1,721,963 research outputs found
On spectral properties of steepest descent methods
No full textIn recent years, it has become increasingly clear that the critical issue in gradient methods is the choice of the step length, whereas using gradient as the search direction may lead to very effective algorithms, whose surprising behaviour has only been partially explained, mostly in terms of the spectrum of the Hessian matrix. On the other hand, the convergence of the classical Cauchy steepest descent (SD) method has been analysed extensively and related to the spectral properties of the Hessian matrix, but the connection with the spectrum of the Hessian has not been exploited much to modify the method in order to improve its behaviour. In this work, we show how, for convex quadratic problems, moving from some theoretical properties of the SD method, second-order information provided by the step length can be exploited to dramatically improve the usually poor practical behaviour of this method. This allows us to achieve computational results comparable with those of the Barzilai and Borwein algorithm, with the further advantage of monotonic behaviour
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
On the regularizing behavior of the SDA and SDC gradient methods in the solution of linear ill-posed problems
Full text linkWe analyze the regularization properties of two recently proposed gradient methods, SDA and SDC, applied to discrete linear inverse problems. By studying their filter factors, we show that the tendency of these methods to eliminate first the eigencomponents of the gradient corresponding to large singular values allows to reconstruct the most significant part of the solution, thus yielding a useful filtering effect. This behavior is confirmed by numerical experiments performed on some image restoration problems. Furthermore, the experiments show that, for severely ill-conditioned problems and high noise levels, the SDA and SDC methods can be competitive with the Conjugate Gradient (CG) method, since they are slightly slower than CG, but exhibit a better semiconvergence behavior
Light Concentrators for Silicon Photomultipliers
No full textPhotosensitive devices represent a key solution for several current and future categories of experiments in which photon detection is the crucial point for the observation of physical phenomena. Astro particle experiments for instance, one of the most promising observation channels for High Energy Physics, typically study energetic phenomena in which charged particles originating from the interactions or decays of primary particles radiate Cherenkov or fluorescence light, which is then detected by photosensitive devices. In these fields of applications, the Silicon Photomultipliers (SiPM) devices based on the limited Geiger-mode avalanche (generally G-APD, Geiger Avalanche Photons Detectors), are extensively under study. Unfortunately, applications of SiPMs are very limited by their small sensitive surfaces. In order to overcome the limits of the small dimensions of the sensitive area of SiPM devices, different solutions are reported. In particular it is discussed the use of Optical Concentrators with the correct refraction index, characteristic and geometry for the improvement of the sensitive surface dimensions of a SiPM device
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
Green tuff: Gamma index in a typical building material of ciglio area (ischia island)
No full textRadiological characterization of tuff of Ciglio area in Ischia Island was performed to assess the potential radiological hazard associated with its use. For this purpose, high resolution gamma-ray spectroscopy was used. In five green tuff samples was measured the activity concentration of natural gamma-ray emitting radionuclides226 Ra,232 Th and40 K so, the mean gamma index was calculated. The mean value of the gamma index resulted lower than the reference level and it meets the dose criterion for the safety use of green tuff as building material
VSiPMT for underwater neutrino telescopes
No full textUnderwater neutrino telescopes are nowadays considered among the most important aims in the field of astroparticle physics. Their structure consists of a cubic-kilometer three-dimensional array of photosensitive devices aimed at the detection of the Cherenkov light emitted by charged particles produced by high energy neutrino interactions with the Earth. To date, a crucial role in this kind of experiments has been played by PhotoMultiplier Tubes (PMTs), however they suffer from many drawbacks such as linearity-to-gain relationship and difficulty in single photon counting. The next generation of experiments will require further improvements in photon detectors performances, therefore alternatives to PMTs are currently under study. In particular the most promising development in this field is represented by the rapidly emerging CMOS p-n Geiger-mode avalanche photodiode technology (G-APD or SiPM), that will allow the detection of highspeed single photons with high gain and linearity. In order to overcome the limit of small sensitive surfaces we suggest an innovative design for a modern hybrid, high gain, silicon based Vacuum Silicon Photomultiplier Tube (VSiPMT) based on the combination of a SiPM with a hemispherical vacuum glass PMT standard envelope. In this work we describe the full SiPM characterization realized by our group and we present the results of our Geant4-based simulations of electron backscattering over the SiPM surface. © 2012 Elsevier B.V. All rights reserved
Social, constructivist and informal learning processes: Together on the edge for designing digital game-based learning environments
No full textThe theoretical conceptions of game-based learning are different from those of traditional instruction. Indeed, the classical approaches of needs and task analysis seem to be not appropriate for designing digital serious games as computer-supported collaborative learning environments. This paper aimed at arguing that social, constructivist and informal learning processes provided accurate frameworks for analyzing needs, activities, and outcomes for designing digital serious games. After focusing on the epistemic assumptions of such theoretical frameworks, this paper described the digital serious game Cibopolis as case study, able to grasp different learning processes, involving players as learners in collaborative participation and knowledge building on nutrition and healthy lifestyle. Especially, the context, the training goal, the adopted learning solutions and the main features of the designed Cibopolis game were specified. Then, the results of the pilot test involving young learners (N=65; Range of Age=14-32 years old) was briefly reported. Specifically, it was pointed out how learners perceived the Cibopolis game in term of usability and engagement. To conclude, some relevant theoretical issues concerning digital game-based learning environments and practical implications that could support IT professionals – such as, instructional designers, developers, web designers, and so on – were highlighted
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