• Journal of Aerospace System Engineering
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• v.17 no.6
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• pp.54-62
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• 2023

Flapping-wing air vehicles, well known for their free vertical take-off and excellent flight capability, are currently under intensive development and research. While most of the studies have explored the effect of various parameters of synchronized motions on the unsteady aerodynamics of flapping wings, limited attention has been given to the effect of nonsynchronous motions on the unsteady aerodynamic characteristics of flapping wings. In the present study, we conducted a numerical analysis to investigate the unsteady aerodynamic characteristics of an airfoil flapping with different frequency ratios between pitch and heave oscillations. We identified the motions and angle of attacks due to nonsynchronous motions. It was found that the synchronous motion produced thrust with zero lift, but the nonsynchronous motion generated a large lift with little drag. The aerodynamic characteristics of the airfoil undergoing the non-synchronous motion were also analyzed using the vorticity distributions and the pressure coefficient around and on the airfoil. When r was equal to 0.5, larger leading and trailing edge vortices were observed compared to the case when r was equal to 1.0, and these vortices significantly affected the aerodynamic characteristics of the airfoil undergoing the nonsynchronous motion. In future, the effect of pitch amplitude on the unsteady aerodynamic characteristics of the airfoil will be studied.

• The Korean Journal of Air & Space Law and Policy
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• v.29 no.2
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• pp.205-237
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• 2014

Last 50 years there were a lot of space subjects launched by space activities of many states and these activities also had created tremendous, significant space debris contaminating the environment of outer space. The large number of space debris which are surrounding the earth have the serious possibilities of destroying a satellite or causing huge threat to the space vehicles. For example, Chinese anti-satellite missile test was conducted by China on January 11, 2007. As a consequence a Chinese weather satellite was destroyed by a kinetic kill vehicle traveling with a speed of 8 km/s in the opposite direction. Anti-satellite missile tests like this,contribute to the formation of enormous orbital space debris which can remain in orbit for many years and could interfere with future space activity (Kessler Syndrome). The test is the largest recorded creation of space debris in history with at least 2,317 pieces of trackable size (golf ball size and larger) and an estimated 150,000 debris particles and more. Several nations responded negatively to the test and highlighted the serious consequences of engaging in the militarization of space. The timing and occasion aroused the suspicion of its demonstration of anti-satellite (ASAT) capabilities following the Chinese test of an ASAT system in 2007 destroying a satellite but creating significant space debris. Therefore this breakup seemed to serve as a momentum of the UN Space Debris Mitigation Guidelines and the background of the EU initiatives for the International Code of Conduct for Outer Space Activities. The UN Space Debris Mitigation Guidelines thus adopted contain many technical elements that all the States involved in the outer space activities are expected to observe to produce least space debris from the moment of design of their launchers and satellites until the end of satellite life. Although the norms are on the voluntary basis which is normal in the current international space law environment where any attempt to formulate binding international rules has to face opposition and sometimes unnecessary screening from many corners of numerous countries. Nevertheless, because of common concerns of space-faring countries, the Guidelines could be adopted smoothly and are believed faithfully followed by most countries. It is a rare success story of international cooperation in the area of outer space. The EU has proposed an International Code of Conduct for Outer Space Activities as a transparency and confidence-building measure. It is designed to enhance the safety, security and sustainability of activities in outer space. The purpose of the Code to reduce the space debris, to allow exchange of the information on the space activities, and to protect the space objects through safety and security. Of the space issues, the space debris reduction and the space traffic management require some urgent attention. But the current legal instruments of the outer space do not have any binding rules to be applied thereto despite the incresing activities on the outer space. We need to start somewhere sometime soon before it's too late with the chaotic situation. In this article, with a view point of this problem, focused on the the Chinese test of an ASAT system in 2007 destroying a satellite but creating significant space debris and tried to analyse the issues of space debris reduction.

• Neonatal Medicine
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• v.17 no.1
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• pp.53-63
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• 2010

Purpose : Extrauterine growth restriction (EUGR) in preterm infants is a major problem in neonatal intensive care units (NICUs) and it has been related to long-term growth deficit and neurodevelopmental issues. The aim of this study was to investigate the frequency of and risk factors for EUGR. Methods : The study subjects consisted of very low birth weight (VLBW) infants with a gestational age $\leq$32 weeks that were born at the Seoul National University Children's Hospital between November 2005 and April 2009. EUGR was defined as weight for gestation, lower than the 10th percentile on discharge. Results : The frequency of EUGR was 67% (n=111/166). By multiple logistic regression, the presence of small for gestational age (SGA) was the greatest predictor of EUGR, birth weight and daily weight gain during the first 28 days were independent predictors of EUGR. Risk factors for EUGR in non-SGA infants were evaluated because 56% (64/114) of non-SGA infants developed EUGR at discharge. Daily weight gain in the first 28 days was also decreased in EUGR group and independently predicted the risk of EUGR in the non-SGA group. Conclusion : EUGR was a common problem in the NICU. SGA was the most significant predictive factor of the EUGR. Half of the non-SGA infants also developed EUGR, revealing poor weight gain in the early days was as an important predictor. These results support the importance of early nutritional intervention for weight gain which have lagged behind other modern therapeutic interventions when the infant is clinically unstable.

• (The) Research of the performance art and culture
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• no.38
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• pp.193-224
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• 2019

Shaman's play is significant in that it provided public theater for a long time in the theatrical and dramatic history. Unlike upper class who could call entertainer or Korean geisha in the traditional society, the majority of ordinary people could see professional performances through gut. Therefore, the shaman of the traditional society pulled the play which developed in the gut and the outside play into the gut and prepared the performance street for the ordinary people. shaman's play, apart from the religious context, has also functioned as a theatrical performance. Through shaman's play, you can see the process of ritual development into play. Shaman's play is a ritual ritual of expel calamity in an agriculture based society. In Korean consciousness, evil spirits are thought to bring disease or disaster to humans, so they should be good for evil spirits. This is a ritual that goes hand in hand with the Confucian Yeoje and the Buddhist Suryukjae. Most traditional plays, including masque performance, tend to weaken and become stifling after the designation of intangible cultural properties. However, shaman's play is transformed every time it is executed and is given a new meaning. Depending on the ability of the shaman to respond to and accommodate social change, adaptability is excellent depending on the situation in the field. Shaman's play has richness, prevent calamity and playful elements such as imitation of god and sexual connection based on the element of shamanism. In addition, it is necessary to pay attention to the meaning and the direction of Shaman's play because it is differentiated into play including social subject beyond mere magic imitation.