1,721,133 research outputs found
Resolution of the mediators of in vitro oxidative reactivity in size-segregated fractions that may be masked in the urban PM10 cocktail
Full text linkPM10 (particulate matter 10μm or less in aerodynamic diameter) has consistently been linked with adverse human health effects, but the physicochemical properties responsible for this effect have not been fully elucidated. The aim of this work was to investigate the potential for carbon black (CB) particles and PM to generate ROS (Reactive Oxygen Species) and to identify the physicochemical properties of the particles responsible for in vitro oxidative reactivity (OR). PM10 was collected in 11 size fractions at a traffic site in Swansea, UK, using an Electrical Low Pressure Impactor (ELPI). The PM physicochemical properties (including size, morphology, type, and transition metals) were tested. The plasmid scission assay (PSA) was used for OR testing of all particles. The ultrafine and fine PM fractions (N28-2399; 28-2399nm) caused more DNA damage than coarse PM (N2400-10,000), and the increased capacity of the smaller particles to exhibit enhanced (OR) was statistically significant (p<0.05). The most bioreactive fraction of PM was N94-155 with a toxic dose (TD50; mass dose capable of generating 50% plasmid DNA damage) of 69μg/ml. The mean TD35 was lower for PM than CB particles, indicating enhanced OR for PM. A difference between CB and PM in this study was the higher transition metal content of PM. Zn was the most abundant transition metal (by weight) in the ultrafine-fine PM fractions, and Fe in the fine-coarse PM. Through this comparison, part of the observed increased PM OR was attributed to Zn (and Fe). In this study PM-derived DNA damage was dependent upon; 1) particle size, 2) surface area, and 2) transition metals. This study supports the view that ROS formation by PM10 is related to physicochemistry using evidence with an increased particle size resolution
Linking particle number concentration (PNC), meteorology and traffic variables in a UK street canyon
Full text linkAmbient particle number concentration (PNC) has been linked with adverse health outcomes such as asthma, reduced lung function and cardiovascular disease. To investigate the relationship between PNC, meteorology and traffic we measured size segregated respirable particles in a busy commuter street in Swansea, UK for ten months using a Dekati Electrical Low Pressure Impactor (ELPI). The ELPI segregates particles into 12 size fractions between 7 nm and 10 ?m. The median PNC for the sampling period was 31,545 cm? 3. For the ultrafine particles (7–93 nm), the highest PNC was found in winter (46,615 cm? 3; 15 minute average) and the lowest for that size fraction in summer (29,696 cm? 3). For the particles below 93 nm there was a trimodal distribution to weekdays (particularly Monday to Wednesday), with PNC peaks at 09:00, 16:00 and 23:00. Wind direction had a significant influence on PNC and differed between particles in the fine range (below 2.5 ?m) and more coarse particles (up to 10 ?m). For fine particles, winds parallel to the canyon were associated with higher PNCs which were attributed to the replenishment of traffic particles. For coarse particles, PNCs were higher from winds perpendicular to the canyon and this was linked to source distribution around the sampling site and the recirculation of pollutants within the canyon. During times when vehicle volumes were high and vehicles were exhibiting stop–start behaviour, if this was combined with low wind speeds, ultrafine PNC was highest. This effect was generally observed during the morning rush hour. Current mass-based legislation does not take into account exposure to the number of particles or the change in population exposure diurnall
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
Airborne particles in Swansea, UK: their collection and characterization
No full textUrban air particulate matter (PM) has previously been associated with a variety of adverse health effects. It is now believed that the smallest particles, ultrafine or nanoparticles, are linked to the greatest health effects. The physicochemistry of these particles is likely to provide information regarding their toxicity. Therefore, the aim of this study was to further the understanding of the heterogeneous and changing particle concentrations in urban air, in conjunction with gaining an understanding of the physicochemistry of the particles. A Dekati electrical low-pressure impactor was used to collect the particles and real-time data in a busy traffic corridor in Swansea, Wales, over a period of 10 nonconsecutive weeks. Particle concentrations in the street canyon were analyzed and particle physicochemistries investigated using a variety of techniques. Particle number concentrations were found to vary both diurnally and from day to day in the traffic corridor. Of all particles, the nano to fine size fraction was consistently identified in the highest concentrations (maximum: 140,000 particles cm-3). Particle physicochemistry was found to vary as a function of size, with larger particles exhibiting a greater variety of morphologies (and consequently particle types) and associated metals
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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