117,665 research outputs found
Impedance spectroscopy of reactive polymers .4. An improved experimental procedure for measurement of effective resistivity
No full textThe kinetics of volume relaxation and related property changes during physical aging of poly(ether ether ketone) (PEEK)
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Impedance Spectroscopy Of Reactive Polymers .1.
No full textDielectric measurements were utilized to follow the advancement of cure in an epoxy/amine formulation. In contrast to earlier studies, complex impedance was measured during cure and used to calculate ionic resistivity. By using complex impedance we were able to separate according to their frequency dependence the contributions to overall polarization from electrode blocking layers, migrating charges, and dipole relaxations. At any stage of cure, there is a unique frequency at which ionic resistivity can be singularly measured. Our approach does not involve trial-and-error frequency search and is conducive to the development of phenomenological models based on equivalent circuits. Excellent agreement was reported between the calculated values of normalized degree of cure obtained by dielectric and calorimetric measurements
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Poly(ethylene oxide)–silica hybrids entrapping sensitive dyes for biomedical optical pH sensors: Molecular dynamics and optical response
No full textPolymer–silica hybrid nanocomposites prepared by sol–gel process based on triethoxisilane-terminatedpoly(ethylene oxide) chains and tetraethoxysilane as silica precursor, doped with organic pH sensitivedyes, have been prepared and their suitability for use as sensors coupled with plastic optic fibers has beenevaluated. Sensors were prepared by immobilizing a drop of the hybrid materials onto the tip of a multimodepoly(methyl methacrylate) optical fiber. The performance of the optical sensor in terms of sensitivityand response time was tested in different experimental conditions, and was found to be markedlyhigher than analogous sensors present on the market. The very fast kinetic of the hybrid’s opticalresponse was supported by studies performed at the molecular level by broadband dielectric relaxationspectroscopy (DRS), investigated over a wide range of frequency and temperature, showing that poly(ethyleneoxide) chains maintain their dynamics even when covalently bonded to silica domains, whichdecrease the self-association interactions and promote motions of polymer chain segments. Due to thefast response kinetic observed, these pH optical sensors result suitable for the fast-detection of biomedicalparameters, i.e. fast esophageous pH-metry
Impedance Spectroscopy Of Reactive Polymers .2. Multifunctional Epoxy-Amine Formulations
No full textSquare Dancing with the Stars to Enhance Dynamic Hirschman Linkages?
No full textIn this Presidential Address, the author takes the reader on a reconnaissance of his life and time as a regional scientist. He points out scenery he found scintillating along the way, hoping that some may pick up the banner and chew on a few of the ideas for a while. He suggests a revisit to Albert O. Hirschman’s notion of key sectors and more empirical analysis related to Marcus Berliant’s and Masahisa Fujita’s notion of knowledge creation and transfer.Presidential Address, San Antonio, Texas, March 29, 2014 (53rd Meetings of the Southern Regional Science Association
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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