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Articles 1 - 13 of 13
Full-Text Articles in Physical Sciences and Mathematics
Computational Geometry Column 36, Joseph O'Rourke
Computational Geometry Column 36, Joseph O'Rourke
Computer Science: Faculty Publications
Two results in "computational origami" are illustrated.
Pushpush Is Np-Hard In 3d, Joseph O'Rourke, The Smith Problem Solving Group
Pushpush Is Np-Hard In 3d, Joseph O'Rourke, The Smith Problem Solving Group
Computer Science: Faculty Publications
We prove that a particular pushing-blocks puzzle is intractable in 3D. 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 3D by reduction from SAT. The corresponding problem in 2D remains open.
Inflation And Preheating In Nonoscillatory Models, Gary Felder, Lev Kofman, Andrei Linde
Inflation And Preheating In Nonoscillatory Models, Gary Felder, Lev Kofman, Andrei Linde
Physics: Faculty Publications
We study inflationary models in which the effective potential of the inflaton field does not have a minimum, but rather gradually decreases at large φ. In such models the inflaton field does not oscillate after inflation, and its effective mass becomes vanishingly small, so the standard theory of reheating based on the decay of the oscillating inflaton field does not apply. For a long time the only mechanism of reheating in such non-oscillatory (NO) models was based on gravitational particle production in an expanding universe. This mechanism is very inefficient. We will show that it may lead to cosmological problems …
Zero-Parity Stabbing Information, Joseph O'Rourke, Irena Pashchenko
Zero-Parity Stabbing Information, Joseph O'Rourke, Irena Pashchenko
Computer Science: Faculty Publications
Everett et al. [EHN96, EHN97] introduced several varieties of stabbing information for the lines determined by pairs of vertices of a simple polygon P, and established their relationships to vertex visibility and other combinatorial data. In the same spirit, we define the “zero-parity (ZP) stabbing information” to be a natural weakening of their “weak stabbing information,” retaining only the distinction among {zero, odd, even > 0} in the number of polygon edges stabbed. Whereas the weak stabbing information’s relation to visibility remains an open problem, we completely settle the analogous questions for zero parity information, with three results: (1) ZP information …
Instant Preheating, Gary Felder, Lev Kofman, Andrei Linde
Instant Preheating, Gary Felder, Lev Kofman, Andrei Linde
Physics: Faculty Publications
We describe a new efficient mechanism of reheating. Immediately after rolling down the rapidly moving inflaton field φ produces particles χ, which may be either bosons or fermions. This is a nonperturbative process which occurs almost instantly; no oscillations or parametric resonance is required. The effective masses of the χ particles may be very small at the moment when they are produced, but they “fatten” when the field φ increases. When the particles χ become sufficiently heavy, they rapidly decay to other, lighter particles. This leads to an almost instantaneous reheating accompanied by the production of particles with masses which …
Structural And Kinetic Studies Of A Cisplatin-Modified Dna Icosamer Binding To Hmg1 Domain B*, Elizabeth R. Jamieson, Matthew P. Jacobson, Carmen M. Barnes, Christine S. Chow, Stephen J. Lippard
Structural And Kinetic Studies Of A Cisplatin-Modified Dna Icosamer Binding To Hmg1 Domain B*, Elizabeth R. Jamieson, Matthew P. Jacobson, Carmen M. Barnes, Christine S. Chow, Stephen J. Lippard
Chemistry: Faculty Publications
The high mobility group (HMG) domain is a DNA-binding motif found in the non-histone chromosomal proteins, HMG1 and HMG2, and some transcription factors. Experimental evidence has demonstrated that HMG-domain proteins can play a role in sensitizing cells to the anticancer drug cisplatin. Fluorescence resonance energy transfer (FRET) experiments were performed in the present study to investigate structural changes that accompany complex formation between the HMG domain B of HMG1 and a cisplatin-modified, 20-base pair double-stranded DNA probe containing fluorescein and rhodamine tethered at its two ends. The binding affinity of HMG1 domain B for the cisplatin-modified DNA probe was investigated …
Weighting Unusual Feature Types, Nicholas Howe, Claire Cardie
Weighting Unusual Feature Types, Nicholas Howe, Claire Cardie
Computer Science: Faculty Publications
Feature weighting is known empirically to improve classification accuracy for k-nearest neighbor classifiers in tasks with irrelevant features. Many feature weighting algorithms are designed to work with symbolic features, or numeric features, or both, but cannot be applied to problems with features that do not fit these categories. This paper presents a new k-nearest neighbor feature weighting algorithm that works with any kind of feature for which a distance function can be defined. Applied to an image classification task with unusual set-like features, the technique improves classification accuracy significantly. In tests on standard data sets from the UCI repository, the …
Stable Isotope And Crystal Chemistry Of Tourmaline Across Pegmatite - Country Rock Boundaries At Black Mountain And Mount Mica, Southwestern Maine, U.S.A, Darby Dyar, Charles V. Guidott, Daniel P. Core, Katherine M. Wearn, Michael A. Wise, Carl A. Francis, Kathleen Johnson, John B. Brady, J. David Robertson, Laura R. Cross
Stable Isotope And Crystal Chemistry Of Tourmaline Across Pegmatite - Country Rock Boundaries At Black Mountain And Mount Mica, Southwestern Maine, U.S.A, Darby Dyar, Charles V. Guidott, Daniel P. Core, Katherine M. Wearn, Michael A. Wise, Carl A. Francis, Kathleen Johnson, John B. Brady, J. David Robertson, Laura R. Cross
Geosciences: Faculty Publications
Major element and stable isotope chemistry of tourmaline from two complexly-zoned rare element pegmatites has been studied to gain insights into the processes by which the pegmatites were formed. Two locations in the Oxford Pegmatite Field of western Maine, U.S.A., were chosen for this study: Black Mountain, an isolated body located in sillimanite zone, highly sulfidic metapelites and quartzite; and Mount Mica, which is bounded by schists and pegmatite and aplitic granite bodies commonly having gradational contacts with each other. At each locality, tourmaline was sampled from the surrounding country rocks into the contact and wall zones through to the …
Lagrangian Systems On Hyperbolic Manifolds, Philip Boyland, Christophe Golé
Lagrangian Systems On Hyperbolic Manifolds, Philip Boyland, Christophe Golé
Mathematics Sciences: Faculty Publications
This paper gives two results that show that the dynamics of a time-periodic Lagrangian system on a hyperbolic manifold are at least as complicated as the geodesic flow of a hyperbolic metric. Given a hyperbolic geodesic in the Poincaré ball, Theorem A asserts that there are minimizers of the lift of the Lagrangian system that are a bounded distance away and have a variety of approximate speeds. Theorem B gives the existence of a collection of compact invariant sets of the Euler-Lagrange flow that are semiconjugate to the geodesic flow of a hyperbolic metric. These results can be viewed as …
Locked And Unlocked Polygonal Chains In 3d, Therese Biedl, Erik D. Demaine, Martin L. Demaine, Sylvain Lazard, Anna Lubiw, Joseph O'Rourke, Mark Overmars, Steve Robbins, Ileana Streinu, Godfried Toussaint, Sue Whitesides
Locked And Unlocked Polygonal Chains In 3d, Therese Biedl, Erik D. Demaine, Martin L. Demaine, Sylvain Lazard, Anna Lubiw, Joseph O'Rourke, Mark Overmars, Steve Robbins, Ileana Streinu, Godfried Toussaint, Sue Whitesides
Computer Science: Faculty Publications
In this paper, we study movements of simple polygonal chains in 3D. We say that an open, simple polygonal chain can be straightened if it can be continuously reconfigured to a straight sequence of segments in such a manner that both the length of each link and the simplicity of the chain are maintained throughout the movement. The analogous concept for closed chains is convexification: reconfiguration to a planar convex polygon. Chains that cannot be straightened or convexified are called locked. While there are open chains in 3D that are locked, we show that if an open chain has a …
Stretchability Of Star-Like Pseudo-Visibility Graphs, Ileana Streinu
Stretchability Of Star-Like Pseudo-Visibility Graphs, Ileana Streinu
Computer Science: Faculty Publications
We present advances on the open problem of characterizing vertex-edge visibility graphs (ve-graphs), reduced by results of O'Rourke and Streinu to a stretchability question for pseudo-polygons. We introduce star-like pseudo-polygons as a special subclass containing all the known instances of non-stretchable pseudo-polygons. We give a complete combinatorial characterization and a linear-time decision procedure for star-like pseudo-polygon stretchability and star-like ve-graph recognition. To the best of our knowledge, this is the first problem in computational geometry for which a combinatorial characterization was found by first isolating the oriented matroid substructure and then separately solving the stretchability question. It is also the …
Embedded Training For Complex Information Systems, Brant A. Cheikes
Embedded Training For Complex Information Systems, Brant A. Cheikes
Computer Science: Faculty Publications
One approach to providing affordable operator training in the workplace is to augment applications with intelligent embedded training systems (ETS). Intelligent embedded training is highly interactive: trainees practice realistic problem-solving tasks on the prime application with guidance and feedback from the training system. This article makes three contributions to the theory and technology of ETS design. First, we describe a framework based on Norman’s “stages of user activity” model for defining the instructional objectives of an ETS. Second, we demonstrate a non-invasive approach to instrumenting software applications, thereby enabling them to collaborate with an ETS. Third, we describe a method …
Computational Geometry Column 35, Joseph O'Rourke
Computational Geometry Column 35, Joseph O'Rourke
Computer Science: Faculty Publications
The subquadratic algorithm of Kapoor for finding shortest paths on a polyhedron is described.