• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.373-378
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• 2004

하모니 영상은 초음파의 비선형 전파 과정에서 발생된 하모닉 성분을 영상화 한다. 하모닉 영상은 초음파에 비선형적으로 반응하는 초음파 조영제를 사용하여 하모닉 성분의 발생을 최대화 하고 있다. 일반적으로 현재 임상적으로 사용되는 하모닉 영상은 2차 고주파 성분을 사용한 것을 의미한다. 2차 하모닉 영상은 주파수의 상승으로 공간 분해능이 향상된다. 초음파 조영제를 이용하는 경우 서브 하모닉, 울트라 하모닉의 발생도 유의할 것으로 기대되지만 이에 대한 연구는 거의 없는 실정이다. 서브 하모닉은 상대적으로 2차 하모닉보다 전파 과정에서 감쇠 효과가 작기 때문에 심부의 영상에 유리하다 서브 하모닉 및 울트라 하모닉 성분 검출은 초음파 변환기의 대역폭에 대한 제한을 2차 하모닉에 비해 상대적으로 덜 받는다. 본 연구에서는 진단용 초음파에 의해 초음파 조영제에서 방사하는 하모닉 성분의 크기를 시뮬레이션 하였다. 수치해석은 Gilmore Equation을 이용하였으며, 초음파 조영제의 탄성 효과는 무시하였다. 초음파 조영제의 크기와 초음파의 MI에 따라 하모닉 성분의 크기를 정량적으로 비교하고, 서브 및 울트라 하모닉 영상의 구현에 대해 토의하였다.

• Elastomers and Composites
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• v.41 no.1
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• pp.57-62
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• 2006

The reaction of fullerene$[C_{60}]$ and 3-chloroperoxy benzoic acid in 1,2-dichlorobenzene was monitored by high resolution ultrasonic spectroscopy and the product of reaction by fullerene $[C_{60}]$ and 3-chloroperoxy benzoic acid in 1,2-dichlorobenzene was characterized using MALDI-TOF-MS spectra.

• Elastomers and Composites
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• v.49 no.2
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• pp.155-159
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• 2014

High resolution ultrasonic spectroscopy was used to observe the oxidation of [$C_{70}$]fullerene with 3-chloroperoxy benzoic acid in 1,2-dichlorobenzene. UV-vis spectroscopy and X-ray diffraction confirmed the resulting roducts of [$C_{70}$]fullerene oxidation.

• Journal of Soil and Groundwater Environment
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• v.21 no.1
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• pp.80-85
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• 2016

Acoustic cavitation can induce various sonochemical effects including pyrolysis and radical reactions and sonophysical effects including microjets and shockwave. In environmental engineering field, ultrasound technology using sonochemical effects can be useful for the removal and mineralization of recalcitrant trace pollutants in aqueous phase as one of emerging advanced oxidation processes (AOPs). In this study, the effect of liquid height, the distance from the transducer to the water surface, on sonochemical oxidation reactions was investigated using KI dosimetry. As the liquid height/volume increased (40~400 mm), the cavitation yield steadily increased even though the power density drastically decreased. It was found that the enhancement at higher liquid height conditions was due to the formation of standing wave field, where cavitation events could stably occur and a large amount of oxidizing radicals such as OH radicals could be continuously provided.

• Journal of the Korea Organic Resources Recycling Association
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• v.26 no.2
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• pp.53-63
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• 2018

The hydrolysis of organic solid waste, such as sludge, is the rate-limiting step of the anaerobic digestion. The longer rate-limiting step lead to decrease of treatment efficiency and increase hydraulic retention time and anaerobic digester. Therefore, the pre-treatment has been applied for accelerating the hydrolysis step. This study was investigated the effects of pre-treatment of waste activated sludge using ultrasonic and alkaline integrated treatment simultaneously. The results showed the cumulative methane production and the methane production rate increased while the lag phase decreased. Therefore ultrasonic and alkaline integrated pre-treatment of waste activated sludge resulted in acceleration of hydrolysis step in anaerobic digestion.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.451-454
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• 2011

Hydro-Reactive metal Fuel (HRF) which has more fuel than general solid propellant reducing oxidizing agent is suitable for ultrahigh speed rocket motor in the water. However, burning rate of HRF has not been studied yet. Through the earlier studies, we established ultrasonics measurement system measuring burning rate of solid propellant as a function of pressure in a single test and verified its reliability. In this paper, we will measure burning rate of HRF using ultrasound with previous development measurement system.

• The Journal of the Acoustical Society of Korea
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• v.18 no.5
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• pp.68-77
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• 1999

The paper looked into the effects of the spectral properties (waveform) of the high intensity focused ultrasound on suppression of the ultrasonic cavitation. Three different types of ultrasound were considered in the study, which were sinusoidal (1 MHz, 5 MPa), frequency modulated (from 1 MHz to 6 MHz for 10 ㎲, 5 MPa), asymmetrically shocked (fundamental frequency 1 MHz, peak positive pressure 12 MPa, peak negative pressure -4 MPa). The temporal response of an air bubble in water initially 1 ㎛ in radius to each type of the ultrasound was predicted using Gilmore bubble dynamic model and Church's rectified gas diffusion equation. It was shown that the radially pulsating amplitude of the bubble was greatly reduced for the frequency modulated wave and was little decreased for the shock wave, compared to the case that the bubble was exposed to the sinusoidal wave. It is interesting that the bubble response to the frequency modulated wave remains similar when the frequency component of the modulated ultrasound is beyond the bubble resonant frequency 3 MHz. This implies that, although the ultrasound is modulated up to 3MHz rather than up to the present 6 MHz, it is likely to produce similar cavitation suppression effects. In practice, it means that a typical narrow band ultrasonic transducer can be taken to generate an appropriate frequency modulated ultrasound to reduce cavitation activity. The present study indicates that ultrasonic cavitation may be suppressed to some extent by a proper spectral modification of high intensity ultrasound.

• Journal of the Korean GEO-environmental Society
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• v.23 no.3
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• pp.23-29
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• 2022

In this study, we investigated the ozone nanobubble process in which nanobubble and ultrasonic cavitation were applied simultaneously to improve the dissolution and self-decomposition of ozone. To confirm the organic decomposition efficiency of the process, a 200 mm × 200 mm × 300 mm scale reactor was designed and phenol decomposition experiments were conducted. The use of nanobubble was 2.07 times higher than the conventional ozone aeration in the 60 minutes reaction and effectively improved the dissolution efficiency of ozone. Ultrasonic irradiation increased phenol degradation by 36% with nanobubbles, and dissolved ozone concentration was lowered due to the promotion of ozone self-decomposition. The higher the ultrasonic power was, the higher the phenol degradation efficiency. The decomposition efficiency of phenol was the highest at 132 kHz. The ozone nanobubble process showed better decomposition efficiency at high pH like conventional ozone processes but achieved 100% decomposition of phenol after 60 minutes reaction even at neutral conditions. The effect by pH was less than that of the conventional ozone process because of self-decomposition promotion. To confirm the change in bubble properties by ultrasonic irradiation, a Zetasizer was used to measure the bubbles' size and zeta potential analysis. Ultrasonic irradiation reduced the average size of the bubbles by 11% and strengthened the negative charge of the bubble surface, positively affecting the gas transfer of the ozone nanobubble and the efficiency of the radical production.

• Membrane Journal
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• v.15 no.4
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• pp.330-337
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• 2005

Water selective silica membranes were prepared fur use as membrane reactor for synthesis of dimethyl ether (DME) by methanol dehydration. Silica membranes formed on a Porous SUS tube by ultrasonic spray Pyrolysis (USP) and chemical vapor deposition (CVD) using tetraethoxysilane (TEOS) as precursor. The CVD-derived membranes formed higher level of trade-off line between water permeance and water/methanol selectivity than that of the USP-derived membranes. The membrane reactor possessing water permeance of $1.2\times10^{-7}\;mol\;{\cdot}\;m^{-2}\;{\cdot}\;S^{-1}\;{\cdot}\;Pa^{-1}$ and water/methanol selectivity of 10 exhibited increase in methanol conversion of about $20\%$ comparing to conventional reactor system. These findings led us to conclude that the dehydration membrane reactor simultaneously separating the water vapour produced in the reaction zone was effective in increasing the reaction conversion.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.210-210
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• 2003

휘스커상의 뮬라이트의 생성온도와 속도는 출발물질로 사용되는 알루미나와 실리카의 화학적 순도, 입자크기 그리고 결정형태에 의존하며, 알루미나와 실리카의 조성비에 따라 생성되는 뮬라이트의 형태가 변한다. 각 원료에 대한 반응성을 관찰하기 위하여 출발원료인 Al(OH)$_3$, 비정질 SiO$_2$, AlF$_3$를 혼합 각각 단일조성과 2상 및 3상의 원료를 혼합 분쇄하여 분무건조한 조립분말을 5$0^{\circ}C$ 구간으로 나누어 상온에서 130$0^{\circ}C$까지 튜브 로에서 열처리하였다. Al(OH)$_3$와 AlF$_3$를 단독으로 열처리하였을 경우에는 안정한 상태로 열처리가 진행되었으나, 혼합하였을 경우에는 40$0^{\circ}C$ 이상의 온도에서 서서히 반응하였다. 각 온도구간에서 열처리한 시편은 미세구조 관찰과 상분석을 통하여 플루오르 토파즈와 휘스커상의 뮬라이트의 생성을 관찰하였으며, 생성된 휘스커 뮬라이트는 조립의 형상을 원형대로 보존하였으며, 조립의 강도를 측정하기 위하여, 초음파 분산기와, 초음파 Homgeniger를 이용하여 처리한 결과 대부분 원래의 형상을 유지하였다.