3,828 research outputs found
Long path and cycle decompositions of even hypercubes
We consider edge decompositions of the -dimensional hypercube into
isomorphic copies of a given graph . While a number of results are known
about decomposing into graphs from various classes, the simplest cases of
paths and cycles of a given length are far from being understood. A conjecture
of Erde asserts that if is even, and divides the number
of edges of , then the path of length decomposes . Tapadia et
al.\ proved that any path of length , where , satisfying these
conditions decomposes . Here, we make progress toward resolving Erde's
conjecture by showing that cycles of certain lengths up to
decompose . As a consequence, we show that can be decomposed into
copies of any path of length at most dividing the number of edges of
, thereby settling Erde's conjecture up to a linear factor
Investigations of Protostellar Outflow Launching and Gas Entrainment: Hydrodynamic Simulations and Molecular Emission
We investigate protostellar outflow evolution, gas entrainment, and star
formation efficiency using radiation-hydrodynamic simulations of isolated,
turbulent low-mass cores. We adopt an X-wind launching model, in which the
outflow rate is coupled to the instantaneous protostellar accretion rate and
evolution. We vary the outflow collimation angle from =0.01-0.1 and
find that even well collimated outflows effectively sweep up and entrain
significant core mass. The Stage 0 lifetime ranges from 0.14-0.19 Myr, which is
similar to the observed Class 0 lifetime. The star formation efficiency of the
cores spans 0.41-0.51. In all cases, the outflows drive strong turbulence in
the surrounding material. Although the initial core turbulence is purely
solenoidal by construction, the simulations converge to approximate
equipartition between solenoidal and compressive motions due to a combination
of outflow driving and collapse. When compared to a simulation of a cluster of
protostars, which is not gravitationally centrally condensed, we find that the
outflows drive motions that are mainly solenoidal. The final turbulent velocity
dispersion is about twice the initial value of the cores, indicating that an
individual outflow is easily able to replenish turbulent motions on sub-parsec
scales. We post-process the simulations to produce synthetic molecular line
emission maps of CO, CO, and CO and evaluate how well
these tracers reproduce the underlying mass and velocity structure.Comment: Accepted to ApJ, 17 pages, 15 figure
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