1,001 research outputs found

    Breaking the scale invariance of the primordial power spectrum in Horava-Lifshitz Cosmology

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    We study the spectral tilt of primordial perturbations in Horava-Lifshitz cosmology. The uniform approximation, which is a generalization of the familiar Wentzel-Kramers-Brillouin (WKB) method, is employed to compute the spectral index both numerically and analytically in a closed form. We clarify how the spectral index depends on the inflation model and parameters in the modified dispersion relation.Comment: 5 pages, 2 figures, accepted for publication in Physical Review

    Indecomposable pure-injective objects in stable categories of Gorenstein-projective modules over Gorenstein orders

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    We give a result of Auslander-Ringel-Tachikawa type for Gorenstein-projective modules over a complete Gorenstein order. In particular, we prove that a complete Gorenstein order is of finite Cohen-Macaulay representation type if and only if every indecomposable pure-injective object in the stable category of Gorenstein-projective modules is compact.Comment: Appendix by Rosanna Laking. 22 page

    Minimal semi-flat-cotorsion replacements and cosupport

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    Over a commutative noetherian ring RR of finite Krull dimension, we show that every complex of flat cotorsion RR-modules decomposes as a direct sum of a minimal complex and a contractible complex. Moreover, we define the notion of a semi-flat-cotorsion complex as a special type of semi-flat complex, and provide functorial ways to construct a quasi-isomorphism from a semi-flat complex to a semi-flat-cotorsion complex. Consequently, every RR-complex can be replaced by a minimal semi-flat-cotorsion complex in the derived category over RR. Furthermore, we describe structure of semi-flat-cotorsion replacements, by which we recover classic theorems for finitistic dimensions. In addition, we improve some results on cosupport and give a cautionary example. We also explain that semi-flat-cotorsion replacements always exist and can be used to describe the derived category over any associative ring.Comment: 28 pages. Final version to appear in Journal of Algebra. We have made a number of minor revisions, including modifications to Lemma 1.1, a new Lemma 3.8, and a corrected Proposition A.1

    La (incumplida) promesa universitaria en el Perú

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    La universidad pública tomó una senda de crisis como producto del descuido del Estado puesto en evidencia en el desfinanciamiento y la desintegración del tramado institucional. Desde nuestra perspectiva, fueron tres las hipótesis de cambio que estuvieron detrás de la decisión de liberalizar la oferta educativa universitaria. La primera consistió en que con la participación privada se conseguiría ampliar la oferta y, por lo tanto, la cobertura universitaria. La segunda fue que, como consecuencia de la primera, el acceso a los estudios superiores se democratizaría; y Finalmente, se supuso que el mercado sería un regulador efectivo de la calidad de este servicio, en el que la competencia dejaría fuera a las malas universidades. El objetivo de este informe es mostrar qué sucedió con aquellas hipótesis de mediados de los años noventa mediante el análisis descriptivo de un conjunto de datos oficiales sobre la educación superior universitaria en el Perú

    Lithium- and oxygen-isotope compositions of chondrule constituents in the Allende meteorite

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    We report in situ ion-microprobe analyses of Li- and O-isotope compositions for olivine, low-Ca pyroxene, high-Ca pyroxene, and chondrule mesostasis/plagioclase in nine chondrules from the Allende CV3 chondrite. Based on their mineralogy and O-isotope compositions, we infer that the chondrule mesostasis/plagioclase and ferroan olivine rims were extensively modified or formed during metasomatic alteration and metamorphism on the Allende parent asteroid. We excluded these minerals in order to determine the correlations between Li and both O and the chemical compositions of olivines and low-Ca pyroxenes in the chondrules and their igneous rims. Based on the O-isotope composition of the olivines, nine chondrules were divided into three groups. Average Δ17O of olivines (Fo>65) in group 1 and 2 chondrules are −5.3 ± 0.4 and −6.2 ± 0.4‰, respectively. Group 3 chondrules are characterized by the presence of 16O-rich relict grains and the Δ17O of their olivines range from −23.7 to −6.2‰. In group 1 olivines, as Fa content increases, variation of δ7Li becomes smaller and δ7Li approaches the whole-rock value (2.4‰; Seitz et al., 2012), suggesting nearly complete Li-isotope equilibration. In group 2 and 3 olivines, variation of δ7Li is limited even with a significant range of Fa content. We conclude that Li-isotope compositions of olivine in group 1 chondrules were modified not by an asteroidal process but by an igneous-rim formation process, thus chondrule olivines retained Li-isotope compositions acquired in the protosolar nebula. In olivines of the group 3 chondrule PO-8, we observed a correlation between O and Li isotopes: In relict 16O-rich olivine grains with Δ17O of ∼−25 to −20‰, δ7Li ranges from −23 to −3‰; in olivine grains with Δ17O > −20‰, δ7Li is nearly constant (−8 ± 4‰). Based on the Li-isotope composition of low-Ca pyroxenes, which formed from melt during the crystallization of host chondrules and igneous rims, the existence of a gaseous reservoir with a δ7Li ∼ −11‰ is inferred

    Little dimension and the improved new intersection theorem

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    Let RR be a commutative noetherian local ring. We define a new invariant for RR-modules which we call the little dimension. Using it, we extend the improved new intersection theorem.Comment: 7 pages, to appear in Math. Scan
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