• International Journal of Aeronautical and Space Sciences
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• 제10권1호
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• pp.67-74
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• 2009

In general, the lunar landing stage can be divided into two distinct phases: de-orbit and descent, and the descent phase usually comprises two sub-phases: braking and approach. And many optimization problems of minimal energy are usually focused on descent phases. In these approaches, the energy of de-orbit burning is not considered. Therefore, a possible low perilune altitude can be chosen to save fuel for the descent phase. Perilune altitude is typically specified between 10 and 15km because of the mountainous lunar terrain and possible guidance errors. However, it requires more de-orbit burning energy for the lower perilune altitude. Therefore, in this paper, the perilune altitude of the intermediate orbit is also considered with optimal thrust programming for minimal energy. Furthermore, the perilune altitude and optimal thrust programming can be expressed by a function of the radius of a parking orbit by using continuation method and co-state estimator.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2012년도 춘계학술발표대회 논문집
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• pp.134-139
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• 2012

This study observed downward long and short-wave radiant environment with selecting 4 areas which have different height in downtown and 1 suburban area to figure out the characteristic of radiant environment in each altitude. The purpose of this study is to collect the preliminary data for interpreting urban thermal environment in summer season by analyzing thermal characteristic of atmosphere in the upper of downtown. The results of this study are as follows. 1) The higher altitude has the lower temperature, and temperature difference was more huge in day time than night time. 2) The short wave radiation according to altitude was higher as altitude was high. 3) Generally, the higher altitude has the lower air temperature, and also the higher altitude has the lower downward long wave radiation by the atmospheric radiation. 4) The ratio short wave radiation of long wave radiation was lower as altitude was high. And the urbanization effect was higher as the ratio was low.

• 한국항공우주학회지
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• 제33권11호
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• pp.80-87
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• 2005

T-50 훈련기에 탑재되어 있는 전기식 비행제어계통 (Digital fly-by-wire flight control system)은 통합 다기능 감지기(IMFP : Integrated Multi-Function Probe)를 이용하여 항공기의 고도/속도/받음각 정보를 획득한다. T-50에는 3개의 IMFP가 장착되어 있으며, 이는 제어법칙에 3중의 소스를 제공한다. IMFP로부터 제공된 3개의 공기 정보는 중간 값을 채택하여 보다 신뢰성 있는 정보를 제어법칙에 제공한다. 고고도 초음속 비행시험 결과, 초음속 영역에서 발생하는 항공기 충격파(Shock wave)의 영향으로 인해 IMFP에서 측정되는 공기정보에 일시적으로 오차가 발생하였다. 이러한 오차정보는 항공기의 안정성에 영향을 미칠 수 있으며, 특히 저고도영역에서 이러한 오차정보가 제어법칙에 제공되어 질 경우, 항공기의 안전성에 영향을 미칠 수 있다. 본 논문에서는 저고도 초음속 영역에서, IMFP 오차정보로 인하여 발생할 수 있는 비행안정성 및 조종성(Controllability)을 해석하기 위해 민감도해석(Sensitivity analysis) 및 HQS(Handling Quality Simulator) 조종사 평가를 수행하였다.

• 한국산림과학회지
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• 제95권3호
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• pp.299-308
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• 2006

본 연구는 위도와 해발고에 따른 우리나라 신갈나무림의 에너지 고정량을 알아보기 위해 강원도 평창군 중왕산 지역(해발 1,300 m, 1,000 m, 800 m), 경기도 광주시 태화산 지역(해발 350 m), 충청북도 제천시 월악산 지역(해발 300 m), 전라남도 광양시 백운산 지역(해발 800 m), 제주도 서귀포시 한라산 지역(해발 1,000 m)을 대상으로 수행되었다. 우리나라 신갈나무림의 에너지량은 2,916~6,550 GJ/ha이고, 연간 에너지 고정량은 250~440 GJ/ha이다. 신갈나무림의 에너지량과 연간 에너지 고정량은 위도가 낮아질수록 더 많아지는 것으로 나타났다. 해발고가 낮을수록 신갈나무림의 에너지량은 증대되는 것으로 나타났다. 신갈나무림의 연간 에너지 고정량과 환경 인자간의 상관관계는 온도, 해발고, 임령, 사면 등의 순서로 크게 나타났다.

• 한국유체기계학회 논문집
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• 제14권1호
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• pp.42-47
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• 2011

Measurement uncertainty analysis of fuel flow using turbine flowmeter was performed for the case of altitude engine test. SAE ARP4990 was used as the fuel flow calculation procedure, as well as the mathematical model for the measurement uncertainty assessment. The assessment was performed using Sensitivity Coefficient Method. 11 parameters involved in the calculation of the flow rate were considered. For the given equipment setup, the measurement uncertainty of fuel flow was assessed in the range of 1.19~1.86 % for high flow rate case, and 1.47~3.31 % for low flow rate case. Fluctuation in frequency signal from the flowmeter had the largest influence on the fuel flow measurement uncertainty for most cases. Fuel temperature measurement had the largest for the case of low temperature and low flow rate. Calibration of K-factor and the interpolation of the calibration data also had large influence, especially for the case of very low temperature. Reference temperature, at which the reference viscosity of the sample fuel was measured, had relatively small contribution, but it became larger when the operating fuel temperature was far from reference temperature. Measurement of reference density had small contribution on the flow rate uncertainty. Fuel pressure and atmospheric pressure measurement had virtually no contribution on the flow rate uncertainty.

• 한국지리정보학회지
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• 제3권1호
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• pp.35-43
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• 2000

DEM(DTED LEVEL 1)을 ARC/INFO로 처리하여 한반도 지형의 경사도를 분석하였다. 한반도는 완경사 사면이 차지하는 비율이 아주 높고, 평탄지나 급경사지의 비율은 낮게 나타난다. 평탄지와 파상지는 고도 150m 이하 지역에 대부분 분포하고, 경사가 가장 급한 고도대는 500m~1,000m 지역이며, 1,000m 이상 지역은 고원의 경관을 보이고 있다. 수치지질도와 경사분석도를 중첩했을 때 고고도와 급경사를 이루는 지질은 화강편마암(ARgr), 편마암(PR1), 평안계 사암(P-T), 자성층군($J_2$) 등으로 나타났고, 저고도에 완만한 경사를 보이는 지질은 엽리상화강암($Jgr_1$), 백악기 퇴적암($K_1$, $K_2$), 신생대 퇴적암(N) 등이며, 제 4기에 분출한 현무암은 높은 고도에 완만한 용암대지를 이루고 있다.

• 한국약용작물학회지
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• 제21권2호
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• pp.130-135
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• 2013

The plant growth and yield of Pinellia ternata (Thunb.) Breit. were studied by altitude and tuber weight. The emergence rates in low land area were not different by tuber weights, but it showed earlier emergence date in heavier weight of seed-tuber and low land area. The higher aerial growth such as plant height and number of leaves per plant was the heavier tuber weight in a planting year, but the growth was not different by the weight of tuber at second year after planting. The distribution pattern of tuber size per $m^2$ was not influenced by different seed-tuber weight. The number of harvested tuber was highest at more than 1 g of tuber weight, and followed 1~2 g and less than 2 g. The distribution pattern of fresh tuber yield was not influenced by different altitude and seed-tuber weight. The marketable tuber, 2 g or more, tends to be produced with more than 0.6 g seed-tuber. As the results above-mentioned, it was thought that the high yield was supposed to use seed-tuber over 0.6 g in the fertile soil.

• 한국항공우주학회지
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• 제34권12호
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• pp.82-89
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• 2006

본 논문에서는 고도 300 km 이상의 고고도 고진공 우주환경에서 발사체의 피치 및 요방향 자세 및 궤적제어를 추력벡터제어 방식으로 수행하는 전기유압식 구동장치시스템의 개발 결과를 기술한다. 성층권 이하에서 운용하는 저고도 발사체용 전기유압식 구동장치시스템과 비교하여 강화된 개발 요구규격 및 이를 충족시키기 위한 신규 설계 및 제작 기술, 성능 검증을 위한 시험장치의 개발 및 이를 사용한 시험 수행 결과를 본 논문에 요약하였다. 시스템 자체 성능 검증을 위한 시험 및 평가가 성공적으로 완료된 구동장치시스템은 관련 시스템과의 접속 및 통합 적합성 검증 후 KSLV-I 발사체에 탑재될 예정이다.

• Advances in aircraft and spacecraft science
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• 제8권1호
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• pp.1-15
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• 2021

Mars exploration demands aerodynamic computations for a proper design of missions of spacecraft carrying instruments and astronauts to Mars. Both Computational Fluid Dynamics (CFD) and Direct Simulation Monte Carlo (DSMC) method play a key role for this purpose. To the author's knowledge, the altitude separating the fields of applicability of CFD and DSMC in Mars atmosphere entry is not yet clearly defined. The limitations in using DSMC at low altitudes are due to technical limitations of the computer. The limitations in using CFD at high altitudes are due to thermodynamic non-equilibrium. Here, this problem is studied in Mars atmosphere entry, considering the Mars Pathfinder capsule in the altitude interval 40-80 km, by means of a DSMC code. Non-equilibrium is quantified by the relative differences between translational temperature and: rotational (θt-r), vibrational (θt-v), overall (θt-ov) temperatures, anisotropy is quantified by the relative difference between the translational temperature component along x and those along y (θx-y) and along z (θx-z). The results showed that θt-r, θt-v, θx-y, θx-z are almost equivalent. The altitude of 45 km should be the limit altitude for a proper use of a CFD code and the altitude of 40 km should be the limit altitude for a reasonable use of a DSMC code.

• Journal of Animal Science and Technology
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• 제64권1호
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• pp.97-109
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• 2022

Species are facing strong selection pressures to adapt to inhospitable high-altitude environments. Yaks are a valuable species and an iconic symbol of the Qinghai-Tibet Plateau. Extensive studies of high-altitude adaptation have been conducted, but few have focused on metabolism. In the present study, we determined the differences in the serum metabolomics between yaks and the closely related species of low-altitude yellow cattle and dairy cows. We generated high-quality metabolite profiling data for 36 samples derived from the three species, and a clear separation trend was obtained between yaks and the other animals from principal component analysis. In addition, we identified a total of 63 differentially expressed metabolites among the three species. Functional analysis revealed that differentially expressed metabolites were related to the innate immune activation, oxidative stress-related metabolism, and energy metabolism in yaks, which indicates the important roles of metabolites in high-altitude adaptation in yaks. The results provide new insights into the mechanism of adaptation or acclimatization to high-altitude environments in yaks and hypoxia-related diseases in humans.