• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.5
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• pp.99-105
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• 2005

Development of an engine with good fuel economy is very important for successful implementation of long endurance miniature UAVs (unmanned aerial vehicles). In the study, a 4-stroke glow-plug engine was modified to a gasoline-fueled spark-ignition engine. Engine tests measuring performance and friction losses were conducted to tune a simulation program for performance prediction. It has been found that excessive friction losses are caused by insufficient lubrication at high speeds. The simulation program predicts that engine power and fuel economy get worse with high altitude due to increasing portion of friction losses. The simulation results suggest quantitative guidelines for further development of a practical engine.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.361-364
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• 2009

Vacuum facility is required for high altitude space environment test to develop small thruster to be applied for micro-satellite. After selecting vacuum equipment and integrating the chamber to simulate 100-120km attitude with max, $10^{-5}\;torr$. We tested the performance of high vacuum chamber. We designed, fabricated the knudsen pump and analyzed pressure gradient efficiency of membrane according to Knudsen number under vacuum conditions. We described the upgrade plan to a thermal vacuum chamber.

• The Korea Journal of Herbology
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• v.27 no.6
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• pp.91-98
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• 2012

Objectives : Rhodiola rosea L. (Crassulaceae) is a plant living at the areas of high-altitude mountain, and Rhodiolae Radix(the root of R. rosea) has been used as a traditional medicine to decrease the symptoms of mental- or physical-stress in Asia and Europe. To examine the efficacy of Rhodiolae Radix on the oxidative stress, the anti-oxidative effects of the radix were examined, Methods : The effects of Rhodiolae Radix on several oxidative factors were examined in vitro, and also the effects were tested in the liver of rats which were treated with a high dose of alcohol during 2 weeks. Results : The extract of Rhodiolae Radix in vitro scavenged some oxidants, such as DPPH, Superoxide anion radical and LDL, and the extract also inhibited the oxidative capacity of linoleic acid, significantly. Meanwhile, in the in vivo test, the methanol-extract decreased some oxidation parameters, such as relative liver weight, TBARS and SOD activities, and also increased catalase activity in the liver of alcohol-loaded rats, But, the extract had no effects on GSH content and GSH-px activiy in the rats. Conclusion : The root of Rhodiola rosea has a strong anti-oxidative capacity, and also has some preventive properties aginst the alcoholic stress.

• Journal of Families and Better Life
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• v.23 no.5 s.77
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• pp.103-122
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• 2005

The purpose of this study was to examine the influences of their money attitudes to spending behaviors of middle, high, and college students. The total number of students selected for this study were 1,252. Factor analysis, Cronbach' ${\alpha}$, two-way ANOVA, Duncan' multiple range test, Pearson correlation analysis, and multiple regression were used for statistical analysis. The results were summarized as followings: 1) The tendency of attitude that money is good was highest. Also, the tendency of attitude that money represents freedom and power was slightly high. On the other hand the attitudes that money represents achievement, and that money is evil were low. Especially the attitude that money represents respect was lowest. 2) Resulting from two-way ANOVA, the attitudes that money is good and represents achievement showed significant interaction effects between sex and age. The altitude that money is good showed significant differences by sex especially among middle and high school students. The altitude that money represents achievement showed significant differences by age among the male students. Three types of attitudes that money is evil, money represents respect, and money represents both freedom and power showed significant main effects in different age groups. Also the attitude that money represents freedom and power showed significant main effect by different sexes. 3) Four different types of measuring spending behaviors scored slightly low mark. 4) Resulting from two-way ANOVA, four different spending behaviors showed significant difference only by sexes and ages. Planned spalding behavior and conscious spending behavior showed significant differences in ages and sexes separately. While impulsive spending behavior by different age groups resulted in significant differences. Excessive spending behavior by sexes resulted in significant differences. 5) Regression analysis showed that planned spending behavior had the linear relationships in no, sex, self-esteem, and attitude that money is good. Conscious spending behavior had the linear relationships in ses, and attitudes that money represent achievement. respect, and freedom. Impulsive spending behavior had the linear relationships in age, self-esteem, and attitudes that money is good and that money is evil, and attitude that money represent freedom, Excessive spending behavior had the linear relationships in sex, self-esteem, and attitudes that money represent achievement, respect and freedom.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.65 no.3
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• pp.182-191
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• 2020

A field test and a phytotron study were performed over two years to examine whether rice varieties originated from higher altitude areas have lower optimum grain filling temperatures for yield improvement than the varieties from South Korea. Three varieties originated from North Korea and three varieties from northern China were compared to the same number of varieties from South Korea. In a field study, the optimum grain filling temperatures over 40 days after heading were 22.6 - 23.0℃, 21.5 - 22.3℃, and 21.5 - 23.6℃ for the varieties from North Korea, northern China, and South Korea, respectively, resulting in no significant difference among varietal groups. Meanwhile, the heading dates of the early maturing varieties from North Korea and China were 7 - 12 days earlier than that of the early maturing Odae variety from South Korea during the first transplant of 2017. The phytotron study, in which different temperature regimes were imposed from flowering/fertilization to harvest with constant daily mean temperatures, revealed that milled rice weight did not decrease under low temperatures, even at 16℃, compared to that at 22℃. At the fourth transplant in the field study, mean temperature lower than 10℃ appeared before rice grains were fully developed, resulting in yield reductions. It was concluded that rice varieties adaptable to high-altitude areas do not have lower optimum grain filling temperatures but, instead, possess shorter growth durations. It was further suggested that the optimum grain filling temperature of rice observed under natural conditions could be attributed to the lowering temperature at the late filling stage under temperate climatic conditions.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.3
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• pp.512-521
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• 2017

This paper reports development process of a university-based sounding rocket using simplified hybrid rocket propulsion system for low-altitude flight application. A hybrid propulsion system was tried to be designed with as few components as possible for more economical, simpler and safer propulsion system, which is essential for the small scale sounding rocket operation as a CanSat carrier. Using blow-down feeding system and catalytic ignition as combustion starter, 250 N class hybrid rocket system was composed of three components: a composite tank, valves, and a thruster. With a composite tank filled with both hydrogen peroxide($H_2O_2$) as an oxidizer and nitrogen gas($N_2$) as a pressurant, the feeding pressure was operated in blowdown mode during thruster operation. The $MnO_2/Al_2O_3$ catalyst was fabricated for propellant decomposition, and ground test of propulsion system showed the almost theoretical temperature of decomposed $H_2O_2$ at the catalyst reactor, indicating sufficient catalyst efficiency for propellant decomposition. Auto-ignition of the high density polyethylene(HDPE) fuel grain successfully occurred by the decomposed $H_2O_2$ product without additional installation of any ignition devices. Performance test result was well matched with numerical internal ballistics conducted prior to the experimental propulsion system ground test. A sounding rocket using the developed hybrid rocket was designed, fabricated, flight simulated and launch tested. Six degree-of-freedom trajectory estimation code was developed and the comparison result between expected and experimental trajectory validated the accuracy of the developed trajectory estimation code. The fabricated sounding rocket was successfully launched showing the effectiveness of the simplified hybrid rocket propulsion system.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.9
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• pp.731-743
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• 2020

The hypersonic glide vehicle ascends to a high altitude by a rocket booster, separates it from the booster, and glides at a hypersonic speed of Mach 5 or higher at an altitude of about 30~70 km, changing its direction in the atmosphere. Since it moves on an unpredictable flight path rather than a parabolic trajectory, it is difficult to intercept with current missile defense systems. The U.S. conducted HTV-2 and AHW flight tests in the early 2010s to confirm the possibility of hypersonic gliding flights, and recently it has been developing hypersonic glide vehicle systems such as LRHW and ARRW. China has conducted several flight tests of the DF-ZF (WU-14) glide vehicle since 2014 and has been operating it with DF-17 missiles. Russia has conducted hypersonic glide vehicle research since the former Soviet Union, but it has repeatedly failed, and recently it has been successfully tested with the Avangard (Yu-71) glide vehicle mounted on the SS-19 ICBM. In this paper, the characteristics, flight test cases, and development trends of hypersonic glide vehicles developed or currently being developed in the United States, China, Russia, Japan, India, and Europe are reviewed and summarized.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.9
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• pp.681-689
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• 2020

This paper presents methods and results of both flight test examining roll angle estimation performance of slowly rolling munition forced to spin in the air, and fabricating a replica of guided munition. Guided munition was deployed from multi rotor type UAV mother ship whose altitude and velocity was conveyed to it as initial state. Flight test scenario is composed of a sequence of munition drop(deployment), munition spin, roll angle estimation and stabilization. Munition was deployed from mother ship at around 200m high with horizontal velocity of 15m/s, and was made spun using internal reaction wheel. Performance analysis on roll angle estimation is provided in comparison with commercial aerospace graded GPS/INS. Moreover, several mechanisms that rotates munition using reaction wheel, and actual product that realizes one of them are introduced.

• Journal of the Korean Institute of Landscape Architecture
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• v.29 no.1
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• pp.80-91
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• 2001

The purpose of this research is to provide a basic knowledge to open up for undeveloped park in process of the park policy establishment by setting up the priority of park development and valuation factor, valuation index as well as building a basic material to undeveloped neighborhood park in Daegu Metropolitan City. Thirteen urban neighborhood parks(1,841,663$m^2$) in the Daegu Metropolitan City were selected for this study. Analyzing and reviewing the previous research and literature review were conducted, and the evaluation index and analysis criteria were constructed to decide the development priority of parks. The results of this research are as follows; 1) Following to the result of the expert questionnaire test in order to estimate weight of valuation factors. It had a high score in available population, and estimated amount of the gross compensation, unpurchased land rate. On the other hand park rate of autonomous district, altitude, rate of population increase in autonomous district and a low score. 2) Generally, most f the plain type parks had a high score in the Sea level, land using pattern, an estimated amount of the gross compensation, but hill type parks had a high score the rate of green covered, park area for one person of administration building. 3) Daebong, Soosung, Dosan, 2.28 youth, Kyungnam parks were selected high priority. Soochang, Donsibong, Janggi, Dongin parks were selected middle priority. Bokhyun, Galsan, Manchon, Gusoosan parks, which were selected low priority. This research for undeveloped park is a basic research step to open up. Three many difficult things in shortage of the basic material for building valuation factor and measuring of the method measurement. The application of weight which make a decision importance among the valuation factor should have ore reasonable study and more scientific research from now because there still remains a lot of shortage of positive materials in there.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.185-188
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• 2009

The rocket motor of the space launch vehicle offers thrust for satellite to enter into the orbit. Characters of the solid propellant for rocket motors are affected by the space conditions such as vacuum and space radiation. The solid propellant used for such a purpose should not undergo physical, internal ballistic and energetic changes when exposed to vacuum and space radiation. This study describes the development of the solid propellant composition for the rocket motor of the space launch vehicle. Also, experimental study was conducted on supersonic diffuser in order to verify the performance of the solid propellant composition which was applied to standard motor on the ground in the vacuum condition.