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Deep learning-based scalable and robust channel estimator for wireless cellular networks
Anseok Lee(Anseok Lee),Yongjin Kwon(Yongjin Kwon),Hanjun Park(Hanjun Park),Heesoo Lee(Heesoo Lee) 한국전자통신연구원 2022 ETRI Journal Vol.44 No.6
In this paper, we present a two-stage scalable channel estimator (TSCE), a deep learning (DL)-based scalable, and robust channel estimator for wireless cellular networks, which is made up of two DL networks to efficiently support different resource allocation sizes and reference signal configurations. Both networks use the transformer, one of cutting-edge neural network architecture, as a backbone for accurate estimation. For computation-efficient global feature extractions, we propose using window and window averaging-based self-attentions. Our results show that TSCE learns wireless propagation channels correctly and outperforms both traditional estimators and baseline DL-based estimators. Additionally, scalability and robustness evaluations are performed, revealing that TSCE is more robust in various environments than the baseline DL-based estimators.
SHS 공정으로 제조된 Mo<SUB>x</SUB>W<SUB>1-x</SUB>Si₂ 발열체의 가속수명시험과 고장분석
이동원(Dong-Won Lee),이상헌(Sang-Hun Lee),김용남(Yong-Nam Kim),이희수(Heesoo Lee),이성철(Sung-Chul Lee),구상모(Sang-Mo Koo),오종민(Jong-Min Oh) 한국전기전자학회 2017 전기전자학회논문지 Vol.21 No.3
고온자전합성과 후열처리 공정으로 MoxW1-xSi₂ 발열체를 제조하였다. MoxW1-xSi₂ 발열체의 신뢰성을 검증하기 위해 가속수명시험을 수행하였으며, 수명시간을 Minitab 프로그램으로 추정하였다. 또한, 가속수명시험 후의 MoxW1-xSi₂ 발열체의 고장분석을 전기적과 구조적 특성으로부터 수행하였다. 그 결과, MoxW1-xSi₂ 발열체의 지배적인 고장 유형은 발열체 내부의 크랙 형성과 SiO₂ 보호층의 박리임을 확인하였다. MoxW1-xSi₂ heaters were fabricated by self-propagating high-temperature synthesis (SHS) process and post sintering process. To validate the reliability of the MoxW1-xSi₂ heaters, the accelerated life test (ALT) was conducted, and then lifetime to MoxW1-xSi₂ heaters was estimated by using Minitab programs. Also, the failure analysis of MoxW1-xSi₂ heaters after ALT was performed through electrical and structural properties. As the results, it was confirmed that the dominant failure mode of MoxW1-xSi₂ heaters is the crack formation in heaters and the delamination of protective SiO₂ layers.
Lee, Dong-Won,Cho, Won-Ju,Song, Jun-Kwang,Lee, Jun-Tae,Park, Chi-Hong,Park, Kyung-Eun,Lee, Heesoo,Kim, Yong-Nam Elsevier 2015 Solar energy materials and solar cells Vol.136 No.-
<P><B>Abstract</B></P> <P>This paper focuses on the degradation behavior of ethylene vinyl acetate (EVA) and Al-doped ZnO (AZO) films in CIGS PV modules after the damp heat test. We observed losses of the <I>FF</I> and efficiency in the modules after 1000h of damp heat (DH) exposure and some of them were discolored from the outside edge and the center. To clarify the degradation behavior of the non-discolored and discolored modules, a failure analysis for each position of the EVA and AZO in the CIGS module films from the edge to the center was performed. The resistivity of the AZO films in the non-discolored modules increased due to the adsorption of oxygen. In discolored modules, the resistivity of the AZO films rapidly increased at the edge region, and the morphologies of the AZO films were also changed due to the chemical degradation of EVA. These degradation behaviors of the AZO films and EVA in discolored modules were attributed to the formation of hydroxyl and carboxylic species caused by water penetration. Moreover, we reported that the transmittance and the mechanical properties of EVA after 1000h DH exposure were deteriorated by water molecules.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Discoloration and performance degradation of the module were observed after damp-heat exposure. </LI> <LI> A failure analysis of the AZO films and EVA in the modules is performed to clarify these phenomena. </LI> <LI> The resistivity of the AZO films in the non-discolored modules increased due to the adsorption of oxygen. </LI> <LI> The resistivity of the AZO films in the discolored modules rapidly increased due to the chemical degradation of EVA. </LI> <LI> The main cause of the degradation is the formation of hydroxyl and carboxylic species caused by water penetration. </LI> </UL> </P>
Lee, Soojin,Pyo, Heesoo,Chung, Bong Chul,Kim, Haidong,Lee, Jeongae Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.11
Alkoxyalcohols are used as solvents or preservatives in various consumer products such as wet wipes. The metabolites of alkoxyalcohols are known to be chronically toxic and carcinogenic to animals. Thus, an analytical method is needed to monitor alkoxyalcohols in wet wipes. The aim of this study was to develop a simultaneous analytical method for 14 alkoxyalcohols using headspace gas chromatography coupled with mass spectrometry to analyze the wet wipes. This method was developed by comparing with various headspace extraction parameters. The linear calibration curves were obtained for the method ($r^2$ > 0.995). The limit of detection of alkoxyalcohols ranged from 2 to $200ng\;mL^{-1}$. The precision of the determinative method was less than 18.20% coefficient of variation both intra and inter days. The accuracy of the method ranged from 82.86% to 119.83%. (2-Methoxymethylethoxy)propanol, 2-phenoxyethanol, and 1-phenoxy-2-propanol were mainly detected in wet wipes.
Lee, Ki-Seuk,Jeon, Seol,Cho, Hyun,Lee, Heesoo The Korea Association of Crystal Growth 2016 한국결정성장학회지 Vol.26 No.2
The degradation behaviors of TiN coating layers under thermo-mechanical stress were investigated in terms of comparison of finite element analysis (FEA) and experimental data. The coating specimen was designed to quarter cylinder model, and the pulsed laser ablation was assumed as heat flux condition. The FEA results showed that heat accumulation at the center of the laser-ablated spot occurred and principle stress was concentrated at the lower region of the coating layer. The microstructural observation revealed that surface melting and decrease of the coating thickness occurred in the TiN/Inconel 617 and the interfacial cracks formed in the TiN/Si. The delamination was caused by the mechanical stress from the center to the outside of the ablated spot as the FEA results expected. It was considered that the improvement of the thermal shock resistance was attributed to higher thermal conductivity of Si wafer than that of Inconel 617.
Lee, Heesoo,Lee, Dae-Hoon,Ha, Jeong Myeong,Kim, Do Heui Elsevier 2018 Applied catalysis. A, General Vol.557 No.-
<P><B>Abstract</B></P> <P>In this study, oxidative coupling of methane (OCM) was carried out to produce C<SUB>2</SUB> and C<SUB>3</SUB> hydrocarbons directly from methane in a plasma-catalyst hybrid system. Since catalyst only reaction requires high temperature above 700 °C, dielectric barrier discharge (DBD) plasma was applied as plasma source to lower the reaction temperature. Among various supports, only SiO<SUB>2</SUB> showed the higher yield than plasma only reaction when combined with DBD plasma, which led us to focus on the SiO<SUB>2</SUB>-based catalyst. It was found that Ag/SiO<SUB>2</SUB> demonstrated the highest C<SUB>2+</SUB> hydrocarbon yield of about 9.7% at 385 °C. In this process, oxygen was proved to play an essential role in the coupling of methane to C<SUB>2+</SUB> hydrocarbons over Ag/SiO<SUB>2</SUB> catalyst. However, Ag/SiO<SUB>2</SUB> catalyst under plasma condition became deactivated with time-on-stream because of coking. It was demonstrated that plasma regeneration at 378 °C gave rise to the full recovery of activity while thermal regeneration did not due to the partial removal of coke and the sintering of Ag.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Oxidative coupling of methane (OCM) was done in plasma-catalyst hybrid system. </LI> <LI> Ag/SiO<SUB>2</SUB> showed the highest C<SUB>2+</SUB> hydrocarbon yield (9.7%) with plasma at 385 °C. </LI> <LI> Oxygen played an important role in OCM using plasma-catalyst hybrid system. </LI> <LI> Ag/SiO<SUB>2</SUB> was deactivated in the hybrid system because of coke formation. </LI> <LI> Plasma regeneration at 378 °C fully recovered the OCM activity of Ag/SiO<SUB>2</SUB>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>