1,721,290 research outputs found
Energetics of the OH radical H-abstraction reactions from simple aldehydes and their geminal diol forms
Full text linkContextCarbonyl compounds, especially aldehydes, emitted to the atmosphere, may suffer hydration in aerosols or water droplets in clouds. At the same time, they can react with hydroxyl radicals which may add or abstract hydrogen atoms from these species. The interplay between hydration and hydrogen abstraction is studied using density functional and quantum composite theoretical methods, both in the gas phase and in simulated bulk water. The H-abstraction from the aldehydic and geminal diol forms of formaldehyde, acetaldehyde, glycolaldehyde, glyoxal, methylglyoxal, and acrolein is studied to determine whether the substituent has any noticeable effect in the preference for the abstraction of one form or another. It is found that abstraction of the H-atom adjacent to the carbonyl group gives a more stable radical than same abstraction from the geminal diol in the case of formaldehyde, acetaldehyde, and glycolaldehyde. The presence of a delocalizing group in the C alpha (a carbonyl group in glyoxal and methylglyoxal, and a vinyl group in acrolein), reverts this trend, and now the abstraction of the H-atom from the geminal diol gives more stable radicals. A further study was conducted abstracting hydrogen atoms from the other different positions in the species considered, both in the aldehydic and geminal diol forms. Only in the case of glycolaldehyde, the radical formed by H-abstraction from the -CH2OH group is more stable than any of the other radical species. Abstraction of the hydrogen atom in one of the hydroxyl groups in the geminal diol is equivalent to the addition of the center dot OH radical to the aldehyde. It leads, in some cases, to decomposition into a smaller radical and a neutral molecule. In these cases, some interesting theoretical differences are observed between the results in gas phase and (simulated) bulk solvent, as well as with respect to the method of calculation chosen.MethodsDFT (M06-2X, B2PLYP, PW6B95), CCSD(T), and composite (CBS-QB3, jun-ChS, SCVECV-f12) methods using Dunning basis sets and extrapolation to the CBS limit were used to study the energetics of closed shell aldehydes in their keto and geminal-diol forms, as well as the radical derived from them by hydrogen abstraction. Both gas phase and simulated bulk solvent calculations were performed, in the last case using the Polarizable Continuum Model
Trends of PM1 aerosol chemical composition, carbonaceous aerosol, and source over the last 10 years at Melpitz (Germany)
Full text linkSubmicron particles (PM 1) play a critical role in air quality, climate, and human health. Long-term monitoring is essential to identify changes in atmospheric composition driven by natural or anthropogenic emissions and processes. This study presents ten years of continuous measurements (Sept. 2012–Aug. 2022) at the TROPOS Melpitz research station in Germany, a Central European rural background site influenced by its location between Eastern and Western Europe. Using an aerosol chemical speciation monitor (ACSM) and a multi-angle absorption photometer (MAAP), alongside a rolling positive matrix factorization (PMF) model for organic aerosol (OA) source apportionment, we analyzed PM 1 trends, chemical composition, and source contributions over a decade. The results reveal a significant negative PM 1 trend of −4.59% y−1 , with pronounced decreases occurring in fall and winter. Eastern air masses showed marked improvements (− 28% y-1), likely reflecting regional mitigation policies. OA, contributing 44% of total PM1 , showed a negative trend of −2.05% y−1 and comprised three primary OA (POA) sources—hydrocarbon-like OA (HOA), biomass burning OA (BBOA), and coal combustion OA (CCOA)—and two oxygenated OA (OOA) factors (less-oxidized and more-oxidized OA, LO-OOA and MO-OOA). HOA (7% of total OA) remained relatively stable, with a minor decline (− 0.25% y-1) under Eastern air masses. In contrast, BBOA (10% of OA) and CCOA (12% of OA) displayed strong seasonality, driven by residential heating and energy production. Notably, BBOA increased by +0.48 % y−1 during summer, likely due to the rise in wood pellet heating, recreative, and/or wildfires, while CCOA showed a modest increase (+0.27% y-1) in Western air masses. The OOA factors, LO-OOA and MO-OOA (31% and 40% of OA, respectively), reflected distinct seasonal patterns tied to atmospheric formation pathways. Both showed declining trends in Eastern air masses (− 1.52% y-1 and − 1.09% y-1), indicating changes in biogenic emissions and/or anthropogenic precursors. Finally, eBC(PM 1) decreased by-1.3 % y-1 with strong source dependency. Compared to urban areas, the overall decrease of PM mass concentration and anthropogenic OA looks limited, emphasizing a potentially lower effect of political mitigation outside cities. Overall, the findings underscore the importance of monitoring long-term changes in P 1 composition and sources, which are crucial for understanding aerosol physical properties, refining climate models and public health, and evaluating the impacts of mitigation efforts on air quality and climate in different environments. Further studies on a similar approach are strongly needed to better understand the geographical variation of the aerosol chemical composition and evaluate their potential effect
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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