10,181 research outputs found
PushPush and Push-1 are NP-hard in 2D
We prove that two pushing-blocks puzzles are intractable in 2D. One of our
constructions improves an earlier result that established intractability in 3D
[OS99] for a puzzle inspired by the game PushPush. The second construction
answers a question we raised in [DDO00] for a variant we call Push-1. Both
puzzles consist of unit square blocks on an integer lattice; all blocks are
movable. An agent may push blocks (but never pull them) in attempting to move
between given start and goal positions. In the PushPush version, the agent can
only push one block at a time, and moreover when a block is pushed it slides
the maximal extent of its free range. In the Push-1 version, the agent can only
push one block one square at a time, the minimal extent---one square. Both
NP-hardness proofs are by reduction from SAT, and rely on a common
construction.Comment: 10 pages, 11 figures. Corrects an error in the conference version:
Proc. of the 12th Canadian Conference on Computational Geometry, August 2000,
pp. 211-21
PushPush is NP-hard in 2D
We prove that a particular pushing-blocks puzzle is intractable in 2D,
improving an earlier result that established intractability in 3D [OS99]. The
puzzle, inspired by the game *PushPush*, consists of unit square blocks on an
integer lattice. An agent may push blocks (but never pull them) in attempting
to move between given start and goal positions. In the PushPush version, the
agent can only push one block at a time, and moreover, each block, when pushed,
slides the maximal extent of its free range. We prove this version is NP-hard
in 2D by reduction from SAT.Comment: 18 pages, 13 figures, 1 table. Improves cs.CG/991101
Semileptonic decays of the Higgs boson at the Tevatron
We examine the prospects for extending the Tevatron reach for a Standard
Model Higgs boson by including the semileptonic Higgs boson decays h --> WW -->
l nu jj for M_h >~ 2 M_W, and h --> W jj --> l nu jj for M_h <~ 2 M_W, where j
is a hadronic jet. We employ a realistic simulation of the signal and
backgrounds using the Sherpa Monte Carlo event generator. We find kinematic
selections that enhance the signal over the dominant W+jets background. The
resulting sensitivity could be an important addition to ongoing searches,
especially in the mass range 120 <~ M_h <~ 150 GeV. The techniques described
can be extended to Higgs boson searches at the Large Hadron Collider.Comment: 68 pages, 19 figure
Cultural Scaffolding and Technological Change: A Preliminary Framework
Technology helps us to do new things, or to do old things in new ways. This, at least, is our common understanding and continual hope. Technologies, however, only become useful when guided by human means to human ends and they therefore do not add to our arsenal of abilities in an unproblematic, straightforward manner. Rather they must confront a complex and preexisting set of biological traits and cultural practices before their potentialities and consequences are clear. My goal here is to sketch an account of how technologies interact with the innate and socially supported human capacities to learn and develop, using cultural scaffolding as an interpretive tool
Resource Letter HCMP-1: History of Condensed Matter Physics
This Resource Letter provides a guide to the literature on the history of condensed matter physics, including discussions of the development of the field and strategies for approaching its complicated historical trajectory. Following the presentation of general resources, journal articles and books are cited for the following topics: conceptual development; institutional and community structure; social, cultural, and political history; and connections between condensed matter physics and technology
Evaluating Hidden Costs of Technological Change: Scaffolding, Agency, and Entrenchment
This paper explores the process by which new technologies supplant or constrain cultural scaffolding processes and the consequences thereof. As elaborated by Wimsatt and Griesemer, cultural scaffolds support the acquisition of new capabilities by individuals or organizations. When technologies displace scaffolds, those who previously acquired capabilities from them come to rely upon the new technologies to complete tasks they could once accomplish on their own. Therefore, the would-be beneficiaries of those scaffolds are deprived of the agency to exercise the capabilities the scaffolds supported. Evaluating how technologies displace cultural scaffolds can ground philosophical assessments of the cultural value of technologies
Examples, Counterexamples, and Enumeration Results for Foldings and Unfoldings between Polygons and Polytopes
We investigate how to make the surface of a convex polyhedron (a polytope) by
folding up a polygon and gluing its perimeter shut, and the reverse process of
cutting open a polytope and unfolding it to a polygon. We explore basic
enumeration questions in both directions: Given a polygon, how many foldings
are there? Given a polytope, how many unfoldings are there to simple polygons?
Throughout we give special attention to convex polygons, and to regular
polygons. We show that every convex polygon folds to an infinite number of
distinct polytopes, but that their number of combinatorially distinct gluings
is polynomial. There are, however, simple polygons with an exponential number
of distinct gluings.
In the reverse direction, we show that there are polytopes with an
exponential number of distinct cuttings that lead to simple unfoldings. We
establish necessary conditions for a polytope to have convex unfoldings,
implying, for example, that among the Platonic solids, only the tetrahedron has
a convex unfolding. We provide an inventory of the polytopes that may unfold to
regular polygons, showing that, for n>6, there is essentially only one class of
such polytopes.Comment: 54 pages, 33 figure
Enumerating Foldings and Unfoldings between Polygons and Polytopes
We pose and answer several questions concerning the number of ways to fold a
polygon to a polytope, and how many polytopes can be obtained from one polygon;
and the analogous questions for unfolding polytopes to polygons. Our answers
are, roughly: exponentially many, or nondenumerably infinite.Comment: 12 pages; 10 figures; 10 references. Revision of version in
Proceedings of the Japan Conference on Discrete and Computational Geometry,
Tokyo, Nov. 2000, pp. 9-12. See also cs.CG/000701
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