1,720,968 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
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
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Characterization of an RTX-Like Toxin and an Alpha-2-Macroglobulin in Pantoea stewartii subsp. stewartii, Causal Agent of Stewart's Wilt of Sweet Corn
Get PDFPantoea stewartii subsp. stewartii DC283, the causal agent of Stewart's wilt, is an important bacterial pathogen of sweet corn. P. stewartii colonizes the apoplastic space and xylem tissue, resulting in characteristic water-soaked (WS) lesions and wilting. A gene encoding a putative RTX-like toxin, rtx2, has been identified in P. stewartii. RTX toxins belong to the pore-forming toxin family and have lytic properties in animal systems. Little is known about the role of RTX toxins in plant pathogenesis. Interestingly, a P. stewartii Δrtx2 mutant was noticeably unable to incite WS lesions in planta implicating it in the cell lysis associated with lesion formation. In addition, rtx2 is genetically linked to components of the Rcs phosphorelay; a global regulatory system of critical virulence factors in P. stewartii. This suggests a possible functional relationship, particularly because they are transcribed from a single promoter. The RTX2 domain structure is consistent with an autotransported protein and contains conserved transmembrane domains suggesting it translocates itself to the cell surface. The signal relay pathway that stimulates the Rcs phosphorelay is unknown, but membrane perturbation plays a key role in stimulating the Rcs system. We hypothesize that RTX2 contributes to the membrane dynamics that are being sensed by the Rcs system, thus modulating activation of signal transduction through the system.Pantoea stewartii is a bacterial plant pathogen that causes Stewart's Wilt of sweet corn. P. stewartii is transmitted by the corn flea beetle, which creates wounds in the plant and allows the bacterium to enter the xylem and leaf apoplast resulting in characteristic water-soaked lesions and wilting. The P. stewartii genome has been fully sequenced and two putative alpha-2-macroglobulin (α2M) genes have been identified. The α2M protein is a known serine protease inhibitor in eukaryotic organisms that binds non-self proteases and degrades them. In prokaryotes, the α2M gene can be found juxtaposed next to a gene that encodes a penicillin-binding protein (PBP) associated with cell wall repair. It has been suggested that the α2M protein protects the bacteria from non-self proteases and the PBP repairs damaged peptidoglycan that may result from a damage cell envelope. Proposed functions of the α2M protein include subverting host proteases. The α2M protein may also function in defense against other bacterial proteases present in multicellular microbial communities. The goal of this study was to characterize the role of α2MI during the host-pathogen interaction between P. stewartii and sweet corn
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Characterization of Xylella fastidiosa Virulence Factors and Host Physiological Responses That Contribute to Pierce's Disease in Grapevine
Get PDFXylella fastidiosa is a xylem-limited bacterium that causes Pierce’s Disease (PD) in grapevine. PD symptom progression is correlated with systemic colonization by X. fastidiosa, which occurs via pit membrane degradation. Previous studies determined that a polygalacturonase, one of several cell wall degrading enzymes (CWDEs) secreted by X. fastidiosa, is necessary for pit membrane degradation. Here, it is demonstrated that the loss of two X. fastidiosa β-1,4-endoglucanases (EGases) in tandem causes significantly slower PD symptom development and progression, and reduces X. fastidiosa virulence and population size. Furthermore, differences in the PD symptom progression rate between two cultivars appear to be caused by variations in pit membrane carbohydrate composition, which influence the rate of enzymatic degradation, and subsequently, the rate of systemic colonization. How these CWDEs and other virulence factors are secreted has not been fully elucidated. However, several are predicted to be secreted via the Type II secretion system (T2SS). T2SS-deficient X. fastidiosa mutants did not induce PD symptoms, and the mutant bacteria were not recovered from infected vines, indicating that the T2SS and its secreted substrates are necessary for virulence and survival. Analysis of wild type X. fastidiosa and T2SS-deficient mutant secretomes found six potential Type II secreted proteins for further characterization, including three lipases, a β-1,4-cellobiohydrolase, a protease, and a hypothetical protein. However, none of the CWDEs were present in the secretomes, but their high transcript abundance indicates that these enzymes could be post-transcriptionally regulated. Several PD symptoms appear similar to drought stress symptoms. Under drought conditions, decreased photosynthesis, cessation of plant growth, and carbon starvation occur. Tylose formation in response to X. fastidiosa infection occludes vessels to prevent the spread of pathogens and air embolisms. Interestingly, genes involved in photosynthesis and plant growth are down-regulated during PD symptom development, and tylose formation increases significantly. This increased vessel occlusion in the absence of new vessel formation over time could cause prolonged water stress. Furthermore, starch in the ray parenchyma depletes as PD symptoms progress, indicating that carbon starvation occurs. These results indicate that, along with X. fastidiosa-mediated virulence factors, host responses also contribute to PD
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Global Regulation of Virulence Determinants During Plant Colonization in the Bacterial Phytopathogen, Pantoea stewartii subsp. stewartii
Get PDFPantoea stewartii subsp. stewartii, the etiological agent of Stewart's wilt, is a bacterial pathogen of sweet corn which colonizes both the apoplast and xylem tissues. During the initial stages of the infection process, the pathogen forms water-soaked lesions through lysis of the plant cells, followed by colonization of the xylem tissue where it can grow to high cell densities and form biofilms. Biofilm formation within the xylem vessels can block water flow, causing the characteristic wilting symptoms of P. stewartii infection. Throughout the infection process, P. stewartii must contend with a variety of stresses inherent to its changing environment, such as production of reactive oxygen species (ROS) in the host, and nutrient limitation. Global regulatory mechanisms that control gene expression in response to environmental conditions therefore play a crucial role in success of the pathogen. We found that ROS exposure initiates an induced stress response through the OxyR and SoxR transcription factors which plays an important biological role in adaptation of the pathogen to different niches in the host during infection. OxyR is essential for the wilting symptoms characteristic of the later stages of infection, likely due to its role in optimal exopolysaccharide (EPS) production. The initial stages of infection (water-soaked lesion formation) rely on SoxR-dependent gene expression in order to colonize to wild type levels. In addition to the oxidative stress response, we found that OxyR indirectly regulates iron transport through a siderophore-dependent mechanism. We found that siderophore-mediated iron acquisition, in addition to its primary role of enhancing bacterial growth under iron-limiting conditions, regulates motility and bacterial movement in planta. As a result, siderophore production is required for full virulence of P. stewartii. In order to investigate a link between OxyR regulation and optimal EPS production, we characterized the Rcs phosphorelay signal transduction system, a known regulator of EPS and biofilm formation. Rcs regulation is crucial for virulence in P. stewartii due to its regulation of motility and EPS production. These studies unravel some of the complexities of global regulation required for P. stewartii and, likely, other bacterial pathogens to adapt to different environments such as the xylem
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