1,721,096 research outputs found
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
How will melting of ice affect volcanic hazards in the 21st century?
Full text linkGlaciers and ice sheets on many active volcanoes are rapidly receding. There is compelling evidence that melting of ice during the last deglaciation triggered a dramatic acceleration in volcanic activity. Will melting of ice this century, which is associated with climate change, similarly affect volcanic activity and associated hazards? This paper provides a critical overview of the evidence that current melting of ice will increase the frequency or size of hazardous volcanic eruptions. Many aspects of the link between ice recession and accelerated volcanic activity remain poorly understood. Key questions include how rapidly volcanic systems react to melting of ice, whether volcanoes are sensitive to small changes in ice thickness, and how recession of ice affects the generation, storage and eruption of magma at stratovolcanoes. A greater frequency of collapse events at glaciated stratovolcanoes can be expected in the near future, and there is strong potential for positive feedbacks between melting of ice and enhanced volcanism. Nonetheless, much further research is required to remove current uncertainties about the implications of climate change for volcanic hazards in the 21st century
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
Finding faults
No full textHugh Tuffen, researcher at Natural Environment Research Council (NERC), has described the Earth's crust as a cause of tectonic earthquakes through his study of lava erupted beneath Icelandic glaciers. The studies have also speculated that gas escaping from magma beneath the surface belches through existing cracks in the volcano, trigger an earthquake. Number of calculations in his study suggested that the size of the faults in Iceland and the size of recorded volcanic earthquakes are directly related to each other. The research also focused to predict the depth magma would fracture and match it with the depth of measured earthquakes, thereby developing a unique facility for breaking rocks at high temperatures and measuring the tiny earthquakes caused by fracturing on a millimeter scale. The measurement of fracturing behavior of a variety of dome samples from different stages of eruption was also highlighted with the help of geophysical observations from volcanoes
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
Primary and secondary water content heterogeneity in volcanic glasses
No full textSpatial heterogeneities in the dissolved water content within volcanic glasses are generated by diffusive degassing and crystallization of melts, as well as subsequent posteruptive hydration of quenched glasses. Characterization of the resultant water diffusion gradients using micro-analytical techniques such as SIMS or synchrotron FTIR allows us to model the timescale of water diffusion and thus key pre-, synand post-eruptive processes. We present a variety of microanalytical data to illustrate three sources of water content heterogeneity within rhyolitic glasses. Firstly, enrichment of water in glass surrounding spherulites reflects its expulsion during growth of anhydrous mineral phases. Our diffusion models have placed new constraints on spherulite growth rates within obsidian flows [1]. Secondly, we have found strong water enrichment adjacent to perlitic fractures in subglacially erupted obsidian lavas [2]. Diffusion and cooling models show that perlitisation starts at ~400 °C and occurs over timescale of days [3]. Finally, we have used SIMS analysis to overcome the hydration problem and successfully measure the dissolved magmatic water content of pumices [4]. This provides new insight into magma storage and degassing prior to an exceptionally violent eruption
What Controls the Explosivity of Eruptions Beneath Ice Sheets? Field Evidence, Model Results and Some Challenging Questions
No full textModels of ice melting and edifice growth during subglacial basaltic eruptions.
Full text linkModels of the early stages of basaltic eruptions beneath temperate glaciers are presented that consider the evolving sizes of volcanic edifices emplaced within subglacial cavities. The cavity size reflects the competing effects of enlargement by melting and closure by downward ductile deformation of the ice roof, which occurs when the cavity pressure is less than glaciostatic due to meltwater drainage. Eruptions of basaltic magma from fissures and point sources are considered, which form either hemicylindrical or hemispherical cavities. The rate of roof closure can therefore be estimated using Nye's law. The cavity size, edifice size, and depth of meltwater above the edifice are predicted by the model and are used to identify two potential eruption mechanisms: explosive and intrusive. When the cavity is considerably larger than the edifice, hydroclastic fragmentation is possible via explosive eruptions, with deposition of tephra by eruption-fed aqueous density currents. When the edifice completely fills the cavity, rising magma is likely to quench within waterlogged tephra in a predominantly intrusive manner. The models were run for a range of magma discharge rates, ice thicknesses and cavity pressures relevant to subglacial volcanism in Iceland. Explosive eruptions occur at high magma discharge rates, when there is insufficient time for significant roof closure. The models correctly predict the style of historic and Pleistocene subglacial fissure eruptions in Iceland and are used to explain the contrasting sedimentology of basaltic and rhyolitic tuyas. The models also point to new ways of unraveling the complex coupling between eruption mechanisms and glacier response during subglacial eruptions
- …
