Measures of non-exchangeability for bivariate random vectors

We introduce a set of axioms for measures of non-exchangeability for bivariate vectors of continuous and identically distributed random variables and give some examples together with possible applications in statistical models based on the copula function.     

Cooperative learning: we can also do it without task structure

The present study focuses on the use of a cooperative methodology with university students during the last year of their degree programme. The task structure could be freely chosen, and there were no restraints on group decisions to deal with the classroom work. All the elements of cooperation were based on a reward structure. The results show that internal group cohesion can be achieved through an inter‐group competitive reward system and positive interdependence can be reached with an extreme cooperative reward structure, grounded on individual assessments of the students. The results also point to the importance of a reward structure, based on grades, when using a cooperative methodology in the university classroom.

Este estudio supone la utilización de una metodología cooperativa con alumnos universitarios en el último curso de la carrera. La estructura de tarea es siempre libre y no hay ninguna restricción a las decisiones del grupo para abordar el trabajo de aula. Todos los elementos de la cooperación se abordan desde la estructura de recompensa: la cohesión interna de los grupos se consigue mediante un sistema de recompensa competitiva intergrupal y la interdependencia positiva se logra mediante una estructura de recompensa cooperativa extrema, basada en las evaluaciones individuales de los alumnos. Los resultados demuestran la importancia que tiene una estructura de recompensa, basada en las calificaciones, para la aplicación de una metodología cooperativa al aula universitaria.     

Population and land use change in the California Mojave: Natural habitat implications of alternative futures

Demographic and land use dynamics have important implications for the natural environment within both developed and developing nations. Within the context of developed nations, popular and policy debates surrounding contemporary patterns of suburbanization attest to the salience of demographic and development issues. We examine the implications of land-use patterns as related to population and development within the context of the California Mojave Desert ecosystem. In a general sense, we aim to better understand the land requirements inferred by varying levels of population growth and density, as well as the natural habitat implications of those requirements. We develop a GIS including remotely sensed imagery, and demographic, economic, and biophysical data to examine of the implications of various demographic scenarios on species diversity. Spatial and statistical models are designed to develop possible alternative land use `futures'. Within the context of the California Mojave region, our results suggest that high-density development could reduce conflict with regions providing potential habitat for threatened or endangered species by over 80 percent. The process of model development demonstrates a potentially useful tool for policymakers, allowing for estimation and visualization of the land use implications of policy decisions.     

Effective strategies for socio-educational intervention during the process of transition to adult life of unaccompanied minors from Africa

The arrival of unaccompanied minors from Africa in Spanish territory has been a constant since the last decade of the twentieth century. This migratory phenomenon has forced the child welfare system to attend to thousands of migrant children. The transition to adult life is a decisive stage in overcoming the situation of social exclusion. This research aims to analyse which socio-educational intervention strategies are effective during the process of transition to independent living with unaccompanied minors of African origin. We designed a qualitative research according to the grounded theory, which we divided into two phases. Twenty-nine young people (26 men and 3 women) participated. In phase 1, we performed two focus groups (N = 11), and in phase 2, we conducted longitudinal follow-ups (N = 18) for 24 months through 180 interviews. The results indicate the effectiveness of designing socio-educational accompaniment, prioritizing spaces of trust from which to attain the goals of emancipation. Young people consider effective those strategies that favour their knowledge of the social, labour and legal reality of the host society, designed considering each minor's individualized situation. We concluded that professional involvement acts as a buffer, reducing the bureaucratic obstacles implemented by the Spanish government.     

A TECHNIQUE TO MINIMIZE OVERTIME IN THE CAPACITATED MRP PROBLEM

Since the development of early versions of material requirements planning (mrp) systems, it has been known that a weak link in this technique is the failure to consider the available capacity at the time the lot sizes for individual items are calculated. Ignoring the available capacity may result in infeasible production plans, i.e., those that can only be accomplished with the use of overtime. We present a technique to search for feasible production plans by means of minimizing the total overtime. The technique is based on modifying periodic-order-quantity (poq) lot sizes within a tabu search framework. Computational experiments with the largest problem structure reported in the literature show that the procedure is effective in determining lot sizes for individual items that either minimize or eliminate overtime. Additional experiments reveal that, with appropriate calibration of search parameters, the procedure is also able to deal with more general cost functions (e.g., those that include holding and setup costs).     

Locking down adolescents: Victims,irresponsible subjects,or just social actors

The article presents the results of a qualitative study investigating the experiences of a sample of Italian adolescents during the COVID-19 pandemic. Data were analysed in the light of the two social representations (adolescents as criminals and as victims) that permeated the Italian public debate throughout the outbreak. The findings showed the ability of boys and girls in dealing with the relationships altered by the pandemic constraints and in adapting to different regulations. This demonstrated their competence as social actors, neither criminals nor victims, who were also able to cope with the coronavirus risk in safeguarding their significant others.     

Accuracy of Numerical Solutions Using the Euler Equation Residuals

This paper is concerned with asymptotic properties on the accuracy of numerical solutions. It is shown that the approximation error of the policy function is of the same order of magnitude as the size of the Euler equation residuals. Moreover, for bounding this approximation error the most relevant parameters are the discount factor and the curvature of the return function. These findings provide theoretical foundations for the construction of tests to assess the performance of alternative computational methods.