The Merger Rates and Mass Assembly Histories of Dark Matter Haloes in the Two Millennium Simulations

We construct merger trees of dark matter haloes and quantify their merger rates and mass growth rates using the joint dataset from the Millennium and Millennium-II simulations. The finer resolution of the Millennium-II Simulation has allowed us to extend our earlier analysis of halo merger statistics to an unprecedentedly wide range of descendant halo mass (10^10 < M0 < 10^15 Msun), progenitor mass ratio (10^-5 < xi < 1), and redshift (0 < z < 15). We update our earlier fitting form for the mean merger rate per halo as a function of M_0, xi, and z. The overall behavior of this quantity is unchanged: the rate per unit redshift is nearly independent of z out to z~15; the dependence on halo mass is weak (M0^0.13); and it is nearly a power law in the progenitor mass ratio (xi^-2). We also present a simple and accurate fitting formula for the mean mass growth rate of haloes as a function of mass and redshift. This mean rate is 46 Msun/yr for 10^12 Msun haloes at z=0, and it increases with mass as M^{1.1} and with redshift as (1+z)^2.5 (for z > 1). When the fit for the mean mass growth rate is integrated over a halo's history, we find excellent match to the mean mass assembly histories of the simulated haloes. By combining merger rates and mass assembly histories, we present results for the number of mergers over a halo's history and the statistics of the redshift of the last major merger.Comment: 12 pages, 9 figures, accepted in MNRA

Dark Matter Halo Growth II: Diffuse Accretion and its Environmental Dependence

Dark matter haloes in Lambda CDM simulations grow by mergers with other haloes as well as accretion of "diffuse" non-halo material. We quantify the mass growth rates via these two processes, dM_mer/dt and dM_dif/dt, and their dependence on halo environment using the ~500,000 haloes in the Millennium simulation. Adopting a local mass density parameter as a measure of halo environment, we find the two rates show strong but opposite environmental dependence, with mergers playing an increasingly important role for halo growths in overdense regions and diffuse accretion dominating growth in voids. This behaviour is independent of the mass cuts used to define haloes vs non-haloes. For galaxy-scale haloes, these two opposite correlations largely cancel out, but a weak environmental dependence remains that results in a slightly lower mean total growth rate, and hence an earlier mean formation redshift, for haloes in denser regions. The mean formation redshift of the ~5000 cluster-mass haloes, on the other hand, appears to have no correlation with halo environment. The origin of the positive correlation of dM_mer/dt with local density can be traced to the surrounding mass reservoir outside the haloes, where more progenitor haloes are available in denser regions. The negative correlation of dM_dif/dt with density, however, is not explained by the available diffuse mass in the reservoir, which is in fact larger in denser regions. The non-halo component may therefore be partially comprised of truly diffuse dark matter particles that are dynamically hotter and are accreted at a suppressed rate in denser regions. We also discuss the implications of these results for how to modify the Extended Press-Schechter model of halo growth, which in its original form does not predict environmental dependence.Comment: 15 pages, 9 figures, accepted in MNRA

Teoría del dolo vs. teoría de la culpabilidad ­ Un modelo para afrontar la cuestión del error en Derecho penal

En el artículo se revisan los presupuestos de la teoría del error manejada por la doctrina mayoritaria tanto en España como en Alemania al hilo de la especial problemática que plantean los tipos penales que introducen remisiones a otras normas para complementar el tipo penal (tipos penales en blanco, elementos normativos del tipo); apuntándose una manera distinta de delimitar entre los errores que excluyen el dolo y los que no tienen ese efecto. Esta solución se ve acompañada de una propuesta de interpretación de la regulación legal, así como por una propuesta de ubicación dentro del sistema del delito

Indentification of non-linear systems using the Wiener Model

Am algorithm for the identification of non-linear systems which can be described by a Wiener model consisting of a linear system followed by a single-valued non-linearity is presented.Cross correlation techniques are employed to decouple the identification of the linear dynamics from the characterization of the non-linear element

Factors Associated With Self-Reported Depression in Arab, Chaldean, and African Americans

Although depression is a chronic illness with high morbidity and personal and economic losses, little is known about depression in immigrants with an Arab or Chaldean ethnic background. Our primary objective was to determine the overall and ethnicity-specific prevalence of self-reported depression in Arab Americans, Chaldean Americans, and African Americans in the Midwest. The secondary objective was to evaluate the associations between potential risk and protective factors and the presence of self-reported depression. A total of 3543 adults were recruited from the Arab and Chaldean communities in Metropolitan Detroit. The sample in this study was restricted to those of Arab, Chaldean, and African ethnic backgrounds, resulting in 81.2% of the original sample (n52878). A health assessment survey questionnaire was administered The overall rate of self-reported depression was 18.2%. The highest rate of depression was found in Arab American participants (23.2%), followed by African Americans (15%) and Chaldeans (13.3%). Self-reported prevalence of depression by country of origin differed significantly. Our results show the need to provide culturally competent mental health services for Arab Americans and other minority American subgroups. Research is needed to identify risk factors, preferably modifiable factors, and to ascertain which factors are similar and non-similar to the general American population