• Korean Journal of Materials Research
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• v.28 no.11
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• pp.627-632
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• 2018

Two dimensional(2D) crystals, composed of a single layer or a few atomic layers extracted from layered materials are attracting researchers' interest due to promising applications in the nanoelectromechanical systems. Worldwide researchers are preparing devices with suspended 2D materials to study their physical and electrical properties. However, during the fabrication process of 2D flakes on a target substrate, contamination occurs, which makes the measurement data less reliable. We propose a dry transfer method using poly-methyl methacrylate(PMMA) for the 2D flakes to transfer onto the targeted substrate. The PMMA is then removed from the device by an N-Methyl-2-pyrrolidone solution and a critical point dryer, which makes the suspended 2D flakes residue free. Our method provides a clean, reliable and controllable way of fabricating micrometer-sized suspended 2D nanosheets.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.04b
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• pp.57-60
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• 2002

In generally, the guest-emitter doped system has been reported to give a bright electroluminescence(EL). The purpose of using doped system is to improve for increasing lifetime and efficiency, and tuning multicolor light. This indicates an enhanced electron-hole recombination rate in emitting layer. The purpose of this study is to obtain the high performance EL devices for flat panel display with red emission. We fabricated EL devices using the guest-host system. where DCM derivatives were taken as a dopant. The devices are fabricated in multilayer system with various concentration of the dopant (red light emitting dye). We measured the I-V characteristics and EL spectra from these devices. and we compared with photoluminescence(PL) quantum yield among the DCM derivatives. The emission mechanism of devices is participated in energy transfer. The energy transfer from these hosts to DCM generates luminescence spectra that vary from yellow red to red, depending on DCM derivatives. Absorption and emission spectra of organic materials composing the devices depend on the emission materials doped with the DCM derivatives. We demonstrated that the high EL efficiency can be achieved by doping host material with DCM derivatives and molecular steric structures

• Journal of the Korean Applied Science and Technology
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• v.20 no.2
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• pp.148-153
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• 2003

Electron transfer through an Langmuir-Blodgett(LB) monolayer film sandwiched between metal electrodes. We used an eicosanoic acid material and the material was very famous as a thin film insulating material. Eicosanoic acid monolayer was deposited by Langmuir-Blodgett(LB) technique and a subphase was a $CdCl_2$ solution as a 2${\times}10^{-4}$ mol/L. Also we used a bottom electrode as an Al/$Al_2O_3$ and a top electrode as a Al and Ti/Al. Here, the $Al_2O_3$ on the bottom electrode was deposited by thermal evaporation method. The $Al_2O_3$ layer was acted on a tunneling barrier and insulating layer in tunnel diode. It was found that the proper transfer surface pressure for film deposition was 25 mN/m and the limiting area per molecule was about 24 ${\AA}^2$/molecule. When the positive and negative bias applied to the molecular device, the behavior shows that a tunnel switching characteristics. This result were analyzed regarding various mechanisms.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.10a
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• pp.719-725
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• 1997

This paper presents results of experimental studies on the heat transfer and solidification of the molten metal pool with overlying coolant with boiling. The metal pool is heated from the bottom surface and coolant is injected onto the molten metal pool. As a result, the crust, which is a solidified layer, may form at the top of the molten metal pool. Heat transfer is accomplished by a conjugate mechanism, which consists of the natural convection of the molten metal pool, the conduction in the crust layer and the convective boiling heat transfer in the coolant. This work examines the crust formation and the heat transfer rate on the molten metal pool with boiling coolant. The simulant molten pool material is tin (Sn) with the melting temperature of 232$^{\circ}C$. Demineralized water is used as the working coolant. The crust layer thickness was ostensibly varied by the heated bottom surface temperature of the test section, but not much affected by the coolant injection rate. The correlation beかeon the Nusselt number and the Rayleigh number in the molten metal Pool region of this study is compared against the crust formation experiment without coolant boiling and the literature correlations. The present experimental results are higher than those from the experiment without coolant boiling, but show general agreement with the Eckert correlation, with some deviations in the high and low ends of the Rayleigh number. This discrepancy is currently attributed to concurrent rapid boiling of the coolant on top of the metal layer.

• Fashion & Textile Research Journal
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• v.11 no.2
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• pp.359-362
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• 2009

This study investigates the behavior of water vapor permeability of a layered system to find out a comfortable combination of a layered system for outdoor activities and examines the water vapor permeability of various types of outdoor clothing fabrics. The layered system includes the base layer such as sportswool and polyester/cotton fabrics, the middle layer such as single and double sided fleece fabrics, and the shell layer such as polyurethane-coated, PTFE-laminated and microfiber fabrics in this experiment. Results show that the layered system was applied, it was working together as a whole having some influence on each other layer, though every layer offered varying degree of water vapor permeability. Water vapor permeability of layered system exactly followed the same trend as the shell layer, which is all vapor permeable water repellent fabrics as a single layer. The rate of water vapor transfer through a layered system is mainly related to the type of vapor permeable water repellent fabrics used for the shell layer.

• Structural Engineering and Mechanics
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• v.16 no.5
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• pp.519-531
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• 2003

Piezoelectric actuators have long been recognised for use in aerospace structures for control of structural shape. This paper looks at active control of the swept shock wave/turbulent boundary layer interaction using smart flap actuators. The actuators are manufactured by bonding piezoelectric material to an inert substrate to control the bleed/suction rate through a plenum chamber. The cavity provides communication of signals across the shock, allowing rapid thickening of the boundary layer approaching the shock, which splits into a series of weaker shocks forming a lambda shock foot, reducing wave drag. Active control allows optimum control of the interaction, as it would be capable of positioning the control region around the original shock position and unimorph tip deflection, hence mass transfer rates. The actuators are modelled using classical composite material mechanics theory, as well as a finite element-modelling program (ANSYS 5.7).

• International Journal of Highway Engineering
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• v.8 no.2 s.28
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• pp.31-35
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• 2006

Cement stabilisation is a common method for stabilising recycled road base material and provides a longer pavement life. With cement effect, the increment of stiffness in the stabilised layer would provide better load transfer to the pavement foundation. The recycling method provides an environmentally option as the existing road base materials will not be removed. This paper presents a case study of a trial section along the North-South Expressway in West Malaysia, where the Falling Weight Deflectometer (FWD) was implemented to evaluate the compressive strength and in-situ stiffness of the cement stabilised road base material. The improvement in stiffness of the cement stabilised base layer was monitored, and samples were tested during the trial. FWD was found to be useful for the structural assessment of the cement-stabilised base layer prior to placement of asphalt layers. Results from the FWD were applied to verify the assumed design parameters for the pavement. Using the FWD, an empirical correlation between the deflection and the stiffness modulus of the pavement foundation is proposed.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.309-314
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• 2007

Optimal layer sequencing of a multi-layered acoustical foam is solved to maximize its sound transmission loss. A foam consisting of air and poroelastic layers can be optimized when a limited amount of a poroelastic material is allowed. By formulating the sound transmission loss maximization problem as a one dimensional topology optimization problem, optimal layer sequencing and thickness were systematically found for several frequencies. For optimization, the transmission losses of air and poroelastic layers were calculated by the transfer matrix derived from Biot's theory. By interpolating five intrinsic parameters among several poroelastic material parameters, dear air-poroelastic layer distributions were obtained; no filtering or post-processing was necessary. The optimized foam layouts by the proposed method were shown to differ depending on the frequency of interest.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.04a
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• pp.393-397
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• 2003

Recently, rotating elements which use mechanical and electrical systems have been utilized for high speed and accuracy to increase the performance. The most important thing to get a more reliable system is to understand the friction, wear and characteristics which has an effect on various coated surfaces. In this study, the tribologicali characteristics of various soft/hard materials were investigated by using a custom-built pin-on-reciprocator tester From the experimental results, it was found that the friction coefficients of the soft material coated surfaces were lower under various normal loads due to trier self-lubricating ability and material transfer to the counter surface.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.3
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• pp.182-192
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• 1994

This paper focuses on the investigation of the heat transfer phenomena that occur inside the cylindrical tube. The inclination of the tube is adopted as a principal parameter varying from vertical to horizontal. The phase change material employed in this experiment is 99 percent pure n-docosane paraffin($C_{22}$ $H_{46}$). It is found that the amount of solidified mass during a prescribed solidifying period is not sensitive to the inclination of the tube but to the local layer thickness. It is studied that the latent energy is the largest contributor to the total extracted energy. The sensible energy($E_{s1}$, $E_{s2}$, $E_{s3}$) may not be negligible at the large wall-subcooling and initial-liquid-superheating, also at the first step of solidifying.