27,540 research outputs found
The large scale geometry of strongly aperiodic subshifts of finite type
A subshift on a group G is a closed, G-invariant subset of A^G, for some
finite set A. It is said to be a subshift of finite type (SFT) if it is defined
by a finite collection of 'forbidden patterns', to be strongly aperiodic if all
point stabilizers are trivial, and weakly aperiodic if all point stabilizers
are infinite index in G. We show that groups with at least 2 ends have a
strongly aperiodic SFT, and that having such an SFT is a QI invariant for
finitely presented torsion free groups. We show that a finitely presented
torsion free group with no weakly aperiodic SFT must be QI-rigid. The domino
problem on G asks whether the SFT specified by a given set of forbidden
patterns is empty. We show that decidability of the domino problem is a QI
invariant.Comment: 23 pages, 6 figures. The proof of the main theorem has been
simplified and some new corollaries deduce
X-Rays From Magnetically Channeled Winds Of OB Stars, In \u27Magnetic Massive Stars\u27
OB stars with strong radiation-driven stellar winds and large-scale magnetic fields generate strong and hard X-ray emission via the Magnetically Channeled Wind Shock (MCWS) mechanism. In this brief paper, I describe four separate X-ray diagnostics of the MCWS mechanism in OB stars, with applications to the prototype young O star, theta-1 Ori C
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