María José Suárez

Estimation of a Structural Model of the Determinants of the Time Spent on Physical Activity and Sport Evidence for Spain

The aim of this article is to extend the standard neoclassical consumer theory to explain the allocation of individual time to physical activity and sports. The authors assume a Constant Elasticity of Substitution (CES) utility function and they estimate the model using the Seemingly Unrelated Regression (SUR) method and the Heckman two-step procedure. They run separate estimates for men and women using the Spanish Time-Use Survey conducted in 2002-2003. The results show that there are gender differences in the determinants of the allocation of time to physical activity. Moreover, participation in physical activity and sports and the time devoted to these activities seem to be based on different decisions.

EDUCING THE VOLUME OUT OF THE PHASE-SPACE BOUNDARY

We explicitly show that, in a system with T-duality symmetry, the configuration space volume degrees of freedom may hide on the surface boundary of the region of accessible states with energy lower than a fixed value. This means that, when taking the decompactification limit (big volume limit), a number of accessible states proportional to the volume is recovered even if no volume dependence appears when energy is high enough. All this behavior is contained in the exact way of computing sums by making integrals. We will also show how the decompactification limit for the gas of strings can be defined from a microcanonical description at finite volume.

Thermodynamic nonextensivity in a closed string gas

Well-known results in string thermodynamics show that there is always a negative specific heat phase in the microcanonical description of a gas of closed free strings whenever there are no winding modes present. We will carefully compute the number of strings in the gas to show how this negative specific heat is related to the fact that the system does not have thermodynamic extensivity. We will also discuss the consequences for a system of having a microcanonical negative specific heat versus the exact result that such a thing cannot happen in any canonical (fixed temperature) description.

Unobserved heterogeneity in work absence

Labour absenteeism may be detrimental to firms and society because of the economic costs, organizational problems and production cuts that it involves. Although involuntary absenteeism due to accident or illness that prevents workers from performing their work is unavoidable, avoidable voluntary absenteeism may also emerge due to asymmetric information given that neither employers nor doctors have perfect information about workers’ health status. Assuming that there is heterogeneity in individual’s behaviour and thus some workers are more likely to take sick leave than others due to differences in observable and unobservable characteristics, we specify a Finite Mixture Model to analyse sick leave days per year using a sample of employees from the 2014 European Health Survey in Spain. This specification accounts for unobserved heterogeneity in a discrete way assuming that there are two types of workers even though the data do not allow us to identify which group any individual belongs to. Our results reveal that, although health indicators have the greatest impact on the proportional change in days of absenteeism, there is heterogeneity in sick leave decisions and individual and job characteristics have different effect on the absenteeism of each group.

On the stability of the primordial closed string gas

We recast the study of a closed string gas in a toroidal container in the physical situation in which the single string density of states is independent of the volume because energy density is very high. This includes the gas for the well known Brandenberger-Vafa cosmological scenario. We describe the gas in the grand canonical and microcanonical ensembles. In the microcanonical description, we find a result that clearly confronts the Brandenberger-Vafa calculation to get the specific heat of the system. The important point is that we use the same approach to the problem but a different regularization. By the way, we show that, in the complex temperature formalism, at the Hagedorn singularity, the analytic structure obtained from the so-called F-representation of the free energy coincides with the one computed using the S-representation.

Female Labor Supply In Spain: The Importance Of Behavioral Assumptions And Unobserved Heterogeneity Specification

We estimate four models of female labor supply using a Spanish sample of married women from 1994, taking into account the complete form of the individuals budget set. The models differ in the hypotheses relating to the presence of optimization errors and/or the way non-workers contribute to the likelihood function. According to the results, the effects of wages and non-labor income on the labor supply of Spanish married women depend on the specification used. The model which has both preference and optimization errors and allows for both voluntarily and involuntarily unemployed females desiring to participate seems to better fit the evidence for Spanish married women.

On the effective character of a non-abelian DBI action

Abstract We study the way Lorentz covariance can be reconstructed from Matrix Theory as a IMF description of M-theory. The problem is actually related to the interplay between a non-abelian Dirac–Born–Infeld action and Super-Yang–Mills as its generalized non-relativistic approximation. All this physics shows up by means of an analysis of the asymptotic expansion of the Bessel functions Kν that profusely appear in the computations of amplitudes at finite temperature and solitonic calculations. We hope this might help to better understand the issue of getting a Lorentz covariant formulation in relation with the N→+∞ limit. There are also some computations that could be of some interest in Relativistic Statistical Mechanics.