38,848 research outputs found
Evaluation of the long-term nutritional potential of a chemically defined liquid diet for small primates Final report, 1 Oct. 1968 - 31 Jan. 1969
Long range nutritional potential of chemically defined liquid diet for squirrel monkey
Culture on the Range: Attracting Audiences and Dollars to One of America's Most Remote Places
Illustrates how the remotely located Western Folklife Center in Elko, Nevada has successfully cultivated donors and members from around the country
Analysis of low resolution mass spectra
Computer program determines gas constituents from measurements of mass/peak-height spectrum from residual gas analyzer. Applications of program include residual gas analysis for work in space environmental simulators, space environment contamination, and air pollution monitoring
Explosions and Outflows during Galaxy Formation
We consider an explosion at the center of a halo which forms at the
intersection of filaments inside a cosmological pancake, a convenient test-bed
model for galaxy formation. ASPH/P3M simulations reveal that such explosions
are anisotropic. The energy and metals are channeled into the low density
regions, away from the pancake. The pancake remains essentially undisturbed,
even if the explosion is strong enough to blow away all the gas located inside
the halo and reheat the IGM surrounding the pancake. Infall quickly replenishes
this ejected gas and gradually restores the gas fraction as the halo continues
to grow. Estimates of the collapse epoch and SN energy-release for galaxies of
different mass in the CDM model can relate these results to scale-dependent
questions of blow-out and blow-away and their implication for early IGM heating
and metal enrichment and the creation of gas-poor dwarf galaxies.Comment: To appear in "The 20th Texas Symposium on Relativistic Astrophysics",
eds. H. Martel and J.C. Wheeler, AIP, in press (2001) (3 pages, 2 figures
Formation and Evolution of Self-Interacting Dark Matter Halos
We study the formation and evolution of self-interacting dark matter (SIDM)
halos. We find analytical, fully cosmological similarity solutions taking
account of the collisional interaction of SIDM particles. This interaction
results in a thermal conductivity that heats the halo core and flattens its
density profile. These similarity solutions are relevant to galactic and
cluster halo formation in the CDM model. We assume an initial mass profile dM/M
M^{-eps}, as in the familiar secondary infall model. If eps=1/6, SIDM halos
will evolve self-similarly, with a cold, supersonic infall terminated by a
strong accretion shock. Different solutions arise for different values of the
collisionality parameter, Q= sigma rho_b r_s, where sigma is the scattering
cross section, rho_b is the cosmic mean density, and r_s is the shock radius.
For all these solutions, a flat-density, isothermal core is present which grows
in size as a fixed fraction of r_s. We find two different regimes for these
solutions: 1) for Q \leq Q_{th}, the core density decreases and core size
increases as Q increases; 2) for Q \geq Q_{th}, the core density increases and
core size decreases as Q increases. Our similarity solutions are in agreement
with previous N-body simulations of SIDM halos, which correspond to the low-Q
regime, if Q=[8.4e-4 - 4.9e-2]Q_{th} (low-Q), or sigma=[0.56-5.6]cm^2/g. As
Q=\infty, our similarity solution aquires a central density cusp, in agreement
with some simulation results which used an ordinary collisional fluid to
approximate the effects of SIDM collisionality. When Q=[18.6-231]Q_{th} or
sigma=[1.2e4 - 2.71e4]cm^2/g, for which we find flat-density cores comparable
to those of the observationally acceptable low-Q solutions, has not previously
been identified. Further study of this regime is warranted.Comment: 7 pages, 5 figures, talk presented at the Second Korean Astrophysics
Workshop (APCTP Workshop) on Formation and Interaction of Galaxies, published
in a special issue of Journal of Korean Astronomical Society, ed. H. M Le
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