1,721,098 research outputs found
Oxidative potential of atmospheric aerosols
Full text linkAtmospheric particulate matter (PM) is one of the leading health risks worldwide [1,2].
Several epidemiological studies have provided evidence of the association between exposure
to PM and the onset of cardiovascular and respiratory diseases [3], as well as
cardiopulmonary diseases and other adverse health effects [4]. The exact mechanisms leading
to PM toxicity are not fully known, however, several studies suggest that the generation
of reactive oxygen species (ROS) could be a major mechanism by which PM leads to both
chronic and acute adverse health effects [5,6]. For this reason, in recent years, the oxidative
potential (OP) of PM, defined as its ability to generate oxidative stress in biological systems,
has been proposed as a relevant metric for addressing PM exposure [7,8]. However, the
link between OP and adverse health effects is still uncertain [9–11], and contrasting results
have been obtained when PM oxidative potential has been compared with the results of
in-vivo and in-vitro toxicological tests or the outcomes of epidemiological studies [12].
The OP can be evaluated through several in vitro assays, but protocols employing
chemical (acellular) assays have become common as well. Acellular assays can be useful for
investigating the PM properties which are responsible for oxidative stress: ROS compounds
can either be carried by components of the aerosol itself (particle-bound ROS) or induced
by the catalytic activity exerted by aerosol constituents (PM-induced ROS). The diverse
OP assays developed so far have certainly improved our knowledge of the mechanisms
underlying PM oxidative stress. At the same time, they pose the issue of comparability
between the different assays and protocols, as well as problems surrounding the actual
correlation between acellular OP and in vitro (or in vivo) toxicity. Measurements of PM
oxidative potential are influenced by the chemical composition of the aerosol, by its size
distribution, and by the weight of different natural and anthropogenic sources of PM
leading to temporal and spatial variabilities that need investigation in current research.
Moreover, recent studies show that photochemical aging increases the oxidative potential
of atmospheric aerosols. However, several aspects regarding the specific chemical species,
aerosol sources, and atmospheric processes that affect OP are not well established, and
further research is needed [13–15]. Another topic that needs extensive research is the
characterization of the OP of indoor aerosols.
This special issue includes five research papers and two review papers discussing
recent advances in the studies of the oxidative potential of atmospheric particulate matter
Ultrafine particle features associated with pro-inflammatory and oxidative responses: Implications for health studies
Full text linkSuspected detrimental health effects associated with ultrafine particles (UFPs) are impressive. However, epidemiological evidence is still limited. This is potentially due to challenges related to UFP exposure assessment and the lack of consensus on a standard methodology for UFPs. It is imperative to focus future health studies on those UFP metrics more likely to represent health effects. This is the purpose of this paper, where we extend the results obtained during the CARE ("Carbonaceous Aerosol in Rome and Environs") experiment started in 2017 in Rome. The major purpose is to investigate features of airborne UFPs associated with pro-inflammatory and oxidative responses. Aerosol chemical, microphysical, and optical properties were measured, together with the oxidative potential, at temporal scales relevant for UFPs (minutes to hours). The biological responses were obtained using both in-vivo and in-vitro tests carried out directly under environmental conditions. Findings indicate that caution should be taken when assessing health-relevant exposure to UFPs through the conventional metrics like total particle number concentration and PM2.5 and Black Carbon (BC) mass concentration. Conversely, we recommend adding to these, a UFP source apportionment analysis and indicators for both ultrafine black carbon and the size of particles providing most of the total surface area to available toxic molecules
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
On the use of anion exchange chromatography for the characterization of water soluble organic carbon
No full textOrganic source apportionment by NMR and GC/MS techniques at two Po Valley sites in the cold season during the SUPERSITO campaign in 2013
No full textUnderstanding secondary organic aerosol (SOA) formation processes is a major challenge for the ambient aerosol science, due to the complexity of chemical matrices and the processes involved.
Several analytical techniques have been explored for aerosol organic source apportionment. Proton-nuclear magnetic resonance (H-NMR) spectroscopy is an emerging one, suitable especially for water-soluble organic carbon (WSOC), and that can be used for organic characterization in three different approaches: a) analysis of molecular tracers, b) analysis of functional groups, c) factor analysis with spectral deconvolution. The latter offers a quantitative and simplified description of the thousands of individual species. NMR “factors” extracted by factor analysis typically correspond to a large group of WSOC constituents with similar chemical composition and time trend behaviour that are characteristic of different sources and/or atmospheric processes (Zhang et al. 2011).
Two intensive field campaigns were conducted in the Po Valley, Italy, in the cold season during 2013, in February and October, in the framework of the Supersito project funded by Region Emilia-Romagna (http://www.arpa.emr.it/index.asp?idlivello=1459). Samples of fine aerosol particles (PM2.5 and PM1) were collected at an urban site (Bologna, BO) and a rural one (San Pietro Capofiume, SPC). ISAC-CNR in Bologna analysed PM1 by H-NMR spectroscopy, while Ferrara University analysed several polar organic tracers such as primary saccharides, sugar alcohols, anhydrosugars and carboxylic acids by GC/MS in PM2.5 (Pietrogrande et all. 2014).
Multivariate factor analysis (positive matrix factorization, PMF) provided four H-NMR factors at both the urban and the rural sites. Dominance of biomass burning is evident at both sites. Specifically, primary organic aerosol from biomass burning (BB-POA) accounted for 30% of WSOC in BO, and 40% in SPC. Two biomass burning secondary organic aerosol factors (BB-SOA) represented 60% of WSOC in BO and are 50% in SPC. Only 10% of WSOC could be attributed to sources other than biomass burning, at both sites.
The correlations between PMF H-NMR factors and the polar organic tracers measured by GC/MS were also evaluated. The molecular tracers included anhydrosugars, which are known biomass burning tracers, and carboxylic acids, which can be formed by traffic exhaust, photo oxidation of unsaturated carboxylic acids, oxidation of polyciclic aromatic hydrocarbons or phtalates, products of secondary photo-oxidation reactions, wood combustion. The results indicate that the anhydrosugars (levoglucosan and its isomers, galactosan and mannosan) showed good correlations with BB-POA factor at both sites. Glycolic, malic, phtalic, pimelic, 2-cheto glutaric, succinic, glutaric, adipic, azelaic acids, erythritol and arabinose showed instead high correlations with the BB-SOA factors.
In conclusion, the comparison of datasets from distinct analytical methodology proved to be particularly useful to constrain the source apportionment of the polar fraction of organic particulate matter
Ground level ice nuclei particle measurements including Saharan dust events at a Po Valley rural site (San Pietro Capofiume, Italy)
No full textFilter-collected aerosol samples in the PM1and PM10fractions and particle number concentration were measured during experimental campaigns in a rural area near Bologna (Italy) in the periods 10–21 February 2014 and 19–30 May 2014. Ice nuclei particle (INP) concentrations measured off-line showed prevalently higher average values in the morning with respect to the afternoon, in the PM1fraction with respect to PM1–10(with the exception of the first campaign, at Sw= 1.01), and at water saturation ratio Sw= 1.01 with respect to Sw= 0.96. The aerosol in the coarse size range (1–10 μm) contributed significantly to the total INP concentration. In the first campaign, the average INP concentration in the coarse fraction was 80% of the total in the morning and 74% in the afternoon, at Sw= 1.01. In the second campaign, the contribution of the coarse size fraction to the INP number concentration was lower. On the whole, the results showed that the freezing activity of aerosol diameters larger than 1 μm needs to be measured to obtain the entire INP population. Sahara dust events (SDEs) took place during both campaigns, in the periods 17–20 February and 21–23 May 2014. Results show that the averaged particle number concentration was higher during SDE than during no-Saharan dust events. A low correlation between INP and total aerosol number concentration was generally measured, except for SDEs observed in February, in which the correlation coefficient between aerosol concentration in the coarse fraction and INP in the same range, at water supersaturation, was about 0.8. Precipitation events influenced the aerosol concentration. In the February campaign, lower values of INP and particle concentrations were measured in case of heavy rain events. During the May campaign, an average number concentration of the aerosol in the range 0.5–10 μm was slightly higher than on days when no precipitation was measured, the rainfall intensity being low. Only in a few cases did we note a sharp drop in INP in the PM10fraction at Sw= 1.01 (26 May, 8 a.m. and 1 p.m.; 27 May, 1 p.m.)
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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