• Journal of Power Electronics
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• 제17권1호
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• pp.115-126
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• 2017

This paper presents a new cascaded asymmetrical single phase multilevel converter with a reduced number of isolated DC sources and power semiconductor switches. The proposed inverter has only two H-bridges connected in cascade, one switching at a high frequency and the other switching at a low frequency. The Low Switching Frequency Inverter (LSFI) generates seven levels whereas the High Switching Frequency Inverter (HSFI) generates only two levels. This paper also presents a solution to the capacitor balancing issues of the LSFI. The proposed inverter has lot of advantages such as reductions in the number of DC sources, switching losses, power electronic devices, size and cost. The proposed inverter with a capacitor voltage balancing algorithm is simulated using MATLAB/SIMULINK. The switching logic of the proposed inverter with a capacitor voltage balancing algorithm is developed using a FPGA SPATRAN 3A DSP board. A laboratory prototype is built to validate the simulation results.

• 건축역사연구
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• 제17권2호
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• pp.83-102
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• 2008

In the book of , it is recorded that the names of ingressive stone stairs to the main shrine were Cheongwoongyo(blue cloud bridge) and Baekwoongyo(white cloud bridge) and the names of stairs to the paradise hall were Yeonwhagyo(lotus bridge) and Chilbogyo(seven treasure bridge). But, the ingressive stone stairs to the main shrine and the paradise hall are single consecutive stairs with 2 levels respectively. Because of this, it is rather hard to clearly designate the names to the upper level and the lower level stairs. But, of the stairs to the Paradise hall, the lower stairs have a carving of lotus, and the upper stairs have seven stairs. In this aspect of artifacts, we can safely assume that the upper stairs are Chilbogyo and the lower are Yeonwhagyo. But, for the ingressive stairs to the main shrine, there is no such artificial hint. So, it is difficult to designate the upper and the lower stairs for the two bridges. Especially, it is not clear whether the descriptive order of "lower stairs upper stairs" in the names of Yeonwhagyo and Chilbogyo can be applied to the names of stairs to the main shrine. It is because the general descriptive order is "upper lower" rather than "lower upper." Even though there have been many studies on the Bulguksa temple, the study on the ingressive stone stairs to the main shrine has not made till now. Therefore, the study on the position of Cheongwoongyo and Baekwoongyo stairs can have its validity. In this paper, the positional approach to Cheongwoongyo and Baekwoongyo has been made in following aspects: First, the temple structure of Bulguksa; Second, the five element theory of oriental philosophy and the Book of Changes; Third, the directional consciousness of Buddhism. Through the aspects, the validity of up-down position of Cheongwoongyo and Baekwoongyo has been sought. In this research, it can be concluded that the upper level of ingressive stone stairs to the main shrine of Bulguksa is Cheongwoongyo and the lower level is Baekwoongyo. When considered in the Buddhist directional consciousness, it forms the total structure of "East-Cheongwoongyo South- Baekwoongyo West-Yeonwhagyo North-Chilbogyo."

• Journal of Species Research
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• 제2권2호
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• pp.203-222
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• 2013

The district of Ganghwa-gun in the western coast (Seohae) of the Korea is consisted of several islands, Ganghwa-do, Seokmo-do, Gyodong-do, Jumun-do, Boreum-do, Seogeom-do and Donggeom-do. Since several islands of them were connected to mainland of Korea by bridges, the islands attract a lot of tourists from Seoul, Incheon and Gyeonggi-do areas. Construction of new roads, pensions, resort areas and restaurants provided economical benefits to local residents while natural vegetation of these islands has deteriorated continuously. Before biodiversity of vascular plants in these regions is damaged seriously by human impacts, it is needed to conserve original vegetation of the islands for restoration and monitoring in the future. Therefore, the primary purpose of the study is to clarify the flora of Donggeom-do, belonging to Ganghwa-gun. From the 15 times of field trips to the island, we have collected a number of vascular plants, 512 taxa in total, including 110 families, 329 genera, 449 species, six subspecies, 52 varieties, four forms and one hybrid. Of 512 taxa investigated, we have identified 12 taxa to be endemic to Korea. Six taxa were endangered or rare species which were designated by the Ministry of Environment and Korea Forest Service, respectively. 25 taxa were recognized as floristic regional indicator species designated specially by the Ministry of Environment. Seven species have shown their northern or southern distributional limit ranges, and 29 taxa were recognized as halophytes. The naturalized plants were identified as 55 taxa, and their naturalization ratio was 10.7%.

• 한국강구조학회 논문집
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• 제23권2호
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• pp.137-146
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• 2011

강교 제작에는 녹, 흑피 등의 이물질 제거 및 도료의 부착성 증대를 위하여 도장 전 블라스트 표면처리가 실시되고 있지만, 이러한 강교 도장용 블라스트 처리가 용접이음의 피로강도에 미치는 영향에 대한 검토는 미흡한 실정이다. 이에 본 연구에서는 강교 제작시 사용되는 블라스트 처리조건에 의한 압축잔류응력 도입량을 정량적으로 평가하고, 압축잔류응력에 의한 용접이음의 피로강도 향상 정도를 검토하기 위하여, 먼저 국내 7개 강구조물 제작사의 블라스트 처리조건을 조사하였다. 이를 근거로 도출한 10가지의 블라스트 처리조건별 알멘스트립의 아크하이트와 강재시편의 표면조도, 경도 및 잔류응력을 측정하여, 이들 측정값과 블라스트 처리조건들과의 상관관계를 검토하여, 아크하이트 측정으로 압축잔류응력을 근사적으로 추정할 수 있음을 제시하였다. 그리고 블라스트 처리 전 후의 맞대기 용접이음의 압축잔류 응력 측정과 피로시험을 실시하여, 블라스트 처리에 의해 맞대기 용접이음부의 용접지단부에는 약 170MPa이상의 압축잔류응력이 발생하였으며, 이로 인하여 맞대기 용접이음의 피로강도는 용접부가 없는 원판 강재 이상으로 크게 향상됨을 확인하였다.

• Advances in nano research
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• 제13권1호
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• pp.97-111
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• 2022

In the present article, silica nanoparticles (SNPs) were exploited to improve the tribological and mechanical properties of vinyl ester/glass fiber composites. To the best of our knowledge, there hasn't been any prior study on the wear properties of glass fiber reinforced vinyl ester SiO₂ nanocomposites. The wear resistance is a critical concern in many industries which needs to be managed effectively to reduce high costs. To examine the influence of SNPs on the mechanical properties, seven different weight percentages of vinyl ester/nano-silica composites were initially fabricated. Afterward, based on the tensile testing results of the silica nanocomposites, four wt% of SNPs were selected to fabricate a ternary composite composed of vinyl ester/glass fiber/nano-silica using vacuum-assisted resin transfer molding. At the next stage, the tensile, three-point flexural, Charpy impact, and pin-on-disk wear tests were performed on the ternary composites. The fractured surfaces were analyzed by scanning electron microscopy (SEM) images after conducting previous tests. The most important and interesting result of this study was the development of a nanocomposite that exhibited a 52.2% decrease in the mean coefficient of friction (COF) by augmenting the SNPs, which is beneficial for the fabrication/repair of composite/steel energy pipelines as well as hydraulic and pneumatic pipe systems conveying abrasive materials. Moreover, the weight loss due to wearing the ternary composite containing one wt% of SNPs was significantly reduced by 70%. Such enhanced property of the fabricated nanocomposite may also be an important design factor for marine structures, bridges, and transportation of wind turbine blades.

• Steel and Composite Structures
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• 제46권2호
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• pp.175-193
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• 2023

Stainless steel-concrete composite beam has become an attractive structural form for offshore bridges and iconic high-rise buildings, owing to the superior corrosion resistance and excellent ductility of stainless steel material. In a composite beam, stainless steel shear connectors play an important role by establishing the interconnection between stainless steel beam and concrete slab. To enable the best use of high strength stainless steel shear connectors in composite beams, high strength concrete is recommended. To date, the application of stainless steel shear connectors in composite beams is still very limited due to the lack of research and proper design recommendations. In this paper, a total of seven pushout specimens were tested to investigate the load-slip behaviour of stainless steel shear connectors. A thorough discussion has been made on the differences between stainless steel bolted connectors and welded studs, in terms of the failure modes, load-slip behaviour and ultimate shear resistance. In parallel with the experimental programme, a finite element model was developed in ABAQUS to simulate the behaviour of stainless steel shear connectors, with which the effects of shear connector strength, concrete strength and embedded connector height to diameter ratio (h/d) were evaluated. The obtained experimental and numerical results were analysed and compared with existing codes of practice, including AS/NZS 2327, EN 1994-1-1 and ANSI/AISC 360-16. The comparison results indicated that the current codes need to be improved for the design of high strength stainless steel shear connectors. On this basis, modified design approaches were proposed to predict the shear capacity of stainless steel bolted connectors and welded studs in the composite beams.

• 콘크리트학회논문집
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• 제22권1호
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• pp.113-122
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• 2010

후 긴장된 PS 강재의 부식과 파단은 프리스트레스 콘크리트 교량의 안전에 매우 심각한 문제를 발생시키고 있다. 따라서 교량의 내하력 평가시 PS 강재의 부식 상태를 조사해야 하며, 부식된 PS 강재가 발견되는 경우, 부식에 의한 강재의 단면적 감소량을 극한강도 평가시 고려해야만 한다. 선행 연구에서는 연속음향감지기법을 그라우팅되고 후 긴장된 PS 강연선의 부식과 파단을 감지할 수 있는 신뢰할 만한 비파괴검사방법으로 평가하였다. 이 연구에서는 긴장재에 도입된 응력 수준이 현행 설계기준에 제시된 수준보다 낮게 도입된 PS 강연선에 대해 부식에 의한 강선 파단을 감지하기 위한 실험적 연구를 수행하였다. 이를 위해 프리스트레스의 크기가 각각 인장강도의 66%와 40%로 도입된 PS 강연선이 포함된 길이 10 m의 PSC 보를 제작하였다. 부식 촉진 장비를 이용하여 긴장재를 인위적으로 부식시켰으며, 7개의 음향센서와 연속음향감지장치를 이용하여 실험부재를 모니터링하였다. 부식 촉진 실험 동안 각 PS 강연선으로부터 2번의 강선 파단음파를 성공적으로 감지하였으며, 또한 오차범위 20 mm 이하로 음원 위치를 표정할 수 있었다. 이상의 실험 결과를 토대로 그라우팅되고 후 긴장된 PSC 보에서 발생되는 PS 강선 파단을 감지하는데 연속음향감지기법을 적용할 수 있다고 판단된다.

• Applied Microscopy
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• 제29권2호
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• pp.163-175
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• 1999

본 실험은 화상을 입은 생쥐에서 SQ의 치유 효과를 알아보기 위함에 있다. 실험군은 7개군으로 구분하였다; 대조군, 화상군, 그리고 화상을 입헌 후 SQ를 처치한 군. 대조군을 제외한 모든 군은 등 부위에 2도 화상을 입혔다. SQ를 처치한 모든 군은 하루에 한 번씩 10초 간격으로 순수한 SQ 3방울을 도포하였다. 화상 후 10일 동안 조직학적 및 미세구조적 변화를 광학 현미경과 전자현미경으로 관찰하였다. 광학현미경으로 관찰한 결과, 화상군의 표피층의 모든 부분은 SQ를 처치한 군보다 더 심한 상처를 입었다. SQ를 처치한 6째와 10일째 군에서, 기저층은 분화가 활발하였고, 가시층의 각화세포는 수적으로 매우 증가하였다. 전자현미경으로 관찰한 결과, SQ를 처치한 모든 군의 기저층에서 세포분열이 화상군에서보다 더 활발하게 나타났다. 특히, SQ를 처치한 10일군에서는 이상적인 결과를 얻을 수 있었다; 대조군보다 더 두꺼운 가시층과 많은 각화세포, 뚜렷한 세포간교, 그리고 멜라닌세포를 포함하는 튼튼한 기저층. 이와 같은 결과로 보아 SQ은 표피성장인자(EGF)를 활성화시키고, 유해산소의 제거 역할을 하며, 막계에 에너지원을 제공할 가능성이 있다. 이 실험의 결과는 SQ가 화상 치료에 특수한 효과가 있다고 사료된다.