1,720,969 research outputs found
A STUDY OF THE DYNAMIC BEHAVIOR OF DISPERSION-TYPE TUBULAR REACTOR MODELS
No full textThe dynamic behavior of dispersion-type tubular reactors, referred to as finite and truncated models depending on the boundary condition representations at the reactor exit, was investigated through numerical simulations. It was found that the dynamic behavior of the two models can be identical or different depending on how the Peclet number changes.113Nsciescopu
Optimization of dual layer phoswich detector consisting of LSO and LuYAP for small animal PET
No full textPhoswich detectors for small animal PET have been developed to measure the depth of interaction and to improve resolution performances. The aim of this study was to perform simulations to design the optimum lengths of crystals composing a dual layer phoswich detector. A simulation tool, the Geant4 Application for Tomographic Emission (GATE), was used and validated against a commercially available small animal PET using a dual layer phoswich detector. The newly designed small PET system employed cerium doped lutetium oxyorthosilicate (LSO) --cerium doped lutetium-yttrium aluminum perovskite (LuYAP) phoswich detector modules, which consisted of 8 x 8 arrays of dual layer crystals, with a 2 x 2 mm sensitive area, coupled to a Hamamatsu R7600-00-M64 position sensitive photomultiplier tube (PSPMT). The sensitivities and variations of the radial resolutions were simulated by varying the length of the LSO front layer from 0 to 10 nun, while the total length (LSO+LuYAP) was fixed to 20 nun for 10 and 19 cut diameter ring scanners. The results support the validity of the simulation tool. The radial resolution uniformity was markedly improved using the depth of interaction (DOI) information, and the optimal lengths of the crystal layers for minimizing the variation of the radial resolutions also existed. In the 10 cm ring scanner configuration, the radial resolution was kept below 3.4 mm, over 8 cm field of view (FOV), while the sensitivity was higher than 7.4 % for the LSO 5 mm : LuYAP 15 mm phoswich detector. The resolution variations were minimized to less than 3.6 mm, over 16 cm FOV, using a LSO 6 turn : LuYAP 14 mm phoswich detector for the 19 cm ring scanner. In this study, the optimal length of the dual layer phoswich detector was derived to achieve a high and uniform radial,resolution.This work was
supported by the Korea Institute of Science and Technology Evaluation and
Planning (KISTEP) and the Ministry of Science and Technology, through the
National Nuclear Technology Program, and by a grant from the Korea Health
21 R&D Project (02-PJ3-PG6-EV06-0002), Ministry of Health and Welfare,
Republic of Kore
Characterization of dual layer phoswich detector performance for small animal PET using Monte Carlo simulation
No full textA positron emission tomograph dedicated to small animal imaging should have high spatial resolution and sensitivity, and dual layer scintillators have been developed for this purpose. In this study, simulations were performed to optimize the order and the length of each crystal of a dual layer phoswich detector, and to evaluate the possibility of measuring signals from each layer of the phoswich detector. A simulation tool GATE was used to estimate the sensitivity and resolution of a small PET scanner. The proposed scanner is based on dual layer phoswich detector modules arranged in a ring of 10 cm diameter. Each module is composed of 8 x 8 arrays of phoswich detectors consisting of LSO and LuYAP with a 2 mm x 2 mm sensitive area coupled to a Hamamatsu R7600-00-M64 PSPMT. The length of the front layer of the phoswich detector varied from 0 to 10 mm at 1 mm intervals, and the total length (LSO + LuYAP) was fixed at 20 mm. The order of the crystal layers of the phoswich detector was also changed. Radial resolutions were kept below 3.4 mm and 3.7 mm over 8 cm FOV, and sensitivities were 7.4% and 8.0% for LSO 5 mm-LuYAP 15 mm, and LuYAP 6 mm-LSO 14 mm phoswich detectors, respectively. Whereas, high and uniform resolutions were achieved by using the LSO front layer, higher sensitivities were obtained by changing the crystal order. The feasibilities for applying crystal identification methods to phoswich detectors consisting of LSO and LuYAP were investigated using simulation and experimentally derived measurements of the light outputs from each layer of the phoswich detector. In this study, the optimal order and lengths of the dual layer phoswich detector were derived in order to achieve high sensitivity and high and uniform radial resolution
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Evaluation of maximum-likelihood position estimation with Poisson and Gaussian noise models in a small gamma camera
No full textIt has been reported that maximum-likelihood position estimation (MLPE) algorithms offer advantages of improved spatial resolution and linearity over conventional Anger algorithm in gamma cameras. While the fluctuation of photon measurements is more accurately described by Poisson than Gaussian distribution model, the likelihood function of a scintillation event assumed to be Gaussian could be more easily implemented and might provide more consistent outcomes than Poisson-based MLPE. The purpose of this study is to evaluate the performances of the noise models, Poisson and Gaussian, in MLPE for the localization of photons in a small gamma camera (SGC) using NaI(Tl) plate and PSPMT. The SGC consisted of a single NaI(Tl) crystal, 10 cm in diameter and 6 mm thick, optically coupled to a PSPMT (Hamamatsu R3292-07). The PSPMT was read out using a resistive charge divider, which multiplexes 28(X) by 28(Y) cross wire anodes into four channels. Poisson and Gaussian-based MLPE methods have been implemented using experimentally measured detector response functions (DRF). The averaged intrinsic spatial resolutions were 3.14, 3.09, and 2.88 mm, the integral uniformities were 15.3%, 12.3%, and 11.4%, and the averaged linearities were 0.75, 0.33, and 0.22 mm for Anger logic, Poisson, and Gaussian-based MLPE, respectively. MLPEs considerably improved linearity and uniformity compared to Anger logic. Gaussian-based MLPE, which is easy to implement, allowed to obtain better linearity and uniformity performances than the Poisson-based MLPE
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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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