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Contribution of large-scale motions to the Reynolds shear stress in turbulent pipe flows
Ahn, Junsun,Lee, Jinyoung,Sung, Hyung Jin Elsevier 2017 The International journal of heat and fluid flow Vol.66 No.-
<P><B>Abstract</B></P> <P>Direct numerical simulation data for turbulent pipe flows with <I>Re<SUB>τ</SUB> </I> = 544, 934, and 3008 were used to investigate the contribution of large-scale motions (LSMs) to the Reynolds shear stress. The relationship between viscous force ( <SUP> d 2 </SUP> <SUP> U + </SUP> / d <SUP> y + 2 </SUP> , VF) and turbulent inertia ( d <SUP> 〈 − <SUP> u ′ </SUP> <SUP> v ′ </SUP> 〉 + </SUP> / d <SUP> y + </SUP> , TI) results in a transition from the inner length scale to the intermediate length scale in the meso-layer. The acceleration force of the LSMs is balanced by the deceleration force of the small-scale motions (SSMs), which makes the zero TI at the wall-normal location of the maximum Reynolds shear stress (<I>y<SUB>m</SUB> </I> <SUP>+</SUP>). As the Reynolds number increases, the enhanced acceleration force of the LSMs expands the nearly zero TI region. The constant-stress layer is formed in the neighborhood of the zero TI, having the relatively strong VF. For sufficiently high Reynolds number flows, the log law is established beyond the meso-layer due to the fact that VF loses its leading order. The role of the LSMs in the wall-scaling behavior of <I>y<SUB>m</SUB> </I> <SUP>+</SUP> is examined.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Direct numerical simulation data for turbulent pipe flows were used to investigate the contribution of large-scale motions to the Reynolds shear stress. </LI> <LI> The acceleration force of the large-scale motions is balanced by the deceleration force of the small-scale motions. </LI> <LI> For sufficiently high Reynolds number flows, the log law is established beyond the meso-layer. </LI> </UL> </P>
Baumann Skin Type in the Korean Female Population
( Sung Ku Ahn ),( Myungsoo Jun ),( Hana Bak ),( Byung Duk Park ),( Seung Phil Hong ),( Sang-Hoon Lee ),( Seong-Jin Kim ),( Hyung Joo Kim ),( Dong Hoon Song ),( Pok Kee Min ),( Ja Woong Goo ),( Tae-Hyu 대한피부과학회 2017 Annals of Dermatology Vol.29 No.5
Background: To meet the need for a subspecialized skin type system, the Baumann skin type (BST) system was proposed. Objective: To evaluate the distribution of BST types and influencing factors among Korean women. Methods: BST questionnaires were administered to 1,000 Korean women. The possible responses were as follows: oily (O) or dry (D), sensitive (S) or resistant (R), pigmented (P) or non-pigmented (N), and wrinkled (W) or tight (T). The correlations of the BST with the subjects` age, location, ultraviolet (UV) ray exposure, drinking and smoking habits, and blood type were assessed. Results: The OSNT, DSNT, DRNT, and OSNW skin types were the most common skin types (55.3%). The O, S, P, and W types accounted for 46.6%, 68.8%, 23.2%, and 31.9%, respectively. The proportion of the O and S type was the highest in Gyeongsangbuk-do (55.0%) and Seoul (77.2%). The proportion of the P and W type was the highest in Gyeongsangbuk-do (33.0%) and Chungcheong-do (39.0%). The O type decreased in the higher age group, whereas the P and W type showed a reversed tendency. In smokers, the proportion of W type was significantly higher than in the non-smokers (66.3% vs. 24.1%, p<0.05). Conclusion: The 4 most common BST types were OSNT, DSNT, DRNT, and OSNW. In the comparison across the 4 BST parameters according to the age, region, smoking and drinking habits, occupation, blood type, and UV exposure, significant differences were observed. Individualized and customized skin care is required according to the personal skin type. (Ann Dermatol 29(5) 586∼596, 2017)
Ahn, Jihoon,Lee, Dae-Hyeok,Kang, Min Seok,Lee, Kyung-Jae,Lee, Jin-Kyu,Sung, Yung-Eun,Yoo, Won Cheol Elsevier 2017 ELECTROCHIMICA ACTA Vol.245 No.-
<P><B>Abstract</B></P> <P>Recently, it has been clearly elucidated that nanostructured Si-based composites hybridized with protective and conductive materials can present enhanced electrochemical performance as anodes for Li-ion batteries (LIBs). One of remaining issues is to develop a sustainable and economic method to synthesize these composites on a large scale for industrial applications. Herein, we introduce a modified magnesiothermic reaction route to prepare the aforementioned Si-based composite electrodes using sea-sand derived Mg<SUB>2</SUB>Si as a reactive precursor. Owing to its reducibility and lability, Mg<SUB>2</SUB>Si can readily reduce group IVA oxides, such as Na<SUB>2</SUB>CO<SUB>3</SUB>, SiO<SUB>2</SUB>, GeO<SUB>2</SUB>, and SnO<SUB>2</SUB>, resulting in macroporous Si surrounded by the reduced forms of the counter reactants (C, Si, Ge, and Sn, respectively), some of which can be electrochemically attractive. Notably, the porous Si-based composite can be synthesized by a simple solid state reaction, so simplicity and scalability can be obtained. Also, the sea sand precursor is naturally–abundant; hence this process can be cost-effective, scalable, and sustainable. Porous Si@C composite can be synthesized from the modified magnesiothermic reaction using a sea sand-derived Mg<SUB>2</SUB>Si precursor, showing a specific capacity of 1000 mAh/g at 200th cycle. Potentially this process can be used for practical synthesis of Si-based composites.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We investigated Mg<SUB>2</SUB>Si as a reactive precursor for Si-based composite materials for Li-ion battery. </LI> <LI> Porous Si@C can be synthesized from naturally abundant sea sand using the reaction between sea sand-derived Mg<SUB>2</SUB>Si and Na<SUB>2</SUB>CO<SUB>3</SUB>. </LI> <LI> The reaction mechanism of the reaction between sea-sand derived Mg<SUB>2</SUB>Si and Na<SUB>2</SUB>CO<SUB>3</SUB> to form porous Si@C was investigated. </LI> <LI> Porous Si@C exhibits a large reversible capacity approximately 1000mAhg<SUP>−1</SUP> even after 200 cycles. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
( Sung Min Kim ),( Ji Su Lee ),( Ji Youn Hong ),( Jin Hee Kim ),( Joo Ran Hong ),( Hye In Cheon ),( Min Seok Hur ),( Yang Won Lee ),( Yong Beom Choe ),( Kyu Joong Ahn ) 대한피부과학회 2019 대한피부과학회 학술발표대회집 Vol.71 No.2
Background: Psoriasis is an inflammatory disease, characterized by erythematous papules or plaques with white scale. Risk of cardiovascular diseases is elevated in patients with psoriasis, and systemic treatments of psoriasis may lower cardiovascular events. Objectives: This study was aimed to assess the association between the rates of cardiovascular diseases and systemic treatments of psoriasis. Methods: This nationwide population-based cohort study analyzed the data of patients with psoriasis using National Health Insurance Service Database. The database was collected from 2006 to 2018 in Korea and a total of 1,201,778 patients with psoriasis over 20 years old were included. In this study, the patients who have never received systemic therapy were defined as mild. The patients were classified as moderate to severe, if they had received any systemic treatments such as methotrexate, cyclosporine, acitretin, phototherapy, or biologics. Results: Overall cumulative incidences for major adverse cardiovascular events (MACEs) were 7.00, 3.17, 2.37, 0.83, and 3.61 for cyclosporine, methotrexate, phototherapy, biologics, and mild group, respectively. Conclusion: The therapeutic modalities in psoriasis were related to cardiovascular outcomes in this study. Methotrexate, phototherapy, and biologics tend to lower the rate of cardiovascular events. The randomized trials are needed to evaluate the effectiveness of systemic antipsoriatic treatments and cardiovascular safety.
Tree-structured Classification based on Variable Splitting
Ahn, Sung-Jin The Korean Statistical Society 1995 Communications for statistical applications and me Vol.2 No.1
This article introduces a unified method of choosing the most explanatory and significant multiway partitions for classification tree design and analysis. The method is derived on the impurity reduction (IR) measure of divergence, which is proposed to extend the proportional-reduction-in-error (PRE) measure in the decision-theory context. For the method derivation, the IR measure is analyzed to characterize its statistical properties which are used to consistently handle the subjects of feature formation, feature selection, and feature deletion required in the associated classification tree construction. A numerical example is considered to illustrate the proposed approach.
Sung, Ho Kyung,Ma, Seung Hyun,Choi, Ji-Yeob,Hwang, Yunji,Ahn, Choonghyun,Kim, Byoung-Gie,Kim, Yong-Man,Kim, Jae Weon,Kang, Sokbom,Kim, Jaehoon,Kim, Tae Jin,Yoo, Keun-Young,Kang, Daehee,Park, Suekyung The Korean Society for Preventive Medicine 2016 예방의학회지 Vol.49 No.6
Objectives: We conducted a systematic review and meta-analysis to summarize current evidence regarding the association of parity and duration of breastfeeding with the risk of epithelial ovarian cancer (EOC). Methods: A systematic search of relevant studies published by December 31, 2015 was performed in PubMed and EMBASE. A random-effect model was used to obtain the summary relative risks (RRs) and 95% confidence intervals (CIs). Results: Thirty-two studies had parity categories of 1, 2, and ${\geq}3$. The summary RRs for EOC were 0.72 (95% CI, 0.65 to 0.79), 0.57 (95% CI, 0.49 to 0.65), and 0.46 (95% CI, 0.41 to 0.52), respectively. Small to moderate heterogeneity was observed for one birth (p<0.01; Q = 59.46; $I^2=47.9%$). Fifteen studies had breastfeeding categories of <6 months, 6-12 months, and >13 months. The summary RRs were 0.79 (95% CI, 0.72 to 0.87), 0.72 (95% CI, 0.64 to 0.81), and 0.67 (95% CI, 0.56 to 0.79), respectively. Only small heterogeneity was observed for <6 months of breastfeeding (p = 0.17; Q = 18.79, $I^2=25.5%$). Compared to nulliparous women with no history of breastfeeding, the joint effects of two births and <6 months of breastfeeding resulted in a 0.5-fold reduced risk for EOC. Conclusions: The first birth and breastfeeding for <6 months were associated with significant reductions in EOC risk.