1,720,981 research outputs found
DFT-based Vibrational Spectra for THz-Spectroscopy and Defect Fingerprinting in Molecular Crystals and Solids.
No full textSpectroscopic techniques based on atomic vibrations provide a powerful tool for the
atomic scale characterization of solids. Unfortunately, the translation of their spectra into
atomistic structures tends to be an inverse-problem, as a structural model is required to
assign the observed spectral peaks. This is further complicated by the fact that the exact
position of the latter is sensitive to the precise underlying atomic structure. This results
in the need for very accurate models.
With the steady growth of computational resources, the calculation of vibrational spectra
for extended and periodic systems has become more attainable at the level of quantum
mechanical calculations. In this work, we first present the example of the THz vibrational
spectrum of lactose-monohydrate (LM), and use our results to identify the spectral lines
of the observed spectra of different phases, obtained experimentally by heating the LM
sample.1 The accompanying water loss induces two phase transitions. According to our
results, all phases, including the starting high purity commercial sample, are mixtures of
different phases. We discuss the impact of both structural—such as water content and
orientation— and methodological—such as Pulay stresses, periodic boundaries, and
supercell sizes—aspects on the calculated spectra, and show that DFT-based spectra
under periodic boundaries can be matched with experimental data.
The importance of an extended periodic system for obtaining an accurate vibrational
spectrum is also shown in studying defects in diamond. However, here, we show that the
qualitative picture of the defect character of each atom in the system is independent of
the system size, allowing for small periodic cells to determine the relevant defect atoms
at much reduced computational cost.2 Defects tend to be very localized, resulting in
atomic modes.3 Therefore, an often-used strategy for selecting the contributing atoms
considers only their relative position with regard to the defect center. Using the atomprojected
vibrational spectrum, we present a quantitative method for determining the
defect character of each atom in the system, allowing for a rational incremental
improvement of the defect spectrum. This method is then applied on several simple
defects in diamond.Author : Danny E.P. Vanpoucke
Author name needs to be updated to include middle names, and correctly linked to the uhasselt personel databas
DFT-based Vibrational Spectra for THz-Spectroscopy and Defect Fingerprinting in Molecular Crystals and Solids.
No full textSpectroscopic techniques based on atomic vibrations provide a powerful tool for the
atomic scale characterization of solids. Unfortunately, the translation of their spectra into
atomistic structures tends to be an inverse-problem, as a structural model is required to
assign the observed spectral peaks. This is further complicated by the fact that the exact
position of the latter is sensitive to the precise underlying atomic structure. This results
in the need for very accurate models.
With the steady growth of computational resources, the calculation of vibrational spectra
for extended and periodic systems has become more attainable at the level of quantum
mechanical calculations. In this work, we first present the example of the THz vibrational
spectrum of lactose-monohydrate (LM), and use our results to identify the spectral lines
of the observed spectra of different phases, obtained experimentally by heating the LM
sample.1 The accompanying water loss induces two phase transitions. According to our
results, all phases, including the starting high purity commercial sample, are mixtures of
different phases. We discuss the impact of both structural—such as water content and
orientation— and methodological—such as Pulay stresses, periodic boundaries, and
supercell sizes—aspects on the calculated spectra, and show that DFT-based spectra
under periodic boundaries can be matched with experimental data.
The importance of an extended periodic system for obtaining an accurate vibrational
spectrum is also shown in studying defects in diamond. However, here, we show that the
qualitative picture of the defect character of each atom in the system is independent of
the system size, allowing for small periodic cells to determine the relevant defect atoms
at much reduced computational cost.2 Defects tend to be very localized, resulting in
atomic modes.3 Therefore, an often-used strategy for selecting the contributing atoms
considers only their relative position with regard to the defect center. Using the atomprojected
vibrational spectrum, we present a quantitative method for determining the
defect character of each atom in the system, allowing for a rational incremental
improvement of the defect spectrum. This method is then applied on several simple
defects in diamond.Author : Danny E.P. Vanpoucke
Author name needs to be updated to include middle names, and correctly linked to the uhasselt personel databas
No Boundaries and Naturally‐Defined Boundaries Obtained via the Electrostatic Potential
No full textThis paper discusses the use of the electrostatic potential in both recent and older literature, with an emphasis upon a 2022 Molecular Physics article by Politzer and Murray entitled ”Atoms do exist in molecules: analysis using electrostatic potentials at nuclei”. We discuss electrostatic potentials at nuclei and how they easily lead to atoms in molecules, without physically separating the individual atoms. We further summarize the work by the Politzer group on definitions of atomic radii by means of the electrostatic potential. The earlier studies began in the 1970’s and continued through the 1990’s. Unfortunately, access to these older publications is often limited, cfr. digital libraries often limit the authorized access until a certain publication year, and these papers are often not cited in current publications. Although still being highly interesting and relevant, this older literature is in danger of being lost. Digging into this older literature thus opens up new views. Our feeling is that Peter passed ‘on’ a vision that boundaries do not exist between atoms in molecules, but that some useful and meaningful radii can be obtained using the electrostatic potential between atoms in molecules
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
- …
