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A study on robust regression estimators in heteroscedastic error models
Nayeong Son,Mijeong Kim 한국데이터정보과학회 2017 한국데이터정보과학회지 Vol.28 No.5
Weighted least squares (WLS) estimation is often easily used for the data with heteroscedastic errors because it is intuitive and computationally inexpensive. However, WLS estimator is less robust to a few outliers and sometimes it may be inefficient. In order to overcome robustness problems, Box-Cox transformation, Huber`s M estimation, bisquare estimation, and Yohai`s MM estimation have been proposed. Also, more efficient estimations than WLS have been suggested such as Bayesian methods (Cepeda and Achcar, 2009) and semiparametric methods (Kim and Ma, 2012) in heteroscedastic error models. Recently, Çelik (2015) proposed the weight methods applicable to the heteroscedasticity patterns including butterfly-distributed residuals and megaphone-shaped residuals. In this paper, we review heteroscedastic regression estimators related to robust or efficient estimation and describe their properties. Also, we analyze cost data of U.S. Electricity Producers in 1955 using the methods discussed in the paper.
Nayeong Kim,Kwang-Nyeong Lee,Mingeun Sagong,Gyeong-Beom Heo,Youn-Jeong Lee 한국예방수의학회 2022 예방수의학회지 Vol.46 No.4
Wild birds, especially aquatic birds, are the natural reservoir of avian influenza virus (AIV), and many kinds of water body can be contaminated with feces of these birds. Seasonally, AIVs can be dissolved in the environmental water from the feces of the infected birds, and this water can be a target for viral detection and identification. In this study, we employed and tested three different filters for concentrating AIV, and it was shown that high concentration factor in terms of viral density could be achieved with viral samples diluted with natural water. Wild bird fecal samples containing low pathogenicity H5 AIVs were successfully concentrated with the adsorption and elution method using mixed cellulose esters membrane; the recovery rate of virus was 35.5 % and the concentration factor was about 50 on average. For the larger volume of water sample, we proved that an inline disposable filter with high surface area, 300 cm2, has a comparable concentration factor to the adsorption and elution method and the filter could be used in the field conveniently by being plugged into peristaltic pump. These validated methods for water sampling may be used as a supplementary for virological surveillance on wild migratory birds or during the epidemiological investigation on the environment near affected premises by AIV.
Kim, Nayeong,Jeong, Soyeon,Jing, Kaipeng,Shin, Soyeon,Kim, Soyeon,Heo, Jun-Young,Kweon, Gi-Ryang,Park, Seung-Kiel,Wu, Tong,Park, Jong-Il,Lim, Kyu Hindawi Publishing Corporation 2015 BioMed research international Vol.2015 No.-
<P>The anticancer properties and mechanism of action of omega-3 polyunsaturated fatty acids (<I>ω</I>3-PUFAs) have been demonstrated in several cancers; however, the mechanism in lung cancer remains unclear. Here, we show that docosahexaenoic acid (DHA), a <I>ω</I>3-PUFA, induced apoptosis and autophagy in non-small cell lung cancer (NSCLC) cells. DHA-induced cell death was accompanied by AMP-activated protein kinase (AMPK) activation and inactivated phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling. Knocking down AMPK and overexpressing Akt increased mTOR activity and attenuated DHA-induced cell death, suggesting that DHA induces cell death via AMPK- and Akt-regulated mTOR inactivation. This was confirmed in Fat-1 transgenic mice, which produce <I>ω</I>3-PUFAs. Lewis lung cancer (LLC) tumor cells implanted into Fat-1 mice showed slower growth, lower phospho-Akt levels, and higher levels of apoptosis and autophagy than cells implanted into wild-type mice. Taken together, these data suggest that DHA-induced apoptosis and autophagy in NSCLC cells are associated with AMPK activation and PI3K/Akt inhibition, which in turn lead to suppression of mTOR; thus <I>ω</I>3-PUFAs may be utilized as potential therapeutic agents for NSCLC treatment.</P>
Kim, Hyun-seung,Kim, Jaekwang,Jang, Jihyun,Kim, Nayeong,Ryu, Ji Heon,Yoon, Songhun,Oh, Seung M. Elsevier 2017 Solid state ionics Vol.311 No.-
<P><B>Abstract</B></P> <P>In this study, polarization behavior during initial lithiation step was comparatively investigated using a tungsten oxide (WO<SUB>3</SUB>) and its reduced one (WO<SUB>3− <I>x</I> </SUB>). Ex-situ X-ray diffraction revealed that the overall lithiation process in WO<SUB>3</SUB> was mostly similar to that of WO<SUB>3− <I>x</I> </SUB>, which was associated with the typical conversion reaction of transition-metal oxide. In the WO<SUB>3− <I>x</I> </SUB> anode, however, insertional lithiation was initiated above 2V vs. Li/Li<SUP>+</SUP> and a following conversion reaction was observed, which was different charging behavior from WO<SUB>3</SUB> electrode. The severe polarization related with the conversion reaction was alleviated owing to the high electrical conductivity in the mixed-valance state of WO<SUB>3− <I>x</I> </SUB>. Furthermore, the different initial polarization in WO<SUB>3− <I>x</I> </SUB> anode resulted in the improvement of cycle performance and efficiency.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Novel estimation method of operating life in lithium-ion pouch cells
Kim, Hyosung,Kim, Jaekwang,Kim, Nayeong,Lee, Ilbok,Hwang, Keebum,Bae, Joongho,Yoon, Songhun THE KOREAN SOCIETY OF INDUSTRIAL AND ENGINEERING 2018 JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY -S Vol.67 No.-
<P><B>Abstract</B></P> <P>Herein, a novel operating life (OL) test method was evaluated with 200mAh pouch-type lithium-ion batteries. By combining the calendar life (CL) test with intermediate pulse power cycling, more realistic life prediction was possible, which encompassed real operation of batteries accompanying with thermal acceleration. Larger capacity decrease and resistance increase of pouch cell were observed in the OL test, which was well explained using the SEI film growth model. After dissemble of pouch cell, capacity loss and resistance increase mostly occurred within anode, reflecting that SEI film growth on anode surface was highly attributable to cell degradation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Suggestion of novel operating life prediction. </LI> <LI> Intermediate pulse power cycling to simulate vehicle operation. </LI> <LI> Combination of pulse power cycling and thermal degradation by calendar life prediction. </LI> <LI> Surface film growth model to explain capacity and resistance change. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>