1,720,955 research outputs found
Data-driven computation of adjoint sensitivities without adjoint solvers: An application to thermoacoustics
Full text linkAdjoint methods have been the pillar of gradient-based optimization for decades. They
enable the accurate computation of a gradient (sensitivity) of a quantity of interest with
respect to all system parameters in one calculation. When the gradient is embedded in an
optimization routine, the quantity of interest can be optimized for the system to have the
desired behavior. Adjoint methods, however, require the system’s governing equations and
their Jacobian. In this paper, we propose a computational strategy to infer the adjoint sensitivities from data when the governing equations might be unknown (or partly unknown),
and noise might be present. The key component of this strategy is an echo state network,
which learns the dynamics of nonlinear regimes with varying parameters, and it evolves
dynamically via a hidden state. Although the framework does not make assumptions on
the dynamical system, we focus on thermoacoustics, which are governed by nonlinear and
time-delayed systems. First, we show that a parameter-aware echo state network (ESN)
infers the parametrized dynamics. Second, we derive the adjoint of the ESN to compute
two types of sensitivity: (i) parameter sensitivity, which is the gradient of a time-averaged
cost functional with respect to physical or design parameters of the system, and (ii) initial
condition sensitivity, which is the gradient of a cost functional of the final state with
respect to the initial condition. Third, we propose the thermoacoustic echo state network
(T-ESN), which embeds the physical knowledge in the network architecture for improved
generalization. Fourth, we apply the framework to a variety of nonlinear thermoacoustic
regimes of a prototypical system. We show that the T-ESN accurately infers the correct
adjoint sensitivities of the acoustic energy with respect to the flame parameters and initial
conditions. The results are robust to noisy data, from periodic, through quasiperiodic, to
chaotic regimes. The inferred adjoint sensitivities are employed to suppress an instability
via steepest descent. We show that a single network predicts the nonlinear bifurcations on
unseen scenarios, which allows it to converge to the minimum of the acoustic energy. This
work opens new possibilities for gradient-based data-driven design optimization
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
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
Adjoint Sensitivities of Chaotic Flows without Adjoint Solvers: A Data-Driven Approach
Full text linkIn one calculation, adjoint sensitivity analysis provides the gradient of a
quantity of interest with respect to all system's parameters. Conventionally,
adjoint solvers need to be implemented by differentiating computational models,
which can be a cumbersome task and is code-specific. To propose an adjoint
solver that is not code-specific, we develop a data-driven strategy. We
demonstrate its application on the computation of gradients of long-time
averages of chaotic flows. First, we deploy a parameter-aware echo state
network (ESN) to accurately forecast and simulate the dynamics of a dynamical
system for a range of system's parameters. Second, we derive the adjoint of the
parameter-aware ESN. Finally, we combine the parameter-aware ESN with its
adjoint version to compute the sensitivities to the system parameters. We
showcase the method on a prototypical chaotic system. Because adjoint
sensitivities in chaotic regimes diverge for long integration times, we analyse
the application of ensemble adjoint method to the ESN. We find that the adjoint
sensitivities obtained from the ESN match closely with the original system.
This work opens possibilities for sensitivity analysis without code-specific
adjoint solvers
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
