1,721,021 research outputs found
Atmospheric response to the 20 March 2015 solar eclipse along the whole aerosol column by lidar measurements
No full textDiurnal and nocturnal aerosol properties by AERONET sun-sky-lunar photometer measurements along four years
No full textResults on day-to-night aerosol parameters retrieved from the Cimel CE318-T photometer, operating at Lecce_University (40°20′N, 18°6′E) since October 2016, are reported. The paper aims to contribute either to the studies on the CE318-T capability for monitoring aerosols in a wide range of moon's illumination and cycles and to the studies on day-to-night columnar aerosol properties by sun-sky-lunar photometry. The reliability of lunar AODs has firstly been evaluated by analysing the AOD differences calculated from the average of the last 1 h of daytime data (AODSS) and the first 1 h of nocturnal data (AODMR), respectively. Similarly, AODMS and AODSR values have been calculated from the average of the last 1 h of nocturnal data and the first 1 h of daytime data, respectively. We found that the AOD differences (AODSS – AODMR) and (AODMS – AODSR) were within the accuracy of solar AODs. Pairwise comparison, correlation coefficients, root mean square errors, and mean bias of AODSS versus AODMR and AODMS versus AODSR also supported the lunar data reliability. The statistical analysis of solar and corresponding lunar daily means has shown that monthly and seasonal AODs from solar and lunar photometry measurements, respectively, are characterized by similar metrics. Monthly and seasonal Ångström exponents (Å) calculated at the 440–870 nm wavelength pair from daily solar and lunar AODs are also characterized by similar metrics. More specifically, pairwise comparisons by the Mann-Whitney test have shown that lunar and solar AOD and Å datasets, based on daily means, are not significantly different in all the months and the seasons at the p-level < 0.02. On the contrary, pairwise comparisons have shown that the Ångström exponent differences (ΔÅ) calculated from solar and lunar Å daily means are statistically different mainly in winter and autumn, likely for the high relative humidity at night-time. Therefore, ΔÅ has been the only intensive parameter characterized by significant day-to-night changes in autumn and winter. Some case studies have been analysed/discussed to support the paper's main results and show the seasonal changes of the aerosol properties
Relationship between the planetary boundary layer height and the particle scattering coefficient at the surface
No full textIntensive optical parameters of pollution sources identified by the positive matrix factorization technique
Full text linkA new methodology based on optical parameters from integrating nephelometer measurements and chemically speciated PM10 mass concentrations, to associate intensive optical parameters with pollution sources identified by the Positive Matrix Factorization (PMF) technique, is presented. PM10 samplings and integrating nephelometer measurements at 450, 525, and 635 nm, co-located in space and time, were performed from November 2011 to November 2012. The PM10 samples were chemically characterized for 16 species, including ions (Na+, NH4 +, K+, Mg2+, Ca2+, Cl−, NO3 −, and SO4 2−), metals (Al, Cd, Cu, Fe, Mn, and Ti), OC, and EC. The scattering σs and backscattering βs coefficients at 450, 525, and 635 nm, and the PM10 chemically speciated data were used as input of the PMF model. Traffic (TRA, 28.3%), Biomass Burning and Nitrates (BBN, 27.4%), Soil Dust (SDU, 14.7%), ammonium Sulphate (SUL, 17.0%), and Aged Sea-salt (ASS, 12.6%) were the identified pollution sources, according to the PM10 mass apportionment, which did not show any significant difference in terms of source assignment and contribution, with respect to the solution without optical variables. The possibility of retrieving intensive optical parameters associated with the pollution sources from the related spectrally resolved σs and βs values is the main feature of the proposed approach. The mass scattering efficiency (ΣPM10), the scattering Ångstrom exponent (Å), the spectral curvature of the scattering Ångstrom exponent (ΔÅ), and the asymmetry parameter (g) were the main intensive parameters calculated at different wavelengths or wavelength pairs to characterize the identified pollution sources. ΣPM10 and g at 450 nm, Å(450, 635 nm) and ΔÅ were equal to 3.4 m2 g−1, 0.57, 0.96, and 0.54 for the TRA-source, to 5.0 m2 g−1, 0.58, 1.57, and − 0.06 for the BBN-source, to 5.0 m2 g−1, 0.67, 1.54, and 0.24 for the SUL-source, and to 0.6 m2 g−1, 0.33, −0.65, and 0.12 for the ASS-source, respectively. The analysis of monitoring days with a prevailing pollution source and the comparison of the paper's results with literature values have demonstrated the reliability of the used methodology
Mineral Dust Impact on Short- and Long-Wave Radiation and Comparison with Ceres Measurements
Full text linkClear-sky downward and upward radiative flux measurements both in the short- and in the long-wave spectral range have been used to estimate and analyze the radiation changes at the surface due to the mineral dust advection at a Central Mediterranean site. Then, short- and long-wave radiative fluxes retrieved from the CERES (Clouds and the Earth’s Radiant Energy System) radiometer sensors operating on board the EOS (Earth Observing System) AQUA and TERRA platforms have been used to evaluate the mineral dust radiative impact at the top of the atmosphere. Satellite-derived radiative fluxes at the surface have been compared with corresponding ground-based flux measurements, collocated in space and time, to better support and understand the desert dust radiative impact. Results referring to the year 2012 are reported
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
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