Barotropic FRW cosmologies with a Dirac-like parameter

Using the known connection between Schroedinger-like equations and Dirac-like equations in the supersymmetric context, we discuss an extension of FRW barotropic cosmologies in which a Dirac mass-like parameter is introduced. New Hubble cosmological parameters H_K(eta) depending on the Dirac-like parameter are plotted and compared with the standard Hubble case H_0(eta). The new H_K(eta) are complex quantities. The imaginary part is a supersymmetric way of introducing dissipation and instabilities in the barotropic FRW hydrodynamicsComment: 7 pages, 4 figures, accepted at MPL

Thermodynamic interpretation of reactive processes in Ni-Al nanolayers from atomistic simulations

Metals which can form intermetallic compounds by an exothermic reaction constitute a class of reactive materials with multiple applications. Ni-Al laminates of thin alternating layers are being considered as model nanometric metallic multilayers for studying various reaction processes. However, the reaction kinetics at short timescales after mixing are not entirely understood. In this work, we calculate the free energies of Ni-Al alloys as a function of composition and temperature for different solid phases using thermodynamic integration based on state-of-the-art interatomic potentials. We use this information to interpret molecular dynamics (MD) simulations of bilayer systems at 800 K and zero pressure, both in isothermal and isenthalpic conditions. We find that a disordered phase always forms upon mixing as a precursor to a more stable nano crystalline B2 phase. We construe the reactions observed in terms of thermodynamic trajectories governed by the state variables computed. Simulated times of up to 30 ns were achieved, which provides a window to phenomena not previously observed in MD simulations. Our results provide insight into the early experimental reaction timescales and suggest that the path (segregated reactants)$\rightarrow$(disordered phase)$\rightarrow$(B2 structure) is always realized irrespective of the imposed boundary conditions

Negative Net Incomes and the Measurement of Poverty: A Note

This note warns about the careless computation of poverty indexes when the welfare of each household is measured by its net income, since this can be negative. As is illustrated in the case of Mexico, even if only a handful of households report negative incomes, the resulting poverty aggregates, when they go beyond a mere headcount measure, can behave rather badly. The note ends with suggestions on how to deal with the problem.Poverty measures, poverty indexes, negative income, income and expenditure survey, Mexico

Riccati nonhermiticity with application to the Morse potential

A supersymmetric one-dimensional matrix procedure similar to relationships of the same type between Dirac and Schrodinger equations in particle physics is described at the general level. By this means we are able to introduce a nonhermitic Hamiltonian having the imaginary part proportional to the solution of a Riccati equation of the Witten type. The procedure is applied to the exactly solvable Morse potential introducing in this way the corresponding nonhermitic Morse problem. A possible application is to molecular diffraction in evanescent waves over nanostructured surfacesComment: 8 pages, 4 figure

TIPs for the Analysis of Poverty in Mexico, 1992-2005

This paper proposes some changes to the official methodology that is currently in use to measure the state of poverty in Mexico. Among other suggestions, it is recommended the use of bootstrapping to estimate confidence intervals for the poverty statistics, as well as the use of dominance analysis when making intertemporal comparisons. In particular, since poverty lines change over time, the paper proposes the use of TIP curves for that end. Using the eight surveys that were made during the period 1992-2005, the paper presents a large number of absolute poverty statistics and TIP curves, as well as comparisons among them.Poverty, confidence intervals, standard error, bootstrap, resampling, FGT measures, TIP curves, dominance, Mexico

TIPs for the Analysis of Poverty in Mexico, 1992-2005

This paper proposes some changes to the official methodology that is currently in use to measure the state of poverty in Mexico. Among other suggestions, it is recommended the use of bootstrapping to estimate confidence intervals for the poverty statistics, as well as the use of dominance analysis when making intertemporal comparisons. In particular, since poverty lines change over time, the paper proposes the use of TIP curves for that end. Using the eight surveys that were made during the period 1992-2005, the paper presents a large number of absolute poverty statistics and TIP curves, as well as comparisons among them. One of the findings is the deterioration of the living conditions of the poorest among the poor, about a half million people, with respect to the conditions they endured before the 1994 economic crisis.Poverty, confidence intervals, standard error, bootstrap, resampling, FGT measures, TIP curves, dominance, Mexico

Jeans instability analysis in the presence of heat in Eckart's frame

It is shown that the coupling of heat with acceleration first proposed by Eckart would have an overwhelming effect in the growth of density mass fluctuations, even in non-relativistic fluids in the presence of a gravitational field. Gravitational effects would be negligible if the heat-acceleration relation is assumed to be valid for the hydrodynamic equations. A direct implication of this result is that recent alternative first order in the gradients theories must be taken into account while describing a special relativistic fluid.Comment: 9 pages, no figure

Classical harmonic oscillator with Dirac-like parameters and possible applications

We obtain a class of parametric oscillation modes that we call K-modes with damping and absorption that are connected to the classical harmonic oscillator modes through the "supersymmetric" one-dimensional matrix procedure similar to relationships of the same type between Dirac and Schroedinger equations in particle physics. When a single coupling parameter, denoted by K, is used, it characterizes both the damping and the dissipative features of these modes. Generalizations to several K parameters are also possible and lead to analytical results. If the problem is passed to the physical optics (and/or acoustics) context by switching from the oscillator equation to the corresponding Helmholtz equation, one may hope to detect the K-modes as waveguide modes of specially designed waveguides and/or cavitiesComment: 14 pages, 9 figures, revised, accepted at J. Phys.