• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.165-165
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• 2017

지난 수 십 년 동안, 전 세계적으로 자원의 소비가 급격히 증가하게 되면서 최근 자원 고갈은 물론 환경오염이 커다란 이슈로 문제가 되고 있다. 이에 따라 재료 관련 분야에 있어서는 보다 효율적이고 친환경적인 방법으로 자원을 활용해야 된다는 필요성이 대두되었고 이와 같은 관점에서 목적하는 성분이 우수하고 환경 친화적인 표면처리 재료 개발연구가 활발하게 진행되고 있는 실정이다. 그 중 플라즈마 전해 산화(Plasma Electrolytic Oxidation, PEO)는 알루미늄, 마그네슘 등의 경금속의 경도를 향상시키고 높은 내마모성, 내식성을 갖게 하는 표면처리로써 그 관심이 증가하고 있다. 이 플라즈마 전해 산화는 일반적으로 공정비용 대비 효과적이고 환경 친화적이며 코팅 성능 면에서 우수하다고 알려져 있다. 이러한 고유한 특성으로 인해 플라즈마 전해 산화 코팅은 최근 몇 년 동안 기계, 자동차, 우주항공, 의학 및 전기 산업 등의 분야에서 그 적용이 점차 증가하고 있는 상황이다. 한편, 플라즈마 전해 산화 코팅을 하는 모재들의 경우 부동태 산화피막을 용이하게 형성할 수 있는 특성의 모재에 한정되고 있어서 그 응용확대에 한계가 있는 것이 사실이다. 따라서 본 연구에서는 플라즈마 전해 산화법을 사용하여 용융알루미늄도금 강판 상에 산화피막 형성을 시도하였다. 전원공급 장치의 양극은 전해질 속에 잠겨있는 작동전극에 연결하고 음극은 대전극 역할을 하는 스테인레스강 전해질 용기에 연결되었다. 전해질은 Sodium Aluminate 및 기타 첨가제를 함유한 것을 사용하였고 온도는 열교환기를 사용하여 $30^{\circ}C$ 이하로 유지되었다. 또한 여기서 전류밀도는 $5{\sim}10A/dm^2$, 실험 주파수는 700Hz, Duty cycle은 30 및 90%의 각 조건에서 공정처리 시간을 각각 30분 및 60분 동안 진행하였다. 이와 같은 조건에서 형성한 막들에 대해서는 주사형전자현미경(SEM)을 이용하여 코팅 막의 표면 및 단면의 모폴로지를 관찰하였음은 물론 EDS 및 XRD 측정을 통하여 원소조성분포 및 결정구조를 각각 분석하였다. 또한 이 코팅 막들에 대한 내식성은 5% 염수분무 환경 중 노출시험(Salt spray test), 3% NaCl 용액에서의 침지 시험 및 전기화학적 동전위 양극분극(Potentiodynamic Polarization) 시험을 진행하여 평가하였다. 이상의 실험결과에 의하면, 제작조건별 플라즈마 전해 산화 코팅 막의 모폴로지 및 결정구조가 상이하게 나타나는 것을 알 수 있었다. 코팅 막의 모폴로지 관찰 결과, 공정 시간에 비례하여 표면에 존재하는 원형 기공의 수는 감소하였으나 그 크기가 커지고 크레이터의 직경 또한 커진 것이 확인되었다. 이 기공은 마이크로 방전에 의해 형성된다고 알려져 있는데 공정 시간이 증가함에 따라 코팅 두께가 점차 증가하여 마이크로 방전의 빈도수가 줄어들고 그 강도는 증가하게 되어 기공 크기가 증가한 것으로 사료된다. 또한 공정시간이 긴 시편에서 표면에 크랙이 다수 존재하는 것으로 확인되었다. 이것은 방전에 의해 고온이 된 소재가 차가운 전해질과 만나게 되어 생긴 큰 온도구배로 인해 강한 열응력이 발생하여 균열을 초래한 것으로 보인다. 조성원소 분석 결과 원형 기공 주변의 크레이터 영역에는 알루미늄이 풍부하였으며 그 주변에 결절상을 갖는 구조에서는 전해질 성분의 원소가 포함되어 있는 것이 확인되었다. 이러한 코팅 막의 표면 특성은 내식성에 영향을 주게 된 원인으로 사료된다. 동전위 분극측정 결과에 의하면 플라즈마 전해 산화 공정 시간이 길어질수록 부식전류밀도가 증가하였다. 이것은 공정시간이 길어짐에 따라 강한 방전이 발생하여 기공의 크기가 증가하고 크랙이 발생하게 되면서 내식성이 저하된 것으로 판단된다. 종합적으로 재료특성 분석 및 내식성 평가를 분석한 결과, 플라즈마 전해 산화의 공정 시간이 너무 길게 되면 오히려 내식성은 저하되는 것이 확인되었다. 이상의 연구를 통하여 고내식 특성을 갖는 플라즈마 전해 산화 막의 유효성을 확인하였으며 용융알루미늄강판 상에 실시한 플라즈마 전해 산화 처리에 대한 기초적인 응용 지침을 제시할 수 있을 것으로 사료된다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.6
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• pp.288-293
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• 2023

To optimize the process parameters of laser powder bed fusion process to fabricate the high density STS316L alloy, the effect of laser power, scanning speed and hatching distance on the relative density was studied. Tensile properties of additively manufactured STS316L alloy using optimized parameters was also evaluated according to the build direction. As a result of additive manufacturing process under the energy density of 55.6 J/mm³, 83.3 J/mm³ and 111.1 J/mm³, high density STS316L specimens was suitably fabricated when the energy density, power and scan speed were 83.3 J/mm³, 225 W and 1000 mm/s, respectively. The yield strength, ultimate tensile strength, and elongation of STS316L specimens in direction perpendicular to the build direction, show the most competitive values. Anisotropic shape of the pores and the lack of fusion defects probably caused strain localization which result in deterioration of tensile properties.

• Journal of Wetlands Research
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• v.26 no.1
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• pp.62-71
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• 2024

To assess the ecological changes of Korean fir (Abies koreana E. H. Wilson) under climate change conditions, growth and physiological responses were analyzed over a 5-year period in a control group (outdoors) and in a treatment group where the temperature and CO2 levels were elevated to closely resemble RCP 4.5 conditions. The results showed an increasing trend in annual branch length of A.koreana in the climate change treatment group over time. While climate change conditions did not significantly impact the morphological differences of A.koreana leaves, they did influence the biomass of the leaves, suggesting that as climate change progresses, the productivity of A.koreana leaves may decline. On the other hand, the chlorophyll content in A.koreana under climate change conditions was higher in the climate change treatment group, whereas the photosynthesis rate, transpiration rate, water use efficiency and stomatal conductance was higher in the control group. This suggests that an environment with elevated temperature and CO2 could influence an increase in stomatal density, but having a negative impact on photosynthetic reactions. Further research on stomatal density under each environmental treatment will be required to confirm this hypothesis. Additionally, as this study only observed changes in leaf biomass, further empirical research should be considered to understand the changes in biomass of A.koreana under climate change conditions. In conclusion, the environmental adaptability of A.koreana is expected to weaken in the long term under elevated temperatures and CO2.

• Food Engineering Progress
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• v.14 no.3
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• pp.193-201
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• 2010

The aim of this study was to analyse the quality of Yukwa puffed by using a vacuum puffing machine and compare to deep-fried Yukwa. The effect of vacuum puffing condition including heating temperature(100-${160^{\circ}C}$), preheating time(0-8 min) and vacuum puffing time(5-20 min) on physical and microstructure characteristics of the Yukwa was investigated. Vacuum puffed Yukwa at ${100^{\circ}C}$ heating temperature, 6 min preheating time and 10 min puffing time had highest value in volumetric expansion ratio(10.04) and lowest value in bulk density(0.15 g/$cm^{3}$). The breaking strength showed the lowest value of 140 g/$cm^{3}$ in vacuum puffing Yukwa at ${100^{\circ}C}$ heating temperature, 6 min preheating time and 15 min puffing time. The Yukwa puffed with the vacuum puffing machine at ${100^{\circ}C}$ heating temperature, 6 min preheating time and 15 min puffing time had the higher value of bulk density and the lower value of volumetric expansion ratio than those of deep-fried Yukwa. Increasing preheating time and vacuum puffing time caused an increase in white and an decrease in yellowness. The vacuum-puffed Yukwa exhibited smaller and uniform cell structure, while deep-fried Yukwa exhibited apparently in larger pores inside and smaller pores near the surface layer. The optimum condition of vacuum puffing machine for the production of vacuum-puffing Yukwa was ${120^{\circ}C}$ heating temperature, 4 min preheating time and 5 min puffing time.

• Journal of Korean Society of Forest Science
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• v.106 no.1
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• pp.40-53
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• 2017

The purpose of this study was to evaluate the effects of container types on physiological characteristics of Zelkova serrata, Fraxinus rhynchophylla and Quercus serrata in the container nursery stage. We used 16 container types [4 growing densities (100, 144, 196 and $256\;seedlings/m^2$)${\times}4$ cavity volumes (460, 380, 300 and $220cm^3/cavity$)] and performed two-way ANOVA to test the differences in photosynthesis, photochemical efficiency and chlorophyll content among container types. Also, multiple regression analysis was conducted to correlate container dimensions with photosynthetic rate. Container types had a strong influence on photosynthesis of three species seedlings. Growing densities and cavity volumes had a significant interaction effect on photosynthetic rate, water use efficiency, stomatal conductance and chlorophyll contents except stomatal conductance of Q. serrata. In all three species, however, interactions between the two factors of container type were not found with regard to photochemical efficiency. Growing density was negatively correlated with photosynthetic rate of F rhynchophylla and Q. serrata, while cavity volumes positively affected on those of three species seedlings. The range of optimal container types was determined by multiple regression analysis based on photosynthetic rate. Consequently, optimal growing density and cavity volume of container by each tree species were found to be approximately $160{\sim}210\;seedlings/m^2$ and $430{\sim}460cm^3/cavity$ for Z. serrata, $130{\sim}150\;seedlings/m^2$ and $390{\sim}440cm^3/cavity$ for F. rhynchophylla and $130{\sim}170\;seedlings/m2$ and $420{\sim}460cm^3/cavity$ for Q. serrata, respectively. Application of adequate container will induce higher quality seedling production in nursery stage, which will also increase seedling growth in plantation stage.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.63 no.1
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• pp.25-34
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• 2018

This study was conducted to investigate the germination and proteome profile characteristics of wheat seeds treated under various concentrations of abscisic acid (ABA). After-ripening, the seeds of three wheat cultivars (Baegjoong, Keumkang, and Uri) showing different levels of dormancy were used. Germination index and germination rate of the cultivars was higher than 0.95% and 98%, respectively, and these were not significantly different under 0, 10, 30, and $50{\mu}M$ ABA at 7 d after germination. However, the growth of the shoot and radicle was significantly inhibited at 10, 30, and $50{\mu}M$ ABA compared to that at $0{\mu}M$ ABA. Mean ABA content of the embryos of seeds germinated at 0 and $50{\mu}M$ ABA for 7 d was 0.8 and $269.0ngmg^{-1}DW$, respectively. Proteins extracted from embryos germinated for 4 d were analyzed by two-dimensional gel electrophoresis, and proteins showing a difference of 1.5-fold or greater in their spot volume relative to that of $0{\mu}M$ ABA were identified. The expression of four protein spots increased at $50{\mu}M$ ABA and two protein spots were detected only at $50{\mu}M$ ABA; these six proteins were all identified as globulin types. Conversely, the expression of three protein spots decreased at $50{\mu}M$ ABA and were identified as cytosolic glutamine sysnthetase, isocitrate dehydrogenase, and S-adenosylmethionine synthetase 2. In conclusion, ABA did not inhibit the germination rate regardless of pre-harvest sprouting characteristics of the cultivars. However, the growth of the shoot and radicle was significantly inhibited by ABA, most likely through the down regulation of glutamine, methyl group donor, and polyamines biosynthesis, among others, while accompanied by globulin accumulation in the embryos.

• Culinary science and hospitality research
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• v.21 no.1
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• pp.77-89
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• 2015

The objective of this study was to optimize processing conditions for the production of an instant puffed rice product using response surface methodology (RSM) and contour analysis. Sensory and texture qualities, and physical properties of the puffed rice were analyzed with various processing conditions related to drying and puffing temperature, and moisture content. Preference, color intensity, cohesiveness, rehydration ratio, density and lightness of the puffed rice product significantly varied depending on the processing conditions. The responses showed high $R^2$ values (0.623, 0.852, 0.735, 0.688, and 0.790) and lack-of-fit. Rehydration ratio was found to have a negative correlation with density in the condition of drying and puffing temperature. Lightness and preference scores of the puffed rice increased as the moisture content increased. According to RSM, the preference scores were very highly related to the moisture content, and the optimum processing conditions of the puffed rice product were at $40^{\circ}C$ of drying temperature, with 11.0% of moisture content, and at $232.7^{\circ}C$ of puffing temperature.

• KSBB Journal
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• v.15 no.3
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• pp.285-292
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• 2000

Support media for yeast immobilization was prepared from a porous volcanic rock used as a moisturizer in orchid growing. The rock was broken to the size of 2-3 mm and burned at $600^{\circ}C$ in a furnace in order to remove organic materials blocking the pores or treated with HCI solution or NaOH solution to remove the inorganic dirts by dissolving. Even through both the acid and the akali solution were effective the latter was not recommendable because it broke the pore structure by dissolving the elements of the media. This media was mainly consisted of SiO2 with $Al_2O_3$ as a minor component and CaO and K2O as trace elements. It had the finely developed pores of $15-80\mu\textrm{m}$size. Yeast immobilization capacity of this media was about $5{\times108}$ cells/ml bed which is large enough to be used for the practical applications. Yeast immobilization capacities of Alumina and Cordierite were much smaller than that of silica-based media. Scanning electron micrograph of Cordierite and Alumina showed uneven surfaces and small size of pores in contrast to relatively smooth surface and large pores of silica based media which means that smooth surface and large pores are desirable for the good adsorption of microbes on the media.

• Journal of the Korean Society of Food Science and Nutrition
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• v.43 no.11
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• pp.1716-1723
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• 2014

This study was designed to examine the change in physical properties of extruded brown rice-vegetable mix at different pregelatinized brown rice contents and $CO_2$ gas injection. Moisture content, screw speed and die temperature were fixed to 30%, 100 rpm and 60, respectively. $CO_2$ gas injection was adjusted to 0, 300, 600, and 800 mL/min. The content of vegetables (carrot, pumpkin, kale and Angelica keiskei) mix was fixed 5%. Pregelatinized and raw brown rice powder were blended as the ratio of 0/95, 30/65 and 50/45. Specific mechanical energy input decreased as pregelatinized brown rice ratio increased. Expansion index increased and the size and number of pores increased but density decreased with the increasing in $CO_2$ gas injection. Gelatinization degree increased as $CO_2$ gas injection increased. In conclusion, cold extrusion with $CO_2$ gas injection at $60^{\circ}C$ die temperature could be applied for Saengsik (uncooked food) making.

• Journal of the Microelectronics and Packaging Society
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• v.14 no.2 s.43
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• pp.17-21
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• 2007

Dense and periodic arrays of holes and Si nano dots were fabricated on silicon substrate. The nanopatterned holes were approximately $15{\sim}40nm$ wide, 40 nm deep and $40{\sim}80\;nm$ apart. To obtain nano-size patterns, self?assembling diblock copolymer were used to produce layer of hexagonaly ordered parallel cylinders of polymethylmethacrylate (PMMA) in polystyrene(PS) matrix. The PMMA cylinders were degraded and removed with acetic acid rinse to produce a PS. $100\;{\AA}-thick$ Au thin film was deposited by using e-beam evaporator. PS template was removed by lift-off process. Arrays of Au nano dots were transferred by using Fluorine-based reactive ion etching(RE). Au nano dots were removed by sulfuric acid. Si nano dots size and height were $30{\sim}70\;nm$ and $10{\sim}20\;nm$ respectively.