1,720,963 research outputs found
The OH product state distribution from the photodissociation of hexafluoroacetylacetone
No full textHexafluoroacetylacetone (1,1,1,5,5,5-hexafluoro-2,4-pentanedione) in the supersonic jet, which exists as its enolic form, has been found to give the OH radical as a result of photodissociation induced by the pi-pi* transition. The nascent OH product state distributions are measured at the photolysis wavelengths of 293.5 and 266 nm. As in the case of the acetylacetone photodissociation, no fluorescence is observed even in the energy region near the origin, indicating ultrafast nonradiative decay of the excited state. The OH fragment is found to be vibrationally cold, and its rotational state distributions are peaked at N = 3 at both pump wavelengths used in this work. The OH fragment is slightly more populated in the (2)Pi(3/2) state than it is in the (2)Pi(1/2) state. The Pi(-)/Pi(+) ratios are found to be unity, suggesting that there is no preferential alignment of the p pi electronic orbital of the OH radical with respect to its plane of rotation. The strength of the intramolecular hydrogen bond and its dynamic role in the chemical bond dissociation of hexafluoroacetylacetone are discussed and compared with the acetylacetone photodissociation dynamics.This work was financially supported by
Korea Research Foundation (Project No. 1998-015-D00158) and 1999 Inha University Fund
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
The OH production from the π–π* transition of acetylacetone
No full textAcetylacetone in its enolic form has been found to produce the OH radical as a photofragment after the pi-pi* transition induced by UV irradiation. The absorption spectrum of the enolic acetylacetone in the supersonic jet, deduced from the OH photofragment excitation spectrum, shows no distinct structures suggesting the very fast decay of the S-1 state being followed by the C-O chemical bond dissociation. The photodissociation mechanism is discussed with a qualitative description of the energetics involved. (C) 1999 Elsevier Science B.V. All rights reserved.Korea Science and Engineering Foundation
Inha Universit
Photodissociation dynamics of acetylacetone: The OH product state distribution
No full textAcetylacetone in the supersonic jet, which exists predominantly as an enolic form, is found to give rise to the OH fragment after the pi-pi(*) transition induced by the UV absorption. The nascent OH product state distributions are determined using a laser-induced fluorescence technique at the excitation wavelengths of 291 and 266 nm. The OH fragment is vibrationally cold, and its rotational state distribution is peaked at N=3 or 4 at the pump wavelength of 291 or 266 nm, respectively. No fluorescence from the excited acetylacetone has been observed even in the energy region near the origin, suggesting the ultrafast nonradiative processes of the excited state. From the measured OH product state distributions, the upper bound for the dissociation energy of the acetylacetone is estimated to be 90.3 kcal/mol. The ratios of Lambda-doublets and spin-orbit states of the OH fragment are also measured. A slight preference of the OH fragment in the (2)Pi(3/2) state over the (2)Pi(1/2) state is observed. The Pi(-)/Pi(+) ratios, determined by the relative intensity ratios of Q and P (or R) lines, are found to be less than unity, suggesting the preferential cleavage of the C-OH bond on the molecular plane probably due to a relatively strong intramolecular hydrogen bonding of the enolic acetylacetone. The prior calculation reproduces the experiment quite well for the OH rotational state distribution at 291 nm, while it does not for that at 266 nm. This suggests that the transition state in the acetylacetone dissociation, at the low energy near threshold, may be completely loosely defined on the potential energy surface which does not have a barrier to recombination, and it becomes tightened as the energy increases above the reaction threshold. (C) 1999 American Institute of Physics. [S0021-9606(99)01824-3].Korea Research Foundatio
Fluorescence excitation spectroscopic study of the jet-cooled acetyl cyanide
No full textFluorescence excitation spectrum of acetyl cyanide (CH3COCN) in a supersonic jet has been obtained for the (1) (n, pi*) transition (S-1-S-0). A spectral origin band is located at 27 511 cm(-1), and its fluorescence lifetime is measured to be 3.5+/-0.3 mu s. The S-1 state vibrational modes associated with CH3 torsion, CCO bend, CCN bend, and CO wag are found to be optically active. The fluorescence intensity decreases with increasing the energy from the origin up to similar to 2000 cm(-1), while the fluorescence lifetime changes little over the same energy region. Instead, a broad background signal appears in the high energy region, indicating that the intramolecular vibrational redistribution (IVR) process becomes important in the S-1 state as the density of states increases. (C) 1999 American Institute of Physics. [S0021-9606(99)00515-2].Korea Science and Engineering Foundation
Korea Research Foundation
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
- …
