• Journal of Life Science
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• v.18 no.7
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• pp.992-998
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• 2008

We evaluated proanthocyanidin contents out of total polyphenolic compounds in two pine needle extracts prepared by combined extraction methods and compared their antioxidative activities. Amounts of total polyphenolic compounds of sub-supercritical hotwater precipitate (SSHP) and sub-supercritical hotwater supermatant (SSHS) were 225.4 and 116.6 mg/g, respectively. Amounts of proanthocyanidin of SSHP and SSHS were 9.9 and 3.6 mg/g, respectively. Thus, the ratio of proanthocyanidin contents over total polyphenolic compounds of SSHP and SSHS were 4.3 and 3.9%, respectively. Antioxidative activities ($IC_{50}$) of SSHP and SSHS measured by DPPH radical scavenging were 41.5 and $50.7\;{\mu}g/ml$, respectively. These results indicates that two combined extracts, SSHP and SSHS showed higher antioxidative activities than extract prepared by hot water or sub-supercritical. In conclusion, extraction procedures for SSHP and SSHS could be useful methods for preparing the effective components of functional food products.

• Food Science and Preservation
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• v.21 no.1
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• pp.62-68
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• 2014

This study was performed in order to investigate the functional components of 5 kinds of marine algae. We have collected 5 samples of marine algae, such as the sea mustard (Undaria pinnatifida), sea tangle (Laminaria iaponice), sea weed fusiforme (Hizikia fusiforme), green laver (Entetomotpha), laver (Phophyratenera), which have been harvested in Jeollanam-do. In order to examine the functional effects, 5 kinds of marine algae were extracted with hot water ($80^{\circ}C$, 4 hr), ethanol and methanol (R.T., 4 hr), and subcritical water extract (SWE, 3 MPa, $90^{\circ}C$, $150^{\circ}C$, $210^{\circ}C$). A higher yield of extract was obtained through SWE method (3 MPa, $210^{\circ}C$) in all of the samples obtained. The highest total sugar content was 427.4 mg/g in green laver extracted with SWE (3 MPa, $210^{\circ}C$). The content of the SWE total phenolic compounds was higher than that of the water and solvent (methanol, ethanol) extracts. The anti-oxidative activities of the extracts from 5 kinds of marine algae were examined through the DPPH radical scavenging activity test. The SWE (3 MPa, $150^{\circ}C$ and $210^{\circ}C$) of the marine algae was the highest among all of the extracts. As per the results, the SWE of the marine algae contained more functional components and it had a higher antioxidant activity than those of the other extracts. The $IC_{50}$ value of tyrosinase in seaweed fusiforme and laver were higher than those of the other samples. These results strongly support the possible use of marine algae as functional materials.

• 한국신재생에너지학회:학술대회논문집
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• 2006.11a
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• pp.525-528
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• 2006

아임계 및 초임계수에 의한 목질바이오매스의 당화특성을 분석하기 위하여 분해공정 동안 압력을 23MPa(물의 임계압력)로 고정하고 물의 아임계 온도$(325^{\circ}C,\;350^{\circ}C)$와 초임계 온도$(380^{\circ}C,\;400^{\circ}C,\;425^{\circ}C)$에서 현사시나무 목분을 각각 60초 동안 처리하였다. 생성된 현사시나무의 분해산물에는 액상과 고형분의 분해산물이 섞여 있었다. 각 처리조건에 따른 목질바이오매스의 분해율은 온도가 상승함에 따라 증가하였으며 초임계 온도인 $425^{\circ}C$에서 최고 83.1%의 분해율을 나타냈다. 아임계 및 초임계수에 의해서 생성된 단당류는 고성능 음이온 교환 크로바토그래프(HPAEC)를 이용하여 분석하였다. 목질바이오매스의 초임계수 분해과정에서 처리 온도가 높아지면서 단당류 수율은 증가하는 경향을 보였으며, $425^{\circ}C$에서 가장 높은 7.3%의 단당류 수율을 나타내었다. 아임계 온도 범위에서는 현사시나무의 섬유소 성분 중에서 자일란이 우선적으로 분해되어 자일로스의 생성비율이 비교적 높았으며, 처리온도가 높아지면서 셀롤로오스의 분해에 의한 글루코오스 생성율이 급격히 상승하였다. 이렇게 생성된 단당류 성분들은 고온의 반응조건하에서 열분해 반응에 의해서 더욱 분해되어 퓨란계 화합물로 변형되었다.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.48 no.2
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• pp.97-104
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• 2022

In this study, the anti-inflammatory and anti-oxidant efficacy of camellia subcritical water extracts (SWE, 135 ~ 180 ℃, 70 bar) was compared with 70% ethanol and hot water extracts. Among these extracts, the yield (57.9%) of the subcritical water extract, which was extracted under the condition of 180 ℃ and 70 bar was the highest, which increased the extraction yield by more than two times compared to the hot water extract (28.1%). The results of the nitric oxide (NO) production inhibition activity experiment using RAW 264.7 macrophages stimulated with lipopolysaccharide (LPS) showed that subcritical water extracts had superior effects in inhibiting the production of NO without cytotoxicity than 70% ethanol and hot water extracts. In addition, DPPH and ABTS⁺ radical scavenging activity experiments showed that the radical scavenging activity of subcritical water extract was similar to that of 70% ethanol and hot water extract. Moreover, the content of gallic acid was determined by HPLC and the quantity was about 1.62 mg/g for the SWE (165 ℃, 70 bar), which was the highest among all of the extracts. Based on these results, it is concluded the SWE of C. japonica flowers could be potentially applicable as anti-inflammatory and anti-oxidative ingredients in cosmetic formulations.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.11
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• pp.699-707
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• 2017

This study presents a comparative thermodynamic analysis of subcritical and transcritical organic Rankine cycles for the recovery of low-temperature heat sources considering nine substances as the working fluids. The effects of the turbine inlet pressure, source temperature, and working fluid on system performance were all investigated with respect to metrics such as the temperature distribution of the fluids and pinch point in the heat exchanger, mass flow rate, and net power production, as well as the thermal efficiency. Results show that as the turbine inlet pressure increases from the subcritical to the supercritical range, the mismatch between hot and cold streams in the heat exchanger decreases, and the net power production and thermal efficiency increase; however, the turbine size per unit power production decreases.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.8
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• pp.29-36
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• 2004

Supersonic inlet buzz can be defined as unstable subcritical operation associated with fluctuating internal pressures and a shock pattern oscillating about the inlet entrance. The flow pulsations could result in flameout in the combustor or even structural damage to the engine. An experimental study was conducted to investigate the phenomenon of supersonic inlet buzz on axisymmetric, external-compression inlet. An inlet model with a cowl lip diameter of 30mm was tested at a free stream Mach number of 2.0. Subcritical instability was investigated by considering the frequency of pressure pulsation and shock wave structure at the inlet entrance. The results obtained show that total pressure recovery ratios were varied from 0.42 to 0.78, and capture area ratio from 0.34 to 0.98. The frequency of the subcritical flow increased with decrease in capture area ratios. Frequency was measured at $224{\sim}240Hz$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1343-1349
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• 2011

In this study, the power enhancement potential of a Rankine power cycle by transcritical operation was investigated by comparing the power of an HFC-134a subcritical cycle with that of an HFC-125 transcritical cycle, for a low-grade heat source with a temperature of about $100^{\circ}C$. For a fair comparison using different working fluids, each cycle was optimized by three design parameters from the viewpoint of power. In contrast to conventional approaches, the working fluid's heat transfer and pressure drop characteristics were considered in the present approach, with the aim of ensuring a more realistic comparison. The results showed that the HFC-125 transcritical cycle yields 9.4% more power than does the HFC-134a subcritical cycle under the simulation conditions considered in the present study.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.1
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• pp.1-6
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• 2018

Temperatures of cryogenic nitrogen jet inside an injector and at three different downstream positions (0.9, 10.6, and 28.1d) were measured with thermocouples in sub- and supercritical states. The jet temperature decreased while cooling the supply line and injector. The jet experienced from flash boiling, boiling and then no boiling according to decreasing temperature. As an analogy to flash-boiling at the subcritical state, pseudo-flash boiling has been assumed considering the existence of pseudo-boiling at the supercritical state. By showing an area where the temperature did not increase downstream, the plausibility of pseudo-flash boiling is proposed.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.4
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• pp.53-58
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• 2021

Based on surrogate model, a hydrocarbon mixture was analyzed by visualizing the impinging break up mechanism in subcritical and supercritical conditions. Decane and methylcyclohexane with different critical pressures and temperatures were selected as experimental fluids. The impinging injector was installed inside the chamber, and the spray was visualized through a speed camera in subcritical and supercritical conditions. The injection condition of the mixture and chamber was kept constant at Pr(P/P_c) = 1, and Tr(T/T_c) was increased from 0.48 to 1.02. As Tr increased, the spray angle increased, and the sheet length decreased as the properties of the mixture reached each critical point. In addition, when the mixture approached the near critical point, it was shown that the change in density gradient was largely observed out of the impinging break up mechanism.

• Proceedings of the Korea Database Society Conference
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• 2000.11a
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• pp.186-197
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• 2000

기업의 해체 이후 등장한 인터넷 비즈니스 기업들은 기존의 오프라인 기업들과는 달리 비즈니스에 의한 수익을 올리지 못하고 있다. 아직도 임계점에 도달하지 못해서 그런 것일까\ulcorner 아니면 기존의 수익 구조로는 어떤 한계가 있는 것일까\ulcorner 많은 연구에서 인터넷 비즈니스는 선점의 효과를 강조하고 있다. 경쟁에서 먼저 임계점에 도달한 인터넷 기업들은 주가로 보상을 받고 있기도 하다. 그러나, 임계점에 도달한 기업이 아직도 비즈니스에 의한 수익의 창출에는 그다지 성과를 올리지 못하고 있는 것 같다. 본 연구에서 주장하는 것은 다음의 두 가지이다. 첫째는, 인터넷 비즈니스 기업들은 임계점을 중시한 나머지 수익 구조에 대한 전략의 수립에 실패하였다. 둘째는, 인터넷 비즈니스 기업들은 기존의 오프라인 기업들과는 달리 온라인 기업 중심으로 이루어 졌기 때문에 기존의 오프라인 기업들과는 근본적으로 다른 수익 구조를 가져야 할 것이다. 즉, 기존의 온라인 기업들의 사업 방식과는 달라야 한다. 누구나 흉내낼 수 있는, 그래서 경쟁상의 우위를 지속적으로 유지시키기가 어려운, 운영의 효율성 중심이 아닌, 어떤 차별화된 전략을 가져야 할 것이다.