• Title/Summary/Keyword: Particle Transition

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

  • Kim, Yong Min
    • Journal of Integrative Natural Science
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    • v.2 no.4
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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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Effects of transition metal-doping on the properties of ZnO nanoparticles and the photocatalytic degradation of methylene blue (전이금속 도핑이 ZnO 나노분말의 특성 및 메틸렌블루 광촉매 분해 특성에 미치는 영향)

  • Chang, Han Kwon;Oh, Kyung Jun;Jang, Hee Dong;Cho, Kuk;Kim, Dong-Jin;Choi, Jin Hoon
    • Particle and aerosol research
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    • v.6 no.1
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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.

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

  • Huang, ShengZhong;Yousif, Mustafa Z.;Lim, Hee-Chang
    • Journal of the Korean Society of Visualization
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    • v.20 no.1
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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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    • v.45 no.6
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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.

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

  • Kim, Heon-Joo
    • Journal of the Korean Society for Heat Treatment
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    • v.15 no.2
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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.

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

  • Kim, Seung-Taek;Kim, Hyung-Tae;Lee, Sang-Ho;Kim, Jong-Seok
    • Journal of the Semiconductor & Display Technology
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    • v.9 no.4
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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.

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

  • Seul, Soo Duk
    • Journal of Adhesion and Interface
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    • v.11 no.3
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    • pp.112-119
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    • 2010
  • Poly(methyl methacrylate)/poly(butyl acrylate) PMMA/PBA core-shell composite particles were prepared by the emulsion polymerization of MMA and BA in the presence of different concentration of sodium dodecyl benzene sulfonate (SDBS). The following conclusions are drawn from the measured conversion and particle size distribution, morphology, average molecular weight distribution, observation of film formation and particle formation, glass transition temperature and physical properties of polymerized core-shell composition particles for using adhesive binder. When the concentration of 0.03 wt% surfactant, the conversions of PMMA and PBA core polymerization are excellent as 95.8% for PMMA core and 92.3% for PBA core. Core-shell composite particles are obtained 90.0% for PMMA/PBA core-shell composite particles and 89.0% for PMMA/PBA core-shell composite particles. It is considered that the core and shell particles are polymerized to be confirmed FT-IR spectra and average molecular weight measured with a GPC, formation of the composite particles is confirmed by the film formation from normal temperature, and composition of inside and outside of the composite particle is confirmed by TEM photograph. The synthesized polymer has two glass transition temperatures, suggesting that the polymer is composed of core polymer and shell polymer unlike general copolymers. It is considered that each core-shell composite particle can be used as a high functionality adhesion binder by the measurement of tensile strength and elongation.