• 소성∙가공
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• 제32권6호
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• pp.344-351
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• 2023

The use of Zn-Al-Mg alloy coatings for enhancing the corrosion resistance of steel sheets is gaining prominence over traditional Zn coatings. There is a growing demand for the development of thermal spray wires made from Zn-Al-Mg alloys, as a replacement for the existing wires produced using Al and Zn. This is particularly crucial to secure corrosion resistance and durability in the damaged areas of coated steel sheets caused by deformation and welding. This study focuses on the casting and extrusion processes of Zn-2Al-1Mg alloy for the fabrication of such spray wires and analyzes the changes in microstructure during the extrusion process. The Zn-2Al-1Mg alloy, cast in molds, was subjected to a heat treatment at 250 ℃ for 3 hours prior to extrusion. The extrusion process was carried out by heating both the material and the mold up to 300 ℃. Microstructural analysis was conducted using FE-SEM and EDS to differentiate each phase. The mechanical properties of the cast specimen were evaluated through compression tests at temperatures ranging from 200 to 300 ℃, with strain rates of 0.1 to 5 sec^-1. Vickers hardness testing was utilized to assess the inhomogeneity of mechanical properties in the radial direction of the extruded material. Finite Element Analysis (FEA) was employed to understand the inhomogeneity in stress and strain distribution during extrusion, which aids in understanding the impact of heterogeneous deformation on the microstructure during the process.

• Nuclear Engineering and Technology
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• 제55권11호
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• pp.4066-4076
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• 2023

Pressure resistance welding is usually used to seal the connection between the cladding tube and the end plug made of zirconium alloy. The seal welded joint has a direct effect on the service performance of the fuel rod cladding structure. In this paper, the pressure resistance welded joints of zirconium alloy tube-plug structure were obtained by thermal-mechanical simulation experiments. The microstructure and microhardness of the joints were both analyzed. The effect of processing parameters on the microstructure was studied in detail. The results showed that there was no β-Zr phase observed in the joint, and no obvious element segregation. There were different types of Widmanstätten structure in the thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ) of the cladding tube and the end plug joint because of the low cooling rate. Some part of the grains in the joint grew up due to overheating. Its size was about 2.8 times that of the base metal grains. Due to the high dislocation density and texture evolution, the microhardnesses of TMAZ and HAZ were both significantly higher than that of the base metal, and the microhardness of the TMAZ was the highest. With the increasing of welding temperature, the proportion of recrystallization in TMAZ decreased, which was caused by the increasing of strain rate and dislocation annihilation.

• 농업과학연구
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• 제12권2호
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• pp.272-281
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• 1985

인삼(人蔘) extract가 유당발효성효모(乳糖醱酵性酵母)인 Kluyveromyces fragilis IFO 0288의 발효(醱酵)에 미치는 영향을 조사(調査)하기 위하여 탈지유(脫脂乳) 배양액(培養液)에 인삼(人蔘) extract를 0~50%의 농도(濃度)로 첨가(添加)하고 $30^{\circ}C$에서 168시간(時間) 정치배양하면서 조사(調査)한 결과(結果)는 다음과 같다. 1. 인삼(人蔘) extract를 1.0% 및 5.0% 첨가(添加)한 구(區)가 대조구(對照區)에 비(比)하여 pH 및 acidity에서 현저한 증가(增加)를 보였다. 2. $CO_2$ 발생량(發生量)에서는 인삼(人蔘) extract 1.0% 첨가구(添加區)가 가장 효과(效果)가 좋았으며 5.0% 첨가구(添加區)는 유제효과(柳制效果)를 나타내었다. 3. alcohol 생산량(生産量)은 인삼(人蔘) extract 1.0%~5.0%가 첨가구(添加區)가 0~0.5% 첨가구(添加區)에 비(比)하여 많은 생산량(生産量)을 나타냈으며 발효시간(醱酵時間)을 단축시켰다. 4. 효모수(酵母數)및 효모성장률(酵母成長率)은 인삼(人蔘) extract 1.0~5.0%가 첨가구(添加區)에서 유도기가 단축되었으며 사멸기를 연장시켰다. 5. 인삼(人蔘) extract 중(中)에 포함되어있는 유리당(遊離糖)은 효모(酵母)의 발효(醱酵)에 별다른 영향을 주지않았다.

• 암석학회지
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• 제23권2호
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• pp.105-117
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• 2014

옥천변성대의 북동 선단부에 위치하는 충청북도 제천시 봉화재 지역은 옥천누층군과 조선누층군이 분포한다. 본 논문은 중첩 변형된 주요 암석 및 미구조의 기하학적 운동학적 특성과 선후관계로부터 봉화재 지역의 지질구조를 연구하였다. 광역엽리의 대부분은 S0 층리가 아닌 신장된 광물들의 정향배열에 의해 정의되는 S0-1의 복합엽리로 나타나고, 일부는 불용해성 불투명 광물과 벽개 라멜라의 정향배열로 정의되는 S0-1-2 복합엽리로 인지된다. 연구지역의 지질구조는 북북동-남남서 방향의 D1 압축작용, 동-서 방향의 D2 압축작용, 남-북 방향의 D3 압축작용 등 적어도 세 번의 변형단계를 거쳐 형성되었다. 조선누층군과 옥천누층군 구성지층의 대상 분포방향과 유사한 S0-1 복합엽리는 D2 변형 이전에 서북서 방향이었으나, D2 변형에 의해 S2 엽리와 평행한 남-북 방향으로 재배열되었고, D3 변형에 의해 현재와 같이 북서, 북동, 남-북 방향으로 재배열되었다. 변형단계별 구조적 특성과 변형작용사는 연구지역의 조선누층군과 옥천누층군이 북북서 방향으로 연장되는 부산지역 동부 영역과 매우 유사하고, 이들 연구결과는 옥천변성대 북동 선단부의 지구조 발달과정을 해석하는데 매우 유용하게 활용될 것으로 기대된다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 추계학술대회 논문집
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• pp.417-423
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• 2007

Oxy-gasification or oxygen-blown gasification, enables a clean and efficient use of coal and opens a promising way to CO2 capture. The coal gasification process of a slurry feed type, entrained-flow coal gasifier was numerically predicted in this paper. The purposes of this study are to develop an evaluation technique for design and performance optimization of coal gasifiers using a numerical simulation technique, and to confirm the validity of the model. By dividing the complicated coal gasification process into several simplified stages such as slurry evaporation, coal devolatilization, mixture fraction model and two-phase reactions coupled with turbulent flow and two-phase heat transfer, a comprehensive numerical model was constructed to simulate the coal gasification process. The influence of turbulence on the gas properties was taken into account by the PDF (Probability Density Function) model. A numerical simulation with the coal gasification model is performed on the Conoco-Philips type gasifier for IGCC plant. Gas temperature distribution and product gas composition are also presented. Numerical computations were performed to assess the effect of variation in oxygen to coal ratio and steam to coal ratio on reactive flow field. The concentration of major products, CO and H2 were calculated with varying oxygen to coal ratio (0.2-1.5) and steam to coal ratio(0.3-0.7). To verify the validity of predictions, predicted values of CO and H2 concentrations at the exit of the gasifier were compared with previous work of the same geometry and operating points. Predictions showed that the CO and H2 concentration increased gradually to its maximum value with increasing oxygen-coal and hydrogen-coal ratio and decreased. When the oxygen-coal ratio was between 0.8 and 1.2, and the steam-coal ratio was between 0.4 and 0.5, high values of CO and H2 were obtained. This study also deals with the comparison of CFD (Computational Flow Dynamics) and STATNJAN results which consider the objective gasifier as chemical equilibrium to know the effect of flow on objective gasifier compared to equilibrium. This study makes objective gasifier divided into a few ranges to study the evolution of the gasification locally. By this method, we can find that there are characteristics in the each scope divided.

• 보존과학회지
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• 제27권4호
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• pp.421-430
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• 2011

본 연구에서는 청동유물에서 관찰되는 다양한 미세조직의 출현과정을 이해하기 위하여 현재 전통방식으로 방짜유기를 제작하는 한국민속촌 유기공방에서 실행되고 있는 제작방법과 담금질 조건을 조사하였으며, 여기에서 제작된 방짜유기의 미세조직과 조성을 살펴보았다. 또한 이 공방에서와 유사한 조건으로 재현실험을 수행하여 그 결과를 비교자료로 사용하였다. 전통 유기공방에서 수행하는 담금질 조건을 자세히 기술함과 동시에 작업 조건에서 나타나는 변동성을 미세조직의 관찰 결과와 함께 제시하였다. 유기공방의 화덕 온도는 $750{\sim}850^{\circ}C$로 측정되었으며 다음 단계의 작업을 위하여 화덕에서 막 꺼낸 청동소재의 표면온도는 대략 $650{\sim}685^{\circ}C$로 측정되었다. 이 같은 큰 폭의 온도 편차는 담금질 과정을 거쳐 생산된 방짜유기에 다양한 미세조직을 초래하였다. 특히 외부기온에 따른 온도편차가 큰 겨울과 비교적 영향이 적은 봄에 각각 제작된 방짜유기의 미세조직을 분석한 결과 ${\alpha}$상을 중심으로 그 배경에서 마르텐사이트(${\beta}$)상, ${\gamma}$상, ${\alpha}+{\delta}$ 공석조직 또는 이들의 혼합물로 이루어진 다양한 조직이 관찰되었다. 특히 실험실에서 재현한 시험편에서도 짧은 시간동안 가열할 경우 ${\alpha}+{\gamma}$상 또는 ${\alpha}+({\beta})+{\gamma}$상 등 다양한 미세조직이 형성되었다. 이처럼 미세조직에서 관찰되는 다양성은 유물에서도 확인되는 것으로 실제 유기공방에서 담금질시 적용하는 열처리 조건이 온도측정으로부터 예측되는 작업조건보다 훨씬 더 복잡하다는 점을 의미한다.

• 한국공간정보시스템학회 논문지
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• 제2권2호
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• pp.59-74
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• 2000

투자의 효율성제시가 불명확한 1단계 국가GIS사업(1995-2000)에 대한 대책으로, 최근 GIS예산 집행의 타당성에 대한 분석이 요구되고 있다. 특히 국가GIS사업의 많은 비중을 차지하는 지자제GIS사업에서 효율적인 투자는 성공적인 사업추진을 위해 매우 중요하다. 그러나 GIS투자의 타당성을 판단하기 위해서는 투자비용의 산정과 함께 그로 인한 편익 내지 효과를 측정할 수 있어야 한다. 또 측정할 수 있다면 얼마나 측정할 수 있고 얼마나 설득력있는 편익을 측정하여 정책결정이나 정치적, 재정적 지지를 얻는 데에 활용할 수 있는가가 핵심적인 주요사안으로 받아들여지고 있다. 따라서 본 연구는 지자체에서 합리적인 의사결정의 자료로 활용될 수 있도록 기존의 다양한 GIS비용효과 분석에 대한 이론적 고찰을 실시하고, 지자제GIS의 특성을 고려한 GIS비용효과분석방안을 고찰하였다. 이를 위해 지자체 GIS 발전단계에 따르는 효과 및 지자체 응용시스템별의 활용효과에 대한 국내외사례를 종합, 국내 지자체 GIS비용효과분석에 적용될 수 있는 비용과 효과의 정량적 정성적 평가항목을 구성하였다. 아울러 편익비용비, 순현재가치, 내부수익률의 평가기법에 따라 다양한 대안선정을 위한 민감도분석과 불확실성분석에 대해서도 살펴봄으로써, 지자제 GIS사업의 투자타당성확보 및 합리적인 의사결정 및 대안선택방향을 모색하였다.

• 대한수의학회지
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• 제25권2호
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• pp.91-101
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• 1985

This study was conducted in order to observe the changes in cellular associations of seminiferous tubules from 8 to 20 weeks of age and to obtain the cycle and relative duration of the seminiferous epithelia from 24 to 32 weeks of age. Twenty-eight Korean native male goats were used in the experiment and divided into 7 groups, consisting of 4 goats each, with four weeks intervals from 8 to 32 weeks of age. The results were summarized as follows; 1. Gonocytes were seen at 8 weeks of age, however they were not observed as from 12 weeks. Both type A-spermatogonia and type B-spermatogonia occurred from 8 weeks, while primary spermatocytes were found from 12 weeks. Secondary spermatocytes and spermatids appeared from 16 weeks, and increased in numbers sequentially until 32 weeks of age. Spermatozoa were observed at first at 20 weeks of age. 2. Type A-spermatogonia appeared approximately twice as many at stage 2 as compared to stage 1, while the same numbers of cells were seen in both stages 1 and 8, showing the least number among 8 stages of the cycle of the seminiferous epithelia. The type B-spermatogonia were found during the stage 5 to 8, not to be detactable during stage 1 to 4. The number of primary spermatocytes of the leptotene phase increased markedly during stage 1 to 4, and decreased afterwards. The primary spermatocytes of the pachytene phase were shown the least in number at stage 4. The secondary spermatocytes could be seen only at stage 4 and the largest number of spermatids was seen at the stage 4 among 8 stages. 3. The relative frequencies of each stage among stages 1 to 8 of the cycle of the seminiferous epithelia were 27.5, 17.5, 12.8, 5.8, 8.9, 8.3, 12.0 and 7.2% respectively. 4. Some of the nuclei of Sertoli cells transformed from the "parallel" type to the "perpendicular" type. This evolution took place from stage 1 to 6, when the number of "perpendicular" type nuclei reached a peak and the number was decreased in the rest of the stages. Thus, establishment of spermatogenesis in Korean native goats was completed at the age of 20 weeks.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2009년도 한국우주과학회보 제18권2호
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• pp.42.3-43
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• 2009

Triplets of identical cubesats will be built to carry out the following scientific objectives: i) multi-observations of ionospheric ENA (Energetic Neutral Atom) imaging, ii) ionospheric signature of suprathermal electrons and ions associated with auroral acceleration as well as electron microbursts, and iii) complementary measurements of magnetic fields for particle data. Each satellite, a cubesat for ion, neutral, electron, and magnetic fields (CINEMA), is equipped with a suprathermal electron, ion, neutral (STEIN) instrument and a 3-axis magnetometer of magnetoresistive sensors. TRIO is developed by three institutes: i) two CINEMA by Kyung Hee University (KHU) under the WCU program, ii) one CINEMA by UC Berkeley under the NSF support, and iii) three magnetometers by Imperial College, respectively. Multi-spacecraft observations in the STEIN instruments will provide i) stereo ENA imaging with a wide angle in local times, which are sensitive to the evolution of ring current phase space distributions, ii) suprathermal electron measurements with narrow spacings, which reveal the differential signature of accelerated electrons driven by Alfven waves and/or double layer formation in the ionosphere between the acceleration region and the aurora, and iii) suprathermal ion precipitation when the storm-time ring current appears. In addition, multi-spacecraft magnetic field measurements in low earth orbits will allow the tracking of the phase fronts of ULF waves, FTEs, and quasi-periodic reconnection events between ground-based magnetometer data and upstream satellite data.

• Wind and Structures
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• 제30권4호
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• pp.433-450
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• 2020

The strong turbulence characteristic of typhoon not only will significantly change flow field characteristics surrounding the large-scale wind turbine and aerodynamic force distribution on surface, but also may cause morphological evolution of coast dune and thereby form sand storms. A 5MW horizontal-axis wind turbine in a wind power plant of southeastern coastal areas in China was chosen to investigate the distribution law of additional loads caused by wind-sand coupling movement of coast dune at landing of strong typhoons. Firstly, a mesoscale Weather Research and Forecasting (WRF) mode was introduced in for high spatial resolution simulation of typhoon "Megi". Wind speed profile on the boundary layer of typhoon was gained through fitting based on nonlinear least squares and then it was integrated into the user-defined function (UDF) as an entry condition of small-scaled CFD numerical simulation. On this basis, a synchronous iterative modeling of wind field and sand particle combination was carried out by using a continuous phase and discrete phase. Influencing laws of typhoon and normal wind on moving characteristics of sand particles, equivalent pressure distribution mode of structural surface and characteristics of lift resistance coefficient were compared. Results demonstrated that: Compared with normal wind, mesoscale typhoon intensifies the 3D aerodynamic distribution mode on structural surface of wind turbine significantly. Different from wind loads, sand loads mainly impact on 30° ranges at two sides of the lower windward region on the tower. The ratio between sand loads and wind load reaches 3.937% and the maximum sand pressure coefficient is 0.09. The coupling impact effect of strong typhoon and large sand particles is more significant, in which the resistance coefficient of tower is increased by 9.80% to the maximum extent. The maximum resistance coefficient in typhoon field is 13.79% higher than that in the normal wind field.