1,720,979 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Measuring and modelling long-distance water and sugar transport in trees
No full textRecently, it is generally recognized in literature that approaching water and sugar transport in an integrated way will broaden our fundamental understanding of how trees, and in general plants, behave. Therefore, this PhD-study aimed to enlarge our insight in sugar transport by simultaneously considering water transport. To this end, experimental and modelling studies were performed in which both transport processes were concomitantly measured or modelled.
In literature, detailed information about the water and the sugar transport is given. The water transport is driven by the cohesion-tension theory, whereas the sugar transport is driven by the Münch theory. The original Münch theory is adapted by introducing (1) active-passive (un)loading and (2) a leakage-retrieval process along the transport phloem. More and more evidence suggests that a relay system is present in the phloem to maintain a feasible pressure gradient in the sieve tubes. Besides sugar transport, the phloem tissue is also involved in information transmission between sources and sinks. It is a challenge to study sugar transport due to the protective nature of sieve tubes which makes sampling very difficult. Water and sugar transport are integrated at the whole plant level mainly by water recycling, but also by the exchange of potassium, sugars and hormones.
Stem diameter variations are influenced by both the water and carbon status of the stem. Therefore, they are a powerful tool to simultaneously study sugar and water transport. In this PhD-study, the effects of a manipulated sugar flow on both transport processes were investigated by analysing stem diameter variations of young oak trees (Quercus robur L.). The manipulation was obtained by mechanically removing two bands of bark (cf. double girdling) and by local stem chilling (cf. cold girdling). Double girdling changed the sugar flow and influenced as such stem growth: stem increment enhanced above the girdled zones (U) and halted below (L) and in between (M) the two girdled zones. The changed sugar transport also resulted in observed time lags between the times of morning shrinkage at different stem heights. These time lags are probably attributed to different sugar contents in the bark. In addition, the water transport was indirectly affected by the manipulated sugar transport. A feedback inhibition of photosynthesis probably provoked stomatal closure, decreasing as such transpiration and the observed xylem sap flow. The effects observed after cold girdling were similar but less pronounced, because chilling only moderately increased the local resistance in both phloem and xylem. The chilling effects were best observed in the middle of the growing season.
In this PhD-study, a comprehensive whole tree model was developed that enabled simulation of stem diameter variations driven by both water and sugar transport. This mechanistic model describes stem diameter variations as volume changes dependent on the water transport according to the cohesion-tension theory, the sugar transport according to the Münch hypothesis and irreversible turgor-driven growth according to the Lockhart equation. Modelled and measured data were compared to verify the implemented mechanisms. The measured data consisted of measurements of stem diameter variations and xylem sap flow rates. These measurements were performed on a young oak tree (Quercus robur L.) and on an adult beech tree (Fagus sylvatica L.). A good correspondence between measured and simulated data proves that the model provides a realistic presentation of the simulated processes. In addition the model is able to simulate some physiological processes which are difficult to measure. Therefore, the model was applied to evaluate the mechanisms behind the girdling responses. When the loading and unloading functions of the original model were adapted, measured and simulated stem diameter variations fitted well. According to these model simulations, changes in the sieve tube pressure seemed to trigger all observed girdling responses. Hence, it seemed that information about local damage to the phloem system was transferred to other plant parts by means of a change in phloem pressure.
To measure processes related to sugar transport, techniques which measure these processes in a non-destructive way have a high scientific potential. Therefore, two non-invasive techniques are applied in this PhD-study. The first applied method was the magnetic resonance imaging (MRI) technique. MRI was used to verify whether stem diameter variations are caused by changes in stem water content. This relationship was experimentally confirmed by comparing MRI data with dendrometer data. Hence, the interpretation and application of dendrometers is validated by this MRI-study. In addition, the same MRI-study confirmed that the xylem contribution to the total stem diameter variations was much lower than the bark contribution. The MRI-study also revealed that the bark tissues, containing the highest amount of water (the cambium and the youngest, probably conductive, phloem), contributed the least to the bark diameter variations. Hence, the bark tissues which are less physiologically active contribute the most to the total stem diameter variations. When MRI was applied to study the stem increment above a girdled zone, MRI data illustrated that both irreversible structural growth as reversible swelling took place. The second applied non-invasive technique was labelling with the radio-active 11C isotope. The 11C data were analysed in two ways: three-dimensional (3D) visualization of the 11C flow and analysing typical 11C-time-series by applying an input-output model and a mechanistic tracer model. The obtained 3D-images illustrated the sectorial behaviour of sugar transport and its breakdown after bark manipulation. The model analyses of the 11C-time-series showed that the transport velocity and the pathway loss of the sugar flow changed after bark manipulation. Based on these model results, it is suggested that the breakdown of sectoriality is induced by an active change in the lateral transport path, for example by modifying the conductance of plasmodesmata.
In conclusion, the performed experimental and modelling studies demonstrated that water and sugar transport are interrelated. Some of the in the literature proposed hypotheses were tested and confirmed. Despite, many questions remain unanswered: which mechanisms trigger the MRI-measured phloem water flow dynamics, which mechanisms drive the altered sugar leakage after girdling and which mechanisms are responsible for sectorial breakdown
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
Get PDFWe 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
Development and verification of a water and sugar transport model using measured stem diameter variations
No full textIn trees, water and sugars are transported by xylem and phloem conduits which are hydraulically linked. A simultaneous study of both flows is interesting, since they concurrently influence important processes such as stomatal regulation and growth. A few mathematical models have already been developed to investigate the influence of both hydraulically coupled flows. However, none of these models were so far tested using real measured field data. In the present study, a comprehensive whole tree model is developed that enables simulation of the stem diameter variations driven by both the water and the sugar transport. Stem diameter variations are calculated as volume changes of both the xylem and the phloem tissue. These volume changes are dependent on: (i) water transport according to the cohesion-tension theory, (ii) sugar transport according to the Münch hypothesis, (iii) loading and unloading of sugars and (iv) irreversible turgor-driven growth. The model considers three main compartments (crown, stem and roots) and is verified by comparison with actual measured stem diameter variations and xylem sap flow rates. These measurements were performed on a young oak (Quercus robur L.) tree in controlled conditions and on an adult beech (Fagus sylvatica L.) tree in a natural forest. A good agreement was found between simulated and measured data. Hence, the model seemed to be a realistic representation of the processes observed in reality. Furthermore, the model is able to simulate several physiological variables which are relatively difficult to measure: phloem turgor, phloem osmotic pressure and the Münch’s counter flow. Simulation of these variables revealed daily dynamics in their behaviour which were mainly induced by transpiration. Some of these dynamics are experimentally confirmed in literature, while others are not
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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