• Journal of Power Electronics
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• 제16권2호
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• pp.685-694
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• 2016

This paper presents a reliability assessment model for the power semiconductors used in wind turbine power converters. In this study, the thermal loadings at different timescales of wind speed are considered. First, in order to address the influence of long-term thermal cycling caused by variations in wind speed, the power converter operation state is partitioned into different phases in terms of average wind speed and wind turbulence. Therefore, the contributions can be considered separately. Then, in regards to the reliability assessment caused by short-term thermal cycling, the wind profile is converted to a wind speed distribution, and the contribution of different wind speeds to the final failure rate is accumulated. Finally, the reliability of an actual power converter semiconductor for a 2.5 MW wind turbine is assessed, and the failure rates induced by different timescale thermal behavior patterns are compared. The effects of various parameters such as cut-in, rated, cut-out wind speed on the failure rate of power devices are also analyzed based on the proposed model.

• 한국지반환경공학회 논문집
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• 제12권7호
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• pp.13-21
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• 2011

동절기와 해빙기의 기온차가 큰 지역에서는 일정 깊이까지 동결, 융해 작용이 반복적으로 발생하여 흙의 역학적 특성이 변화를 보이게 된다. 특히 세립분이 많은 흙인 경우 팽창과 수축을 통한 입자의 재배열 등으로 인하여 노반의 연약화가 많이 발생된다. 이러한 노반의 연약화는 지지력이 낮은 지반에서 반복하중이 재하 되었을 때 급격하게 나타날 수 있다. 본 연구에서는 국내의 철도 노반재료로 사용되는 대표 토질 3가지를 대상으로 세립분의 함유량, 간극비의 영향 등을 고려하여 동결융해 반복횟수에 따른 직접전단 시험을 실시하여 그 감소량을 정량적으로 평가하였으며, 이를 통하여 세립분의 함유량과 함수비 조건, 동결융해 횟수 등을 고려할 수 있는 전단강도 저감 모델 식을 제안하였다.

• Steel and Composite Structures
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• 제48권3호
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• pp.305-320
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• 2023

The mechanical properties of polymeric composites are degraded under elevated temperatures due to the effect of temperature on the mechanical behavior of the resin and resin fiber interfaces. In this study, the effect of temperature on the impact response of the carbon fiber reinforced plastics (CFRP) was investigated at low-velocity impact (LVI) using a drop-weight impact tester machine. All the composite plates were fabricated using a vacuum infusion process with a stacking sequence of [45/0_2/-45/90_2]s, and a thickness of 2.9 mm. A group of the specimens was exposed to an environment with a temperature cycling at the range of -30 ℃ to 65 ℃. In addition, three other groups of the specimens were aged at ambient (28 ℃), -30 ℃, and 65 ℃ for ten days. Then all the conditioned specimens were subjected to LVI at three energy levels of 10, 15, and 20 J. To assess the behavior of the damaged composite plates, the force-time, force-displacement, and energy-time diagrams were analyzed at all temperatures. Finally, radiography, optical microscopy, and scanning electron microscopy (SEM) were used to evaluate the effect of the temperature and damages at various impact levels. Based on the results, different energy levels have a similar effect on the LVI behavior of the samples at various temperatures. Delamination, matrix cracking, and fiber failure were the main damage modes. Compared to the samples tested at room temperature, the reduction of temperature to -30 ℃ enhanced the maximum impact force and flexural stiffness while decreasing the absorbed energy and the failure surface area. The temperature increasing to 65 ℃ increased the maximum impact force and flexural stiffness while decreasing the absorbed energy and the failure surface area. Applying 200 thermal cycles at the range of -30 ℃ to 65 ℃ led to the formation of fine cracks in the matrix while decreasing the absorbed energy. The maximum contact force is recorded under cyclic temperature as 5.95, 6.51 and 7.14 kN, under impact energy of 10, 15 and 20 J, respectively. As well as, the minimum contact force belongs to the room temperature condition and is reported as 3.93, 4.94 and 5.71 kN, under impact energy of 10, 15 and 20 J, respectively.

• 한국동물번식학회:학술대회논문집
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• 한국동물번식학회 2001년도 춘계학술발표대회
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• pp.69-69
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• 2001

The cell cycle phase in which donor nuclei exist prior to nuclear transfer is an important factor governing developmental rates of reconstituted embryos. It was suggested that quiescent G0 and cycling G1 cells could support normal development of reconstituted embryos. In a quest of optimized donor nuclei treatment prior to nuclear transfer, this study was undertaken to examine the cell cycle characteristics of bovine fetal and adult somatic cells when cultured under a variety of culture treatments and the cell cycle change with the lapse of time after trypsinization. This was archived by measuring the DNA content of cells using flow cytometry, Cultured fetal fibroblast cells, adult skin and muscle cells, and cumulus cells were divided by 3 culture treatments; 1) grown to 60-70% confluency (cycling), 2) serum starved culture, 3) culture to confluency. Trypsinized cells were fixed by 70% ethanol and stained with propidium iodide. For one experiment, trypsinized cells were resuspended in DMEM＋10% FBS and incubated for 1.5, 3 and 6 h with occasional shaking before ethanol fixation. Cell cycle phases were determined by flow cytometry enabling calculation of percentages of G0＋G1, S and G2＋M. The majority of cells were in G0＋Gl stage regardless of origin of cells. Cultures that were serum starved or cultured to confluency contained significantly (P<0.05) higher percentages of cells in G0＋G1 (89.5-95.4%). For every cell lines and culture treatments, percentages of cells in existing in G0＋G1 increased with decreasing of the cell size from large to small. In the serum starved and confluency groups, about 98% of small cells were in G0＋G1 Serum starved culture contained higher percentages of small-sized cells (38.5-66.9%) than cycling and confluent cultures regardless of cell lines (P<0.05). After trypsinization of fetal fibroblast and adult skin cells that were serum starved and cultured to confluency, the percentages of cells in G0＋G1 significantly increased by incubation for 1.5(95.7-99.5%) and 3.0 h (95.9-98.6%). The results suggest that the efficient synchronization of bovine somatic cells in G0＋G1 for nuclear transfer can be established by incubation for a limited time period after trypsinization of serum starved or confluent cells.

• 한국환경과학회지
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• 제20권1호
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• pp.35-47
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• 2011

The effect of the variation of aeration time on the removal of organics, nitrogen and phosphorus using synthetic wastewater was investigated in sequencing batch reactors (SBRs) which included DNPAOs and DNGAOs. The cycling times in four SBRs were adjusted to 12 hours and then included different aerobic times as 1 hr, 2.5 hr, 4 hr and 5.5 hr, respectively. Four SBR systems have been operated and investigated for over 40 days. Average TOC removal efficiencies were about 71 % in all SBRs. The $NH_4^+$-N removal efficiency was increased as the increase of aeration time. After changing aeration time, the total nitrogen removal efficiencies of SBRs were shown as 35 %, 85 %, 75 % and 65 %, respectively. Higher phosphorus release and uptake were occurred as the decrease of the aeration time. After all, the overall phosphorus removal efficiency decreased and the deterioration of phosphorus removal was occurred when aeration time was over 4 hr. Denitrification in aerobic conditions was observed, which showed the presence of DNPAOs and DNGAOs. In batch experiments, PAOs were shown as the most important microorganisms for the phosphorus removal in this experiment, and the role of DNGAOs was higher than that of DNAPOs for the nitrogen removal.

• 조명전기설비학회논문지
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• 제18권6호
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• pp.191-196
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• 2004

이 논문에서는 버스시스템의 성능 평가를 위한 순환시간의 계측방법이 제안 되었다. 센서와 엑튜에이터가 주를 이루는 생산시스템에서 순환시간은 버스시스뎀의 성능평가의 중요한 파라미터이다. 순환시간을 계측하기 위하여 제안된 방법은 간단한 알고리즘의 구성에 기반을 두었으나 주변기기나 PLC의 내부에 존재하는 지연요소들을 고려 해야만 한다. 계측결과의 개선을 기하기 위해 시험방법은 최적, 최저의 경우로 나누어 이에 대응되는 파라미터를 구성하여 값을 설정한다. 수학적인 모델을 기반으로 필드버스 시스템의 순환시간에 대한 계측을 통해 제안된 방법이 효율적임을 입증하였다. 그 결과로서 제안된 방법의 간편성과 편리함으로 인해 순환시간의 측정에 요구되는 엔지니어링 비용과 시간을 절감할 수 있었다.

• 한국진공학회지
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• 제8권4A호
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• pp.432-437
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• 1999

We have fabricated an in situ ellipsometer operating at He-Ne wavelength. It can be applied to the real-time, in-situ tracking of the ellisometric change which occurs during various sample treatments. As a rotating analyzer type, all optical elements and related parts are designed to share a common hollow-axis configuration, and hence the ellipsometer is compact in shape and simple in design. It is mountable on the spare ports of vacuum chamber with ease. Using this ellipsometer, we observed the effective density variation of previously grown $TiO_2$ thin films by using electron beam evaporation. The packing density of the as-grown film was 82%. When exposed to atomsphere, the micro-void of the film was filled with water vapor. This water-filled $TiO_2$ thin film was subject to heating/cooling cycles in vacuum and the ellipsometric variation versus temperature and cycling number was measured in real time using this in situ He-Ne ellipsometer.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 하계종합학술대회 논문집 II
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• pp.1153-1156
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• 2003

In this paper, we present a reducing power consumption of a scheduling for module selection under the time constraint. Traditional high-level synthesis do not allow reuse of complex, realistic datapath component during the task of scheduling. On the other hand, the proposed scheduling of reducing power consumption is able to approach a productivity of the design the low power to reuse which given a library of user-defined datapath component and to share of resource sharing on the switching activity in a shared resource. Also, we are obtainable the optimal the scheduling result in experimental results of our approach various HLS benchmark environment using chaining and multi-cycling in the scheduling techniques..

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 추계학술발표대회 논문집
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• pp.79-82
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• 2005

In this study, mechanical properties of carbon fabrics composite under the thermal shock cycling were evaluated. Due to the interactions between fiber and polymer matrix, it is reasonable to conclude that both thermal cycles of thermal shock result in improvement of interlaminar shear strength(ILSS) for the longer conditioning time duration. The rise in ILSS may be attributed to the improved adhesion by cryogenic compressive stress and also by the post-curing strengthening effect. However, the flexural and tensile strength were decreased with increasing conditioning time of thermal cycle.

• 한국태양에너지학회 논문집
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• 제30권5호
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• pp.63-68
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• 2010

To guarantee life time more than 20 years for manufacturer without stopping photovoltaic(PV) system, it is really important to test the module in realistic time and condition compared to outside weather. In here, we tested PV modules in highly stressed condition compared to IEC standards. In IEC 61215 and IEC 61646 standards, damp-heat, thermal cycle(TC200) and mechanical test are main test items for evaluating long-term durability of PV module in controlled temperature and humidity condition. So in this paper, we have lengthened the test time for TC200 and damp-heat test and increased the loading stress on surface of module. Through this test, we can get some clue of proper the method for measuring realistic life cycle of PV modules and suggested the minimum time for PV test method. The detail description is specified as the following paper.