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Oh H.-U.,Chosun University | Lee K.-J.,ADD | Jo M.-S.,Samsung
Aerospace Science and Technology | Year: 2013

To enhance the pointing performance by isolating disturbances induced by a spaceborne payload mounted cryogenic cooler during the on-orbit operation, a passive launch and on-orbit vibration isolation system has been proposed and investigated. The isolation system is also effective for reducing the transmitted launch loads to the cooler. In order to demonstrate the effectiveness of the isolation system, launch environment tests such as sine, random and shock tests and a micro-vibration measurement test of the cooler combined with the isolator have been performed. The test results indicate that the isolation system guarantees both the structural safety of the cooler under the launch environment and the micro-vibration isolation of the cooler under the on-orbit condition. © 2012 Elsevier Masson SAS. All rights reserved. Source


Yoon Y.H.,ADD | Kim S.J.,Korea Electronics Technology Institute | Kim D.H.,Seoul National University of Science and Technology
Microscopy | Year: 2015

The scanning electron microscope is used in various fields to go beyond diffraction limits of the optical microscope. However, the electron pathway should be conducted in a vacuum so as not to scatter electrons. The pretreatment of the sample is needed for use in the vacuum. To directly observe large and fully hydrophilic samples without pretreatment, the atmospheric scanning electron microscope (ASEM) is needed. We developed an electron filter unit and an electron detector unit for implementation of the ASEM. The key of the electron filter unit is that electrons are transmitted while air molecules remain untransmitted through the unit. The electron detector unit collected the backscattered electrons. We conducted experiments using the selected materials with Havar foil, carbon film and SiN film. © The Author 2015. Source


Lee M.-S.,ADD | Lee C.-H.,Chungnam National University
IEICE Transactions on Information and Systems | Year: 2014

For battery based real-time embedded systems, high performance to meet their real-time constraints and energy efficiency to extend battery life are both essential. Real-Time Dynamic Voltage Scaling (RT-DVS) has been a key technique to satisfy both requirements. This paper presents EccEDF (Enhanced ccEDF), an efficient algorithm based on ccEDF. ccEDF is one of the most simple but efficient RT-DVS algorithms. Its simple structure enables it to be easily and intuitively coupled with a real-time operating system without incurring any significant cost. ccEDF, however, overlooks an important factor in calculating the available slacks for reducing the operating frequency. It calculates the saved utilization simply by dividing the slack by the period without considering the time needed to run the task. If the elapsed time is considered, the maximum utilization saved by the slack on completion of the task can be found. The proposed EccEDF can precisely calculate the maximum unused utilization with consideration of the elapsed time while keeping the structural simplicity of ccEDF. Further, we analytically establish the feasibility of EccEDF using the fluid scheduling model. Our simulation results show that the proposed algorithm outperforms ccEDF in all simulations. A simulation shows that EccEDF consumes 27% less energy than ccEDF. Copyright © 2014 The Institute of Electronics, Information and Communication Engineers. Source


Bang B.H.,Korea University | Yoon S.S.,Korea University | Kim H.Y.,Korea University | Heister S.D.,Purdue University | And 2 more authors.
International Journal of Multiphase Flow | Year: 2011

A two-phase flow model using the boundary element method was applied to investigate the physics of a liquid drop impacting onto a solid, dry plate. Xu et al. showed that air pressure plays an important role in splashing: as air pressure was reduced, splashing of an ethanol drop with a Weber number of 838 was suppressed. This remarkable observation provided the motivation for the current modeling effort. We numerically investigate how air pressure affects the behavior of an impacting drop. Surveying both inside and outside the impacting drop, velocities of both the liquid and gas are computed. Simulations show that gas speed, as it is displaced by the falling drop, is more than three times higher than the incoming drop speed. Air entrainment induced by the displaced gas seems to be an important contributor to corona formation, which always precedes any instability, fingering, or splashing of the liquid. To describe drop-impact phenomena, the maximum spreading diameter of the drop and the topology of the impacting fluid are reported as functions of Weber number and gas density. © 2010 Elsevier Ltd. Source


Bang K.-H.,Korea University | Chung G.-Y.,Korea University | Koo H.-H.,ADD
Korean Journal of Chemical Engineering | Year: 2011

The preparation of C/C composites by the chemical vapor infiltration (CVI) of the pyrolysis carbon from propane was studied. Pyrolysis carbon was deposited at 30 torr and at temperatures between 1,173 and 1,233 K. The rate of carbon deposition increased slightly with time. The main gas products in the exit gas were methane, ethylene, and acetylene. The fraction of ethylene decreased and that of acetylene increased with the reaction temperature and the propane concentration. The produced propyl radicals reacted further at a high temperature and at a high propane concentration. These trends were similar to those of the reported data. Changes of the shapes of deposited carbon in the pores of preform were confirmed with SEM photos. The mathematical modeling of the system with the deposition rate constant from the reference estimated experimental data well. © 2010 Korean Institute of Chemical Engineers, Seoul, Korea. Source

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