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Visualizing latent domain knowledge
Knowledge discovery and data mining commonly rely on finding salient patterns of association from a vast amount of data. Traditional citation analysis of scientific literature draws insights from strong citation patterns. Latent domain knowledge, in contrast to the mainstream domain knowledge, often consists of highly relevant but relatively infrequently cited scientific works. Visualizing latent domain knowledge presents a significant challenge to knowledge discovery and quantitative studies of science. We build upon a citation-based knowledge visualization procedure and develop an approach that not only captures knowledge structures from prominent and highly cited works, but also traces latent domain knowledge through low-frequency citation chains. We apply this approach to two cases: (1) identifying cross-domain applications of Pathfinder networks (PFNETs) and (2) clarifying the current status of scientific inquiry of a possible link between Bovine spongiform encephalopathy (BSE), also known as mad cow disease, and a new variant Creutzfeldt-Jakob disease (vCJD), a type of brain disease in human
Imaging with two-axis micromirrors
We demonstrate a means of creating a digital image by using a two axis tilt
micromirror to scan a scene. For each different orientation we extract a single
grayscale value from the mirror and combine them to form a single composite
image. This allows one to choose the distribution of the samples, and so in
principle a variable resolution image could be created. We demonstrate this
ability to control resolution by constructing a voltage table that compensates
for the non-linear response of the mirrors to the applied voltage.Comment: 8 pages, 5 figures, preprin
Peeling Bifurcations of Toroidal Chaotic Attractors
Chaotic attractors with toroidal topology (van der Pol attractor) have
counterparts with symmetry that exhibit unfamiliar phenomena. We investigate
double covers of toroidal attractors, discuss changes in their morphology under
correlated peeling bifurcations, describe their topological structures and the
changes undergone as a symmetry axis crosses the original attractor, and
indicate how the symbol name of a trajectory in the original lifts to one in
the cover. Covering orbits are described using a powerful synthesis of kneading
theory with refinements of the circle map. These methods are applied to a
simple version of the van der Pol oscillator.Comment: 7 pages, 14 figures, accepted to Physical Review
Star Cluster Ecology: VII The evolution of young dense star clusters containing primordial binaries
We study the first 100Myr of the evolution of isolated star clusters
initially containing 144179 stars, including 13107 (10%) primordial hard
binaries. Our calculations include the effects of both stellar and binary
evolution. Gravitational interactions among the stars are computed by direct
N-body integration using high precision GRAPE-6 hardware. The evolution of the
core radii and central concentrations of our simulated clusters are compared
with the observed sample of young (about 100Myr) star clusters in the large
Magellanic cloud. Even though our simulations start with a rich population of
primordial binaries, core collapse during the early phase of the cluster
evolution is not prevented. Throughout the simulations, the fraction of
binaries remains roughly constant (about 10%). Due to the effects of mass
segregation the mass function of intermediate-mass main-sequence stars becomes
as flat as in the central part of the cluster (where the initial
Salpeter mass function had ). About 6--12% of the neutron stars
were retained in our simulations; the fraction of retained black holes is
40--70%. In each simulation about three neutron stars become members of close
binaries with a main-sequence companion. Such a binary will eventually become
an x-ray binary, when the main-sequence star starts to fill its Roche lobe.
Black holes are found more frequently in binaries; in each simulated cluster we
find about 11 potential x-ray binaries containing a black hole. Abstract
abbreviated....Comment: MNRAS in pres
Discovery of a Gravitationally Lensed Quasar from the Sloan Digital Sky Survey: SDSS J133222.62+034739.9
We report the discovery of the two-image gravitationally lensed quasar SDSS
J133222.62+034739.9 (SDSS J1332+0347) with an image separation of
Delta_theta=1.14". This system consists of a source quasar at z_s=1.445 and a
lens galaxy at z_l=0.191. The agreement of the luminosity, ellipticity and
position angle of the lens galaxy with those expected from lens model confirms
the lensing hypothesis.Comment: 16 pages, 4 figures, the Astronomical Journal accepte
Hydraulic Resistance of Vegetation in River Flow Applications
Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732If vegetated regions become part of a riverâs flow field, the hydraulic resistance of vegetation affects
the overall conveyance. Several descriptions exist to describe this type of flow; among them are
empirical relations and relations that are process-based. In the current work three expressions are
considered that have equal input parameters, similar levels of complexity but different theoretical
backgrounds. The performance of the three methods is evaluated by comparison with flow
measurements (collected from literature), and limits are given for their practical use
Multimodal oscillations in systems with strong contraction
One- and two-parameter families of flows in near an Andronov-Hopf
bifurcation (AHB) are investigated in this work. We identify conditions on the
global vector field, which yield a rich family of multimodal orbits passing
close to a weakly unstable saddle-focus and perform a detailed asymptotic
analysis of the trajectories in the vicinity of the saddle-focus. Our analysis
covers both cases of sub- and supercritical AHB. For the supercritical case, we
find that the periodic orbits born from the AHB are bimodal when viewed in the
frame of coordinates generated by the linearization about the bifurcating
equilibrium. If the AHB is subcritical, it is accompanied by the appearance of
multimodal orbits, which consist of long series of nearly harmonic oscillations
separated by large amplitude spikes. We analyze the dependence of the
interspike intervals (which can be extremely long) on the control parameters.
In particular, we show that the interspike intervals grow logarithmically as
the boundary between regions of sub- and supercritical AHB is approached in the
parameter space. We also identify a window of complex and possibly chaotic
oscillations near the boundary between the regions of sub- and supercritical
AHB and explain the mechanism generating these oscillations. This work is
motivated by the numerical results for a finite-dimensional approximation of a
free boundary problem modeling solid fuel combustion
Affine insertion and Pieri rules for the affine Grassmannian
We study combinatorial aspects of the Schubert calculus of the affine
Grassmannian Gr associated with SL(n,C). Our main results are: 1) Pieri rules
for the Schubert bases of H^*(Gr) and H_*(Gr), which expresses the product of a
special Schubert class and an arbitrary Schubert class in terms of Schubert
classes. 2) A new combinatorial definition for k-Schur functions, which
represent the Schubert basis of H_*(Gr). 3) A combinatorial interpretation of
the pairing between homology and cohomology of the affine Grassmannian.
These results are obtained by interpreting the Schubert bases of Gr
combinatorially as generating functions of objects we call strong and weak
tableaux, which are respectively defined using the strong and weak orders on
the affine symmetric group. We define a bijection called affine insertion,
generalizing the Robinson-Schensted Knuth correspondence, which sends certain
biwords to pairs of tableaux of the same shape, one strong and one weak. Affine
insertion offers a duality between the weak and strong orders which does not
seem to have been noticed previously.
Our cohomology Pieri rule conjecturally extends to the affine flag manifold,
and we give a series of related combinatorial conjectures.Comment: 98 page
Gravitational shear, flexion, and strong lensing in Abell 1689
We present a gravitational lensing analysis of the galaxy cluster Abell 1689, incorporating measurements of the weak shear, flexion, and strong lensing induced in background galaxies. This is the first time that a shapelet technique has been used to reconstruct the distribution of mass in this cluster and the first time that a flexion signal has been measured using cluster members as lenses. From weak shear measurements alone, we generate a nonparametric mass reconstruction, which shows significant substructure corresponding to groups of galaxies within the cluster. In addition, our galaxy-galaxy flexion signal demonstrates that the cluster galaxies can be well fit by a singular isothermal sphere model with a characteristic velocity dispersion of Ïv = (295 ± 40) km s^(-1). We identify a major, distinct dark matter clump, offset by 40 h^(-1) kpc from the central cluster members, which was not apparent from shear measurements alone. This secondary clump is present in a parametric mass reconstruction using flexion data alone, and its existence is suggested in a nonparametric reconstruction of the cluster using a combination of strong and weak lensing. As found in previous studies, the mass profile obtained by combining weak and strong lensing data shows a much steeper profile than that obtained from only weak lensing data
Explaining Actual Causation via Reasoning About Actions and Change
In causality, an actual cause is often defined as an event responsible for bringing about a given outcome in a scenario. In practice, however, identifying this event alone is not always sufficient to provide a satisfactory explanation of how the outcome came to be. In this paper, we motivate this claim using well-known examples and present a novel framework for reasoning more deeply about actual causation. The framework reasons over a scenario and domain knowledge to identify additional events that helped to "set the stage" for the outcome. By leveraging techniques from Reasoning about Actions and Change, the approach supports reasoning over domains in which the evolution of the state of the world over time plays a critical role and enables one to identify and explain the circumstances that led to an outcome of interest. We utilize action language AL for defining the constructs of the framework. This language lends itself quite naturally to an automated translation to Answer Set Programming, using which, reasoning tasks of considerable complexity can be specified and executed. We speculate that a similar approach can also lead to the development of algorithms for our framework
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