1,721,114 research outputs found
LA MEMORIA STORICA DEL M.C.E. VOLUME 2
No full textRisultati della seconda ricerca sulla sotira del Moveimento di Cooperazione Eductiva attraverso interviste e analisi di materiali delCentro di Documentazione su alcune tematiche pedagogich
Two-dimensional seismic wave modeling and inversion using the boundary element method
No full textSubsurface mechanical characterization is a crucial issue in many fields of both Earth Sciences and Geotechnical Engineering. Besides the use of direct investigations, common alternative methods comprise the surface waves methods (SWM) that have been widely used for near surface characterization. This includes the original Spectral Analysis of Surface Waves (Nazarian et al. 1984; Stokoe et al. 1994), multi-channel methods (Park et al. 1999) and passive techniques (Louie, 2001). Recently, soil damping ratios were estimated as well (Rix et al. 2001). SWM assumes Rayleigh waves propagating through a stack of horizontal soil layers. Such methods are well established and computationally efficient. However they only capture the vertical variation of elastic properties. Further, the flat-layered model is only an approximation and Rayleigh waves cannot describe the scattered wave-field when strong lateral variations occur. Observations and modeling of earthquakes confirm, for example, that geometry dramatically affects the seismic wave propagation. There have been several attempts to include lateral variations by combining successive 1D inversions via the so-called "pseudo-2D" (Luo et al. 2008). However this approach still retains the 1D approximation and can only capture weak variations. SWM has been thus limited by the lack of strategies accounting more realistic soil representations. Recently, for the crustal scale such limitations have been overcome by the full waveform inversion (FWI) which exploits a finite differences (FD) forward modeling (Virieux and Operto 2009). Unfortunately, when FD is used, the subsurface is finely discretized and the number of parameters associated largely exceeds the number of measurements available leading to severely ill-posed problems that can suffer from slow convergence and instability. Here, we propose an alternative inversion formulation based on the boundary element method (BEM) that overcomes the above mentioned limitations of both FWIs and SWMs (Bignardi et al, 2011)
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
Revealing the shape of turbulence in channel flows
No full textThe proposed research focuses on a novel geometric approach to study Navier- Stokes turbulence. In the last century, the study of turbulence has been ap- proached following the great Kolmogorov’s physical insights on the inertial energy cascade and, more recently, by investigating the geometry of the state space of the Navier-Stokes equations treated as a dynamical system. This novel geometric approach arises from the evidence that what is observed in physical space sometimes is not always suggestive of the hidden laws of physics of the turbulent motion. Thus, looking at the turbulent dynamics in state space may lead to a new understanding of the associated physical processes. In particular, vortices in a channel flow change shape as they are transported by the mean flow at the Taylor speed, or dynamical velocity. Removing the translational (Toric) symmetry in state space reveals that the shape-changing dynamics of vortices influences their own motion, and it induces an additional self-propulsion velocity, or geometric velocity. Thus, in strong turbulence, the Taylor’s hypothesis (Taylor, 1938) of frozen vortices is not satisfied because the geometric velocities can be significant. In my PhD work, I aim at revealing the shape of turbulence in channel flows. In particular, I study how vortices change shape as they are transported by the mean flow, and how these shape- changing dynamics influence their own motion. This study yields the discovery that the geometric velocity, induced by vortex shape changes, is the physical manifestation of hidden wave-like dispersion properties of turbulence
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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