1,722,104 research outputs found
A SIMULATION STUDY OF THE BEHAVIOR OF FINE MESH PHOTOMULTIPLIERS IN MAGNETIC-FIELD
No full textResults of a comparison between experimental data and a Monte Carlo simulation study on fine-mesh photomultipliers (PM) behaviour in magnetic field (B) are reported. This work is accomplished in order to understand the details of the electron cascade between the dynodes; the PM amplification gain is investigated, with respect of several relative orientations of the field and the PM axis and for different values of the B-field intensity. Some characteristic of the energy spectrum of the secondary electron emission (SEE) is also taken into account in this work. The aim is to better understand which technical constructive parameters are more sensitive to the optimization of the PM performance in presence of high B-fields (e.g. as required for the KLOE experiment). The simulation results are compared with those experimentally obtained with the Hamamatsu R2490-05 fine mesh tubes
LIGHT TRANSPORT IN A FLEXIBLE LIQUID SCINTILLATOR FIBER
No full textFirst results on attenuation length, photon yield and timing properties of a liquid scintillator flexible fiber are presented. Possible applications and systematic effects are also discussed
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
The connection between gamma-ray bursts and supernovae Ib/c
Full text linkContext. It has been established that Gamma-Ray Bursts (GRBs) are connected to Supernovae (SNe) explosions of type Ib/c. Aims. We intend to test whether the hypothesis of type Ib/c SNe from different massive progenitors can reproduce the local GRB rate as well as the GRB rate as a function of redshift. We aim to predict the GRB rate at very high redshift under different assumptions about galaxy formation and star formation histories in galaxies. Methods. We assume different star formation histories in galaxies of different morphological types: ellipticals, spirals and irregulars, which have already been tested in self-consistent galaxy models reproducing both chemical and photometrical properties of galaxies. We explore different hypotheses concerning the progenitors of type Ib/c SNe: i) single massive stars (M > 25 M ⊙, Wolf-Rayet stars), ii) massive close binaries (12-20 M ⊙), and iii) both Wolf-Rayet stars and massive binaries. We conclude that the mixed scenario (iii) is preferable to reproduce the local type Ib/c SN rates in galaxies and we adopt this scenario for comparison with the GRB rates. Results. We find an excellent agreement between the observed GRB local rate and the predicted type Ib/c SN rate in irregular galaxies, when a range for single Wolf-Rayet stars of 40-100 M⊙ is adopted. We also predict the cosmic type Ib/c SN rate by taking into account all the galaxy types in a unitary volume of the Universe and we compare it with the observed cosmic GRB rate as a function of redshift. By assuming the formation of spheroids at high redshift, we predict a cosmic type Ib/c SN rate, which is always higher than the GRB rate, suggesting that only a small fraction (0.1-1%) of type Ib/c SNe become GRBs. In particular, we find a ratio between the cosmic GRB rate and the cosmic type Ib/c rate in the range 10-2-10 -3, in agreement with previous estimates. Finally, due to the high rate of star formation in spheroids at high redshift, which is our preferred scenario for galaxy formation, we predict more GRBs at high redshift than in the hierarchical scenario for galaxy formation, a prediction which remains to be proven by future observations. © ESO 2007
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
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