• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.2
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• pp.354-356
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• 2017

We focused on light management technology in amorphous silicon solar cells to suppress increase in absorber thickness for improving power conversion efficiency (PCE). $MgF_2$ and $TiO_2$ anti-reflection layers were coated on both sides of Asahi VU ($glass/SnO_2:F$) substrates, which contributed to increase in PCE from 9.16% to 9.81% at absorber thickness of only 150 nm. Also, we applied very thin $MgF_2$ as a rear reflector at n-type nanocrystalline silicon oxide/Ag interface to boost photocurrent. By reinforcing rear reflection, we could find the PCE increase from 10.08% up to 10.34% based on thin absorber about 200 nm.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.72.2-72.2
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• 2010

Nowadays, the crystalline Si Solar cell are expected for economical renewable energy source. The cost of the crystalline Si solar cell are decreasing by improvement of its efficiency and decrease of the cost of the raw Si wafers for Solar cells. This Si wafer based crystalline Si solar cell is the verified technology from several decade of its history. Now, I will introduce one method that can be upgrade the efficiency by using simple and economical method. The name of this method is Rear Side Etching(RSE). The purpose of rear side etching is the elimination of n+ layer of rear side and increase of the flatness. The effects of rear side etching are the improvement of Voc and increase of efficiency by reducement series resistance and forming of uniform BSF. The experimental procedure for rear side etching is very simple. After anti-reflection coating on solar cell wafer, Solar cell wafer is etched by the etching chemical that react with only rear side not front side. This special chemical is no harmful to anti-reflection coating layer. It can only etched rear side of solar cell wafer. We can use etching image by optical microscope, minority carrier life time by WCT 120, SiNx thickness and refractive index by ellipsometer, cell efficiency for the RSE effect measurement. The key point of rear side etching is development of etching process condition that react with only rear side. If we can control this factor, we can achieve increase of solar cell efficiency very economically without new device.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1996.10a
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• pp.176-183
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• 1996

In order to reduce wave reflection from a breakwater, a perforated wall caisson is often used. A conventional perforated wall caisson breakwater for which the water depth inside the wave chamber is the same as that on the rubble mound berm has less weight than a vertical solid caisson with the same width and moreover the weight is concentrated on the rear side of the caisson. (omitted)

• Journal of Ocean Engineering and Technology
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• v.27 no.6
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• pp.90-94
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• 2013

This paper reports the results obtained for there flection and transmission coefficients on rubble mound breakwaters in Busan Yacht Harbor. A2D physical model test was conducted in the wave flume at the Coastal Engineering Research Laboratory at Pusan National University, Busan, South Korea. In this study, physical model tests were completed to further our understanding of the hydrodynamic processes that surround a rubble mound structure subjected to irregular waves. In particular, the reflection and transmission coefficients, as well as the spectrum transformation, were analyzed. This analysis suggests that with an increase in wave height around a rubble mound, the reflection coefficient drastically increases at each water level (HHW or MSL or LLW). Moreover, when the water level changes from HHW to LLW, the reflection coefficient is suddenly reduced. A further result of the analysis is that the transmission coefficient strongly drops away from the rear of the structure. Finally, in regard to the rubble mound breakwater in Busan Yacht Harbor, a consideration of the reflection and transmission coefficients plays an important role in the design.

• Journal of the Korean Institute of Educational Facilities
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• v.20 no.1
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• pp.37-44
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• 2013

The present study examines the effects of periodic type diffusers for producing the preferred acoustics for speech and determines the more successful configurations of sound-absorbing and diffusing treatments for achieving good acoustics in classrooms. The measurements were carried out in a 1/10 scale model classroom systematically adding diffusers to one or more of four surfaces of the room. A total of 13 combination of diffusers with absorptive treatments were investigated. Adding diffusers on the ceiling were more effective to increasing the early-arriving reflection energy($G_{50}$) than adding absorptive materials on the entire ceiling. The late arriving reflection energy($G_{late}$) was decreased with increasing amounts of diffusing treatments of upper front or rear wall and this resulted in achieving higher early-to-late ratios($G_{50}$). Adding diffusers on the upper front wall($AC_{100}DUFW_{26}$) achieved more uniform acoustical conditions over the receiver positions than adding diffusers on the upper rear wall($AC_{100}DUFW_{26}$). Adding diffusers on the ceiling and absorptive materials on the lower front wall($AC_{75}DC_{25}ALFW_{26}$) achieved better acoustical conditions than adding the absorptive materials on the entire ceiling and lower front wall($AC_{100}ALFW_{26}$).

• Journal of Ocean Engineering and Technology
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• v.16 no.3
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• pp.1-7
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• 2002

In this paper, a numerical model to analyze the performance of a vertical slit-type wave absorber is developed under the assumption of inviscid water waves. The formulation combines the linear potential theory with a semi-empirical description of the eddy-shedding at a slit-type wave absorber. We investigated the reflection coefficients over a wide frequency range for a vertical slit-type wave absorber both with and without a solid rear wall. Model test was conducted at KRISO' s two dimensional wave tank to validate the theoretical results. It is found that the agreement between theoretical results and experimental data is surprisingly good. We found that the wave absorbing system using a vertical slit plate has sufficient potentials for breakwaters for ocean development.

• Korean Journal of Optics and Photonics
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• v.8 no.5
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• pp.395-402
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• 1997

We have obtained the optimum thickness of anti-reflection(AR) coating on one of facets of a $\1.55mu\textrm{m}$ InGaAsP MQW FP semiconductor laser by in-site monitoring of the light emitted from the rear facet during the film deposition on the fore facet. The optimum thickness of $SiO_x$ thin film whose refractive index is 1.85 was found to be 188 nm. The reflectivity of the coated facet was calculated by the threshold current ratio of before and after AR coating, which was obtained from exprimental data, and it was about 2$\times$ $10^{-4}$. The results show that the output power is increased by 87% at bias current 60 mA, the slope efficiency is increased by 3.4 times, and the threshold current is increased by 2.64 times. By in-situ depositing of the $Si/SiO_2$ thin film HR coating on the rear facet, the output power was increased by 160% than before the AR and HR coatings, the slope efficiency was increased by 3.8 times, the threshold current was increased by 1.07 times, which is similar to the value of before AR coating. Due to the AR and HR coatings the output light power characteristics were enhanced.

• Journal of the Korean Solar Energy Society
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• v.29 no.4
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• pp.28-33
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• 2009

In 2008, the global photovoltaic(PV) market reached 5.6GW and the cumulative PV power installed totalled almost 15GW compared to 9GW in 2007. Due to a favourable feed-in-tariff, Korea emerged in 2008 as the 4th largest PV market worldwide. PV power installation rose 495.5 percent to 268MW in 2008 compare to 45MW in 2007. Building integrated photovoltaic(BIPV) has the potential to become a major source of renewable energy in the urban environment. BIPV has significant influenced on the reflection by rear materials such as white back sheet and the heat transfer through the building envelope because of the change of the thermal resistance by adding or replacing the building elements. In this study, to use as suitable building materials into environmentally friendly house like green home, characteristic analysis of BIPV module according to rear materials achieved. Electrical output of PV module with white back sheet is high about 10% compared to other pv module because of 83% reflectivity of white back sheet compared to 8.4% reflectivity of other PV modules with different rear materials(black back sheet and glass). In the result of outdoor experiment during a year, electrical output of four different PV module is decreased about 3.72%.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.975-978
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• 2007

This paper investigates stage acoustics in concert halls for ensemble performance in terms of stage support parameters. A concert hall with large stage area was selected. Objective measurements were carried out according to Gade's methods for investigating stage support (ST1). The sound field on the stage was evaluated using stage and audience acoustical parameters. According to the positions at stage, different acoustical characteristics were found. Higher ST1 and lower $IACC_{E3}$ were measured near side and rear stage walls. In case of conductor/soloist vs. orchestra player, objective measurement of acoustical parameters shows that early sound fields depend on the source-receiver distance but late sound fields depend on the location of side and rear walls. In addition, in-situ evaluation of the trio instrumentalists was carried out. Results show that ensemble is favored by higher early reflection of sounds and sound diffusion affecting ‘blending’ of their performance.

• International Journal of Advanced Culture Technology
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• v.1 no.1
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• pp.15-18
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• 2013

This paper describes new gestures on the Multi-touch table. The 2 new gestures with 3 fingers are used for minimizing of all windows that is already open and converting Aero mode. We also implement a FTIR (Frustrated Total Internal Reflection) Multi-touch table that consists of sheet of acrylic, infrared LEDs, camera and rear projector. The operation of proposed gestures is verified on the implemented Multi-touch table.