1,720,997 research outputs found
Radiocarbon measurement tests on OC/EC fractions of atmospheric aerosol at LABEC
No full textCarbonaceous particles are among the main components of the atmospheric aerosol. They are mainly composed of soot and organic compounds. Large uncertainties still affect the estimates on source contributions, especially for what concerns natural emissions and secondary formation. The identification of natural, biomass burning, and fossil fuel combustion contributions is important for the development of efficient pollution abatement strategies and for the correct assessment of global radiative aerosol effects. 14C analysis on total carbon (TC) in atmospheric aerosol by accelerator mass spectrometry (AMS) is a good tool for the evaluation of the contributions from either fossil fuel combustion or modern sources (i.e. wood burning, biogenic activity). At our latitudes, wood burning has to be considered of anthropogenic origin; thus, further analyses are needed to identify natural and anthropogenic contributions. TC in the aerosol is composed by two main fractions: elemental (EC) and organic (OC) carbon, which have different thermal and optical properties. EC is produced only during combustion processes, while OC can be related to combustion processes or biogenic activity. Szidat et al. (2006) proposed the use of radiocarbon measurements on the separate OC and EC fractions of carbonaceous aerosol as a tool to separate natural and anthropogenic contributions. In the last years, a new sample preparation line for 14C analysis on aerosol was designed and set up at LABEC-INFN. The line was tested for TC: reproducibility, accuracy and background tests were performed, indicating that reliable results can be obtained for total carbon (Calzolai et al.,2010). In this work, the sample preparation line was tested for 14C analysis on OC and EC. Suitable sample pre-treatment procedures and thermal protocols were set up for a correct separation of the two fractions. Two different thermal protocols for EC isolation were tested. A few samples collected in Milan (Po Valley) during wintertime were analysed for TC and its fractions, thus allowing to obtain first indication on the apportionment of carbonaceous sources in the area.
References
Calzolai G., Bernardoni V., Chiari M., Fedi M., Lucarelli F., Nava S., Riccobono F., Taccetti F., Valli G., Vecchi R., Nucl. Instr. Meth. B, in press
Szidat, S., Jenk, T.M., Synal, H.-A., Kalberer, M., Wacker, L., Hajdas, I., Kasper-Giebl, A. & Baltensperger, U. (2006). J. Geophys. Res., 111 D07206 12
Pulsed proton beam as a diagnostic tool for the characterization of semiconductor detectors at high charge densities
No full textGoing 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
May 14C be used to date contemporary art?
No full textThe use of radiocarbon in forensics is by now widespread, thanks to the so-called bomb peak, which makes it possible to perform high-precision dating. Since 1955, 14C concentration in the atmosphere had strongly increased due to nuclear explosions, reaching its maximum value in 1963–1965. After the Nuclear Test Ban Treaty, 14C started to decrease as a consequence of the exchanges between atmosphere and the other natural carbon reservoirs. Nowadays, it is still slightly above the pre-bomb value. The work presented in this paper is based on the idea of exploiting the bomb peak to “precisely” date works of contemporary art, with the aim at identifying possible fakes
Characterization and diagnostics of fast X-ray imaging detectors for X-ray free electron laser sources
No full text
May 14C be used to date contemporary art?
No full textRadiocarbon dating of works of art since second half of 20th century using the "bomb spike", raised in the C14 concentration in atmosphere, is presented
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