• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.1
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• pp.53-59
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• 2010

In this paper, we propose a novel chaotic micromixer of which mixing mechanism is based upon magnetohydrodynamic (MHD) multi-vortical flow generation in a simple straight microchannel. In the microchannel of the micromixer has electrodes patterned on two side walls and bottom wall. Lorentz forces are variously induced by changing applied voltages at the patterned electrodes in order to pump and mix conductive fluids in the microchannel. Three-dimensional computational fluid dynamics simulations were conduced to characterize mixing behaviors inside the MHD micromixer. The mixing efficiencies were also evaluated for the various flow conditions.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2003.05b
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• pp.335-336
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• 2003

미세입자는 오염된 도심지역 분진수의 90~99%에 이르는 높은 비율을 보이고 있고, 폐 깊숙이 침투하여 폐암을 비롯한 폐질환을 일으킬 수 있다. 더욱이 동일 질량의 분진인 경우 입자의 크기가 감소함에 따라 미세 입자의 표면적은 급증하기 때문에 As, Cr(Ⅵ), Cd등과 같은 발암 중금속을 쉽게 흡착하여 미세 입자가 인체에 미치는 영향은 거대입자에 비하여 매우 크다. 따라서 미국은 1990년대부터 미세 분진의 입경별 위해성을 집중적으로 연구하여 공기 역학적 직경이 10$\mu\textrm{m}$이하인 PM 10 기준과 더불어 PM 2.5 기준을 신설하였다. (중략)

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2002.04a
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• pp.53-54
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• 2002

도시대기중의 분진은 입경 분포에 따라 공기 역학적 직경 2.5$\mu\textrm{m}$를 기준으로 미세 입자(fine particles)와 거대 입자(coarse particles)로 나누어지는 쌍극분포를 보인다. 미세 입자는 주로 화석연료의 연소, 자동차의 배기가스 등과 같은 인위적 발생원에 의한 것이며, 거대입자는 토사의 재 비산, 해염 통과 같은 자연적 발생원에 의한 것이다. 미세 입자는 오염된 도심지역 분진수의 90-99%에 이르는 높은 비율을 보이고 있고, 폐 깊숙히 침투하여 폐 질환을 일으킬 수 있다. (중략)

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2001.11a
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• pp.231-232
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• 2001

도시지역의 주 오염물질 중 하나인 입자상 물질(Particulate Matter:PM)은 공기역학적 직경 2.5$\mu\textrm{m}$을 기준으로 이산형 분포를 하여 2.5$\mu\textrm{m}$이하를 미세입자, 2.5$\mu\textrm{m}$이상을 조대입자로 나뉜다. 이 미세입자는 주로 자동차 배출, 산업연소에서 배출되는 가스상 물질의 2차 반응으로 발생한다(Pope et al., 1995). 미세입자는 상당량이 2차 반응에서 생성되는 물질이며, 크기가 작은 대신 상대적으로 표면적이 크기 때문에 각종 중금속과 유해 대기오염물질과의 흡착이 용이하여 호흡기 계통의 질병을 일으킬 수 있는 확률이 조대입자에 비해 높다고 알려져 있어 인체에 미치는 영향이 클 것으로 시사되고 있다(Dockery et al., 1998). (중략)

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.39 no.2
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• pp.29-33
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• 2002

Various nanometer-scale structures are fabricated on hydrogen-passivated p-type Si(100) surface by scanning probe microscopy(SPM). The hydrogen-passivation is performed by dipping the samples in diluted 10% HF solution for one min.. Pt alloy wires are used for tips and the tips are made by cutting the wires at 45$^{\circ}$ slanted. Various line features are fabricated in various bias voltage. The optimal structure is the line of about 30 nm width on 1.7V bias voltage and 1 nA tunneling current.  

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.1
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• pp.33-40
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• 2024

The volume of shells, a prominent form of marine waste, is steadily increasing each year. However, a significant portion of these shells is either discarded or left near coastlines, posing environmental and social concerns. Utilizing shells as a substitute for traditional aggregates presents a potential solution, especially considering the diminishing availability of natural aggregates. This approach could effectively reduce transportation logistics costs, thereby promoting resource recycling. In this study, we explore the feasibility of employing wasted shell aggregates in 3D concrete printing technology for marine structures. Despite the advantages, it is observed that 3D printing concrete with wasted shells as aggregates results in lower strength compared to ordinary concrete, attributed to pores at the interface of shells and cement paste. Microstructure characterization becomes essential for evaluating mechanical properties. We conduct an analysis of the mechanical properties and microstructure of 3D printing concrete specimens incorporating wasted shells. Additionally, a mix design is proposed, taking into account flowability, extrudability, and buildability. To assess mechanical properties, compression and bonding strength specimens are fabricated using a 3D printer, and subsequent strength tests are conducted. Microstructure characteristics are analyzed through scanning electron microscope tests, providing high-resolution images. A histogram-based segmentation method is applied to segment pores, and porosity is compared based on the type of wasted shell. Pore characteristics are quantified using a probability function, establishing a correlation between the mechanical properties and microstructure characteristics of the specimens according to the type of wasted shell.

• Composites Research
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• v.18 no.4
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• pp.21-26
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• 2005

Nondestructive damage sensing and load transfer mechanisms of carbon nanotube (CNT) and nanofiber (CNF)/epoxy composites have been investigated by using electro-micromechanical technique. The electrospun PVDF nanofibers were also prepared as a piezoelectric sensor. The electro-micromechanical techniques were applied to evaluate sensing response of carbon nanocomposites by measuring electrical resistance under an uniform cyclic loading. Composites with higher volume content of CNT showed significantly higher tensile properties than neat and low volume$\%$ CNT composites. CNT composites showed humidity sensing within limited temperature range. CNT composites with smaller aspect ratio showed higher apparent modulus due to high volume content in case of shorter aspect ratio. Thermal treated electrospun PVDF nanofiber showed higher mechanical properties than the untreated case due to crystallinity increase, whereas load sensing decreased in heat treated case. Electrospun PVDF nanofiber web also showed sensing effect on humidity and temperature as well as stress transferring. Nanocomposites and electrospun PVDF nanofiber web can be applicable for sensing application.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.579-585
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• 2009

In this paper, a series of finite element analyzes were carried out to evaluate the performance of the RC beams strengthened with sprayed fiber reinforced polymer(SFRP) coating. A damage constitutive model based on the micromechanical constitutive model(Lee, 2001) in conjunction with the damage models(Lee 등, 2000) for SFRP coating was implemented into the finite element code ABAQUS. The present prediction results were compared with experimental data(Ha, 2007; Ha 등, 2009) to assess the accuracy of the damage constitutive model. It was concluded from the comparative study that the computational model developed by implementing the damage constitutive model into ABAQUS is suitable for the prediction of the performance of RC beams strengthened with SFRP coating.

• Polymer(Korea)
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• v.28 no.4
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• pp.285-290
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• 2004

Nondestructive damage sensitivity of carbon nanotube(CNT) and nanofiber (CNF)/epoxy composites with their adding contents was investigated using electro-micromechanical technique. Carbon black (CB) was used only for the comparison with CNT and CNF. The fracture of carbon fiber was detected by acoustic emission (AE), which was correlated to the change in electrical resistance, ΔR under double-matrix composites (DMC) test. Stress sensing on carbon nanocomposites was performed by electro-pullout test under uniform cyclic loading. At the same volume fraction, the damage sensitivity for fiber fracture, matrix deformation and stress sensing were highest for CNT/epoxy composite, whereas for CB/epoxy composite they were the lowest among three carbon nanomaterials (CNMs). Damage sensitivity was correlated with morphological observation of carbon nanocomposites. Homogeneous dispersion among CNMs could be keying parameters for better damage monitoring. In this study, damage sensing of carbon nanocomposites could be evaluated well nondestructively by the electrical resistance measurement with AE.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.1
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• pp.77-82
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• 2010

Our study aims to understand the flow of liquid in an open-top rectangular microchannel that can be used in micro total analysis systems ($\mu$-TAS) because it has advantages in terms of light transmission and energy efficiency. We measured the liquid velocity using particle tracking technique and conducted a simulation with computational fluid dynamics by altering the area of channel cross section and channel length for the capillary-driven flow in the open-top rectangular microchannel. When liquid water drops to an entrance of the fabricated microchannel with a height of 20 μm and a width of 20 ${\mu}m$, it flows along the microchannel by only capillary force. In the wetting behavior of the liquid, important parameters of this flow are channel size, contact angle and liquid properties such as surface tension and viscosity, which are used to control the flow of liquid in the microchannel.