1,721,358 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
Dissecting the mechanism underlying T cell receptor-mediated intercellular transfer of peptide-Major Histocompatibility complexes
No full textCell surface molecules have been observed to pass from one cell to another as part of their interaction. This phenomenon, known as trogocytosis, has been observed in many cell types, particularly in the immune system. One receptor that is fundamental to the body`s defence against many pathogens is the expressed polymorphic T cell receptor (TCR), which interacts with major histocompatibility complex molecules loaded with antigenic peptides (pMHC). While TCR-mediated trogocytosis of MHC complexes has been described in a number of publica- tions, the underlying mechanisms as well as the fate of the acquired pMHC molecules remain unclear. The aim of this thesis is to gain a better understanding of TCR-mediated trogocytosis of pMHC. The transfer of pMHC from donor to recipient cells was quantified by flow cytometry using both fluorescent proteins covalently linked to the intracellular domain of pMHC and fluorescent an- tibodies. We demonstrated that TCR-mediated trogocytosis of pMHC occurs across a species barrier, as murine 58ab OT-1 T cells were able to acquire corresponding murine pMHC from Chinese hamster ovary cells. This limited trogocytosis to one type of receptor-ligand interaction and improved the reliability of our experimental system. In the first part, we investigated the role of pMHC-TCR affinity on the efficacy of trogocytosis. By generating a library of cell lines expressing pMHC with different LCMV gp33 peptides, we were able to show a positive correlation between TCR-pMHC affinity and the efficiency of tro- gocytosis. In the second part, we investigated whether TCR-mediated trogocytosis depends on this TCR signalling function or occurs independently. TCR-mediated pMHC trogocytosis was unaffected by blocking TCR signalling with the Src kinase inhibitors PP2 or A77. Furthermore, efficient trogocytosis could be achieved by cell lines expressing variants of CD3e, namely C80G and K76T, which have been reported to block TCR signalling. Taken together, our data suggest that TCR-mediated trogocytosis of pMHCs is independent of TCR signalling. Lastly, we analysed the fate determinants of trogocytosed pMHC. The generation of pMHC as single chain trimers with non-cleavable linkers increased the surface expression of acquired pMHC compared to pMHC constructs with cleavable linkers. Trogocytosis of pMHC is known to involve internalization of TCR-pMHC into intracellular vesicles, exposing this association to the environment within the vesicles. As we have shown that non-cleavable linkers increase the susceptibility of pMHC to acidification and proteases, we hypothesise, that this facilitates dis- sociation of TCR and pMHC, leading to recycling of the pMHC
Der Transkriptionsfaktor T-bet wird durch IL-15 und Agonistenselektion induziert und kontrolliert die Entwicklung von CD8[alpha][alpha]+ intraepithelialen Lymphozyten
No full textCD8aa+ intraepithelial lymphocytes (IELs) are instru- mental in maintaining the epithelial barrier in the in- testine. Similar to natural killer cells and other innate lymphoid cells, CD8aa+ IELs constitutively express the T-box transcription factor T-bet. However, the precise role of T-bet for the differentiation or function of IELs is unknown. Here we show that mice geneti- cally deficient for T-bet lacked both TCRab+ and TCRgd+ CD8aa+ IELs and thus are more susceptible to chemically induced colitis. Although T-bet was induced in thymic IEL precursors (IELPs) as a result of agonist selection and interleukin-15 (IL-15) recep- tor signaling, it was dispensable for the generation of IELPs. Subsequently, T-bet was required for the IL-15-dependent activation, differentiation, and expansion of IELPs in the periphery. Our study re- veals a function of T-bet as a central transcriptional regulator linking agonist selection and IL-15 signaling with the emergence of CD8aa+ IELs
Hospital acquired infections and their investigation – dealing with the impact of time in hospital epidemiology
No full textThe topic of this thesis is the investigation of hospital acquired infections (HAI) and how to deal with time dependency in this context. When investigating the risk of HAI, researchers face the challenge of competing risks. The complete picture can be illustrated and investigated via an illness-death model. Considering HAI as an outcome, there are two perspectives to distinguish amongst: The clinicians’ and the epidemiologists’ perspective, concerning risk and aetiology of HAI, respectively. A common approach for risk factor analysis of HAI is logistic regression. This is a valid but rather crude approach as time is ignored. This thesis examines the analysis of HAI via logistic regression adjusted for time, either length of stay(LOS) or time at risk (TAR). Both approaches are attempts to incorporate time dependency. However, clarification is needed about what is modeled and whether this is appropriate. The investigation of adjustment for LOS demonstrates that this approach is not valid. LOS consists of the time before and the time after HAI. Thus, not only effects on the occurrence of HAI impact LOS, but also effects on death and discharge after the infection. A simulation study shows that risk factor analysis via logistic regression adjusted for LOS can result in misleading effect estimates leading to wrong conclusions. Furthermore, adjustment for TAR is investigated. While there are well understood regression models available for investigationof the cumulative incidence function (CIF), insights are needed in what logistic regression adjusted for TAR models. A simulation study shows, that it is unclear how the results can be translated into a measure modeling the CIF and thus addressing the clinicians’ perspective. Furthermore, the results show that this approach is no measure corresponding to the epidemiologists’ perspective, distinguishing between direct and indirect effects on HAI.A further challenge arising when investigating HAI are unknown infection times. It may occur that only the infection status and LOS are known, but the time of infection is not. This is an extreme version of interval censoring of time-to-event data. There are tools for interval censored data motivated by studies collecting data at scheduled visit times. Investigation via real and simulated data shows that these methods can be applied in an extreme interval censoring setting. The results for analysis of the clinicians’ and epidemiologists’ perspective are promising when considering HAI as an outcome. Considering HAI as a time-dependent exposure and its burden measured by change in LOS or its effect on the death and discharge hazard, estimates of each transition can be obtained from the existing tools for interval censored data. These estimates can be used for manual calculation of the quantity of interest. The topics covered in this thesis are important in recent hospital epidemiology. There are many settings where time dependency plays an important role but infection times are unknown. For instance, this is also the case when investigating COVID-19. In conclusion, even with rough data it is worthwhile considering more sophisticated approaches in order to investigate HAI incorporating time. Thus, a better reflection of the reality of HAI development in can be given.
Der Trankriptionsfaktor T-bet wird durch IL-15 und Agonistenselektion induziert und kontrolliert die Entwicklung von CD8αα+ intraepithelialen Lymphozyten
No full textCD8αα(+) intraepithelial lymphocytes (IELs) are instrumental in maintaining the epithelial barrier in the intestine. Similar to natural killer cells and other innate lymphoid cells, CD8αα(+) IELs constitutively express the T-box transcription factor T-bet. However, the precise role of T-bet for the differentiation or function of IELs is unknown. Here we show that mice genetically deficient for T-bet lacked both TCRαβ(+) and TCRγδ(+) CD8αα(+) IELs and thus are more susceptible to chemically induced colitis. Although T-bet was induced in thymic IEL precursors (IELPs) as a result of agonist selection and interleukin-15 (IL-15) receptor signaling, it was dispensable for the generation of IELPs. Subsequently, T-bet was required for the IL-15-dependent activation, differentiation, and expansion of IELPs in the periphery. Our study reveals a function of T-bet as a central transcriptional regulator linking agonist selection and IL-15 signaling with the emergence of CD8αα(+) IELs
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
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