• 한국전산유체공학회지
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• 제14권1호
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• pp.70-77
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• 2009

In this study, time-dependent numerical analysis was carried out to investigate the plasma jet impingement on a flat plate, and a compressible form of two-dimensional inviscid gas dynamics equations were solved using the flux corrected transport algorithm. The mathematical modeling of Joule heating in the polycarbonate capillary bore and the mass ablation from the bore wall was incorporated in the numerical analysis and the series of computation was performed for three cases depending on the distance of the opposing plate from the capillary exit. The computational results reveal that the presence of the opposing plate does not affect the flow conditions inside the capillary when compared to the case of open-air plasma discharge. In the exterior region, the flow structure shows the typical supersonic underexpanded jet which consists of the strong Mach disk in front of the opposing plate and the barrel shock at the side of the jet. It is found that the shock evolution becomes more quasi-steady when the plate distance decreases. Also, the effects of the distance between the capillary bore exit and the opposing plate on the flow conditions along the opposing plate are investigated and the pressure variation on the plate shows more complicated interaction between the plasma discharge and the opposing plate when the location of plate becomes closer to the capillary exit.

• Bulletin of the Korean Chemical Society
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• 제31권4호
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• pp.819-824
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• 2010

We report the laser-induced formation of peanut-shaped gold nanoparticles (Au nanopeanuts) and gold nanowires (AuNWs), and their morphological properties. Pulsed laser irradiation of citrate-capped gold nanoparticles at 532 nm induces fragmentation, spherical growth, the formation of Au nanopeanuts, and the formation of AuNWs, sequentially. High-resolution transmission electron microscopy images reveal that the Au nanopeanuts are formed by instantaneous fusion of spherical nanoparticles in random orientation by laser heating. Furthermore, Au nanopeanuts are bridged in a linear direction to form AuNWs by an amorphous accumulation of gold atoms in the junction. The laser-produced Au nanopeanuts and AuNWs slowly disintegrate, restoring the spherical shape of the original Au nanoparticles when the laser irradiation is stopped. The addition of citrate effectively prevents them from transforming back to the nanospheres.

• 한국자기공명학회논문지
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• 제12권1호
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• pp.51-59
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• 2008

Convection effect in liquids has been one of the main targets to be overcome in pulsed-field-gradient NMR measurements of self-diffusion coefficients since the temperature gradient along the sample tube generated by the heating and/or cooling process causes the effect, resulting in additional diffusion. It is known that the capillary is the most appropriate tube type for diffusion experiments at variable temperatures since the narrower tube suppresses convection effectively. For evaluating the properties of hydrogen bonding, diffusion coefficients of the $K^+$-complexed and free valinomycin in a micro tube have been determined at various temperatures. From the analysis of the obtained diffusion coefficient values, we could conclude that the intramolecular hydrogen bonding in both of the $K^+$ complexed and free valinomycin in a non-polar solvent is preserved over the observed temperature range, and the temperature dependence of hydrogen bonding is more pronounced in free valinomycin. It is also thought that there is no big change in the radius of the $K^+$-complexed as temperature is varied, and the ratio of overall radius, $r_{complex}/r_{free}$ is slightly decreased as temperature rises.

• 대한금속재료학회지
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• 제56권12호
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• pp.854-860
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• 2018

In spite of the many attractive properties of (W,Ti)C, its low fracture toughness limits its wide application. To improve the fracture toughness generally a second phase is added to fabricate a nanostructured composite. In this regard, graphene was considered as the reinforcing agent of (W,Ti)C. (W,Ti)C-graphene composites that were sintered within 2 min using pulsed current activated heating under a pressure of 80 MPa. The rapid consolidation method allowed retention of the nano-scale microstructure by blocking the grain growth. The effect of graphene on the hardness and microstructure of the (W,Ti)C-graphene composite was studied using a Vickers hardness tester and FE-SEM. The grain size of (W,Ti)C was reduced remarkably by the addition of graphene. Furthermore, the hardness decreased and the fracture toughness improved with the addition of graphene.

• 대한금속재료학회지
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• 제47권11호
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• pp.754-758
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• 2009

Dense $5Cu_{0.6}Fe_{0.4}-Al_{2}O_{3}$ composite was consolidated from mechanically synthesized powders by high frequency induction heating method within 2 min. Consolidation was accomplished under the combined effects of a induced current and mechanical pressure. Dense $5Cu_{0.6}Fe_{0.4}-Al_{2}O_{3}$ with relative density of up to 95% was produced under simultaneous application of a 80 MPa pressure and the pulsed current. Fracture toughness and hardness of the composite are $7.6MPa{\cdot}m^{1/2}$ and $844kg/mm^{2}$ respectively.

• Journal of Animal Science and Technology
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• 제65권1호
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• pp.32-56
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• 2023

This review explores the factors that improve meat protein digestibility and applies the findings to the development of home meal replacements with improved protein digestion rates in older adults. Various methods improve the digestion rate of proteins, such as heat, ultrasound, high pressure, or pulse electric field. In addition, probiotics aid in protein digestion by improving the function of digestive organs and secreting enzymes. Plant-derived proteases, such as papain, bromelain, ficin, actinidin, or zingibain, can also improve the protein digestion rate; however, the digestion rate is dependent on the plant enzyme used and protein characteristics. Sous vide processing improves the rate and extent of protein digestibility, but the protein digestion rate decreases with increasing temperature and heating time. Ultrasound, high pressure, or pulsed electric field treatments degrade the protein structure and increase the proteolytic enzyme contact area to improve the protein digestion rate.

• 한국식품영양학회지
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• 제29권5호
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• pp.753-759
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• 2016

노계육의 물리적 처리를 통한 조직감 개선과 가공특성을 조사하였다. 각 처리 조건은 스팀(Steam, S) $85^{\circ}C$/20 min, 펄스 전기 자기장(Pulsed Electric Field, PEF) 1.5 KV/cm, 초고압 증기 가열법(Super Heated Steam, SHS) 오븐온도($300^{\circ}C$), 스팀 온도($350^{\circ}C$), 시간(8 min)을 선정하여 실험 하였다. 수율에서는 육계육과 노계육 모두 대조구에서 66.85%, 63.80%로 높은 결과를 얻었으며 처리구에서는 모두 감소하여 노계육을 전기장 처리한(PEF) 처리구에서 61.05%로 가장 낮은 수율을 나타냈다(p<0.05). 색도는 노계와 육계의 품종과 관계없이 가열 중 L 값은 낮아지고 a 값과 b 값은 높아지는 전형적인 현상을 보였으며, 가열 감량은 가열 감량은 노계육스팀처리(S)에서 45.25%로 가장 높았으며, 육계육의 초고압증기(B-SH) 가열 처리할 때는 30.66%로 가장 낮았다. 처리구별로는 노계육을 PEF 및 SH 병행 처리 시 PEF와 SH를 단독으로 처리한 물리적인 처리구보다 가열 감량이 낮게 나타나는 것을 알 수 있었다. 조직감은 hardness의 경우 시료별로는 부드러운 조직감을 갖는 육계육에서 초고압스팀처리구(B-SH)에서 5.57 kg으로 가장 낮았다(p<0.05). 반면에 노계육은 PEF 처리한 후 스팀처리구 경우 14.08 kg으로 육계육에 비해서는 질긴 조직감을 보였으나 PEF 처리 후 초고압증기처리(SL-PSH) 시료에서는 10.73 kg까지 유의적으로 감소하여 연도개선에 효과가 있었다. 관능평가에서는 전반적 기호도가 가장 좋은 점수를 보인 것은 육계육 7.8점이었고, 노계육에서는 PEF 처리 후 초고압증기 처리구(SL-PSH)에서 6.3점으로 가장 좋은 점수를 보였다. 따라서 노계육의 연도를 개선하기 위한 물리적 방법에서는 PEF 처리 후 초고압증기처리(PSH)가 가장 이상적인 방법이라고 생각된다.

• 한국축산식품학회지
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• 제29권6호
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• pp.695-701
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• 2009

본 연구는 축산물가공장 작업환경에 설정된 CCP의 유효성을 평가하기 위하여, 원료도체에서부터 포장에 이르는 전 공정에서 Escherichia coli를 검출하고 PFGE genotyping으로 genetic strain의 흐름을 분석하여 CCP의 적합성을 평가하였다. 시료채취를 위한 작업장은 도축장에서 냉장차량으로 원료도체를 공급받는 독립형 소규모 HACCP 가공장(100두 처리/일)과 축산물종합처리장내 HACCP 가공장(500두 처리/일)을 각각 1곳씩 선정하였다. 시료는 원료도체, 시설 및 장비(발골기, 박피기, 작업대, 벨트, 칼, 면장갑), 환경(벽, 바닥)과 작업공정상의 발골육, 부분육, 최종육을 무균적으로 채취하였다. 작업공정에서 E. coli의 높은 분리율(59.6%)과 작업환경 전반에서의 고른 검출로 E. coli가 축산물가공장 위생지표균으로의 활용 가능성을 확인할 수 있었다. 분리된 E. coli의 genotype 분포는 작업장내 미생물 오염의 흐름을 보여주었다. 소규모가공장의 경우 오염된 원료육 반입이 작업공정을 오염시키고 공정중의 교차오염 발생으로 최종육에 영향을 주었고, 축산물종합처리장내 작업장은 원료육 오염보다는 작업환경에 상존하는 오염미생물의 교차오염이 최종육에 영향을 주는 양상이었다. 따라서 포장육가공장과 같이 작업공정에 멸균처리 과정이 없는 경우는 선행요건에 해당되는 원료반입과 작업환경의 세척 및 소독이 CCP로 관리되거나 이에 준하는 특별관리가 필요하였다. 결과적으로, 작업공정에서의 E. coli 검출과 genotyping은 작업공정상의 미생물 오염의 흐름을 파악하는데 유용하였으며, 이러한 방법은 HACCP 작업장의 미생물 오염원 분석과 설정된 생물학적 critical control point의 적합성 평가에 효과적이었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.297.2-297.2
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• 2016

Photoacoustic generation of ultrasound is an effective approach for development of high-frequency and high-amplitude ultrasound transmitters. This requires an efficient energy converter from optical input to acoustic output. For such photoacoustic conversion, various light-absorbing materials have been used such as metallic coating, dye-doped polymer composite, and nanostructure composite. These transmitters absorb laser pulses with 5-10 ns widths for generation of tens-of-MHz frequency ultrasound. The short optical pulse leads to rapid heating of the irradiated region and therefore fast thermal expansion before significant heat diffusion occurs to the surrounding. In this purpose, nanocomposite thin films containing gold nanoparticles, carbon nanotubes (CNTs), or carbon nanofibers have been recently proposed for high optical absorption, efficient thermoacosutic transfer, and mechanical robustness. These properties are necessary to produce a high-amplitude ultrasonic output under a low-energy optical input. Here, we investigate carbon nanotube (CNT)-polydimethylsiloxane (PDMS) composite transmitters and their nanostructure-originated characteristics enabling extraordinary energy conversion. We explain a thermoelastic energy conversion mechanism within the nanocomposite and examine nanostructures by using a scanning electron microscopy. Then, we measure laser-induced damage threshold of the transmitters against pulsed laser ablation. Particularly, laser-induced damage threshold has been largely overlooked so far in the development of photoacoustic transmitters. Higher damage threshold means that transmitters can withstand optical irradiation with higher laser energy and produce higher pressure output proportional to such optical input. We discuss an optimal design of CNT-PDMS composite transmitter for high-amplitude pressure generation (e.g. focused ultrasound transmitter) useful for therapeutic applications. It is fabricated using a focal structure (spherically concave substrate) that is coated with a CNT-PDMS composite layer. We also introduce some application examples of the high-amplitude focused transmitter based on the CNT-PDMS composite film.

• 한국분말재료학회지
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• 제12권6호
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• pp.422-427
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• 2005

The $Al_2O_3$ with various phases were prepared by simple ex-situ hydrolysis and spark plasma sintering (SPS) process of Al powder. The nano bayerite $(\beta-Al(OH)_3)$ phase was derived by hydrolysis of commercial powder of Al with micrometer size, whereas the bohemite (AlO(OH)) phase was obtained by hydrolysis of nano Al powder synthesized by pulsed wire evaporation (PWE) method. Compaction as well as dehydration of both nano bayerite and bohemite was carried out simultaneously by SPS method, which is used to fabricate dense powder compacts with a rapid heating rate of $100^{\circ}C$ per min. under the pressure of 50MPa. After compaction treatment in the temperature ranges from $100^{\circ}C\;to\; 1100^{\circ}C$, the bayerite and bohemite phases change into various alumina phases depending on the compaction temperatures. The bayerite shows phase transition of $Al(OH)_3{\to}{\eta}-Al_2O_3{\to}{\theta}-Al_2O_3{\to}\alpha-Al_2O_3$ sequences. On the other hand, the bohemite experiences the phase transition from AlO(OH) to ${\gamma}-Al_2O_3\;at\;350^{\circ}C.$ It shows AlO(OH) ${\gamma}-Al_2O_3{\to}{\delta}-Al_2O_3{\to}{\alpha}-Al_2O_3$ sequences. The ${\gamma}-Al_2O_3$ compacted at $550^{\circ}C$ shows a high surface area $(138m^2/g)$.