1,721,114 research outputs found
Partitioning of forest evapotranspiration:the impact of edge effects and canopy structure
No full textThe magnitude of small scale variability in tree transpiration was explored in a structurally heterogeneous Norway spruce (Picea abies (L.) H. Karst.) plantation in western Denmark. The trees are arranged in a distinctive small scale mosaic (0.25 ha) of young open-canopy stands interspaced with older mature closed-canopy stands. Tree transpiration was measured in the open and closed canopy stands using Granier type thermal dissipation probes; forest floor evapotranspiration (ET) was estimated by monitoring the weight of cut out sections of forest floor; and total ET was estimated using the eddy covariance (EC) method. We show that (a) canopy structure had a major impact on transpiration rate allowing the open-canopy stands to transpire at approximately 30% higher rate than the closed-canopy stands; (b) within the open-canopy stand there was a significant relation between tree size and sap-flux density; and (c) within the closed-canopy stands there was an edge effect with trees next to access roads and aisles being responsible for a disproportionately large part of the stand transpiration. Through careful scaling, taking into account the observed variability, it was possible to get good agreement on dry days between independent measures of transpiration plus forest floor ET and the EC estimate of total forest ET. On average transpiration and forest floor ET amounted to 86% of the EC estimate on dry days. (c) 2012 Elsevier B.V. All rights reserved.Villum foundatio
Partitioning forest evapotranspiration:interception evaporation and the impact of canopy structure, local and regional advection
No full textSpatial and temporal variation in interception evaporation, energy balance during rain and total water loss was explored in a structurally heterogeneous Norway spruce [Picea abies (L.) H. Karst.] plantation in western Denmark. The trees are arranged in a distinctive small scale mosaic (0.25 ha) of young open canopy stands interspaced with older mature closed canopy stands. The mature stands are bound by a single line of taller Grand Fir [Abies grandis] on their northern edge. Interception loss (I) was measured and modeled in the open and closed canopy stands and under a Grand Fir row using net precipitation gauges and the Gash rain interception model. Incorporating complementary data on individual stand transpiration, forest floor evaporation and total ET (Ringgaard et al., 2012) we show that (a) I is 3% points higher in the closed canopy than in the open canopy (34% and 31% of P-G respectively) while the Grand Fir row promotes a zone of relative drought with I = 47%, (b) in terms of total water loss, the open canopy has an annual ET of about 7.5% higher than the closed canopy stand and (c) in months with little precipitation there is good agreement between the individual components of the evaporation balance and the gap-filled eddy-covariance evapotranspiration (EC-ET) estimate while in months with high precipitation the EC-ET data underestimate both the magnitude and variability of I. The Gash model had to be parameterized separately for summer and winter. In winter, the available energy for evaporation during rain was dominated by regional scale advection of heat from the North Sea, while in summer half the available energy came from local advection. The mean evaporation rate during rain was 0.09 mm h(-1) in winter and 0.21 mm h(-1) in summer. (C) 2014 Elsevier B.V. All rights reserved.Villum foundatio
Modeling canopy CO2 exchange in the European Russian Arctic
No full textIn this study, we use the coupled photosynthesis-stomatal conductance model of Collatz et al. (1991) to simulate the current canopy carbon dioxide exchange of a heterogeneous tundra ecosystem in European Russia. For the parameterization, we used data obtained from in situ leaf level measurements in combination with meteorological data from 2008. The modeled CO2 fluxes were compared with net ecosystem exchange (NEE), measured by the eddy covariance technique during the snow-free period in 2008. The findings from this study indicated that the main state parameters of the exchange processes were leaf area index (LAI) and Rubisco capacity (v(cmax)). Furthermore, this ecosystem was found to be functioning close to its optimum temperature regarding carbon accumulation rates. During the modeling period from May to October, the net assimilation was greater than the respiration, leading to a net accumulation of 58 g C m(-2). The model results suggest that the tundra ecosystem could change from a carbon sink to a carbon source with a temperature rise of only 2-3 degrees C. This is due to the fact that, in the continental Arctic, a global warming of a few degrees might restrict the net assimilation, due to high temperatures, whereas the respiration is predicted to be enhanced. However, future changes in vegetation composition and growth, along with acclimation to the new thermal regime, might facilitate the assimilation to counterbalance the carbon losses
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
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