74,979 research outputs found
What does a typical metric space look like?
The collection of all metric spaces on points whose
diameter is at most can naturally be viewed as a compact convex subset of
, known as the metric polytope. In this paper, we
study the metric polytope for large and show that it is close to the cube
in the following two senses.
First, the volume of the polytope is not much larger than that of the cube,
with the following quantitative estimates: Second, when sampling a metric space from
uniformly at random, the minimum distance is at least with high
probability, for some . Our proof is based on entropy techniques. We
discuss alternative approaches to estimating the volume of
using exchangeability, Szemer\'edi's regularity lemma, the hypergraph container
method, and the K\H{o}v\'ari--S\'os--Tur\'an theorem.Comment: 64 pages, 2 figures. v2: Swapped Sections 5 and 6 and added a
reader's guid
Slices, slabs, and sections of the unit hypercube
Using combinatorial methods, we derive several formulas for the volume of
convex bodies obtained by intersecting a unit hypercube with a halfspace, or
with a hyperplane of codimension 1, or with a flat defined by two parallel
hyperplanes. We also describe some of the history of these problems, dating to
Polya's Ph.D. thesis, and we discuss several applications of these formulas.Comment: 11 pages; minor corrections to reference
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Automated Design of Tissue Engineering Scaffolds by Advanced CAD
The design of scaffolds with an intricate and controlled internal structure represents a
challenge for Tissue Engineering. Several scaffold manufacturing techniques allow the
creation of complex and random architectures, but have little or no control over geometrical
parameters such as pore size, shape and interconnectivity- things that are essential for tissue
regeneration. The combined use of CAD software and layer manufacturing techniques allow
a high degree of control over those parameters, resulting in reproducible geometrical
architectures. However, the design of the complex and intricate network of channels that are
required in conventional CAD, is extremely time consuming: manually setting thousands of
different geometrical parameters may require several days in which to design the individual
scaffold structures. This research proposes an automated design methodology in order to
overcome those limitations. The combined use of Object Oriented Programming and
advanced CAD software, allows the rapid generation of thousands of different geometrical
elements. Each has a different set of parameters that can be changed by the software, either
randomly or according to a given mathematical formula, so that they match the different
distribution of geometrical elements such as pore size and pore interconnectivity.
This work describes a methodology that has been used to design five cubic scaffolds with
pore size ranging from about 200 to 800 µm, each with an increased complexity of the
internal geometry.Mechanical Engineerin
A stability result for the cube edge isoperimetric inequality
We prove the following stability version of the edge isoperimetric inequality
for the cube: any subset of the cube with average boundary degree within of
the minimum possible is -close to a union of disjoint cubes,
where is independent of the dimension. This extends
a stability result of Ellis, and can viewed as a dimension-free version of
Friedgut's junta theorem.Comment: 12 page
Integer cells in convex sets
Every convex body K in R^n has a coordinate projection PK that contains at
least vol(0.1 K) cells of the integer lattice PZ^n, provided this volume is at
least one. Our proof of this counterpart of Minkowski's theorem is based on an
extension of the combinatorial density theorem of Sauer, Shelah and
Vapnik-Chervonenkis to Z^n. This leads to a new approach to sections of convex
bodies. In particular, fundamental results of the asymptotic convex geometry
such as the Volume Ratio Theorem and Milman's duality of the diameters admit
natural versions for coordinate sections.Comment: Historical remarks on the notion of the combinatorial dimension are
added. This is a published version in Advances in Mathematic
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