1,720,971 research outputs found
Calculating all multiple parameter solutions of ODE models to avoid biological misinterpretations
No full textBiological system's dynamics are increasingly studied with nonlinear ordinary differential equations, whose parameters are estimated from input/output experimental data. Structural identifiability analysis addresses the theoretical question whether the inverse problem of recovering the unknown parameters from noise-free data is uniquely solvable (global), or if there is a finite (local), or an infinite number (non identifiable) of parameter values that generate identical input/output trajectories. In contrast, practical identifiability analysis aims to assess whether the experimental data provide information on the parameter estimates in terms of precision and accuracy. A main difference between the two identifiability approaches is that the former is mostly carried out analytically and provides exact results at a cost of increased computational complexity, while the latter is usually numerically tested by calculating statistical confidence regions and relies on decision thresholds. Here we focus on local identifiability, a critical issue in biological modeling. This is the case when a model has multiple parameter solutions which equivalently describe the input/output data, but predict different behaviours of the unmeasured variables, often those of major interest. We present theoretical background and applications to locally identifiable ODE models described by rational functions. We show how structural identifiability analysis completes the practical identifiability results. In particular we propose an algorithmic approach, implemented with our software DAISY, to calculate all numerical parameter solutions and to predict the corresponding behaviour of the unmeasured variables, which otherwise would remain hidden. A case study of a locally identifiable HIV model shows that one should be aware of the presence of multiple parameter solutions to comprehensively describe the biological system and avoid biological misinterpretation of the results
New Perspectives and Practical Tools for Local Identifiability Analysis of Biomathematical Models.
No full textStructural vs Practical Identifiability of Nonlinear Differential Equation Models in Systems Biology.
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A New Version of DAISY to Test Structural Identifiability of Biological Models
No full textOften ODE models in systems biology, medical research, epidemiology, ecology and many other areas, contain unknown parameters which need to be estimated from experimental data. Identifiability deals with the uniqueness of the relation between model parameters and ODE solution thus being a prerequisite for the well-posedness of parameter estimation. In this paper a novel extension of the software tool DAISY (Differential Algebra for Identifiability of SYstems) is presented. DAISY performs structural identifiability analysis for linear and nonlinear dynamic models described by polynomial or rational ODE’s. The major upgrades of this new version regard the ability to include in the identifiability analysis either known and unknown model initial conditions, the possibility of entering a parameter estimate to calculate all the equivalent parameter solutions, the portability to MacOS platforms and an user-friendly interface. These upgrades make DAISY surely more general and easy to use. Practical examples are presented. DAISY is available at the web site daisy.dei.unipd.it
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
Modeling glucose kinetics in vivo in the human forearm. Rationale and a dual tracer study
No full textIn vivo evaluation in humans of transport and metabolism of substrates in skeletal muscle of the forearm is important but difficult. Available approaches are briefly reviewed. In this paper we first outline a general modeling strategy to address this issue in the context of multiple tracer experiment design. A partly-flow compartmental model to assess the kinetics of glucose transport from a dual-tracer study is then presented. The effect of insulin is examined
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