• Journal of the Korean earth science society
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• v.34 no.7
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• pp.693-710
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• 2013

This study investigates the distribution of suspended particulates during the Asian dust period in Busan, Korea in the spring of 2009. Weather map and automatic weather system (AWS) data were used to analyze the synoptic weather conditions during the period. Particulate matter 10, laser particle counter data, satellite images and a backward trajectories model were used to analyze the aerosol particles distribution and their origins. In Case 1 (20 February 2009), when the $PM_{10}$ concentration increased, the aerosol volume distribution of small ($0.3-1.0{\mu}m$) particles decreased, while the concentration of large ($1.0-10.0{\mu}m$) particles increased. When the $PM_{10}$ concentration decreased, the aerosol volume distribution was observed to decrease as well. The prevailing winds changed from weak northerly winds to strong southwesterly winds when the concentration of the large particles increased. The correlation coefficient between the $PM_{10}$ concentration and aerosol volume distribution of large particles showed a high positive value of over 0.9. The results from the trajectory model show that the Asian dust originated in the Gobi desert and the Nei Mongol plateau. In Case 2 (25 April 2009), when the $PM_{10}$ concentration increased, the aerosol volume concentration of small ($0.3-0.5{\mu}m$) particles decreased, but the concentration of large ($0.5-10.0{\mu}m$) particles increased. The opposite was observed when the $PM_{10}$ concentration decreased. The prevailing winds changed from northeasterly winds to southwesterly and northeasterly winds. The correlation coefficient between the $PM_{10}$ concentration and aerosol volume distribution of large particles ($1.0-10.0{\mu}m$) showed a high positive value of about 0.9. The results from the trajectory model show that the Asian dust originated in Manchuria and the eastern coast of China.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.23-23
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• 2011

Chemical-Mechanical Planarization (CMP) 공정이란 화학적 반응 및 기계적인 힘이 복합적으로 작용하여 표면을 평탄화하는 공정이다. 이러한 CMP 공정은 반도체 산업에서 회로의 고집적화와 다층구조를 형성하기 위하여 도입되었으며 반도체 제조를 위한 필수공정으로 그 중요성이 강조되고 있다. 특히 최근에는 Inter-Level Dielectric (ILD)의 형성과 Shallow Trench Isolation (STI) 공정에서실리콘 산화막을 평탄화하기 위한 CMP 공정에 대해 연구가 활발히 이루어지고 있다. 그러나 CMP 공정 후 scratch, pitting corrosion, contamination 등의 Defect가 발생하는 문제점이 존재한다. 이 중에서도 scratch는 기계적, 열적 스트레스에 의해 생성된 패드의 잔해, 슬러리의 잔유물, 응집된 입자 등에 의해 표면에 형성된다. 반도체 공정에서는 다양한 종류의 실리콘 산화막이 사용되고 gks이러한 실리콘 산화막들은 종류에 따라 경도가 다르다. 따라서 실리콘 산화막의 경도에 따른 CMP 공정 및 이로 인한 Scratch 발생에 관한 연구가 필요하다고 할 수 있다. 본 연구에서는 scratch 형성의 거동을 알아보기 위하여 boronphoshposilicate glass (BPSG), plasma enhanced chemical vapor deposition (PECVD) tetraethylorthosilicate (TEOS), high density plasma (HDP) oxide의 3가지 실리콘 산화막의 기계적 성질 및 이에 따른 CMP 공정에 대한 평가를 실시하였다. CMP 공정 후 효율적인 scratch 평가를 위해 브러시를 이용하여 1차 세정을 실시하였으며 습식세정방법(SC-1, DHF)으로 마무리 하였다. Scratch 개수는 Particle counter (Surfscan6200, KLA Tencor, USA)로 측정하였고, 광학현미경을 이용하여 형태를 관찰하였다. Scratch 평가를 위한 CMP 공정은 실험에 사용된 3가지 종류의 실리콘 산화막들의 경도가 서로 다르기 때문에 동등한 실험조건 설정을 위해 동일한 연마량이 관찰되는 조건에서 실시하였다. 실험결과 scratch 종류는 그 형태에 따라 chatter/line/rolling type의 3가지로 분류되었다 BPSG가 다른 종류의 실리콘 산화막에 비해 많은 수에 scratch가 관찰되었으며 line type이 많은 비율을 차지한다는 것을 확인하였다. 또한 CMP 공정에서 압력이 증가함에 따라 chatter type scratch의 길이는 짧아지고 폭이 넓어지는 것을 확인하였다. 본 연구를 통해 실리콘 산화막의 경도에 따른 scratch 형성 원리를 파악하였다.

• Transactions on Electrical and Electronic Materials
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• v.5 no.3
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• pp.89-92
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• 2004

For improving solar efficiencies, down conversion of high-energy photons to visible lights is discussed. The losses due to thermalization of charge carriers generated by the absorption of high-energy photons, can largely be reduced in a solar cell if more than one electron-hole pair can be generated per incident photon. The solar cell was constructed of dye-sensitized anatase-based TiO$_2$, approximately 30nm particle size, 6$\mu\textrm{m}$thickness, and 6${\times}$6$\textrm{mm}^2$ active area, Pt counter electrode and I$_3$$\^$-/I$_2$$\^$-/ electrolyte. After correction for losses due to light reflection and absorption by the conducting glass, the conversion of photons to electric current is practically quantitative in the plateau region of the curves. The incident photon to current conversion efficiency(IPCE) of N3 used as a dye in this work is about 80% at around 590nm and 610nm which is the emission spectrum of Eu doped LGF. The Eu doped LGF powder was prepared by conventional ceramic process, and used as a down converter for DSC after spin coated on the slide glass and fired.

• Korean Journal of Materials Research
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• v.27 no.3
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• pp.132-136
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• 2017

We synthesized potassium hexatitanate, ($K_2Ti_6O_{13}$, PT6), with a non-fibrous shape, by acid leaching and subsequent thermal treatment of potassium tetratitanate ($K_2Ti_4O_9$, PT4), with layered crystal structure. By controlling nucleation and growth of PT4 crystals, we obtained splinter-type crystals of PT6 with increased width and reduced thickness. The optimal holding temperature for the layered PT4 was found to be ${\sim}920^{\circ}C$. The length and width of the PT4 crystals were increased when the nucleation and growth time were increased. After a proton exchange reaction using aqueous 0.3 M HCl solution, and subsequent heat treatment at $850^{\circ}C$, the PT4 crystal transformed into splinter-type PT6 crystals. The frictional characteristics of the friction materials show that as the particle size of PT6 increases, the coefficient of friction (COF) and wear amounts of both the friction materials and counter disc increase.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.10a
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• pp.27-27
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• 1999

To illustrate the global variation of the droplet mean diameters and the turbulent flow characteristics in counterflowing internal mixing pneumatic nozzle, the experimental measurements at five axial downstream locations(i.e., at Z=30, 50, 80, 120, and 170mm) were made using a PDPA(Phase Doppler Particle Analyzer) under the different air injection pressures ranging from 40 ㎪ to 120 ㎪. A nozzle with axi-symmetric tangential-drilled four holes at an angle of 15$^{\circ}$ has been designed and manufactured. The distributions of velocities, turbulence intensities, turbulence kinetic energy, turbulent correlation coefficients, spray angle, droplet mean diameters, volume flux, number density are quantitatively analyzed. It is possible to discern the effects of increasing air pressure. It indicates that the strong axial momentum in spite of more or less disparity between the velocity components means more reluctant to disperse radially, and that axial fluctuating velocities are substantially higher than those of radial and tangential ones, suggesting that the disintegration process is enhanced under higher air assist. The larger droplets are detected in the spray centerline at the near stations and smaller ones are generated due to further subsequent breakup at farther axial locations are attributed to the internal mixing type nozzle characteristics. Despite of the strong axial momentum, the poor atomization around the centre close to the nozzle exit is attributed to the lower rates of spherical particles which are not subject to instantaneous breakup. As it goes downstream, however, substantial increases in SMD(Sauter Mean Diameter) from the central part toward spray periphery are understandable because the droplet relative velocity is too low to bring about any subsequent disintegration.

• Journal of Hydrogen and New Energy
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• v.21 no.3
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• pp.201-206
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• 2010

In present work, $La_{0.8}Ca_{0.2}CrO_3$ (LCC) ceramic interconnect layer for SOFC was prepared by using thermal plasma spray coating process. The LCC powders were synthesized by Pechini method and calcined at the temperature of $1000^{\circ}C$. The prepared LCC powder was characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), particle counter, BET analysis, respectively. In addition, basic and essential properties of LCC layer coated by thermal plasma spray coating process such as the morphology of surface and cross section for coated layer, gas leak rate, and electrical conductivity were analyzed and discussed. Based on these experimental results, it can be concluded that the LCC layer coated by thermal plasma spray coating process can be suitable as a ceramic interconnect of SOFC operated at $800^{\circ}C$.

• Journal of Radiation Protection and Research
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• v.18 no.2
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• pp.17-25
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• 1993

Beta ray spectra of $^3H,\;^{14}C\;and\;^{36}Cl$ in liquid scintillation counting system have been calculated using the Monte Carlo method by which physical behaviors of particle transport in medium were simulated. The calculations have been carried out on the basis of beta rays being slowing down according to the continuous slowing down approximation(CSDA) model. Beta rays generated in simulation geometry were traced until they lost their energy below 0.3keV that in known to be the detection limit in the liquid scintillation counter. Scintillator solution in which pure beta emitting radionuclides were dissolved uniformly was assumed to be bottled in the shape of right circular cylinder with 12.5mm in radius and 35mm in height. The comparison of the calculated and measured results showed satisfactory agreement between those two, with slight discrepancy due to self quenching in the case of lower energy of emitted beta particles in the solution.

• Journal of Korean Society of Water and Wastewater
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• v.19 no.2
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• pp.135-143
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• 2005

It was evaluated that the effect of turbidity removal by Pore Controllable Fiber Filter(PCF) installed in NS(Naksang) small water treatmant plant(system) using under flow water as raw water in the study. The results of the study are as the followings. Firstly, the removal efficiency of turbidity by PCF without coagulation(in operation mode not using coagulants) was mostly below 20 percent. On the other hand, when operation using proper coagulants, that of turbidity was mostly over 80 percent. Secondly, slow sand filtration after PCF, total turbidity removal efficiency of final treated water was 84.3 percent, and the contribution by PCF was 57.1 percent and that of slow sand filtration was 27.7 percent. Therefore the introduction of PCF as pre-treatment process would be helpful to reduce the loading of high turbidity of slow sand filtration. Thirdly, the results of particle counter measurements showed that when operated PCF with coagulants, fine flocs captured or adsorbed at the pore of PCF were flow out into the effluents from 120 minutes after backwashing because of the increase of headloss of PCF. Therefore the decision of backwashing time should made consideration into the outflow of fine flocs from PCF. Fourth, coagulant dosages on PCF at the same turbidity was largely variable because of the effect of the raw water characteristics and the turbidity increase velocity at rainy days, therefore flexible coagulant dosages should be considered rather than fixed coagulant dosage by the influent jar-test result.

• Journal of Convergence for Information Technology
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• v.9 no.12
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• pp.147-156
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• 2019

Numerical study was performed to investigate the convective heat transfer of Al₂O₃/water nanofluid flowing through the concentric double pipe counterflow heat exchangers. Hot fluid flowing through the inner pipe transfers its heat to cooling fluid flowing in the outer pipe. Effects of important parameters such as hot and cold volume flow rates, fluid type in the outer and inner pipes, and nanoparticles concentration on the heat transfer and flow characteristics are investigated. The results indicated that the heat transfer performance increases with increasing the hot and cold volume flow rates, as well as the particle concentrations. When both outer and inner pipes are nanofluids with 8% nanoparticle volume concentration, nanofluids showed up to 17% better heat transfer rate than basic fluids. Also, the average heat transfer coefficient of the base fluid for annulus-side improved by 31%. Approximately 20% enhancement in the heat exchanger effectiveness can be achieved with the addition of 8% alumina particles in base fluid. But, addition of nanoparticles to the base fluid enhanced friction factor by about 196%.

• Journal of the Korean earth science society
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• v.33 no.3
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• pp.259-268
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• 2012

To investigate the fluctuation of marine aerosol number concentration at each different size with vertical winds in ocean area, aerosol particles and vertical wind components were measured in the Ieodo Ocean Research Station, which is located to 419 km southwest of Marado, the southernmost island of Korea, from 8 to 22 June 2009. The Laser Particle Counter (LPC) and ultrasonic anemometer were used to measure the number of aerosol particles and vertical wind speed. Surface weather chart, NCEP/NCAR reanalysis data and sounding data were used to analyze the synoptic condition. The distribution of aerosol number concentration had a large fluctuation of bigger particles more than 1.0 ${\mu}m$ in diameter by vertical wind speed during precipitation. The aerosol particles larger than 1.0 ${\mu}m$ in diameter increased as the wind changed from downward to upward during precipitation. The aerosol number concentration of bigger size than 1.0 ${\mu}m$ in diameter increased about 5 times when vertical velocity was about 0.4 $ms^{-1}$. In addition, the accumulation and coarse mode aerosol number concentration decreased about 45% and 92%, respectively compared to concentrations during precipitation period. It is considered that vertical wind plays an important role for the increasing of coarse mode aerosol number concentration compared to the large aerosol particles sufficiently removed by the scavenging effect of horizontal winds. Therefore, the upward vertical winds highly contribute to the formation and increase in aerosol number concentration below oceanic boundary layer.