96 research outputs found

    Synthesis of highly thermally stable daidzein-based main-chain-type benzoxazine resins

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    In recent years, main-chain-type benzoxazine resins have been extensively investigated due to their excellent comprehensive properties for many potential applications. In this work, two new types of main-chain benzoxazine polymers were synthesized from daidzein, aromatic/aliphatic diamine, and paraformaldehyde. Unlike the approaches used synthesizing traditional main-chain-type benzoxazine polymers, the precursors derived from daidzein can undergo a further cross-linking polymerization in addition to the ring-opening polymerization of the oxazine ring. The structures of the new polymers were then studied by 1H nuclear magnetic resonance spectroscopy (NMR) and Fourier-transform infrared spectroscopy (FT-IR), and the molecular weights were determined by using gel permeation chromatography (GPC). We also monitored the polymerization process by differential scanning calorimetry (DSC) and in situ FT-IR. In addition, the thermal stability and flame-retardant properties of the resulting polybenzoxazines were investigated using TGA and microscale combustion calorimeter (MCC). The polybenzoxazines obtained in this study exhibited a very high thermal stability and low flammability, with a Tg value greater than 400 °C, and a heat release capacity (HRC) value lower than 30 J/(g K)

    Benzoxazine Atropisomers: Intrinsic Atropisomerization Mechanism and Conversion to High Performance Thermosets

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    Atropisomers have inspired chemists and biologists for decades due to their chiral structures and associated biological properties. However, most of atropisomers reported so far arise in highly substituted biaryls and related compounds, and other types have been rarely observed. Here we report a new type of atropisomerism in ortho-tetrahydrophthalimide functional 1,3-benzoxazine family, where the atropisomerism is evident from NMR spectra, with the branching ratio of the atropisomeric configurations invariant with the measurement temperatures. Density functional theory calculations suggested that the reaction intermediate, ortho-tetrahydrophthalimide phenol, is key to the atropisomerism, which creates a large energy barrier after deprotonation and thus determines the branching ratios of the benzoxazine atropisomers. In addition, the ring-opening polymerization of benzoxazine atropisomers has also been investigated. The benzoxazine atropisomers bearing acetylene exhibit unexpectedly low polymerization temperature in the absence of catalysts, suggesting a self-catalyzed polymerization process. Despite the absence of antiflammable additives, the corresponding polybenzoxazine deriving from benzoxazine atropisomers containing acetylene shows exceptionally low heat release capacity (67.2 J g1–K–1) and excellent char residue value (62%). With this work we demonstrate atropisomerism in the 1,3-benzoxazine family for the first time, and provide molecular-level insights to the mechanism, which can open up possibilities for new applications of atropisomers spanning from the microelectronic to the aerospace industries

    The joint effect of personality traits and perceived stress on pedestrian behavior in a Chinese sample

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    <div><p>While improper pedestrian behavior has become an important factor related to road traffic fatalities, especially in developing countries, the effects of personality traits and/or stress on pedestrian behavior have been rarely reported. The current study explored the joint effects of five personality traits (i.e., extraversion, openness, neuroticism, normlessness and altruism) and global perceived stress (measured with the Perceived Stress Scale-10) on pedestrian behavior (measured with the Pedestrian Behavior Scale) in 311 Chinese individuals. Results showed that altruism, neuroticism and openness significantly affected different pedestrian behavior dimensions, while global perceived stress also significantly and positively predicted positive behavior. Moreover, the effect of neuroticism on positive behavior was fully mediated by stress. Some explanations and implications are provided in the discussion section.</p></div

    Highly Efficient Solar Water Splitting from Transferred TiO<sub>2</sub> Nanotube Arrays

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    We report a synergistic effect of flame and chemical reduction methods to maximize the efficiency of solar water splitting in transferred TiO<sub>2</sub> nanotube (TNT) arrays on a transparent conducting oxide (TCO) substrate. The flame reduction method (>1000 °C) leads to few oxygen vacancies in the anatase TNT arrays, but it exhibits unique advantages for excellent interfacial characteristics between transferred TNT arrays and TCO substrates, which subsequently induce a cathodic on-set potential shift and sharp photocurrent evolution. By contrast, the employed chemical reduction method for TNT arrays/TCO gives rise to an abrupt increase in photocurrent density, which results from the efficient formation of oxygen vacancies in the anatase TiO<sub>2</sub> phase, but a decrease in charge transport efficiency with increasing chemical reduction time. We show that flame reduction followed by chemical reduction could significantly improve the saturation photocurrent density and interfacial property of TNT arrays/TCO photoanodes simultaneously without mechanical fracture via the synergistic effects of coreducing methods

    A Meta-Analysis of <i>P2X7</i> Gene-762T/C Polymorphism and Pulmonary Tuberculosis Susceptibility

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    <div><p>Aim</p><p>We performed a comprehensive meta-analysis to determine the association between <i>P2X7</i> -762T/C polymorphism and pulmonary tuberculosis susceptibility.</p><p>Methodology</p><p>Based on comprehensive searches of the PubMed, SCI, Elsevier, China National Knowledge Infrastructure (CNKI) and Wanfang Database, we identified eligible studies about the association between <i>P2X7</i> -762T/C polymorphism and pulmonary tuberculosis risk. Pooled odds ratio (ORs) and 95% confidence intervals (95%CIs) were calculated in random-effects model.</p><p>Results</p><p>A total of 2207 tuberculosis cases and 2220 controls in 8 case-control studies were included in this meta-analysis. Allele model (C vs. T: p = 0.15; OR = 0.83, 95% CI = 0.65–1.07), homozygous model (CC vs. TT: p = 0.23; OR = 0.73, 95% CI = 0.44 to 1.22), and heterozygous model (CT vs. TT: p = 0.57; OR = 0.92, 95% CI = 0.68 to 1.24) did not show increased risk of developing pulmonary tuberculosis. Similarly, dominant model (CC+CT vs. TT: p = 0.32; OR = 0.84, 95% CI = 0.59 to 1.19) and recessive model (CC vs. CT+TT: p = 0.08; OR = 0.77, 95% CI = 0.57 to 1.04) failed to show increased risk of developing pulmonary tuberculosis. Subgroup analysis by ethnicity did not detect any significant association between <i>P2X7</i>–762T/C polymorphism and pulmonary tuberculosis susceptibility.</p><p>Conclusions</p><p><i>P2X7</i> -762T/C gene polymorphism is not associated with pulmonary tuberculosis susceptibility.</p></div

    Highly Efficient Solar Water Splitting from Transferred TiO<sub>2</sub> Nanotube Arrays

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    We report a synergistic effect of flame and chemical reduction methods to maximize the efficiency of solar water splitting in transferred TiO<sub>2</sub> nanotube (TNT) arrays on a transparent conducting oxide (TCO) substrate. The flame reduction method (>1000 °C) leads to few oxygen vacancies in the anatase TNT arrays, but it exhibits unique advantages for excellent interfacial characteristics between transferred TNT arrays and TCO substrates, which subsequently induce a cathodic on-set potential shift and sharp photocurrent evolution. By contrast, the employed chemical reduction method for TNT arrays/TCO gives rise to an abrupt increase in photocurrent density, which results from the efficient formation of oxygen vacancies in the anatase TiO<sub>2</sub> phase, but a decrease in charge transport efficiency with increasing chemical reduction time. We show that flame reduction followed by chemical reduction could significantly improve the saturation photocurrent density and interfacial property of TNT arrays/TCO photoanodes simultaneously without mechanical fracture via the synergistic effects of coreducing methods

    The descriptive statistics of the PDBS items and subscales (<i>N</i> = 421).

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    <p>The descriptive statistics of the PDBS items and subscales (<i>N</i> = 421).</p

    Hierarchical regression models of full PDBS.

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    <p>Hierarchical regression models of full PDBS.</p

    Measures of behavioral performance.

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    <p>(A) The mean distance between the tracking circle and the target ball. (B) The reaction time to the random red dot. (C) The signal detection accuracy rate to the random red dot. *p < 0.05, **p < 0.01.</p
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