117 research outputs found
Experimental designs for controlling the correlation of estimators in two parameter models
The state of the art related to parameter correlation in two-parameter models
has been reviewed in this paper. The apparent contradictions between the
different authors regarding the ability of D--optimality to simultaneously
reduce the correlation and the area of the confidence ellipse in two-parameter
models were analyzed. Two main approaches were found: 1) those who consider
that the optimality criteria simultaneously control the precision and
correlation of the parameter estimators; and 2) those that consider a
combination of criteria to achieve the same objective. An analytical criterion
combining in its structure both the optimality of the precision of the
estimators of the parameters and the reduction of the correlation between their
estimators is provided. The criterion was tested both in a simple linear
regression model, considering all possible design spaces, and in a non-linear
model with strong correlation of the estimators of the parameters
(Michaelis--Menten) to show its performance. This criterion showed a superior
behavior to all the strategies and criteria to control at the same time the
precision and the correlation.Comment: 30 pages, 8 figures, 5 table
Optimal dose calibration in radiotherapy
In this paper, the tools provided by the theory of Optimal Experimental Design are applied to a nonlinear calibration model. This is motivated by the need of estimating radiation doses using radiochromic films for radiotherapy purposes. The calibration model is in this case nonlinear and the explanatory variable cannot be worked out explicitly from the model. In this case an experimental design has to be found on the dependent variable. For that, the inverse function theorem will be used to obtain an information matrix to be optimized. Optimal designs on the response variable are computed from two different perspectives, first for fitting the model and estimating each of the parameters and then for predicting the proper dose. While the first is a common point of view in a general context of the Optimal Experimental Design, the latter is actually the main objective of the calibration problem for the practitioners and algorithms for computing these optimal designs are also provided.
The optimal designs obtained have just three different points in their support, but practitioners usually demand for more support points. Thus, a methodology for computing space-filling designs is also provided when the support points are forced to follow some mathematical rule, such as arithmetic or geometric sequences. Cross efficiencies of all these designs are computed in order to show their ability for different goals
Convergence and computation of simultaneous rational quadrature formulas
22 pages, no figures.-- MSC2000 codes: Primary 41A55. Secondary 41A28, 65D32.MR#: MR2286008 (2008a:65049)Zbl#: Zbl 1168.65326We discuss the convergence and numerical evaluation of simultaneous quadrature formulas which are exact for rational functions. The problem consists in integrating a single function with respect to different measures using a common set of quadrature nodes. Given a multi-index n, the nodes of the integration rule are the zeros of the multi-orthogonal Hermite–Padé polynomial with respect to (S, α, n), where S is a collection of measures, and α is a polynomial which modifies the measures in S. The theory is based on the connection between Gauss-type simultaneous quadrature formulas of rational type and multipoint Hermite–Padé approximation. The numerical treatment relies on the technique of modifying the integrand by means of a change of variable when it has real poles close to the integration interval. The output of some tests show the power of this approach in comparison with other ones in use.The work of U.F.P. and G.L.L. was partially supported by Dirección General de Enseñanza
Superior under grant BFM2003-06335-C03-02 and of G.L.L. by INTAS under Grant INTAS 03-51-6637. The work of J.R.I. was supported by a research grant from the Ministerio de Educación y Ciencia, project code MTM 2005-01320.Publicad
An equivalence theorem for design optimality with respect to a multi-objective criterion.
[EN]Maxi-min efficiency criteria are a kind of multi-objective criteria, since they enable
us to take into consideration several tasks expressed by different component-wise
criteria. However, they are difficult tomanage because of their lack of differentiability.
As a consequence, maxi-min efficiency designs are frequently built through heuristic
and ad hoc algorithms, without the possibility of checking for their optimality. The
main contribution of this study is to prove that the maxi-min efficiency optimality
is equivalent to a Bayesian criterion, which is differentiable. In addition, we provide
an analytic method to find the prior probability associated with a maxi-min efficient
design, making feasible the application of the equivalence theorem. Two illustrative
examples show how the proposed theory works
Not solely influencers in the communication plan: a comparative study in the fashion field
En los últimos años, las redes sociales e influencers están dominando las campañas de comunicación, debido a su poder de influencia en los consumidores. Como resultado, algunos de los actores tradicionales de la comunicación no están siendo considerados en los planes de comunicación. Sin embargo, no existe ningún estudio que confirme su pérdida de influencia sobre el consumidor y sus decisiones de compra. Tomando el caso de la compra en moda, el objetivo de este artículo es comparar el poder de influencia de siete actores de la comunicación: medios, marcas de moda, celebridades, influencers (mega, macro y micro) e influyentes. Con datos de 1176 cuestionarios respondidos a través del método de autodenominación, podemos concluir que los influencers son superados por los influyentes (círculos cercanos) como los líderes de opinión con mayor impacto en el consumidor, seguidos incluso por las marcas de moda y los medios de moda.In recent years, social media and influencers are dominating communication campaigns, due to their power to influence consumers. As a result, some of the traditional communication actors are not being considered in communication plans. However, no study has as yet confirmed their loss of influence over the consumer and their purchasing decisions. Taking the case of fashion into account, this article seeks to compare the power of influence of seven communication actors: media, fashion brands, celebrities, influencers (mega, macro and micro) and influentials. With data from 1176 questionnaires answered through the self-naming method, we can conclude that influencers are surpassed by influentials (close circles) as the opinion-leaders with the greatest impact on the consumer, followed then by fashion brands and the fashion media
Optimal experimental design for cytogenetic dose-response calibration curves
Purpose: To introduce optimal experimental design techniques in the cytogenetic
biological dosimetry practice. This includes the development of a new optimatility
criterion for the calibration of radiation doses.
Materials and Methods: The most typical optimal design criterion and the one
developed in this research are introduced and applied in an example from the litera-
ture. In another example from the literature, a simulation study has been performed
to compare the standard error of the dose estimation using di erent experimental
designs. An RStudio project and a GitHub project have been developed to repro-
duce these results.
Results: It is appreciated how the application of optimal experimental design tech-
niques can reduce the standard error of biodosimetric dose estimations.
Conclusions: Optimal experimental design techniques jointly with practitioners re-
quirements may be applied. This practice would not involve an additional laboratory
work
Design issues for population growth models
We briefly review and discuss design issues for population growth and decline models. We then use a flexible growth and decline model as an illustrative example and apply optimal design theory to find optimal sampling times for estimating model parameters, specific parameters and interesting functions of the model parameters for the model with two real applications. Robustness properties of the optimal designs are investigated when nominal values or the model is mis-specified, and also under a different optimality criterion. To facilitate use of optimal design ideas in practice, we also introduce a website for generating a variety of optimal designs for popular models from different disciplines
Cyber physical systems implementation for asset management improvement: A framework for the transition
Libro en Open AccessThe transformation of the industry due to recent technologies introduction is an evolving
process whose engines are competitiveness and sustainability, understood in its broadest sense (environmental,
economic and social). This process is facing, due to the current state of scientific and technological
development, a new challenge yet even more important: the transition from discrete technological solutions
that respond to isolated problems, to a global conception where the assets, plant, processes and engineering
systems are conceived, designed and operated as an integrated complex unit. This vision is evolving
besides a set of concepts that are, in some way, to guide this development: Smart Factories, Cyber-Physical
Systems, Factory of the Future or Industry 4.0, are examples. The full integration of the operation and
maintenance (O&M) processes in the production systems is a key topic within this new paradigm. Not
only that, this evolution necessarily results in the emergence of new processes and needs of O&M, i.e.
also, the O&M will undergo a profound transformation. The transition from actual isolated production
assets to such Industry 4.0 with CPS is far from easy. This document presents a proposal to develop such
transition adapting one iteration of the Model of Maintenance Management (MMM) integrated into
ISO 55000 to the complexity of incorporating “System of Systems” CPSs maintenance. It involves several
stages: identification, prioritization, risk management, planning, scheduling, execution, control, and
improvement supported by system engineering techniques and agile/concurrent project managemen
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