1,725,322 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
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
Spectral reflectance and photosynthetic properties of Sphagnum mosses exposed to progressive drought
No full textThis article explores the utility of spectral reflectance signals to assess changes in the photosynthetic efficiency (?PSII) of
Sphagnum mosses exposed to reductions in water availability. Reflectance was measured in parallel to moisture content and
chlorophyll fluorescence in five species of Sphagnum exposed to progressive drought. Decreases in moisture availability
caused a significant reduction in ?PSII for all samples tested. An objective was to ascertain whether Sphagnum ?PSII was
better correlated with (i) spectral indices directly related to photosynthetic processes through association with xanthophyll
cycle pigmentation (the photochemical reflectance index; PRI), or (ii) indices indirectly correlated with photosynthetic activity
but able to detect changes in canopy morphology (the normalized difference vegetation index; NDVI), chlorophyll stability
(the structure insensitive pigment index; SIPI), or canopy moisture content (the floating water band index; fWBI). Strongest
correlations were found between ?PSII and indices which were indirectly related to ?PSII. Both the SIPI and the NDVI exhibited
linear correlations although these relationships were sometimes sample-specific. The fWBI was the index least affected by
sample-specific relationships and showed a strong curvilinear correlation with ?PSII. Photosynthetic efficiency was correlated
with the PRI but relationships were much weaker than for the other indices used, and in some cases negative. The NDVI and
the fWBI show the most potential for monitoring Sphagnum photosynthetic activity at the ecosystem scale. The results from
this study will help to monitor and understand the responses of these key species to hydrological disturbances
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
The potential of the MERIS terrestrial chlorophyll index for carbon flux estimation
Full text linkIn this study we evaluated the potential of the Medium Resolution Imaging Spectrometer (MERIS) Terrestrial Chlorophyll Index (MTCI) for monitoring gross primary productivity (GPP) across fifteen eddy covariance towers encompassing a wide variation in North American vegetation composition. The across-site relationship between MTCI and tower GPP was stronger than that between either the MODIS GPP or EVI and tower GPP, suggesting that data from the MERIS sensor can be used as a valid alternative to MODIS for estimating carbon fluxes. Correlations between tower GPP and both vegetation indices (EVI and MTCI) were similar only for deciduous vegetation, indicating that physiologically.
A new approach for estimating northern peatland gross primary productivity using a satellite-sensor-derived chlorophyll index
No full textCarbon flux models that are largely driven by remotely sensed data can be used to estimate gross primary productivity (GPP) over large areas, but despite the importance of peatland ecosystems in the global carbon cycle, relatively little attention has been given to determining their success in these ecosystems. This paper is the first to explore the potential of chlorophyll-based vegetation index models for estimating peatland GPP from satellite data. Using several years of carbon flux data from contrasting peatlands, we explored the relationships between the MERIS terrestrial chlorophyll index (MTCI) and GPP, and determined whether the inclusion of environmental variables such as PAR and temperature, thought to be important determinants of peatland carbon flux, improved upon direct relationships. To place our results in context, we compared the newly developed GPP models with the MODIS (Moderate Resolution Imaging Spectrometer) GPP product. Our results show that simple MTCI-based models can be used for estimates of interannual and intra-annual variability in peatland GPP. The MTCI is a good indicator of GPP and compares favorably with more complex products derived from the MODIS sensor on a site-specific basis. The incorporation of MTCI into a light use efficiency type model, by means of partitioning the fraction of photosynthetic material within a plant canopy, shows most promise for peatland GPP estimation, outperforming all other models. Our results demonstrate that satellite data specifically related to vegetation chlorophyll content may ultimately facilitate improved quantification of peatland carbon flux dynamics
Identification and modelling of variable convective regimes at Erta Ale lava lake
No full textBetween February 17 and 19, 2002, we collected a combined thermal and seismic data set for studying the persistent lava lake activity at Erta Ale volcano, Ethiopia. These data indicate that the lake cycles between periods characterized by low (~0.05 m s -1 ) and high (~0.2 m s -1 ) rates of convection, respectively.
We use our measurements to constrain two models to explain such convection cycles. The first model relates variable convection rates to pulses in the rate at which magma is supplied to the lake. This model requires supply rates to cycle between high convection rate phases fed by a magma volume flux of 0.2 m 3 s -1 with a viscosity of 140 Pa s, and low convection rate phases fed by a magma volume flux of 0.03 m 3 s -1 with a viscosity of 3100-3600 Pa s. The second model assumes that supply to the lake is steady and that cyclic convection is set up by the generation of convective instabilities within the lake. In this case, cooling of the surface layer generates a slow moving, viscous convection cell at the lake surface overlying a faster moving convection cell of lower viscosity. Recharge of the lower cell, at the expense of draining degassed magma, increases the buoyancy of the lower layer to eventually trigger an overturn event. At this point the surface of the low viscosity cell extends to the lake surface and the high viscosity cell sinks to be drained from the lake
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