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Authors' Previous Work (author + previous_work)
Selected AbstractsHigh-Performance Alkaline Polymer Electrolyte for Fuel Cell ApplicationsADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Jing Pan Abstract Although the proton exchange membrane fuel cell (PEMFC) has made great progress in recent decades, its commercialization has been hindered by a number of factors, among which is the total dependence on Pt-based catalysts. Alkaline polymer electrolyte fuel cells (APEFCs) have been increasingly recognized as a solution to overcome the dependence on noble metal catalysts. In principle, APEFCs combine the advantages of and alkaline fuel cell (AFC) and a PEMFC: there is no need for noble metal catalysts and they are free of carbonate precipitates that would break the waterproofing in the AFC cathode. However, the performance of most alkaline polyelectrolytes can still not fulfill the requirement of fuel cell operations. In the present work, detailed information about the synthesis and physicochemical properties of the quaternary ammonia polysulfone (QAPS), a high-performance alkaline polymer electrolyte that has been successfully applied in the authors' previous work to demonstrate an APEFC completely free from noble metal catalysts (S. Lu, J. Pan, A. Huang, L. Zhuang, J. Lu, Proc. Natl. Acad. Sci. USA2008, 105, 20611), is reported. Monitored by NMR analysis, the synthetic process of QAPS is seen to be simple and efficient. The chemical and thermal stability, as well as the mechanical strength of the synthetic QAPS membrane, are outstanding in comparison to commercial anion-exchange membranes. The ionic conductivity of QAPS at room temperature is measured to be on the order of 10,2,S cm,1. Such good mechanical and conducting performances can be attributed to the superior microstructure of the polyelectrolyte, which features interconnected ionic channels in tens of nanometers diameter, as revealed by HRTEM observations. The electrochemical behavior at the Pt/QAPS interface reveals the strong alkaline nature of this polyelectrolyte, and the preliminary fuel cell test verifies the feasibility of QAPS for fuel cell applications. [source] Influence of Point-Defect Reaction Kinetics on the Lattice Parameter of Ce0.8Gd0.2O1.9ADVANCED FUNCTIONAL MATERIALS, Issue 4 2009Anna Kossoy Abstract The kinetics of point-defect association/dissociation reactions in Ce0.8Gd0.2O1.9 and their influence on the crystal lattice parameter are investigated by monitoring thermally induced stress and strain in substrate- and self-supported thin films. It is found that, in the temperature range of 100,180,°C, the lattice parameter of the substrate-supported films and the lateral dimensions of annealed, self-supported films both exhibit a hysteretic behavior consistent with dissociation/association of oxygen vacancy,aliovalent dopant complexes. This leads to strong deviation from linear elastic behavior, denoted in the authors' previous work as the "chemical strain" effect. At room temperature, the equilibrium state of the point defects is reached within a few months. During this period, the lattice parameter of the substrate-supported films spontaneously increases, while the self-supported films are observed to transform from the flat to the buckled state, indicating that formation of the dopant,vacancy complex is associated with a volume increase. The unexpectedly slow kinetics of establishing the defect equilibrium at room temperature can explain the fact that, depending on the sample history, the "observable" lattice parameters of Ce0.8Gd0.2O1.9, as reported in the literature, may differ from one another by a few tenths of a percent. These findings strongly suggest that the lattice parameter of the materials with a large concentration of interacting point defects is a strong function of time and material preparation route. [source] A study on the convergence of least-squares meshfree method under inaccurate integrationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2003Sang-Hoon Park Abstract In the authors' previous work, it has been shown through numerical examples that the least-squares meshfree method (LSMFM) is highly robust to the integration errors while the Galerkin meshfree method is very sensitive to them. A mathematical study on the convergence of the solution of LSMFM under inaccurate integration is presented. New measures are introduced to take into account the integration errors in the error estimates. It is shown that, in LSMFM, solution errors are bounded by approximation errors even when integration is not accurate. Copyright © 2003 John Wiley & Sons, Ltd. [source] Methyl methacrylate emulsion polymerization at low monomer concentration: Kinetic modeling of nucleation, particle size distribution, and rate of polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2001Jorge Herrera-Ordóñez Abstract The results of a mathematical model developed in the authors' previous work are discussed and compared against final number (N) and size distribution of particles (PSD) and the rate of polymerization (RP) experimental data of methyl methacrylate (MMA) emulsion polymerization above the critical micelle concentration (cmc) of the surfactant. On the basis of the model results, the hypothesis that the observed bimodal PSD can be ascribed to secondary nucleation as proposed in the literature is questionable. It is discussed that this PSD can also be caused by differences in the growing rate of different-size particles as predicted for styrene emulsion polymerization. Because of the small particle size obtained at low initial monomer concentration, the high rate of free-radical desorption reduces the accumulation of these species; therefore, the autoacceleration effect is less pronounced for the conditions under study compared with the usual behavior of the RP during MMA emulsion polymerization above cmc. Similarities and differences between model predictions and experimental data are discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2547,2556, 2001 [source] Temporal analysis of a very large topically categorized Web query logJOURNAL OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE AND TECHNOLOGY, Issue 2 2007Steven M. Beitzel The authors review a log of billions of Web queries that constituted the total query traffic for a 6-month period of a general-purpose commercial Web search service. Previously, query logs were studied from a single, cumulative view. In contrast, this study builds on the authors' previous work, which showed changes in popularity and uniqueness of topically categorized queries across the hours in a day. To further their analysis, they examine query traffic on a daily, weekly, and monthly basis by matching it against lists of queries that have been topically precategorized by human editors. These lists represent 13% of the query traffic. They show that query traffic from particular topical categories differs both from the query stream as a whole and from other categories. Additionally, they show that certain categories of queries trend differently over varying periods. The authors key contribution is twofold: They outline a method for studying both the static and topical properties of a very large query log over varying periods, and they identify and examine topical trends that may provide valuable insight for improving both retrieval effectiveness and efficiency. [source] Association Between Birth Control Pills and Voice QualityTHE LARYNGOSCOPE, Issue 6 2004Ofer Amir PhD Abstract Objectives/Hypothesis: The objective was to extend our knowledge of the effect of birth control pills on voice quality in women based on various acoustic measures. Study Design: A longitudinal comparative study of 14 healthy young women over a 36- to 45-day period. Methods: Voices of seven women who used birth control pills and seven women who did not were recorded repeatedly approximately 20 times. Voice samples were analyzed acoustically, using an extended set of frequency perturbation parameters (jitter, relative average perturbation, pitch period perturbation quotient), amplitude perturbation parameters (shimmer, amplitude average perturbation quotient), and noise indices (noise-to-harmonics ratio, voice turbulence index). Results: Voice quality and stability were found to be better among the women who used birth control pills. Lower values were found for all acoustic measures with the exception of voice turbulence index. Results also provided preliminary indication for vocal changes associated with the days preceding ovulation. Conclusion: In contrast to the traditional view of oral contraceptives as a risk factor for voice quality, and in keeping with the authors' previous work, the data in the present study showed that not only did oral contraceptives have no adverse effect on voice quality but, in effect, most acoustic measures showed improved voice quality among women who used the birth control pill. The differences in the noise indices between groups may also shed light on the nature of the effect of sex hormones on vocal fold activity. It was suggested that hormonal fluctuations may have more of an effect on vocal fold regulation of vibration than on glottal adduction. [source] | ||||||||||