1,721,106 research outputs found
A G4MP2 theoretical study on the gas phase enthalpies of formation for various polycyclic aromatic hydrocarbons (PAHs) and other C~10~ through C~20~ unsaturated hydrocarbons
Full text linkGas phase enthalpies of formation at 298.15 and 1 atm (Δ~f~H~(g),298K~) were calculated using the atomization approach at the G4MP2 composite method level of theory for 86 polyaromatic hydrocarbons (PAHs) and other C~10~ through C~20~ unsaturated hydrocarbons. Where available, good agreement with prior experimental data and/or high level theoretical estimates was obtained. Linear regressions between semiempirical MNDO, MNDO-d, AM1, PM3, RM1, and PM6 estimated Δ~f~H~(g),298K~ and the corresponding G4MP2 values were employed to obtain G4MP2 corrected semiempirical Δ~f~H~(g),298K~ for a suite of 156 C~11~ through C~42~ unsaturated hydrocarbons and PAHs
Sustainability and Environmental Chemistry in Semi-Arid/Arid Regions: A Unique Research Opportunity with Global Implications
Full text linkDr. Sierra Rayne will be speaking on the interplay of sustainability and environmental chemistry in semi-arid and arid regions worldwide. Drawing on his previous, current, and proposed research on organic and inorganic contaminants in aquatic systems, Dr. Rayne will illustrate the importance of multidisciplinary and interdisciplinary approaches towards tackling environmental problems. A key element of his work is looking at chemical dynamics in environmental matrices, and in particular, photochemically generated reactive intermediates and their impact on biological systems and net ecosystem functions. Semi-arid/arid regions also offer unique opportunities to focus on the role of photochemistry in the biogeochemical cycling of oxyanion-forming heavy metals such as arsenic, molybdenum, selenium, and uranium (among others). Given the importance of semi-arid/arid regions in hosting major mineral deposits, multidisciplinary environmental chemistry research can also help make contributions towards sustainability in the worldwide mining industry. These fields offer great opportunities for researchers and students interested in semi-arid/arid landscapes, and understanding the role and impact of these regions on global contaminant fluxes is at the core of Dr. Rayne’s program
Structures, enthalpies of formation, and ionization energies for the parent and binary mixed carbon, silicon, nitrogen, and phosphorus cubane derivatives: A G4MP2 theoretical study
Full text linkGas phase standard state (298.15 K, 1 atm) structures, enthalpies of formation, and ionization energies (IEs) were calculated at the G4MP2 composite method level of theory for the parent and binary mixed carbon, silicon, nitrogen, and phosphorus cubane derivatives. Increasing nitrogen content increases the enthalpies of formation for the carbon-nitrogen, nitrogen-phosphorus, and silicon-nitrogen binary cubanes, with the opposite enthalpies of formation trend for increasing phosphorus content within the carbon-phosphorus, nitrogen-phosphorus, and silicon-phosphorus derivatives. Varying carbon/silicon content in the carbon-silicon cubanes results in no general trends for enthalpies of formation. Isomerization enthalpies within the homolog groups having more than one isomer vary widely with atomic composition and substitution patterns. Increasing nitrogen content of the carbon-nitrogen and nitrogen-phosphorus derivatives increases the IE, increasing silicon content in the carbon-silicon cubanes and phosphorus content of the carbon-phosphorus cubanes decreases the IE, while no IE clear trends are evident based on relative atomic content for the silicon-nitrogen and silicon-phosphorus compounds. The binary mixed carbon, silicon, nitrogen, and phosphorus cubane derivatives are predicted to display potentially tunable thermodynamic stability and redox behavior depending on the atom identities and relative positions
Performance of the M062X density functional against the ISOL set of benchmark isomerization energies for large organic molecules
Full text linkGas phase standard state (298.15 K, 1 atm) isomerization energies were calculated using the M062X functional with the QZVP, 6-311++G(d,p), 6-311++G(2d,2p), and cc-pVTZ basis sets against the 24 reactions in the ISOL set of benchmark isomerization energies for large organic molecules. The M062X functional appears to offer comparable isomerization energy prediction performance to the best performing currently available dispersion corrected functionals against this benchmark dataset
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
Gas phase homolytic bond dissociation enthalpies of common laboratory solvents: A G4 theoretical study
Full text linkGas phase standard state (298.15 K, 1 atm) calculations were conducted at the Gaussian-4 (G4) composite method level of theory to estimate the bond dissociation enthalpies (BDEs) of various common laboratory solvents. Excellent agreement was obtained between experimental and G4 estimated BDEs. The current study demonstrates the BDE prediction accuracy of the G4 method, and is also intended to function as a potentially useful resource in any reevaluations of the preferred BDEs for these common laboratory solvents
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
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