• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.138-138
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• 2009

Recently, thin-film solar cells of Cu(In,Ga)$Se_2$(CIGS) have reached a high level of performance, which has resulted in a 19.9%-efficient device. These conventional devices were typically fabricated using chemical bath deposited CdS buffer layer between the CIGS absorber layer and ZnO window layer. However, the short wavelength response of CIGS solar cell is limited by narrow CdS band gap of about 2.42 eV. Taking into consideration the environmental aspect, the toxic Cd element should be replaced by a different material. It is why during last decades many efforts have been provided to achieve high efficiency Cd-free CIGS solar cells. In order to alternate CdS buffer layer, ZnS buffer layer is grown by using chemical bath deposition(CBD) technique. The thickness and chemical composition of ZnS buffer layer can be conveniently by varying the CBD processing parameters. The processing parameters were optimized to match band gap of ZnS films to the solar spectrum and exclude the creation of morphology defects. Optimized ZnS buffer layer showed higher optical transmittance than conventional thick-CdS buffer layer at the short wavelength below ~520 nm. Then, chemically deposited ZnS buffer layer was applied to CIGS solar cell as a alternative for the standard CdS/CIGS device configuration. This CIGS solar cells were characterized by current-voltage and quantum efficiency measurement.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.106.1-106.1
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• 2011

The Cu(In,Ga)Se2 (CIGS) thin film solar cells have been achieved until almost 20% efficiency by NREL. These solar cells include chemically deposited CdS as buffer layer between CIGS absorber layer and ZnO window layer. Although CIGS solar cells with CdS buffer layer show excellent performance, the short wavelength response of CIGS solar cell is limited by narrow CdS band gap of about 2.42 eV. Taking into consideration the environmental aspect, the toxic Cd element should be replaced by a different material. Among Cd-free candidate materials, the CIGS thin film solar cells with ZnS buffer layer seem to be promising with 17.2%(module by showa shell K.K.), 18.6%(small area by NREL). However, ZnS/CIGS solar cells still show lower performance than CdS/CIGS solar cells. There are several reported reasons to reduce the efficiency of ZnS/CIGS solar cells. Nakada reported ZnS thin film had many defects such as stacking faults, pin-holes, so that crytallinity of ZnS thin film is poor, compared to CdS thin film. Additionally, it was known that the hetero-interface between ZnS and CIGS layer made unfavorable band alignment. The unfavorable band alignment hinders electron transport at the heteo-interface. In this study, we focused on growing defect-free ZnS thin film and for favorable band alignment of ZnS/CIGS, bandgap of ZnS and CIGS, valece band structure of ZnS/CIGS were modified. Finally, we verified the photovoltaic properties of ZnS/CIGS solar cells.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.466-471
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• 2014

The interior vehicle noise due to the exterior aerodynamic field is an important topic in the acoustic design of a car. The air flow detached from the A-pillar and impacting the side windows are of particular interest as they are located close to the driver / passenger and provides a lower insulation index than the trimmed car body parts. This paper presents a numerical analysis method for a simplified vehicle model. The internal air cavity including trim component are included in the simulation. The car body includes the windshield and two side windows. The body is made of aluminum and trimmed with porous layers. The methodology proposed in this paper relies on two steps: the first step involves the computation of the exterior flow and turbulence induced non-linear acoustic field using PowerFlow. The second step consists in the computation of the vibro-acoustic transmission through the window using the finite element vibro-acoustic solver Actran. Additionally in order to validate the numerical process, an experimental set-up has been created based on the simplified vehicle. The vibration of the windshield and windows, the total wind noise level results and the relative contributions of the different windows are then presented and compared to measurements. The influence of the flow yaw angle (different wind orientation) is also assessed.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.10 no.1
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• pp.90-95
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• 2014

Local wall thinning is a point of concern in almost all steel structures such as pipe lines covered with a thermal insulator made up of materials with low thermal conductivity(fiberglass or mineral wool); hence, Non Destructive Technique(NDT) methods that are capable of detecting the wall thinning and defects without removing the insulation are necessary. In this study we developed a Pulsed Eddy Current(PEC) system to detect the wall thinning of Ferro magnetic steel pipes covered with fiber glass thermal insulator and shielded with Aluminum plate. The developed system is capable of detecting the wall thickness change through an insulation of thickness 10cm and 0.4mm aluminum shielding. In order to confirm the thickness change due to wall thinning, two different sensors, a hall sensor and coil sensor were used as a detecting element. In both cases, the results show a very good change corresponding to the thickness change of the test specimen. During these experiments a carbon steel tube of diameter 210mm and a length of 620mm, which is covered with insulator of 95mm thickness was used. To simulate the wall thinning, the thickness of the tube is changed for a specified length such as 2.5mm, 5mm and 8 mm from the inner surface of the tube. A 0.4mm thick Aluminum plate was covered on the Test specimen to simulate the shielding of the insulated pipelines. For both hall sensor and coil detection methods Fast Fourier transform(FFT) was calculated using window approach and the results for the test specimen without Aluminum shielding were summarized which shows a clear identification of thickness change in the test specimen by comparing the magnitude spectra. The PEC system can detect the wall thinning under the 95 mm thickness insulation and 0.4 mm Al shielding, and the output signal showed linear relation with tube wall thickness.

• Korean Institute of Interior Design Journal
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• v.17 no.1
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• pp.30-38
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• 2008

Borrowed landscape is an Oriental gardening method to draw inside external natural landscape, and borrowed landscape of Japan has a different characteristic from that of Korea or China nature is manipulated and re-interpreted by human will in the course of applying it to architectural space. In other words, not the original scenery, but manipulated one appears which is cut, reduced, or deleted by architectural elements such as wall, window, or fence. Therefore, this study examined how architectural structure of Ando Tadao symbolizing modernist architecture understood and adopted Japanese traditional views on nature, that is, borrowed landscape. To this end, on the basis of the understanding on 'polymerization of abstraction and form' he mentioned, his geometric architectural principles are discussed, since this serves to be an important beginning of architectural concretization by the concept of 'form' experienced and perceived by human being through geometric means called architecture 'abstraction.' The findings of this study are as follows: first, it was found that Ando Tadao generates borrowed landscape effects by polymerizing and manipulating his simple and geometric structures with each other and thereby editing natural scenery, while Japanese traditional borrowed landscape introduces source scenery inside, through condensation and symbolization. Second, the results of this study revealed that his architecture functions to transcend external and internal realm of a space, which is also observed in Japanese traditional architectural borrowed landscape. Therefore, this study is considered significant in the sense that it proved that Ando Tadao's architectural language is based on borrowed landscape as a specific Japanese traditional element, going beyond the scope of previous studies focusing simply on the introduction of natural elements.

• Structural Engineering and Mechanics
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• v.75 no.4
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• pp.435-444
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• 2020

Ultrasonic guided wave testing is a very promising non-destructive testing method for rails, which is of great significance for ensuring the safe operation of railways. On the basis of the semi-analytical finite element (SAFE) method, a analytical model of 59R2 grooved rail was proposed, which is commonly used in the ballastless track of modern tram. The dispersion curves of ultrasonic guided waves in free rail and supported rail were obtained. Sensitivity analysis was then undertaken to evaluate the effect of rail elastic modulus on the phase velocity and group velocity dispersion curves of ultrasonic guided waves. The optimal guided wave mode, optimal excitation point and excitation direction suitable for detecting rail integrity were identified by analyzing the frequency, number of modes, and mode shapes. A sinusoidal signal modulated by a Hanning window with a center frequency of 25 kHz was used as the excitation source, and the propagation characteristics of high-frequency ultrasonic guided waves in the rail were obtained. The results show that the rail pad has a relatively little influence on the dispersion curves of ultrasonic guided waves in the high frequency band, and has a relatively large influence on the dispersion curves of ultrasonic guided waves in the low frequency band below 4 kHz. The rail elastic modulus has significant influence on the phase velocity in the high frequency band, while the group velocity is greatly affected by the rail elastic modulus in the low frequency band.

• Cartoon and Animation Studies
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• s.34
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• pp.367-386
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• 2014

The development of science was crucial to recent advancements in design such as digital contents, UI, GUI, UX design. Not until the DOS evolved into Windows OS were many kinds of digital media design created, namely due to the invention of the computer mouse. A necessary element of mobile phones and Window OS is icons, since icons act as visual symbols, touch buttons and gateways into software content. Icons have undergone many stages of development simultaneously with developments in digital science. We can observe changes in mobile icon design from Skeuomorphism Design to Minimalism to Flat Design. These changes were caused by macro-level trends in design across all other industries. Apple iPhone's Skeuomorphism Design of 2013 evolved into IOS7's Minimalism and Flat Design of 2014. In the mobile world, flat design will again create big changes in design. This research aims to contribute to basic research data of GUI design that are used by creators of mobile apps to understand and anticipate future trends.

• The Transactions of the Korea Information Processing Society
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• v.4 no.12
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• pp.2985-2995
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• 1997

In this paper, we proposed the "synchronous & asynchronous distance education system" which is able to interact among teachers and students for open education in cyberspace, and it is based telecommunication technology and multimedia technology. Specially, This system gets rid of the nufamiliarity and inconvenient feeling during the distance education. Also it supports the mediation of floor mode, for a group lecture and supports the synchronous mode for face-to-face effective and asynchronous mode for self-learning. The asynchronous mode has the down load function and the consultant mode (between teacher and student). The element technologies of this system consists of application sharing technique, whiteboard, various video window display, audio support, user interface, environment setup, session management, access control, network control and media control for collaborative distance education.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.35.1-35.1
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• 2010

The Cu(In,Ga)Se2(CIGS) thin film solar cells have been achieved until almost 20% efficiency by NREL. These solar cells include chemically deposited CdS as buffer layer between CIGS absorber layer and ZnO window layer. Although CIGS solar cells with CdS buffer layer show excellent performance, many groups made hard efforts to overcome its disadvantages in terms of high absorption of short wavelength, Cd hazardous element. Among Cd-free candidate materials, the CIGS thin film solar cells with Zn compound buffer layer seem to be promising with 15.2%(module by showa shell K.K.), 18.6%(small area by NREL). However, few groups were successful to report high-efficiency CIGS solar cells with Zn compound buffer layer, compared to be known how to fabricate these solar cells. Each group's chemical bah deposition (CBD) condition is seriously different. It may mean that it is not fully understood to grow high quality Zn compound thin film on the CIGS using CBD. In this study, we focused to clarify growth mechanism of chemically deposited Zn compound thin film on the CIGS, especially. Additionally, we tried to characterize junction properties with unfavorable issues, that is, slow growth rate, imperfect film coverage and minimize these issues. Early works reported that film deposition rate increased with reagent concentration and film covered whole rough CIGS surface. But they did not mention well how film growth of zinc compound evolves homogeneously or heterogeneously and what kinds of defects exist within film that can cause low solar performance. We observed sufficient correlation between growth quality and concentration of NH3 as complex agent. When NH3 concentration increased, thickness of zinc compound increased with dominant heterogeneous growth for high quality film. But the large amounts of NH3 in the solution made many particles of zinc hydroxide due to hydroxide ions. The zinc hydroxides bonded weakly to the CIGS surface have been removed at rinsing after CBD.

• The KIPS Transactions:PartA
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• v.8A no.3
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• pp.269-278
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• 2001

Routing region modeling method of auto_routing systems are use the grid and the non-grid type. Though grid type has a few electrical and physical element on PCB, grid type has disadvantage which decrease the auto-routing speed dur to constraint with board and gird size. Thus it increase the memory capacity, Non-grid type(Shape baed type) use the region processing type, so it has 44.2% memory decrease effect than grid type in routing region. Thus, via number has 55% decrease effect, total routing time is increased 83.8% than conventional PCB system. In this paper we developed high speed PCB auto-routing system without memory waste by using shaped type applicant with auction algorithm which reaching the destination from one-point with best speed and solving the path problem. Also, this system developed by Visual C++ in IBM Pentium computer Window environment, and compatible with other PC.