• 한국대기환경학회지
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• 제21권5호
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• pp.537-545
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• 2005

A new dispersion model for dense gas is constructed in the Lagrangian framework. Prediction of concentration by the proposed model is compared with measure data obtained in the experiment conducted in Thorney Island in 1984. Two major effects of dense gas dispersion, gravity slumping and stratification effect, are successfully incorporated into LDM (Lagrangian dense gas model). Entrainment effect is naturally modelled by introducing stochastic dispersion model with the effect of turbulence suppression by stratification. Not only various releasing conditions but also complex terrain can be extended to, although proposed model is appropriate for flat terrain.

• 대한기계학회논문집B
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• 제27권8호
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• pp.1165-1173
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• 2003

The effects of (1) phonon dispersion on thermal conductivity model and (2) differentiation of group velocity and phase velocity are examined for germanium. The results show drastic change of thermal conductivity regardless of the same relaxation time model. Also the contribution of transverse acoustic (TA) phonon and longitudinal acoustic (LA) phonon on the thermal conductivity at high temperatures is reassessed by considering more rigorous dispersion model. Holland model, which is commonly used for modeling thermal conductivity, underestimates the scattering rate for TA phonon at high frequency. This leads the conclusion that TA is dominant heat transfer mode at high temperatures. But according to the rigorous consideration of phonon dispersion, the reduction of thermal conductivity is much larger than the estimation of Holland model, thus the TA at high frequency is expected to be no more dominant heat transfer mode. Another heat transfer mechanism may exist at high temperatures. Two possible explanations we the roles of (1) Umklapp scattering of LA phonon at high frequency and (2) optical phonon.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 춘계학술대회 논문집
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• pp.163-166
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• 2009

알루미늄슬러리 연료 제조 시 알루미늄의 분산안정성에 미치는 공정변수의 영향을 조사하였다. 알루미늄슬러리연료의 분산안정성은 Laser의 산란 현상을 이용하여 물질의 분산 안정성을 파악하는 Turbiscan을 이용하여 확인하였다. 여러 종류의 첨가제 적용시 시간 경과에 따른 입자 크기 및 농도 변화를 측정한 결과, TPAB (Tetrapropyl ammonium bromide) 사용시 다른 첨가제보다 좋은 결과를 나타내었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.899-904
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• 2003

A new model for dense gas dispersion is formulated within the Lagrangian framework. In several accidental released situations, denser-than-air vapour clouds are formed which exhibit dispersion behavior markedly different from that observed for passive atmospheric pollutants. For relevant prediction of dense gas dispersion, the gravity and entrainment effects need to implemented. The model deals with negative buoyancy which is affected by gravity. Also, the model is subjected to entrainment. The mean downward motion of each particle was accounted for by considering the Langevin equation with buoyancy correction term.

• 한국정밀공학회지
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• 제27권7호
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• pp.49-54
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• 2010

The cryogenic ball milling was performed on carbon nanotubes (CNTs) at an extremely low temperature to increase the dispersion of CNTs. The effects of milling speed and time on the deagglomeration and structural changes of CNTs were studied. FESEM was used to analyze the dispersion and the change of particle size before and after milling process. Transmission electron microscopic (TEM) analysis was also investigated the effect of cryogenic ball milling on the morphological characteristics of CNTs. The structural changes by the cryogenic ball milling process were further confirmed by x-ray diffraction (XRD) and Raman spectroscopic analysis. The results showed that the agglomeration of CNTs was significantly reduced and amorphous structure was observed at high milling speed. However, the milling time has no great effect on the dispersion property and structural change of CNTs compared with milling speed.

• Nuclear Engineering and Technology
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• 제46권2호
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• pp.159-168
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• 2014

In order to advance understanding of the breakaway swelling behavior of U-Mo/Al dispersion fuel under a high-power irradiation condition, the effects of fuel-matrix interaction on the fuel performance of U-Mo/Al dispersion fuel were investigated. Fission gas release into large interfacial pores between interaction layers and the Al matrix was analyzed using both mechanistic models and observations of the post-irradiation examination results of U-Mo dispersion fuels. Using the model predictions, advantageous fuel design parameters are recommended to prevent breakaway swelling.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2016년도 추계학술대회
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• pp.940-941
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• 2016

분산 제어가 적용된 광전송 링크에서 각 중계 구간 당 잉여 분산의 크기가 중계 구간 수가 증가할수록 선형 (또는 비선형)적으로 점차 증가 (또는 감소)하는 경우에서의 왜곡된 WDM 채널의 보상정도를 시뮬레이션을 통해 살펴보았다.

• 반도체디스플레이기술학회지
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• 제21권2호
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• pp.1-6
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• 2022

This computational investigation of micro-sized particle dispersion concerns the fume particle contamination over target surface in high-precision laser line machining process of semiconductor and display device materials. Employing the random sampling based on probabilistic fume particle generation distributions, the effects of sphericity for nonspherical fume particles are analyzed for the fume particle dispersion and contamination near the laser machining line. The drag coefficient correlation for nonspherical particles in a low Reynolds number regime is selected and utilized for particle trajectory simulations after drag model validation. When compared to the corresponding results by the assumption of spherical fume particles, the sphericity of nonspherical fume particles show much less dispersion and contamination characteristics and it also significantly affects the particle removal rate in a suction air flow patterns.

• Nuclear Engineering and Technology
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• 제56권6호
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• pp.2039-2049
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• 2024

The radioactive pollutant could migrate to the downstream urban area under the action of atmospheric dispersion due to the turbulent mixing under actual pollution accidents. A scenario in which radioactive contaminants from the upstream (for example, a nearshore nuclear power plant accident) migrates to the downstream urban blocks have been considered in this study. Numerical simulations using computational fluid dynamics (CFD) are then conducted to investigate the effects of the urban morphology (building packing density and layout) on the atmospheric dispersion of radioactive pollutants in this scenario. The building packing density and structure can significantly affect urban areas' mean flow pattern and the turbulent kinetic energy (TKE). The flow pattern and the TKE distribution influence the radioactive pollution dispersion. It is found that the radioactive pollution at the urban canyons is significantly affected by the vertical transport at the canyon. A comparison of the distributions of radioactive and traditional non-radioactive pollutants is also provided.

• 한국통신학회논문지
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• 제33권10B호
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• pp.855-864
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• 2008

대용량 장거리 WDM ($24{\times}40$ Gbps) 전송 시스템의 구현을 위해 단일 모드 광섬유에서 발생하여 WDM 채널 신호에 왜곡을 발생시키는 색 분산과 비선형 효과를 보상하는 광 링크 기술을 전산 시늉을 통해 살펴보고 그 설계 기준을 제안하였다. 링크 전송 기술은 전체 전송로에서 축적된 분산을 분산 보상 광섬유를 통해 보상하는 분산 제어 (DM; dispersion management)와 전체 전송로 중간에서 왜곡된 신호의 주파수를 반전시켜 보상하는 광위상 공액 기술로 구성된다. 본 연구에서 살펴본 DM은 집중형과 inline의 2 가지 구조이다. 전송 링크에 OPC (optical phase conjugator)만 적용된 WDM 전송 시스템에서의 경우에 비해 DM이 추가적으로 적용되면 모든 WDM 채널들의 눈 열림 패널티가 크게 개선되는 것을 확인하였다. 그리고 두 DM 구조 모두에서 유효 잉여 분산 범위를 이용하여 전송 링크의 설계 기준을 제시하였다. WDM 전체 채널들의 EOP 개선과 유효 잉여 분산 범위 모두 inline DM 구조가 집중형 DM 구조보다 더욱 양호한 결과를 나타냄을 확인하였다.