1,721,013 research outputs found
Nonparametric inference in hidden Markov models using P-splines
No full textHidden Markov models (HMMs) are flexible time series models in which the distributions of the observations depend on unobserved serially correlated states. The state-dependent distributions in HMMs are usually taken from some class of parametrically specified distributions. The choice of this class can be difficult, and an unfortunate choice can have serious consequences for example on state estimates, on forecasts and generally on the resulting model complexity and interpretation, in particular with respect to the number of states. We develop a novel approach for estimating the state-dependent distributions of an HMM in a nonparametric way, which is based on the idea of representing the corresponding densities as linear combinations of a large number of standardized B-spline basis functions, imposing a penalty term on non-smoothness in order to maintain a good balance between goodness-of-fit and smoothness. We illustrate the nonparametric modeling approach in a real data application concerned with vertical speeds of a diving beaked whale, demonstrating that compared to parametric counterparts it can lead to models that are more parsimonious in terms of the number of states yet fit the data equally well
Nonparametric inference in hidden Markov models using P‐splines
Full text linkLangrock R, Kneib T, Sohn A, DeRuiter SL. Nonparametric inference in hidden Markov models using P-splines. Biometrics. 2015;71(2):520-528
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
Echolocation-based foraging by harbor porpoises and sperm whales, including effects of noise and acoustic propagation
Full text linkSubmitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2008.In this thesis, I provide quantitative descriptions of toothed whale
echolocation and foraging behavior, including assessment of the effects of noise
on foraging behavior and the potential influence of ocean acoustic propagation
conditions on biosonar detection ranges and whale noise exposure. In addition
to presenting some novel basic science findings, the case studies presented in
this thesis have implications for future work and for management.
In Chapter 2, I describe the application of a modified version of the Dtag to
studies of harbor porpoise echolocation behavior. The study results indicate how
porpoises vary the rate and level of their echolocation clicks during prey capture
events; detail the differences in echolocation behavior between different animals
and in response to differences in prey fish; and show that, unlike bats, porpoises
continue their echolocation buzz after the moment of prey capture.
Chapters 3-4 provide case studies that emphasize the importance of
applying realistic models of ocean acoustic propagation in marine mammal
studies. These chapters illustrate that, although using geometric spreading
approximations to predict communication/target detection ranges or noise
exposure levels is appropriate in some cases, it can result in large errors in other
cases, particularly in situations where refraction in the water column or multi-path
acoustic propagation are significant.
Finally, in Chapter 5, I describe two methods for statistical analysis of
whale behavior data, the rotation test and a semi-Markov chain model. I apply
those methods to test for changes in sperm whale foraging behavior in response
to airgun noise exposure. Test results indicate that, despite the low-level
exposures experienced by the whales in the study, some (but not all) of them
reduced their buzz production rates and altered other foraging behavior
parameters in response to the airgun exposure.Work presented in this thesis was supported by a National Science Foundation
Graduate Research Fellowship, the WHOI Ocean Life Institute (Grant Numbers
32031300 and 25051351), the Office of Naval Research, the U.S. Department of
the Interior Minerals Management Service (Cooperative Agreement Numbers
1435-01-02-CA-85186 and NA87RJ0445; WHOI Grant Number 15205601), the
Industry Research Funding Coalition, and the WHOI/MIT Joint Program in
Oceanography/Applied Ocean Science & Engineering (including a Fye Teaching
Fellowship)
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
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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