Of lice and math: using models to understand and control populations of head lice

In this paper we use detailed data about the biology of the head louse (pediculus humanus capitis) to build a model of the evolution of head lice colonies. Using theory and computer simulations, we show that the model can be used to assess the impact of the various strategies usually applied to eradicate head lice, both conscious (treatments) and unconscious (grooming). In the case of treatments, we study the difference in performance that arises when they are applied in systematic and non-systematic ways. Using some reasonable simplifying assumptions (as random mixing of human groups and the same mobility for all life stages of head lice other than eggs) we model the contagion of pediculosis using only one additional parameter. It is shown that this parameter can be tuned to obtain collective infestations whose variables are compatible with what is given in the literature on real infestations. We analyze two scenarios: one where group members begin treatment when a similar number of lice are present in each head, and another where there is one individual who starts treatment with a much larger threshold ('superspreader'). For both cases we assess the impact of several collective strategies of treatment.Comment: manuscript of 23 pages and 13 figures, also a supporting file of 13 pages and 13 figure

Strengths and weakness of neuroscientific investigations of childhood poverty: Future directions

The neuroscientific study of child poverty is a topic that has only recently emerged. In comparison with previous reviews (e.g., Hackman and Farah, 2009; Lipina and Colombo, 2009; Hackman et al., 2010; Raizada and Kishiyama, 2010; Lipina and Posner, 2012), our perspective synthesizes findings, and summarizes both conceptual and methodological contributions, as well as challenges that face current neuroscientific approaches to the study of childhood poverty. The aim of this effort is to identify target areas of study that could potentially help build a basic and applied research agenda for the coming years.Fil: Lipina, Sebastián Javier. Centro de Educación Médica e Investigaciones Clínicas “Norberto Quirno”; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Segretin, María Soledad. Centro de Educación Médica e Investigaciones Clínicas “Norberto Quirno”; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

The Quest for Productivity Growth in Agriculture and Manufacturing

We develop a theory to explain the transition from stagnation to modern growth. We focus on the forces that shaped the evolution of total factor productivity in agriculture and manufacturing across history. More specifically, we build a multisector model of endogenous technical-change and economic growth. We consider an expanding-variety setup with rising labor specialization and two different R&D technologies, one for agriculture and another for manufacturing. As a consequence, total factor productivity in the model can increase via two different channels. First, population growth allows larger levels of specialization of land and labor in the economy that bring efficiency gains. This type of productivity improvement is capital saving, but can not generate sustained growth. Technical change is also possible by investing in R&D. Unlike specialization, new technologies generated in this way are land and labor augmenting, and are the key to modern growth. In the model, the economy has not incentives to invest in R&D until a minimum knowledge base is available to researchers. This is in line with ideas contained in Mokyr (2005). To make possible the accumulation of this minimum knowledge base, we assume that learning-by-doing is the implicit underlying force that leads to specialization. However, land and labor specialization is based on knowledge whose nature differs in agriculture and in manufacturing. More specifically, whereas this knowledge is farm-specific in agriculture, mainly concern with the acquisition of uncodified information about local conditions of soil and whether, specialization in manufacturing is the result of general knowledge, mainly codified, that contributes at a larger extent to the knowledge base.stagnation, modern growth, specialization, learning-by-doing, R&D, Knowledge base

PATHS OF DEVELOPMENT IN OPEN ECONOMIES: THE ROLE OF LAND

This paper shows, within a Heckscher-Ohlin version of the two-sector neoclassical growth model, that land, besides having long-run effects, is also a main determinant of the speed of convergence toward the steady state when there are cross-sector capital share differences. This result stands in sharp contrast to the predictions of standard neoclassical growth frameworks, and calls for a reinterpretation of the conditional-convergence and the resource-curse findings. More specifically, the model predicts that the former finding requires the existence not only of diminishing returns but also of relatively small differences in capital shares across sectors. With respect to the latter finding, our results imply that it may be a consequence of purely transitional effects of natural riches on growth, and that it can not be interpreted as evidence that natural inputs necessarily harm long-run welfare. We produce empirical evidence on the relationship between land, income levels, and growth rates, and present data on cross-sector capital shares. We claim that most of that evidence is consistent with the predictions of the model.Small-Open Economy, land, long-run income, convergence speed

The Dirac theory of constraints, the Gotay-Nester theory and Poisson geometry

The Dirac theory of constraints has been widely studied and applied very successfully by physicists since the original works by Dirac and by Bergmann. From a mathematical standpoint, several aspects of the theory have been exposed rigorously afterwards by many authors. However, many questions related to, for instance, singular or infinite dimensional cases remain open. The work of Gotay and Nester presents a mathematical generalization in terms of presymplectic geometry, which introduces a dual point of view. We present a study of the Dirac theory of constraints emphasizing the duality between the Poisson-algebraic and the geometric points of view, related respectively to the work of Dirac and of Gotay and Nester, under strong regularity conditions. We deal with some questions insufficiently treated in the literature: a study of uniqueness of solution; avoiding almost completely the use of coordinates; the role of the Pontryagin bundle. We also show how one can globalize some results usually treated locally in the literature. For instance, we introduce the globalnotion of second class submanifoldas being tangent to a second class subbundle. A general study of global results for Dirac and Gotay-Nester theories remains an open question in this theory.La Teoría de ligaduras deDirac, lateoría de Gotay-Nester y geometría dePoissin. La teoría de Dirac ha sido ampliamente estudiada y aplicada muy exitosamente por los físicos desde los trabajos originales de Dirac y de Bergmann. Desde un punto de vista matemático, varios aspectos de la teoría han sido expuestos rigurosamente por varios autores. Sin embargo, aún quedan abiertas varias preguntas relacionadas, por ejemplo, con casos singulares o infinito-dimensionales. El trabajo de Gotay y Nester presenta una generalización matemática en términos de la geometría presimpléctica, lo cual introduce un punto de vista dual. Presentamos un estudio de la teoría de ligaduras de Dirac enfatizando la dualidad entre los puntos de vista de las álgebras de Poisson y de la geometría presimpléctica, relacionados respectivamente con los trabajos de Dirac y de Gotay-Nester, bajo condiciones de regularidad fuertes. Abordamos algunas cuestiones insuficientemente tratadas en la literatura: un estudio de la unicidad de solución; evitar casi completamente el uso de coordenadas; el rol del fibrado de Pontryagin. También mostramos cómo se pueden globalizar algunos resultados usualmente tratados localmente en la literatura. Por ejemplo, introducimos la noción globalde subvariedad de segunda clasecomo variedad tangente a un subfibrado de segunda clase. Un estudio general de resultados globales para las teorías de Dirac y de Gotay-Nester sigue siendo una pregunta abierta en esta teoría.Fil: Cendra, Hernan. Universidad Nacional del Sur. Departamento de Matemática; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; ArgentinaFil: Etchechoury, María del Rosario. Universidad Nacional de La Plata; ArgentinaFil: Ferraro, Sebastián José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Matemática Bahía Blanca. Universidad Nacional del Sur. Departamento de Matemática. Instituto de Matemática Bahía Blanca; Argentin

Information Policies in Spain: Towards the New “Information Society”

The concept of a society based on information and knowledge is becoming the norm in every country, including Spain. The need to have well-designed information policies that allow us to come to terms with the new upsurge of media, technology and services that has taken place in our society is discussed first. Information policies required by these changes in society have been implemented in Spain and are described in relation to the new challenges of the “Society of Knowledge.” Similarly, the background and past efforts made in the field of information policy in Spain are analysed, along with the latest government projects that comprise an attempt to get this country to form part of the “Information Society” with the help of the supra-national information policy of the European Union