1,720,982 research outputs found
Dissolved organic matter in newly formed sea ice and surface seawater
Full text link© The Author(s), 2015. This is the author's version of the work and is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geochimica et Cosmochimica Acta 171 (2015): 39-49, doi:10.1016/j.gca.2015.08.014.Changes in sea ice in the Arctic will have ramifications on regional and global carbon
cycling. Research to date has primarily focused on the regional impacts to biological activity and
global impacts on atmospheric processes. The current project considers the molecular-level
composition of organic carbon within sea ice compared to the organic matter in seawater. The
project revealed that the composition of organic matter within sea ice was more variable than the
composition of organic matter within the surface ocean. Furthermore, sea ice samples presented
two distinct patterns in the composition of organic matter with a portion of the sea ice samples
containing protein-like organic matter. Yet, the samples were collected in the early winter period
when little biological activity is expected. Thus, one hypothesis is that physical processes acting
during the formation of sea ice selectively transferred organic matter from seawater into sea ice.
The present project expands our understanding of dissolved organic matter in sea ice and surface
seawater and thereby increases our knowledge of carbon cycling in polar regions.This research was funded by a grant from WHOI’s Arctic Research Initiative to KL.2016-09-0
Using stable isotope probing to characterize differences between free-living and sediment-associated microorganisms in the subsurface
Full text linkAuthor Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of Taylor & Francis for personal use, not for redistribution. The definitive version was published in Geomicrobiology Journal (2013): 362-370, doi:10.1080/01490451.2012.689090.Aquifers are subterranean reservoirs of freshwater with heterotrophic bacterial communities attached to the sediments and free-living in the groundwater. In the present study, mesocosms were used to assess factors controlling the diversity and activity of the subsurface bacterial community. The assimilation of 13C, derived from 13C-acetate, was monitored to determine whether the sediment-associated and free-living bacterial community would respond similarly to the presence of protozoan grazers. We observed a dynamic response in the sediment-associated bacterial community and none in the free-living community. The disparity in these observations highlights the importance of the sediment-associated bacterial community in the subsurface carbon cycle.This research was supported by NSF grant EAR-0525166 to EBK
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
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Bacterioplankton in the Oregon upwelling system: distribution, cell-specific leucine incorporation, and diversity
Full text linkMarine bacterioplankton play an important role in global elemental cycles because they return carbon dioxide and nutrients to the biosphere as they reduce organic matter. Furthermore, marine bacterioplankton are not uniformly active, and subpopulations of the in situ community may be more or less active at any given time. Defining whether or not a cell is 'active' is not without difficulty, and the result varies depending on the assay used, since different assays examine different physiological processes within a cell. Linking the level of activity of a cell with its phylogenetic identity is an additional important step in examination of the role of marine prokaryotes in global elemental cycles. In this project, flow cytometry was used in two ways to examine relative cell-specific metabolic activity in bacterioplankton cells: as relative cell-specific nucleic acid content via staining with SYBR Green I, and as
ability to reduce sufficient 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) to be identified as having an active electron transport system. Based on flow cytometric sorting of cells labeled with ³H-leucine, the high nucleic acid (HNA) cells had higher cell-specific leucine incorporation rates than the low nucleic acid (LNA) cells. The HNA cells were also responsible for proportionately more of the leucine incorporation by the total heterotrophic population. While the CTC-positive cells had higher average cell-specific leucine incorporation rates than the HNA cells, their low abundances meant that they were responsible for less than 15% of the total leucine incorporation. The diversity ofBacteria observed within the HNA and LNA assemblages was examined using phylogenetic analysis based on the V3-V4-V5 variable regions of 16S rRNA genes. Most of the phylogenetic groups ofBacteria identified in this study were
present in both the HNA and LNA assemblage and had, at times, an active electron transport system (i.e., were able to reduce CTC). Finally, non-metric multidimensional scaling was presented as a new method to analyze DNA sequence data in conjunction with measured environmental parameters
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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Microbial diversity of sulfide structures from hydrothermal vent sites at 9°N, Guaymas Basin and the Juan de Fuca Ridge
Full text linkThe microbial diversity associated with sulfide structures from three
different hydrothermal vent fields was examined using phylogenetic analysis
based on the small subunit ribosomal RNA gene (16S rDNA). Samples were
collected from sites at 9°N, Guaymas Basin and the Juan de Fuca Ridge and
analyzed with denaturing gradient gel electrophoresis (DGGE). In addition,
clone libraries were constructed for two samples from Guaymas Basin. The
Bacteria from Juan de Fuca Ridge all clustered within the e-Proteobacteria, while
the Archaea identified from all three sites were Euryarchaeota. Among the
Euryarchaeota were sequences clustering within the Methanococcales,
Methanosarcinales, Methanobacteriales, and Methanomicrobiales; the later two
groups have not previously been identified as part of the microbial
community at deep-sea hydrothermal vents. Two groups of sequences were
identified that cluster with sequences previously only identified from
hydrothermal systems in the western Pacific and the Mid-Atlantic Ridge; these
groups may be endemic to deep-sea hydrothermal vents
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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