1,721,049 research outputs found
Simulation of the measured ionisation-cluster distributions of alpha-particles in nanometric volumes of propane
No full textIn the last years, the probability of the formation of ionisation clusters by primary alpha particles at 5.4 MeV in nanometric volumes of propane (20.6 and 24.0 nm in a material of density 1.0 g cm(-3)) was studied experimentally and by Monte Carlo simulation. Calculations were performed taking into account the single electron detection efficiency of the track-nanodosimetric counter, which was estimated on the base of Monte Carlo calculations of electron transport inside the detector. Now a new evaluation of the efficiency has been performed, pointing out a value lower than previously estimated. Besides, the efficiency of the counter in resolving temporally the collected electrons has been calculated, together with its effect on the measured distribution. On the base of these evaluations, a new comparison has been performed between measurements and calculations, pointing out a better agreement than previously reported
An Accelerator-Based Neutron Source for BNCT of Skin Melanoma
No full textBNCT of skin malignant melanoma bas been developed in Japan since 1972. Primary lesions and unobservable satellite metastasis can be selectively treated with this technique. The clinical results related to 18 patients treated in Japan up to January 1996 are analysed in ref. 1. The survival rate after two or more years resulted to be 78%, regardless the level of melanoma progression. 10B-paraboronphenylanine (BPA) was used as the boron carrier to the tumour. The patiens were irradiated at a research reactor facility for 1-2 hours with thermal neutrons and the related maximum fluences at the tumour sites were in the range (1.0-2.0)x1013 cm-2.The design of the accelerator-based neutron source for BNCT of skin melanoma discussed in the present work is described in ref. 3. Neutrons are produced by bombarding a thick beryllium target with 7 MeV deuterons. The target is contained in a heavy water moderator in turn enclosed in a graphite structure. Lead filters are placed on the Faraday cup containing the beryllium target and on the heavy water container to reduce the prompt gamma ray dose. The experimental verification of the accelerator-based source was performed at the CN Van De Graaff accelerator of the Laboratori Nazionali di Legnaro (LNL, Italy). Measurements of thermal fluence uniformity and prompt gamma ray dose at the irradiation position, together with estimates of the neutron fluences inside an Alderson phantom are discussed in this paper
Towards a compact experimental setup for gas-based microdosimetry
No full textMicrodosimetry measures the stochastics of imparted energy at the micrometer scale and is a reliable experimental technique to monitor complex radiation fields such as those used in hadron therapy. At the Legnaro National Laboratories of INFN, miniaturized gas-based micro dosimeters were developed specifically for this kind of applications. However, their use outside research facilities has been hindered by the encumbrance of the gas-flow system which
is used to preserve gas purity and of the high-resolution analog electronic chain. To overcome this drawback, a new detector designed to work without gas flow was developed recently. The stability and reproducibility of its response in sealed conditions were studied in two measuring
shifts one year apart from each other, both with the analog electronic chain and with a compact digital acquisition system. Preliminary results confirm the possibility to operate the detector with a very compact experimental setup, which could be a major advantage in clinical facilities.This work is supported by the 5th Scientific Commission of the Italian Istituto Nazionale di Fisica Nucleare (INFN) in the framework of the project CIMICE
BAYESIAN ANALYSIS OF NANODOSIMETRIC IONISATION DISTRIBUTIONS DUE TO ALPHA PARTICLES AND PROTONS
No full textTrack-nanodosimetry has the objective to investigate the stochastic aspect of ionisation events in particle tracks, by evaluating the probability distribution of the number of ionisations produced in a nanometric target volume positioned at distance d from a particle track. Such kind of measurements makes use of electron (or ion) gas detectors with detecting efficiencies non-uniformly distributed inside the target volume. This fact makes the reconstruction of true ionisation distributions, which correspond to an ideal efficiency of 100%, non-trivial. Bayesian unfolding has been applied to ionisation distributions produced by 5.4 MeV alpha particles and 20 MeV protons in cylindrical volumes of propane of 20 nm equivalent size, positioned at different impact parameters with respect to the primary beam. It will be shown that a Bayesian analysis performed by subdividing the target volume in sub-regions of different detection efficiencies is able to provide a good reconstruction of the true nanodosimetric ionisation distributions
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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