8 research outputs found

    A Comparison of Imputation Strategies for Ordinal Missing Data on Likert Scale Variables

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    <div><p>This article compares a variety of imputation strategies for ordinal missing data on Likert scale variables (number of categories = 2, 3, 5, or 7) in recovering reliability coefficients, mean scale scores, and regression coefficients of predicting one scale score from another. The examined strategies include imputing using normal data models with naïve rounding/without rounding, using latent variable models, and using categorical data models such as discriminant analysis and binary logistic regression (for dichotomous data only), multinomial and proportional odds logistic regression (for polytomous data only). The result suggests that both the normal model approach without rounding and the latent variable model approach perform well for either dichotomous or polytomous data regardless of sample size, missing data proportion, and asymmetry of item distributions. The discriminant analysis approach also performs well for dichotomous data. Naïvely rounding normal imputations or using logistic regression models to impute ordinal data are not recommended as they can potentially lead to substantial bias in all or some of the parameters.</p></div

    Janus Composite Nanorod from a Molecular Bottlebrush Containing a Block Copolymer

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    The asymmetric ABC-type Janus polymer composite nanorods are synthesized by the in situ preferential growth of functional materials against the molecular bottlebrush containing a triblock copolymer of poly­(ethylene oxide)-<i>b</i>-poly­(2-meth­acryl­oyl­oxy­ethyl pentyn­oate-<i>g</i>-poly­(acrylic acid))-<i>b</i>-polystyrene. PEO and PS single chains are terminated onto the opposite ends of the composite nanorods. The two polymer chains are responsible for amphiphilic performance, while the composite nanorod is responsible for the functionality. The Janus nanorods can stand vertically at an emulsion interface, making the interfaces easily functionalized and manipulated. Protection of the PAA molecular bottlebrush via electrostatic interaction is important to obtaining individual nanorods at high solid contents. A huge family of Janus composite nanorods is expected by changing the compositions of the two polymer chains and the nanorod

    Amide Bond Formation through Iron-Catalyzed Oxidative Amidation of Tertiary Amines with Anhydrides

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    A general and efficient method for amide bond synthesis has been developed. The method allows for synthesis of tertiary amides from readily available tertiary amines and anhydrides in the presence of FeCl<sub>2</sub> as catalyst and <i>tert</i>-butyl hydroperoxide in water (T-Hydro) as oxidant. Mechanistic studies indicated that the in situ-generated α-amino peroxide of tertiary amine and iminium ion act as key intermediates in this oxidative transformation

    Three-Dimensional Phosphorus-Doped Graphitic‑C<sub>3</sub>N<sub>4</sub> Self-Assembly with NH<sub>2</sub>‑Functionalized Carbon Composite Materials for Enhanced Oxygen Reduction Reaction

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    Oxygen reduction reaction (ORR) is the major reaction that occurs at the cathodes of fuel cells and metal–air batteries. Development of inexpensive, active, and durable heteroatom doped carbon-based ORR catalysts can lead to significant cost reduction of these electrochemical energy devices, which therefore has recently attracted enormous research attentions. This work reports a three-dimensional porous composite (P-<i>g</i>-C<sub>3</sub>N<sub>4</sub>@NH<sub>2</sub>–CB) for the highly efficient ORR catalyst. P-<i>g</i>-C<sub>3</sub>N<sub>4</sub>@NH<sub>2</sub>–CB was prepared by mixing phosphorus-doped graphitic carbon nitride nanosheets (P-<i>g</i>-C<sub>3</sub>N<sub>4</sub> NSs) with NH<sub>2</sub>-functionalized carbon black (NH<sub>2</sub>–CB) via a novel self-assembly approach. The NH<sub>2</sub>–CB was rationally chosen as the spacer that enables the self-assembled with the P-<i>g</i>-C<sub>3</sub>N<sub>4</sub> NSs driven by the electrostatic interaction. The intercalation of NH<sub>2</sub>–CB induces the transformation of 2-D P-<i>g</i>-C<sub>3</sub>N<sub>4</sub> NSs into a 3-D composites material of higher surface area, thereby exposing more ORR active sites. The P-<i>g</i>-C<sub>3</sub>N<sub>4</sub>@NH<sub>2</sub>–CB exhibited a remarkable ORR activity with an electron transfer number of 3.83 and Tafel slope of 89 mV dec<sup>–1</sup> in alkaline electrolyte, which is comparable to the ORR performance on Pt/Vulcan XC-72. It is found that the incorporated P atoms as well as employing NH<sub>2</sub>–CB spacer not only reduces the overpotential of ORR, but also enhances the ORR activity of carbon nitride-based materials, owing to the synergistic effect between P and N in tri-s-triazine rings of carbon nitrides and the optimum interaction between the oppositely charged P-<i>g</i>-C<sub>3</sub>N<sub>4</sub> and NH<sub>2</sub>–CB

    Direct Benzothiophene Formation via Oxygen-Triggered Intermolecular Cyclization of Thiophenols and Alkynes Assisted by Manganese/PhCOOH

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    An intermolecular oxidative cyclization between thiophenols and alkynes for benzothiophene formation has been established. A variety of multifunctional benzothiophenes are synthesized. In addition, we demonstrated that the obtained benzothiophenes can be used for further transformation to give diverse benzothiophene derivatives efficiently and selectively

    Janus Nanoparticles of Block Copolymers by Emulsion Solvent Evaporation Induced Assembly

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    We present a facile approach toward straightforward synthesis of Janus nanoparticles (NPs) of poly­(4-vinylpyridine)-based block copolymers by solvent evaporation induced assembly within emulsion droplets. Formation of the Janus NPs is arisen from the synergistic effect between solvent selectivity and interfacial selectivity. This method is robust without the requisites of narrow molecular weight distribution and specific range of block fraction of the copolymers. Janus NPs can also be achieved from mixtures of copolymers, whose aspect size ratio and thus Janus balance are finely tunable. The Janus NPs are capable to self-assemble into ordered superstructures either onto substrates or in dispersions, whose morphology relies on Janus balance

    Surface-Adaptive Gold Nanoparticles with Effective Adherence and Enhanced Photothermal Ablation of Methicillin-Resistant Staphylococcus aureus Biofilm

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    Biofilms that contribute to the persistent bacterial infections pose serious threats to global public health, mainly due to their resistance to antibiotics penetration and escaping innate immune attacks by phagocytes. Here, we report a kind of surface-adaptive gold nanoparticles (AuNPs) exhibiting (1) a self-adaptive target to the acidic microenvironment of biofilm, (2) an enhanced photothermal ablation of methicillin-resistant Staphylococcus aureus (MRSA) biofilm under near-infrared (NIR) light irradiation, and (3) no damage to the healthy tissues around the biofilm. Originally, AuNPs were readily prepared by surface modification with pH-responsive mixed charged zwitterionic self-assembled monolayers consisting of weak electrolytic 11-mercaptoundecanoic acid (HS-C<sub>10</sub>-COOH) and strong electrolytic (10-mercaptodecyl)­trimethylammonium bromide (HS-C<sub>10</sub>-N<sub>4</sub>). The mixed charged zwitterion-modified AuNPs showed fast pH-responsive transition from negative charge to positive charge, which enabled the AuNPs to disperse well in healthy tissues (pH ∼7.4), while quickly presenting strong adherence to negatively charged bacteria surfaces in MRSA biofilm (pH ∼5.5). Simultaneous AuNP aggregation within the MRSA biofilm enhanced the photothermal ablation of MRSA biofilm under NIR light irradiation. The surrounding healthy tissues showed no damage because the dispersed AuNPs had no photothermal effect under NIR light. In view of the above advantages as well as the straightforward preparation, AuNPs developed in this work may find potential applications as a useful antibacterial agent in the areas of healthcare
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