1,354,287 research outputs found
Stability of Hydrocarbons of the Polyhedrane Family Containing Bridged CH Groups: A Case of Failure of the Colle-Salvetti Correlation Density Functionals (Erratum)
No full textDFT-computed energies of polyhedric hydrocarbons, such as dodecahedrane C20H20, its smaller analogs C16H16 and C12H12, and the larger C24H24, estimated in comparison with corresponding isomeric hydrocarbons, vary widely with the choice of the density functional. In particular, large discrepancies were observed with the functionals that are based on the B88 (as well as G96, B86) exchange and the LYP (as well as OP) correlation parts. The problem is not related to the presence of the smaller cyclopropane rings in the C12H12 polyhedrane, for its hydrogenated products do show similar errors; moreover, the larger dodecahedrane that is free from the Bayer strain shows a similar trend. DFT-D corrections that are very useful in fixing long- and medium-range correlation issues with GGA DFT do not help in this case either. We show that these errors stem from the B88 (G96, B86) exchange functionals and are not compensated by Colle-Salvetti-based GGA correlation functionals such as LYP, OP, TCA, etc. However, they can be corrected by the PBE correlation functional based on the PW92 uniform electron gas (UEG) parametrization. Range-separated hybrids (Iikura and Hirao's LC-BOP, LC-BLYP) perform much better than the parent GGAs. Comparisons of polyhedranes with a well-studied system of similar size, the set of CnHn cyclophanes, reveal a completely different performance for the latter-for instance, RHF results are the poorest, and LC-type functionals do not give any improvement, but dispersion-corrected BLYP-D performs very well. We conclude that, while for polyhedranes medium-range delocalization errors from exchange dominate, for cyclophanes, the correlation/overlap-dispersion interactions are more important. The OPTX exchange functional shows significantly lower errors compared to B88 and G96; its combinations like OLYP and especially KT3 perform well for both test sets. The OPTX-based double hybrid, O2PLYP, also outperforms the corresponding B88-based B2PLYP functional for polyhedranes. Our computations also suggest that the (CH)16 and (CH)24 polyhedranes could be possible synthetic targets
Performance of the Empirical Dispersion Corrections to Density Functional Theory: Thermodynamics of Hydrocarbon Isomerizations and Olefin Monomer Insertion Reactions
No full textMost of the commonly used approximate density functionals have systematic errors in the description of the stability of hydrocarbons. This poses a challenge for the realistic modeling of reactions involving hydrocarbons, such as olefin polymerization. Practical remedies have been proposed, including the application to usual black-box DFT of additional empirical correction CR(-6) terms for the van der Waals interaction (termed DFT-D), or introducing additional pseudopotentials that introduce some medium-to-long-range attraction (C-Pot). In this Article, we use the DFT-D scheme as realized in our BOptimize package to evaluate the performance of a range of commonly used DFT functionals (combinations of xPBE, B88, OPTX with LYP and cPBE GGAs and hybrids) for the modeling of the thermodynamics of reactions of the growth of common polyolefins. We also review and reproduce some of the previously done benchmarks in the area: alkane branching and relative stability of C12H12 and C10H16 isomers. In addition to the common DFT methods, computations with correlated wave function methods (MP2) and the new functionals B97-D and M06-L were performed. The performance of the special density functionals B97-D and M06-L is, in general, similar to the best DFT-D corrected regular functionals (BPBE-D and PBE-D). The results show that (1) the DFT-D correction is sufficient to describe alkane branching, but its performance depends on the parametrization; (2) inclusion of the correction is essential for a proper description of the thermodynamics of reactions of polymer growth; and (3) not all approximate density functionals perform effectively for the description of hydrocarbons even with the correction. The C-Pot method for the B3LYP functional shows quantitatively correct results for our test cases. The enthalpies of hydrocarbon reactions were analyzed in terms of the repulsion characteristics of a given DFT method. PBE is the least repulsive, while OLYP is the most. However, there are cases where the failure of a DFT method cannot be correlated with its repulsive character. A striking example is the performance of B3LYP and BLYP for caged molecules with small carbocycles, such as the [D3d]-octahedrane. The stability of [D3d]-octahedrane is underestimated by the B3LYP, BLYP, and B97-D functionals, but not by DFT methods that contain either B88 exchange or LYP correlation functionals separately. While DFT-D cannot amend the performance of the former functionals for the octahedrane, C-Pot for B3LYP does
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
No full text“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
No full textWe 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
No full textWe 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
A note on tail triviality for determinantal point processes
No full textWe give a very short proof that determinantal point processes have a trivial tail σ σ -field. This conjecture of the author has been proved by Osada and Osada as well as by Bufetov, Qiu, and Shamov. The former set of authors relied on the earlier result of the present author that the conjecture held in the discrete case, as does the present short proof
Author, publisher and bookseller : a tripartite synergy in Nigerian book industry
No full textThis work is about the roles of Author, Publisher and Bookseller in Book development in
Nigeria. The paper started by delving into the history of Book Publishing in Nigeria after
which it proceeded by defining who an author, a publisher, and a bookseller is and
expatiated on the indispensable roles of these key actors in Nigerian Book Industry and in
the emerging Information Society. Furthermore, the various constraints to book
development were identified while the paper advised on how the Book Industry can be
further promoted in Nigeria. However, the paper concluded and made recommendations
on how the Book sector can help in enhancing scholarship in the country
The Thursday Murder Club: Launching a megabrand author - a publishing case study
No full textIn 2020, the Christmas book charts in the UK made headlines: Barack Obama’s eagerly awaited autobiography, The Promised Land, was beaten to the top spot by The Thursday Murder Club by Richard Osman, a debut cosy crime novel set in a retirement village. Not only did Osman’s book beat the former US president’s expected bestseller, it also broke records, becoming the fastest-selling debut crime novel of all time. Although Osman has a certain level of fame in the UK from his TV appearances on shows such as Pointless, his celebrity status does not entirely explain the novel’s huge sales. This article tracks the acquisition, publication, and promotion journey of The Thursday Murder Club in order to understand the industry and cultural context of its success and to interrogate the role of celebrity in the creation of author brands. The findings suggest that the unexpected scale of the success of the book owed to a number of factors, including in-depth editing by the novel’s agent, editor, and author to tighten up the plot, an extensive and strategic promotional campaign, the pandemic (which drove interest in the book’s genre and themes), and the quality of the writing. We find that the book’s success was accentuated by Osman’s celebrity status rather than being entirely reliant on it. This research adds to the growing scholarship on celebrity authorship by means of an in-depth case study and provides insight into the processes behind publishing a ‘celebrity’ book and launching a megabrand author
A note on tail triviality for determinantal point processes
No full textWe give a very short proof that determinantal point processes have a trivial tail σ σ -field. This conjecture of the author has been proved by Osada and Osada as well as by Bufetov, Qiu, and Shamov. The former set of authors relied on the earlier result of the present author that the conjecture held in the discrete case, as does the present short proof
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