1,721,137 research outputs found
POLLEN RECORDS, POSTGLACIAL | South America
No full textThe postglacial pollen records from South America indicate that different ecosystems were not stable during the Holocene. The variation in Atlantic sea level was probably the major factor in paleoenvironmental changes for the low-lying Amazon Basin region. Large areas of seasonally inundated Várzea and Igapó forests developed after about 3,000 yr. Relatively high water stands might also be due to greater annual rainfall in western, central, and eastern Amazonia, which is also indicated by the marked expansion of Amazon rainforest, both north and south of the equator since the mid-Holocene, but especially during the late Holocene period. This climate change contrasts with that of the Caatinga region in northeastern Brazil. Evidence of significant vegetational and climate change is also found in southeastern Brazil by the marked expansion of semideciduous forest and Atlantic rainforest reducing the Cerrado area during mid- and late Holocene and in southern Brazil by the expansion of Araucaria forests, reducing the area of Campos during the late Holocene, specially during the last 1 kyr. The amount of annual precipitation must have been higher and the length of the annual dry season must have been shorter than during early and mid-Holocene times. The strongest human impact is evident from pollen records specially for the late Holocene period
Holocene vegetation and environmental changes of peat ecosystems in southwestern and northeastern Amazonia
No full texthttp://dx.doi.org/10.13039/501100004543 China Scholarship Counci
Pollen-based temperature and precipitation inferences for the montane forest of Mt. Kilimanjaro during the last Glacial and the Holocene
No full textThe relationship between modern pollen-rain taxa and measured climate variables was explored along the elevational gradient of the southern slope of Mt. Kilimanjaro, Tanzania. Pollen assemblages in 28 pollen traps positioned on 14 montane forest vegetation plots were identified and their relationship with climate variables was examined using multivariate statistical methods. Canonical correspondence analysis revealed that the mean annual temperature, mean annual precipitation and minimum temperature each account for significant fractions of the variation in pollen taxa. A training set of 107 modern pollen taxa was used to derive temperature and precipitation transfer functions based on pollen subsets using weighted-averaging-partial-least-squares (WA-PLS) techniques. The transfer functions were then applied to a fossil pollen record from the montane forest of Mt. Kilimanjaro and the climate parameter estimates for the Late Glacial and the Holocene on Mt. Kilimanjaro were inferred. Our results present the first quantitatively reconstructed temperature and precipitation estimates for Mt Kilimanjaro and give highly interesting insights into the past 45 000 yr of climate dynamics in tropical East Africa. The climate reconstructions are consistent with the interpretation of pollen data in terms of vegetation and climate history of afro-montane forest in East Africa. Minimum temperatures above the frostline as well as increased precipitation turn out to be crucial for the development and expansion of montane forest during the Holocene. In contrast, consistently low minimum temperatures as well as about 25% drier climate conditions prevailed during the pre LGM, which kept the montane vegetation composition in a stable state. In prospective studies, the quantitative climate reconstruction will be improved by additional modern pollen rain data, especially from lower elevations with submontane dry forests and colline savanna vegetation in order to extend the reference climate gradient
Holocene vegetation dynamics, carbon deposition, sea level changes, and human impact inferred from the Lagoa da Fazenda core in the Baía de Caxiuanã region, Northern Brazil
No full texthttp://dx.doi.org/10.13039/501100003593 Conselho Nacional de Desenvolvimento Cientifico e Tecnologicohttp://dx.doi.org/10.13039/501100004543 China Scholarship Counci
Amazonian mangrove dynamics during the last millennium: The relative sea-level and the Little Ice Age
No full text
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
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