arXiv subjects

J. H. Rubinstein

Publications and source records attributed to J. H. Rubinstein.

3 recordsLinked to original sources

arXiv2016

Determining the open pit to underground transition: A new method

Many Ore Reserves are harvested by a combination of open pit and underground mining methods. In these cases there is often material that could be mined by either method, and a choice has to be made. The area containing this material is referred to as the transition zone. Deciding where to finish the open pit and start the underground is referred to as the transition problem and it has received some attention in the literature since the 1980s. In this paper we provide a review of existing approaches to the transition problem encompassing: graph-theory based optimisation employing an opportunity cost approach; heuristics and integer programming. We also present a novel opportunity cost approach, allowing it to take into account a crown pillar, and show how the new approach can be best applied through the unconventional application of an existing mine optimisation tool.

math.OC↗

arXiv2011

Diffeomorphisms of Elliptic 3-Manifolds

The elliptic 3-manifolds are the closed 3-manifolds that admit a Riemannian metric of constant positive curvature, that is, those that have finite fundamental group. The (Generalized) Smale Conjecture asserts that for any elliptic 3-manifold M, the inclusion from the isometry group of M to the diffeomorphism group of M is a homotopy equivalence. The original Smale Conjecture, for the 3-sphere, was proven by J. Cerf and A. Hatcher, and N. Ivanov proved the generalized conjecture for many of the elliptic 3-manifolds that contain a geometrically incompressible Klein bottle. Our main results are 1. The Smale Conjecture holds for all elliptic 3-manifolds containing geometrically incompressible Klein bottles. These include all quaternionic and prism manifolds. 2. The Smale Conjecture holds for all lens spaces L(m,q) with m at least 3. These results complete the Smale Conjecture for all cases except the 3-dimensional real projective space and those admitting a Seifert fibering over the 2-sphere with three exceptional fibers of types (2,3,3), (2,3,4), or (2,3,5). The technical work needed for these results includes the result that if V is a Haken Seifert-fibered 3-manifold, then apart from a small list of known exceptions, the inclusion from the space of fiber-preserving diffeomorphisms of V to the full diffeomorphism group is a homotopy equivalence. This has as a consequence: 3. The space of Seifert fiberings of V has contractible components, and apart from a small list of known exceptions, is contractible. Considerable foundational and background material on diffeomorphism groups is included.

math.GT↗

arXiv1997

The Generalized Smale Conjecture for 3-manifolds with genus 2 one-sided Heegaard splittings

The Generalized Smale Conjecture asserts that if M is a closed 3-manifold with constant positive curvature, then the inclusion of the group of isometries into the group of diffeomorphisms is a homotopy equivalence. For the 3-sphere, this was the classical Smale Conjecture proved by A. Hatcher. N. Ivanov proved the Generalized Smale Conjecture for the M which contain a 1-sided Klein bottle and such that no Seifert fibering is nonsingular on the complement of any vertical Klein bottle. We prove it in all remaining cases containing a one-sided Klein bottle, except for the lens space L(4,1).

math.GT↗