1,721,096 research outputs found
Coupling Radiation Transport and Track-Structure Simulations: Strategy Based on Analytical Formulas Representing DNA Damage Yields
No full textExisting radiation codes for biomedical applications face the challenge of dealing with largely different spatial scales, from nanometer scales governing individual energy deposits to macroscopic scales of dose distributions in organs and tissues in radiotherapy. Event-by-event track-structure codes are needed to model energy deposition patterns at cellular and subcellular levels. In conjunction with DNA and chromatin models, they predict radiation-induced DNA damage and subsequent biological effects. Describing larger-scale effects is the realm of radiation transport codes and dose calculation algorithms. A coupling approach with a great potential consists in implementing into radiation transport codes the results of track-structure simulations captured by analytical formulas. This strategy allows extending existing transport codes to biologically relevant endpoints, without the need of developing dedicated modules and running new computationally expensive simulations. Depending on the codes used and questions addressed, alternative strategies can be adopted, reproducing DNA damage in dependence on different parameters extracted from the transport code, e.g., microdosimetric quantities, average linear energy transfer (LET), or particle energy. Recently, a comprehensive database on DNA damage induced by ions from hydrogen to neon, at energies from 0.5 GeV/u down to their stopping, has been created with PARTRAC biophysical simulations. The results have been captured as a function of average LET in the cell nucleus. However, the formulas are not applicable to slow particles beyond the Bragg peak, since these can have the same LET as faster particles but in narrower tracks, thus inducing different DNA damage patterns. Particle energy distinguishes these two cases. It is also more readily available than LET from some transport codes. Therefore, a set of new analytical functions are provided, describing how DNA damage depends on particle energy. The results complement the analysis of the PARTRAC database, widening its potential of application and use for implementation in transport codes
Modelling initial radiation-induced damage to mitochondrial DNA by PARTRAC
No full textAlterations to mitochondria as the sites of energy production in human cells have been identified in a number of severe diseases. Mitochondria may initiate and/or amplify bystander signalling [1]. Mitochondrial alterations have been implicated in radiation-induced cardiovascular effects, too [2].
To extend the applicability of PARTRAC biophysical tool [3] towards effects on mitochondria, the nuclear DNA and chromatin as the primary target of radiation has been complemented by a model of mitochondrial DNA (mtDNA). Following experimental information [4], the mtDNA model consists of a circular 16.6 kbp double-helix with U-turns every about 20 bp, with compact higher-order structure so that the whole molecule packs into a 100 nm nucleoid. 10 such nucleoids have been placed within a mitochondrion, and a model heart cell has been populated with 1000 mitochondria placed randomly in the cytoplasm.
This model of mitochondria and their DNA has been overlaid with tracks of 60Co photons and 5 MeV α-particles. The event-by-event simulation includes ionizations and excitations in liquid water by both primary and all secondary particles, as well as production of radicals, their diffusion, mutual reactions, and attacks to mtDNA, as described for nuclear DNA previously [3].
Single- and double-strand breaks have been scored, assuming alternative radical scavenging capacities within the mitochondria. While direct radiation effects in mtDNA are identical to nuclear DNA, indirect effects in mtDNA are in general larger due to lesser scavenging and the lack of DNA-protecting histones. The predicted fragmentation patterns in mtDNA reflect the frequent U-turns of the molecule. Detailed results will be presented at the meeting. The simulations complement the scarce experimental data on radiation-induced mtDNA damage [5] and help elucidate the relative roles of initial mtDNA vs nuclear DNA damage and of pathways that amplify their respective effects
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
La Guerre des Paysans en Allemagne d'Engels, préface de D. Riazanov, et notes de Z. Friedland. W. Zimmermann, Allgemeine Geschichte des grossen Bauern- krieges nach handschriftlichen und gedruckten Quellen
No full textFebvre Lucien. La Guerre des Paysans en Allemagne d'Engels, préface de D. Riazanov, et notes de Z. Friedland. W. Zimmermann, Allgemeine Geschichte des grossen Bauern- krieges nach handschriftlichen und gedruckten Quellen. In: Annales d'histoire économique et sociale. 2ᵉ année, N. 7, 1930. pp. 437-438
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
- …
