• 정보저장시스템학회논문집
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• 제8권2호
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• pp.39-43
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• 2012

In spite of many advantages, the practical application of the thin film solar cell is restricted due to its low efficiency compared with the bulk type solar cells. This study intends to adopt the surface plasmon effect using nano particles to solve the low efficiency problem in thin film solar cells. By inserting Ag nano-particles in the absorbing layer of a thin film solar cell, the poynting vector value of the absorbing layer is increased due to the strong energy field. Increasing the value may give thin film solar cells chance to absorb more energy from the incident beam so that the efficiency of the thin film solar cell can be improved. In this work, we have designed the optimal shape of Ag nano-particle in the absorbing laser of a basic type thin film solar cell using the finite element analysis commercial package COMSOL. Design parameters are set to the particle diameter and the distance between each Ag nano-particle and by changing those parameters using the full factorial design variable set-up, we can determine optimal design of Ag nano-particles for maximizing the poynting vector value in the absorbing layer.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2005년도 전력전자학술대회 논문집
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• pp.380-384
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• 2005

Plasma display panel (PDP) has a serious thermal problem, because the luminance efficiency of the conventional PDP is about 1.5 lm/W and it is less than $3{\sim}5$ lm/W of cathode ray tube (CRT). Thus there is a need for improving the luminance efficiency of the PDP There are several approaches to improve the luminance efficiency of the PDP and we adopt the driving PDP at high frequency range from 400 kHz up to over 700 kHz. Since a PDP is regarded as an equivalent inherent capacitance, many types of sustaining drivers have been proposed and widely used to recover the energy stored in the PDP. However, these circuits have some drawbacks for driving PDP at high frequency range. In this paper, we investigate the effect of the parasitic components of PDP itself and driver when the reactive energy of panel is recovered. Various drivers are classified and evaluated whether it is suitable for high frequency driver, and finally current-fed type with do input voltage biased is proposed. This driver overcomes the effect of parasitic component in panel and driver and fully achieves ZVS of all full-bridge switches and reduces the transition time of the panel polarity.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 1999년도 춘계종합학술대회
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• pp.389-393
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• 1999

디바이스 효율에 커다란 영향을 미치고 있는 임팩트이온화현상의 정확한 모델이 디바이스 시뮬레이션에 필수적인 요소가 되고 있다. 최근에는 정확한 GaAs 임팩트이온화 모델을 위해 각 에너지 범위에 파라서 7.8과 5.6의 지수를 갖는 수정된 Keldysh 공식이 사용되고 있다. 그러나 이 모델 또한 임팩트이온화의 방향성을 무시한 등방성 모델로서 저에너지에서 이방성을 보이는 임팩트이온화모델로서는 부적합하다. 임팩트이온화율은 낮은 전자에너지에서는 강한 이방성 성질을 나타내는 반면에, 임팩트이온화현상이 자주 발생하는 높은 에너지 범위에서는 등방성이 된다. 임팩트이온화율을 계산하기 위하여 Fermi 황금법칙과 의사 포텐셜방법에 의하여 계산된 full 에너지 밴드구조를 사용하였다. Form factor 및 실험값을 비교하였으며, 방향에 따른 전도대의 에너지 밴드 구조를 <100>, <110>, <111>의 방향에 대하여 조사하였다. 결과적으로, 임팩트이온화의 문턱에너지가 이방성을 갖음을 알 수 있었다. 또한 상대적으로 낮은 에너지 즉, 문턱에너지 근처에서 임팩트이온화율이 더욱 심하게 변화함을 알 수 있다.

• 한국수소및신에너지학회논문집
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• 제13권4호
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• pp.304-312
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• 2002

In this study, the performance of the $5Nm^3/hr$ compact type steam reformer which was developed for application of fuel cell or hydrogen station was evaluated in terms of gas process efficiency. For these purposes, reforming efficiency and total efficiency with system load change were analyzed. The reforming efficiency was calculated from the total molar flow of hydrogen output over total fuel flow input to the reformer and the burner on the higher heating value(HHV). In the case of the total efficiency, recovered heat at the heat recovery exchanger was considered. From the results, it was known that system performance was stable, because methane conversion showed the a slight decline which is about 2% though increasing system load to full. Reforming efficiency was increased from 20% to 58%, respectively as increasing system load from 10% to 90%. It was found that total efficiency was higher then reforming efficiency because of terms of heat recovered. As a results, it was known that total efficiency was increased form 75% to 83% at the 10% and 90% system load, respectively. From these results, it is concluded that compact steam reformer which is composed of stacking plate-type reactors is suitable to on-site hydrogen generator or to fuel cell application because of quick start within 1 hr and good performance.

• KIEAE Journal
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• 제14권1호
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• pp.75-81
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• 2014

This study aims at investigating the benefit of actively controlling humidity to improve thermal comfort and energy efficiency in climate zones other than hot-dry. For this research purpose, three thermal control strategies, which adopted different initiative degrees in humidity control, were developed - i) temperature controls, ii) temperature and humidity controls, and iii) thermal sensation controls. Performance of the developed strategies were experimentally tested in a full scale mock up of an office environment. The study revealed that air temperature was better controlled in the occupied zone under the first two strategies than the thermal sensation based strategy. On the other hand, the thermal sensation-based strategy maintained thermal sensation levels more comfortably. In addition, energy consumption was significantly reduced when humidity was actively controlled for thermal comfort. The thermal sensation-based control strategy consumed significantly less electricity than the first two strategies. From these findings, this study indicated that adoption of an active humidity control system based on thermal sensation can provide increased thermal comfort as well as energy savings for summer seasons in climatic zones other than hot-dry.

• Coupled systems mechanics
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• 제2권1호
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• pp.53-83
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• 2013

Sea waves induce significant pressures on coastal surfaces, especially on rocky vertical cliffs or breakwater structures (Peregrine 2003). In the present work, this hydrodynamic pressure is considered as the excitation acting on a piezoelectric material sheet, installed on a vertical cliff, and connected to an external electric circuit (on land). The whole hydro/piezo/electric system is modeled in the context of linear wave theory. The piezoelectric elements are assumed to be small plates, possibly of stack configuration, under a specific wiring. They are connected with an external circuit, modeled by a complex impedance, as usually happens in preliminary studies (Liang and Liao 2011). The piezoelectric elements are subjected to thickness-mode vibrations under the influence of incident harmonic water waves. Full, kinematic and dynamic, coupling is implemented along the water-solid interface, using propagation and evanescent modes (Athanassoulis and Belibassakis 1999). For most energetically interesting conditions the long-wave theory is valid, making the effect of evanescent modes negligible, and permitting us to calculate a closed-form solution for the efficiency of the energy harvesting system. It is found that the efficiency is dependent on two dimensionless hydro/piezo/electric parameters, and may become significant (as high as 30 - 50%) for appropriate combinations of parameter values, which, however, corresponds to exotically flexible piezoelectric materials. The existence or the possibility of constructing such kind of materials formulates a question to material scientists.

• Journal of Power Electronics
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• 제9권2호
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• pp.300-307
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• 2009

In this paper, design and control is proposed for a four input-series-output-series-connected ZVS full bridge converter for the photovoltaic power conditioning system (PCS). The novel topology for a photovoltaic (PV) DC/DC converter that can dramatically reduce the power rating and increase the efficiency of a PV system by analyzing PV module characteristics is proposed. The control scheme, including an input voltage controller is proposed to achieve equal sharing of the input voltage as well output voltages by a four series connected module. Design methods for ZVS power stage are also introduced. The total PV system is implemented for a 250-kW PV power conditioning system (PCS). This system has only three DC/DC converters with a 25-kW power rating and uses only one-third of the total PV PCS power. The 25-kW prototype PV DC/DC converter is introduced to verify experimentally the proposed topology. In addition, an experimental result shows that the proposed topology exhibits good performance.

• 한국소음진동공학회논문집
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• 제19권12호
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• pp.1338-1346
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• 2009

We present a one-dimensional annular plate element with which the in-plane vibration of full disks can be analyzed efficiently and accurately by using the FEM. Its elementary mass matrix and stiffness matrix are derived, respectively, from the virtual work by effective forces and the virtual strain energy. The static deformation modes obtained from an integration of the differential equilibrium equations of the annular plate are used as interpolation functions of the one-dimensional annular plate element. The in-plane natural vibration characteristics of a 2-step full disk and a uniform full disk are analysed. Its results are compared with the results obtained by utilizing two-dimensional 8-node quadrilateral plane elements and cyclic symmetry of the disk. And also, by comparing with the theoretical results of previous researchers, the efficiency and accuracy of the presented element are verified.

• 방사성폐기물학회지
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• 제2권2호
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• pp.97-104
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• 2004

NIPS 시스템은 중성자 핵반응 결과 방출되는 즉발 감마선을 정량적으로 측정하는 장치이며 고체 및 액체 폐기물 중 존재하는 다양한 원소를 비파괴적으로 분석할 수 있는 장점이 있다. 본 연구에서는 NIPS 시스템에 이용된 고순도반도체 검출기의 계측효율을 $^{l33}$Ba 및 $^{152}$Eu 방사성 동위원소 선원과 $^{35}$ Cl(n, ${\gamma}$)$^{36}$ Cl 핵반응 시 발생되는 즉발감마선을 이용하여 80 keV에서 8 MeV까지 넓은 영역에 대하여 구하였다. $^{35}$ Cl(n, ${\gamma}$)$^{36}$ Cl 핵반응을 이용한 고에너지 감마선의 계측효율은 즉발감마선의 방사능 값을 정확히 알 수 없기 때문에 저 에너지 영역에서 정확히 알고 있는 검출기 효율곡선에 규격화시켜 전 에너지 영역에서의 효율보정곡선을 구하였다. 또한 KCl 표준용액에 $^{252}$ Cf 중성자 선원을 조사시켜 표준용액으로부터 방출되는 즉발 감마선을 고순도반도체 검출기로 측정하고 광대역 계측효율 곡선을 이용하여 수용액 시료에서의 평균 열중성자 속을 예측하였다. NIPS 측정시스템은 주변 재료 물질의 핵반응으로 방출되는 감마선 background를 줄이기 위해 두 개의 고순도반도체 검출기를 이용한 동시계수 장치가 고안되었으며, 동시계수 모드에서의 계측효율도 함께 고려되었으며, 표준선원을 이용하여 전 계수 또는 동시계수모드에서의 background에 대한 측정감도를 비교하였다.다.

• Interaction and multiscale mechanics
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• 제7권1호
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• pp.543-561
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• 2014

We present a full energy and force formulation of the quasicontinuum method with non-local and local transition elements. Non-local transition elements are developed to transmit inhomogeneity from the atomistic to the continuum regions. Local transition elements are developed to resolve the mathematical mismatch between non-local atoms and the local continuum. The rationale behind these transition elements is provided by analyzing the energy and force transitions between atoms and continuum under the Cauchy-Born rule. We show that breakdown of the Cauchy-Born rule occurs for slaved atoms of local elements within the cutoff of non-local atoms. The inadequacy of the Cauchy-Born rule at the transition region naturally leads to the need of atomistic treatment of transition slaved and transition representative atoms. Such an atomistic treatment together with a full or cutoff sampling allows non-local transition elements containing these transition entities to transmit inhomogeneity. Different force formulations for transition representative atoms and pure local representative atoms allow the local transition elements to resolve non-local and local mismatches. The method presented herein is validated by force calculations in an unstressed perfect crystal as well as an unrelaxed grain boundary model. A nanoindentation simulation in 3D is conducted to demonstrate the accuracy and efficiency of the proposed method.