• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.5
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• pp.21-28
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• 2009

This experimental study was performed to find the important design parameters and the starting characteristics of a supersonic exhaust diffuser. The experimental study was carried out on a scaled down model of straight cylindrical supersonic exhaust diffuser, in order to evaluate the effects of operating fluid(air, nitrogen), the diffuser inlet area over the primary nozzle throat area($A_d/A_t$), the inlet pressure of primary nozzle, diffuser length over diffuser inner diameter($L_d/D_d$) and existence or nonexistence of diffuser divergence. The test results showed that the starting pressure increased with decrease in diameter of primary nozzle, and the measured starting pressure of the diffuser had approximately 90~98% efficiency as compared with the predicted starting pressure. Also, the diffuser was started at all case, regardless of $L_d/D_d$ (above 8.4) and diffuser divergence. The result of this study can be used as an essential database for developing a simulated high-altitude facility for real-scale model.

• Korean Journal of Plant Resources
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• v.24 no.6
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• pp.688-695
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• 2011

The composition of free sugar, free amino acid, and fatty acid in tubers of the cultivars 'Superior', 'Sinnamjak', and 'Chubaek' were evaluated at the two sites with different altitude, Gangneung (20 m altitude) as lowland and Daekwallyeong (760 m altitude) as highland. The average reducing sugar content of the three potato cultivars harvested in Daekwallyeong and Gangneung was 1.1% and 2.3%, respectively, which showed two-fold difference between the two locations. Average total sugar content was also two-folds lower in potatoes harvested in Daekwallyeong (6.3%) than those harvested in Gangneung (12.2%). Average content of free amino acids of the three potato cultivars harvested in Daekwallyeong and Gangneung was 1,325 mg/100g and 1,051 mg/100g, respectively. The cultivar 'Chubaek' has the highest amino acid content among the three tested cultivars. Potatoes from Daekwallyeong have higher unsaturated fatty acid levels than those from Gangneung. During the tuber development, unsaturated fatty acids levels increased in tubers grown in Daekwallyeong, but decreased in those grown in Gangneung. These results indicate that the quality of potatoes from Daekwallyeong is from Gangneung for food processing purpose for human consumption.

• Journal of the Korean Society of Earth Science Education
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• v.10 no.3
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• pp.254-261
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• 2017

This study is to investigate preconception of elementary school students and Belizean elementary school teachers and to devise experiment to understand a cause of seasonal change. An open-ended questionnaire and interviews were conducted for 91 6th grade students who didn't learn seasonal change and 10 Belizean teachers to find out preconception of seasonal change and they were categorized by using inductive analysis. They thought that the Earth's rotation, the distance between the Sun and the Earth, the Earth's revolution, pollution and climate change cause seasonal change. And it found out that these misconceptions come from difficulty in awareness of space and impreciseness of textbooks and books and so on. The experiment was designed to correct inaccurate preconception and to improve lessons of seasonal change. It is to measure a meridian altitude and a length of daytime and nighttime and to compare them. This experiment can help to understand the cause of seasonal change by measuring natural phenomenons like the meridian altitude and the change of length of daytime by model.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.6
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• pp.520-529
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• 2016

The main purpose of this study was to analyze the performance of a medium-altitude long endurance unmanned aerial vehicle through reverse-engineering method. The external configuration data of the RQ-1 Predator was reverse-engineered from related photos and specification data available on public domains, which also were used to generate the CATIA modeling and weigh distribution data of the UAV. The aerodynamic characteristics of RQ-1 Predator were mainly predicted the vortex lattice method and an empirical method, which the propeller performance was analyzed by the empirical method proposed by Howe. The rate of climb, service ceiling, range, and the loiter endurance of the UAV was analyzed, which showed good agreement with the reference data.

• Economic and Environmental Geology
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• v.43 no.3
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• pp.249-258
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• 2010

In general, a crustal geomagnetic (or gravity) anomaly compiled at one altitude can be estimated at a different altitude by continuation using the Fourier transform (FT). However, in case of continuation with a great distance between the two elevations, or, in particular, in case of downward continuation, the estimated anomalies by the FT are likely to be mathematically unstable so that the estimated values are not realistic. To solve this problem, two independently measured magnetic field anomalies at different altitudes, such as aeromagnetic and satellite magnetic observations, are implemented to estimate values at in-between altitude for better understanding and interpreting geophysical and geological features. This ‘'dual continuation’' technique is straightforward in the FT and gives a more realistic estimate in all altitudes when we simulated with a set of prismatic bodies at different altitudes. This implies that we add up another constraint like satellite-based observations on the geopotential field modeling for the non-unique geological and geophysical problems to a conventional Fourier-type continuation technique with a single set of observations.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.1
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• pp.47-58
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• 2014

In this research, the initial sizing of a HALE(High Altitude Long Endurance) UAV which uses solar power and hydrogen fuel cell as an alternative energy was performed. Instead of a wing box type, a glider type was chosen since it is relatively easy to get a data thanks to many researches abroad. Maximum takeoff weight is around 150Kg and the propulsion system is composed of motor, propeller, solar cell, and hydrogen fuel cell which can be recharged through electrolysis. Maximum takeoff weight was estimated as aspect ratio, wing span, wing area change while considering energy balance of required energy which is necessary for flight during the entire day and available energy which can be taken from the solar cell.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.1
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• pp.120-131
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• 2016

The full results of troubleshooting process related to the flight control system of a tilt-rotor type UAV in the flight tests are described. Flight tests were conducted in helicopter, conversion, and airplane modes. The vehicle was flown using automatic functions, which include speed-hold, altitude-hold, heading-hold, guidance modes, as well as automatic take-off and landing. Many unexpected problems occurred during the envelope expansion tests which were mostly under those automatic functions. The anomalies in helicopter mode include vortex ring state (VRS), long delay in the automatic take-off, and the initial overshoot in the automatic landing. In contrast, the anomalies in conversion mode are untrimmed AOS oscillation and the calibration errors of the air data sensors. The problems of low damping in rotor speed and roll rate responses are found in airplane mode. Once all of the known problems had been solved, the vehicle in airplane mode gradually reached the maximum design speed of 440km/h at the operation altitude of 3km. This paper also presents a comprehensive detailing of the control systems of the tilt-rotor unmanned air vehicle (UAV).

• Journal of Astronomy and Space Sciences
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• v.27 no.2
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• pp.97-106
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• 2010

To prepare for a Korean lunar orbiter mission, a precise lunar orbit propagator; Yonsei precise lunar orbit propagator (YSPLOP) is developed. In the propagator, accelerations due to the Moon's non-spherical gravity, the point masses of the Earth, Moon, Sun, Mars, Jupiter and also, solar radiation pressures can be included. The developed propagator's performance is validated and propagation errors between YSPOLP and STK/Astrogator are found to have about maximum 4-m, in along-track direction during 30 days (Earth's time) of propagation. Also, it is found that the lifetime of a lunar polar orbiter is strongly affected by the different degrees and orders of the lunar gravity model, by a third body's gravitational attractions (especially the Earth), and by the different orbital inclinations. The reliable lifetime of circular lunar polar orbiter at about 100 km altitude is estimated to have about 160 days (Earth's time). However, to estimate the reasonable lifetime of circular lunar polar orbiter at about 100 km altitude, it is strongly recommended to consider at least $50\;{\times}\;50$ degrees and orders of the lunar gravity field. The results provided in this paper are expected to make further progress in the design fields of Korea's lunar orbiter missions.

• Journal of Electrical Engineering and Technology
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• v.9 no.6
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• pp.2049-2057
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• 2014

In this paper, a numerical method for analyzing coupling between high-altitude electromagnetic pulse (HEMP) as external field and a shielded twisted pair (STP) cable is proposed, which is based on an expanded chain matrix. Load responses of electromagnetic (EM) field excitation in uniform transmission line (TL) are solved by Baum-Liu-Tesche (BLT) equations in frequency domain, however, it is difficult to apply BLT equations to solve load responses of STP cable because the iteratively changing configuration of each twisted pairs are involved in cable. To avoid this problem and decrease memory and CPU time, we proposed the expanded chain matrix modeling method that is calculated using ABCD parameters, and applied multi-conductor transmission line (MTL) theory to consider the EMP coupling effectiveness of each twisted pairs. The results implemented by the proposed method are presented and compared with those obtained by the finite-difference time domain (FDTD) method as a kind of 3D full wave analysis.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.26 no.2
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• pp.91-97
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• 2018

High-energy charged particles are comprised of galactic cosmic rays and solar energetic particles which are mainly originated from the supernova explosion, active galactic nuclei, and the Sun. These primary charged particles which have sufficient energy to penetrate the Earth's magnetic field collide with the Earth's upper atmosphere, that is $N_2$ and $O_2$, and create secondary particles and ionizing radiation. The ionizing radiation can be measured at commercial flight altitude. So it is recommended to manage radiation dose of aircrew as workers under radiation environment to protect their health and safety. However, it is hard to deploy radiation measurement instrument to commercial aircrafts and monitor radiation dose continuously. So the numerical model calculation is performed to assess radiation exposure at flight altitude. In this paper, we present comparison result between measurement data recorded on several flights and estimation data calculated using model and examine the characteristics of the radiation environment in the atmosphere.