• Preventive Nutrition and Food Science
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• 제15권4호
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• pp.356-359
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• 2010

Glass transition phenomena in nine Korean pure honeys (moisture content 18.3~20.1%) and honey-water mixtures by different water contents (0, 2, 5, and 10% w/w) were investigated with modulated different scanning calorimetry (MDSC). The total, reversing, and non-reversing heat flows were quantified during heating using MDSC. Glass transition was observed from reversing heat flow separated from the total heat flow. The glass transition temperatures ($T_g$) of pure honeys, which are in the range of $-42.7^{\circ}C$ to $-50.0^{\circ}C$, varied a lot with low determination coefficient ($R^2$=0.63), whereas those of honey-water mixtures decreased with a decrease in honey content. The $T_g$ values were also more significantly different among honey-water mixtures when compared to pure honeys, indicating that in the honey-water mixture system the $T_g$ values appear to be greatly dependent on moisture content. The measured heat capacity change (${\Delta}C_p$) was not influenced by moisture content.

• 한국주거학회논문집
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• 제9권1호
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• pp.133-141
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• 1998

This study was to provide fundamental information on the characteristics and the process of water pollution in Korea and to establish proper policy and strategies to establish proper policy and strategies to deal with the future situation. Content analysis method with a daily newspaper was applied to achieve the purpose of the study. Total 447 articles about water pollution were obtained from the DongA daily newspaper during 1920-1993. The results showed like there. The articles were categorized to three aspects: water pollutant, the affect of the water pollution, and management and measures of water quality. Based on the number of articles and the analysis of the content, the transition of water pollution could be categorized to four periods. 1920~1971 (Period 1), 1972~1978(Period 2). 1979~1990(Period 3.). 1991~1993(Period 4).

• 한국지하수토양환경학회지:지하수토양환경
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• 제15권6호
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• pp.91-98
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• 2010

The effective thermal conductivity of porous materials is usually determined by porosity, water content, and the conductivity of the matrix. In addition, it is also affected by the internal structure of the materials such as the size, arrangement, and connectivity of the matrix-forming grains. Based on the structural models for multi-phase materials, thermal conductivities of soils and sands measured with varying the water content were analyzed. Thermal conductivities of dry samples were likely to fall in the region between the Maxwell-Eucken model with air as the continuous phase and the matrix as the dispersed phase ($ME_{air}$) and the co-continuous (CC) model. However, water-saturated samples moved down to the region between the $ME_{wat}$ model and the series model. The predictive inconsistency of the structural models for dry and water-saturated samples may be caused by the increase of porosity for water-saturated samples, which leads to decrease of connectivity among the grains of matrix. In cases of variably saturated samples with a uniform grain size, the thermal conductivity showed progressive changes of the structural models from the $ME_{air}$ model to the $ME_{wat}$ model depending on the water content. Especially, an abrupt increase found in 0-20% of the water content, showing transition from the $ME_{air}$ model to the CC model, can be attributed to change of water from the dispersed to continuous phase. On the contrary, the undisturbed soil samples with various sizes of grains showed a gradual increase of conductivity during the transition from the $ME_{air}$ model to the CC model.

• 폴리머
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• 제26권5호
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• pp.653-660
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• 2002

가교제 poly(ethylene glycol) diacrylate (PEGDA)를 사용하여 제조한 poly(N-iso-propylacrylamide) (PNIPAAm) 및 poly (N-isopropylacrylamide-co-sodium methacrylate) (P(NIPAAm-co-SMA)) hydrogels의 부피 상전이 현상을 함수율과 표면적의 변화로 고찰하였다. Hydyogel의 부피 상전이 온도는 가교제의 농도에는 영향을 받지 않았으나 공단량체인 SMA의 소량 첨가로 4$0^{\circ}C$ 이상 상승하였다. 특히 PEGDA를 가교제로 사용하였을 경우 가교 길이가 길어짐에 따라 부피 상전이 온도가 더 높게 상승하였다. PNIPAAm 및 P(NIPAAm-co-SMA) hydrogels의 표면적 역시 부피 상전이 온도를 전후하여 감소하였는데 이는 부피 상전이 과정에서 기공의 크기가 현저하게 감소하였기 때문이다. 따라서 표면적과 기공 크기의 변화가 부피 상전이를 나타내는 주요한 인자임을 알 수 있다.

• Food Science and Biotechnology
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• 제18권6호
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• pp.1487-1494
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• 2009

The effects of drying temperature (55, 60, and $65^{\circ}C$) and addition levels of maltodextrin (MD) (10, 20, and 30%) on the physicochemical properties and nutritional quality of purple sweet potato flour were investigated. MD-added flours had higher $L^*$ values, water soluble index, total phenolic, and anthocyanin contents than untreated flour. However, $a^*$, $b^*$ values, water absorption index, and swelling capacity were dependent on the drying temperature and MD concentration. On the other hand, untreated flour had a higher ascorbic acid content compared to the MD-treated flour. Ascorbic acid contents decreased, whereas anthocyanin content was not significantly different, with increasing drying temperatures. MD was positively correlated with phenolic content, anthocyanin, hue angle, and water soluble index. However, there was no correlation between quality parameters and glass transition temperature. The best quality product was obtained when samples were pretreated with MD before drying, regardless of drying temperature.

• 한국식품과학회지
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• 제51권5호
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• pp.432-437
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• 2019

본 연구에서는 국내에서 육종된 쌀품종의 전분에 대한 분자 및 결정구조을 밝히고 이와 같은 결과들이 상전이 특성에 미치는 영향을 조사하였다. 새미면 전분은 아밀로스 함량이 가장 높았으며, 다른 쌀전분에 비해 상대적으로 아밀로펙틴의 짧은 사슬(DP 6-12)과 평균사슬길이, 치반점도와 최종점도, 호화온도와 엔탈피, 2차 상전이인 ${T_g}^{\prime}$이 유의적으로 높았으며, 반대로 최고점도와 강하점도, ice melting 온도와 엔탈피가 유의적으로 낮았다. 아밀로스 함량이 가장 낮은 선향흑미는 다른 전분에 비해 유의적으로 높은 ice melting 엔탈피를 나타냈고 ${T_g}^{\prime}$이 높았다. 결과적으로 쌀 전분의 상전이 특성은 분자 및 결정 구조에 큰 영향을 받는 것을 확인할 수 있었다.

• Geomechanics and Engineering
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• 제22권3호
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• pp.245-254
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• 2020

The interaction between the frozen soil and building structures deteriorates with the increasing temperature. A nuclear magnetic resonance (NMR) stratification test was conducted with respect to the unfrozen water content on the interface and a shear test was conducted on the frozen soil-structure interface to explore the shear characteristics of the frozen soil-structure interface and its failure mechanism during the thawing process. The test results showed that the unfrozen water at the interface during the thawing process can be clearly distributed in three stages, i.e., freezing, phase transition, and thawing, and that the shear strength of the interface decreases as the unfrozen water content increases. The internal friction angle and cohesive force display a change law of "as one falls, the other rises," and the minimum internal friction angle and maximum cohesive force can be observed at -1℃. In addition, the change characteristics of the interface strength parameters during the freezing process were compared, and the differences between the interface shear characteristics and failure mechanisms during the frozen soil-structure interface freezing-thawing process were discussed. The shear strength parameters of the interface was subjected to different changes during the freezing-thawing process because of the different interaction mechanisms of the molecular structures of ice and water in case of the ice-water phase transition of the test sample during the freezing-thawing process.

• Geomechanics and Engineering
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• 제31권1호
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• pp.87-97
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• 2022

The excessive settlement and deformation of disintegrated carbonaceous mudstone (DCM) embankments under dynamic loading have long been problems for engineers and technicians. In this work, the characteristics and mechanism of the plastic deformation of DCM under different degrees of compaction, water contents and confining pressures were studied by static triaxial, dynamic triaxial and scanning electron microscopy testing. The research results show that the axial stress increases with increasing confining pressure and degree of compaction and decreases with increasing water content when DCM failure. The axial strain at failure of the DCM decreases with increasing confining pressure and degree of compaction and increases with increasing water content. Under cyclic dynamic stress, the change in the axial stress level of the DCM can be divided into four stages: the stable stage, transition stage, safety reserve stage and unstable stage, respectively. The effects of compaction, water content and confining pressure on the critical axial stress level which means shakedown of the DCM are similar. However, an increase in confining pressure reduces the effects of compaction and water content on the critical axial stress level. The main deformation of DCM is fatigue cracking. Based on the allowable critical axial stress, a method for embankment deformation control was proposed. This method can determine the degree of compaction and fill range of the embankment fill material according to the equilibrium moisture content of the DCM embankment.

• Bulletin of the Korean Chemical Society
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• 제9권6호
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• pp.368-376
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• 1988

Transition metal PSSA ionomers containing Co(II), Ni(II), Cr(III), Ru(III), and Rh(III) are investigated by IR, Far-IR, UV-Vis and DSC. Reliable IR Spectroscopic criteria are established for assessing the degree of ion-exchange of PSSA ionomers and the local structures around metal cations in them. In the hydrated transition metal PSSA ionomers, the ionic groups are solvated by water molecules and there is no significant interactions between sulfonate group and metal cations. The visible spectra indicated that metal cations are present as [M$(H_2O)_6$]$^{n+}$ with Oh symmetry. Their $T_g$ values increase as the extent of ionic site concentration increases, but there is no direct dependence of $T_g$ on the nature of metal cations or their oxidation states. Thus, the water content in PSSA ionomer is found to have dominant influence on $T_g$ of hydrated transition metal PSSA ionomers. Dehydration of the hydrated transition metal PSSA ionomers results in direct interaction between ionic groups and significant color changes of the ionomers due to the changes of the local structures around metal cations. On the base of spectral data, their local structures are discussed. In case of dehydrated 12.8 and 15.8 mol % transition metal PSSA ionomers, no glass transition is observed in 25-$250^{\circ}C$ region and this is believed to arise from the formation of highly crosslinked structures caused by direct coordination of sulfonate groups of metal cations. In the 6.9 mol % transition metal PSSA ionomers, the glass transition is always observed whether they are hydrated or dehydrated and this is though to be caused by the sufficient segmental mobility of the polymer backbone.

• 한국수자원학회논문집
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• 제33권3호
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• pp.375-382
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• 2000

대유역의 지표면 수문현상은 추계학적 변동에 의해 야기되는 안정된 상태의 변이와 함께 몇 개의 발생빈도가 높은 안정된 상태의 영향을 받기가 쉬운데 그 이유는 지표면과 대기 상호관계의 밀접한 조합과도 관계가 있다. 따라서 각 안정상태에서의 체류기간 즉, 가뭄기나 홍수기의 지속기간이 중요한 연구 과제라 할 수 있으며 본 연구에서는 한강유역에 대하여 안정상태의 평균 변이기간을 분석하였다. 비선형 물수지모형을 한강 유역에 대하여 과거의 자료를 바탕으로 검정하였고 모형을 통한 물리과정의 추계학적 표현과 산정된 모형변수들로부터 안정상태사이의 평균 변이기간이 계산되었다. 본 연구는 안정상태 사이의 변이기간 혹은 거주기간, 즉 시스템이 주어진 안정상태에 머무는 기간(가뭄이나 홍수상태의 지속기간)의 예측과 밀접한 관계가 있다.