1,721,198 research outputs found
ESR spectroscopy for analyzing the spatial distribution of free radicals in ammonium tartrate
Full text linkIn the last few years the worldwide spread of radiation therapy with hadrons has
stimulated the research on the effects produced by these particles on biological sys
tems. This investigation on complex systems (such as cells) is aided by the study of
the effects on simpler organic compounds in order to better model how the defects
are produced by various types of ionizing radiations. Among the various experi
mental techniques the contribution of electron spin resonance (ESR) spectroscopy
is valuable because it does measure not only the total number of radiation-induced
defects (and therefore the absorbed dose), but it can also provide useful information
on the distribution of defects inside the matter and therefore on the linear energy
transfer (LET) and quality of the radiations. In this work the applications of three
experimental ESR methods for discriminating radiations with different quality on
ammonium tartrate samples are reviewed. In particular, continuous wave ESR (cw
ESR) spectroscopy allows to measure the ESR signal saturation with microwave
power, whereas pulsed ESR spectroscopy permits to measure the microscopic local
concentration by means of the analysis of the instantaneous diffusion and to measure
the distance distribution through the Double Electron-Electron Resonance (DEER)
Hydrogels for three-dimensional ionizing-radiation dosimetry
Full text linkRadiation-sensitive gels are among the most recent and promising developments for radiation therapy (RT) dosimetry. RT dosimetry has the twofold goal of ensuring the quality of the treatment and the radiation protection of the patient. Benchmark dosimetry for acceptance testing and commissioning of RT systems is still based on ionization chambers. However, even the smallest chambers cannot resolve the steep dose gradients of up to 30–50% per mm generated with the most advanced techniques. While a multitude of systems based, e.g., on luminescence, silicon diodes and radiochromic materials have been developed, they do not allow the truly continuous 3D dose measurements offered by radiation-sensitive gels. The gels are tissue equivalent, so they also serve as phantoms, and their response is largely independent of radiation quality and dose rate. Some of them are infused with ferrous sulfate and rely on the radiation-induced oxidation of ferrous ions to ferric ions (Fricke-gels). Other formulations consist of monomers dispersed in a gelatinous medium (Polyacrylamide gels) and rely on radiation-induced polymerization, which creates a stable polymer structure. In both gel types, irradiation causes changes in proton relaxation rates that are proportional to locally absorbed dose and can be imaged using magnetic resonance imaging (MRI). Changes in color and/or opacification of the gels also occur upon irradiation, allowing the use of optical tomography techniques. In this work, we review both Fricke and polyacrylamide gels with emphasis on their chemical and physical properties and on their applications for radiation dosimetry
Gel dosimeters for radiotherapy applications: results of a “research project of national interest” (PRIN)
No full textGoing 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
A 2D-FEM Model of Nonlinear Ultrasound Propagation in Trans-cranial MRgFUS Technique
No full textMagnetic Resonance guided Focused Ultrasound (MRgFUS) is a non-invasive technique based on the thermal ablation of a target using high intensity focused ultrasound. MRgFUS treatment applied to brain is challenging due to the skull presence that attenuates ultrasound, leading to heating effects in bone region. In this study, we simulate trans-cranial nonlinear ultrasound propagation considering the detailed structure of bone tissue. We developed a 2D Finite Element (FE) model that mimics the propagation of focused ultrasound through skin, skull and brain tissue. The skull is represented as a three-layered system with two cortical tables packing a layer of trabecular bone. We assume that the space between the concave transducer and tissue is filled by water. Nonlinear ultrasound propagation is determined through Westervelt equation. To control reflection, absorbing layers have been implemented on the boundaries of the domains. The solution of the pressure equation is subsequently coupled with Pennes bioheat equation to determine the temperature distribution in the tissue region. The acoustic pressure, acoustic intensity and temperature distribution are achieved from FE simulation. Highest values of acoustic pressure occur in the focal area and in the bone tissue region. Ablative temperatures, i.e. superior to 55 °C, are achieved in the target zone and at the cortical-trabecular interface. The thermal response in the focal region is in agreement with available literature and allows to validate the model effectiveness. The FE model offers new insights to predict secondary heating effects of ultrasound propagation in the skull region and to improve treatment planning
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
An EPR method for discriminating radiation beams in ammonium tartrate and tooth enamel
No full textThe radiation linear energy transfer (LET), which is the energy released by ionizing radiation per path unit, arouses great scientific interest because the biological damage produced by ionizing radiation in tissues is strictly related to LET. Radiation beams with different LETs will cause different spatial energy distribution and therefore different effects inside matter.
In the last twenty years the EPR spectroscopy has become a valuable dosimetric tool. This technique allows absorbed dose measurements through the detection of free radicals produced by ionizing radiation in organic and/or inorganic compounds.
In this work we have analyzed the possibility of using the acquisition of two components (first harmonic in-phase, FH-0, and second harmonic out-of-phase, SH-90, components with respect to the modulation field) of EPR signal to discriminate the radiation quality. Studies have shown that the second harmonic absorption signal detection out-of-phase of the tooth samples could be promising for the enhancement of the tooth EPR signal [1]. In fact, the tooth EPR signal due to irradiation has large relaxation times and the SH-90 detection is very sensitive to this kind of signals. In particular, in this work we have performed a study of the dependence of the two components of the EPR signal on microwave power in order to achieve information on quality beam and on the effective radiation LET. Actually, for different LET beams the different spatial distributions of the free radicals brings about differences in the relaxation times T1 and T2 (longitudinal and transversal, respectively). These differences involve differences in the relative intensities of the two components analyzed. The analyses were carried out on samples of ammonium tartrate which is a promising compound for the measurement of the absorbed ionizing radiation dose, as it shows suitable features, such as high efficiency of radiation-matter energy transfer, and a linear relation between radiation dose [2, 3] and on tooth samples. In particular, ammonium tartrate samples were exposed to 21 MeV protons, 60Co γ-photons and thermal neutrons as radiation beams with different LET. On the other hand, the tooth samples were irradiated to UV and gamma radiation.
References
[1] V. E. Galtsev, E.V. Galtseva,Ya. S. Lebedev 1996 47, 1311-1315
[2] S. K. Olsson, S. Bagherian, E. Lund, G. A. Carlsson, A. Lund, Appl. Radiat. Isot. 1999, 50, 95565.
[3] M. Marrale, M. Brai, A. Triolo, A. Bartolotta, M. C. DOca, 2006. Radiat. Res. 166, 802809
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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