Ahorro y pensiones en México: un estudio al nivel de las familias

This paper analyzes the savings behavior of Mexican households under a PAYG pension system. We use a cohort analysis and construct a synthetic panel, that allow us to follow a particular cohort over time by considering repeated cross sections. We use data from five household surveys that allow us to identify those household heads with social security and those without it. Pure results suggest that the existence of a PAYG pension system has a small negative effect on savings.

Harmonically Trapped Quantum Gases

We solve the problem of a Bose or Fermi gas in $d$-dimensions trapped by $\delta \leq d$ mutually perpendicular harmonic oscillator potentials. From the grand potential we derive their thermodynamic functions (internal energy, specific heat, etc.) as well as a generalized density of states. The Bose gas exhibits Bose-Einstein condensation at a nonzero critical temperature $T_{c}$ if and only if $d+\delta >2$, and a jump in the specific heat at $T_{c}$ if and only if $d+\delta >4$. Specific heats for both gas types precisely coincide as functions of temperature when $d+\delta =2$. The trapped system behaves like an ideal free quantum gas in $d+\delta$ dimensions. For $\delta =0$ we recover all known thermodynamic properties of ideal quantum gases in $d$ dimensions, while in 3D for $\delta =$ 1, 2 and 3 one simulates behavior reminiscent of quantum {\it wells, wires}and{\it dots}, respectively.Comment: 14 pages including 3 figures and 3 table

Improved Quantum Hard-Sphere Ground-State Equations of State

The London ground-state energy formula as a function of number density for a system of identical boson hard spheres, corrected for the reduced mass of a pair of particles in a sphere-of-influence picture, and generalized to fermion hard-sphere systems with two and four intrinsic degrees of freedom, has a double-pole at the ultimate \textit{regular} (or periodic, e.g., face-centered-cubic) close-packing density usually associated with a crystalline branch. Improved fluid branches are contructed based upon exact, field-theoretic perturbation-theory low-density expansions for many-boson and many-fermion systems, appropriately extrapolated to intermediate densities, but whose ultimate density is irregular or \textit{random} closest close-packing as suggested in studies of a classical system of hard spheres. Results show substantially improved agreement with the best available Green-function Monte Carlo and diffusion Monte Carlo simulations for bosons, as well as with ladder, variational Fermi hypernetted chain, and so-called L-expansion data for two-component fermions.Comment: 15 pages and 7 figure

Redescription of the Mexican scorpion \u3cem\u3eCentruroides hoffmanni\u3c/em\u3e Armas, 1996 (Scorpiones: Buthidae)

The Mexican scorpion Centruroides hoffmanni Armas, 1996 is redescribed, based on adults of both sexes. It is readily diagnosed by its medium size, dark brown two-banded tergites and brown marbling on carapace, appendages and metasoma, pectinal tooth counts, the shape of the female basal plate of the pectines, development of metasomal carinae, and shape of the telson and subaculear tubercle. The geographical distribution of this species ranges from southeastern Oaxaca to southwestern Chiapas, Mexico. It was originally compared with Centruroides thorelli (Kraepelin, 1891), but actually it seems to be closely related to C. infamatus (C. L. Koch, 1845) and C. baergi Hoffmann, 1932

Melanin, from an Evolutionary Remnant to the Myeloid Lineage Cell’s Main Energy Source. The Unsuspected Intrinsic Property of Melanin to Dissociate the Molecule from Water. Possible Implications in the Context of Acute Leukemias

Melanin is one of the most stable substances known. The study of the ink bags of fossilized squid that died 160 million years ago has found it in good condition. Its extraordinary stability is what had prevented, to date; assign a relevant role in biology. Sir Everard Holmes’ proposal in London; in the eighteenth century, about the role of melanin as a simple sunscreen, it has permeated to this day, especially among dermatologists. Despite the unique physical–chemical qualities of melanin, its biological role as a simple sunscreen that protects us from the dangerous UV rays remained immutable. Our circumstantial discovery during an observational study that lasted 12 years (1990–2002) and which included the ophthalmologic studies of 6000 patients, about the relationship between the vessels of the optic nerve and the three main causes of blindness (Macular degeneration, diabetes, and glaucoma) allowed us to discern the unexpected and surprising true role of melanin in Biology as an energy transducer. The unsuspected intrinsic property of melanin to transform light into chemical energy through water dissociation, like chlorophyll in plants; opens a new era in Biology and therefore in Medicine. And Acute Leukemias are no exception