1,720,968 research outputs found
Understanding the long-term trends and seasonality of Arctic atmospheric aerosol : Through the lens of black carbon and new particle formation
No full textThe Arctic region is witnessing changes on an unprecedented level. Surface air temperatures have increased at a rate four times the global average. Two of the main climate forcers that are responsible for perturbing the radiative balance in the Arctic are greenhouse gases and atmospheric aerosols. Aerosols are tiny solid or liquid particles suspended in the atmosphere that range in size from a few nanometres to tens of microns. These particles affect the climate by interacting with radiation and influencing cloud formation, brightness, and longevity. The work presented in this thesis aims to improve our understanding of the drivers and mechanisms involved in controlling both the seasonal variations and the long-term changes in Arctic aerosols, and analyse the general aerosol lifecycle. In a changing Arctic, both the emissions of anthropogenic and natural aerosol particles have and are expected to continue to change. For one, the long-range transport of anthropogenic aerosols is likely to continue to decline with reductions in emissions. Measurements of Arctic aerosols were carried out at a research observatory on Svalbard. In this thesis, a variety of instrumentation and measurements were used to assess seasonal and long-term changes in various aerosol-related variables. The work in this thesis shows that the concentration of light-absorbing aerosol particles has decreased significantly over the past two decades, with the largest decrease in contributions from northern Siberia. This thesis argues that a quarter of the overall reduction is due to changes to the removal processes via wet scavenging. In this thesis, the changes in environmental parameters along the transport pathway to the site are explored. From this perspective, precipitation is shown to act as both a source and a sink, impacting the number of particles depending on their size, whilst solar radiation is shown to promote an increase in the number of aerosol particles over the entire size spectrum. Furthermore, using the first long-term time series measuring light-absorbing particles inside and outside of clouds, the process of nucleation scavenging is explored. Increased uptake of light-absorbing particles into cloud droplets is presented from April until October. Incorporation of these particles into cloud droplets is shown to be dependent on temperature and cloud water content. Lastly, the frequency in the production of small particles, barely a nanometre in diameter, in the vicinity of Svalbard is shown to be heavily influenced by solar radiation and the total surface area of pre-existing aerosol particles. The Greenland Sea is shown to be a relatively larger source of these small particles compared to neighbouring seas. Its shown that the total surface area of pre-existing aerosols within airmasses is reduced through cloud and precipitation events, setting the stage for new particle formation and the replenishment of aerosol particles in the presence of solar radiation. Understanding how these findings can be broadened and applied across a larger geographical region remains to be answered. Additionally, the overall effect these mechanisms and changes can have on the radiative balance in the Arctic requires further exploration
Understanding the long-term trends and seasonality of Arctic atmospheric aerosol : Through the lens of black carbon and new particle formation
No full textThe Arctic region is witnessing changes on an unprecedented level. Surface air temperatures have increased at a rate four times the global average. Two of the main climate forcers that are responsible for perturbing the radiative balance in the Arctic are greenhouse gases and atmospheric aerosols. Aerosols are tiny solid or liquid particles suspended in the atmosphere that range in size from a few nanometres to tens of microns. These particles affect the climate by interacting with radiation and influencing cloud formation, brightness, and longevity. The work presented in this thesis aims to improve our understanding of the drivers and mechanisms involved in controlling both the seasonal variations and the long-term changes in Arctic aerosols, and analyse the general aerosol lifecycle. In a changing Arctic, both the emissions of anthropogenic and natural aerosol particles have and are expected to continue to change. For one, the long-range transport of anthropogenic aerosols is likely to continue to decline with reductions in emissions. Measurements of Arctic aerosols were carried out at a research observatory on Svalbard. In this thesis, a variety of instrumentation and measurements were used to assess seasonal and long-term changes in various aerosol-related variables. The work in this thesis shows that the concentration of light-absorbing aerosol particles has decreased significantly over the past two decades, with the largest decrease in contributions from northern Siberia. This thesis argues that a quarter of the overall reduction is due to changes to the removal processes via wet scavenging. In this thesis, the changes in environmental parameters along the transport pathway to the site are explored. From this perspective, precipitation is shown to act as both a source and a sink, impacting the number of particles depending on their size, whilst solar radiation is shown to promote an increase in the number of aerosol particles over the entire size spectrum. Furthermore, using the first long-term time series measuring light-absorbing particles inside and outside of clouds, the process of nucleation scavenging is explored. Increased uptake of light-absorbing particles into cloud droplets is presented from April until October. Incorporation of these particles into cloud droplets is shown to be dependent on temperature and cloud water content. Lastly, the frequency in the production of small particles, barely a nanometre in diameter, in the vicinity of Svalbard is shown to be heavily influenced by solar radiation and the total surface area of pre-existing aerosol particles. The Greenland Sea is shown to be a relatively larger source of these small particles compared to neighbouring seas. Its shown that the total surface area of pre-existing aerosols within airmasses is reduced through cloud and precipitation events, setting the stage for new particle formation and the replenishment of aerosol particles in the presence of solar radiation. Understanding how these findings can be broadened and applied across a larger geographical region remains to be answered. Additionally, the overall effect these mechanisms and changes can have on the radiative balance in the Arctic requires further exploration
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
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
Drivers controlling black carbon temporal variability in the lower troposphere of the European Arctic
No full textISSN:1680-7324ISSN:1680-7375ISSN:1680-737
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