• 대한기계학회논문집A
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• 제29권11호
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• pp.1439-1444
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• 2005

A two-dimensional boundary element method was used for the scattering analysis of side-drilled hole(SDH). The far-field scattering amplitude was calculated for shear vertical(SV) wave, and their frequency and time-domain results were presented. The time-domain scattering amplitude showed the directly reflected wave from the SDH leading edge as well as the creeping wave. In an immersion, pulse-echo testing, two measurement models were introduced to predict the response from SDHs. The 2-D boundary element scattering amplitude was converted to the 3-D amplitude to be used in the measurement model. The receiver voltage was calculated fer SV wave incidence at 45$^{\circ}C$ on the 1 m diameter SDH, and the result was compared with experiment.

• Carbon letters
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• 제10권4호
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• pp.325-328
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• 2009

This cycloaddition of [70]fullerene with methyl azidoacetate in benzene under ultrasonic irradiated condition afforded the closed [5,6]-bridged aziridino[70]fullerene derivative, which was unusual product of cycloaddition to the 5,6-junction of fullerene. Its structure was determined by FAB-MS, UV-vis, $^1H-$ and $^{13}C$-NMR spectral data. The closed [5,6]-bridged aziridino[70]fullerene-functionalized gold nanoparticle films were self-assembled using the layer-by-layer method on the reactive of glass slides functionalized with 3-mercaptopropyl trimethoxysilane. The functionalized glass slides were alternately soaked in the solution containing closed the [5,6]-bridged aziridino[70]fullerene and 4-aminothiophenoxide/hexanethiolate-protected gold nanoparticles. The closed [5,6]-bridged aziridino[70]fullerene-functionalized gold nanoparticle films have grown up to 5 layers depending on the immersion time. The self-assembled nanoparticle multilayer films were characterized using UV-vis spectroscopy showed that the surface plasmon band of gold at 527 nm gradually became more evident as successive layers were added to the films.

• Elastomers and Composites
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• 제40권4호
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• pp.272-276
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• 2005

3-aminopropyltrimethoxysilane을 처리한 반응성 있는 유리표면 위에 'dirt-ball' 방법을 사용하여 $C_{70}$-금 나노입자 다중성막 필름을 자기조립하였다. 표면처리한 유리막을 $C_{70}$ 과 ${\omega}$-아미노기를 가진 금 나노입자를 포함하고 있는 용액속에 담그었다. 유기반응(아민화 반응)은 여러층으로 쌓인 다중성막 $C_{70}$-금 나노입자 필름을 용이하게 자기조립 할 수 있었다. $C_{70}$-금 나노입자 필름의 화학적 안정성은 산성용액에 필름을 담근후 흡수도의 변화를 측정함으로 조사되었다. 또한 나노입자 필름의 초음파적 안정성은 초음파 조건에 $C_{70}$-금 나노입자 필름을 노출하여 초음파를 조사 시킨후 고체 표면 위에 부분적인 탈착도의 변화와 작은 정도의 응집성이 일어남을 알 수 있었다.

• Structural Engineering and Mechanics
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• 제64권2호
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• pp.243-257
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• 2017

Investigating the properties and durability of high-strength concrete exposed to sulfuric acid attack for the purpose of its application in structures exposed to this acid is of outmost importance. In this research, the resistance and durability of high-strength concrete containing macro-polymeric or steel fibers together with the pozzolans of silica fume or nano-silica against sulfuric acid attack are explored. To accomplish this goal, in total, 108 high-strength concrete specimens were made with 9 different mix designs containing macro-polymeric and steel fibers at the volume fractions of 0.5, 0.75, and 1.0%, as well as the pozzolans of silica fume and nano-silica with the replacement levels of 10 and 2%, respectively. After placing the specimens inside a 5% sulfuric acid solution in the periods of 7, 21, and 63 days of immersion, the effect of adding the fibers and pozzolans on the compressive properties, ultrasonic pulse velocity (UPV), and weight loss of high-strength concrete was investigated and the respective results were compared with those of the reference specimens. The obtained results suggest the dependency of the resistance and durability loss of high-strength concrete against sulfuric acid attack to the properties of fibers as well as their fraction in concrete volume. Moreover, compared with using nano-silica, using silica fume in the fibrous concrete mix leads to more durable specimens against sulfuric acid attack. Finally, an optimum solution for the design parameters where the crushing load of high-strength fibrous concrete is maximized was found using response surface method (RSM).

• 비파괴검사학회지
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• 제25권2호
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• pp.95-102
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• 2005

원자력 발전소의 많은 배관부는 고온, 고압환경에서 적용되고 있어 환경적 및 기계적 요인에 의하여 부식결함이 빈번히 발생하고 있다. 이와 같은 부식 결함은 초음파 기법 등에 의하여 평가되어야 하고, 본 연구에서는 주사형 레이저 유도 초음파(SLS) 기법을 도입하여 배관부 부식결함의 영상화 기법을 적용하였다. 본 기법은 표면이 거칠거나 배관재와 같은 곡면의 표면에서 적용할 수 있는 장점이 있다. 한편 기존의 주사형 초음파 기법은 초음파 센서와 검사대상체 사이의 초음파 전달 매개체를 확보하기 위하여 시험편이 수침되거나 워터젯을 이용하였으나 주사형 레이저 초음파 기법은 광학적 기법을 이용하여 초음파를 발생시키므로 비접촉 방법에 의한 주사 이미지 획득이 가능하다. 따라서 본 주사형 레이저 초음파 기법은 복잡한 구조물의 검사, 비접촉 원격 및 고화질의 결함 이미지 탐상이 가능하다. 본 연구에서는 배관 결함의 검출능 향상을 위하여 결함 영상 획득에 있어서 다양한 조건의 레이저 유도 초음파 발생 기법을 적용하였고, 배관에 존재하는 응력부식 균열의 결함 영상을 얻게 되었다.

• 한국표면공학회지
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• 제53권5호
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• pp.241-248
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• 2020

The change of the deposition behavior of diamond through a pretreatment process of the base metal prior to diamond deposition using HFCVD was investigated. To improve the specific surface area of the base material, sanding was performed using sandblasting first, and chemical etching treatment was performed to further improve the uniform specific surface area. Chemical etching was performed by immersing the base material in HCl solutions with various etching time. Thereafter, seeding was performed by immersing the sanded and etched base material in a diamond seeding solution. Diamond deposition according to all pretreatment conditions was performed under the same conditions. Methane was used as the carbon source and hydrogen was used as the reaction gas. The most optimal conditions were found by analyzing the improvement of the specific surface area and uniformity, and the optimal diamond seeding solution concentration and immersion time were also obtained for the diamond particle seeding method. As a result, the sandblasted base material was immersed in 20% HCl for 60 minutes at 100 ℃ and chemically etched, and then immersed in a diamond seeding solution of 5 g/L and seeded using ultrasonic waves for 30 minutes. It was possible to obtain optimized economical diamond film growth rates.

• Journal of Microbiology and Biotechnology
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• 제34권4호
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• pp.846-853
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• 2024

Adzuki bean (Vigna angularis), which provides plant-based proteins and functional substances, requires a long soaking time during processing, which limits its usefulness to industries and consumers. To improve this, ultrasonic treatment using high pressure and shear force was judged to be an appropriate pretreatment method. This study aimed to determine the optimal conditions of ultrasound treatment for the improved hydration of adzuki beans using the response surface methodology (RSM). Independent variables chosen to regulate the hydration process of the adzuki beans were the soaking time (2-14 h, X₁), treatment intensity (150-750 W, X₂), and treatment time (1-10 min, X₃). Dependent variables chosen to assess the differences in the beans post-immersion were moisture content, water activity, and hardness. The optimal conditions for treatment deduced through RSM were a soaking time of 12.9 h, treatment intensity of 600 W, and treatment time of 8.65 min. In this optimal condition, the values predicted for the dependent variables were a moisture content of 58.32%, water activity of 0.9979 a_w, and hardness of 14.63 N. Upon experimentation, the results obtained were a moisture content of 58.28 ± 0.56%, water activity of 0.9885 ± 0.0040 a_w, and hardness of 13.01 ± 2.82 g, confirming results similar to the predicted values. Proper ultrasound treatment caused cracks in the hilum, which greatly affects the water absorption of adzuki beans, accelerating the rate of hydration. These results are expected to help determine economically efficient processing conditions for specific purposes, in addition to solving industrial problems associated with the low hydration rate of adzuki beans.

• 생명과학회지
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• 제21권1호
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• pp.56-61
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• 2011

본 연구는 청나래고사리 성엽 추출물의 항산화물질의 함량과 항산화능을 향상시킬 수 있는 효과적인 추출방법을 개발하기 위하여 시행하였다. 동결건조한 청나래고사리 성엽의 분쇄시료 1 g을 메탄올, 80% 에탄올 및 물 등 3가지 용매와 섞은 후 6시간 동안 상온 침지, $60^{\circ}C$ 가열 및 200 rpm에서 교반하여 추출하거나 42 kHz의 초음파 수조에서 15, 30, 45분 동안 추출하였다. 추출물은 여과한 다음 가용성고형분, 총 폴리페놀 및 총 플라보노이드의 함량을 측정하였으며, 항산화활성은 DPPH와 ABTS radical 소거활성을 $RC_{50}$으로 환산하여 측정하였다. 80% 에탄올을 용매로 하여 30분 동안 초음파추출 하였을 때 가용성고형분(0.317 $g{\cdot}g^{-1}$ db), 총 폴리페놀(70.90 $mg{\cdot}g^{-1}$ db) 및 총 플라보노이드(41.53 $mg{\cdot}g^{-1}$ db)의 추출수율이 가장 우수하였으며, DPPH와 ABTS radical 소거활성 또한 가장 우수하였다(각 $RC_{50}$=0.14 $mg{\cdot}ml^{-1}$와 0.09 $mg{\cdot}ml^{-1}$). 상기의 연구결과에 따라 청나래고사리의 성엽은 천연항산화소재로 활용가능하며, 80% 에탄올을 용매로 15-30분 동안 초음파추출하는 것이 추출물의 항산화효과를 증가시키며 추출에 소요되는 시간을 줄일 수 있는 효과적인 추출방법으로 생각되었다.