In this study, effects of carbon and nickel on microstructure and low temperature Charpy impact properties of HSLA (high strength low alloy) steels are investigated. To understand the complex phase transformation behavior of HSLA steels with high strength and toughness before and after welding processes, three kinds of HSLA steels are fabricated by varying the carbon and nickel content. Microstructure analysis, low temperature Charpy impact test, and Vickers hardness test are performed for the base metals and CGHAZ (coarse-grain heat affected zone) specimens. The specimens with the lowest carbon and nickel content have the highest volume fraction of AF, the lowest volume fraction of GB, and the smallest GB packet size. So, the low temperature Charpy absorbed energy of the CGHAZ specimen is the highest. The specimens with increased carbon and nickel content have the lowest volume fraction of AF, the highest volume fraction of GB, and the largest GB packet size. So, the low temperature Charpy absorbed energy of the CGHAZ specimen is the lowest.

Graphene has attracted the interest of many researchers due to various its advantages such as high mobility, high transparency, and strong mechanical strength. However, large-area graphene is grown at high temperatures of about 1,000 °C and must be transferred to various substrates for various applications. As a result, transferred graphene shows many defects such as wrinkles/ripples and cracks that happen during the transfer process. In this study, we address transfer-free, large-scale, and high-quality monolayer graphene. Monolayer graphene was grown at low temperatures on Ti (10nm)-buffered Si (001) and PET substrates via plasma-assisted thermal chemical vapor deposition (PATCVD). The graphene area is small at low mTorr range of operating pressure, while 4 × 4 cm2 scale graphene is grown at high working pressures from 1.5 to 1.8 Torr. Four-inch wafer scale graphene growth is achieved at growth conditions of 1.8 Torr working pressure and 150 °C growth temperature. The monolayer graphene that is grown directly on the Ti-buffer layer reveals a transparency of 97.4 % at a wavelength of 550 nm, a carrier mobility of about 7,000 cm2/V×s, and a sheet resistance of 98 W/□. Transfer-free, large-scale, high-quality monolayer graphene can be applied to flexible and stretchable electronic devices.

본 연구는 제비동자꽃의 대량번식을 위한 효과적인 발아 조건을 선발하고자 수행되었다. 제비동자꽃 종자는 저온습윤 처리(5°C, 0, 4, 8, 12, 16주), GA3 처리(0, 500, 1000mg･L-1), 프라이밍 처리(0.1M, 0.2M의 NH4NO3, K2HPO4, KCl, KNO3)를 하였다. 모든 종자는 25°C, 12시간 광조건(40μmol･m-2 ･s-1)에 서 발아 실험이 진행되었으며, GA3 처리구는 비닐온실(평균 23.4°C)에서도 비교실험이 진행되었다. 저온습윤 8주 처리구 에서 20.4%로 가장 높은 발아율을 나타냈으며, 12주 이상의 저온습윤 처리는 오히려 제비동자꽃의 발아율을 감소시켰다. GA3 0, 500, 1000mg･L-1 처리된 종자는 25°C에서 각각 3.3, 44.0, 62.0%, 비닐온실에서 각각 5.3, 16.7, 42% 발아하였다. 제비동자꽃 종자는 GA3 농도가 높아질수록 발아율이 증가하였다. 또한 제비동자꽃 종자는 0.2M KNO3-프라이밍 처리구에서 가장 높은 발아율(54.7%)을 나타냈으며, 평균발아소요일수는 처리 간 유의성을 보이지 않았다. 이상의 결과로 효과적인 제비종자꽃 종자 번식을 위한 전처리 조건으로 24시간 GA3 1000mg･L-1 침지 처리 또는 0.2M-KNO3 프라이밍 처리를 추천한다.

본 연구는 저온살균(60oC, 5-20분)과 대기압플라즈마(5- 20분)를 병용한 고춧가루 중의 E. coli 저감화 및 시너지 효과를 조사하였다. 저온살균 단일처리시 대장균의 불활 성화는 최대 2 log10 CFU/g(=99% 감소) 이상 나타내었으며, 대기압플라즈마 5, 10, 15, 및 20분간 단일처리 하였을 때 각각 0.4, 0.8, 0.9 및 1.4 log10 CFU/g 감소되었다. 저온 살균 및 대기압플라즈마 단독 처리만으로는 만족할 만한 미생물 저감화효과를 얻을 수 없었기에 저온살균 처리 후, 대기압플라즈마를 병용처리 하여 대장균의 불활성화는 1- 6 log10 CFU/g 이상 감소되었다. 그러나, 저온살균과 대기 압플라즈마 병용처리에 따른 관능적 품질 (색, 이취, 맛, 조 직감 및 전체적인 기호도)에 대한 유의적인 차이는 관찰 되지 않았다(P>0.05). 따라서 고춧가루의 미생물학적 안전성 확보를 위해 저온살균과 대기압플라즈마 단독처리보다 이 둘의 병용처리가 E. coli의 확실한 저감화 효과를 유도 하고 식품 고유의 품질특성을 유지하는데 효과적이었음을 본 연구를 통해 확인되었다.

콜레마니진디벌 머미는 처리한 온도조건(6, 8, 10 및 12 ± 1℃) 중, 8℃에서 저장 10일 까지 50% 이상의 우화율을 보였다. 머미 우화율이 가장 높았던 8℃에서 콜레마니진디벌 머미의 저장기간에 따른 기생된 기장테두리진딧물 머미 수를 조사한 결과, 저장 후 진딧물 기생율이 급격히 떨어지는 것이 확인되었으며, 13일 이상의 저장할 경우 평균 기생율이 20%를 넘지 못하였다. 머미 상태로 저장기간 3일부터 10일까지는 기생율의 차이를 보이지 않았다. 콜레마니진디벌 성충은 3일 이상의 저장은 생존율이 급격히 감소하는 경향을 보여 성충태로의 저온저장은 불가능할 것으로 판단되었다. 고치 형성 후 2일차 된 예쁜가는배고치벌 고치를 6, 8 및 10 ± 1℃ 에서의 저장 기간에 따른 우화율을 조사한 결과, 8℃에서 가장 높은 우화율을 나타냈으며 최대 63일까지 저장이 가능하였다. 8℃ 조건에서 저장기간이 길어질수록 산란기주인 담배거세미나방 2, 3령 유충의 치사율과 고치 형성 수가 급격히 감소하는 경향이었으며, 최적 저장기간은 2주 정도인 것으로 판단되었다.

PURPOSES : It is well known that low temperature cracking is one of the most serious distresses on asphalt pavement, especially for northern U.S. (including Alaska), Canada and the northern part of south Korea. The risk of thermal cracking can be numerically measured by estimating thermal stress of a given asphalt mixture. This thermal stress can be computed by low temperature creep testing. Currently, in-direct tensile (IDT) mixture creep test mentioned in AASHTO specification is used for measuring low temperature creep properties of a given asphalt mixture. However, IDT requires the use of expensive testing equipment for performing the sophisticated analysis process, however, very few laboratories utilize this equipment. In this paper, a new and simple performance test (SPT) method: bending beam rheometer (BBR) mixture creep testing equipment is introduced, and the estimated experimental results were compared with those of conventional IDT tests. METHODS: Three different asphalt mixtures containing reclaimed asphalt pavement (RAP) and roofing shingles were prepared in the Korea Expressway Corporation (KEC) research laboratory. Using the BBR and IDT, the low temperature creep stiffness data were measured and subsequently computed. Using a simple power-law function, the creep stiffness data were converted into relaxation modulus, and subsequently compared. Finally, thermal stress results were computed from relaxation modulus master curve using Gaussian quadrature approach with condierations of 24 Gauss number. RESULTS: In the case of the conventional asphalt mixture, similar trends were observed when the relaxation modulus and thermal stress results were compared. In the case of RAP and Shingle added mixtures, relatively different computation results were obtained. It can be estimated that different experimental surroundings and specimen sizes affected the results. CONCLUSIONS: It can be said that the BBR mixture creep test can be a more viable approach for measuring low temperature properties of asphalt mixture compared to expensive and complex IDT testing methods. However, more extensive research and analysis are required to further verify the feasibility of the BBR mixture creep test.

참딱부리긴노린재의 약충과 성충 모두 5℃ 조건에서 30일 이상 50%의 누적생존율을 나타내며 저장이 가능하였다. 생존율이 가장 높았던 저장 온도인 5℃에서의 저장기간별 참딱부리긴노린재의 산란수는 저장기간이 길어질수록 감소하였으나, 4주까지의 저장은 산란수에 영향을 주지 않았다. 3주간의 저온저장된 참딱부리긴노린재 성충은 담배가루이 4~5령 약충을 포식하는데 포식량에 영향을 받지 않았다. 따라서 참딱부리 긴노린재 약충과 성충은 5℃ 조건에서 3주간의 저장이 가능한 것으로 판단되었다. 갈고리뱀잠자리붙이 성충은 꿀물을 제공하며 5℃에서 저장하 였을 때 20주(140일)까지 50%의 누적생존율을 나타내며 저장이 가능하였지만, 2주 이상의 저온저장은 산란력에 부정적인 영향을 주는 것으로 나타났다. 저온저장기간이 길어질수록 갈고리뱀잠자리붙이의 진딧물 포식량은 감소하였으나. 5주까지의 저온저장은 진딧물 포식량에 영향을 주지 않는 것으로 나타났다. 따라서 참딱부리긴노린재와 갈고리뱀잠자리붙이 두 종 천적의 단일 저온저장이 가능할 것으로 보여 생물학적 방제의 유용한 도구로 활용 가능할 것으로 사료된다.

본 실험은 저온처리 기간과 일장이 자생 돌마타리의 휴면타파와 생장 및 개화에 미치는 영향을 구명하기 위해 실시되었다. 노지에서 재배중인 돌마타리의 생물계절현상 반응(phenology) 을 3월부터 10월까지 조사하였다. 또한 저온처리 기간이 돌마타리 휴면타파 및 개화에 미치는 영향을 알아보기 위해 4°C 저온에 0, 3, 6, 9, 12주간 처리한 후 장일환경(16h), 25°C 온도조건에서 재배하면서 생육특성을 관찰하였다. 일장이 돌마타리의 생육 및 개화에 미치는 영향을 알아보기 위해 자연저온 처리된 돌마타리를 단일(9h), 중일(12h), 장일조건(16h)에서 재배하여 생육 특성을 관찰하였다. 야외에서 재배중인 돌마타리는 늦여름인 8월부터 9월까지 개화하는 특성을 보였다. 저온처리 기간에 따른 실험결과 9, 12주 저온처리를 받은 식물이 3, 6주간 저온처리 한 식물에 비해 개화소요일수가 유의하게 단축되었다. 돌마타리는 4°C 온도에서 9주 이상 처리시 33%의 개화율을 보이는 것으로 조사되었다. 일장에 따른 실험결과, 장일환경에서 재배된 돌마타리의 초장은 50.1cm였으나 단일 및 중일환경에서 재배된 식물의 초장은 각각 16.7, 16.1cm로 조사되었다. 돌마타리는 장일환경에서 16주간 재배 시 100% 개화하였으나 단일 및 중일 환경에서 재배 시 전혀 개화하지 않았다. 결론적으로 돌마타리 는 휴면타파 및 개화를 위해 저온을 필수적으로 요구하며 장일 환경조건에서만 개화하는 질적장일식물임을 확인하였다.

The gas adsorption isotherm requires accurate measurement for the analysis of porous materials and is used as an index of surface area, pore distribution, and adsorption amount of gas. Basically, adsorption isotherms of porous materials are measured conventionally at 77K and 87K using liquid nitrogen and liquid argon. The cold volume calibration in this conventional method is done simply by splitting a sample cell into two zones (cold and warm volumes) by controlling the level sensor in a Dewar filled with liquid nitrogen or argon. As a result, BET measurement for textural properties is mainly limited to liquefied gases (i.e. N2 or Ar) at atmospheric pressure. In order to independently investigate other gases (e.g. hydrogen isotopes) at cryogenic temperature, a novel temperature control system in the sample cell is required, and consequently cold volume calibration at various temperatures becomes more important. In this study, a cryocooler system is installed in a commercially available BET device to control the sample cell temperature, and the automated cold volume calibration method of temperature variation is introduced. This developed calibration method presents a reliable and reproducible method of cryogenic measurement for hydrogen isotope separation in porous materials, and also provides large flexibility for evaluating various other gases at various temperature.

The effect of C, Mn, and Al additions on the tensile and Charpy impact properties of austenitic high-manganese steels for cryogenic applications is investigated in terms of the deformation mechanism dependent on stacking fault energy and austenite stability. The addition of the alloying elements usually increases the stacking fault energy, which is calculated using a modified thermodynamic model. Although the yield strength of austenitic high-manganese steels is increased by the addition of the alloying elements, the tensile strength is significantly affected by the deformation mechanism associated with stacking fault energy because of grain size refinement caused by deformation twinning and mobile dislocations generated during deformation-induced martensite transformation. None of the austenitic high-manganese steels exhibit clear ductile-brittle transition behavior, but their absorbed energy gradually decreases with lowering test temperature, regardless of the alloying elements. However, the combined addition of Mn and Al to the austenitic high-manganese steels suppresses the decrease in absorbed energy with a decreasing temperature by enhancing austenite stability.

Flexible dye-sensitized solar cells using binder free TiO2 paste for low temperature sintering are developed. In this paste a small amount of titanium gel is added to a paste of TiO2 nanoparticle. Analysis of titanium gel paste prepared at 150 ℃ shows that it has a pure anatase phase in XRD and mesoporous structure in SEM. The formation of the titanium gel 1- 2 nm coated layer is confirmed by comparing the TEM image analysis of the titanium gel paste and the pristine paste. This coating layer improves the excited electron transfer and electrical contact between particles. The J-V curves of the organic binder DSSCs fabricated at 150℃ shows a current density of 0.12 mA/cm2 and an open-circuit voltage of 0.47 V, while the titanium gel DSSCs improves electrical characteristics to 5.04 mA/cm2 and 0.74 V. As a result, the photoelectric conversion efficiency of the organic binder DSSC prepared at low temperature is as low as 0.02 %, but the titanium gel paste DSSCs has a measured effciency of 2.76%.

본 연구에서는 저온 소성 굴 패각의 재활용을 위한 기초적 연구로서 메조코즘 실험을 통해 저온 소성 굴 패각의 피복에 따른 연안 오염 퇴적물의 성상 변화를 조사하였다. 이를 위해 350 °C에서 소성시킨 굴 패각을 연안 오염 퇴적물에 피복하여 직상수와 간극수의 성상변화를 분석하는 메조코즘 실험을 수행하였다. 실험 결과, 굴 패각의 피복에 의해 수층과 퇴적층이 분리되었기 때문에 직상수의 산화 환원전위(ORP) 증가 및 DIN 중의 NH3-N의 비율의 감소가 실험구에서 관측되었다. 실험구의 DIP의 농도는 대조구와 비교하여 유의한 차이를 확인하기 어려웠다. 굴 패각의 피복에 의한 퇴적물의 총유기탄소(TOC)는 감소하였으며, 산휘발성황화물(AVS)은 저온 소성 굴 패각의 황화물 흡착 능력으로 인해 최대 50%까지 감소한 것으로 확인되었다. 본 연구의 결과로부터 저온 소성 굴 패각은 연안 오염 퇴적물의 정화를 위해 이용될 수 있는 재료인 것으로 결론 지을 수 있다.

In aluminum brazing processes, corrosive flux, which is used in preventing oxidation, is currently raising environmental concerns because it generates many pollutants such as dioxin. The brazing process involving noncorrosive flux is known to encounter difficulties because the melting temperature of the flux is similar to that of the base material. In this study, a new brazing filler material is developed based on aluminum and non-corrosive flux composite powder. To minimize the interference of consolidation aluminum alloy powder by the flux, the flux is intentionally embedded in the aluminum alloy powder using a mechanical milling process. This study demonstrates that the morphology of the composite powder can be varied according to the mixing process, and this significantly affects the relative density and mechanical properties of the final filler samples.

PURPOSES: Using recyclable materials in asphalt pavement industry is one of the essential tasks not only for saving construction budgets but also for mitigating environmental pollutions. Over the past decades, several efforts have been made by road maintenance agencies to incorporate various recyclable materials into virgin asphalt paving mixtures. As a result, reclaimed asphalt pavement (RAP), which consists of old pavement material was selected as one of most widely used recyclable materials. In this paper, the effects of using different amounts of single-recycled RAP (SRRAP) and double-recycled RAP (DRRAP) on the low-temperature characteristics of asphalt mixtures were investigated. METHODS: To evaluate the low-temperature characteristics of SRRAP and DRRAP mixtures, two experiments, the bending beam mixture creep test and semicircular bending fracture test were performed. The experimental parameters: creep stiffness, m-value, thermal stress, critical cracking temperature, fracture energy, and fracture toughness were computed then compared. RESULTS : RAP mixtures (SRRAP or DRRAP) showed lower mechanical performance compared with conventional asphalt mixtures. The differences became distinct with increased RAP addition. However, the performance differences between SRRAP and DRRAP mixtures were not significant in all cases, which indicate the possible application of re-recycling technology (DRRAP) in the asphalt pavement industry. CONCLUSIONS : The addition of RAP to virgin asphalt can mitigate low-temperature performance despite the improvement in fracture performance observed in some cases. Therefore, using RAP (SRRAP or DRRAP) mixtures on inter or sublayer construction, but not on the surface layer, is recommended. Moreover, the possibility of applying double-recycling technology in asphalt pavement industry can be introduced in this study because not significant performance differences were found between SRRAP and DRRAP mixtures especially at low temperature.

This Study is carried out to stabilize the system according to the change of superheat and subcooling in binary refrigeration system by applying cascade system. When the system on 1 st stage was started and the system on the other side was operated, a temperature reversal phenomenon occurred in which the temperature of the 1 st cascade outlet was temporarily lowered. This means that the condensate heat exchange on the 2 nd is not good, which can cause the compressor to overheated. In order to maintain stable system operation, the opening degree of the expansion valve is controlled to increase the refrigerant circulation amount, thereby facilitating the condensation heat exchange on the 2 nd stage system. We have found that the most suitable refrigerant circulation amount is found by stabilizing the operation of the system while lowerning the super low temperature from -65℃ to -70℃ and increasing again to -60℃.