Acoustical properties of double porosity granular materials

Granular materials have been conventionally used for acoustic treatment due to their sound absorptive and sound insulating properties. An emerging field is the study of the acoustical properties of multiscale porous materials. An example of these is a granular material in which the particles are porous. In this paper, analytical and hybrid analytical-numerical models describing the acoustical properties of these materials are introduced. Image processing techniques have been employed to estimate characteristic dimensions of the materials. The model predictions are compared with measurements on expanded perlite and activated carbon showing satisfactory agreement. It is concluded that a double porosity granular material exhibits greater low-frequency sound absorption at reduced weight compared to a solid-grain granular material with similar mesoscopic characteristics

On Consumption, Investment and Risk

The Mexican episode of 1992-1994 was characterized by a steep rise in consumption accompanied by a sharp fall in investment. This paper provides an explanation of the negative response of investment to political risk, as occurred in Mexico between 1992 and 1994. It is assumed that, inside an adjustable band, the expected rate of depreciation is driven by a mixed diffusion-jump process and the expected real rate of return on an international bond is governed by a diffusion process, both processes being correlated. This paper analyzes a small open stochastic economy. Two cases are considered: i) a cash-in-advance, Ramsey-type economy, and ii) a Sidrauski-type economy.

White Pre-Service Teachers’ Perceptions and their Development of Culturally Relevant Literacy Practices

Existent literature purports that providing White teacher candidates with increased exposure to urban schools in order to create culturally competent educators has failed. These findings reflect the notion that teacher ideologies and overall perspectives about working with diverse student groups must be harnessed in a genuine ethic of care and intentionality for students of color. However, few studies have taken the approach of examining the development of culturally relevant pedagogy through context-specific field experiences using content-specific courses. This study examines the perspectives of twenty-five White pre-service teachers from a predominately White, private university regarding their initial perceptions and gained conceptual understanding of culturally relevant pedagogy while teaching reading at an urban middle school. Findings were consistent with previous literature that White pre-service teachers are more interested and comfortable teaching in suburban and private schools and held implicit about teaching in urban schools. However, through the course and urban field experience, pre-service teachers were able to develop teaching behaviors that were deemed culturally relevant(Ladson-Billings, 1995) for teaching reading, and were better prepared to work with students from diverse backgrounds

An Economist´s guide to the Kalman filter

Almost since its appearance, the Kalman Filter (KF) has been successfully used in control engineering. Unfortunately, most of its important results have been published in engineering journals with language, notation and style proper of engineers. In this paper, we want to present the KF in an attractive way to economists by using information theory and Bayesian inference.