• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.226-226
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• 2010

Boron Nitride (BN) doped GeSbTe films were grown by the ion beam sputtering deposition (IBSD). The in-situ sheet resistance data and the x-ray diffraction patterns showed the crystallization is suppressed due to the BN incorporation. The phase change speed in BN doped GeSbTe films were investigated using the static tester equipped with nanosecond pulsed laser. The phase change speed for BN doped GST films become faster than the corresponding values for an undoped GST film. The Johnson-Mehl-Avrami(JMA) plot and Avrami coefficient for laser crystallization showed that the change in growth mode during the laser crystallization is a most important factor for the phase change speed in the BN doped GST films. The JMA results and the atomic force microscopy (AFM) images indicate that the origin of the change in the crystalline growth mode is due to an increase in the number of initial nucleation sites which is produced by the incorporated BN. In addition, the retension properties for the laser writing/erasing are remarkably improved in BN doped GeSbTe films owing to the stability of the incorporated BN.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.228.2-228.2
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• 2014

Characteristics of high Fermi velocity, high mechanical strength, and transparency offer tremendous advantages for using graphene as a promising transparent conducting material [1] in electronic devices. Although graphene is a prospective candidate for touch sensor with strong mechanical properties [2] and flexibility, only few investigations have been carried out in the field of sensor as a device form. In this study, we suggest ultra-highly sensitive and transparent graphene touch sensor fabricated by single layer graphenes. One of the graphene layers is formed in the top panel as a disconnected graphene beam transferred on PDMS, and the other of the graphene layer is formed with line-patterning on the bottom panel of triple structure PET/PI/SiO2. The touch sensor shows characteristics of flexible. Its transmittance is approximately 75% where transmittance of the top panel and the bottom panel are 86.3% and 87%, respectively, at 550 nm wavelength. Sheet resistance of each graphene layer is estimated as low as $971{\Omega}/sq$. The results show that the conductance change rate (${\Delta}C/C0$) is $8{\times}105$ which depicts ultra-high sensitivity. Moreover, reliability characteristic confirms consistent behavior up to a 100-cycle test.

• International Journal of Fluid Machinery and Systems
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• v.10 no.1
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• pp.1-8
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• 2017

Bifurcation refers to wye division of penstock to divide the flow symmetrically or unsymmetrically into two units of turbine for maintaining economical, technical and geological substrates. Particularly, water shows irrelevant behavior when there is a sudden change in flow direction, which results into the transition of the static and dynamic behavior of the flow. Hence, special care and design considerations are required both hydraulically and structurally. The transition induced losses and extra stresses are major features to be examined. The research on design and analysis of bifurcation is one of the oldest topics related to R&D of hydro-mechanical components for hydropower plants. As far as the earlier approaches are concerned, the hydraulic designs were performed based on graphical data sheet, head loss considerations and the mechanical analysis through simplified beam approach. In this paper, the multi prospect approach for design of Bifurcation, incorporating the modern day's tools and technology is identified. The hydraulic design of bifurcation is a major function of dynamic characteristics of the flow, which is performed with CFD analysis for minimum losses and better hydraulic performances. Additionally, for the mechanical design, a simplified conventional design method as pre-estimation and Finite Element Method for a relevant result projections were used.

• Journal of ILASS-Korea
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• v.7 no.2
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• pp.7-15
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• 2002

A particle flow visualization, electrostatic charging measurement and separation of triboelectrically charged particles in the external electric field by a fluidized bed tribocharger are conducted for the removal of PVC particles from mixed waste plastics. The laboratory-scale triboelectrostatic separation system consists of the fluidized bed tribocharger, a separation chamber, a collection chamber and a controller. PVC and PET particles can be imparted negative and positive surface charges respectively due to the difference of triboelectric charging series between particles and particles in the fluidized bed tribocharger, and can be separated by passing them through an external electric field. To visualize these charged particles, He-Ne laser is used with cylindrical lenses to generate a sheet beam. In the charging measurement, the particle motion analysis system (PMAS), capable of determining particle velocity and diameter. is used to non-intrusively measure particle behavior in high strength electric field. The average charge-to-mass ratios of PVC and PET particles are $1.4\;and\;1.2{\mu}C/kg$, respectively. The highly concentrated PVC (91.9%) can be recovered with a yield of about 96.1% from the mixture of PVC and PET materials for a single-stage processing. The triboelectrostatic separation system using the fluidized tribocharger shows the potential to be an effective method for removing PVC from mixed plastics for waste plastic recycling.

• Korean Journal of Optics and Photonics
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• v.30 no.6
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• pp.230-236
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• 2019

We propose and demonstrate a searching and autoalignment method for indoor optical wireless communication, using a cost-effective retroreflective sheet and a microelectromechanical system (MEMS) mirror. We use an extremum-seeking method for a single axis and beam steering with a MEMS mirror to maintain a line of sight (LOS) with the optical link. This autoalignment method shows a receiver sensitivity of -31.87 dBm for a bit rate of 2.5 Gb/s over a 7 m communication link.

• Journal of the Korea institute for structural maintenance and inspection
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• v.2 no.2
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• pp.195-201
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• 1998

The purpose of this study is to evaluate the flexural strengthening effects of RC beams reinforced with carbon fiber sheets (CFS) in variable of strengthening amount and anchorage length of CFS. This study can be summarized as follows ; The CFS shares the tensile stress such as rebar during loading test. Also, as the strengthening amount of CFS is increased, the maximum flexural strength of RC beams reinforced with CFS is increased. Therefore, it is confirmed that the CFS's strengthening method is very effective to improve the flexural strength of RC beams. The maximum flexural strength of RC beams with CFS is determined by bond failure between CFS and concrete surface. So, the evaluation of CFS's strengthening effect can be calculated using the tensile stress of CFS which is peeling. When the anchorage length of CFS is increased, the ductility of RC beams is increased because of delaying the peeling of CFS. But, in case of same anchorage length of CFS, when the strengthening amount of CFS is increased, the ductility is decreased. Therefore, it is considered that the anchorage of CFS in the end zone is necessary.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 1997.11a
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• pp.464-471
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• 1997

Convective smoke spread in a corridor is experimentally investigated using thermocouples and visualization technique with a laser beam sheet. The speed of smoke front under a ceiling is measured by a series of thermocouples. Visualization of the ceiling jet formation and of smoke filling process is carried out to observe the lowering of a smoke layer. From the results, a large-scale convective motion plays dominant roles for smoke spread in the vicinity of the end of the corridor from visualized photos along with temperature records. The large-scale convective motion of the smoke is generated from the impingement of the ceiling jet front on the end of the corridor, and thus turning the flows toward the floor. Such a circulating motion of fluid transports some smoke to some region where its momentum is effective. It is therefore shown that the conventional concept of lowering smoke in the two-layer zone model has some restrictions for the corridor because the lowering of smoke layer has been thought to be mass transport due to relatively small scale motions such as the decrease of buoyancy, mass diffusion and momentum exchanges.

• Computers and Concrete
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• v.27 no.3
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• pp.253-268
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• 2021

The present paper treats the free vibration problem of the masonry wall strengthened with thin composite plate by viscoelastic adhesive layer. For this goal two steps are considered in the analytical solution. In the first one, an efficient homogenisation procedure is given to provide the anisotropic properties of the masonry wall. The second one is dedicated to purpose simplified mathematical models related to both in-plane and out-of-plane vibration problems. In these models, the higher order shear theories (HSDT's) are employed for a more rigours description of the shear deformation trough the masonry wall and the composite sheet. Ritz's method is deployed as solution strategy in order to get the natural frequencies and their corresponding loss factors. The obtained results are validated with the finite element method (FEM) and then, a parametric study is undertaken for different kinds of masonry walls strengthened with composite sheets.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.5
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• pp.121-129
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• 2006

This study look into the mechanisms of growth and magnification of the cracks and delamination in the pre-cracked RC beams repaired with carbon fiber sheets. The experimental parameters were loading type, loading speed and crack. In the experiments, it was confirmed that a failure of beams began with development and propagation of the stepped delamination in the below the loading point due to the rapid change of shear force, but mechanisms of the failure were not influenced with loading type, loading speed and pre-cracks. Particularly, in the case of beams having the pre-cracks, growth of crack concentrated at the special crack below the loading point and led to failure of the beam by delamination due to magnification of crack.

• Journal of Science Education
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• v.35 no.2
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• pp.173-192
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• 2011

The purpose of this study was to develop inquiry modules for learning straight propagation of light, to verify their efficiency, and to acquire implications. this study proposes teaching modules for improvements of light experiments, which were developed in this work. Inquiry modules were applied to 75 school teachers(8 elementary school teachers, 67 middle school and high school teachers) for examining that the modules make teachers have the scientific concepts. Then, conception changes were analyzed except 5 teachers who responded poorly. The pre-test result shows that most teachers have alternative conceptions, which is that they thought the bright shape on apparatus's bottom panel itself shown in the textbook as evidence for the path of light's straight propagation. The post-test result shows this alternative conception was changed into scientific conception. Unlikely pretest, most teachers' conception was changed into the scientific conception that the light come from a light source. Teachers are able to express that the light beam comes from a miniature electric bulb. Further more, most teachers can draw light's path correctly; from the miniature electric bulb, through vertical panel having a hole, to the apparatus bottom.