78,371 research outputs found
Size-Dependent Tile Self-Assembly: Constant-Height Rectangles and Stability
We introduce a new model of algorithmic tile self-assembly called
size-dependent assembly. In previous models, supertiles are stable when the
total strength of the bonds between any two halves exceeds some constant
temperature. In this model, this constant temperature requirement is replaced
by an nondecreasing temperature function that depends on the size of the smaller of the two halves. This
generalization allows supertiles to become unstable and break apart, and
captures the increased forces that large structures may place on the bonds
holding them together.
We demonstrate the power of this model in two ways. First, we give fixed tile
sets that assemble constant-height rectangles and squares of arbitrary input
size given an appropriate temperature function. Second, we prove that deciding
whether a supertile is stable is coNP-complete. Both results contrast with
known results for fixed temperature.Comment: In proceedings of ISAAC 201
Optimal Staged Self-Assembly of General Shapes
We analyze the number of tile types , bins , and stages necessary to
assemble squares and scaled shapes in the staged tile assembly
model. For squares, we prove stages suffice and
are necessary for almost all .
For shapes with Kolmogorov complexity , we prove
stages suffice and are necessary to
assemble a scaled version of , for almost all . We obtain similarly tight
bounds when the more powerful flexible glues are permitted.Comment: Abstract version appeared in ESA 201
The structure and assembly history of cluster-size haloes in Self-Interacting Dark Matter
We perform dark-matter-only simulations of 28 relaxed massive cluster-sized
haloes for Cold Dark Matter (CDM) and Self-Interacting Dark Matter (SIDM)
models, to study structural differences between the models at large radii,
where the impact of baryonic physics is expected to be very limited. We find
that the distributions for the radial profiles of the density, ellipsoidal axis
ratios, and velocity anisotropies () of the haloes differ considerably
between the models (at the level), even at of the
virial radius, if the self-scattering cross section is cm
gr. Direct comparison with observationally inferred density profiles
disfavours SIDM for cm gr, but in an intermediate
radial range ( of the virial radius), where the impact of baryonic
physics is uncertain. At this level of the cross section, we find a narrower
distribution in SIDM, clearly skewed towards isotropic orbits, with no
SIDM (90\% of CDM) haloes having at of the virial radius. We
estimate that with an observational sample of (
M) relaxed clusters, can potentially be used to put competitive
constraints on SIDM, once observational uncertainties improve by a factor of a
few. We study the suppression of the memory of halo assembly history in SIDM
clusters. For cm gr, we find that this happens
only in the central halo regions ( of the scale radius of the halo),
and only for haloes that assembled their mass within this region earlier than a
formation redshift . Otherwise, the memory of assembly remains and is
reflected in ways similar to CDM, albeit with weaker trends.Comment: 15 pages, 15 figures. Submitted to MNRAS. Revisions: added new figure
with an observational comparison of density profiles, improvements and
corrections to the section on velocity anisotropie
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