786 research outputs found

    A Sensitivity and Array-Configuration Study for Measuring the Power Spectrum of 21cm Emission from Reionization

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    Telescopes aiming to measure 21cm emission from the Epoch of Reionization must toe a careful line, balancing the need for raw sensitivity against the stringent calibration requirements for removing bright foregrounds. It is unclear what the optimal design is for achieving both of these goals. Via a pedagogical derivation of an interferometer's response to the power spectrum of 21cm reionization fluctuations, we show that even under optimistic scenarios, first-generation arrays will yield low-SNR detections, and that different compact array configurations can substantially alter sensitivity. We explore the sensitivity gains of array configurations that yield high redundancy in the uv-plane -- configurations that have been largely ignored since the advent of self-calibration for high-dynamic-range imaging. We first introduce a mathematical framework to generate optimal minimum-redundancy configurations for imaging. We contrast the sensitivity of such configurations with high-redundancy configurations, finding that high-redundancy configurations can improve power-spectrum sensitivity by more than an order of magnitude. We explore how high-redundancy array configurations can be tuned to various angular scales, enabling array sensitivity to be directed away from regions of the uv-plane (such as the origin) where foregrounds are brighter and where instrumental systematics are more problematic. We demonstrate that a 132-antenna deployment of the Precision Array for Probing the Epoch of Reionization (PAPER) observing for 120 days in a high-redundancy configuration will, under ideal conditions, have the requisite sensitivity to detect the power spectrum of the 21cm signal from reionization at a 3\sigma level at k<0.25h Mpc^{-1} in a bin of \Delta ln k=1. We discuss the tradeoffs of low- versus high-redundancy configurations.Comment: 34 pages, 5 figures, 2 appendices. Version accepted to Ap

    Constraining cosmological ultra-large scale structure using numerical relativity

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    Cosmic inflation, a period of accelerated expansion in the early universe, can give rise to large amplitude ultra-large scale inhomogeneities on distance scales comparable to or larger than the observable universe. The cosmic microwave background (CMB) anisotropy on the largest angular scales is sensitive to such inhomogeneities and can be used to constrain the presence of ultra-large scale structure (ULSS). We numerically evolve nonlinear inhomogeneities present at the beginning of inflation in full General Relativity to assess the CMB quadrupole constraint on the amplitude of the initial fluctuations and the size of the observable universe relative to a length scale characterizing the ULSS. To obtain a statistically significant number of simulations, we adopt a toy model in which inhomogeneities are injected along a preferred direction. We compute the likelihood function for the CMB quadrupole including both ULSS and the standard quantum fluctuations produced during inflation. We compute the posterior given the observed CMB quadrupole, finding that when including gravitational nonlinearities, ULSS curvature perturbations of order unity are allowed by the data, even on length scales not too much larger than the size of the observable universe. Our results illustrate the utility and importance of numerical relativity for constraining early universe cosmology.Comment: 14 pages, 6 figures v3: Clarifications added regarding the generality of results - conclusions unchanged, version accepted for publication in PRD, v2: updated with minor clarifications, submitte

    Diseño de un sismómetro electromagnético para medir movimientos telúricos verticales

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    El siguiente trabajo presenta el diseño de una sismómetro para medir movimientos telúricos verticales a través de la generación de tensión por medio de un conjunto magneto-bobina, midiendo la diferencia de tensión de salida que es proporcional a la velocidad de la masa del sismómetro, obteniendo así una señal que representa el movimiento terrestre. El enfoque de este proyecto es motivar la inclusión de las vibraciones mecánicas e instrumentación aplicada a la sismología dentro de los proyectos de investigación que realice la universidad

    Multiple Cosmic Collisions and the Microwave Background Power Spectrum

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    Collisions between cosmic bubbles of different vacua are a generic feature of false vacuum eternal inflation scenarios. While previous studies have focused on the consequences of a single collision event in an observer's past, we begin here an investigation of the more general scenario allowing for many "mild" collisions intersecting our past light cone (and one another). We discuss the general features of multiple collision scenarios and consider their impact on the cosmic microwave background (CMB) temperature power spectrum, treating the collisions perturbatively. In a large class of models, one can approximate a multiple collision scenario as a superposition of individual collision events governed by nearly isotropic and scale-invariant distributions, most appearing to take up less than half of the sky. In this case, the shape of the expected CMB temperature spectrum maintains statistical isotropy and typically features a dramatic increase in power in the low multipoles relative to that of the best-fit Λ\LambdaCDM model, which is in tension particularly with the observed quadrupole. We argue that this predicted spectrum is largely model-independent and can be used to outline features of the underlying statistical distributions of colliding bubbles consistent with CMB temperature measurements.Comment: 19 PRD-style pages, 7 figure

    The Philosopher against the Rhapsodist. Socrates and Ion as Characters in Plato’s Ion

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    The critique of the poetry in Plato’s Ion unfolds in a clearly political context in which, in contrast to the old model of knowledge represented by poetry, Plato presents a new model, identified with philosophy, which questions the legitimacy of poets and rhapsodists as competent guides of the polis and citizens. In this critique, the characters and dramatic elements of dialogue are fundamental. Thus in Ion and Socrates the Athenian philosopher brings together all the characteristics that describe a real rhapsodist of that time as well as the philosophical activity of the historical Socrates

    El problema de la desigualdad social y económica en Argentina. Un estudio sociológico en el marco del Programa de Investigación sobre la Sociedad Argentina Contemporánea (PISAC)

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    Reseña del libro: PIOVANI, J. I. y SALVIA, A. (2018). La Argentina en el siglo XXI. Cómo somos, vivimos y convivimos en una sociedad desigual. Buenos Aires: Siglo XXI

    Políticas de educación docente situadas. Una necesidad para la disputa de sentidos.

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    La educación docente es parte de un complejo entramado de políticas públicas estatales que no solo se circunscriben al sector educativo en general o al ámbito docente en particular sino que también se entraman con aquellas políticas que dan cuenta, estructuralmente, del proyecto de país que se quiera desplegar. En tiempos actuales en donde tienden a reaparecer discursos y prácticas que recrean posicionamientos neoconservadores en educación, consideramos que poner en debate las políticas docentes estimulando su situacionalidad y horizontalidad se vuelve una necesidad y una práctica de resistencia en pos de disputar sentidos sobre la educación de maestros y profesores

    La ética y valores morales en la enseñanza universitaria desde la perspectiva de los estudiantes: conjunción de intelecto, compromiso, afecto y pasión en los profesores memorables

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    Este trabajo recupera algunas categorías que se trabajan en el Grupo de Investigaciones en Educación y Estudios Culturales (GIEEC) de la Facultad de Humanidades de la Universidad Nacional de Mar del Plata, y se desprende del proyecto de beca de la categoría Estudiante Avanzado de la UNMDP “La Formación del Profesorado: Narrativas sobre las prácticas de enseñanza de profesores memorables del Profesorado en Historia de la UNMDP”. En este artículo nos proponemos indagar en la cuestión ética de la enseñanza a partir de los retazos narrativos de los estudiantes avanzados del profesorado en Historia, quienes definieron a los profesores memorables de nuestro estudio. Sabemos que la buena enseñanza involucra aspectos morales que inciden favorablemente en el aprendizaje. Los valores morales que los estudiantes perciben en sus profesores memorables generan un espacio de análisis que nos permite vislumbrar aspectos de docencia del Nivel Superior corridos de la mirada tecnocrática, y no siempre tenidos en cuenta en la práctica docente. Es partir de los estudiantes universitarios que las categorías “ética” “intelecto”, “afecto” “compromiso” y “pasión” surgen como características insoslayables de aquellos profesores que han dejado una huella en su recorrido universitario
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