12,402 research outputs found
Early degenerate selection of thymocytes by class I major histocompatibility complex
No full textOntogeny of T cells is accomplished in the thymus by a process of positive selection, in which interaction of the T cell receptor (TcR) expressed on CD4+8+ thymocytes with self major histocompatibility complex (MHC), expressed on cortical epithelial cells, determines the progress along the maturation pathway and confers self restriction to T cells. Conversely, cells behaving as self reactive by interaction with bone marrow-derived antigen-presenting cells are negatively selected by apoptosis. We show here that the presence of a class I-restricted soluble TcR (sTcR) in the fetal thymic microenvironment, early in T cell ontogeny, determines an enhanced negative selection of a sizeable number of CD4+8+ thymocytes, which have been previously subjected to a positive-selection event. We hypothesize that the generation of the mature thymic T cell repertoire stems from an interaction of TcR, under a critical affinity threshold, with a self peptide-MHC complex which is common to a great number of TcR specificities using the same restriction element. A shift in this affinity threshold, caused by sTcR, results in the generation of cells acting in a self-reactive manner, which are then deleted. In extended fetal thymus organ culture in the presence of sTcR, we have also observed the appearance of mature CD8+ T cells,which once adoptively transferred to syngeneic nude mice are expanded in the periphery, consistent with an enhanced avidity of these cells for self MHC
Cohomology of Lie Superalgebras: Forms, Integral Forms and Coset Superspaces
No full textWe study Chevalley-Eilenb erg cohomology of physically relevant Lie superalgebras related to supersymmetric theories, providing explicit expressions for their cocycles in terms of their Maurer-Cartan forms. We include integral forms in the picture by defining the notions of constant densities and integral forms related to a Lie superalgebra. We develop a suitable generalization of Chevalley-Eilenb erg cohomology extended to integral forms and we prove that it is isomorphic via a Poincare duality-type pairing to the ordinary Chevalley-Eilenb erg cohomology of the Lie superalgebra. Next, we study equivariant Chevalley-Eilenb erg cohomology for coset superspaces, which play a crucial role in supergravity and superstring models. Again, we treat explicitly several examples, providing cocycles' expressions and revealing a characteristic infinite -dimensional cohomology
Characteristics of PA cost-effectiveness studies by the first author, setting, number of PAs & design.
No full textCharacteristics of PA cost-effectiveness studies by the first author, setting, number of PAs & design.</p
Surface expression and functional competence of CD3-independent TCR ζ-chains in immature thymocytes
No full textIn recombinase-deficient (RAG-2(-/-)) mice, double-negative thymocytes can be stimulated to proliferate and differentiate by anti-CD3 Abs. CD3 molecules are expressed on the surface of these cells in association with calnexin. In this study, we show that ζ-chains can be recovered as phosphorylated proteins in association with phosphorylated ZAP-70 from anti- CD3-stimulated RAG-2(-/-) thymocytes, even though they are not demonstrably associated with the CD3/calnexin complex. The lack of a physical association of ζ dimers with the CD3 complex in RAG-2(-/-) thymocytes and also in a pre- TCR-expressing cell line, as well as the efficient association of ζ dimers with ZAP-70 in the RAG-2(-/-) thymocytes, suggest that these ζ-chain dimers could contribute to pre-TCR signaling. This idea is supported by the finding that in RAG-2(-/-) ζ-deficient thymocytes, ZAP-70 and p120(cbl) were only weakly phosphorylated
South African responses to Open Access publishing: a survey of the research community
No full textOpen access publishing offers wide benefits to the scholarly community and may also afford relief to financially embattled academic libraries. The progress of the open access model rests upon the acceptance and validation of open access journals and open archives or institutional repositories by the academic mainstream, particularly by publishing researchers. To what extent are the key actors in the South African research system aware of the advantages of open access? This article reports on the findings of a recent survey undertaken to assess the current awareness, concerns and depth of support for open access amongst local researchers, research managers and policy makers in South Africa. The study focuses on issues of quality, article or author charges and the established academic reward system. It concludes that within the prevailing framework, there is little prospect that academics would choose to publish within open access
journals. Recommendations for advocacy by the library community are proposed
Author Co-Citation Analysis (ACA): a powerful tool for representing implicit knowledge of scholar knowledge workers
No full textIn the last decade, knowledge has emerged as one of the most important and valuable organizational assets. Gradually this importance caused to emergence of new discipline entitled ―knowledge management‖. However one of the major challenges of knowledge management is conversion implicit or tacit knowledge to explicit knowledge. Thus Making knowledge visible so that it can be better accessed, discussed, valued or generally managed is a long-standing objective in knowledge management. Accordingly in this paper author co- citation analysis (ACA) will be proposed as an efficient technique of knowledge visualization in academia (Scholar knowledge workers)
Relative (pa,pb,pa,pa−b)-difference sets in p-subgroups of SL(n,K)
No full textAbstractIn this note, we study relative (pa,pb,pa,pa−b)-relative difference sets in certain p-subgroups of SL(n,K), K=Fq, where q is a prime power
Uma análise das políticas macroeconômicas do governo FHC, governo LULA
No full textTCC (graduação) - Universidade Federal de Santa Catarina. Centro Sócio-Econômico. Economia.0 presente trabalho tem por objetivo fazer uma análise das políticas macroeconômicas dos governos FHC e Lula. Ele apresenta a trajetória dessas políticas durante os dois mandatos, enfatizando as conseqüências que elas produziram na economia brasileira. Nesse período a condução da política econômica objetivou a contenção e o controle da inflação, em detrimento de uma taxa um pouco maior de crescimento. 0 trabalho apresenta com detalhes o funcionamento dos instrumentos de políticas macroeconômicas. Ressaltando a) a tríplice mudança na condução das políticas macroeconômica ocorridas no Governo FHC b) como a condução das políticas monetária, fiscal e cambial não mudou de um Governo para o outro, mas o seu resultado sim c) como as políticas macroeconômicas reagiram a os choques externos, principalmente no Governo FHC d) como o Governo Lula conseguiu reduzir a relação divida pública/PI
Open access self-archiving: An author study
No full textThis, our second author international, cross-disciplinary study on open access had 1296 respondents. Its focus was on self-archiving. Almost half (49%) of the respondent population have self-archived at least one article during the last three years. Use of institutional repositories for this purpose has doubled and usage has increased by almost 60% for subject-based repositories. Self-archiving activity is greatest amongst those who publish the largest number of papers. There is still a substantial proportion of authors unaware of the possibility of providing open access to their work by self-archiving. Of the authors who have not yet self-archived any articles, 71% remain unaware of the option. With 49% of the author population having self-archived in some way, this means that 36% of the total author population (71% of the remaining 51%), has not yet been appraised of this way of providing open access. Authors have frequently expressed reluctance to self-archive because of the perceived time required and possible technical difficulties in carrying out this activity, yet findings here show that only 20% of authors found some degree of difficulty with the first act of depositing an article in a repository, and that this dropped to 9% for subsequent deposits. Another author worry is about infringing agreed copyright agreements with publishers, yet only 10% of authors currently know of the SHERPA/RoMEO list of publisher permissions policies with respect to self-archiving, where clear guidance as to what a publisher permits is provided. Where it is not known if permission is required, however, authors are not seeking it and are self-archiving without it. Communicating their results to peers remains the primary reason for scholars publishing their work; in other words,
researchers publish to have an impact on their field. The vast majority of authors (81%) would willingly comply with a mandate from their employer or research funder to deposit copies of their articles in an institutional or subject-based repository. A further 13% would comply reluctantly; 5% would not comply with such a mandate
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