1,720,998 research outputs found
Fatigue crack growth and failure on a composite helicopter main rotor hub: experimental and numerical investigation
No full textExperimental and numerical investigation on fatigue failure of composite helicopter main rotor hub
No full textAbstract: The Main Rotor Hub is a very critical component of the helicopter considering that its failure may determine catastrophic consequences for the whole rotorcraft. A complete experimental and numerical analysis is so necessary to certificate the fail safe and eventually the damage tolerant behavior of the component. In this paper the fail safe behavior of a composite titanium-graphite Rotor Hub is analyzed. The component, with artificial technological defects, was tested with complex contingent fatigue load in order to cause the failure of the titanium section. The failure started in proximity of a high stressed area and it propagated quickly in the whole titanium section but without involve the surrounding filament winding graphite, that is a fail safe device. The behavior of the hub during the whole test is simulated, with good accuracy, by means of a complete FE model that reproduces also the 3D propagation of the crack in the titanium section
Le imposte sul reddito
No full textIl lavoro si propone l’obiettivo di analizzare il trattamento contabile delle imposte sul reddito, secondo i principi contabili internazionali, muovendo, secondo la struttura dello standard vigente in materia, da un breve inquadramento generale per poi procedere all’investigazione delle regole che governano, in particolare, la ricognizione delle imposte differite nei prospetti di sintesi contabile
UNVEILING OLIGODENDROCYTE PRECURSOR CELL HETEROGENEITY: FOCUS ON BRAIN'S REGIONAL DIFFERENCES AND ON THE G PROTEIN COUPLED RECEPTOR GPR17
No full textOligodendrocyte Precursor Cells (OPCs, also referred to NG2 cells) have been proposed as the fourth glial population of the adult brain besides astrocytes, microglia and oligodendrocytes. In the past 30 years the interest in this class of cells has raised and led to important discoveries. It is now well known that adult OPCs are cycling precursors in the adult central nervous system (CNS), that have the ability to generate mature, and subsequently myelinating oligodendrocytes during development but also in the adulthood. Interestingly OPCs showed also the potential to generate astrocytes and neurons, both in vitro and in vivo. OPCs are not only multipotential but they also display the unique property, among glial cells, to form synapses with neurons. All these multiple functions raised the hypothesis that adult OPCs consist of a heterogeneous population of cells devoted to different tasks. The idea of heterogeneity, among OPCs, has been raised also for their differentiation properties. Previous studies indeed showed a regional difference in the rate of OPCs differentiation. However since the mechanisms of differentiation of adult OPCs have not been yet fully resolved, it is not clear whether this observation is determined by intrinsic differences among adult OPCs (supporting the thesis of heterogeneity), or by diverse environmental cues (fostering, on the contrary, the idea of homogeneity among adult OPCs, at least in terms of differentiation).
In this study we aimed to unveil the diversity between adult OPCs with respect to differentiation properties and to the expression of the G-protein coupled receptor GPR17.
To understand if the diversity in differentiation properties between grey matter (GM) and white matter (WM) OPCs is due to intrinsic determinants or environmental cues, we set up a series of transplantation experiments of adult OPCs derived from GM or WM into the adult brain WM or GM. Transplanted cells showed a good rate of survival and the ability to differentiate. Interestingly, only WM cells differentiated in both cortical areas, whereas GM cells differentiate only in the WM. These results suggest that both intrinsic determinants and environmental cues are important in the fate decision of OPCs.
With the aim to find possible candidates of such difference, we focused the study on the expression and possible function of the G protein receptor GPR17 (previously shown to be involved in postnatal OPCs differentiation), in the oligodendrocyte lineage of the adult brain. GPR17 is expressed only in a precise window of OPCs differentiation. A fraction of adult OPCs indeed transiently expressed the receptor, that is maintained on the cell membrane until a premyelinating stage. Proliferation and label-retaining studies pointed out that GPR17 expression starts immediately after adult OPCs division, suggesting that GPR17 labels a specific postmitotic stage of OPCs. With this deep characterization of GPR17 expression and relation to adult OPCs proliferation, we provided a new valuable tool to study a specific phase of the oligodendrocyte lineage. However, from our analysis is still not clear whether all OPCs are transiently expressing GPR17 or if the receptor labels only a subpopulation of OPCs. To solve this issue, the transgenic mouse line (GPR17-iCreERT2), that has been generated in parallel during this study, will be of great help. Moreover, the GPR17-iCreERT2 mouse model will be extremely useful to characterize the expression of GPR17 in other tissues besides the CNS. The unique possibility, to exploit this line to specifically knock out or overexpress other proteins, in cells expressing GPR17, will also increase the knowledge regarding GPR17 function in different systems.
In conclusion, we provided new insights in the differentiation properties of adult cortical OPCs, new tools to study in detail the function of GPR17 in OPCs differentiation and to define the pattern of expression of GPR17 and its role in different tissues
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
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