1,720,968 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
Drought tolerant traits of triticale and cowpea genotypes under semi-arid conditions
Full text linkThesis (Ph.D. Agriculture (Soil Science)) -- University of Limpopo, 2017.Climate change and variability pose a significant challenge to future global food security due to changes in mean climatic conditions which are rendering many areas marginally suitable for crop production. Erratic rains, drought, heat stress and declining soil fertility are some of the factors limiting crop productivity in many arid and semi-arid areas. Furthermore, water resources that could be used to mitigate drought and erratic rains, are also threatened by both scarcity and overuse. To ensure food security in the future, adaptation strategies at crop and management levels should be explored. Adaptation to future drier and warmer climates calls, among others, for improvement in drought resistance of crops through measures such as screening traits for drought tolerance and water use efficiency.
This PhD study was carried out at University of Limpopo experimental farm, Limpopo Province, South Africa, a region with a semi-arid climate and mean annual rainfall of ca. 500 mm. The main aim of the study was to evaluate the use of plant δ13C and δ18O as screening traits for potential yield and water use efficiency of crop genotypes under drought conditions. The study also determined the agronomic performance of cowpea (Vigna unguiculata L. Walp.) and triticale (x. Triticosecale Wittmack) genotypes under varying soil moisture conditions including biological nitrogen fixation for cowpea. Both crops were grown under field conditions and the following four moisture levels (averages per level) were applied: well-watered (ca. 420 mm), moderately well-watered (ca. 350 mm), medium stress (ca. 290 mm), and severe stress (ca. 220 mm).
The triticale experiment evaluated the agronomic performance and the spectral response of triticale to water stress under semi-arid conditions. The results showed a significant (P 0.05) respond to genotypes probably due to the pre-screening of the genotypes or the lack of distinct genetic diversity in the studied parameters. Under well-watered conditions, triticale produced a grain yield of 3.9 t ha-1 in 2013 and 4.9 t ha-1 in 2014. These yields were however, found to be low when compared to other studies. Even though, no statistical differences were observed among the genotypes, Agbeacon showed a tendency of higher performance compared to the other genotypes. Of the four spectral indices tested, water based indices i.e. the water index (WI) and normalised difference water index (NDWI) were found to be more effective in detecting leaf water status compared to greenness based indices (normalised difference vegetation index and nitrogen reflectance index). This is because NDWI and WI respond to short term changes in water content of leaves. Overall, the performance of triticale showed a good adaptation to semi-arid conditions.
The evaluation of δ13C and δ18O as screening traits for potential yield and water use efficiency under drought conditions produced interesting results. The findings showed that, Δ13C was positive and strongly related to grain yield and thus has potential to be used as a surrogate for grain yield in triticale under water stress. We also found a negative relationship between Δ13C and intrinsic water use efficiency (WUEintrinsic), which suggests that breeding for higher WUEintrinsic in triticale may not necessarily yield the desired improved grain yield. Measured grain Δ13C and flag leaf Δ13C suggested minimum contribution of pre-anthesis assimilates to grain filling under water stress, contrary to what is reported in literature. However, for concrete conclusions on the source of assimilates to the grains under drought conditions, further studies are still needed. Combining δ13C and δ18O provided more information on the physiological responses of triticale to varying moisture levels. The δ13C and δ18O were used to test the dual isotope model by Scheidegger et al 2000 and the results showed that, vapour pressure deficit (VPD) of air plays an important role in the operation of the model. The study indicated that the model worked only under high VPD when stomatal conductance limits transpiration rate but failed to work when VPD was relatively low and limiting transpiration rate.
In order to address the declining soil fertility in the smallholder farming sector as well as the predicted loss in productivity of the commonly grown dry bean, this PhD study evaluated cowpea genotypes for biomass yield, grain yield and biological nitrogen fixation (BNF) under varying moisture levels. The results showed that soil moisture levels indeed affect biomass production, grain yield, nodule formation and the ability of cowpea to fix atmospheric nitrogen. BNF and nodule formation were the most sensitive to water stress compared to the other parameters. Severe water stress reduced BNF by 57% relative to well-watered conditions while nodule mass was reduced by 80% for the same soil moisture levels. Genotype TV4607 was superior in most of the parameters determined except for grain yield. As a result, TV4607 produced the highest biomass and returned the most nitrogen back to the soil compared to the other genotypes. However, IT00K-1263 emerged as the superior genotype due to its ability to produce the optimum balance of biomass, grain yield and BNF. Stomatal behaviour of cowpea under varying moisture levels was also investigated and the results showed sensitivity of stomatal conductance to soil moisture levels. As expected, stomatal conductance was high under well-watered conditions compared to water stressed conditions. Genotypic variation in stomatal conductance was only observed at early stages of cowpea growth i.e. at 47 and 54 days after planting (DAP).
In conclusion, this PhD has shown that δ13C has potential to be used in breeding for drought resistance in triticale and probably other small grain crops. This study also revealed that there is minimum contribution of pre-anthesis assimilates to grain filling under water stress, contrary to what is reported in literature and hence more research is needed.The evaluated genotypes of triticale and cowpea showed tolerance to drought stress under semi-arid conditions. Agbeacon for triticale and IT00K-1263 for cowpea were identified as the most promising genotypes and hence their adoption in the smallholder farming system could be a step towards adapting to future warmer and drier climate
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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