633 research outputs found
Flat Zipper-Unfolding Pairs for Platonic Solids
We show that four of the five Platonic solids' surfaces may be cut open with
a Hamiltonian path along edges and unfolded to a polygonal net each of which
can "zipper-refold" to a flat doubly covered parallelogram, forming a rather
compact representation of the surface. Thus these regular polyhedra have
particular flat "zipper pairs." No such zipper pair exists for a dodecahedron,
whose Hamiltonian unfoldings are "zip-rigid." This report is primarily an
inventory of the possibilities, and raises more questions than it answers.Comment: 15 pages, 14 figures, 8 references. v2: Added one new figure. v3:
Replaced Fig. 13 to remove a duplicate unfolding, reducing from 21 to 20 the
distinct unfoldings. v4: Replaced Fig. 13 again, 18 distinct unfolding
An extensive English language bibliography on graph theory and its applications, supplement 1
Graph theory and its applications - bibliography, supplement
Sturm 3-ball global attractors 3: Examples of Thom-Smale complexes
Examples complete our trilogy on the geometric and combinatorial
characterization of global Sturm attractors which consist of a
single closed 3-ball. The underlying scalar PDE is parabolic, on the unit interval with Neumann boundary
conditions. Equilibria are assumed to be hyperbolic. Geometrically, we
study the resulting Thom-Smale dynamic complex with cells defined by the fast
unstable manifolds of the equilibria. The Thom-Smale complex turns out to be a
regular cell complex. In the first two papers we characterized 3-ball Sturm
attractors as 3-cell templates . The
characterization involves bipolar orientations and hemisphere decompositions
which are closely related to the geometry of the fast unstable manifolds. An
equivalent combinatorial description was given in terms of the Sturm
permutation, alias the meander properties of the shooting curve for the
equilibrium ODE boundary value problem. It involves the relative positioning of
extreme 2-dimensionally unstable equilibria at the Neumann boundaries and
, respectively, and the overlapping reach of polar serpents in the
shooting meander. In the present paper we apply these descriptions to
explicitly enumerate all 3-ball Sturm attractors with at most 13
equilibria. We also give complete lists of all possibilities to obtain solid
tetrahedra, cubes, and octahedra as 3-ball Sturm attractors with 15 and 27
equilibria, respectively. For the remaining Platonic 3-balls, icosahedra and
dodecahedra, we indicate a reduction to mere planar considerations as discussed
in our previous trilogy on planar Sturm attractors.Comment: 73+(ii) pages, 40 figures, 14 table; see also parts 1 and 2 under
arxiv:1611.02003 and arxiv:1704.0034
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