31,828 research outputs found
Modeling the Void H I Column Density Spectrum
The equivalent width distribution function (EWDF) of \hone absorbers specific
to the void environment has been recently derived (Manning 2002), revealing a
large line density of clouds (dN/dz ~500 per unit z for Log (N_HI)> 12.4). I
show that the void absorbers cannot be diffuse (or so-called filamentary)
clouds, expanding with the Hubble flow, as suggested by N-body/hydro
simulations. Absorbers are here modeled as the baryonic remnants of
sub-galactic perturbations that have expanded away from their dark halos in
response to reionization at z ~ 6.5. A 1-D Lagrangian hydro/gravity code is
used to follow the dynamic evolution and ionization structure of the baryonic
clouds for a range of halo circular velocities. The simulation products at z=0
can be combined according to various models of the halo velocity distribution
function to form a column density spectrum that can be compared with the
observed. I find that such clouds may explain the observed EWDF if the halo
velocity distribution function is as steep as that advanced by Klypin (1999),
and the halo mass distribution is closer to isothermal than to NFW.Comment: 21 pages, 15 figures. Paper in press; ApJ 591, n
A Network Model of Alcoholism and Alcohol Policy
The evolution of alcohol dependence in populations of people on different social networks is studied. Two models are studied. One is the evolution of the states of individuals on hypothesized social structures from a rewired connected caveman model. This model spans a range of social structures (networks) from very ordered to effectively random with small world structures in between. The second model is a zip-code-level model which uses data from a recent survey in Delaware. The model is a discrete model using 10 zip codes. The results show that the evolution of alcohol dependence, as governed by the simple rules that we use, depends sensitively on the network structure and a hypothetical treatment regime
Three Generations on the Quintic Quotient
A three-generation SU(5) GUT, that is 3x(10+5bar) and a single 5-5bar pair,
is constructed by compactification of the E_8 heterotic string. The base
manifold is the Z_5 x Z_5-quotient of the quintic, and the vector bundle is the
quotient of a positive monad. The group action on the monad and its
bundle-valued cohomology is discussed in detail, including topological
restrictions on the existence of equivariant structures. This model and a
single Z_5 quotient are the complete list of three generation quotients of
positive monads on the quintic.Comment: 19 pages, LaTeX. v2: section on anomaly cancellation adde
QSO Absorption Line Constraints on Intragroup High-Velocity Clouds
We show that the number statistics of moderate redshift MgII and Lyman limit
absorbers may rule out the hypothesis that high velocity clouds are infalling
intragroup material.Comment: 4 pages, no figures; submitted to Astrophysical Journal Letters;
revised version, more general and includes more about Braun and Burton CHVC
Documentation of the Analyses of the Benefits and Costs of Aeronautical Research and Technology models (ABC-ART). Volume 2: Appendices
Fleet variables are defined, and source codes for each module are presented
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