• Journal of Ship and Ocean Technology
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• 제10권1호
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• pp.1-9
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• 2006

The resistance reduction by an air lubrication effect of a large air cavity covering the hull bottom surface and the similarity relations involved have been investigated with a series of towing tank tests of three geometrically similar models. The test results of geometrically similar models have indicated that a large air cavity was formed beneath the bottom having a backward-facing step by artificially supplying air is effective for resistance reduction. The areas of air cavity and the required flow rates of air are directly related to the effective wetted surface area. The traditional extrapolation methods seem to be applicable to the estimation of the resistance in the tested range if corrections are made to account the changes in the frictional resistance caused by the changes in the effective wetted surface area. To investigate the effectiveness of air lubrication in improving the resistance performance of a practical ship, a small test boat having a backward-facing step under its bottom has been manufactured and speed trials in a river have been performed. Air has been supplied artificially into the downstream region of the bottom step to form a large air cavity covering the bottom surface. The results have confirmed the practical applicability of air lubrication for the resistance reduction of a small high-speed boat.

• 미생물학회지
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• 제33권2호
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• pp.125-130
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• 1997

미생물에 의한 6가이온 크롬의 3가이온으로의 환원은 세균에게 크롬내성을 제공할 수 있는 것으로 알려져 있다. 본 연구에서는 이러한 가설을 확인하기 위하여 크롬오염 토양과 오염되지 않은 토양으로부터 형태적으로 다른 20종의 세균을 순수분리하고 각각의 균주에서 크롬내성과 크롬환원능을 상호 비교하였다. 전자의 공여체로 glucose를 사용했을 때 세포현탁액에 의한 크롬의 환원은 시간당 0.014-0.305mM Cr(VI)의 범위로 관찰되었으며, 액체배지에서 2mM의 크롬에 대한 내성은 크롬을 첨가하지 않은 배지에서 배양한 경우와 혼탁도를 비교한 결과 전혀 저해를 받지 않는 경우부터 93.4%의 성장저해를 받는 경우까지 다양하게 관찰되었다. 이러한 결과로부터 상관관계를 분석한 결과 크롬내성과 크롬환원은 전혀 상관이 없는 것으로 계산되었다. 한편 군집수준에서의 크롬내성비교는 크롬오염 토양과 오염되지 않은 토양에서 각각 19.1%와 0.4%로 나타나 크롬의 존재는 내성균주의 선택적 성장을 유도하는 것으로 밝혀졌다. 그러나 이때 획득된 크롬에 대한 내성은 크롬의 환원에 의해서 제공되는 것이 아님을 상관관계 분석으로부터 알 수 있었다.

• 한국가시화정보학회지
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• 제18권1호
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• pp.11-17
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• 2020

The reduction of CO2 emissions has been a key target in the marine industry since the IMO's MEPC published its findings in 2009. Air lubrication method is one of the mature technologies for commercialization to reduce the frictional resistance and enhance fuel efficiency of ships. Since the air lubrication pattern varies according to the ship's standing position and injection flow rate, in order to effectively control the air lubrication system, it is necessary to be able to judge the air layer development state based on the information collected from the monitoring sensor. In this study, we performed the air lubrication ship simulation experiment to measure the void fraction and the frictional resistance. The void fraction was measured to confirm the behavior of the air. Through the measurement of the frictional resistance, the change in frictional resistance reduction rate from the injection point to the longitudinal direction of the ship was confirmed. Based on the measurement results, correlation analysis was performed on void fraction and frictional resistance reduction rate.

• 콘크리트학회논문집
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• 제12권2호
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• pp.21-30
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• 2000

In the Ultimate Strength Design, the design strength of a member is determined by multiplying the strength reduction factor to the nominal strength. This concept may be a reasonable approach, however it can not consider failure modes appropriately. Moreover, column design strength diagram show an abrupt change at a low level of axial load, which does not seem to be reasonable. This research compares the design strength determined by the strength resistance factors. As the material resistance factors for flexure and compression, 0.65 and 0.90 are proposed for concrete and steel, respectively. The design strength calculation process by applying material resistance factors addresses failure modes more effectively than by applying member strength reduction factor, and provides more resnable design strength for reinforced concrete flexural and compression members.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권4호
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• pp.867-875
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• 2014

Planing crafts were specifically designed to achieve relatively high speeds on the water. When a planing craft is running at high speed, dynamic pressure on the bottom makes the boat rise on the surface of the water. This reduces the area of the sinking surface of the boat to increase air resistance. Air resistance means the resistance that occurs when the hull and deck house over the surface of the water come in contact with the air current. In this paper, we carried out a CFD numerical analysis to find optimal deck houses that decreased air-resistance on the water when planing crafts are running at high speed. We finally developed the deck house shape of high-speed planing crafts that optimally decreased air resistance.

• 한국도로학회논문집
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• 제15권6호
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• pp.17-23
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• 2013

PURPOSES : This study aimed to measure the skid resistance of the sidewalk in order to find out the relationship between different surface types and skid resistance. By using British Pendulum Tester, skid resistance of sidewalk was measured in a wet after snow-melt, sludgy, and snowy conditions. METHODS : The skid resistance was measured on surfaces including Concrete Interlocking Block Paving, Colour Asphalt Pavement, Granite Block Paving, Manhole, and Tactile Paving for Visually Impaired. Five trials at each measurement were made, and the average and standard deviation were derived. RESULTS : The skid resistance measured in wet after snow-melt, sludgy, and snowy conditions for the various surface types are summarized and compared. Reduction rates of skid resistance of sludgy and snowy against wet after snow-melt are also analysed. The skid resistance variation between measurement points which mimic pedestrian route in study site are analysed to check out the consistency of the skid resistance along the sidewalk. CONCLUSIONS : The study concluded that the skid resistance of sidewalk surfaces varied depending on the surface types and weather conditions. Secondly, reduction rates of skid resistance according to weather changes are varied depending on the surface types, Thirdly, consistency of skid resistance along the pedestrian route is hardly acquired in the study site at least. So, future study on the consistency evaluation for skid resistance along sidewalk is strongly recommended.

• 한국태양에너지학회 논문집
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• 제29권5호
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• pp.20-27
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• 2009

The effect of borehole thermal resistance on the borehole length is studied. In performing this work a new concept BLRR(borehole length reduction rate) is developed based on the line source model. The solution of line source model is shown to be valid through the comparison with the data of thermal response test. It is shown that BLRR is a function of soil thermal conductivity(k) and borehole thermal resistance($R_b$). The value of BLRR increases with increasing k, which means reducing $R_b$ is more effective when k is high. The reduction of borehole length with change of $R_b$ is easily estimated with BLRR. The validity of BLRR is also examined with EED analysis.

• 조명전기설비학회논문지
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• 제22권2호
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• pp.155-161
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• 2008

접지시스템은 고장전류나 상시 전류를 낮은 저항의 대지로 흘러 보낸다. 접지전극 주변에 접지저감재를 매설하면 접촉 면적을 증가시켜 낮은 접지저항을 얻을 수 있다. 접지전극의 접촉면적을 확대시키면 접지저항값이 낮아진다는 특성을 이용하여 접지 시공시 팽창 특성을 가진 도전성 팽창 접지저감재를 개발하였다. 본 논문에서는 실험을 통하여 도전성 팽창 접지저감재가 일반 접지저감재보다 접지저항 저감 효과가 뛰어남을 검증하였다.

• JSTS:Journal of Semiconductor Technology and Science
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• 제16권2호
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• pp.210-214
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• 2016

In this paper, the decrease in the contact resistance of Ni germanide/Ge contact was studied as a function of the thickness of the antimony (Sb) interlayer for high performance Ge MOSFETs. Sb layers with various thickness of 2, 5, 8 and 12 nm were deposited by RF-Magnetron sputter on n-type Ge on Si wafers, followed by in situ deposition of 15nm-thick Ni film. The contact resistance of samples with the Sb interlayer was lower than that of the reference sample without the Sb interlayer. We found that the Sb interlayer can lower the contact resistance of Ni germanide/Ge contact but the reduction of contact resistance becomes saturated as the Sb interlayer thickness increases. The proposed method is useful for high performance n-channel Ge MOSFETs.

• Carbon letters
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• 제14권3호
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• pp.171-174
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• 2013

The high quality contact between graphene and the metal electrode is a crucial factor in achieving the high performance of graphene transistors. However, there is not sufficient research about contact resistance reduction methods to improve the junction of metal-graphene. In this paper, we propose a new method to decrease the contact resistance between graphene and metal using directly grown graphene over a metal surface. The study found that the grown graphene over copper, as an intermediate layer between the copper and the transferred graphene, reduces contact resistance, and that the adhesion strength between graphene and metal becomes stronger. The results confirmed the contact resistance of the metal-graphene of the proposed structure is nearly half that of the conventional contact structure.