1,720,995 research outputs found
Mechanistic and phenomenological models for the estimate of radiation-induced biological damage. Physica Medica 17, 3-12.
No full textDifferent techniques for modelling the radiation action on biological targets are analysed, focussing the attention on phenomenological and mechanistic approaches. Phenomenological models allow practical applications (typically in radioprotection and radiotherapy) and are characterised by descriptive features aimed to organise the experimental observations within a formal structure. Mechanistic models are used in basic research and are aimed to reach a better understanding of the physical, chemical and biological processes that, from the initial energy depositions, lead to biological damage. Many different orders of magnitude are involved, both at a spatial level (from atomic dimensions to cellular and organ dimensions) and at a temporal level (from the 10(-15) s of the physical interactions to the hours, and possibly years, of the biological processes). The following aspects are treated: track structure; DNA damage; chromosome aberrations; cell inactivation; low doses and mixed fields. The attention focuses on the comparison between simulations and experiments, the comparison between mechanistic and phenomenological approaches, the determination of the model parameters (in particular on the uncertainties and correlations) and the role of the models in radioprotection and radiotherapy applications
Nuclear architecture and radiation-induced chromosome aberrations: models and simulations.
No full textKnowledge of radiation track structure and its interaction with biological targets is a fundamental starting point
in understanding the mechanisms underlying the induction of biological damage. In this context Monte Carlo codes are a
powerful tool of investigation, allowing one to simulate both track structure and the features of the target(s) of interest at
different scales, from nanometres (linear dimensions of DNA) to micrometres (linear dimensions of human cell nuclei and
interphase chromosome territories). In the light of recent experimental findings on nuclear architecture, different approaches
in modelling chromosome structure and aberration induction are discussed. In particular, a model is presented in which
chromosome territories were explicitly described as subnuclear regions and aberration induction was modelled by coupling
the structure of the target with that of the radiation track. Comparisons between model predictions and experimental results
from the literature are also reported
Cellular communication and bystander effects in modelling low-dose radiation action
No full textAvailable data suggesting the occurrence of “bystander effects” (i.e. damage induction in cells not traversed by radiation)
were collected and critically evaluated, in view of the development of low-dose risk models. Although the underlying mechanisms
are largely unknown, cellular communication seems to play a key role. In this context, the main features of cellular
communication were summarised and a few representative studies on bystander effects were reported and discussed. Three
main approaches were identified: (1) conventional irradiation of cell cultures with very low doses of light ions; (2) irradiation
of single cells with microbeam probes; (3) treatment with irradiated conditioned medium (ICM), i.e. feeding of unexposed
cells with medium taken from irradiated cultures. Indication of different types of bystander damage (e.g. cell killing, gene
mutations and modifications in gene expression) has been found in each of the three cases. The interpretations proposed
by the investigators were discussed and possible biases introduced by specific experimental conditions were outlined. New
arguments and experiments were suggested, with the main purpose of obtaining quantitative information to be included in
models of low-dose radiation action. Implications in interpreting low-dose data and modelling low-dose effects at cellular and
supra-cellular level, including cancer induction, were analysed. Possible synergism with other low-dose specific phenomena
such as adaptive response (AR) (i.e. low-dose induced resistance to subsequent irradiation) was discussed
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
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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