Dark Matter annihilation energy output and its effects on the high-z IGM

We study the case of DM self annihilation, in order to assess its importance as an energy injection mechanism, to the IGM in general, and to the medium within particular DM haloes. We consider thermal relic WIMP particles with masses of 10GeV and 1TeV and we analyse in detail the clustering properties of DM in a $\Lambda$CDM cosmology, on all hierarchy levels, from haloes and their mass function, to subhaloes and the DM density profiles within them, considering adiabatic contraction by the presence of a SMBH. We then compute the corresponding energy output, concluding that DM annihilation does not constitute an important feedback mechanism. We also calculate the effects that DM annihilation has on the IGM temperature and ionization fraction, and we find that assuming maximal energy absorption, at z ~ 10, for the case of a 1TeV WIMP, the ionization fraction could be raised to $6 \times 10^{-4}$ and the temperature to 10K, and in the case of a 10GeV WIMP, the IGM temperature could be raised to 200K and the ionization fraction to $8 \times 10^{-3}$. We conclude that DM annihilations cannot be regarded as an alternative reionization scenario. Regarding the detectability of the WIMP through the modifications to the 21 cm differential brightness temperature signal ($\delta$Tb), we conclude that a thermal relic WIMP with mass of 1TeV is not likely to be detected from the global signal alone, except perhaps at the 1-3mK level in the frequency range 30MHz < $\nu$ < 35MHz corresponding to 40 < z < 46. However, a 10GeV mass WIMP may be detectable at the 1-3mK level in the frequency range 55MHz < $\nu$ < 119MHz corresponding to 11 < z < 25, and at the 1-10mK level in the frequency range 30MHz < $\nu$ < 40MHz corresponding to 35 < z < 46.Comment: 23 pages, 12 figures, accepted for publication in MNRA

¿Quién le susurra al presidente? Asesores vs. ministros en América Latina

 This article examines who influences presidential decisions within the Executive and how this occurs. Based on interviews with twenty-one former presidents, this paper argues that the tension between advisors and ministers varies according to the type of presidential leadership and whether the president freely appoints ministers or they are imposed by political parties. The interaction between both variables conditions relations between advisors and ministers, allowing advisors to complement, substitute, accommodate or compete with ministers’ duties. To systematize this argument, this paper proposes a categorization of the degree of conflict that exists between ministers and advisors.  Este artículo analiza quiénes y cómo influyen en la toma de decisiones presidenciales al interior del Poder Ejecutivo. En base a entrevistas realizadas a 21 ex presidentes, se argumenta que la tensión entre asesores presidenciales y ministros varía según el tipo de liderazgo presidencial y si los ministros son seleccionados libremente por el mandatario o son impuestos por partidos políticos. La interacción de estas dos variables condiciona las relaciones entre ministros y asesores, la cual puede llevar a que los asesores complementen, sustituyan, acomoden o compitan con las tareas de los ministros. Para sistematizar este argumento, se propone una categorización del grado de conflicto que existe entre ministros y asesores.

Radiation driven winds with rotation: The oblate finite disc correction factor

We have incorporated the oblate distortion of the shape of the star due to the stellar rotation, which modifies the finite disk correction factor (f_D) in the m-CAK hydrodynamical model. We implement a simplified version for the f_D allowing us to solve numerically the non-linear m- CAK momentum equation.We solve this model for a classical Be star in the polar and equatorial directions. The star's oblateness modifies the polar wind, which is now much faster than the spherical one, mainly because the wind receives radiation from a larger (than the spherical) stellar surface. In the equatorial direction we obtain slow solutions, which are even slower and denser than the spherical ones. For the case when the stellar rotational velocity is about the critical velocity, the most remarkable result of our calculations is that the density contrast between the equatorial density and the polar one, is about 100. This result could explain a long-standing problem on Be stars.Comment: 2 pages, to appear in the proceedings of the IAUS 272 on "Active OB stars: structure, evolution, mass loss and critical limits" (Paris, July 19-23, 2010), Cambridge University Press. Editors C. Neiner, G. Wade, G. Meynet and G. Peter

Exploitation de la monotonie des fonctions dans la propagation de contraintes sur intervalles

National audienceWe propose a new interval constraint propagation algorithm, called MOnotonic Hull Consistency (Mohc), that exploits monotonicity of functions. The propagation is standard, but the Mohc-Revise procedure, used to filter/contract the variable domains w.r.t. an individual constraint, uses monotonic versions of the classical HC4- Revise and BoxNarrow procedures. Mohc-Revise appears to be the first adaptive revise procedure ever proposed in constraint programming. Also, when a function is monotonic w.r.t. every variable, Mohc-Revise is proven to compute the optimal/ sharpest box enclosing all the solutions of the corresponding constraint (hull consistency). Very promising experimental results suggest that Mohc has the potential to become an alternative to the state-of-the-art HC4 and Box algorithms

An Interval Extension Based on Occurrence Grouping: Method and Properties

In interval arithmetics, special care has been brought to the definition of interval extension functions that compute narrow interval images. In particular, when a function f is monotonic w.r.t. a variable in a given domain, it is well-known that the monotonicity-based interval extension of f computes a sharper (interval) image than the natural interval extension does. This paper presents a so-called ''occurrence grouping'' interval extension [f]_{og} of a function f. When f is not monotonic w.r.t. a variable x in a given domain, we try to transform f into a new function f^{og} that is monotonic w.r.t. two subsets x_a and x_b of the occurrences of x: f^{og} is increasing w.r.t. x_a and decreasing w.r.t. x_b. [f]_{og} is the interval extension by monotonicity of f^{og} and produces a sharper interval image than the natural extension does. For finding a good occurrence grouping, we propose a linear program and an algorithm that minimize a Taylor-based over-estimate of the image diameter of [f]_{og}. Experiments show the benefits of this new interval extension for solving systems of nonlinear equations.L'analyse d'intervalles a proposé plusieurs extensions aux intervalles qui essaient de calculer des images étroites des fonctions. En particulier, quand une fonction f est monotone par rapport à une variable sur un domaine donné, il est bien connu que l'extension aux intervalles par monotonie de f permet de calculer un intervalle image plus étroit que l'extension naturelle. Cet article présente une nouvelle extension aux intervalles d'une fonction f appelée regroupement d'occurrences et notée [f]_{og}. Quand f n'est pas monotone par rapport à une variable x sur un domaine donné, nous essayons de transformer f en une nouvelle fonction f^{og} qui est monotone par rapport à deux sous-ensembles x_a et x_b des occurrences de x : f^{og} est croissante par rapport à x_a et décroissante par rapport à x_b. [f]_{og} est l'extension aux intervalles par monotonie de f^{og} et produit une image plus étroite que l'extension naturelle. Pour trouver un bon regroupement d'occurrences, nous proposons un programme linéaire et un algorithme qui minimisent une surestimation du diamètre de l'image de [f]_{og} basée sur une forme de Taylor de f. Finalement, des expérimentations montrent les avantages de cette nouvelle extension pour la résolution de systèmes d'équations non linéaires

Node selection strategies in interval Branch and Bound algorithms

International audienceWe present in this article new strategies for selecting nodes in interval Branch and Bound algorithms for constrained global optimization. For a minimization problem the standard best-first strategy selects a node with the smallest lower bound of the objective function estimate. We first propose new node selection policies where an upper bound of each node/box is also taken into account. The good accuracy of this upper bound achieved by several contracting operators leads to a good performance of the node selection rule based on this criterion. We propose another strategy that also makes a trade-off between diversification and intensification by greedily diving into potential feasible regions at each node of the best-first search. These new strategies obtain better experimental results than classical best-first search on difficult constrained global optimization instances

Node Selection Heuristics Using the Upper Bound in Interval Branch and Bound

International audienceWe present in this article a new strategy for selecting the current node in an interval Branch and Bound algorithm for constrained global optimization. The standard best-first strategy selects the node with the lowest lower bound of the objective estimate. We propose in this article new node selection policies where an upper bound of each node/box is also taken into account. The good accuracy of this upper bound achieved by several operators leads to a good performance of the criterion. These new strategies obtain better experimental results than classical best-first search on difficult instances