1,934 research outputs found
Generalizations of the Kolmogorov-Barzdin embedding estimates
We consider several ways to measure the `geometric complexity' of an
embedding from a simplicial complex into Euclidean space. One of these is a
version of `thickness', based on a paper of Kolmogorov and Barzdin. We prove
inequalities relating the thickness and the number of simplices in the
simplicial complex, generalizing an estimate that Kolmogorov and Barzdin proved
for graphs. We also consider the distortion of knots. We give an alternate
proof of a theorem of Pardon that there are isotopy classes of knots requiring
arbitrarily large distortion. This proof is based on the expander-like
properties of arithmetic hyperbolic manifolds.Comment: 45 page
On the homotopy invariance of configuration spaces
For a closed PL manifold M, we consider the configuration space F(M,k) of
ordered k-tuples of distinct points in M. We show that a suitable iterated
suspension of F(M,k) is a homotopy invariant of M. The number of suspensions we
require depends on three parameters: the number of points k, the dimension of M
and the connectivity of M. Our proof uses a mixture of Poincare embedding
theory and fiberwise algebraic topology.Comment: Published by Algebraic and Geometric Topology at
http://www.maths.warwick.ac.uk/agt/AGTVol4/agt-4-35.abs.htm
Hamiltonian submanifolds of regular polytopes
We investigate polyhedral -manifolds as subcomplexes of the boundary
complex of a regular polytope. We call such a subcomplex {\it -Hamiltonian}
if it contains the full -skeleton of the polytope. Since the case of the
cube is well known and since the case of a simplex was also previously studied
(these are so-called {\it super-neighborly triangulations}) we focus on the
case of the cross polytope and the sporadic regular 4-polytopes. By our results
the existence of 1-Hamiltonian surfaces is now decided for all regular
polytopes.
Furthermore we investigate 2-Hamiltonian 4-manifolds in the -dimensional
cross polytope. These are the "regular cases" satisfying equality in Sparla's
inequality. In particular, we present a new example with 16 vertices which is
highly symmetric with an automorphism group of order 128. Topologically it is
homeomorphic to a connected sum of 7 copies of . By this
example all regular cases of vertices with or, equivalently, all
cases of regular -polytopes with are now decided.Comment: 26 pages, 4 figure
Eliminating Higher-Multiplicity Intersections, II. The Deleted Product Criterion in the -Metastable Range
Motivated by Tverberg-type problems in topological combinatorics and by
classical results about embeddings (maps without double points), we study the
question whether a finite simplicial complex K can be mapped into R^d without
higher-multiplicity intersections. We focus on conditions for the existence of
almost r-embeddings, i.e., maps from K to R^d without r-intersection points
among any set of r pairwise disjoint simplices of K.
Generalizing the classical Haefliger-Weber embeddability criterion, we show
that a well-known necessary deleted product condition for the existence of
almost r-embeddings is sufficient in a suitable r-metastable range of
dimensions (r d > (r+1) dim K +2). This significantly extends one of the main
results of our previous paper (which treated the special case where d=rk and
dim K=(r-1)k, for some k> 3).Comment: 35 pages, 10 figures (v2: reference for the algorithmic aspects
updated & appendix on Block Bundles added
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