Physical activity among Spanish adolescents: relationship with their relatives' physical activity - the AVENA study     

Martin-Matillas M  Ortega FB  Chillon P  Perez IJ  Ruiz JR  Castillo R  Gomez-Martinez S  Moreno LA  Delgado-Fernandez M  Tercedor P;AVENA Study 《Journal of sports sciences》2011,29(4):329-336

Identifying factors related to physical activity levels in young people is important for a more efficient health promotion. The aims of this study were to assess physical activity levels in a national sample of urban Spanish adolescents, and to examine the association between significant others' physical activity (father, mother, brother, sister, and close friends) and that of the adolescents. The present study comprised 2260 adolescents (1157 boys, 1103 girls) aged 13.0-18.5 years participating in the AVENA Study. Both the adolescents' physical activity and that of their relatives and close friends was assessed by questionnaire. The odds of being active were higher in boys than girls (odds ratio?=?2.79, 95% confidence interval?=?2.34-3.33) and tended to decrease across age groups in both boys and girls. Father's and older brother's physical activity was associated with boys' physical activity, while that of any significant other was associated with girls' physical activity. When both parents reported being active, boys had nearly two times higher odds of being active and girls had nearly three times higher odds of being active. The physical activity levels of Spanish adolescents are in line with those previously reported. Physical activity levels in girls are strongly related to the physical activity of any significant other, whereas physical activity levels in boys are only related to their male relatives' physical activity.  相似文献   

How Mathematicians Obtain Conviction: Implications for Mathematics Instruction and Research on Epistemic Cognition     

Keith Weber  Matthew Inglis  Juan Pablo Mejia-Ramos 《教育心理学家》2014,49(1):36-58

The received view of mathematical practice is that mathematicians gain certainty in mathematical assertions by deductive evidence rather than empirical or authoritarian evidence. This assumption has influenced mathematics instruction where students are expected to justify assertions with deductive arguments rather than by checking the assertion with specific examples or appealing to authorities. In this article, we argue that the received view about mathematical practice is too simplistic; some mathematicians sometimes gain high levels of conviction with empirical or authoritarian evidence and sometimes do not gain full conviction from the proofs that they read. We discuss what implications this might have, both for mathematics instruction and theories of epistemic cognition.  相似文献   

Socioeconomic school segregation in a market-oriented educational system. The case of Chile     

Juan Pablo Valenzuela  Danae de los Ríos 《教育政策杂志》2014,29(2):217-241

This paper presents an empirical analysis of the socioeconomic status (SES) school segregation in Chile, whose educational system is regarded as an extreme case of a market-oriented education. The study estimated the magnitude and evolution of the SES segregation of schools at both national and local levels, and it studied the relationship between some local educational market dynamics and the observed magnitude of SES school segregation at municipal level. The main findings were: first, the magnitude of the SES segregation of both low-SES and high-SES students in Chile was very high (Duncan Index ranged from 0.50 to 0.60 in 2008); second, during the last decade, SES school segregation tended to slightly increase in Chile, especially in high schools (both public and private schools); third, private schools – including voucher schools – were more segregated than public schools for both low-SES and high-SES students; and finally, some market dynamics operating in the Chilean education (like privatization, school choice, and fee-paying) accounted for a relevant proportion of the observed variation in SES school segregation at municipal level. These findings are analyzed from an educational policy perspective in which the link between SES school segregation and market-oriented mechanisms in education plays a fundamental role.  相似文献   

Sliding mode controller design for linear stochastic systems with unknown parameters     

Michael Basin  Pablo Rodriguez-Ramirez 《Journal of The Franklin Institute》2014

This paper presents the sliding mode mean-square and mean-module controllers for linear stochastic systems with unknown parameters. In both cases, the controller equations are obtained using the separation principle, whose applicability to the considered problem is substantiated. Performance of the obtained controllers is verified in the illustrative example against the sliding mode mean-square and sliding mode controllers that are optimal for linear systems with known parameters. Simulation graphs demonstrating overall performance and computational accuracy of the designed optimal controller are included.  相似文献   

Application of symbolic dynamics to characterize coordinated activity in the context of biological neural networks     

David Arroyo  Roberto Latorre  Pablo Varona  Francisco B. Rodríguez 《Journal of The Franklin Institute》2013,350(10):2967-2981

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Relevance-based language modelling for recommender systems     

Javier Parapar  Alejandro Bellogín  Pablo Castells  Álvaro Barreiro 《Information processing & management》2013

Relevance-Based Language Models, commonly known as Relevance Models, are successful approaches to explicitly introduce the concept of relevance in the statistical Language Modelling framework of Information Retrieval. These models achieve state-of-the-art retrieval performance in the pseudo relevance feedback task. On the other hand, the field of recommender systems is a fertile research area where users are provided with personalised recommendations in several applications. In this paper, we propose an adaptation of the Relevance Modelling framework to effectively suggest recommendations to a user. We also propose a probabilistic clustering technique to perform the neighbour selection process as a way to achieve a better approximation of the set of relevant items in the pseudo relevance feedback process. These techniques, although well known in the Information Retrieval field, have not been applied yet to recommender systems, and, as the empirical evaluation results show, both proposals outperform individually several baseline methods. Furthermore, by combining both approaches even larger effectiveness improvements are achieved.  相似文献   

Determining the minimum number of passive stretches necessary to alter musculotendinous stiffness     

Eric D. Ryan  Trent J. Herda  Pablo B. Costa  Jason M. Defreitas  Travis W. Beck  Jeffrey Stout 《Journal of sports sciences》2013,31(9):957-961

Abstract

In this study, we examined the minimum number of constant-torque passive stretches necessary to reduce musculotendinous stiffness. Thirteen healthy individuals (mean age 22 years, s = 3; stature 1.67 m, s = 0.1; mass 66 kg, s = 13 kg) volunteered to participate in the investigation and underwent four 30-s constant-torque passive stretches of the plantar flexor muscles. Musculotendinous stiffness was examined from the angle–torque curves generated prior to the passive stretches, at the beginning of each 30-s stretch, and immediately following the four 30-s passive stretches. The results indicated that musculotendinous stiffness of the plantar flexors was reduced following two 30-s constant-torque passive stretches (P < 0.05) compared with the pre- musculotendinous stiffness assessment. Musculotendinous stiffness remained depressed following the third and fourth stretches, but did not decrease further. These findings suggest that two 30-s bouts of constant-torque passive stretching may be necessary to cause a significant decrease in musculotendinous stiffness of the plantar flexor muscles.  相似文献   

Sliding mode optimal control for linear systems     

Michael Basin  Pablo Rodriguez-Ramirez  Antonella Ferrara  Dario Calderon-Alvarez 《Journal of The Franklin Institute》2012,349(4):1350-1363

This paper addresses the optimal control problem for a linear system with respect to a Bolza–Meyer criterion with a non-quadratic non-integral term. The optimal solution is obtained as a sliding mode control, whereas the conventional linear feedback control fails to provide a causal solution. Performance of the obtained optimal controller is verified in the illustrative example against the conventional LQ regulator that is optimal for the quadratic Bolza–Meyer criterion. The simulation results confirm an advantage in favor of the designed sliding mode control.  相似文献   

Building user profiles based on sequences for content and collaborative filtering     

Pablo Sánchez  Alejandro Bellogín 《Information processing & management》2019,56(1):192-211

Modeling user profiles is a necessary step for most information filtering systems – such as recommender systems – to provide personalized recommendations. However, most of them work with users or items as vectors, by applying different types of mathematical operations between them and neglecting sequential or content-based information. Hence, in this paper we study how to propose an adaptive mechanism to obtain user sequences using different sources of information, allowing the generation of hybrid recommendations as a seamless, transparent technique from the system viewpoint. As a proof of concept, we develop the Longest Common Subsequence (LCS) algorithm as a similarity metric to compare the user sequences, where, in the process of adapting this algorithm to recommendation, we include different parameters to control the efficiency by reducing the information used in the algorithm (preference filter), to decide when a neighbor is considered useful enough to be included in the process (confidence filter), to identify whether two interactions are equivalent (δ-matching threshold), and to normalize the length of the LCS in a bounded interval (normalization functions). These parameters can be extended to work with any type of sequential algorithm.We evaluate our approach with several state-of-the-art recommendation algorithms using different evaluation metrics measuring the accuracy, diversity, and novelty of the recommendations, and analyze the impact of the proposed parameters. We have found that our approach offers a competitive performance, outperforming content, collaborative, and hybrid baselines, and producing positive results when either content- or rating-based information is exploited.  相似文献   

Some numerical tests for an alternative approach to optimal feedback control     

Roberto Font  Pablo Pedregal 《Journal of The Franklin Institute》2018,355(15):7011-7026

We test a recently proposed approach to optimal feedback control of nonlinear systems leading to an iterative descending strategy [24]. We start by discussing the numerical implementation of this strategy, and propose a number of improvements that can speed up the computation process by up to two orders of magnitude. The resulting algorithm is then applied to a series of test problems of increasing complexity. Results seem to show that this can be a promising strategy to bear in mind for more realistic situations.  相似文献