11,452 research outputs found
On the Destruction and Over-Merging of Dark Halos in Dissipationless N-body Simulations
N-body simulations that follow only a collisionless dark matter component
have failed to produce galaxy halos or substructure within dense environments.
We investigate the `over-merging' problem analytically and with numerical
simulations, by calculating dissolution timescales of halos due to physical and
artificial dynamical effects. The numerical resolution that has recently been
attained is such that mass-loss from two-body relaxation is negligible. We
demonstrate that substructure is destroyed in present simulations as a result
of large force softening combined with the heating sources of tides and
encounters with dissolving substructure. In the limit of infinite numerical
resolution, whether or not individual halos or substructure can survive depends
sensitively on their inner density profiles. Singular isothermal halos will
always survive at some level, however, if halos form with large core radii then
the over-merging problem will always exist within dissipationless N-body
simulations. In this latter case a dissipational component can increase the
halos central density enabling galaxies to survive.Comment: submitted to ApJL. compressed postscript file includes figures
Angular Momentum on the Lattice: The Case of Non-Zero Linear Momentum
The irreducible representations (IRs) of the double cover of the Euclidean
group with parity in three dimensions are subduced to the corresponding cubic
space group. The reduction of these representations gives the mapping of
continuum angular momentum states to the lattice in the case of non-zero linear
momentum. The continuous states correspond to lattice states with the same
momentum and continuum rotational quantum numbers decompose into those of the
IRs of the little group of the momentum vector on the lattice. The inverse
mapping indicates degeneracies that will appear between levels of different
lattice IRs in the continuum limit, recovering the continuum angular momentum
multiplets. An example of this inverse mapping is given for the case of the
``moving'' isotropic harmonic oscillator.Comment: v3) Little groups for lattice momenta corrected. Includes corrections
from erratum submitted to Phys. Rev. D and a more consistent labeling scheme.
v2) Minor changes to little groups. (9 pages
Waterfowl Harvest and Hunter Use at Carlyle Lake During the 1973 Season
Division of Wildlife Resources Migratory Bird Section, Periodic Report No. 7Report issued on: April 15, 197
New insights on repellent recognition by <i>Anopheles gambiae</i> odorant-binding protein 1
It is generally recognized that insect odorant binding proteins (OBPs) mediate the solubilisation and transport of hydrophobic odorant molecules and contribute to the sensitivity of the insect olfactory system. However, the exact mechanism by which OBPs deliver odorants to olfactory receptors and their role, if any, as selectivity filters for specific odorants, are still a matter of debate. In the case of Anopheles gambiae recent studies indicate that ligand discrimination is effected through the formation of heterodimers such as AgamOBP1 and AgamOBP4 (odorant binding proteins 1 and 4 from Anopheles gambiae). Furthermore, AgamOBPs have been reported to be promiscuous in binding more than one ligand simultaneously and repellents such as DEET (N,N-diethyl-3-toluamide) and 6-MH (6-methyl-5-hepten-2-one) interact directly with mosquito OBPs and/or compete for the binding of attractive odorants thus disrupting OBP heterodimerisation. In this paper, we propose mechanisms of action of DEET and 6-MH. We also predict that ligand binding can occur in several locations of AgamOBP1 with partial occupancies and propose structural features appropriate for repellent pharmacophores
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