1,721,070 research outputs found
A reference multiparameter viscosity equation for propane with an optimized functional form.
No full textSpectroscopy, Electrochemistry and Photochemistry of Phenylazonaphthalene Dyes
Full text linkThe spectroscopy, electrochemistry and photochemistry of seven 2-(4-R-phenylazo)naphthalene-4,8-disulfonate dyes (R-Span dyes), were studied to report on their structure and reactivity in water. The dyes differ in their structure by only the R substituent attached to the phenyl ring, representing a range of electron-donating and electron-withdrawing substituents; most studies were carried out on OH-Span.
A combination of UV/Visible, NMR, Raman and IR spectroscopy together with DFT calculations has shown that the dyes are planar in their stable trans-isomer form. The spectra were found to be sensitive to the R substituent and generally they show good correlations with Hammett σp substituent constants. The structures of OH-Span (pKa = 7.98) and NH2-Span (pKa = 2.88) are pH dependent, and none of the dyes show aggregation at ≤ 3 * 10^-2 mol dm^-3.
Spectroelectrochemistry and controlled potential electrolysis studies showed that OH-Span undergoes an irreversible four electron reduction process, where detailed product analysis showed that naphthyl and phenyl fragments of the dye are produced due to azo bond scission; similar results were observed for the other R-Span dyes. Dyes containing electron-donating R substituents are more resistant to reduction, whereas dyes containing electron-withdrawing R substituents are more resistant to oxidation.
The stability of the R-Span dyes was assessed by reaction with photoinitiator generated 2-hydroxy-2-propyl radicals to study reductive fading. Time-resolved studies were carried out on OH-Span:photoinitiator solutions and rate constants for electron transfer to produce the dye radical anion and subsequent disproportionation were found to be 6.00 * 10^9 and 5.00 * 10^8 dm^3 mol^-1 s^-1, respectively. The detailed product analysis identified the naphthyl fragment of the dye, which was also observed for other R-Span dyes, indicating that the reduction mechanism occurs via disproportionation resulting in azo bond scission.
The R-Span dyes show trans to cis photoisomerisation, and NH2-, OH-, OMe- and NHAc-Span showed complete cis to trans thermal back reactions within ca. 30 ms, 35 μs, 11 days and 1 day, respectively
A reference multiparameter viscosity equation for R134a in optimized functional form.
No full textAn optimization technique was applied to develop a functional form for a multiparameter viscosity equation η = η(ρ,T) for R134a. The results obtained are very promising, with an average absolute deviation of 0.55% for the currently available 549 primary data points. Compared to viscosity equations available in the literature, this is a significant improvement. Advantages become evident especially at gaseous states. As usual, both the development and the use of the viscosity equation require a highly accurate equation of state in order to convert the independent variables used for the experimental data and in most applications, (P,T), into the independent variables of the viscosity equation, (ρ,T). Though the equation was developed directly using the available data, the zero-density viscosity and the reduced second viscosity virial coefficient are correctly reproduced in the data range. The technique used to develop the equation, which is heuristic and not theoretically founded, is capable of selecting consistent data sets and thus is a powerful tool for screening the available experimental data. For the viscosity surface representation of a pure fluid this study shows that the limit in the achievement of a better accuracy is much more due to the present experimental uncertainty level for this property rather than to the effectiveness of the proposed modeling method
A reference multiparameter thermal conductivity equation for carbon dioxide with an optimized functional form.
No full textA new thermal conductivity equation λ = λ(T,ρ) in a multiparameter format was developed for carbon dioxide through the application of an optimization technique of the functional form. The proposed equation is valid for temperatures from the triple point (Tt = 216.592 K; Pt = 0.51795 MPa) to 1000 K and pressures up to 200 MPa. The calculation of density, which is an independent variable of the equation, from the experimental (T,P) conditions is performed with a high accuracy equation of state for the fluid. The thermal conductivity equation shows an average absolute deviation of 1.19% on the selected 1407 primary data points. Its performances are slightly better than those of the corresponding conventional model by Vesovic et al. [J. Phys. Chem. Ref. Data 19, 763 (1990)] available from the literature; moreover the new equation is simpler to use in particular for the near-critical region. Tables of generated values of carbon dioxide thermal conductivity are provided for check of the code implementations and for quick evaluations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
