Sustainable storage assignment and dwell-point policies for automated storage and retrieval systems

Picking time reduction has been the traditional perspective for warehouse optimisation. When sustainability is considered, optimisation of warehouse operations should be read in terms of energy efficiency other than response time. Each location in the rack of an automated storage and retrieval system is associated with the value of energy consumed by the crane to reach it. Since picking performance strictly depends on storage location assignments, the time-based full turnover strategy is compared to the energy-based one. Three models of energy consumption are considered for traditional and new-generation cranes. Assignments are then compared in terms of dedicated zone shapes, time and energy performances within a given time horizon. Different shapes of the rack and product ABC curves are analysed. Dwell-point policies are also analysed from the new sustainable perspective, adding energy-saving performance to the traditional picking time reduction.     

A geometric approach to transdimensional markov chain monte carlo

The authors present theoretical results that show how one can simulate a mixture distribution whose components live in subspaces of different dimension by reformulating the problem in such a way that observations may be drawn from an auxiliary continuous distribution on the largest subspace and then transformed in an appropriate fashion. Motivated by the importance of enlarging the set of available Markov chain Monte Carlo (MCMC) techniques, the authors show how their results can be fruitfully employed in problems such as model selection (or averaging) of nested models, or regeneration of Markov chains for evaluating standard deviations of estimated expectations derived from MCMC simulations.     

Graphics for studying logistic regression models

In this article we focus on logistic regression models for binary responses. An existing result shows that the log-odds can be modelled depending on the log of the ratio between the conditional densities of the predictors given the response variable. This suggests that relevant statistical information could be extracted investigating the inverse problem. Thus, we present different methods for studying the log-density ratio through graphs, which allow us to select which predictors are needed, and how they should be included in a logistic regression model. We also discuss data analysis examples based on real datasets available in literature in order to provide further insights into the methodology proposed.     

Weighted likelihood mixture modeling and model-based clustering

Statistics and Computing - A weighted likelihood approach for robust fitting of a mixture of multivariate Gaussian components is developed in this work. Two approaches have been proposed that are...     

Livestock in the Household Economy: Cross‐Country Evidence from Microeconomic Data

The development of the livestock sector can contribute to economic growth and poverty reduction, but there is inadequate understanding of livestock‐livelihoods linkages. This article draws on household‐level data from 12 developing countries to investigate the livestock‐asset position of rural households and its contribution to their income. The majority keep livestock; the less well‐off are more likely to keep livestock than the better‐off, but the very poor often lack the resources to invest in small animals. The key policy conclusion is that, contrary to common belief, there are no universal messages about livestock: policy needs to be tailored to farming systems, species, uses of livestock and different wealth groups.     

‘Would you like to present me with a piece of your wardrobe?’ The fortuitous reasons for cohabiting

The purpose of the article is to analyse the reasons for cohabiting. Or, in other words, the reasons for which marriage is postponed and not flatly excluded. In fact, from the data (interviews with 50 cohabitating couples) it appears that cohabitation is a fortuitous and occasional event rather than a conscious and reflective choice made by the couples: cohabitation is the best practice and a prompt solution to likewise practical and urgent problems. So, there is a sort of gap between intention and the effective realization of the decision which determines both the choice of cohabiting and the one of marrying. In fact, most of the reasons which could explain marriage (being Catholic, the solemnity of the marriage, a moment of joy) – which could reach or go beyond the moment of acting on the basis of a specific intention – have to face many other choices that continue to be attractive or based on other reasons (cohabitation is as if it was marriage, the wedding is expensive). And the couples act exactly following these reasons, ignoring the original or desired intention. On the contrary, this intention is further strengthened or confirmed by these other reasons. For explaining the behavior of the couples, the author thinks that the category of akrasia is helpful since it shows how the couple mirrors and reformulates those fortuitous reasons which, at the beginning, affected the choice of going to live together in an active way, trying to overcome the casual order.     

Archimedean copulae for risk measurement

In this paper some Archimedean copula functions for bivariate financial returns are studied. The choice of this family is due to their ability to capture the tail dependence, which is an association measure we can detect in many bivariate financial time-series. A time-varying version of these copulae is also investigated. Finally, the Value-at-Risk is computed and its performance is compared across different copula specifications.     

Estimates of Household Consumption Expenditure at Provincial Level in Italy by Using Small Area Estimation Methods: “Real” Comparisons Using Purchasing Power Parities

Household consumption expenditure represents a crucial measure to be used for assessing individuals’ material living conditions and well-being. Indeed, the analysis of household conditions can provide policy makers with a clear picture of the economic and social situation of the area in which they are operating. However, official sample surveys which are generally used for this purpose, such as the Household Budget Survey in Italy carried out by the National Institute of Statistics, do not allow for reliable disaggregated estimates thus hindering appropriate and effective planning and evaluation of political interventions at local level. By referring to the 2012 Italian Household Budget Survey, this paper aims at obtaining reliable provincial estimates of household consumption expenditure in Italy. We use Small Area Estimation methods and we adjust the estimates for spatial differences in price levels by computing and using sub-national Purchasing Power Parities, thus obtaining “real” estimates of consumption expenditure to be used for intra-national comparisons.