Dark-Halo Cusp: Asymptotic Convergence

We propose a model for how the buildup of dark halos by merging satellites produces a characteristic inner cusp, of a density profile \rho \prop r^-a with a -> a_as > 1, as seen in cosmological N-body simulations of hierarchical clustering scenarios. Dekel, Devor & Hetzroni (2003) argue that a flat core of a<1 exerts tidal compression which prevents local deposit of satellite material; the satellite sinks intact into the halo center thus causing a rapid steepening to a>1. Using merger N-body simulations, we learn that this cusp is stable under a sequence of mergers, and derive a practical tidal mass-transfer recipe in regions where the local slope of the halo profile is a>1. According to this recipe, the ratio of mean densities of halo and initial satellite within the tidal radius equals a given function psi(a), which is significantly smaller than unity (compared to being 1 according to crude resonance criteria) and is a decreasing function of a. This decrease makes the tidal mass transfer relatively more efficient at larger a, which means steepening when a is small and flattening when a is large, thus causing converges to a stable solution. Given this mass-transfer recipe, linear perturbation analysis, supported by toy simulations, shows that a sequence of cosmological mergers with homologous satellites slowly leads to a fixed-point cusp with an asymptotic slope a_as>1. The slope depends only weakly on the fluctuation power spectrum, in agreement with cosmological simulations. During a long interim period the profile has an NFW-like shape, with a cusp of 1<a<a_as. Thus, a cusp is enforced if enough compact satellite remnants make it intact into the inner halo. In order to maintain a flat core, satellites must be disrupted outside the core, possibly as a result of a modest puffing up due to baryonic feedback.Comment: 37 pages, Latex, aastex.cls, revised, ApJ, 588, in pres

Endoplasmic reticulum aminopeptidase 1 (ERAP1) polymorphism relevant to inflammatory disease shapes the peptidome of the birdshot chorioretinopathy-associated HLA-A∗29:02 Antigen

Birdshot chorioretinopathy is a rare ocular inflammation whose genetic association with HLA-A∗29:02 is the highest between a disease and a major histocompatibility complex (MHC) molecule. It belongs to a group of MHCI- Associated inflammatory disorders, also including ankylosing spondylitis, psoriasis, and Behç et's disease, for which endoplasmic reticulum aminopeptidases (ERAP) 1 and/or 2 have been identified as genetic risk factors. Since both enzymes are involved in the processing of MHC-I ligands, it seems reasonable that common peptide- mediated mechanisms may underlie the pathogenesis of these diseases. In this study, comparative immunopeptidomics was used to characterize >5000 A∗29:02 ligands and quantify the effects of ERAP1 polymorphism and expression on the A∗29:02 peptidome in human cells. The peptides predominant in an active ERAP1 context showed a higher frequency of nonamers and bulkier amino acid side chains at multiple positions, compared with the peptides predominant in a less active ERAP1 background. Thus, ERAP1 polymorphism has a large influence, shaping the A∗29:02 peptidome through length-dependent and length-independent effects. These changes resulted in increased affinity and hydrophobicity of A∗29:02 ligands in an active ERAP1 context. The results reveal the nature of the functional interaction between A∗29:02 and ERAP1 and suggest that this enzyme may affect the susceptibility to birdshot chorioretinopathy by altering the A∗29:02 peptidome. The complexity of these alterations is such that not only peptide presentation but also other potentially pathogenic features could be affectedThis work was supported by grants SAF2011/25681 (Plan Nacional de I+D+i) to JALC, Binational Science Foundation Grant 2009393 to AA, and an institutional grant of the Fundacion Ramon Areces to the CBMS

Conocimientos actuales y perspectivas de investigación de elementos traza en la nutrición infantil: parte III. Biodisponibilidad y necesidades de investigación futura

La alimentación de los lactantes mediante las fórmulas lácteas no suplementadas, durante periodos de tiempo prolongados, presenta el riesgo del desarrollo de deficiencias nutricionales de diversos oligoelementos; en contraste, los lactantes alimentados con leche materna rara vez presentan alguna deficiencia mineral Puesto que la concentración de estos oligoelementos en la leche humana con frecuencia es más baja o igual que aquella de las fórmulas lácteas, incluso sin suplementar, está implicada claramente una más alta biodisponibilidad de estos elementos desde la leche humana. Es conveniente la comparación entre la leche humana y la de vaca, ya que esta última va a ser, en definitiva, materia prima principal de muchas fórmulas infantiles. Ello permite utilizar sus valores de concentración con fines comparativos, en cuanto a la cantidad de elementos traza suministrada, y el establecimiento de su distinta distribución entre los componentes mayoritarios. Este trabajo presenta una amplia revisión de los principales estudios de biodisponibilidad de elementos traza en leche humana, de vaca y fórmulas infantiles. Dado que la absorción y posterior utilización de los elementos traza por el neonato, no solo depende del contenido total en la fórmula infantil, sino de la forma química en la cual se encuentra y los compuestos en los que se integran, parece oportuno caracterizar, no solo los componentes principales de la fórmula infantil, sino los micronutrientes para encontrar las formas químicas más adecuadas y de mejor biodisponibiliad, mediante estudios de especiación, para evitar las posibles interacciones debido a las altas concentraciones inorgánicas añadidas, con la finalidad de asemejar aún más si cabe, al estándar de la alimentación infantil, la leche materna

Conocimientos actuales y perspectivas de investigación de elementos traza en la nutrición infantil: parte I. Situación actual de la alimentación infantil

La nutrición infantil ha experimentado una creciente evolución en función de los estudios de investigación desarrollados y los diferentes criterios adoptados para establecer unas recomendaciones que satisfagan plenamente las necesidades fisiológicas y demandas nutricionales del neonato. La normativa de composición de las fórmulas ha sido dictadas por la Sociedad Europea de Gastroenterología y Nutrición Pediátrica (ESPGAN) y la Academia Americana de Pediatría (AAP). Recientemente el Panel de Expertos del Life Sciences Resarch Office (LSRO) de la American Society for Nutritional Sciences (ASNS) ha sido establecido las últimas disposiciones en relación a los niveles recomendados de diferentes nutrientes en las formulas infantiles de manera que su cumplimiento asegure y proporcione, por si mismas, la única fuente de alimento de los lactantes a término durante su primer año de vida. No hay duda de que la lactancia natural es la más adecuada para el recién nacido y que es preferible a cualquier otro tipo de alimentación infantil. No obstante, el empleo de las fórmulas infantiles se hace imprescindible en aquellos casos en que no sea posible la alimentación del lactante con leche materna. El modelo de lactancia natural en España es similar al de los países del área industrializada del mundo, aunque su duración es sensiblemente inferior a la descrita para otros países del área europea, se abandona masivamente a lo largo del primer semestre de vida. No sólo se debe considerar la leche materna bajo aspectos analíticos cuantitativos en cuanto a su contenido en nutrientes esenciales, sino también es necesario que las fórmulas infantiles proporcionen una fuente de micronutrientes biodisponibles y, en este sentido, todavía hoy los conocimientos sobre ingesta, requerimientos, biodisponibilidad e intervalos de tolerancia de gran parte de los oligoelementos, con respecto a su influencia en el desarrollo infantil, son todavía limitados e insuficientes

Conocimientos actuales y perspectivas de investigación de elementos traza en la nutrición infantil: parte II. Niveles de concentración, ingesta dietética y requerimientos de la alimentación infantil.

La leche materna sirve de referencia en cuanto al contenido de micronutrientes, ya que, por razones de ética, dichos datos no pueden ser obtenidos de lactantes humanos en buen estado de salud. La concentración de los distintos oligoelementos en la leche materna va disminuyendo a medida que transcurre el tiempo de lactancia, por lo que llegado el cuarto mes, si el niño es exclusivamente alimentado con leche materna y pertenece a un grupo particularmente predispuesto (bajos depósitos orgánicos, incremento de las necesidades, aumento de pérdidas, reducción de la absorción intestinal), pueden desarrollarse cuadros de deficiencias nutricionales dependientes del oligoelemento deficitario. El presente trabajo recoge los contenidos de los principales elementos traza esnciales (hierro, zinc, cobre, manganeso y selenio) y aquellos potencialmente tóxicos (aluminio, plomo y cadmio), hallados en las fórmulas infantiles en una amplia revisión bibliográfica. Los requerimientos nutricionales de elementos traza son específicos de cada neonato. Las recomendaciones dietéticas deben establecerse de manera que observen pautas bastante generosas, considerando la amplia variación interindividual, para que se cubra las necesidades de la mayor parte de la población neonatal. Atendiendo a esta consideración, el Comité conjunto de la OMS/FAO/IAEA incorpora dos nuevos conceptos, no considerados anteriormente, sobre requerimientos de elementos traza: requerimientos basales y normalizados. Con este estudio se ha dado un gran paso en el establecimiento de recomendaciones dietéticas para lactantes, aunque no se debe perder de vista que esta estimación de ingesta dietética no es suficiente en si misma; siendo necesaria una mayor investigación en los balances metabólicos de elementos traza en el organismo neonatal y se requiere de un mayor conocimiento de las formas químicas biodisponibles adecuadas a la nutrición pediátrica

Universal stability of coherently diffusive 1D systems with respect to decoherence

Static disorder in a 3D crystal degrades the ideal ballistic dynamics until it produces a localized regime. This Metal-Insulator Transition is often preceded by coherent diffusion. By studying three different paradigmatic 1D models, the Harper-Hofstadter-Aubry-Andr\'e and the Fibonacci tight-binding chains, and the power-banded random matrix model, we show that whenever coherent diffusion is present, transport is exceptionally stable against decoherent noise. This is completely at odds with what happens for ballistic and localized dynamics, where the diffusion coefficient strongly depends on the environmental decoherence. A universal dependence of the diffusion coefficient on the decoherence strength is analytically derived: the diffusion coefficient remains almost decoherence-independent until the coherence time becomes comparable with the mean elastic scattering time. Thus, systems with a quantum diffusive regime could be used to design stable quantum wires and may explain the functionality of many biological systems, which often operate at the border between the ballistic and localized regimes.Comment: Main: 8 pages, 3 figures. Supplementary: 17 pages, 10 figure

The First Galaxies: Chemical Enrichment, Mixing, and Star Formation

Using three-dimensional cosmological simulations, we study the assembly process of one of the first galaxies, with a total mass of 10^8 M_sun, collapsing at z = 10. Our main goal is to trace the transport of the heavy chemical elements produced and dispersed by a pair-instability supernova exploding in one of the minihalo progenitors. To this extent, we incorporate an efficient algorithm into our smoothed particle hydrodynamics code which approximately models turbulent mixing as a diffusion process. We study this mixing with and without the radiative feedback from Population III stars that subsequently form in neighboring minihalos. Our simulations allow us to constrain the initial conditions for second-generation star formation, within the first galaxy itself, and inside of minihalos that virialize after the supernova explosion. We find that most minihalos remain unscathed by ionizing radiation or the supernova remnant, while some are substantially photoheated and enriched to supercritical levels, likely resulting in the formation of low-mass Population III or even Population II stars. At the center of the newly formed galaxy, 10^5 M_sun of cold, dense gas uniformly enriched to 10^-3 Z_sun are in a state of collapse, suggesting that a cluster of Population II stars will form. The first galaxies, as may be detected by the James Webb Space Telescope, would therefore already contain stellar populations familiar from lower redshifts.Comment: 13 pages, 9 figures, published in Ap

Aluminium content of spanish infant formula

Aluminium toxicity has been relatively well documented in infants with impaired renal function and premature neonates. The aims of this study were to analyse the concentration of aluminium in the majority of infant formulae sold commercially in Spain, to determine the influence of aluminium content in the tap water in reconstituted powder formulae and to estimate the theoretical toxic aluminium intake in comparison with the PTWI, and lastly, to discuss the possible interactions of certain essential trace elements added to formulation with aluminium according to type or main protein based infant formula. A total of 82 different infant formulae from 9 different manufacturers were studied. Sample digestion was simulated in a closed acid-decomposition microwave system. Aluminium concentration was determined by atomic absorption spectrophotometry with graphite furnace. In general, the infant formulae studied provide an aluminium level higher than that found in human milk, especially in the case of soya, preterm or hydrolysed casein-based formulae. Standard formulae provide lower aluminium intakes amounting to about 4 % PTWI. Specialised and preterm formulae result in moderate intake (11 – 12 % and 8 – 10 % PTWI, respectively). Soya formulae contribute the highest intake (15 % PTWI). Aluminium exposure from drinking water used for powder formula reconstitution is not considered a clear potential risk. In accordance with the present state of knowledge about aluminium toxicity, it seems prudent to call for continued efforts to standardise routine quality control and reduce aluminium levels in infant formula as well as to keep the aluminium concentration under 300 g l-1 for all infant formulae, most specifically those formulae for premature and low birth neonates

Critical Behavior of Three-Dimensional Disordered Potts Models with Many States

We study the 3D Disordered Potts Model with p=5 and p=6. Our numerical simulations (that severely slow down for increasing p) detect a very clear spin glass phase transition. We evaluate the critical exponents and the critical value of the temperature, and we use known results at lower $p$ values to discuss how they evolve for increasing p. We do not find any sign of the presence of a transition to a ferromagnetic regime.Comment: 9 pages and 9 Postscript figures. Final version published in J. Stat. Mec