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Changhee Lee,Eiji Tomota,Nobuyuki Kawahara,Kyungbin Lim,MoonChul Kim 한국자동차공학회 2009 한국자동차공학회 부문종합 학술대회 Vol.2009 No.4
Non-intrusive measurement of transient unburned gas temperatures was developed with a fiber-optic heterodyne interferometry system. Using the value of the Gladstone-Dale constant for DME gas and combustion pressure we can calculate the in-cylinder temperature inside unburned and burned region. In this experimental study, it was performed to set up a fiber-optic heterodyne interferometry technique to measure the temperature before and behind the combustion region in a DME-HCCI engine. At first, measured temperature was almost the same as the temperature history assuming that the process that changes of the unburned and the burned are polytropic. In addition, we measured the temperature after combustion which of condition was burned gas with DME-HCCI combustion.
Failure Mode of Piezoelectric Sensor for Accelerated Life Test
Changhee Park,Hyun-Joong Hwang,Gyechun Cho,Chang-Ho Hong 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.2
The high-level nuclear waste (HLW) repository is a 500-1,000 m deep geological disposal system with a very long life expectancy for disposing of high-level waste, which is known to have a half-life of several thousand years. This repository is subject to harsh environmental conditions, such as high temperature and radiation from high-level waste, that can cause deterioration and crack. When radiation escapes through cracks, it can injure persons on the ground. Therefore, it is essential to install a sensor that can detect problems such as cracks. But, since the high-level nuclear waste (HLW) repository is sealed with bentonite and backfill, the sensor cannot be removed or replaced once it has been installed. Therefore, it is necessary to develop a highly durable monitoring sensor that can withstand harsh environmental conditions. Before attempting to improve durability, it is first required to assess durability quantitatively. And an accelerated life test is a widely used method for assessing durability. However, it is important to obtain the same failure mode when conducting a reliability test, such as an accelerated life test. If the accelerated life test is conducted using different failure modes, the dependability of the results is inevitably diminished. Therefore, in this study, a representative failure mode for the piezoelectric sensor used in the accelerated life test was derived through experiments and literature research.
Local Greedy Approximation for Scheduling in Multihop Wireless Networks
Changhee Joo,Shroff, Ness B. IEEE 2012 IEEE TRANSACTIONS ON MOBILE COMPUTING Vol.11 No.3
<P>In recent years, there has been a significant amount of work done in developing low-complexity scheduling schemes to achieve high performance in multihop wireless networks. A centralized suboptimal scheduling policy, called Greedy Maximal Scheduling (GMS) is a good candidate because its empirically observed performance is close to optimal in a variety of network settings. However, its distributed realization requires high complexity, which becomes a major obstacle for practical implementation. In this paper, we develop simple distributed greedy algorithms for scheduling in multihop wireless networks. We reduce the complexity by relaxing the global ordering requirement of GMS, up to near zero. Simulation results show that the new algorithms approximate the performance of GMS, and outperform the state-of-the-art distributed scheduling policies.</P>
Analysis of Educational Use Cases based on the Metaverse Platform
( Changhee Seo ),( Youngjo Yoo ),( Jieun Kwon ) 한국감성과학회 2023 한국감성과학회 국제학술대회(ICES) Vol.2023 No.-
Due to the pandemic phenomenon, a nonface- to-face metaverse has emerged as a medium that provides a new type of communication method in various fields different from before. This is also prominent and expanded in the field of education for the immersive and interactive way between students and educators. Therefore, a new education and learning method incorporating the metaverse platform is developed using educational technology. It generates positive results such as free, active and creative learning based on self-directed learning for students and new knowledge transfer method. Considering this educational influence of the metaverse, we focus on cases of educational contents to which the metaverse platform and suggests the direction of education based on the metaverse in the future. To do this, the analysis of the metaverse platform from the definition by the literature survey forms the foundation at the first. And next, the metaverse case study for educational contents is conducted. Through this, the criteria of educational metaverse for analysis is established with its own and unique characteristics. It helps to make the direction of education utilizing the metaverse platform. It can be settled down as an interesting and effective guideline for future-oriented educational approaching with the metaverse platform.