1,720,958 research outputs found
The problems with acoustics on a small planet
No full textIn recent years increased attention has been paid to the potential uses of acoustics for extraterrestrial exploration. This paper concerns two aspects which should be taken into account when transposing terrestrial experience with acoustics to smaller worlds. These are, specifically, the effect on the acoustics of the variation of gravity with depth, and the curvature of the world's surface. A case resembling Europa is used quantitatively to illustrate these effects, indicating significant errors if these factors are neglected
Cavitación y cetáceos. [Cavitation and cetacean]
No full textBubbles are the most acoustically active naturally occurring
entities in the ocean, and cetaceans are the most
intelligent. Having evolved over tens of millions of years
to cope with the underwater acoustic environment,
cetaceans may have developed techniques from which we
could learn. This paper outlines some of the possible interactions,
ranging from the exploitation of acoustics in
bubble nets to trap prey, to techniques for echolocating in
bubbly water, to the possibility that man-made sonar signals
could be responsible for bubble generation and death
within cetaceans.ResumenLas burbujas son las entidades naturales del océano más activas acústicamente, y los cetáceos las más inteligentes. Tras decenas de millones de años de evolución para adaptarse al entorno acústico submarino, los cetáceos pueden haber desarrollado una serie de técnicas de las que bien podríamos aprender.Este artículo pone de relieve algunas posibles interacciones, que van desde la explotación de la acústica en redes de burbujas utilizadas como trampas para presas, hasta técnicas para la ¿ecolocación¿ en aguas burbujeantes, o la posibilidad de que las señales sonares provocadas por el hombre sean responsables de la generación de burbujas y de muerte de cetáceos
The sounds of seas in space
No full textOn 14 January 2005 the Huygens space probe landed on Titan, the surface of which had previously been obscured by smog. This exercise was undertaken prior to the probe’s successful landing, in an attempt to calculate the sounds which would be associated with splashdowns and methane-falls, in the hypothetical scenario that (of the many sensing systems on Huygens) only the acoustic information was available in order to interpret conditions on Titan. The exercise includes innovations in the inversion of bubble entrainment noise to estimate bubble populations, and illustrates the benefits of using acoustics for space exploration
Waterfalls in space, and other problems of "underwater" acoustics on a small planet
No full textWhilst extraterrestrial liquids do occur in the Solar System, today's acoustical oceanographers have fewer sites to which they can apply their experience of Earth's oceans than perhaps they would have had in the early Solar System, with its magma oceans. Possible sites are Saturn's moons Titan and Enceladus, and Jupiter's moon Europa. The ability to transfer our understanding of Earth's acoustical oceanography to other moons and planets is particularly valuable, given that current understanding is sufficient to undertake complex inversions to estimate Earth's ocean environmental parameters from relatively sparse, or even naturally-occurring, acoustical signals. However such transference should be done with care, as terms familiar in Earth's acoustical oceanography may not be correct on other worlds. For example, in a deep ocean on a small world (such as Europa), the hydrostatic pressure will not equal the product of the density, the depth, and the surface value of the acceleration due to gravity, since the latter can vary with depth, and because vertical lines are not parallel on a small planet. This paper explores two cases of transferring our terrestrial experience off world, to the ice seas of Europa, and to the methane lakes and waterfalls of Titan. ©2008 Acoustical Society of Americ
Wake penetrating sonar
No full textThis paper describes a sonar which can operate in bubbly water. It is here deployed to penetrate the wake of a ship of 3,953 gross register tonnage. Orthodox Cold War sonar technology is not optimized for the shallow coastal waters that typify many current operations. The United States use dolphins in such waters, and the Twin Inverted Pulse Sonar (TWIPS) described here arose as a demonstration that echolocation was possible in bubbly water in response to a video showing dolphins generating bubble nets when hunting: if echolocation were impossible in these nets, then during this hunt the dolphins would have compromised their sonar. In this paper TWIPS detects and classifies targets against clutter by distinguishing between linear and nonlinear scatterer. For other applications, it has the potential to distinguish those nonlinear targets which scatter energy at the even-powered harmonics from those which scatter in the odd-powered harmonics. TWIPS can also, in some manifestations, require no range correction (and therefore does not require the a priori environment knowledge necessary for many remote detection technologies). The method applies to a range of sensors, including the use of radar to distinguish between circuitry, metal and soil; the use of LIDAR to detect combustion products; and MRI
Cetacean acoustics in bubbly water (Invited Paper)
No full textMarine mammal signals often propagate through bubbly water, be they generated under breaking waves, wakes, or even by the mammals themselves. Two circumstances are of particular interest: the possible use of acoustic signals to trap prey in bubble nets; and the ability of dolphin sonar to operate in bubbly water (such as the surf zone) that would confound the best human sonar, despite the fact that the dolphins possess ‘hardware’ which is comparatively mediocre. This paper examines these circumstances
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
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
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