1,721,111 research outputs found
The Italian affair: the employment of parallel-plate ionization chambers for dose measurements in high dose-per-pulse IORT electron beams.
No full textPURPOSE: At the high dose-per-pulse rates used by some intraoperative radiotherapy (IORT) units, the employment of ionization chambers for dose measurements needs an appropriate correction (k(sat)) for ion recombination. Through a revision of the existing literature, the authors compared different methods for the determination of the recombination correction factor and their impact on clinical dosimetry.
METHODS: A dosimetric characterization of IORT electron beams from a Linac Hitesys Novac7 (Aprilia-Latina, Italy) was performed. Dose-to-water (D(w)) values were measured with dose-per-pulse independent chemical dosimeters (operated by the Italian Primary Standard Dosimetry Laboratory, ENEA) and compared to doses obtained by two different parallel-plate ionization chamber models (Markus and Advanced Markus, PTW, Freiburg, Germany). For dose measurements using ionization chambers, the authors applied two different methods for the determination of the ion recombination correction factor (k(sat)), as suggested in previous articles. The first method is based on the experimental estimation of the free-electron fraction values p; the second one is based on the "nonstandard" two-voltage analysis including the free-electron component.
RESULTS: For a Markus type chamber, there is a good agreement between the results on k(sat) and those reported in the literature for both methods, while for the Advanced Markus chamber, no data are available for comparison.
CONCLUSIONS: Comparing values of D(w) obtained by dose-per-pulse independent dosimeters and by ionization chambers measurements corrected using the two different approaches, the authors can conclude that the k(sat) factor determination is very critical and that only an experimental protocol using ionization chamber intercalibration can be considered reliable
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
Quantitative methods to detect phospholipids at the oil-water interface
No full textPhospholipids are the main constituents of cell membranes and act as natural stabilizers of milk fat globules. Phospholipids are used in a wide range of applications, e.g. as emulsifiers in cosmetic, pharmaceutical and food products. While processed emulsion droplets are usually stabilized by a monolayer of phospholipids, cell membranes have a phospholipid bilayer structure and milk fat globules are stabilized by a complex phospholipid trilayer membrane. Despite the broad relevance of phospholipids, there are still many scientific challenges in understanding how their behavior at the fluid-fluid interface affects microstructure, stability, and physico-chemical properties of natural and industrial products. Most of these challenges arise from the experimental difficulties related to the investigation of the molecular arrangement of phospholipids in situ at the fluid-fluid interface and the quantification of their partitioning between the bulk phase and the interface, both under static and flow conditions. This task is further complicated by the presence of other surface-active components, such as proteins, that can interact with phospholipids and compete for space at the interface. Here, we review the methodologies available from the literature to detect and quantify phospholipids, focusing on oil-water interfaces, and highlight current limitations and future perspectives
Swelling-induced structural changes and microparticle uptake of gelatin gels probed by NMR and CLSM
No full textGelatin gels are increasingly involved in many industrial applications due to several advantages including cost efficiency and biocompatibility. Generally, their production requires the use of aqueous solvents, which cause significant swelling, due to the ability of solvent molecules to penetrate through the gel microstructure and increase its volume. Since swelling mechanisms and their effect on the gel structure are not fully understood, further investigations are required. In this work, we combine macroscopic measurements of the swelling ratio (SR) with Nuclear Magnetic Resonance (NMR) and Confocal Laser Scanning Microscopy (CLSM) to investigate changes in the gelatin structure as a function of both polymer concentration and swelling time. SR values increase as a function of time until a maximum is reached and then show a slight drop for all the gelatin concentrations after 24 h swelling time, probably due to a network relaxation process. NMR allows determination of mass transport and molecular dynamics of water inside the gelatin pores, while CLSM is used to visualize the penetration of tracers (polystyrene microbeads) with a diameter much larger than the gel pores. Structural parameters, such as average pore size and tortuosity, are estimated. In particular, the pore size decreases for higher polymer concentration and increases during swelling, until reaching a maximum, and then dropping at longer times. The penetration of tracers provides evidence of the heterogeneity of the gel structure and shows that single microcarriers can be loaded in gelatin gels upon swelling
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
Usefulness of stress cardiac single-photon emission computed tomographic imaging late after percutaneous coronary intervention for assessing cardiac events and time to such events
No full textThis study assessed the predictors and temporal characteristics of cardiac risk in patients undergoing stress single-photon emission computed tomography (SPECT) after percutaneous coronary intervention (PCI). Stress SPECT was performed in 346 patients 12 to 18 months after PCI. Cardiac death and myocardial infarction were considered events. Cox proportional hazards analysis was used to identify predictors of events and parametric survival analysis to predict time to events. During follow-up (31 +/- 10 months), 17 events occurred (4.9% cumulative event rate). Prescan likelihood of ischemia and ischemia at SPECT were independent predictors of events (p or =2% risk of events were >48 months in those with low prescan likelihood of ischemia and >20 months in those with intermediate to high prescan likelihood. Ischemia at SPECT was associated with higher probability of failure accelerating over time. In conclusion, clinical variables and stress SPECT performed 12 to 18 months after PCI are useful to characterize risk of cardiac events and its temporal variation. Parametric survival models seem useful to estimate predicted time to risk and levels of risk at specific intervals after PCI
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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