• Journal of Microbiology and Biotechnology
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• 제31권1호
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• pp.130-136
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• 2021

Persister cell formation and biofilms of pathogens are extensively involved in the development of chronic infectious diseases. Eradicating persister cells is challenging, owing to their tolerance to conventional antibiotics, which cannot kill cells in a metabolically dormant state. A high frequency of persisters in biofilms makes inactivating biofilm cells more difficult, because the biofilm matrix inhibits antibiotic penetration. Fatty acids may be promising candidates as antipersister or antibiofilm agents, because some fatty acids exhibit antimicrobial effects. We previously reported that fatty acid ethyl esters effectively inhibit Escherichia coli persister formation by regulating an antitoxin. In this study, we screened a fatty acid library consisting of 65 different fatty acid molecules for altered persister formation. We found that undecanoic acid, lauric acid, and N-tridecanoic acid inhibited E. coli BW25113 persister cell formation by 25-, 58-, and 44-fold, respectively. Similarly, these fatty acids repressed persisters of enterohemorrhagic E. coli EDL933. These fatty acids were all medium-chain saturated forms. Furthermore, the fatty acids repressed Enterohemorrhagic E. coli (EHEC) biofilm formation (for example, by 8-fold for lauric acid) without having antimicrobial activity. This study demonstrates that medium-chain saturated fatty acids can serve as antipersister and antibiofilm agents that may be applied to treat bacterial infections.

• Bulletin of the Korean Chemical Society
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• 제18권3호
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• pp.287-291
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• 1997

The photochemical reaction of aqueous dichloromethane in the absence (saturated with argon) and the presence of O2 (saturated with air or oxygen) has been investigated using 184.9 nm UV light. The irradiation of the solution causes the formation of 1,2-dichloroethane, 1,1,2-trichloroethane, 1,1,2,2-tetrachloroethane and chloride ion. The initial quantum yield of the products in the absence of oxygen was determined to be 8.6 × 10-3, 7.3 × 10-3, 4.4 × 10-3 and 2.3 × 10-2, respectively. In addition to these main products, small amounts of 1,2,3-trichloropropane, 1,1,2,2,3-pentachloropropane, 1,1,2,3,3-pentachloropropane, 1,3-dichloropropane and 1,1,2,2,3,3-hexachloropropane were detected. In the presence of oxygen, hydrogen peroxide was also detected along with the products listed above. With increasing the concentration of oxygen, while formation of the chlorinated organic products diminished, formation of chloride ion increased. Probable reaction mechanisms for the photochemical reaction were presented on the basis of products analysis.

• 대한화학회지
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• 제38권4호
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• pp.271-275
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• 1994

아르곤과 일산화탄소가 포화된 에탄올 수용액의 광화학 반응을 184.9 nm의 자외선을 이용 연구하였다. 아르곤이 포화된 $1{\times}10^{-2}$M의 에탄올 수용액에서는 acetaldehyde와 2,3-butanediol만이 얻어졌으나, 일산화탄소가 포화된 용액의 광반응에서는 이들 두 가지 생성물 이외에 carboxylation 및 carboxylation반응이 진행되어 ${\alpha}$-hydroxypropionaldehyde, formaldehyde, glyoxal, formic acid, oxalic acid and glyoxylic acid등이 생성되었다. 그러나 에탄올의 농도가 증가한 용액의 광반응에서는 일산화탄소의 존재유무에 관계없이 carboxylation과 carboxylation반응은 관찰되지 않았다. 반응의 결과 얻어진 각 생성물들에 대한 initial quantum yield의 값들을 결정하였으며, 산소가 제거된 에탄올 수용액의 광반응에서 얻은 결과와 비교하여 가능한 반응메카니즘을 제시하였다.

• Bulletin of the Korean Chemical Society
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• 제20권6호
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• pp.683-688
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• 1999

In deuterium NMR spectra of phosphatidylethanolamine bilayers with an extremely high content of saturated fatty acids, each C1 deuteron of the glycerol backbone gave rise to a doublet. This suggests the presence of two backbone conformations, the exchange between which is slow on an NMR time scale. The origin of the two conformations has been investigated in this work using saturated 1,2-diacyl-sn-glycero-3-phosphoethanolamine specifically deuterated in the glycerol backbone. The results showed that the two conformations originate from different domains, which have different fatty acid compositions. The differential scanning calorimetry of the bilayers suggested that the size of the domain is not large enough to show an independent phase transition. Thus, the formation of microdomains in the phosphatidylethanolamine bilayers has been concluded. Conformational difference in different domains was shown to be restricted to the C1 position of the glycerol backbone. The microdomains of phosphatidylethanolamine were retained even in the presence of other phospholipids.

• 대한기계학회논문집B
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• 제23권11호
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• pp.1363-1370
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• 1999

A study of scaling and heat transfer has been carried out for a vertical tube evaporator in which $CaSO_4$ saturated water flows upward. Experimental apparatus including vacuum chambers and heaters has been designed and manufactured to study scaling phenomena for three different pressures(1atm, 0.27atm and 0.16atm). Overall heat transfer coefficients have been measured and shown to decrease with time as scaling proceeds. After the end of experiments, the vertical tube has been cut to measure the thickness of scale at different heights. Below the height where the bulk fluid temperature does not reach saturated temperature, the thickness of scale increases, however, beyond that height occurring saturated condition, the thickness does not vary much or even decreases a little. The measured fouling resistances also support these variations of scale thickness.

• 한국환경과학회지
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• 제1권2호
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• pp.105.2-117
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• 1992

The formation mechanism of the vortex streets in the lee of the mountain Is Investigated by a three-dimensional numerical model. The model is based upon the hydrostatic Boussinesq equations in which the vertical turbulent momentum flux is estimated by a turbulence parameterization scheme, but the horizontal viscosity is assumed to be constant. The results show that Karman vortex streets can form even without surface friction in a constant ambient flow with uniform stratification. The vortex formation is related to breaking of the mountain wave, which depends on the Froude number (Fr). In the case of a three-dimensional bell-shaped mountain, the wave breaking occurs when Fr is less than about 0.8, while a barman vortex forms when Fr is less than about 0.22. Vortex formation also depends on Reynolds number, which is estimated from the horizontal diffusivity. The vortex formation can be explained by the wave saturation theory given by Lindzen (1981) with some modification. Simulations in this study show that in the case of Karman vortex formation the momentum flux in the lower level is much larger than the saturated momentum flux, whereas it is almost equal to the saturated momentum at the upper levels as expected from the saturation theory. As a result, large flux divergence is produced in the lower layer, the mean flow is decelerated behind the mountain, and the horizontal wind shear forms between unmodified ambient wind. The momentum exchange between the mean flow and the mountain wave is produced by the turbulence within a breaking wave. From the result, well developed vortices like Karman vortex can be formed. . The results of the momentum budget calculated by the hydrostatic model are almost the same as nonhydrostatic results as long as horizontal scale of the mountain is 10 km. A well developed barman vortex similar to the hydrostatic one was simulated in the nonhydrostatic case. Therefore, we conclude that the hydrostatic assumption is adequate to investigate the origin of the Km8n vortex from the viewpoint of wave breaking.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• 제1권2호
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• pp.105-117
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• 1997

The formation mechanism of the vortex streets in the lee of the mountain is investigated by a three-dimensional numerical model. The model is based upon the hydrostatic Boussinesq equations in which the vertical turbulent momentum flux is estimated by a turbulence parameterization scheme, but the horizontal viscosity is assumed to be constant. The results show that Karman vortex streets can form even without surface friction in a constant ambient flow with uniform stratification. The vortex formation is related to breaking of the mountain wave, which depends on the Froude number (Fr). In the case of a three-dimensional bell-shaped mountain, the wave breaking occurs when Fr is less than about 0.8, while a Karman vortex forms when Fr is less than about 0.22. Vortex formation also depends on Reynolds number, which is estimated from the horizontal diffusivity. The vortex formation can be explained by the wave saturation theory given by Lindzen (1981) with some modification. Simulations in this study show that in the case of Karman vortex formation the momentum flux in the lower level is much larger than the saturated momentum flux whereas it is almost equal to the saturated momentum at the upper levels as expected from the saturation theory. As a result, large flux divergence is produced in the lower layer, the mean flow is decelerated behind the mountain, and the horizontal wind shear forms between unmodified ambient wind. The momentum exchange between the mean flow and the mountain wave is produced by the turbulence within a breaking wave. From the result, well developed vortices like Karman vortex can be formed. The results of the momentum budget calculated by the hydrostatic model are almost the same as nonhydrostatic results as long as horizontal scale of the mountain is 10 km. A well developed Karman vortex similar to the hydrostatic one was simulated in the nonhydrostatic case. Therefore, we conclude that the hydrostatic assumption is adequate to investigate the origin of the Karman vortex from the viewpoint of wave breaking.

• Corrosion Science and Technology
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• 제7권1호
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• pp.22-26
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• 2008

Formation of protective iron carbonate films in $CO_2$ corrosion can reduce corrosion rate substantially and the effects have been incorporated in various prediction models. The $CO_2$ corrosion with the presence of free acetic acid is known to increase corrosion rate below scaling temperature. The possible interaction between the formation of iron acetate and iron carbonate films can affect the protectiveness of the film. The study is done using 3% NaCl solution under stagnant $CO_2$ -saturated condition at the scaling temperatures at various pH values and HAC concentrations. The result show that the presence of HAc does not affect the formation of protective iron carbonate film but delays the attainment of protective iron carbonate due to a possibility of solubilising of ferrous ions and thinning of the films.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2005년도 제7회 특별심포지움 논문집
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• pp.55-71
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• 2005

현무암으로 구성된 제주도에서 다양한 물리검층 수행하여 용암분출에 따른 물성변화 특성 및 동부지역에서 광범위한 해수침투대의 특성을 파악하고자 하였다. 제주도는 해안가를 따라서 해수침투 관측망을 구축, 운영하고 있으며 지하수자원의 평가와 이와 관련된 지질특성 파악 목적으로 다양한 조사와 모니터링을 수행하고 있다. 제주도의 29개 해수침투 관측정에서 방사능검층(자연감마선, 중성자검층 및 감마-감마(밀도)검층), 전기검층, 공경검층, 공내수의 온도/전기전도도검층, 유향유속검층 등을 수행하였다. 포화대 구간에 대한 물리검층 자료는 현무암 지질 특성을 잘 반영하였으며 일관성 있는 결과를 나타냈다. 자연감마선검층은 포화/불포화대 구간에 관계없이 퇴적층, 미고결 U층, 서귀포층에서 높은 값을 보였으며 중성자검층은 용암의 분출과 관련된 특성 파악에 효과적이었다. 수중화산쇄설성퇴적층은 높은 공극률, 낮은 전기비저항을 나타내며 주요 지하수의 유동통로로 해석되었다. 침상현무암은 높은 전기비저항과 넓은 범위의 공극률을 보이고 퇴적층과 U층은 낮은 전기비저항, 높은 공극률을 보인다. 동부지역의 온도검층 자료는 수문학적인 해석이 유용하며 수산지역의 해수침투 특성의 해석에도 이용되었다.

• Journal of Photoscience
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• 제4권1호
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• pp.17-21
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• 1997

The photochemical reactions of the neat chloroform and the aqueous chloroform in the absence (saturated with argon) and presence of 02 (saturated with air or oxygen) have been investigated using 184.9 nm UV light. The irradiation of the deoxygenated neat chloroform causes the formation of hexachloroethane, pentachloroethane, and 1, 1, 2, 2-tetrachloroethane. The initial quantum yields of the products were determined to be 6.37 x 10$^{-4}$, 4.04 x 10$^{-4}$ and 1.76 x 10$^{-4}$, respectively. In the irradiation of aqueous chloroform, chloride ion was also formed along with the products listed above and 1, 1, 2, 2-tetrachloroethane was the predominant product among the chlorinated organic products, which contrasts to the case of the neat chloroform. The presence of oxygen during the irradiation of aqueous chloroform had an effect on the yield of the products. With increasing the concentration of oxygen, the formation of the products was decreased. Probable reaction mechanisms for the photochemical reaction were presented on the basis of products analysis.