1,721,083 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
Evaluatie van de doeltreffendheid van geselecteerde defensie elicitoren tegen de wortel-knobbelnematode Meloidogyne incognita in tomaat
No full textSummary
Plant-parasitic root-knot nematodes, Meloidogyne spp., can cause major damage to their host plants. They are globally widespread and their host range encompasses more than 250,000 plants, including many economical important crops. For example, yield losses resulting from Meloidogyne incognita infestation can range between 50 to 100%. The damage they cause, results from the fact that they influence that vascular system of their host plant in such a way, that it can take up less and less water and nutrients from the soil, eventually leading to death. Furthermore, root-knot nematodes make the plant more sensitive to secondary infections by other pathogens and abiotic stress, such as drought. The control of these nematodes is, however, problematic as they reside in the soil and are difficult to reach, they have a short life cycle and are able to produce many offspring, they can cause much damage and have a wide host range. Moreover, the use of traditional nematicides has been prohibited due to their toxicity for humans and environment. For example, the use of the fumigant methyl bromide was one of the most used control practice, but is now illegal in Belgium. This prohibition urges for research into alternative nematode control strategies, such as defense elicitors to replace the traditional chemical nematicides. Defense elicitors or elicitors, can induce systemic resistance in plants against plant-parasitic nematodes upon exogenous application. Some examples are chitosan (poly-D-glucosamine), the plant hormone or growth regulator methyl jasmonate and acibenzolar-S-methyl, the active component of the commercially available product Bion (Syngenta). These elicitors were selected based on literature reports. The state of the art concerning defense elicitation and root-knot nematodes is discussed in Chapter 1.
In the study reported in Chapter 2, the three elicitors mentioned above are tested for their direct toxic effect on the root-knot nematodes. This has been investigated by an in vitro bio-assay. In this study, second-stage juveniles (J2) of Meloidogyne incognita were incubated into a range of concentrations of the elicitors. The mortality percentage was noted at 24 and 48 h after incubation. After 48 h, an overload of water was added, in such that after 12 h it could be noted whether the nematodes were indeed dead or only temporarily sedated. Our results show that all elicitors can have a nematoxic effect. This means that in experiments the elicitors should be applied in such a way that they do not come in direct contact with the nematodes. Otherwise, this could influence results when investigating systemic defense elicitation. Our results did show that it would be interesting in the future to apply these elicitors through soil applications against root-knot nematodes.
In the study reported in Chapter 3, the efficacy of the three selected elicitors was further investigated. Their efficacy was tested in several greenhouse experiments, in which the leaves of tomato plants (cultivar Marmande) were sprayed with the elicitors. Two days later, the plants were inoculated with root-knot nematodes. Every elicitor was also applied in three different concentrations. All tomato plants were then investigated in galling (“root-knots”), nematode reproduction and several plant growth variables. The results of these experiments were not according to expectations. Namely, there was no effect on the root-knot nematodes, not even at the application of the highest concentration of the elicitors, which only resulted in some cases in phytotoxicity. Therefore, a verification was needed that the plants were indeed elicitated after defense elicitor application before continuing the research. Through a quantitative Real-Time Polymerase Chain Reaction (qRT-PCR), there was confirmation that the defense system was indeed elicitated at the time point where the nematodes were inoculated. Furthermore, it was clear that both methyl jasmonate and chitosan a systemic effect had. Namely, there was also defense induction in the root system of the plant when these elicitors were sprayed on the leaves. Our results did not indicate that Bion had a systemic effect, and this elicitor was then not included in the next experiments. Chitosan was also left out because of a limited knowledge on its effect on the plant and root-knot nematodes in particular. The next studies then focused on methyl-jasmonate.
One reason why defense elicitation did not work in our study, could have been the pathogen pressure. To investigate this factor, we researched this in the study reported in Chapter 4 through a greenhouse experiment. In this experiment, we sprayed methyl-jasmonate on tomato plants and two days later, these plants were subsequently inoculated with root-knot nematodes in 4 different densities. At the termination of the experiment, the same variables were measured as mentioned in Chapter 3. The results pointed towards no effect of nematode inoculation densities on the efficacy of defense induction by methyl jasmonate. Interestingly, a facilitation effect was observed, as nematode reproduction was positively influenced by the presence of other nematodes. However, from a certain population density, nematodes started to compete with each other, probably for nutrients.
Because inoculation density was not a factor influencing the efficacy of defense elicitation by methyl jasmonate, another factor was investigated, namely, repetitive application of the defense elicitor (Chapter 5). In a greenhouse experiment, we investigated whether weekly spraying could increase the efficacy of defense elicitation by methyl jasmonate. At the termination of the experiment, again, the same variables were measured as mentioned in Chapter 3. There was also a qRT-PCR coupled to this experiment, to try to elucidate what the influence was of the nematode infection on the elicitation of the defense system. Samples were therefore taken at 1 hour, 1, 2, 3, 4 and 7 days after the first spray, and 2 days after the fourth and last spray. From the results emanating from the qRT-PCR, it became clear that the root-knot nematodes already down regulated the up regulated defense system of the plants. These results thus can explain at least part of the former results obtained in Chapter 3 and Chapter 4. Furthermore, the results showed that the systemic effect manifested itself 1 day after spray, and that this lasted until at least 4 days, but no longer than 7 days after spray. Therefore, to have a continuous methyl jasmonate elicitated tomato plant, one should spray at least weekly. It also became clear that tomato plants indeed can be elicitated repetitively. However, our results showed that weekly spraying methyl jasmonate had an unexpected detrimental effect. Namely, the nematodes developed faster in weekly sprayed plants versus single sprayed plants or water sprayed plants. This resulted, however, not in a higher reproduction by the nematodes. This last observation could be explained by the competition for available nutrients between the nematodes.
In the study reported in Chapter 6, the influence of the tomato genotype on the efficacy of the defense elicitation by methyl jasmonate was investigated. Therefore, four different tomato cultivars (Marmande, Money Maker, Tiny Tim and Roma) were selected based on the reports in which successful defense elicitation was observed. In our study, the four cultivars were sprayed a single time with methyl jasmonate or water, and were inoculated 2 days later with nematodes. At the termination of the experiment, the same variables as mentioned in Chapter 3 were measured. Only in cv. Roma plants, methyl jasmonate spray resulted in a significant decrease of egg masses. Therefore, to investigate whether this was a result of either less nematode penetration into the roots, or a slower development or only an effect in the reproduction phase of the nematodes, the roots of cv. Roma plants were further analyzed. The results pointed towards an effect of methyl jasmonate spray on all three of the phases, but was most apparent on the reproduction phase.
Finally, in Chapter 7, all results were generally discussed in order to end up with a general conclusion. Several suggestions for future research were also stated.status: Publishe
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
Cryopreservatie van de genetische lijnen van Daphnia magna
No full textThe water flea Daphnia magna is an important model organism in many research areas, such as ecology, ecotoxicology, evolutionary biology and eco-genomics and most of these applications use clonal lines produced via asexual reproduction. To date, maintenance of the clonal lines can only be achieved through continuous culturing. This is a labor-intensive process and entails the risk of losing important lines because of contamination, disease or accidents. In this PhD research, we tried to solve this problem by developing a cryopreservation protocol for the asexual eggs of Daphnia magna.
The dormant eggs of Daphnia, produced by sexual reproduction, are drought and freeze resistant and are thereby an excellent reference to determine what is needed for eggs to survive cryopreservation. We determined the main biochemical differences between sexual and asexual eggs. We found that asexual eggs have higher concentrations of fatty acids than sexual eggs, however a certain concentration of long-chain PUFA, especially EPA and ARA, is maintained in sexual eggs even when they are not provided by the food and this in both neutral lipids and phospholipids. Sugar content of sexual and asexual eggs was very distinct, sexual eggs contained high amounts of trehalose (4.15% of their dry weight), while asexual only contain 0.006% trehalose. Also polyamine analysis revealed some difference between the two egg types. Asexual eggs always contained higher amounts of the metabolite diaminopropane and lower amounts of putrescine and spermidine in comparison with sexual eggs.
In a second step we tried to modify the composition of asexual eggs in order to increase their stress resistance. Fatty acid composition of asexual is strongly influenced by the maternal food, so to boost the PUFA composition of these eggs we simply switch to a diet containing more long-chain PUFA. PUFA composition of the asexual eggs of D. magna is also strongly influence by the culturing temperature of the females, they allocate more unsaturated fatty acids to their eggs at colder temperatures. In addition, we tried to increase trehalose concentration of the asexual eggs by supplementation of the maternal diet with trehalose containing liposomes, but changes were only minor.
In parallel, the protocol for cryopreservation was optimized. To obtain sufficient dehydration we choose for a two-step pretreatment for the eggs before applying droplet vitrification. The pretreatment consisted of a glycerol loading in a 10% glycerol solution for 30 min. This was followed by osmotic dehydration in a vitrification solution. The vitrification solution with the lest mortality after exposure for 10 or 20 min contains 10% glycerol, 30% methanol and 0.5M trehalose.
In the last step, we combined the procedure to alter the biochemical properties of asexual eggs and our most suitable cryopreservation protocol. This stepwise approach led to successful cryopreservation of subitaneous Daphnia magna eggs. Although survival rates are still low, this is a large step forward in the process towards safe storage of clonal lines.status: Publishe
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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