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    ABSTRACT: Let A∈Fq×pA∈Fq×p be a nonzero matrix over a field FF, and let f be any monic polynomial of degree n=p+qn=p+q with coefficients in FF. A completion problem proposed and solved by de Oliveira asks for the existence of a matrix of order n with characteristic polynomial f and such that its q×pq×p submatrix in the left down corner is equal to A . Let C(f)∈Fn×nC(f)∈Fn×n be the companion matrix of f . We will construct a matrix XA∈Fn×nXA∈Fn×n (which depends exclusively on A ) such that XA−1C(f)XA is a closed form solution of this completion problem.
    Linear Algebra and its Applications 10/2014; 458:99–107.
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    ABSTRACT: Rats belonging to three different strains (15 Wistar, 8 Spontaneously Hypertensive-SHR- and 8 Wistar Kyoto-WKY-) were used to evaluate the possible relationship between different levels of impulsivity and development of schedule-induced polydipsia (SIP). We first measured the rats' levels of impulsivity by means of delay-discounting and indifference-point procedures. Secondly, development of SIP was studied under a series of fixed time 15, 30, 60 and 120seconds food schedules, which were counterbalanced by means of a Latin-square design. Finally, we re-assessed the rats' levels of impulsivity by replicating the delay-discounting test. The findings showed that, starting from equivalent levels of impulsivity, development of SIP differed among the groups of rats. In comparison with the rest of the animals, the SHRs were observed to attain elevated drinking rates under SIP. On the other hand, the Wistar rats which had initial high impulsivity levels similar to those of the SHRs, displayed the lowest rates of induced drinking. Moreover, low levels of impulsivity in Wistar rats prior to SIP acquisition were reflected into high drinking rates. Relation of SIP and impulsivity is questioned by present results, which gives ground to the understanding of the behavioural mechanisms involved in adjunctive behaviour and its usefulness as an animal model of excessive behaviour.
    Behavioural brain research. 06/2014;
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    ABSTRACT: Among the factors involved in school attainment, the construct “working memory” (WM) has gained particular significance, given that it is considered a basic capacity probably related to essential components of fluid intelligence. This paper presents the adaptation and validation of a WM span test (the PAR-a), based on a correlational study in a sample of high school students. In order to examine the empirical and theoretical consistency of the new measure, we assessed its predictive power on school qualifications, as well as its relations with another WM span test and an intelligence g Factor measure. The results support the construct and criterion validity of PAR-a, confirming its predictive and discriminative power regarding general cognitive ability as well as specific performance in academic subjects. This confirms, therefore, the usefulness of the test in educational contexts as a suitable tool to predict school achievement.
    Psicología Educativa. 06/2014; 20(1):1–10.

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Psicothema, ISSN 0214-9915, Vol. 11, Nº. 4, 1999, pags. 705-723.
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