• 대한금속재료학회지
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• 제49권12호
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• pp.967-976
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• 2011

Conventional fracture tests of resistance spot welds have been performed without consideration of the paint baking process in the automobile manufacturing line. The aim of this paper is to investigate the effect of the paint baking process on load carrying capacity and fracture mode for resistance spot welded 590 dual phase (DP), 780DP, 980DP, 590 transformation in duced plasticity (TRIP), 780TRIP and 1180 complex phase (CP) steels. With paint baking after resistance spot welding, the l-shape tensile test (LTT) and nano-indentation test were conducted on the as-welded and paint baked samples. Paint baking increased the load-carrying capacity of the resistance spot welded samples and improved the fracture appearance from partial interfacial fracture (PIF) to button fracture (BF). Improvement in fracture appearance after LTT is observed on weldments of 780 MPa grade TRIP steels, especially in the low welding current range with paint baking conditions. The higher carbon contents (or carbon equivalent) are attributed to the low weldability of the resistance spot welding of high strength steels. Improvement of the fracture mode and load carrying ability has been achieved with ferrite hardening and carbide formation during the paint baking process. The average nano-indentation hardness profile for each weld zone shows hardening of the base metal and softening of the heat affected zone (HAZ) and the weld metal, which proves that microstructural changes occur during low temperature heat treatment.

• 한국식품영양학회지
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• 제32권2호
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• pp.89-97
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• 2019

In this paper, quality properties and antioxidant capacity of cooked black carrot has been studied. Five different cooking methods have been applied: microwave (45 sec), boiling ($100^{\circ}C$, 14 min), steaming ($100^{\circ}C$, 20 min), sous vide ($75^{\circ}C$, 80 min), sous-vide ($95^{\circ}C$, 30 min). The color value was slightly different (p<0.05), the boiling method was the highest in L-value and Sous vide $75^{\circ}C$ method was the lowest. The steaming method indicated the highest a-value at 5.50. The b-value was significantly different between the samples (p<0.05). The microwave method was the highest at 3.49 while the sous vide $95^{\circ}C$ method was the lowest at -0.34. No significant difference was observed between the samples when only the moisture content results were considered. The highest pH was observed in samples cooked using the boiling method. The softening (%) was higher when the cooking water was in contact with samples and it was dependent on the temperatures. In addition, this study shows that not only temperature but also cooking time and cooking media are very crucial in the preparation and cooking of black carrot to prevent the loss of the antioxidant compound. In conclusion, the comparison of the quality characteristics and antioxidant properties of black carrots indicated that the most appropriate cooking method is sous-vide method.

• 농업과학연구
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• 제45권4호
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• pp.601-614
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• 2018

Chitosan with a natural antimicrobial property has been introduced to protect horticultural crops from diseases as an environmentally friendly method. The purpose of this study was to investigate the effects of the pre-harvest application of chitosan on growth and quality during the late stage of fruit development and on the simulated marketing of the peach fruit (Prunus persica L.). The application of chitosan with calcium chloride ($100mg{\cdot}L^{-1}$) three times at one week intervals 4 weeks before the harvest significantly increased the fruit weight, changed the fruit shape, and reduced the fruit length/diameter ratio giving the peach fruits a round oblate shape. The calcium treatment contributed to enhancing or maintaining the storage potential by increasing the flesh firmness. However, at higher concentrations of $CaCl_2$, i.e., > $600mg{\cdot}L^{-1}$, the positive effects of the chitosan application were offset, and fruit growth was not affected by calcium alone. The application of the chitosan/calcium mixture delayed fruit softening; however, this effect was shortened when the storage temperature was $20^{\circ}C$ rather than $15^{\circ}C$. The internal quality of the fruit was profoundly affected by the concentration of calcium added to the chitosan, and delayed fruit maturation was observed at a higher concentration of calcium. The pre-harvest application of chitosan with calcium contributes to the enhancement of food safety by inhibiting the occurrence of diseases during postharvest handling. Considering the above results, chitosan has the potential to improve both the yield of peach fruits and their storability. Because chitosan can enhance the freshness and shelf-life of fresh produce, it is necessary to examine its effects on other horticultural crops.

• 대한안전경영과학회지
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• 제22권4호
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• pp.9-15
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• 2020

As of 2018, total yield of lettuce and strawberry amounted to 93,543 tons (representing 1.0 percent) and 183,639 tons (2.0 percent), respectively, among total yields worth 9,185,889 tons in South Korea. Lettuce is affected by a combination of numerous elements such as varieties, cultivation methods and pests during each growth phase (Lee et al., 1999). It is mainly cultivated in spring and fall. Especially due to respiration rate after harvest leading to reduced quality and poor storage, maintaining annual supply is unavailable (Jang et al., 2018). With the distribution of new varieties, forcing culture and indoor insulated facilities for plant cultivation during winter, strawberries are produced every year except for late summer and early fall. Due to active respiration, transpiration, soft flesh and high water content, the fruit is vulnerable to go bad and got rotten compared to other fruits. Furthermore, it is difficult to maintain freshness due to the possibility of softening, discoloration and fungi (Lee et al., 2012). In this regard, developing improved storage and package techniques is needed to ensure maintaining quality and safety even just two to three days after harvest. In order to ensure improved quality and safety of strawberries and lettuce after harvest, the present study applied a modified atmosphere packaging (MAP) technology (Mostofi et. al., 2008). Going forward, it compared the quality and safety of the two products while being stored in a way that put them in an MAP-applied container and a plastic container at room temperature and 4 degree Celsius.

• 한국분말재료학회지
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• 제30권5호
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• pp.431-435
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• 2023

An irradiation hardening of Inconel 718 produced by selective laser melting (SLM) was studied based on the microstructural observation and mechanical behavior. Ion irradiation for emulating neutron irradiation has been proposed owing to advantages such as low radiation emission and short experimental periods. To prevent softening caused by the dissolution of γ' and γ" precipitates due to irradiation, only solution annealing (SA) was performed. SLM SA Inconel 718 specimen was ion irradiated to demonstrate the difference in microstructure and mechanical properties between the irradiated and non-irradiated specimens. After exposing specimens to Fe³⁺ ions irradiation up to 100 dpa (displacement per atom) at an ambient temperature, the hardness of irradiated specimens was measured by nano-indentation as a function of depth. The depth distribution profile of Fe³⁺ and dpa were calculated by the Monte Carlo SRIM (Stopping and Range of Ions in Matter)-2013 code under the assumption of the displacement threshold energy of 40 eV. A transmission electron microscope was utilized to observe the formation of irradiation defects such as dislocation loops. This study reveals that the Frank partial dislocation loops induce irradiation hardening of SLM SA Inconel 718 specimens.

• Geomechanics and Engineering
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• 제36권2호
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• pp.145-156
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• 2024

The mechanical properties of the concrete-frozen soil interface play a significant role in the stability and service performance of construction projects in cold regions. Current research mainly focuses on the precast concrete-frozen soil interface, with limited consideration for the more realistic cast-in-place concrete-frozen soil interface. The two construction methods result in completely different contact surface morphologies and exhibit significant differences in mechanical properties. Therefore, this study selects silty clay as the research object and conducts direct shear tests on the concrete-frozen soil interface under conditions of initial water content ranging from 12% to 24%, normal stress from 50 kPa to 300 kPa, and freezing temperature of -3℃. The results indicate that (1) both interface shear stress-displacement curves can be divided into three stages: rapid growth of shear stress, softening of shear stress after peak, and residual stability; (2) the peak strength of both interfaces increases initially and then decreases with an increase in water content, while residual strength is relatively less affected by water content; (3) peak strength and residual strength are linearly positively correlated with normal stress, and the strength of ice bonding is less affected by normal stress; (4) the mechanical properties of the cast-in-place concrete-frozen soil interface are significantly better than those of the precast concrete-frozen soil interface. However, when the water content is high, the former's mechanical performance deteriorates much more than the latter, leading to severe strength loss. Therefore, in practical engineering, cast-in-place concrete construction is preferred in cases of higher negative temperatures and lower water content, while precast concrete construction is considered in cases of lower negative temperatures and higher water content. This study provides reference for the construction of frozen soil-structure interface in cold regions and basic data support for improving the stability and service performance of cold region engineering.

• 한국식품영양학회지
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• 제23권3호
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• pp.428-433
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• 2010

미숙 토마토를 대상으로 숙성에 미치는 저장 온도의 영향을 측정한 결과는 다음과 같았다. 미숙 토마토가 숙성이 되는 최적의 온도는 알아보기 위해 저장 온도를 달리 설정하여 5 일간의 숙성 기간을 가지고 실험을 하였다. 저장 온도별로 변화되는 화학적 품질 변화를 측정한 결과, 토마토의 당도 변화에서는 초기당도가 9.10 brix에서 저장 온도에 따라 8.77 brix에서 8.93 brix로 다소 감소하는 경향을 보이나, 저장 온도 간에 유의적 차이가 없는 것으로 나타났으며, 그 중 실온에서의 당도 변화가 가장 적음을 알 수 있었다. 토마토의 pH의 변화에서는 미숙 토마토의 pH가 4.2에서 저장 5일 후 4.11에서 4.13 으로 저장 온도에 따른 유의적 차이를 보이지 않았다. 그러나 Hunter's color value 변화에서는 L값은 미숙 토마토의 경우 41.2에서 저장 5일 후 36.81에서 38.77로 다소 값이 낮아졌으며, $10^{\circ}C$의 경우에는 40.71로 다른 저장 온도보다는 덜 감소하였다. a값은 미숙 토마토의 경우 -6.22에서 저장 5일 후 11.87에서 15.74로 증가하였으며, $10^{\circ}C$의 경우에는 8.50으로 다른 저장 온도보다는 덜 증가하였다. 그리고 b값은 미숙 토마토의 경우 20.16에서 저장 5일 후 16.13에서 17.63로 다소 값이 낮아졌으며 저장 온도가 차이는 없었다. Rheometer에 의한 토마토의 texture 변화도 미숙 토마토의 경도가 1,253 g에서 경도의 $10^{\circ}C$ 저장 5일 후에도 1,150 g이었으며, 저장 2일 후 $20^{\circ}C$의 경우 899 g, 실온의 경우 404 g, $30^{\circ}C$의 경우 486 g으로 급격히 감소하였다. 저장 온도에 따른 비타민 C 변화에서는 미숙 토마토의 경우 7.98 mg/100 g의 함량을 나타냈으며, 5일간 저장 시 $10^{\circ}C$에서는 9.08 mg/100 g으로 증가하였고, $20^{\circ}C$에서는 12.01 mg/100 g, 실온은 17.65 mg/100 g으로 증가하였으며, $30^{\circ}C$에서는 17.81 mg/100 g을 나타내었다. 저장 온도에 따른 lycopene 변화에서는 미숙 토마토의 경우 0.37 mg/kg의 함량을 나타냈으며, 5일간 저장 시 $10^{\circ}C$에서는 3.81 mg/kg으로 증가하였고, $20^{\circ}C$에서는 26.85 mg/kg, 실온은 34.19 mg/kg으로 증가하였으며, $30^{\circ}C$에서는 34.56 mg/kg을 나타내었다. 토마토의 숙성 지표로 색차의 a값, 경도, vitamin C 함량, lycopene 함량을 사용할 수 있으며, 토마토의 적숙온도는 실온이 적절하였다.

• Applied Biological Chemistry
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• 제41권3호
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• pp.228-233
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• 1998

제주산 온주밀감의 저장전 온도처리에 의한 저장효과를 검토하기 위하여 궁천조생을 각각 무처리, 상온처리, $10,\;20,\;35^{\circ}C$의 저장전 처리를 한 다음 $4^{\circ}C$, 85% 상대습도에서 저온저장하였다. $35^{\circ}C$ 고온처리한 감귤의 중량감소가 매우 적었으며 부패율은 저장 초기에 다소 많았으나 저장 후기에는 오히려 떨어졌다. 과육율과 가용성 고형물은 저장기간 중 큰 변화를 보이지 않았으나 경도는 저장 115일 후부터 심하게 감소하였다. 에틸렌 발생은 저장 $55{\sim}65$일 사이에 약간 증가하다가 115일 이후 급격히 증가하여 부패과의 발생 및 생리활성과 연관이 있는 것으로 보인다. 감귤내 $CO_2$ 함량은 초기에 약간 감소하다가 저장 $55{\sim}100$일 사이에 다소 증가하였으며, 저장 후기에는 감소하는 경향을 나타내었다. 산 및 비타민 C함량은 호흡작용에 의해 저장기간이 경과함에 따라 계속하여 감소하였다. 저장전 $35^{\circ}C$에서 24시간 고온처리는 중량감소와 호흡작용의 억제에 효과가 있었다. 외관 및 내용 성분을 기준한다면 품질 유지를 위해서는 수확후 100일 정도가 조생온주밀감의 최적저장기간으로 판단되었다.

• 한국수산과학회지
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• 제14권3호
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• pp.130-138
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• 1981

굴 보일드 통조림의 저장중 품질저하에 영향을 미치는 변색과 영양가의 손실이 전저리와 저장조건을 달리함으로써 억제가 가능한지를 검토하기 위하여 본 연구를 착수하였으며 실험에서 얻은 결과를 요약하면 다음과 같다. 1. 첨가제의 처리는 밀봉직전에 첨가제 용액을 직접 주입하거나 자숙후 첨가제 용액에 침지하는 것이 효과적이었다. 2. 클로로필과 카로티노이드는 산성보다는 알칼리성에서 더 안정했으며, 아미노태질소와 유효성 lysine은 반대현상을 보였다. 3. 자숙굴의 육과 내장에 대한 클로로필의 분배비는 1/55, 카로티노이드의 분배비는 1/68이였으며 5개월 후에는 각각 $1/14\sim1/40$과 $1/4\sim1/20$으로서 카로티노이드가 클로로필에 비하여 훨씬 이행속도가 빨랐다. 4. $Na_{2}EDTA$의 처리는 변색과 영양가 손실의 억제에 상당한 효과가 있었으며, sodium-polyphosphate의 처리는 육의 연화 또는 붕괴를 촉진시키는 역효과를 보였다. 5. 굴통조림 저장중 아미노태질소와 유효성 lysine은 저장초기에 빨리 감소하였으며, 2개월 일 때는 전감소율의 $50\%$에 달하였다. 6. $4^{\circ},\;20^{\circ}C,\;55^{\circ}C$의 각 온도별로 저장한 굴 통조림의 변색과 영양가의 손실은 온도가 다른 요인에 비해 훨씬 큰 영향을 끼쳤으며 온도가 낮을수록 그 손실이 적었다. 7. 관능검사 결과$Na_{2}EDTA$로 처리하여 $4^{\circ}C$에서 저장한 시료가 가장 품질이 우수하였으며, sodium-polyphosphate로 처리하여 $55^{\circ}C$에서 저장한 시료가 품질이 가장 나빴다.

• 한국식품영양과학회지
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• 제44권12호
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• pp.1819-1825
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• 2015

강력분 80%와 쌀가루 20%를 혼합한 후 검류로 HPMC, xanthan gum, guar gum, glucomannan 등을 각각 1% 첨가하여 반죽의 물성학적 특성을 분석하였다. 혼합분의 Amylograph 분석에서 호화온도는 xanthan gum 첨가구가 가장 낮았으며 유의적 차이가 있었다(P<0.05). 최고점도 온도도 같은 경향을 나타냈으며, 최고점도는 xanthan gum 첨가구가 가장 높았고 glucomannan 첨가구가 가장 낮았으며 유의적 차이가 있었다. Viscograph 분석에서 호화개시온도와 최고점도는 Amylograph 결과와 일치하였으며, 유지온도와 냉각온도에서의 점도는 xanthan gum 첨가구가 가장 높았다. Breakdown은 xanthan gum 첨가구의 값이 가장 높았고 대조구와 HPMC 첨가구가 가장 낮았으며, setback은 HPMC 첨가구가 가장 높았고 xanthan gum 첨가구가 가장 낮았다. Farinograph에서 반죽의 되기는 HPMC 및 xanthan gum 첨가구가 유의적으로 높았으며, 흡수율은 glucomannan 첨가구가 가장 높았다. 반죽형성시간은 대조구에 비하여 guar gum 첨가구가 길었다. 안정도는 대조구에 비하여 HPMC와 guar gum 첨가구는 유의적 차이가 없었으나 xanthan gum 첨가구는 훨씬 짧아져 유의적 차이가 있었다(P<0.05). 약화도는 대조구에 비하여 HPMC와 guar gum 첨가구는 짧아졌으나 xanthan gum과 glucomannan 첨가구는 길어졌다. FQN은 HPMC와 guar gum 첨가구가 대조구에 비해 높았다. 반죽의 발효부피 분석에서 guar gum과 HPMC 첨가구의 부피가 컸고, 반죽의 pH는 HPMC 첨가구가 가장 낮았다. 이상의 실험으로 hydrocolloids가 밀가루와 쌀가루 혼합분의 paste, 반죽, 발효부피, 반죽의 pH 등에 영향을 주었다.