27 research outputs found
Smooth invariant densities for random switching on the torus
We consider a random dynamical system obtained by switching between the flows
generated by two smooth vector fields on the 2d-torus, with the random
switchings happening according to a Poisson process. Assuming that the driving
vector fields are transversal to each other at all points of the torus and that
each of them allows for a smooth invariant density and no periodic orbits, we
prove that the switched system also has a smooth invariant density, for every
switching rate. Our approach is based on an integration by parts formula
inspired by techniques from Malliavin calculus.Comment: 19 page
Sticky central limit theorems on open books
Given a probability distribution on an open book (a metric space obtained by
gluing a disjoint union of copies of a half-space along their boundary
hyperplanes), we define a precise concept of when the Fr\'{e}chet mean
(barycenter) is sticky. This nonclassical phenomenon is quantified by a law of
large numbers (LLN) stating that the empirical mean eventually almost surely
lies on the (codimension and hence measure ) spine that is the glued
hyperplane, and a central limit theorem (CLT) stating that the limiting
distribution is Gaussian and supported on the spine. We also state versions of
the LLN and CLT for the cases where the mean is nonsticky (i.e., not lying on
the spine) and partly sticky (i.e., is, on the spine but not sticky).Comment: Published in at http://dx.doi.org/10.1214/12-AAP899 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
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Tracking Student Propositions in an Inquiry System
We built software to support student reasoning about a phenomenon and development of hypotheses to explain it. The goal is to engage students in asking questions, generating hypotheses and testing predictions. Rashi, an intelligent tutor, tracks students’ investigations (e.g., hypotheses, questions, data collection, and inferences) and helps articulate how evidence and theories are related. The tutor provides advice, such as recognizing when data does not support a hypothesis Cases are presented in geology, biology or engineering, and students are scaffolded to use an inquiry-based approach to posit a theory to explain the situation. Generic and reusable structured tools guide students through exploration of ill-structured problem spaces, supporting student knowledge and scaffolding reasoning and diagnostic skills
Testing Lorentz Invariance with Neutrinos from Ultrahigh Energy Cosmic Ray Interactions
We have previously shown that a very small amount of Lorentz invariance
violation (LIV), which suppresses photomeson interactions of ultrahigh energy
cosmic rays (UHECRs) with cosmic background radiation (CBR) photons, can
produce a spectrum of cosmic rays that is consistent with that currently
observed by the Pierre Auger Observatory (PAO) and HiRes experiments. Here, we
calculate the corresponding flux of high energy neutrinos generated by the
propagation of UHECR protons through the CBR in the presence of LIV. We find
that LIV produces a reduction in the flux of the highest energy neutrinos and a
reduction in the energy of the peak of the neutrino energy flux spectrum, both
depending on the strength of the LIV. Thus, observations of the UHE neutrino
spectrum provide a clear test for the existence and amount of LIV at the
highest energies. We further discuss the ability of current and future proposed
detectors make such observations.Comment: final version to appear in Astroparticle Physic
Simplified Post Processing of Cine DENSE Cardiovascular Magnetic Resonance for Quantification of Cardiac Mechanics
BACKGROUND: Cardiovascular magnetic resonance using displacement encoding with stimulated echoes (DENSE) is capable of assessing advanced measures of cardiac mechanics such as strain and torsion. A potential hurdle to widespread clinical adoption of DENSE is the time required to manually segment the myocardium during post-processing of the images. To overcome this hurdle, we proposed a radical approach in which only three contours per image slice are required for post-processing (instead of the typical 30-40 contours per image slice). We hypothesized that peak left ventricular circumferential, longitudinal and radial strains and torsion could be accurately quantified using this simplified analysis.
METHODS AND RESULTS: We tested our hypothesis on a large multi-institutional dataset consisting of 541 DENSE image slices from 135 mice and 234 DENSE image slices from 62 humans. We compared measures of cardiac mechanics derived from the simplified post-processing to those derived from original post-processing utilizing the full set of 30-40 manually-defined contours per image slice. Accuracy was assessed with Bland-Altman limits of agreement and summarized with a modified coefficient of variation. The simplified technique showed high accuracy with all coefficients of variation less than 10% in humans and 6% in mice. The accuracy of the simplified technique was also superior to two previously published semi-automated analysis techniques for DENSE post-processing.
CONCLUSIONS: Accurate measures of cardiac mechanics can be derived from DENSE cardiac magnetic resonance in both humans and mice using a simplified technique to reduce post-processing time by approximately 94%. These findings demonstrate that quantifying cardiac mechanics from DENSE data is simple enough to be integrated into the clinical workflow
The Palomar Transient Factory Orion Project: Eclipsing Binaries and Young Stellar Objects
The Palomar Transient Factory (PTF) Orion project is an experiment within the
broader PTF survey, a systematic automated exploration of the sky for optical
transients. Taking advantage of the wide field of view available using the PTF
camera at the Palomar 48" telescope, 40 nights were dedicated in December
2009-January 2010 to perform continuous high-cadence differential photometry on
a single field containing the young (7-10Myr) 25 Ori association. The primary
motivation for the project is to search for planets around young stars in this
region. The unique data set also provides for much ancillary science. In this
first paper we describe the survey and data reduction pipeline, and present
initial results from an inspection of the most clearly varying stars relating
to two of the ancillary science objectives: detection of eclipsing binaries and
young stellar objects. We find 82 new eclipsing binary systems, 9 of which we
are candidate 25 Ori- or Orion OB1a-association members. Of these, 2 are
potential young W UMa type systems. We report on the possible low-mass (M-dwarf
primary) eclipsing systems in the sample, which include 6 of the candidate
young systems. 45 of the binary systems are close (mainly contact) systems; one
shows an orbital period among the shortest known for W UMa binaries, at
0.2156509 \pm 0.0000071d, with flat-bottomed primary eclipses, and a derived
distance consistent with membership in the general Orion association. One of
the candidate young systems presents an unusual light curve, perhaps
representing a semi-detached binary system with an inflated low-mass primary or
a star with a warped disk, and may represent an additional young Orion member.
Finally, we identify 14 probable new classical T-Tauri stars in our data, along
with one previously known (CVSO 35) and one previously reported as a candidate
weak-line T-Tauri star (SDSS J052700.12+010136.8).Comment: 66 pages, 27 figures, accepted to Astronomical Journal. Minor
typographical corrections and update to author affiliation