1,721,047 research outputs found
On the Role of the Kuroshio Extension Bimodality in Modulating the Surface Eddy Kinetic Energy Seasonal Variability
No full textThe modulation of the seasonal variability of the surface eddy kinetic energy (EKE) in the Kuroshio extension (KE) region induced by the stable and unstable KE states is analyzed using satellite-based observations and high-resolution ocean reanalysis data. The two KE states are found to strongly modulate the seasonal variability of the local surface EKE: the latter reaches its maximum in May–July if the KE is in its stable state, while it peaks in August–October if the KE is in its unstable state. Further investigation indicates that such behavior is mainly caused by the different baroclinic energy transfers induced by the meridional density gradients associated with the two KE states
Parameter sensitivity analysis of the short-range prediction of Kuroshio extension transition processes using an optimization approach
No full textThe fastest growing initial error in prediction of the Kuroshio Extension state transition processes and its growth
No full textIn this study, the predictability of the Kuroshio Extension (KE) transition processes is explored from an error growth perspective. The fastest growing initial errors (FGIEs) are obtained through the conditional nonlinear optimal perturbation approach within a reduced-gravity shallow-water model forced by steady winds, which provides a fairly realistic simulation of the KE low-frequency variability of intrinsic origin. The large amplitudes of the FGIEs for both the transitions from a typical low-energy state to a typical high-energy state (LH) and the opposite transition (HL), are found mainly in the Kuroshio large meander region south of Japan and in the KE region. The FGIE grows more rapidly for the HL process than for the LH process, implying that the HL transition process may be more difficult to predict. The evolution processes of the FGIEs and the related mechanisms are revealed by investigating the evolution of the potential vorticity anomalies caused by the FGIEs. The dominant physical processes governing the FGIE growth are found to be different for the LH and HL processes. For the LH process, the evolution is mainly governed by linear advection processes and interfacial friction, while for the HL process, in addition to these two processes, the nonlinear advection process also plays a vital role in the evolution. This indicates that nonlinear intrinsic oceanic processes affect considerably the error growth, especially in the HL transition process, suggesting that the intrinsic processes should be carefully considered when exploring the predictability and forecast of the KE low-frequency variability
Transdimensional and Hamiltonian Monte Carlo inversions of Rayleigh-wave dispersion curves: A comparison on synthetic datasets
Full text linkWe compare two Monte Carlo inversions that aim to solve some of the main problems of dispersion curve inversion: deriving reliable uncertainty appraisals, determining the optimal model parameterization and avoiding entrapment in local minima of the misfit function. The first method is a transdimensional Markov chain Monte Carlo that considers as unknowns the number of model parameters, that is the locations of layer boundaries together with the Vs and the Vp/Vs ratio of each layer. A reversible-jump Markov chain Monte Carlo algorithm is used to sample the variable-dimension model space, while the adoption of a parallel tempering strategy and of a delayed rejection updating scheme improves the efficiency of the probabilistic sampling. The second approach is a Hamiltonian Monte Carlo inversion that considers the Vs, the Vp/Vs ratio and the thickness of each layer as unknowns, whereas the best model parameterization (number of layer) is determined by applying standard statistical tools to the outcomes of different inversions running with different model dimensionalities. This work has a mainly didactic perspective and, for this reason, we focus on synthetic examples in which only the fundamental mode is inverted. We perform what we call semi-analytical and seismic inversion tests on 1D subsurface models. In the first case, the dispersion curves are directly computed from the considered model making use of the Haskell–Thomson method, while in the second case they are extracted from synthetic shot gathers. To validate the inversion outcomes, we analyse the estimated posterior models and we also perform a sensitivity analysis in which we compute the model resolution matrices, posterior covariance matrices and correlation matrices from the ensembles of sampled models. Our tests demonstrate that major benefit of the transdimensional inversion is its capability of providing a parsimonious solution that automatically adjusts the model dimensionality. The downside of this approach is that many models must be sampled to guarantee accurate posterior uncertainty. Differently, less sampled models are required by the Hamiltonian Monte Carlo algorithm, but its limits are the computational effort related to the Jacobian computation, and the multiple inversion runs needed to determine the optimal model parameterization
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
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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