33,400 research outputs found
A class of equations with peakon and pulson solutions (with an Appendix by Harry Braden and John Byatt-Smith)
We consider a family of integro-differential equations depending upon a
parameter as well as a symmetric integral kernel . When and
is the peakon kernel (i.e. up to rescaling) the
dispersionless Camassa-Holm equation results, while the Degasperis-Procesi
equation is obtained from the peakon kernel with . Although these two
cases are integrable, generically the corresponding integro-PDE is
non-integrable. However,for the family restricts to the pulson family of
Fringer & Holm, which is Hamiltonian and numerically displays elastic
scattering of pulses. On the other hand, for arbitrary it is still possible
to construct a nonlocal Hamiltonian structure provided that is the peakon
kernel or one of its degenerations: we present a proof of this fact using an
associated functional equation for the skew-symmetric antiderivative of .
The nonlocal bracket reduces to a non-canonical Poisson bracket for the peakon
dynamical system, for any value of .Comment: Contribution to volume of Journal of Nonlinear Mathematical Physics
in honour of Francesco Caloger
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Improving parallel program performance using critical path analysis
A programming tool that performs analysis of critical paths for parallel programs has been developed. This tool determines the critical path for the program as scheduled onto a parallel computer with P processing elements, the critical path for the program expressed as a data flow graph (when maximal parallelism can be expressed), and the minimum number of processing elements (P_opt) needed to obtain maximum program speedup. Experiments were performed using several versions of a Gaussian elimination program to examine how speedup varied with changes in granularity and critical path length. These experiments showed that when the available numer of processing elements P < P_opt, increasing granularity improved program speedup more than reducing (the data flow graph's) critical path length, whereas when P ≥ P_opt, increasing granularity degraded program speedup while reducing critical path length improved program speedup
Photometric Selection of QSO Candidates From GALEX Sources
We present a catalog of 36,120 QSO candidates from the Galaxy Evolution
Explorer (GALEX) Release Two (GR2) UV catalog and the USNO-A2.0 optical
catalog. The selection criteria are established using known quasars from the
Sloan Digital Sky Survey (SDSS). The SDSS sample is then used to assign
individual probabilities to our GALEX-USNO candidates. The mean probability is
~50%, and would rise to ~65% if better morphological information than that from
USNO were available to eliminate galaxies. The sample is ~40% complete for
i<=19.1. Candidates are cross-identified in 2MASS, FIRST, SDSS, and XMM-Newton
Slewing Survey (XMMSL1), whenever such counterparts exist. The present catalog
covers the 8000 square degrees of GR2 lying above 25 degrees Galactic latitude,
but can be extended to all 24,000 square degress that satisfy this criterion as
new GALEX data become available.Comment: AASTeX v5.2, 31 pages, 9 figures. Accepted for publication in ApJ.
Extended tables available in the online edition of the journa
The impact of feed cost on U.S. poultry production: implications for the impact of increased ethanol production
Crop Production/Industries, Livestock Production/Industries,
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When it comes to teaching and tenure it is time to walk the walk.
Institutions should value teaching and service, and not just research, when considering faculty for promotion and tenure
Residual Symmetries Applied to Neutrino Oscillations at NOA and T2K
The results previously obtained from the model-independent application of a
generalized hidden horizontal symmetry to the neutrino mass
matrix are updated using the latest global fits for the neutrino oscillation
parameters. The resulting prediction for the Dirac phase is in
agreement with recent results from T2K. The distribution for the Jarlskog
invariant has become sharper and appears to be approaching a particular
region. The approximate effects of matter on long baseline neutrino experiments
are explored, and it is shown how the weak interactions between the neutrinos
and the particles that make up the Earth can help to determine the mass
hierarchy. A similar strategy is employed to show how NOA and T2K could
determine the octant of . Finally, the exact
effects of matter are obtained numerically in order to make comparisons with
the form of the approximate solutions. From this analysis there emerges some
interesting features of the effective mass eigenvalues.Comment: 9 pages, 1 table, 17 figure
Determining the Mass of Kepler-78b With Nonparametric Gaussian Process Estimation
Kepler-78b is a transiting planet that is 1.2 times the radius of Earth and
orbits a young, active K dwarf every 8 hours. The mass of Kepler-78b has been
independently reported by two teams based on radial velocity measurements using
the HIRES and HARPS-N spectrographs. Due to the active nature of the host star,
a stellar activity model is required to distinguish and isolate the planetary
signal in radial velocity data. Whereas previous studies tested parametric
stellar activity models, we modeled this system using nonparametric Gaussian
process (GP) regression. We produced a GP regression of relevant Kepler
photometry. We then use the posterior parameter distribution for our
photometric fit as a prior for our simultaneous GP + Keplerian orbit models of
the radial velocity datasets. We tested three simple kernel functions for our
GP regressions. Based on a Bayesian likelihood analysis, we selected a
quasi-periodic kernel model with GP hyperparameters coupled between the two RV
datasets, giving a Doppler amplitude of 1.86 0.25 m s and
supporting our belief that the correlated noise we are modeling is
astrophysical. The corresponding mass of 1.87 M
is consistent with that measured in previous studies, and more robust due to
our nonparametric signal estimation. Based on our mass and the radius
measurement from transit photometry, Kepler-78b has a bulk density of
6.0 g cm. We estimate that Kepler-78b is 3226% iron
using a two-component rock-iron model. This is consistent with an Earth-like
composition, with uncertainty spanning Moon-like to Mercury-like compositions.Comment: 10 pages, 5 figures, accepted to ApJ 6/16/201
Safe Policy Synthesis in Multi-Agent POMDPs via Discrete-Time Barrier Functions
A multi-agent partially observable Markov decision process (MPOMDP) is a
modeling paradigm used for high-level planning of heterogeneous autonomous
agents subject to uncertainty and partial observation. Despite their modeling
efficiency, MPOMDPs have not received significant attention in safety-critical
settings. In this paper, we use barrier functions to design policies for
MPOMDPs that ensure safety. Notably, our method does not rely on discretization
of the belief space, or finite memory. To this end, we formulate sufficient and
necessary conditions for the safety of a given set based on discrete-time
barrier functions (DTBFs) and we demonstrate that our formulation also allows
for Boolean compositions of DTBFs for representing more complicated safe sets.
We show that the proposed method can be implemented online by a sequence of
one-step greedy algorithms as a standalone safe controller or as a
safety-filter given a nominal planning policy. We illustrate the efficiency of
the proposed methodology based on DTBFs using a high-fidelity simulation of
heterogeneous robots.Comment: 8 pages and 4 figure
Barrier Functions for Multiagent-POMDPs with DTL Specifications
Multi-agent partially observable Markov decision processes (MPOMDPs) provide a framework to represent heterogeneous autonomous agents subject to uncertainty and partial observation. In this paper, given a nominal policy provided by a human operator or a conventional planning method, we propose a technique based on barrier functions to design a minimally interfering safety-shield ensuring satisfaction of high-level specifications in terms of linear distribution temporal logic (LDTL). To this end, we use sufficient and necessary conditions for the invariance of a given set based on discrete-time barrier functions (DTBFs) and formulate sufficient conditions for finite time DTBF to study finite time convergence to a set. We then show that different LDTL mission/safety specifications can be cast as a set of invariance or finite time reachability problems. We demonstrate that the proposed method for safety-shield synthesis can be implemented online by a sequence of one-step greedy algorithms. We demonstrate the efficacy of the proposed method using experiments involving a team of robots
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