8,054 research outputs found
A spacetime calculus based on a single null direction
No full textA spacetime calculus based on a single null direction is developed. The fundamental objects are totally symmetric spinors formed from the Ricci rotation coefficients together with four new differential operators which only depend upon the choice of O A up to a complex scaling. The formalism combines features of the GHP formalism with those of one which is invariant under null rotations. Einstein's equations and the full Bianchi identities are given in this new formalism
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Estimation in threshold autoregressive models with a stationary and a unit root regime
No full textThis paper treats estimation in a class of new nonlinear threshold autoregressive models with both a stationary and a unit root regime. Existing literature on nonstationary threshold models have basically focused on models where the nonstationarity can be removed by differencing and/or where the threshold variable is stationary. This is not the case for the process we consider, and nonstandard estimation problems are the result. This paper proposes a parameter estimation method for such nonlinear threshold autoregressive models using the theory of null recurrent Markov chains. Under certain assumptions, we show that the ordinary least squares (OLS) estimators of the parameters involved are asymptotically consistent. Furthermore, it can be shown that the OLS estimator of the coefficient parameter involved in the stationary regime can still be asymptotically normal while the OLS estimator of the coefficient parameter involved in the nonstationary regime has a nonstandard asymptotic distribution. In the limit, the rate of convergence in the stationary regime is asymptotically proportional to n-1/4, whereas it is n-1 in the nonstationary regime. The proposed theory and estimation method are illustrated by both simulated data and a real data example.Autoregressive process; null-recurrent process; semiparametric model; threshold time series; unit root structure.
Interpreting null findings from trials of alcohol brief interventions
No full textThe effectiveness of alcohol brief intervention (ABI) has been established by a succession of meta-analyses but, because the effects of ABI are small, null findings from randomized controlled trials are often reported and can sometimes lead to skepticism regarding the benefits of ABI in routine practice. This article first explains why null findings are likely to occur under null hypothesis significance testing (NHST) due to the phenomenon known as ‘the dance of the p-values’. A number of misconceptions about null findings are then described, using as an example the way in which the results of the primary care arm of a recent cluster randomized trial of ABI in England (the SIPS project) have been misunderstood. These misinterpretations include the fallacy of ‘proving the null hypothesis’ that lack of a significant difference between the means of sample groups can be taken as evidence of no difference between their population means, and the possible effects of this and related misunderstandings of the SIPS findings are examined. The mistaken inference that reductions in alcohol consumption seen in control groups from baseline to follow-up are evidence of real effects of control group procedures is then discussed and other possible reasons for such reductions, including regression to the mean, research participation effects, historical trends, and assessment reactivity, are described. From the standpoint of scientific progress, the chief problem about null findings under the conventional NHST approach is that it is not possible to distinguish ‘evidence of absence’ from ‘absence of evidence’. By contrast, under a Bayesian approach, such a distinction is possible and it is explained how this approach could classify ABIs in particular settings or among particular populations as either truly ineffective or as of unknown effectiveness, thus accelerating progress in the field of ABI research
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No full textEn este artículo el autor analiza la definición de reconstrucción del tejido social en relación con los temas sobre el derecho a la ciudad, marginamiento urbano y desplazamiento forzado en Colombia. El autor considera la reconstrucción del tejido social como el conjunto de actos orientados a reconstruir las relaciones significativas que determinan formas particulares de ser, producir, interactuar y proyectarse en los ámbitos familiar, comunitario, laboral y ciudadano. Además, como un proceso pedagógico y vital donde son importantes las redes de apoyo social, la atención integral al ser humano, el fortalecimiento de la acción colectiva y el apoyo a la autogestión.In this paper the author analyze the definition reconstruction of the social tissue in relation with the themes right to city, urban marginality and forced migrations in Colombia. The author considers the reconstruction of the social tissue as the set of acts to reconstruct the significant relations that determine particular forms of being, producing, interacting and projecting in the family, community, labour and citizen contexts. Also as a pedagogic and vital process where they are important the nets of social support, the integral attention to the human being, the invigoration of the collective action and the support to the self-management
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No full textEn este artículo el autor analiza la definición de reconstrucción del tejido social en relación con los temas sobre el derecho a la ciudad, marginamiento urbano y desplazamiento forzado en Colombia. El autor considera la reconstrucción del tejido social como el conjunto de actos orientados a reconstruir las relaciones significativas que determinan formas particulares de ser, producir, interactuar y proyectarse en los ámbitos familiar, comunitario, laboral y ciudadano. Además, como un proceso pedagógico y vital donde son importantes las redes de apoyo social, la atención integral al ser humano, el fortalecimiento de la acción colectiva y el apoyo a la autogestión.In this paper the author analyze the definition reconstruction of the social tissue in relation with the themes right to city, urban marginality and forced migrations in Colombia. The author considers the reconstruction of the social tissue as the set of acts to reconstruct the significant relations that determine particular forms of being, producing, interacting and projecting in the family, community, labour and citizen contexts. Also as a pedagogic and vital process where they are important the nets of social support, the integral attention to the human being, the invigoration of the collective action and the support to the self-management
Estudio ecologico de algunos aspectos de la biologia de Prays Oleae Bern (Lepidoptera Plutellidae)
No full textBibliografía al final de la obraEstación Experimental del Zaidin (C.S.I.C.). Leida el 14 de abril de 197
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No full textEl análisis de la reconocida obra de la música popular cubana titulada Guantanamera, mediante la investigación de las bibliografías, fonogramas y partituras que documentan la génesis de dicha pieza, revela al verdadero autor de la melodía con la que se cantan los versos de José Martí en la mencionada canción y demuestra las causas que provocaron la incertidumbre acerca de la autoría de dicha melodía.Con esta investigación concluyo que la melodía con la que se cantan los versos de José Martí en la pieza Guantanamera es una creación del compositor hispano–cubano Julián Orbón (1925–1991) y no de Joseíto Fernández como se ha repetido acríticamente. Igualmente, concluyo que la melodía de la tonada conocida con el título de Guajira guantanamer, popularizada con textos en décimas improvisadas y adjudicada a Joseíto Fernández, es bien diferente a la melodía utilizada por Orbón y popularizada por Pete Seeger para cantar los versos de Martí. Por causas políticas el Estado Cubano ha difundido el desacierto de que el autor de la melodía con la que se cantan los versos de José Martí en la pieza titulada Guantanamera es Joseíto Fernández y que Julián Orbón solamente adaptó los versos de Martí a la melodía de Fernández.An analysis of bibliography, phonograms and scores documenting the genesis of the well–known Cuban folk song Guantanamera, reveals the identity of its true author, and demonstrates the causes of the uncertainty that surrounds the authorship of the famous setting of José Marti’s poem. The author of this article concludes that the piece is an original creation of the Cuban–Hispanic composer Julián Orbón (1925–1991), rather than Joseíto Fernández, to whom it has been repeatedly attributed.The article concludes as well, that the melody of the tune known as Guajira guantanamera –made famous as a setting of improvised decasyllabic verses, and also attributed to Joseíto Fernández– is completely different from the one used by Orbón, which was the one internationalized by Pete Seeger with Marti’s words.Political causes motivated Cuban government to broadcast (wrongly) that the author of the tune, with words by José Martí, known as Guantanamera is Joseíto Fernández, and that Julián Orbón was responsible only for the setting of Martí’s poem to Fernández melody
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