Optimal number of strata for the stratified methods in computerized adaptive testing

Test security can be a major problem in computerized adaptive testing, as examinees can share information about the items they receive. Of the different item selection rules proposed to alleviate this risk, stratified methods are among those that have received most attention. In these methods, only low discriminative items can be presented at the beginning of the test and the mean information of the items increases as the test goes on. To do so, the item bank must be divided into several strata according to the information of the items. To date, there is no clear guidance about the optimal number of strata into which the item bank should be split. In this study, we will simulate conditions with different numbers of strata, from 1 (no stratification) to a number of strata equal to test length (maximum level of stratification) while manipulating the maximum exposure rate that no item should surpass (rmax) in its whole domain. In this way, we can plot the relation between test security and accuracy, making it possible to determine the number of strata that leads to better security while holding constant measurement accuracy. Our data indicates that the best option is to stratify into as many strata as possible.This research was supported by a grant from the Spanish Ministerio de Ciencia e Innovación (project number PSI2009–10341), and by a grant from the Fundación Universitaria Antonio Gargallo and the Obra Social de Ibercaja

Relajación de problemas de control en los coeficientes con un funcional dependiendo del gradiente

Se considera un problema de diseño ´optimo consistente en mezclar dos materiales (eléctricos o térmicos) anisótropos de tal forma que se inimice un funcional coste dependiente del gradiente de la función estado. En general, este tipo de problemas no admite solución, lo que obliga a introducir una formulación relajada. Mostramos en este trabajo como esta relajación puede ser obtenida usando materiales compuestos, construidos por homogeneización, y realizando una determinada extensión del funcional coste a estos nuevos materiales. Esta extensión admite una representación integral. Nuestros resultados contienen en particular los obtenidos por otros autores en el caso de materiales isótropos

Relaxation of a control problem in the coefficients with a functional of quadratic growth in the gradient

We study an optimal design problem consisting in mixing two anisotropic (electric or thermal) materials in order to minimize a functional depending on the gradient of the state. It is known that this type of problem has no solution in general, and then it is necessary to introduce a relaxed formulation. Here we prove that this relaxation is obtained by using composite materials, is constructed by homogenization, and takes a particular extension of the cost functional to these new materials. We obtain an integral representation of this relaxed cost functional. Besides, we show that our results contain some previous results obtained by other authors for isotropic materials.Ministerio de Educación y CienciaJunta de Andalucí

Optimality conditions for nonconvex multistate control problems in the coefficients

The purpose of this paper is to attain some optimality conditions for the identification of a diffusion matrix (material) under several restrictions. Assuming that the set of such diffusion matrices is closed for the H-convergence, we give a method to obtain admissible directions which applies to a not-necessarily convex control set. Our results permit obtaining the diffusion matrix from the state functions.Dirección General de Investigación (Ministerio de Ciencia y Tecnología)Junta de Andalucí

La autopublicación, un nuevo paradigma en la creación digital del libro

Self-publishing is the publication of any book or other media by the author of the work, without the intervention of a third party established or publisher. The author is responsible for controlling the whole process, including design (covered indoor), formats, pricing, distribution, marketing and public relations. Authors can do it all themselves or outsource all or part of the process in companies that offer these services. The aim of this paper is analyze the phenomenon of self-publishing in the new digital environment. An analysis of the advantages and disadvantages of self-publishing systems, data are provided in the publishing world and reflects the main players in this market remains a vanity press to attend directly in the publishing market with unprecedented bestsellers

The Comparison Study of Short-Term Prediction Methods to Enhance the Model Predictive Controller Applied to Microgrid Energy Management

Electricity load forecasting, optimal power system operation and energy management play key roles that can bring significant operational advantages to microgrids. This paper studies how methods based on time series and neural networks can be used to predict energy demand and production, allowing them to be combined with model predictive control. Comparisons of different prediction methods and different optimum energy distribution scenarios are provided, permitting us to determine when short-term energy prediction models should be used. The proposed prediction models in addition to the model predictive control strategy appear as a promising solution to energy management in microgrids. The controller has the task of performing the management of electricity purchase and sale to the power grid, maximizing the use of renewable energy sources and managing the use of the energy storage system. Simulations were performed with different weather conditions of solar irradiation. The obtained results are encouraging for future practical implementation

Exploratory factor analysis in validation studies: uses and recommendations

The Exploratory Factor Analysis (EFA) procedure is one of the most commonly used in social and behavioral sciences. However, it'is also one of the most criticized due to the poor management researchers usually display. The main goal is to examine the relationship between practices usually considered more appropriate and actual decisions made by researchers. Method: The use of exploratory factor analysis is examined in 117 papers published between 2011 and 2012 in 3 Spanish psychological journals with the highest impact within the previous five years. Results: Results show significant rates of questionable decisions in conducting EFA, based on unjustified or mistaken decisions regarding the method of extraction, retention, and rotation of factors. Conclusions: Overall, the current review provides support for some improvement guidelines regarding how to apply and report an EFAEl análisis factorial exploratorio en estudios de validación: usos y recomendaciones. Antecedentes: la técnica del Análisis Factorial Exploratorio (AFE) es una de las más utilizadas en el ámbito de las Ciencias Sociales y del Comportamiento; no obstante, también es una de las técnicas más criticadas por la escasa solvencia con que se emplea en investigación aplicada. El objetivo principal de este artículo es describir y valorar el grado de correspondencia entre la aplicación del AFE en las publicaciones revisadas y las prácticas que habitualmente se consideran más adecuadas. Método: se analizan 117 estudios en los que se aplica la técnica del AFE, publicados en 2011 y 2012, en las tres revistas españolas de Psicología con mayor índice de impacto medio en los últimos cinco años. Resultados: se obtienen importantes tasas de decisiones injustificadas o erróneas respecto al método de extracción, retención y rotación de factores. Conclusiones: en conjunto, la presente revisión proporciona una guía sobre posibles mejoras al ejecutar e informar de un AF

On the Design of Ambient Intelligent Systems in the Context of Assistive Technologies

The design of Ambient Intelligent Systems (AISs) is discussed in the context of assistive technologies. The main issues include ubiquitous communications, context awareness, natural interactions and heterogeneity, which are analyzed using some examples. A layered architecture is proposed for heterogeneous sub-systems integration with three levels of interactions that may be used as a framework to design assistive AISs.Ministerio de Ciencia y Tecnología TIC2001-1868-C0

Analysis of contexts and conceptual variables for a sustainable approach into systemic model

The research deals with an approximation to systemic design focused on sustainability, analyzing issues affecting the conceptualization of a product-system or service, in the initial stages of the design process, determining from a qualitative perspective on this phase of the project, a set of variables that are articulated both from basic design criteria as well as from sustainability criteria. For it, one resorts to the use of a multiobjective design model, in order to manage data, information and knowledge as well as its networks of relationships. It starts from the consideration of multiple sources of uncertainty that are reduced by a filtering process of the outer system, from an approach proposed for such purposes. Similarly, is raised the highlighting of variables that contribute to complement the emotional aspects, spiritual and scale of values related to users or consumers, as a strategy to assist in the process of providing a new pillar to the triad of sustainability, traditionally supported by environmental, economic and social pillars. For the description of procedures, structures and functions, a case study is presented in which are outlined the intrinsic qualities of a reference system and their interaction networks, starting with the filtering process of the outer system, till the obtaining of the key variables that have greater impact on the definition of formal, functional and ergonomic objectives in the inner subsystems

A computerized adaptive test for the assessment of written English: design and psychometric properties

El presente artículo muestra el trabajo desarrollado para diseñar un test adaptativo informatizado que evalúa el nivel de conocimientos de inglés escrito en castellano-parlantes. Se describe el proceso seguido para la elaboración del banco de ítems, la comprobación de sus propiedades psicométricas, el ajuste obtenido al modelo logístico de tres parámetros y las principales características del algoritmo adaptativo. Se aportan algunos resultados iniciales sobre la validez de los niveles de rasgo estimados. Se comentan los resultados obtenidos en un estudio de simulación, cuyo objetivo es comprobar algunas propiedades de los niveles de inglés estimados (precisión y sesgo). Los primeros estudios de fiabilidad y validez han dado resultados satisfactoriosThis article describes the development of a computer adaptive test to assess the written English level of Spanish speakers. A short description is given of the steps followed for the elaboration of the item bank, the evaluation of its psychometric properties, the fit to the 3-parameter logistic model and the main characteristics of the adaptive algorithm. Some initial results on the validity of estimated ability measures are provided. The article includes the results of a simulation study which aims to obtain information on precision and bias of English level estimates. First results on reliability and validity are encouragingEste trabajo ha sido financiado por los proyectos DGES BSO2002-1485 y DGES BSO2000-005