1,720,990 research outputs found
Mass Spectrometric Analysis of Organic Aerosol Composition: Laboratory and Ambient
Get PDFOrganic compounds contribute a significant mass fraction of ambient aerosol and play a role in determining the physiochemical properties of ambient aerosol. A significant fraction of organic aerosol is secondary organic aerosol (SOA), which is produced when the volatile organic compounds (VOCs) originated from various anthropogenic and biogenic sources react with atmospheric oxidants such as ozone, hydroxyl radicals, and nitrate radicals to form lower volatility organic compounds, which subsequently partition into the particle phase. Understanding the composition of ambient aerosol is crucial for identifying their sources and formation mechanisms and predicting their properties and effects on various ambient processes. This thesis focuses on investigating the composition of laboratory–generated SOA formed from the oxidation of biogenic VOCs of atmospheric importance (isoprene and β–caryophyllene) and ambient aerosol collected in the field campaigns using advanced mass spectrometric techniques. By comparing the mass spectrometric data collected for the both laboratory–generated SOA and ambient aerosol, we propose reaction pathways and new chemical tracers for these biogenic VOCs, which enhance our knowledge of the composition, sources, and formation pathways of SOA in the atmosphere. With a better knowledge of the SOA composition, a product–specific model is proposed to predict the composition and aerosol mass yields (mass of SOA formed per mass of hydrocarbon reacted) of laboratory–generated α–pinene SOA
Experimental measurements of phase transition and hygroscopic growth of water-soluble organic compounds in atmospheric aerosols
No full textThe hygroscopicity, the water uptake property, of atmospheric aerosols describes the interaction between water vapor and aerosols. It affects the phase, size, and chemical composition of aerosols, and thus influences many atmospheric processes such as cloud activation activity, light scattering, and chemical reactions. Recent studies have revealed that organic species derived from biomass burning, amino acids, and macromolecular polyacids contribute to a substantial portion of water-soluble organic compounds (WSOC) and the aerosol mass. This thesis focuses on studying the hygroscopicity of particles of these three major groups of WSOC using the single particle levitation technique in an electrodynamic balance (EDB). The hygroscopic measurements were performed by equilibrating singly levitated particles at different relative humidity (RH) in the EDB for in-situ mass determination.Levoglucosan, marnosan, and galactosan are commonly detected in the biomass burning aerosols, derived from the combustion of cellulose. The particles of these species exist as highly concentrated solutions at RH as low as 5%. Our results suggest that biomass burning aerosols, which contain these non-crystallizing organic species, may not be completely dry and absorb water at low RH. Our results support the reports in the literature that the light scattering coefficient of biomass burning aerosols starts to increase with increasing RH, even at low RH.Crystallization was observed in some amino acid particles (glycine, alanine, serine, glutamine, and threonine) upon evaporation of water while no phase transition was observed in some others (arginine and asparagine), even at 5%RH. Best fittings of the literature and experimental data with the model estimates yield a new set of UNIFAC interaction parameters that give predictions to within 15% of the measurements up to the supersaturation regime for atmospheric application.Water-soluble macromolecular polyacids have molecular structures similar to natural fulvic acids (FA) and are referred to as humic-like substances (HULIS). The role of HULIS on the hygroscopicity of atmospheric aerosols was studied using their model compounds: two natural FA: Nordic Aquatic Fulvic Acid (NAFA) and Suwannee River Fulvic Acid (SRFA). The NAFA and SRFA particles absorbed and desorbed water reversibly without crystallization and retained water at RH < 10%. Our measurements of the crystallization characteristics of these natural FA particles are different from the literature data of another natural FA. The differences are attributed to the difference in the composition of the natural FA, which depends the isolation methods. A standardization of the isolation methods of natural FA and HULIS in atmospheric aerosols is needed for a more systematic understanding their hygroscopicity and their role on the properties of atmospheric aerosols.</p
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
Variations 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
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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