1,720,982 research outputs found
Shielding buildings from surface waves with “Seismic Metastructures”
No full textPhononic crystals and metamaterials constitute a broad class of artificially engineered materials able to manipulate the
propagation of acoustic/elastic waves at different lengths scale. Filtering and directivity properties of these materials can be controlled and tuned by designing their fundamental building blocks, usually referred as unit cells. Phononic crystals exploit periodicity to induce total wave reflection at selected frequencies. The obtained filtering properties emerge at wavelengths comparable to the periodicity. On the other hand, phononic metamaterials exploit the coupling between propagating waves and local resonators in the fundamental unit cells. As a result, propagation of waves with frequencies around the resonance is inhibited.
More recently the use of phononic crystals and metamaterials has been envisioned for large-scale applications in the field of civil engineering as a mean to shield buildings and infrastructures from natural or man-induced seismic waves. Among these, a solution based on metamaterial concepts and referred as “seismic metastructure” has been recently proposed by some of the authors. The proposed system is realized by an array of buried heavy-cylindrical steel units encased in cylindrical concrete pipes that constitute the metamaterial resonant units. The proper design and arrangement of these resonant units allows filtering longitudinal and shear waves in the typical frequency range of seismic waves (1-10Hz). In fact, analytical/numerical models as well as experimental evidences on a scaled setup proved the shielding capabilities of the proposed seismic isolation system with respect to bulk waves.
Building on the initial results on bulk waves, here we design “seismic metastructure” able to mitigate Rayleigh surface
waves. This is of special interest as they are considered the most harmful seismic threat. An analytical model to analyze the propagation of seismic surface waves through a soil engineered with seismic metastructures is developed. The analytical model allows predicting the frequency range within seismic Rayleigh waves are inhibited. A full 3D finite element model is used to numerically validate the prediction of the analytical model. Experimental evidences of the filtering properties of the designed metastructures are obtained on a scaled experimental setup. The excellent agreement of analytical/numerical and experimental results demonstrates the potential of this novel class of seismic isolation devices
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
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
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