추계학술대회 논문집
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• pp.128-130
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• 2008

One of methods to increase the efficiency of a dye-sensitized solar cell(DSC) is the effective usage of the incident light. It can be controlled by using a light scattering layer. The light scattering effect makes that the optical path length of incident light to DSC increases. And then, the photocurrent and the efficiency is increased because of the increase of dye adsorption and the abundant amount of the light. In this study, we apply the light scattering layer to DSC by using two $TiO_2$ pastes that have different particle sizes. As a result, the photocurrent increases and the total efficiency is also increases in the case of using large-sized $TiO_2$ particle as the light scattering layer.

• 천문학회보
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• 제36권1호
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• pp.54.2-54.2
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• 2011

It is the conventional wisdom that the Poynting-Robertson effect is essentially the outcome of the interplay between absorption and reemission processes. For a better understanding of the motion of charged particles around a compact star with strong radiation, we reached an alternative interpretation for the Poynting-Robertson effect based on the covariant formalism and found that it is attributed to the combination of the aberration and the Lorentz transformation of the radiation stress-energy tensor. As a general relativistic application of the Poynting-Robertson effect, we studied the dynamics of test particles around the spinning relativistic star with strong radiation. We discovered that the combination of the angular momentum and the finite size of the star generates "radiation counter drag" which exerts on the test particle to enhance its specific angular momentum, contrary to the radiation drag. The balance of the radiation drag and the radiation counter drag renders the particle to hover around the spinning luminous star at the "suspension orbit". The radial position and the angular velocity of the particle on the "suspension orbit" are determined by the angular momentum, the luminosity, and the size of the central star only, and they are independent of the initial position and velocity of the particle.

• 대한기계학회논문집B
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• 제21권11호
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• pp.1509-1517
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• 1997

Charged and uncharged particle motions and collection characteristics around a bipolar charged rectangular shape electret fiber are studied numerically. Particle inertia, fluid drag, Coulomb force and polarization force are considered to predict the particle motion around the electret fiber. The effects of particle sizes, flow velocities, number of charges and polarities are also systematically investigated. For small size particles, the single fiber collection efficiency is greatly dependent on the charge polarity and the number of charges on a particle. However, particles larger than 5.mu.m do not show charging effect on collection efficiencies in the flow velocity ranges from 1.5 cm/s to 150 cm/s when the maximum charges are within +5 to -10. The results show that a strong electric field gradient at the corner of the bipolar charged fiber plays a very important role on collecting particles regardless of its charge polarity because of the polarization force. It also shows that the most penetrating particle size for a single electret fiber decreases as the flow velocity increases and the number of charges of a particle decreases.

• 한국입자에어로졸학회지
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• 제10권1호
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• pp.27-31
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• 2014

A simple bimodal model has been developed to analyze charged particle coagulation by modifying previously suggested bimdal model for evolution of particle generation and growth. In the present model, two monodisperse modes are used and 40 charge nodes are assigned to each mode to account both change of the particle size and charge distribution. In addition, we also implemented the effect of electrostatic dispersion loss in the present model. Based on the developed model, we analyzed coagulation of asymmetric bipolar charged particles by computing evolutions of particle number concentration, geometric mean diameter of particles, charge asymmetric ratio and geometric standard deviation of particle size distribution for various initial charge asymmetric ratios. The number concentration of asymmetric bipolar charged particles decreases faster than that of neutral particles but that does not give faster growth of particles since the electrostatic dispersion loss overwhelms particle growth by coagulation.

• 상하수도학회지
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• 제20권6호
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• pp.823-828
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• 2006

For this study, an online particle counter was installed before and after the activated carbon filtration process of D water treatment plant where has advanced water treatment processes, produces average 900,000ton/day of drinking water and supply the produced drinking water to Busan citizens. We collected and analyzed particle count data for about 1 year. We inspected particle breakthrough in three out of sixteen filter processes operated at same conditions, i.e. 5th filter, 6th filter and 7th filter. According to the monitoring results, 6th and 7th filters showed similar results while 5th filter showed different results. When compared seasonal effect, the particle count for dry season was below 10 particles/ml while the particle count for August when monthly average rainfall is over 200mm was much higher than for dry season. In January and August, there was a difference in breakthrough particle size. In January, small particles in 2~3um were mainly detected while in August 10um particles were mainly detected and the size distribution was 40% of total count.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.217-221
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• 2002

In the coarse grain HAZ adjacent to the fusion line, most of the TiN particles in conventional Ti added steel are dissolved and austenite grain growth is easily occupied during welding process. To avoid this difficulty, thermal stability of TiN particle is improved by increasing the nitrogen content in steel. In this study, the effect of high nitrogen TiN particle on preventing austenite grain growth in HAZ was investigated. Increased thermal stability of TiN particle is helpful for preventing the austenite grain growth by pinning effect. High nitrogen TiN particle in simulated HAZ were not dissolved even at high temperature such as 1400 C and prevented the austenite grain growth in simulated HAZ. Owing to small austenite grain size in HAZ the width of coarse grain HAZ in high nitrogen TiN steel was decreased to 1/10 of conventional TiN steel. Even high heat input welding, the microstructure of coarse grain HAZ consisted of fine polygonal ferrite and pearlite and toughness of coarse grain HAZ was significantly improved.