1,720,986 research outputs found
Foreste che infiammano il clima
No full textThe chemical mechanisms that occur during a forest fire event generate high quantity of particulate matter, greenhouse gases and a lot of
other compounds which affect atmospheric dynamics, biogeochemical cycles of the elements and create persistent haze of unbreathable air. Since the Neolithic, fires were used by men for land clearance. First farmers and ranchers needed to grow cereals and to graze cattle, and fire
as the fastest way to obtain free lands for these purposes. Nowadays, fire still remains the most used and cheapest instrument to get new
lands ready for plantations. The worst threat from fires seems to be happening in Indonesia, where companies are uncontrollably burning a
lot of forests, both legally and illegally, and selling the burned fields to palm oil firms, in a big fire-business at the expenses of the environmental quality. Local and global climate changes, air pollution, worsening human health and biodiversity loss are the outcomes of this increasingly intense biomass-burning process
Biomass burning reconstruction analysing lacustrine sediment cores from the Tibetan plateau
No full textThe present PhD research gives information about Holocene fire events and vegetation changes occurred in the Tibetan Plateau. Asiatic region is a strategic area to explore biomarkers accumulated in lacustrine sedimentary cores during the past millennia. In order to improve the scientific knowledge in this area, sediment samples from lakes Paru Co and Hala Hu, in the South-Eastern and North-Eastern Tibetan Plateau respectively, were analysed. Accelerated Solvent Extraction technique was used to extract organic compounds from the samples. Analyses were performed with gas and liquid chromatographers coupled with mass spectrometers. The molecules of interest are monosaccharide anhydrides (MAs), specific markers of vegetation fires, polycyclic aromatic hydrocarbons, as combustion proxies, n-alkanes, indicators of vegetation, and faecal sterols, indicators of past human and grazing animals presence. Paru Co MAs results show that a very high intensity of biomass burning recorded in the Early Holocene samples is parallel with the drier climate of the same period, following the deglaciation. The local ecosystem and vegetation changes are in agreement with intensity’s variations in the Indian Summer Monsoon rainfall. Hala Hu MAs results instead show higher fire intensity between 4.5 and 7 ky BP. The information obtained from these organic geochemical data were compared with other records and charcoal data, allowing the contextualization of the biomass burning events
PALEOMIGRAZIONI E TRACCIATI CLIMATICI
No full textNeolithic’s migrations are useful tools to understand the human influence on the environment in all continents of the planet. During this period, especially in Asia, man began to cultivate the land and to raise animals, and this may have had a pre-industrial impact on Earth's climate. Traces left by humans in the environment do not consist only in historical and archaeological finds but also in biological and chemical indicators that accumulated in soils and sediments over the past millennia. Collecting and radiodating these environmental matrices and analyzing samples in the labs, the partial reconstruction of past human activities in the studied area is possible. Then, the comparison with historical and archeological data is needed, and with this multidisciplinary approach we aim to have a global view of the matter
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
Multi-biomarker analysis of sediments for paleoclimate research
Full text linkLacustrine sedimentary cores provide continuous records of large-scale and local environmental modifications, intelligible thanks to specific organic markers that accumulated in these archives during past millennia. In order to improve our knowledge on ecosystem changes due to biomass burning events and human presence during the Holocene, an effective analytical method to detect organic compounds contained in sediment samples is needed.
We used Accelerated Solvent Extraction (ASE) technique followed by analysis with gas and liquid chromatographers coupled with mass spectrometers (GC-MS, IC-MS). The extraction of the molecules of interest from the sediments is made with a mixture of DCM:MeOH 9:1 v/v and it is followed by a 3 steps purification with silica gel columns. The first fraction is eluted with HEX:DCM 9:1 v/v and contains n-alkanes, indicators of vegetation, and polycyclic aromatic hydrocarbons (PAHs) as combustion proxies. Then, a second fraction is eluted with DCM and derivatized with the silylation process, in order to get the faecal sterols and stanols (FeSts), indicators of past human and grazing animals presence. These two fractions are analysed with the GC-MS technique. The third and last fraction is eluted with MeOH and contains the monosaccharide anhydrides (MAs), specific indicators of vegetation burning processes, which are analysed with IC-MS. Internal standards labelled C13 are used for the quantification and procedural blanks are extracted every batch of 12 samples.
The method may undergo variations, on the basis of the complex sediment matrices which not always lend itself to the same kind of treatment. However, the technique was applied in different lakes from different continents and the obtained results, compared with historical and climate literature data, seem to demonstrate the potentiality of the method as a resourceful instrument to reconstruct past burning events and human-ecosystem interactions
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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