1,720,961 research outputs found
Study of Quantum Confinement of H 2 + Ion and H2 Molecule with Monte Carlo. Respective Role of the Electron and Nuclei Confinement
No full textVariational Monte Carlo Method with Dirichlet Boundary Conditions: Application to the Study of Confined Systems by Impenetrable Surfaces with Different Symmetries
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The effect of space restriction on the bonding and vibrational properties of H
No full textWhen the space surrounding an atom or molecule is restricted, its electron density is modified compared to its unrestricted counterpart, which further alters its physical and chemical properties. To model the effect of space restriction, or confinement, on atoms and molecules, often the hard-boundary condition is employed to solve the corresponding Schrödinger equation. In the present work, we analyze the modifications in a chemical bond when the space surrounding the molecule is restricted such that some part of the space is forbidden to the electrons. To this end, we choose the simplest hydrogen molecular ion H, in the presence of an external hard-sphere simulating the restriction of space available to the electrons due to Pauli exclusion by an atom close to the molecule. The hard-sphere is moved along the molecular axis and the axis transverse to it to study the changes in the ground-state energy, stretching frequency, kinetic, and potential energies of an H molecule. For this purpose, we employ a variational approach using a suitably constructed energy estimator that goes beyond the Born–Oppenheimer approximation. We find that as the sphere moves closer to the molecule along the molecular axis, the ground-state energy and the vibrational frequencies get enhanced. On the other hand, for the same case, the potential energy decreases, and the kinetic energy increases. When the sphere moves along the axis transverse to the molecular axis, the changes in the energy and vibrational frequencies show similar trends; however, the magnitude of the changes is significantly smaller than in the corresponding molecular axis case. For the transverse case, both potential and kinetic energies get enhanced marginally. These results demonstrate that the axial approach of the hard surface is more efficient in inducing a bond breaking of the H molecular ion. The shift of the electron bond by the external sphere explains these results
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
A variational approach to the Dirichlet boundary condition: application to confined H<sup>−</sup>, He and Li
No full textVariations 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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