• 제목/요약/키워드: Particle Transition

검색결과 279건 처리시간 0.031초

GaAs 이중 양자우물구조에서 고자기장에 유도된 대전된 엑시톤의 발생 (Formation of Charged Exciton in GaAs-AlGaAs Double-Quantum-Well Structure at High Magnetic Field)

  • 김용민
    • 통합자연과학논문집
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    • 제2권4호
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    • pp.265-269
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    • 2009
  • The photoluminescence was measured in GaAs-AlGaAs double-quantum-well structure at high magnetic field. Although the phototransition characteristics displayed a free-particle transition at low magnetic field, the change of free-particle transition into bound-exciton transition was observed at high magnetic field (above 10 T). A charged exciton formation due to charge-unbalanced electron-hole was identified by using a spin-polarized photoluminescence method. An increase of exciton formation due to the localization of free-particle at magnetic field was observed according to the increase of magnetic field.

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전이금속 도핑이 ZnO 나노분말의 특성 및 메틸렌블루 광촉매 분해 특성에 미치는 영향 (Effects of transition metal-doping on the properties of ZnO nanoparticles and the photocatalytic degradation of methylene blue)

  • 장한권;오경준;장희동;조국;김동진;최진훈
    • 한국입자에어로졸학회지
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    • 제6권1호
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    • pp.29-35
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    • 2010
  • Transition metals such as V, Fe, and Ni were used to synthesize doped zinc oxide nanoparticles from mixed liquid precursors by using the flame spray pyrolysis (FSP). The effects of dopants on the powder properties such as morphology, specific surface area, crystal structure, and light adsorption were analyzed by TEM, BET, XRD, and UV-Vis diffuse reflection spectrum (DRS), respectively. The results showed that hexagonal wurtzite structured ZnO:M (M = V, Fe, Ni) nanoparticles were successfully synthesized by the FSP. The transition metal-doping resulted in the decrease in its particle size and crystallite size. The UV-vis absorption spectra of ZnO:M nanoparticles were also red-shifted. ZnO:V showed the highest MB degradation of 99.4% under the UV irradiation after 3 hrs.

자연대류 경계층의 천이특성에 대한 실험적 연구 (Experimental study of natural transition in natural convection boundary layer)

  • 황성충;요시프 무스타파;임희창
    • 한국가시화정보학회지
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    • 제20권1호
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    • pp.29-37
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    • 2022
  • We carried out a laboratory experiment about the thermo-fluidic characteristics of natural convection boundary layer over a vertical heated plate under constant heat flux condition. Particle image velocimetry has been applied to observe the surface convection velocity close to the vertical plate submerged in the water chamber with the condition of Ra = 7 × 109 and Pr = 8.1. The velocity distributions indicate that the distinct stripe-like structures appears in the upstream (earlier transition region) and the distinct negative-positive and Λ(λ)-shaped flow structures in the downstream (mid-transition region). In addition, the temporal variation of spanwise and streamwise velocity is also presented.

Effect of Process Parameters and Kraft Lignin Additive on The Mechanical Properties of Miscanthus Pellets

  • Min, Chang Ha;Um, Byung Hwan
    • Journal of the Korean Wood Science and Technology
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    • 제45권6호
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    • pp.703-719
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    • 2017
  • Miscanthus had a higher lignin content (19.5 wt%) and carbohydrate (67.6 wt%) than other herbaceous crops, resulting in higher pellet strength and positive effect on combustion. However, miscanthus also contains a high amount of hydrophobic waxes on its outer surface, cuticula, which limits the pellet quality. The glass transition of lignin and cuticula were related to forming inter-particle bonding, which determined mechanical properties of pellet. To determine the effects of surface waxes, both on the pelletizing process and the pellet strength were compared with raw and extracted samples through solvent extraction. In addition, to clarify the relationship between pellet process parameters and bonding mechanisms, the particle size and temperature are varied while maintaining the moisture content of the materials and the die pressure at constant values. Furthermore, kraft lignin was employed to determine the effect of kraft lignin as an additive in the pellets. As results, the removal of cuticula through ethanol extractions improved the mechanical properties of the pellet by the formation of strong inter-particle interactions. Interestingly, the presence of lignin in miscanthus improves its mechanical properties and decreases friction against the inner die at temperatures above the glass transition temperature ($T_g$) of lignin. Consequently, it could found that the use of kraft lignin as an additive in pellet reduced friction in the inner die upon reaching its glass transition temperature.

6061AI 복합재료 마모특성에 미치는 SiC입자 강화재 체적분율의 영향 (Effect of Volume fraction of SiC Particle Reinforcement on the Wear Properties of 6061AI Composites)

  • 김헌주
    • 열처리공학회지
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    • 제15권2호
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    • pp.82-92
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    • 2002
  • In the present investigation wear behavior of the 6061AI composites reinforced with 5, 10, 20% SiC particles for dry sliding against a SM45C counterface was studied as a function of load and sliding velocity. Sliding wear tests were conducted at two loads(19.6 and 49N) and three sliding velocities(0.2, 1 and 2 m/sec) at constant sliding distance of 4000 m using pin-on-disk machine under room temperature. Presence of SiC reinforcement particles in the composites has displayed a transition from mild to severe wear at relatively higher applied load and sliding velocity compare to that of the matrix metal. As the volume fraction of SiC particles increased, the transition moved to a more severe wear conditions. Eventually, mild wear prevailed at a most severe wear conditions in this study, that was 49N load and 2 m/sec sliding velocity in 20% SiC particle/6061AI composite.

전자 종이용 하전 입자의 부착력 분석 (Adhesion Force Analysis of Charged Particles for the E-paper)

  • 김승택;김형태;이상호;김종석
    • 반도체디스플레이기술학회지
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    • 제9권4호
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    • pp.87-91
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    • 2010
  • Charged micro-particles are widely used as the key components for many electrical applications such as an e-paper, a touch panel, a printer toner and an electronic ink. Among them, the e-paper is an emerging reflective type display using the charged particles that has the advantages of the extremely low power consumption and sunlight readability. To create images on the e-paper, we confine black positively-charged and white negatively-charged particles between bottom and top electrodes and selectively apply the electric field. When the Coulomb force by an applied electric field is greater than the adhesion force between the charged particle and the electrode, the particles' transition happens resulting in the change of color between black and white. Therefore, the adhesion force is a very important factor for designing and estimating e-paper's operation. In this study, we constructed a basic model for particle's transition and an adhesion force equation describing particle's transition with three different forces: electrostatic image force, Van der Waals force and gravitational force. The simulation results showed that the gravitational force is negligible for the interesting range for the charge and the radius, and the adhesion force can be strongly dependent on the particle's charge and radius.

PMMA/PBA와 PBA/PMMA Core Shell 복합입자의 제조 - 유화제의 영향 - (Manufacture of PMMA/PBA and PBA/PMMA core Shell Composite Particles - Effect of emulsifier -)

  • 설수덕
    • 접착 및 계면
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    • 제11권3호
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    • pp.112-119
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    • 2010
  • PMMA와 PBA core 제조 시 개시제는 APS를, 유화제 SDBS의 농도를 0.01에서 0.03 wt% 일 때 전환율이 95.8과 92.3%로 가장 우수하였으며, core-shell 복합입자의 제조 시에는 SDBS의 농도 0.02 wt% 일 때 PMMA/PBA core-shell 복합입자는 전환율이 90.0%, PBA/PMMA core-shell 복합입자는 89.0%가 되었다. FT-IR 분석과 GPC에 의한 평균분자량 측정을 통해 core와 shell 단량체들이 중합되어 있음을 확인하고, 복합입자의 형태는 상온에서의 필름형성정도와 TEM 분석으로 확인하였다. DSC에 의해 유리전이온도를 측정함으로써 일반 공중합체와는 달리 2개의 유리전이온도가 존재하여 core-shell 복합입자가 형성되었음을 알 수 있고, 각각의 core-shell 복합입자의 인장강도와 신율의 측정을 통해 고기능성 접착바인더로서의 사용가능성을 확인하였다.