1,720,973 research outputs found
Water management reduces greenhouse gas emissions in a Mediterranean rice paddy field
No full textRice paddy fields are one of the largest anthropogenic sources of methane (CH4), the second most important anthropogenic greenhouse gas (GHG) after carbon dioxide (CO2). For this reason most studies on the GHG budget in these agricultural systems focus on the evaluation of CH4 production. However, these systems also exchange other GHGs with the atmosphere, such as CO2 and nitrous oxide (N2O). To estimate the total global warming potential (GWP) of rice cultivation, a field experiment was carried out in a Mediterranean rice paddy field in the Po Valley (Italy), the largest rice producing region in Europe. For two consecutive years, ecosystem CO2 and CH4 fluxes were assessed using the eddy covariance technique and CH4 and N2O fluxes were measured with closed chambers. The net biome productivity indicated a nearly carbon (C) neutral system in 2009 while it accumulated C in 2010, due to the application of organic fertilizers and the midseason drainage of the otherwise flooded field, the latter having the additional benefit of leading to lower water consumption. The rice paddy field acted as a strong GHG source with a GWP of 1148 g CO(2-)eq m(-2) yr(-1) in 2009 and decreased four-fold in 2010 (289 g CO(2-)eq m(-2) yr(-1)). In both years, the site was a large CH4 source. Differences in the GHG budget between the two years of measurements were mainly caused by the lower CH4 emissions in 2010 (21.0 g CH4 m(-2) compared to 37.4 g CH4 m(-2) in 2009), probably driven by drainage of the otherwise flooded field in the middle of the growing season during 2010 and moderately larger CO2 uptake. The increased N2O fluxes (29%), had a marginal contribution to the GWP. However, midseason drainage, which needs to be evaluated in combination with the concurrent application of organic fertilizers, resulted in small decreases of yield. Our results therefore suggest that an adequate management of the water table level reduces CH4 fluxes and has the potential to decrease the GWP and water losses through evapotranspiration of rice paddy fields, confirming that full GHG budgets should be assessed in combination with yields in order to develop and evaluate effective mitigation strategies. (C) 2016 Elsevier B.V. All rights reserved.FPVI project Nitroeurope-I
Optimal use of buffer volumes for the measurement of atmospheric gas concentration in multi-point systems
Full text linkAccurate multi-point monitoring systems are required to
derive atmospheric measurements of greenhouse gas concentrations both for
the calculation of surface fluxes with inversion transport models and for
the estimation of non-turbulent components of the mass balance equation
(i.e. advection and storage fluxes) at eddy covariance sites. When a single
analyser is used to monitor multiple sampling points, the deployment of
buffer volumes (BVs) along sampling lines can reduce the uncertainty due to
the discrete temporal sampling of the signal. In order to optimize the use
of buffer volumes we explored various set-ups by simulating their effect on
time series of high-frequency CO2 concentration collected at three Fluxnet
sites. Besides, we proposed a novel scheme to calculate half-hourly weighted
arithmetic means from discrete point samples, accounting for the
probabilistic fraction of the signal generated in the averaging period.
Results show that the use of BVs with the new averaging scheme reduces the
mean absolute error (MAE) up to 80 % compared to a set-up without BVs and up
to 60 % compared to the case with BVs and a standard, non-weighted
averaging scheme. The MAE of CO2 concentration measurements was observed to
depend on the variability of the concentration field and on the size of BVs,
which therefore have to be carefully dimensioned. The optimal volume size
depends on two main features of the instrumental set-up: the number of
measurement points and the time needed to sample at one point (i.e. line
purging plus sampling time). A linear and consistent relationship was
observed at all sites between the sampling frequency, which summarizes the
two features mentioned above, and the renewal frequency associated with the
volume. Ultimately, this empirical relationship can be applied to estimate
the optimal volume size according to the technical specifications of the
sampling system
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
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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