1,721,045 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Try Everything: Coupling Phytolith and Isotope Records to Reconstruct South American Landscapes During Global Warming and Cooling Events of the Cenozoic
No full textThesis (Ph.D.)--University of Washington, 2025The Intergovernmental Panel on Climate Change (IPCC, 2024) predicts that, regardless of policy changes, atmospheric CO₂ levels, and consequently, global temperatures, will rise over the next century to levels unprecedented in human history. However, these levels are not unprecedented in Earth's geologic past. Over the Cenozoic (the last 66 million years), global climate has undergone repeated warming and cooling episodes driven by fluctuations in atmospheric CO₂, superimposed on a long-term trend of cooling and declining pCO₂. To better predict how future climate change may affect global ecosystems, we can turn to the fossil record to examine how climate and biospheres responded to similar variability in the past.In this dissertation, I combine phytolith (opaline silica particles deposited in or around plant cells) and isotope records to reconstruct landscape evolution in South America during periods of global climate warming and cooling in the early and late Cenozoic. I also conduct a modern reference study to test and compare the spatial resolution of phytolith assemblages and isotope signatures across a spatially complex landscape.In Chapter 1, I explore the evolutionary history of lowland vegetation in southern South America during the Paleocene and Eocene using phytolith records. Previous reconstructions, including some paleobotanical data, proposed that grass-dominated ecosystems may have existed in the region at this time, contradicting global patterns of grassland evolution and other fossil evidence. I present a basin-wide phytolith analysis of Paleocene and Eocene terrestrial deposits from the San Jorge Basin, Argentine Patagonia. This expands on earlier phytolith studies and integrates new radiometric dates to provide a temporally resolved reconstruction of early Cenozoic vegetation. My results show that forests dominated lowland ecosystems from the Paleocene through the middle Eocene. Palm abundance increased from the middle to late Eocene as these forests began transitioning to cooler, drier, and more open vegetation types. These findings are supported by paleobotanical, geochemical, and faunal records. Grasses remained rare and were likely restricted to forest understories until at least the Early or Middle Miocene, challenging hypotheses that propose extensive early Cenozoic grassy habitats in South America.
In Chapter 2, I test the spatial resolution of phytolith assemblages across a heterogeneous landscape and compare them to the carbon isotope composition of the soil organic matter from which they were extracted. This study addresses a key uncertainty in fossil phytolith interpretation: to what extent do phytoliths reflect local versus regional vegetation? This is especially important for fossil reconstructions, where sample coverage is often sparse. Can we detect vegetation heterogeneity from just a few assemblages? How do phytolith signals compare to carbon isotopes, a widely used proxy for vegetation structure? To explore this, I analyzed samples from three transects in the piedmont of the Eastern Colombian Andes, a region that includes grasslands, forests, and palm swamps, each sharply demarcated. My results show that phytolith assemblages reflect both the vegetation at the collection site and surrounding plant communities. Phytoliths and carbon isotopes capture overlapping but distinct aspects of vegetation structure and are most powerful when used together. Additionally, phytoliths can offer insight into fire regimes, potentially indicating where and what kinds of vegetation were burning. These results underscore the value of phytoliths for reconstructing vegetation heterogeneity and fire history in both modern and ancient ecosystems.
In Chapter 3, I focus on a cooling period that followed the last major Cenozoic warming event, the Miocene Climatic Optimum (17 to 15 million years ago). This subsequent cooling, is recorded in the fossil-rich deposits of La Venta, a semi-arid region in Colombia. Despite its significance as one of the most important vertebrate fossil sites in the Neotropics, little is known about the vegetation that supported its fauna or how tropical climate changed during this time. To address these gaps, I use phytoliths and clumped isotope paleothermometry to reconstruct vegetation and climate between 14 and 7 million years ago. The results suggest that the region remained forested throughout the interval and that vegetation density increased as local temperatures cooled and seasonal rainfall may have intensified, creating more humid conditions overall. These findings contrast sharply with climate models that predict drying across the tropics during the Miocene Climatic Transition and provide the first terrestrial temperature record for tropical South America during this time. This discrepancy highlights the importance of regional proxy records in validating and improving global climate models
Variations on the Author
Get PDF“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
Try Everything: Coupling Phytolith and Isotope Records to Reconstruct South American Landscapes During Global Warming and Cooling Events of the Cenozoic
No full textThesis (Ph.D.)--University of Washington, 2025The Intergovernmental Panel on Climate Change (IPCC, 2024) predicts that, regardless of policy changes, atmospheric CO₂ levels, and consequently, global temperatures, will rise over the next century to levels unprecedented in human history. However, these levels are not unprecedented in Earth's geologic past. Over the Cenozoic (the last 66 million years), global climate has undergone repeated warming and cooling episodes driven by fluctuations in atmospheric CO₂, superimposed on a long-term trend of cooling and declining pCO₂. To better predict how future climate change may affect global ecosystems, we can turn to the fossil record to examine how climate and biospheres responded to similar variability in the past.In this dissertation, I combine phytolith (opaline silica particles deposited in or around plant cells) and isotope records to reconstruct landscape evolution in South America during periods of global climate warming and cooling in the early and late Cenozoic. I also conduct a modern reference study to test and compare the spatial resolution of phytolith assemblages and isotope signatures across a spatially complex landscape.In Chapter 1, I explore the evolutionary history of lowland vegetation in southern South America during the Paleocene and Eocene using phytolith records. Previous reconstructions, including some paleobotanical data, proposed that grass-dominated ecosystems may have existed in the region at this time, contradicting global patterns of grassland evolution and other fossil evidence. I present a basin-wide phytolith analysis of Paleocene and Eocene terrestrial deposits from the San Jorge Basin, Argentine Patagonia. This expands on earlier phytolith studies and integrates new radiometric dates to provide a temporally resolved reconstruction of early Cenozoic vegetation. My results show that forests dominated lowland ecosystems from the Paleocene through the middle Eocene. Palm abundance increased from the middle to late Eocene as these forests began transitioning to cooler, drier, and more open vegetation types. These findings are supported by paleobotanical, geochemical, and faunal records. Grasses remained rare and were likely restricted to forest understories until at least the Early or Middle Miocene, challenging hypotheses that propose extensive early Cenozoic grassy habitats in South America.
In Chapter 2, I test the spatial resolution of phytolith assemblages across a heterogeneous landscape and compare them to the carbon isotope composition of the soil organic matter from which they were extracted. This study addresses a key uncertainty in fossil phytolith interpretation: to what extent do phytoliths reflect local versus regional vegetation? This is especially important for fossil reconstructions, where sample coverage is often sparse. Can we detect vegetation heterogeneity from just a few assemblages? How do phytolith signals compare to carbon isotopes, a widely used proxy for vegetation structure? To explore this, I analyzed samples from three transects in the piedmont of the Eastern Colombian Andes, a region that includes grasslands, forests, and palm swamps, each sharply demarcated. My results show that phytolith assemblages reflect both the vegetation at the collection site and surrounding plant communities. Phytoliths and carbon isotopes capture overlapping but distinct aspects of vegetation structure and are most powerful when used together. Additionally, phytoliths can offer insight into fire regimes, potentially indicating where and what kinds of vegetation were burning. These results underscore the value of phytoliths for reconstructing vegetation heterogeneity and fire history in both modern and ancient ecosystems.
In Chapter 3, I focus on a cooling period that followed the last major Cenozoic warming event, the Miocene Climatic Optimum (17 to 15 million years ago). This subsequent cooling, is recorded in the fossil-rich deposits of La Venta, a semi-arid region in Colombia. Despite its significance as one of the most important vertebrate fossil sites in the Neotropics, little is known about the vegetation that supported its fauna or how tropical climate changed during this time. To address these gaps, I use phytoliths and clumped isotope paleothermometry to reconstruct vegetation and climate between 14 and 7 million years ago. The results suggest that the region remained forested throughout the interval and that vegetation density increased as local temperatures cooled and seasonal rainfall may have intensified, creating more humid conditions overall. These findings contrast sharply with climate models that predict drying across the tropics during the Miocene Climatic Transition and provide the first terrestrial temperature record for tropical South America during this time. This discrepancy highlights the importance of regional proxy records in validating and improving global climate models
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
From Cells to Canopies: Reconstructing Vegetation Structure and its Response to Climate Change in the Middle Cenozoic of Patagonia Using Phytolith Morphology
No full textThesis (Ph.D.)--University of Washington, 2013Reconstructing ancient ecosystems to answer outstanding questions in paleoecology requires a multidisciplinary approach. This dissertation research integrates geochronology and conventional phytolith analysis, with a new method for reconstructing vegetation structure (Leaf Area Index) based on the response of epidermal cell (and phytolith) morphology to light. First, a highly resolved U-Pb dated chronology provides precise ages for a densely sampled phytolith record of fossil samples ranging from 42-18 Ma. Second, two experiments were conducted to examine epidermal cell response to varying levels of light. Based on the observation that epidermal cells of shade leaves are more undulated and larger than those of sun leaves in several species of dicots, the first study tested whether this same pattern occurs in grasses in a controlled growth experiment. We found that grass cell undulation is not affected by light, but their morphology changes in other ways. For instance, grass cells tend to have longer epidermal cells in the shade treatments, though this pattern was not found in all species. The second experiment tests the same idea, but uses a different approach. Instead, it tests whether non-grass phytolith assemblages extracted from soils vary with canopy complexity, measured as Leaf Area Index (LAI). We hypothesized that phytoliths from soils under denser canopies will be larger and more undulated than phytoliths growing in more open habitats. Soils were collected across an LAI gradient in Costa Rican habitats and phytoliths were extracted and measured. We found that mean phytolith undulation and mean phytolith area are highly correlated to LAI. We constructed a robust model to predict LAI and using this model, we reconstructed LAI (rLAI) from 44 fossil phytolith assemblages from Patagonia. The synthesis of this research is a long deep-time record of environmental change that relates to climate in southern South America spanning from 50-11 Ma. The results reveal new details about the environmentmental history of temperature and rainfall, and how LAI responds to these variables. Additionally, the rLAI record may track Patagonian habitat response to major climatic changes associated with the opening of the Drake Passage
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
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