• Journal of Astronomy and Space Sciences
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• v.34 no.4
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• pp.303-314
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• 2017

With increased human activity in space, the risk of re-entry and collision between space objects is constantly increasing. Hence, the need for space situational awareness (SSA) programs has been acknowledged by many experienced space agencies. Optical and radar sensors, which enable the surveillance and tracking of space objects, are the most important technical components of SSA systems. In particular, combinations of radar systems and optical sensor networks play an outstanding role in SSA programs. At present, Korea operates the optical wide field patrol network (OWL-Net), the only optical system for tracking space objects. However, due to their dependence on weather conditions and observation time, it is not reasonable to use optical systems alone for SSA initiatives, as they have limited operational availability. Therefore, the strategies for developing radar systems should be considered for an efficient SSA system using currently available technology. The purpose of this paper is to analyze the performance of a radar system in detecting and tracking space objects. With the radar system investigated, the minimum sensitivity is defined as detection of a $1-m^2$ radar cross section (RCS) at an altitude of 2,000 km, with operating frequencies in the L, S, C, X or Ku-band. The results of power budget analysis showed that the maximum detection range of 2,000 km, which includes the low earth orbit (LEO) environment, can be achieved with a transmission power of 900 kW, transmit and receive antenna gains of 40 dB and 43 dB, respectively, a pulse width of 2 ms, and a signal processing gain of 13.3 dB, at a frequency of 1.3 GHz. We defined the key parameters of the radar following a performance analysis of the system. This research can thus provide guidelines for the conceptual design of radar systems for national SSA initiatives.

• Korea and Global Affairs
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• v.2 no.1
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• pp.137-162
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• 2018

This paper covers the issues including geopolitical effects of sea power on sea space in East Asia and its nature in a perspective of the past and the present. This paper analyzes the significance of Sea Power which is emphasized in Mahan's Theory of Insular Dominance and grasps the geopolitical nature of Sea Power. Along with this awareness, it deals with the problem of designated strategic phenomenon that is spreading to the Pacific Ocean with the concept of the Island Chain in China in the 21st century. Around the turn of 20th century, Japan materialized the policy of Greater East Asia Co-prosperity Sphere which was planned to expand power sphere in sea space in the East Asia based on sea power and China took shape of the concept of Island Chain in the 21st century, which has divided sea space in East Asia. Under the circumstance that China's policy of island chain faced the resistance from countries in the East Asia as well as the USA, the question about whether Korea's policy of depending on sea power is valuable even in the 21st century has been raised.

• International Journal of Aeronautical and Space Sciences
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• v.2 no.2
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• pp.19-27
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• 2001

This research attempts to find an active control strategy which reduces acoustic power and acoustic energy in lightly-damped enclosed sound field such as a vehicle compartment or an operating room of heavy industrial machinery. An active control strategy, which takes into consideration of the acoustic radiation power of the source as a cost function, is formulated and examined to find capability of reducing noise. An adaptive filtering algorithm for sound power control is suggested and implemented to control lightly-damped sound field. To verify the method, sound power based active noise control algorithm was implemented on a rectangular box with lightly-damped wall, and popular acoustic energy based control with modal coupling reduction was performed to compare the noise reduction performance. It was shown that a total sound power based strategy provides a practical mean for global noise reduction for lightly damped sound field.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.615-619
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• 1998

Active power filter is a kind of device used for compensating instantaneous reactive and harmonic current in three-phase circuits. An essential technology that determines the behavior of an active power filter is the method of detecting the distorted current. Using three-dimensional space vectors, this paper describes a simple method for detecting the distorted current without any coordinate transformation. The effectiveness of the novel method is verified by the theoretical analysis and simulation.

• Journal of Electrical Engineering and Technology
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• v.12 no.1
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• pp.302-309
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• 2017

The ageing of XLPE cable insulation will lead to the accelerating accumulation of space charge, which will greatly affect the safe operation of the HVDC cable. In order to investigate the influence of different ageing modes on the space charge distribution of the HVDC cable, thermal stressed, electrical stressed and electro-thermal stressed endurance tests were carried out on the XLPE peelings. The tested XLPE peelings were obtained from 160kV HVDC cable insulation. The endurance tests were carried at thermal stress of 363K, electrical stress of 20kV/mm DC and a combination of both. The Pulsed Electro-Acoustic (PEA) method was used to measure the space charge distribution of the samples. The influences of ageing on the trap energy distribution were analyzed based on the isothermal relaxation theory and the decay characteristics of the space charge. The results showed that thermal ageing would help to improve the crystalline morphologies of the XLPE at the early stage. The total amount of space charge decreased compared to the ones before thermal ageing. The long term of electrical stress would result in the cleavage of polymer molecule chains which would intensify the accumulation of space charge and increase the density and depth of electron traps. With a combination of electrical and thermal stress, the injection and migration of space charge were more significant. Besides, the depth and density of electron traps increased rapidly with the increase of endurance time.

• Korean Institute of Interior Design Journal
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• v.19 no.2
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• pp.99-106
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• 2010

This study is about Foucault's conceptual and methodological relevance for structural analysis of Korean traditional space design history. By Foucault's Theory, regionalism is product of the instrumentality of space, power, knowledge and provide the basis for making the operation of power both spatial and temporal. The purpose of this study is to establish topographical map of historical progress and to shed new light on the forming of identity in Korean traditional space design on the poststructural-archaeological aspect. The process of this study is illustrated as follows: At first, it suggests Foucault's 'Theory of archaeology'. It mentions 'historical apriori' and archive, collateral space and general grammar as theoretical background of archaeological logic. Secondly, it clarifies 'statements' depending on the conditions that is 'episteme' in which they emerge and exist within a field of discourse. And it discuss Korean traditional space design concept as a social product on the situated character of interaction in time-space. Finally, it studies genetic variation process of Korean traditional space design based on the social progress in Korean society. And it analyses practical actions of 'Statements' in terms of general grammar and textuality.

• Bulletin of the Korean Space Science Society
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• 2007.10a
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• pp.56.1-56.1
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• 2007

• Journal of the Korean Institute of Rural Architecture
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• v.12 no.2
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• pp.13-22
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• 2010

This study is to analyze women's power in family to be related to Anbang, kitchen, dining room, and utility room planning in a unit plan of condominium apartment housing in rural area Data were collected 194 unit plans from 9 eastern regions of Kungi-Do. The results are as followed: 1) Anbang reflects the women's power on changing its space character into mater bedroom, the highest hierarchy in private zone, and planning a dress room in it. 2) Dining room and kitchen is openly centered on the unit plan, but kitchen is still only women's working space for family and agriculture depended on literature review. Dining space is not activated family interaction, so it is not different from urban apartment housing. However, its location and character are changed, and its hierarchy is relatively higher with women. Dining room and kitchen tend to plan visually separated after 2001, so its trend seems to establish women's territory at home. 3) Whole family can't be easy to access utility and back balcony close to kitchen, and these spaces are functionally separated for women's house work. This design trend seems to establish for women's area. 4) Finally, women's power seems to be effective in house working area including kitchen space depended on results. Also, these results from rural condominium apartment are similar to urban ones in previous study.

• Corrosion Science and Technology
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• v.17 no.6
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• pp.317-323
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• 2018

Assumptions have always been that wall thinning on the secondary side piping in nuclear power plants is mostly caused by Flow-Accelerated Corrosion (FAC). Recent studies have showed that wall thinning on the secondary side piping is caused by Liquid Droplet Impingement Erosion (LDIE), Solid Particle Erosion (SPE), cavitation, and flashing. To manage those aging mechanisms, several software such as CHECWORKS, COMSY, and BRT-CICERO have been used in nuclear power plants. Korean nuclear power plants have been using the CHECWORKS program since 1996 to date. However, many site engineers have experienced a lot of inconveniences and problems in using the CHECWORKS program. In order to work through the inconveniences and to remedy problems, KEPCO-E&C has developed a "3D-based pipe wall thinning management program (ToSPACE)" based on the experience of over 30 years in relation to the pipe wall thinning management. This study compares the results of FAC and LDIE analysis using both the CHECWORKS and ToSPACE programs with respect to validation of the wall thinning analysis results.

• Journal of Astronomy and Space Sciences
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• v.33 no.1
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• pp.55-62
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• 2016

Heumgyeonggaknu (欽敬閣漏) is powered by a water-hammering-type water wheel. The technique that maintains the constant speed of the water wheel is assumed to be the one used in the Cheonhyeong (天衡) apparatus in Shui Yun Yi Xiang Tai (水運儀象臺) made by the Northern Song (北宋) dynasty in the 11^th century. We investigated the history of the development and characteristics of the Cheonhyeong apparatus, and we analyzed ways to transmit the power of Heumgyeonggaknu. In addition, we carried out a conceptual design to systematically examine the power control system. Based on the conceptual design, we built a model for a water wheel control system that could be used in experiments by drawing a 3D model and a basic design.