2,143 research outputs found
Low Redshift QSO Lyman alpha Absorption Line Systems Associated with Galaxies
In this paper we present Monte-Carlo simulations of Lyman alpha absorption
systems which originate in galactic haloes, galaxy discs and dark matter (DM)
satellites around big central haloes. It is found that for strong Lyman alpha
absorption lines galactic haloes and satellites can explain ~20% and 40% of the
line number density of QSO absorption line key project respectively. If big
galaxies indeed possess such large numbers of DM satellites and they possess
gas, these satellites may play an important role for strong Lyman alpha lines.
However the predicted number density of Lyman-limit systems by satellites is
\~0.1 (per unit redshift), which is four times smaller than that by halo
clouds. Including galactic haloes, satellites and HI discs of spirals, the
predicted number density of strong lines can be as much as 60% of the HST
result. The models can also predict all of the observed Lyman-limit systems.
The average covering factor within 250 kpc/h is estimated to be ~0.36. And the
effective absorption radius of a galaxy is estimated to be ~150 kpc/h. The
models predict W_r propto rho^{-0.5} L_B^{0.15} (1+z)^{-0.5}. We study the
selection effects of selection criteria similar to the imaging and
spectroscopic surveys. We simulate mock observations through known QSO
lines-of-sight and find that selection effects can statistically tighten the
dependence of line width on projected distance. (abridged)Comment: 23 pages, 9 postscript figures; references updated, minor change in
section
More animals than markers: a study into the application of the single step T-BLUP model in large-scale multi-trait Australian Angus beef cattle genetic evaluation
International audienceAbstractMulti-trait single step genetic evaluation is increasingly facing the situation of having more individuals with genotypes than markers within each genotype. This creates a situation where the genomic relationship matrix (G\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}\end{document}) is not of full rank and its inversion is algebraically impossible. Recently, the SS-T-BLUP method was proposed as a modified version of the single step equations, providing an elegant way to circumvent the inversion of the G\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}\end{document} and therefore accommodate the situation described. SS-T-BLUP uses the Woodbury matrix identity, thus it requires an add-on matrix, which is usually the covariance matrix of the residual polygenic effet. In this paper, we examine the application of SS-T-BLUP to a large-scale multi-trait Australian Angus beef cattle dataset using the full BREEDPLAN single step genetic evaluation model and compare the results to the application of two different methods of using G\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}\end{document} in a single step model. Results clearly show that SS-T-BLUP outperforms other single step formulations in terms of computational speed and avoids approximation of the inverse of G\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}\end{document}
Numerical Simulation of Probe Measurements in a Non-equilibrium Plasma, Using a Detailed Model Electron Fluid
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77027/1/AIAA-2007-995-806.pd
Numerical Simulation of Probe Measurements in a Non-equilibrium Plasma
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76058/1/AIAA-2005-4790-683.pd
Comparison of Detailed Electron Fluid Model Formulations for Non-equilibrium Plasma Simulations
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76082/1/AIAA-2007-3879-812.pd
Thermal Diagnostics with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory: A Validated Method for Differential Emission Measure Inversions
We present a new method for performing differential emission measure (DEM)
inversions on narrow-band EUV images from the Atmospheric Imaging Assembly
(AIA) onboard the Solar Dynamics Observatory (SDO). The method yields positive
definite DEM solutions by solving a linear program. This method has been
validated against a diverse set of thermal models of varying complexity and
realism. These include (1) idealized gaussian DEM distributions, (2) 3D models
of NOAA Active Region 11158 comprising quasi-steady loop atmospheres in a
non-linear force-free field, and (3) thermodynamic models from a
fully-compressible, 3D MHD simulation of AR corona formation following magnetic
flux emergence. We then present results from the application of the method to
AIA observations of Active Region 11158, comparing the region's thermal
structure on two successive solar rotations. Additionally, we show how the DEM
inversion method can be adapted to simultaneously invert AIA and XRT data, and
how supplementing AIA data with the latter improves the inversion result. The
speed of the method allows for routine production of DEM maps, thus
facilitating science studies that require tracking of the thermal structure of
the solar corona in time and space.Comment: 21 pages, 18 figures, accepted for publication in Ap
Testing Theoretical Models for the Higher-Order Moments of Dark Halo Distribution
Using high--resolution N--body simulations, we test two theoretical models,
based either on spherical or on ellipsoidal collapse model, for the
higher--order moments of the dark matter halo distribution in CDM models. We
find that a theoretical model based on spherical collapse describes accurately
the simulated counts--in--cells moments for haloes of several mass ranges. It
appears that the model using ellipsoidal collapse instead of spherical collapse
in defining dark haloes is unable to improve the models for the higher--order
moments of halo distribution, for haloes much smaller than (the mass
scale on which the fluctuation of the density field has a rms about 1). Both
models are particularly accurate for the descendants of haloes selected at high
redshift, and so are quite useful in interpreting the high--order moments of
galaxies. As an application we use the theoretical model to predict the
higher--order moments of the Lyman break galaxies observed at and
their descendants at lower redshifts.Comment: 10 pages, 9 figures, MN2e LaTex class, Accepted for publication in
MNRAS, Major change
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