1,721,031 research outputs found
Abrupt climate change
No full textLarge, abrupt, and widespread climate changes with major impacts have occurred repeatedly in the past, when the Earth system was forced across thresholds. Although abrupt climate changes can occur for many reasons, it is conceivable that human forcing of climate change is increasing the probability of large, abrupt events. Were such an event to recur, the economic and ecological impacts could be large and potentially serious. Unpredictability exhibited near climate thresholds in simple models shows that some uncertainty will always be associated with projections. In light of these uncertainties, policy-makers should consider expanding research into abrupt climate change, improving monitoring systems, and taking actions designed to enhance the adaptability and resilience of ecosystems and economies
A review of Pine Island Glacier, West Antarctica: hypotheses of instability vs. observations of change
No full textThe Pine Island Glacier ice-drainage basin has been cited as the part of the West Antarctic ice sheet most prone to substantial retreat on human time-scales. Here we review the literature and present new analyses showing that this ice-drainage basin is glaciologically unusual. Due to high precipitation rates near the coast, Pine Island Glacier basin has the second highest balance flux of any extant ice stream or glacier. Well-defined tributaries flow at intermediate velocities through the interior of the basin and have no regions of rapid velocity increase. The tributaries coalesce to form Pine Island Glacier which has characteristics of outlet glaciers (e.g. high driving stress) and of ice streams (e.g. shear margins bordering slow-moving ice). The glacier flows across a complex grounding zone into an ice shelf. There, it comes into contact with warm Circumpolar Deep Water which fuels the highest basal melt-rates yet measured beneath an ice shelf. The ice front position may have retreated within the past few millennia but during the last few decades it appears to have shifted around a mean position. Mass balance calculations of the ice-drainage basin as a whole show that there is currently no measurable imbalance, although there is evidence that some specific areas within the basin are significantly out of balance. The grounding line has been shown to have retreated in recent years. The Pine Island Glacier basin is clearly important in the context of the future evolution of the West Antarctic ice sheet because theoretically, it has a high potential for change and because observations already show change occurring. There is, however, no clear evidence to indicate sustained retreat or collapse over the last few decades
Rutford Ice Stream, Antarctica
No full textRutford Ice Stream is in many ways a typical Antarctic outlet glacier. Constrained by a subglacial-bed trough to the east of the Ellsworth Mountains, it drains an area of 49,000 km2 of the West Antarctic Ice Sheet. Varying in width from 20 to 30 km, flowing fast (up to 400 m/a) for more than 150 km before it starts to float, and over 2000 m thick along most of its length, it discharges 18.5±2 Gt of ice per year across its grounding line. It has an average driving stress of 40 kPa, which is resisted by lateral shear stresses at the margins in boundary layers up to about 10 km wide, and by basal shear stress in the middle third of the ice stream. Seismic studies of the base reveal varied conditions, with soft deformable till and more competent sediments. Stresses in the margins of up to 160 kPa lead to fracturing and crevassing, highlighted as bright bands in satellite synthetic aperture radar (SAR) images. Shallow seismic refraction and radar measurements indicate that fracture is initiated at depths around 10–20 m, consistent with the SAR penetration depths. Indications of change come from SAR interferometry of the upstream shear margin, where decadal fluctuations in the velocity profile suggest the effective width of the ice stream is varying. The limit of tidal flexing has been accurately located with SAR interferometry and shows no change in position between 1992 and 1996. Downstream of the grounding line there is a strong pattern of ice thickness variation advecting with the flow. We do not have a good explanation for the pattern, but it could have been caused by fluctuations in the position of the grounding line as a consequence of changes in ice thickness advecting downstream. The extent of the pattern suggests that the changes were occurring between 100 and 400 years ago
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
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
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
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
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