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RISS 인기검색어
- 검색키워드
- 저자 : Siwei Chen (검색결과 5 건)
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Chen Xu,Boyu Zhang,Siwei Liu,Qingtian Su 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.35 No.3
The steel-concrete double composite girder in the negative flexural region combines an additional concrete slab to the steel bottom flange to prevent the local steel buckling, however, the additional concrete slab may lower down the neutral axis of the composite section, which is a sensitive factor to the tensile stress restraint on the concrete deck. This is actually of great importance to the structural rationality and durability, but has not been investigated in detail yet. In this case, a series of 5.5 m-long composite girder specimens were tested by negative bending, among which the bottom slab configuration and the longitudinal reinforcement ratio in the concrete deck were the parameters. Furthermore, an analytical study concerning about the influence of bottom concrete slab thickness on the cracking and sectional bending-carrying capacity were carried out. The test results showed that the additional concrete at the bottom improved the composite sectional bending stiffness and bending-carrying capacity, whereas its effect on the concrete crack distribution was not obvious. According to the analytical study, the additional concrete slab at the bottom with an equivalent thickness to the concrete deck slab may provide the best contributions to the improvements of crack initiation bending moment and the sectional bending-carrying capacity. This can be applied for the design practice.
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Liang, Siwei,Chen, Quan,Choi, U Hyeok,Bartels, Joshua,Bao, Nanqi,Runt, James,Colby, Ralph H. The Royal Society of Chemistry 2015 Journal of Materials Chemistry A Vol.3 No.42
<▼1><P>Copolymerized (CPP) and oligomeric (OP) plasticizers containing ethylene oxide and cyclic carbonate units.</P></▼1><▼2><P>To prepare a safe electrolyte for lithium ion batteries, two groups of novel low-volatility plasticizers combining pendant cyclic carbonates and short ethylene oxide chains have been successfully synthesized, as confirmed by <SUP>1</SUP>H, <SUP>13</SUP>C and <SUP>29</SUP>Si NMR spectroscopy. The Fox equation describes the composition dependence of the glass transition temperature (<I>T</I>g) very well for the random polysiloxane-based copolymer plasticizers (11 000 < <I>M</I> < 13 000) while the smaller oligomer plasticizers have <I>T</I>g as much as 20 K lower than the Fox equation prediction because of their lower molecular weight (450 < <I>M</I> < 700). The Landau–Lifshitz mixing rule describes the dielectric constant of the random polysiloxane-based copolymer plasticizers at all temperatures above <I>T</I>g. Mixing with 20 wt% polysiloxane tetraphenyl borate – Li ionomer (14 mol% borate and 86 mol% cyclic carbonate) increases conductivity relative to the neat ionomer by lowering <I>T</I>g, increasing dielectric constant and providing better solvation of Li<SUP>+</SUP>. The best oligomeric plasticizer only has <I>T</I>g 10 K lower than the Fox prediction but has dielectric constant 30% larger than expected by the Landau–Lifshitz mixing rule, owing to a surprisingly low viscosity, resulting in ambient conductivity 2 × 10<SUP>−5</SUP> S cm<SUP>−1</SUP>. For both groups of plasticizers, the fraction of cyclic carbonates relative to ethylene oxide governs the magnitude and temperature dependence of the ionic conductivity.</P></▼2>
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Choi, U Hyeok,Liang, Siwei,Chen, Quan,Runt, James,Colby, Ralph H. American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.5
<P>Dielectric relaxation spectroscopy was used to investigate the segmental dynamics of a series of siloxane-based polar copolymers combining pendant cyclic carbonates and short poly(ethylene oxide) (PEO) chains. The homopolymer with cyclic carbonate as the only side chain exhibits higher glass transition temperature T-g and dielectric constant epsilon(s) than the one with only PEO side chains. For their copolymers the observed T-g (agreeing well with the predicted values from the Fox equation) and epsilon(s) decrease with increasing PEO side chain content. These polar polymers exhibit a glassy beta relaxation with Arrhenius character, attributed to local chain motions of side groups attached to the main chain, and a segmental beta relaxation, associated with the glass transition with a Vogel temperature dependence. As PEO side chain content increases, narrowing of the local glassy beta relaxation was observed in the copolymers. The segmental a dynamics were observed to be faster, with an increase in breadth and decrease in strength with increasing PEO side chain content. Owing to the trade-off between T-g and epsilon(s) copolymers of intermediate composition result in the highest ionic conductivity when these copolymers are used to plasticize Li single-ion conducting ionomers.</P>
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Fangfang Jie,Mingjia Liao,Siwei Jiang,Chunyu Song,Chengli Tang,Boshui Chen 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.12
Phosphonation and nitrogenation of methyl epoxyoleate (MEO) were done to prepare phosphonitrogenated methyl epoxyoleate (PNMEO). The structural characteristics of PNMEO were characterized. The tribological properties of PNMEO and MEO as additives in a paraffin oil and a rapeseed oil were evaluated, and the morphologies, element compositions and tribochemical species of worn surfaces were analyzed. Results showed that PNMEO was more efficient in enhancing tribological properties of oils than MEO. Results also showed that PNMEO and MEO were more powerful in paraffin oil than in rapeseed oil in improving loadcarrying, friction-reducing and anti-wear performances, but in rapeseed oil than in paraffin oil in improving extreme pressure property. The tribological mechanisms of PNMEO in reducing friction and wear were attributed to PNMEO-involved tribo-adsorptions and tribo-reactions to produce a composite boundary lubrication film which consisted of a matrix of PNMEO with inclusions of iron oxide, polyphosphates, aminic compounds, and the base oil molecules.
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Peng Jiang,Xiujuan Fu,Hong Niu,Siwei Chen,Feifei Liu,Yu Luo,Dan Zhang,Hui Lei 대한약학회 2023 Archives of Pharmacal Research Vol.46 No.6
Strains of the fungal genus Pestalotiopsis are reported as large promising sources of structurally varied biologically active metabolites. Many bioactive secondary metabolites with diverse structural features have been derived from Pestalotiopsis. Moreover, some of these compounds can potentially be developed into lead compounds. Herein, we have systematically reviewed the chemical constituents and bioactivities of the fungal genus Pestalotiopsis, covering a period ranging from January 2016 to December 2022. As many as 307 compounds, including terpenoids, coumarins, lactones, polyketides, and alkaloids, were isolated during this period. Furthermore, for the benefit of readers, the biosynthesis and potential medicinal value of these new compounds are also discussed in this review. Finally, the perspectives and directions for future research and the potential applications of the new compounds are summarized in various tables.
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