• 콘크리트학회논문집
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• 제17권3호
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• pp.335-342
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• 2005

천연 건설자원이 고갈되어감에 따라, 심각한 환경오염을 일으키고 있는 각종 산업폐기물의 재활용을 통해 새로운 건설소재를 개발하기 위하여, 폐플라스틱과 폐 콘크리트를 재활용한 폴리머콘크리트의 역학적 특성을 분석하였다. 본 연구에서는 폐 PET를 재생한 불포화 폴리에스테르 수지를 재생골재와 결합시켜, 재생골재 및 수지변화량에 따른 역학적 특성과 내화학성 실험을 실시하였으며 실험결과, 재생수지 및 골재를 사용한 폴리머콘크리트(RPC)의 강도는 수지의 함량이 증가함에 따라 차츰 증가하는 추세를 보였다. 하지만 어느 수지량의 한계점 (대략 $13{\~}17\%$)에선 더 이상의 강도증가는 나타내지 않고 있음을 확인할 수 있었다 또한 재생골재 함량이 증가할수록 강도와 탄성계수는 감소하였으나 수지량 $17\%$에서는 이러한 현상이 나타나지 않았다. 선형대수회귀 분석을 통해 수지량 $9\%$일 때의 압축강도와 휨, 할렬 인장강도의 상관관계를 확인한 결과 높은 신뢰도를 보임을 알 수 있었다. 하지만 수지량이 증가함에 따라 뚜렷한 상관관계가 나타나지 않는 경향을 나타내었다. 재생골재를 사용한 폴리머콘크리트의 내화학성에 따른 중량변화와 강도실험은 비교적 산과 염에 강한 특성을 나타내었다. 그리고 염산 $30\%$의 수용액에선 알칼리수용액 $40\%$ 보다는 강한 저항성을 나타내었음을 압축강도 및 중량변화를 통해 확인할 수 있었다.

• 한국의학물리학회지:의학물리
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• 제19권4호
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• pp.305-312
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• 2008

본 연구에서는 측정 방법이 다른 두 전리함을 이용하여 고선량율 근접치료용 방사성 선원의 겉보기 활성도를 측정하여 선원의 활성도 정확성 및 두 장비간의 정확도를 비교 분석하였다. 국내 5개 의료기관을 선정하여 공기 중 기준거리에서 겉보기 활성도를 측정하고 동일한 선원에 대하여 측정 방법이 다른 두 팬톰을 동시에 측정하여 측정방법에 따른 상호 오차와 측정용 전리함의 정확도를 평가하였다. 우물형 전리함과 Jig 팬톰의 상대 오차는 각각 -2.1%~0.2%, -2.8%~-1.0%로 나타났다. 동일한 방사성선원에 대하여 두 교정 장비간의 정확도 평가는 최대 상대오차 1%로 나타났다. 선원의 세기 검증 시 측정 방법에 따른 의존도는 없었다. 고 선량율 근접방사선치료에 사용되는 방사성 선원의 세기의 변화는 환자의 종양 및 인접장기에 미치는 영향이 매우 크므로 방사성 선원의 세기 오차는 환자치료의 최적화에 심각한 영향을 미칠 수 있다. 그러므로 새로운 선원 교체 시 뿐만 아니라 주기적인 선원 점검이 요구된다.

• International Journal of Aeronautical and Space Sciences
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• 제17권3호
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• pp.285-295
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• 2016

A contact strip shape of a high speed train pantograph system was optimized with CFD to increase the aerodynamic performance and stability of contact force, and the results were validated by a wind tunnel test. For design of the optimal contact strip shape, a Kriging model and genetic algorithm were used to ensure the global search of the optimal point and reduce the computational cost. To enhance the performance and robustness of the contact strip for high speed pantograph, the drag coefficient and the fluctuation of the lift coefficient along the angle of attack were selected as design objectives. Aerodynamic forces were measured by a load cell and HWA (Hot Wire Anemometer) was used to measure the Strouhal number of wake flow. PIV (Particle Image Velocimetry) was adopted to visualize the flow fields. The optimized contact strip shape was shown a lower drag with smaller fluctuation of vertical lift force than the general shaped contact strip. And the acoustic noise source strength of the optimized contact strip was also reduced. Finally, the reduction amount of drag and noise was assessed when the optimized contact strip was applied to three dimensional pantograph system.

• 한국생산제조학회지
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• 제23권1호
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• pp.64-68
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• 2014

This paper introduces the use of a crown-shaped (CR) lens to effectively diffuse the light from a light-emitting diode (LED) without any loss in the light intensity, in contrast to polymer-bulb-type diffusers. The diffusion lens was designed based on the Snell's law, which describes the physical path of a ray passing through the boundary between different media. CR lenses were fabricated by polydimethylsiloxane (PDMS) casting and UV-embossing processes, which used a pre-designed metal mold and UV-curable resin, respectively. Through experiments and optical evaluations, it was verified that the newly proposed CR lens not only decreased the vertical light strength and glare effect from an LED light source but also improved the diffusion characteristics while maintaining the quality of the LED's light intensity.

• Journal of Korean Society for Atmospheric Environment
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• 제21권E1호
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• pp.1-11
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• 2005

The concentration levels of gaseous elemental mercury (GEM) in ambient air have been investigated from a monitoring station located in Yang Jae district of Seoul, Korea for a long-term period covering 1997 through 2002. The mean concentration of Hg, if computed based on its hourly measurement data for this six-year period, was $5.32\pm3.53 ng m^{-3} (N = 27,170)$. The inspection of the diurnal distribution patterns indicated the presence of notably high concentration levels during nighttime relative to daytime (e.g., the mean hourly value as high as $9 ng m^{-3}$ in winter nighttime). When divided seasonally, the highest mean of $6.12 ng m^{-3}$ was also observed during winter followed by spring, fall, and summer. The results of our analysis confirmed the relative dominance of winter (seasonally) or nighttime (diurnally), while exhibiting a complicated trend on a long-term basis. Examination of our data over a different temporal scale consistently indicated that dynamic changes in Hg concentrations occurred through time in line with changes in the strength and diversity of the source processes. It is thus acknowledged that the presence of unusually high Hg levels is the consequence of intense man-made activities, while such signatures can vary in a competitive manner.

• 한국음향학회지
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• 제19권7호
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• pp.3-6
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• 2000

일반적으로 보고되어있는 방사임피던스는 무한강체 배플에 진동면을 두고있는 경우에 대하여 계산되어져 있어, 실제 유한한 크기의 배플을 갖는 트랜스듀서의 설계에는 적용하기 어려운 경우가 많다. 본 연구에서는 피스톤의 진동면을 작은 점음원의 모임으로 가정하고, 각 점음원의 음원강도와 배플의 크기를 관련지어 유한배플을 갖는 진동면에 대한 방사임피던스의 새로운 계산법을 제안하였다. 그에 대한 예로서 정방형의 피스톤 진동면에 대하여 배플의 크기에 따른 자기방사임피던스의 변화를 계산함으로써 제안한 방법의 유효성을 확인하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.186-191
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• 2001

Tensile residual stress happen by difference of coefficients of thermal expansion between fiber and matrix is one of the serious problems in metal matrix composite(MMC). In this study, TiNi alloy fiber was used to solve the problem of the tensile residual stress as the reinforced material. TiNi alloy fiber improves the tensile strength of composite by occurring compressive residual stress in matrix using shape memory effect of it. Pre-strain was added to generate compressive residual stress inside TiNi/A16061 shape memory alloy(SMA) composite. It was also evaluated the effect of compressive residual stress corresponding to pre-strains variation and volume fraction of TiNi alloy. AE technique was used to clarify the microscopic damage behavior at high temperature and the effect of pre-strain difference of TiNi/A16061 SMA composite. In addition, two dimensional AE source location technique was applied to inspect the crack initiation and propagation in composite.

• 한국환경보건학회지
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• 제32권5호
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• pp.398-403
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• 2006

Indoor air quality can be affected by indoor sources, ventilation, decay and outdoor levels. Understanding the effectiveness of indoor air quality control depends on knowledge of the characteristics of air pollutants in indoor air, especially their quantities and persistence, and the relevance of indoor sources to these factors. Toluene within new and established houses has been determined and factors significant to its presence have been identified. A total of 30 selected houses in Seoul, Asan and Daegu areas that were constructed within 4 years and over 4 years of construction were measured the concentration of toluene from July to September in 2004. Toluene emission decay of double-exponential model exhibited good fit of $Y=276.37e^{-1.21x}(R^{2}=0.34,\;P=0.06)$ for 2 years and then $Y=51.54e^{-0.11x}(R^{2}=0.40,\;P=0.0)$ from 23 years in new houses. In case of living in new houses, noncarcinogenic health effects of exposure to toluene was 1.38 of hazard quotient (HQ) comparing to toluene reference dose of 0.13 mg/kg-day.

• 대한기계학회논문집A
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• 제32권10호
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• pp.856-865
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• 2008

Damage mechanisms in bending piezoelectric actuators under electric fatigue loading are addressed in this work with the aid of an acoustic emission (AE) technique. Electric cyclic fatigue tests have been performed up to $10^7$ cycles on the fabricated bending piezoelectric actuators. An applied electric loading range is from -6 kV/cm to +6 kV/cm, which is below the coercive field strength of the PZT ceramic. To confirm the fatigue damage onset and its pathway, the source location and distributions of the AE behavior in terms of count rate and amplitude are analyzed over the fatigue range. It is concluded that electric cyclic loading leads to fatigue damages such as transgranular damages and intergranular cracking in the surface of the PZT ceramic layer, and intergranular cracking even develops into the PZ inner layer, thereby degrading the displacement performance. However, this fatigue damage and cracking do not cause the final failure of the bending piezoelectric actuator loaded up to $10^7$ cycles. Investigations of the AE behavior and the linear AE source location reveal that the onset time of the fatigue damage varies considerably depending on the existence of a glass-epoxy protecting layer.

• 대한조선학회논문집
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• 제29권3호
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• pp.71-79
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• 1992

선체 표면상에 Havelock 쏘오스를 분포시켜 선체 표면상의 경계조건을 만족시키는 N-K 이론을 사용하여 선체에 작용하는 조파저항을 구하였다. 수치계산시 Havelock 쏘오스, 혹은 Green 함수는 Noblesse(1977)가 제시한 형태를 사용하였고, 국부교란항은 Newman(1987), 파도교란항은 Baar & Price(1988)를 따라 각각 수행하였다. 선체표면에 대한 수치적분은 Gauss 구적법을 사용하여 수행하였고, 쏘오스의 세기는 겹선형함수로 선체표면에 걸쳐 연속이라고 가정하였다. 또 조파저항계산은 원장에서의 자유표면을 나타내는 식을 사용하여 de Sendagorta & Grases(1988)의 방법에 따라 구하였다. Wigley선형에 대한 계산을 수행하여 선적분항에 미치는 영향을 고찰하였고, 계산치를 기존의 실험치와 비교한 결과 잘 일치하고 있음을 확인하였다.