An analytic model for the transition from decelerated to accelerated cosmic expansion

We consider the scenario where our observable universe is devised as a dynamical four-dimensional hypersurface embedded in a five-dimensional bulk spacetime, with a large extra dimension, which is the {\it generalization of the flat FRW cosmological metric to five dimensions}. This scenario generates a simple analytical model where different stages of the evolution of the universe are approximated by distinct parameterizations of the {\it same} spacetime. In this model the evolution from decelerated to accelerated expansion can be interpreted as a "first-order" phase transition between two successive stages. The dominant energy condition allows different parts of the universe to evolve, from deceleration to acceleration, at different redshifts within a narrow era. This picture corresponds to the creation of bubbles of new phase, in the middle of the old one, typical of first-order phase transitions. Taking $\Omega_{m} = 0.3$ today, we find that the cross-over from deceleration to acceleration occurs at $z \sim 1-1.5$, regardless of the equation of state in the very early universe. In the case of primordial radiation, the model predicts that the deceleration parameter "jumps" from $q \sim + 1.5$ to $q \sim - 0.4$ at $z \sim 1.17$. At the present time $q = - 0.55$ and the equation of state of the universe is $w = p/\rho \sim - 0.7$, in agreement with observations and some theoretical predictions.Comment: The abstract and introduction are improved and the discussion section is expanded. A number of references are adde

On a new NBUE property in multivariate sense: an application

Since multivariate lifetime data frequently occur in applications, various properties of multivariate distributions have been previously considered to model and describe the main concepts of aging commonly considered in the univariate setting. The generalization of univariate aging notions to the multivariate case involves, among other factors, appropriate definitions of multivariate quantiles and related notions, which are able to correctly describe the intrinsic characteristics of the concepts of aging that should be generalized, and which provide useful tools in the applications. A new multivariate version of the well-known New Better than Used in Expectation univariate aging notion is provided, by means of the concepts of the upper corrected orthant and multivariate excess-wealth function. Some of its properties are described, with particular attention paid to those that can be useful in the analysis of real data sets. Finally, through an example it is illustrated how the new multivariate aging notion influences the final results in the analysis of data on tumor growth from the Comprehensive Cohort Study performed by the German Breast Cancer Study Grou

Reconstruction of the Derivative of the Conductivity at the Boundary

We describe a method to reconstruct the conductivity and its normal derivative at the boundary from the knowledge of the potential and current measured at the boundary. This boundary determination implies the uniqueness of the conductivity in the bulk when it lies in $W^{1+\frac{n-5}{2p}+,p}$, for dimensions $n\ge 5$ and for $n\le p<\infty$

A Bilinear Strategy for Calderón's Problem

Electrical Impedance Imaging would suffer a serious obstruction if for two different conductivities the potential and current measured at the boundary were the same. The Calder\'on's problem is to decide whether the conductivity is indeed uniquely determined by the data at the boundary. In $\mathbb{R}^d$, for $d=5,6$, we show that uniqueness holds when the conductivity is in $W^{1+\frac{d-5}{2p}+,p}(\Omega)$, for $d\le p<\infty$. This improves on recent results of Haberman, and of Ham, Kwon and Lee. The main novelty of the proof is an extension of Tao's bilinear Theorem

A characterization of the multivariate excess wealth ordering

In this paper, some new properties of the upper-corrected orthant of a random vector are proved. The univariate right-spread or excess wealth function, introduced by Fernández-Ponce et al. (1996), is extended to multivariate random vectors, and some properties of this multivariate function are studied. Later, this function was used to define the excess wealth ordering by Shaked and Shanthikumar (1998) and Fernández-Ponce et al. (1998). The multivariate excess wealth function enable us to define a new stochastic comparison which is weaker than the multivariate dispersion orderings. Also, some properties relating the multivariate excess wealth order with stochastic dependence are describe

Diagnóstico sobre la incorporación de la Nch 2957/2006 en los viveros forestales de la Región del Maule

Aravena, F. Ingeniera Forestal. Universidad de Talca, Talca. Chile. Ponce, M. Facultad de Ciencias Forestales. Universidad de Talca. Casilla 747, Talca. Chile.La investigación estuvo enfocada a diagnosticar la incorporación de la NCh2957/2006 en los viveros forestales de la Región del Maule. Para ello se empleó la “Taxonomía de Wroclaw”, obteniéndose tres clases de acercamiento a la norma. Se descubrió que lo anterior estaría en función de las capacidades y objetivos de la producción. Los viveros con un nivel de gestión alto, orientados al autoabastecimiento o a cumplir contratos con terceros, estarían más cerca del cumplimiento. Se dio también una relación directa entre: nivel de acercamiento, precios, y niveles de venta. Al evaluar las variables normadas, el nivel alto (clase I) obtuvo el 65% de las calificaciones de “buena a excelente”; el nivel medio (clase II), alcanzó el 54% de esta calificación; y en el nivel bajo (clase III), sólo el 33% de las variables resultaron como “buena”. La clase I presenta alta capacidad empresarial, con orientación al autoabastecimiento de planes de forestación/reforestación o a cumplir contratos, además demuestran interés en la norma. La clase II tiene nivel empresarial medio a alto, destinando la producción a sus patrimonios, o a cumplir contratos, y expresan escaso interés. La clase III, debido a sus deficientes capacidades, errónea noción de calidad y nulo interés en el tema, no podría certificarse por este sistema de evaluación. Se considera necesaria la implementación de la norma, pues el mercado de plantas forestales carece de estándares de calidad y se estarían empleando conceptos erróneos, sumado al desconocimiento de las ventajas que entrega la implementación de un sistema de calidad