Non-LTE Abundances and Consequences for the Evolution of the alpha elements in the Galaxy

Abundances of alpha-elements such as Ca and Mg in disk and halo stars are usually derived from equivalent widths lines measured on high resolution spectra, and assuming Local Thermodynamic Equilibrium (LTE) . In this paper, we present non-LTE differential abundances derived by computing the statistical equilibrium of CaI and MgI atoms, using high resolution equivalent widths available in the literature for 252 dwarf to subgiant stars. These non-LTE abundances combined with recent determination of non-LTE abundances of iron, seem to remove the dispersion of the [Ca/Fe] and [Mg/Fe] ratios in the galactic halo and disk phases, revealing new and surprising structures. These results have important consequences for chemical evolution models of the Galaxy. In addition, non-LTE abundance ratios for stars belonging to the M92 cluster apparently have the same behavior. More high resolution observations, mainly of globular clusters, are urgently needed to confirm our results.Comment: 15 pages, 3 tables, 7 figure

Rupture of a liposomal vesicle

We discuss pore dynamics in osmotically stressed vesicles. A set of equations which govern the liposomal size, internal solute concentration, and pore diameter is solved numerically. We find that dependent on the internal solute concentration and vesicle size, liposomes can stay pore-free, nucleate a short lived pore, or nucleate a long-lived pore. The phase diagram of pore stability is constructed, and the different scaling regimes are deduced analytically.Comment: in press, Phys. Rev.

Capacidades Institucionales e Implementación de Programas Sociales: Las Transformaciones de los Programas Materno Infantiles en Argentina en la Última Década.

The paper argues that the implementation process of the Child-Maternal Programs (PMIs), at the local level, allows the study of three interrelated problems: social policies, institutional capabilities and, from a public policy perspective, the program’s implementation aspects. The paper, briefly, describes the main characteristics and transformations of two PMI´s in Argentina at national level: the classic and traditional program and the “modern” program, which was created in theearly nineties – Matern and Child Nutritional Program (PROMIN) -, following international tendencies in the design and implementation of social programs. After characterizing these programs, the author uses the Hilberbrand and Grindle’s (1997) institutional capabilities framework to identify capabilities gaps related to formulation and implementation.El artículo plantea que el análisis del proceso de implementación en Argentina de los Programas Materno-Infantiles (PMIs) a nivel local permite estudiar el punto de encuentro de tres problemáticas entrelazadas: las políticas sociales, las capacidades institucionales y, desde el ámbito del estudio de las políticas públicas, el problema de la implementación. El objetivo del presente artículo es, en primer lugar, describir brevemente las características y transformaciones de dos PMIs a nivel nacional en Argentina: el programa clásico de larga trayectoria en el país --el Programa Materno-Infantil (PMI)-- y el moderno programa creado a comienzos de los noventa –Programa Materno Infantil y Nutrición (PROMIN)–, siguiendo nuevas tendencias internacionales de diseño e implementación de programas sociales. Luego de esta caracterización inicial, se aplica el marco de análisis de capacidades institucionales elaborado por Hilderbrand y Grindle (1997) para identificar brechas de capacidades asociadas a problemas de formulación e implementación

Bounding the plastic strength of polycrystalline solids by linear-comparison homogenization methods

The elastoplastic response of polycrystalline metals and minerals above their brittle- ductile transition temperature is idealized here as rigid-perfectly plastic. Bounds on the overall plastic strength of polycrystalline solids with prescribed microstructural statistics and single-crystal plastic strength are computed by means of a linear-comparison homogenization method recently developed by Idiart & Ponte Castañeda (Idiart & Ponte Castañeda 2007 Proc. R. Soc. A 463, 907-924 (doi:10.1098/rspa.2006.1797)). Hashin- Shtrikman and self-consistent results are reported for cubic and hexagonal polycrystals with varying degrees of crystal anisotropy. Improvements over earlier linear-comparison bounds are found to be modest for high-symmetry materials but become appreciable for low-symmetry materials. The largest improvement is observed in self-consistent results for low-symmetry hexagonal polycrystals, exceeding 15 per cent in some cases. In addition to providing the sharpest bounds available to date, these results serve to evaluate the performance of the aforementioned linear-comparison method in the context of realistic material systems.Facultad de Ingenierí

Bounding the plastic strength of polycrystalline solids by linear-comparison homogenization methods

The elastoplastic response of polycrystalline metals and minerals above their brittle- ductile transition temperature is idealized here as rigid-perfectly plastic. Bounds on the overall plastic strength of polycrystalline solids with prescribed microstructural statistics and single-crystal plastic strength are computed by means of a linear-comparison homogenization method recently developed by Idiart & Ponte Castañeda (Idiart & Ponte Castañeda 2007 Proc. R. Soc. A 463, 907-924 (doi:10.1098/rspa.2006.1797)). Hashin- Shtrikman and self-consistent results are reported for cubic and hexagonal polycrystals with varying degrees of crystal anisotropy. Improvements over earlier linear-comparison bounds are found to be modest for high-symmetry materials but become appreciable for low-symmetry materials. The largest improvement is observed in self-consistent results for low-symmetry hexagonal polycrystals, exceeding 15 per cent in some cases. In addition to providing the sharpest bounds available to date, these results serve to evaluate the performance of the aforementioned linear-comparison method in the context of realistic material systems.Facultad de Ingenierí

Determinación teórica de la histéresis eléctrica en materiales compuestos ferroeléctricos

En este trabajo se establecen relaciones entre la histéresis eléctrica macroscópica y el comportamiento de las fases constitutivas en materiales compuestos ferroeléctricos con microestructuras complejas y sometidos a historias de carga arbitrarias. El comportamiento ferroeléctrico de cada fase se describe mediante una densidad de energía almacenada y un potencial de disipación en el marco de los ‘materiales estándar generalizados’. Discretizando en el tiempo las ecuaciones diferenciales correspondientes siguiendo un esquema implícito, se obtiene una representación variacional de la respuesta macroscó- pica del compuesto que involucra un solo potencial incremental. Las estimaciones teóricas se obtienen luego mediante ciertas ‘microgeometrías resolubles’ cuyo potencial incremental macroscópico puede determinarse en forma exacta. Por ser exactas para una clase de materiales, estas estimaciones satisfacen automáticamente todos las características comunmente buscadas en una aproximación teórica: estar de acuerdo con restricciones materiales, satisfacer todas las cotas pertinentes, y poseer todas las propiedades de convexidad correspondientes. La metodología propuesta se aplica a sistemas materiales representativos y los resultados se discuten a la luz de observaciones experimentales existentes.Theoretical estimates are given for the overall hysteretic response of two-phase ferroelectric composites with complex particulate microstructures under arbitrary loading histories. The ferroelectric behavior of the constituent phases is described via a stored energy density and a dissipation potential in accordance with the theory of generalized standard materials. An implicit time-discretization scheme is used to generate a variational representation of the overall response in terms of a single incremental potential. Estimates are then generated by constructing sequentially laminated microgeometries of particulate type whose overall incremental potential can be computed exactly. Because they are realizable, by construction, these estimates are guaranteed to conform with any material constraints, to satisfy all pertinent bounds, and to exhibit the required convexity properties with no duality gap. Predictions for composites and porous ferroelectrics are reported and discussed in the light of existing experimental data.Fil: Idiart, Martín Ignacio. Universidad Nacional de la Plata. Facultad de Ingeniería. Departamento de Aeronautica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Ages of Elliptical Galaxies: Single versus Multi Population Interpretation

New calibrations of spectrophotometric indices of elliptical galaxies as functions of spectrophotometric indices are presented, permitting estimates of mean stellar population ages and metallicities. These calibrations are based on evolutionary models including a two-phase interstellar medium, infall and a galactic wind.Free parameters were fixed by requiring that models reproduce the mean trend of data in the color-magnitude diagram as well as in the plane of indices Hbeta-Mg2 and Mg2-. To improve the location of faint ellipticals(MB > -20) in the Hbeta-Mg2 diagram, down-sizing was introduced. An application of our calibrations to a sample of ellipticals and a comparison with results derived from single stellar population models is given. Our models indicate that mean population ages span an interval of 7-12 Gyr and are correlated with metallicities, which range from approximately half up to three times solar.Comment: 10 pages and 6 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journa