1,720,955 research outputs found
Ocean Acoustic Waveguide Remote Sensing: Visualizing Life Around Seamounts
No full textCollectively, seamounts form a significant biome the size of
Europe with important but heavily depleted fisheries (see
Box 12 on page 206 of this issue [Etnoyer et al., 2010]). Recently,
large seamount tracts have been put aside as protected areas
(see Pitcher et al., 2010). Yet, we remain largely ignorant of the
dynamics of fish and other nektonic organism movements around
seamounts. Hence, there is a pressing need for a survey tool to
effectively monitor how stocks respond to management closures,
and to determine which fisheries might actually be sustainable
Analytic model for matched-filtered scattered intensity of volume inhomogeneities in an ocean waveguide calibrated to measured seabed reverberation
No full textThesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 117-119).In this thesis, we derive full theoretical expressions for the moments of the matched filtered scattered field due to volume inhomogeneities in an ocean waveguide and provide a computationally efficient time harmonic approximation to the matched filtered model. Following the approach developed by Galinde et al 16], the expressions are derived from first principles, by applying Green's theorem and the Born approximation. The scattered field and the total moment expressions are in terms of the fractional changes in the bottom compressibility and density, as well as the waveguide Green function and its gradients. The volume inhomogeneities are assumed to be statistically stationary, and assumed to be correlated in all three directions following a delta correlation function. Sound propagation in the ocean is modeled using the parabolic equation model and actual measurements of bathymetry and sound speed at the experimental locations. Monte Carlo simulations are used to account for the sound speed variability in the ocean waveguide due to internal waves or other sources of acoustic field randomization. The computationally efficient time-harmonic model is shown to provide a good approximation to the full broadband matched filtered model for a standard Pekeris waveguide. The time-harmonic model is then calibrated for ocean bottom reverberation at several frequencies in the 415-1325 Hz band, with data collected during the 2003 and 2006 ONR Geoclutter Experiments on the New Jersey continental shelf and on the northern flank of Georges Bank in the Gulf of Maine, respectively. The statistics for the inverted bottom parameters are summarized for all frequencies and experimental locations considered. The acoustically determined bottom parameters are shown to vary with approximately the wavelength cubed, suggesting that, by different frequencies selecting the scale of the acoustic inhomogeneities, the acoustic effects dominate over the geophysical effects.by Anamaria Ignisca.S.M
Feasibility of Ocean Acoustic Waveguide Remote Sensing (OAWRS) of Atlantic Cod with Seafloor Scattering Limitations
Get PDFRecently reported declines in the population of Atlantic cod have led to calls for additional survey methods for stock assessments. In combination with conventional line-transect methods that may have ambiguities in sampling fish populations, Ocean Acoustic Waveguide Remote Sensing (OAWRS) has been shown to have a potential for providing accurate stock assessments (Makris N.C., et al. Science 2009, 323, 1,734–1,737; 54th Northeast Regional Stock Assessment Workshop (54th SAW) US Department of Commerce, Northeast Fisheries Science Center, 2012). The use of OAWRS technology enables instantaneous wide-area sensing of fish aggregations over thousands of square kilometers. The ratio of the intensity of scattered returns from fish versus the seafloor in any resolution cell typically determines the maximum fish detection range of OAWRS, which then is a function of fish population density, scattering amplitude and depth distribution, as well as the level of seafloor scattering. With the knowledge of oceanographic parameters, such as bathymetry, sound speed structure and attenuation, we find that a Rayleigh–Born volume scattering approach can be used to efficiently and accurately estimate seafloor scattering over wide areas. From hundreds of OAWRS measurements of seafloor scattering, we determine the Rayleigh–Born scattering amplitude of the seafloor, which we find has a ƒ2,4 frequency dependence below roughly 2 kHz in typical continental shelf environments along the US northeast coast. We then find that it is possible to robustly detect cod aggregations across frequencies at and near swim bladder resonance for observed spawningconfigurations along the U.S. northeast coast, roughly the two octave range 150–600 Hzfor water depths up to roughly 100 m. This frequency range is also optimal for long-rangeocean acoustic waveguide propagation, because it enables multimodal acoustic waveguidepropagation with minimal acoustic absorption and forward scattering losses. As the sensingfrequency moves away from the resonance peak, OAWRS detection of cod becomesincreasingly less optimal, due to a rapid decrease in cod scattering amplitude. In otherenvironments where cod depth may be greater, the optimal frequencies for cod detectionare expected to increase with swim bladder resonance frequency
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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