1,720,975 research outputs found
The umbrella motion of core-excited CH3 and CD3 methyl radicals
No full textAn accurate experimental and theoretical study of the lowest core excitation of CH3 and CD3 methyl
radicals is presented. The complex vibrational structure of the lowest band of the x-ray absorption
spectrum XAS is due to the large variation of the molecular geometry, which is planar in the
ground state and pyramidal in the core-excited state. The XAS spectra of the two radicals were
recorded at high resolution and assigned by theoretical simulations of the spectra, taking into
account the coupling of symmetrical stretching and symmetrical bending umbrellalike
deformations of the radicals. An excellent agreement between experimental and theoretical spectral
profiles allowed us to accurately characterize the vibrational structure of the electronic transition.
The similarities, as well as the differences, of the peculiar vibrational progression observed for the
two radicals are explained by the strong anharmonicity along the umbrella coordinate and by the
isotopic variation, leading to a different probing of the double-well potential energy surface of the
core excited state during the nuclear motion
Probing the potential energy surface by high-resolution x-ray absorption spectroscopy: The umbrella motion of the core-excited CH3 free radical
No full textA detailed study of the umbrellalike vibration in inner-shell spectroscopy is presented. The high-resolution
x-ray absorption spectrum for the lowest lying core excitation of the CH3 free radical was recorded. High
quality potential energy surfaces PES for the initial and final states of the transition were calculated as a
function of the symmetrical stretching and the umbrella deformation coordinates. The strong anharmonicity
along the umbrella coordinate in the double-well region of the PES of the core excited state has a strong effect
on the bending vibrational progressions. The excellent agreement between the experiment and theory allows an
accurate spectroscopic characterization of the vibrational structure of the electronic transition, and the estimation
of the umbrella inversion time of 149 fs
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Double photoionization of N2O molecules in the 28-40 eV energy range
No full textThe double photoionization of N2O molecules, in the 28–40 eV energy range, has been studied by synchrotron radiation. In the whole
energy range, dissociative ionization producing N++NO+ or Nþ
2 þ Oþ has been observed. Below 35.5 eV, these two processes involve
the formation of some autoionizing states. In the range between 35.5 and 38.5 eV the two processes occur instead by a direct coulomb
explosion of the N2O2+ dication. Above 38.5 eV the dissociation leading to NO++N+ is also promoted by the formation of a dication
metastable state which decays by fluorescence to the ground state and then dissociates
Dissociative double photoionization of CO2 molecules in the 36-49 eV energy range: angular and energy distribution of ion products
No full textDissociative double photoionization of CO2, producing CO+ and O+ ions, has been studied in the 36–49 eV energy range using synchrotron radiation and ion–ion coincidence imaging
detection. At low energy, the reaction appears to occur by an indirect mechanism through the formation of CO+ and an autoionizing state of the oxygen atom. In this energy range the reaction leads to an isotropic distribution of products with respect to the polarization vector of the light. When the photon energy increases, the distribution of products becomes anisotropic, with the two ions preferentially emitted along the direction of the light polarization vector. This
implies that the molecule photoionizes when oriented parallel to that direction and also that the CO2 2+ dication just formed dissociates in a time shorter than its typical rotational period. At low photon energy, the CO+ and O+ product ions separate predominantly with a total kinetic energy between 3 and 4 eV. This mechanism becomes gradually less important when the photon energy
increases and, at 49 eV, a process where the two products separate with a kinetic energy between 5 and 6 eV is dominant
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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
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