675 research outputs found
Assembly bias and the dynamical structure of dark matter halos
Based on the Millennium Simulation we examine assembly bias for the halo
properties: shape, triaxiality, concentration, spin, shape of the velocity
ellipsoid and velocity anisotropy. For consistency we determine all these
properties using the same set of particles, namely all gravitationally
self-bound particles belonging to the most massive sub-structure of a given
friends-of-friends halo. We confirm that near-spherical and high-spin halos
show enhanced clustering. The opposite is true for strongly aspherical and
low-spin halos. Further, below the typical collapse mass, M*, more concentrated
halos show stronger clustering whereas less concentrated halos are less
clustered which is reversed for masses above M*. Going beyond earlier work we
show that: (1) oblate halos are more strongly clustered than prolate ones; (2)
the dependence of clustering on the shape of the velocity ellipsoid coincides
with that of the real-space shape, although the signal is stronger; (3) halos
with weak velocity anisotropy are more clustered, whereas radially anisotropic
halos are more weakly clustered; (4) for all highly clustered subsets we find
systematically less radially biased velocity anisotropy profiles. These
findings indicate that the velocity structure of halos is tightly correlated
with environment.Comment: 5 pages, 2 figures, accepted for publication in Ap
Interaction between IRF6 and TGFA Genes Contribute to the Risk of Nonsyndromic Cleft Lip/Palate
Previous evidence from tooth agenesis studies suggested IRF6 and TGFA interact. Since tooth agenesis is commonly found in individuals with cleft lip/palate (CL/P), we used four large cohorts to evaluate if IRF6 and TGFA interaction contributes to CL/P. Markers within and flanking IRF6 and TGFA genes were tested using Taqman or SYBR green chemistries for case-control analyses in 1,000 Brazilian individuals. We looked for evidence of gene-gene interaction between IRF6 and TGFA by testing if markers associated with CL/P were overtransmitted together in the case-control Brazilian dataset and in the additional family datasets. Genotypes for an additional 142 case-parent trios from South America drawn from the Latin American Collaborative Study of Congenital Malformations (ECLAMC), 154 cases from Latvia, and 8,717 individuals from several cohorts were available for replication of tests for interaction. Tgfa and Irf6 expression at critical stages during palatogenesis was analyzed in wild type and Irf6 knockout mice. Markers in and near IRF6 and TGFA were associated with CL/P in the Brazilian cohort (p<10-6). IRF6 was also associated with cleft palate (CP) with impaction of permanent teeth (p<10-6). Statistical evidence of interaction between IRF6 and TGFA was found in all data sets (p = 0.013 for Brazilians; p = 0.046 for ECLAMC; p = 10-6 for Latvians, and p = 0.003 for the 8,717 individuals). Tgfa was not expressed in the palatal tissues of Irf6 knockout mice. IRF6 and TGFA contribute to subsets of CL/P with specific dental anomalies. Moreover, this potential IRF6-TGFA interaction may account for as much as 1% to 10% of CL/P cases. The Irf6-knockout model further supports the evidence of IRF6-TGFA interaction found in humans. © 2012 Letra et al
Neutrinos in Non-linear Structure Formation - The Effect on Halo Properties
We use N-body simulations to find the effect of neutrino masses on halo
properties, and investigate how the density profiles of both the neutrino and
the dark matter components change as a function of the neutrino mass. We
compare our neutrino density profiles with results from the N-one-body method
and find good agreement. We also show and explain why the Tremaine-Gunn bound
for the neutrinos is not saturated. Finally we study how the halo mass function
changes as a function of the neutrino mass and compare our results with the
Sheth-Tormen semi-analytic formulae. Our results are important for surveys
which aim at probing cosmological parameters using clusters, as well as future
experiments aiming at measuring the cosmic neutrino background directly.Comment: 20 pages, 8 figure
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