6,021 research outputs found
Twisting Flux Tubes as a cause of Micro-Flaring Activity
High-cadence optical observations of an H-alpha blue-wing bright point near
solar AR NOAA 10794 are presented. The data were obtained with the Dunn Solar
Telescope at the National Solar Observatory/Sacramento Peak using a newly
developed camera system, the Rapid Dual Imager. Wavelet analysis is undertaken
to search for intensity-related oscillatory signatures, and periodicities
ranging from 15 to 370 s are found with significance levels exceeding 95%.
During two separate microflaring events, oscillation sites surrounding the
bright point are observed to twist. We relate the twisting of the oscillation
sites to the twisting of physical flux tubes, thus giving rise to reconnection
phenomena. We derive an average twist velocity of 8.1 km/s and detect a peak in
the emitted flux between twist angles of 180 and 230 degrees.Comment: 8 pages, 10 figure
Frequency-Dependent Template Profiles for High Precision Pulsar Timing
Pulsar timing experiments require high fidelity template profiles in order to
minimize the biases in pulse time-of-arrival (TOA) measurements and their
uncertainties. Efforts to acquire more precise TOAs given fixed effective area
of telescopes, finite receiver noise, and limited integration time have led
pulsar astronomers to the solution of implementing ultra-wideband receivers.
This solution, however, has run up against the problem that pulse profile
shapes evolve with frequency, which raises the question of how to properly
measure and analyze TOAs obtained using template-matching methods. This paper
proposes a new method for one facet of this problem, that of template profile
generation, and demonstrates it on the well-timed millisecond pulsar
J1713+0747. Specifically, we decompose pulse profile evolution into a linear
combination of basis eigenvectors, the coefficients of which change slowly with
frequency such that their evolution is modeled simply by a sum of low degree
piecewise polynomial spline functions. These noise-free, high fidelity,
frequency-dependent templates can be used to make measurements of so-called
"wideband TOAs" simultaneously with an estimate of the instantaneous dispersion
measure. The use of wideband TOAs is becoming important for pulsar timing array
experiments, as the volume of datasets comprised of conventional, subbanded
TOAs are quickly becoming unwieldly for the Bayesian analyses needed to uncover
latent gravitational wave signals. Although motivated by high precision timing
experiments, our technique is applicable in more general pulsar observations.Comment: 16 pages, 6 figures, accepted to Ap
Spike detection using the continuous wavelet transform
This paper combines wavelet transforms with basic detection theory to develop a new unsupervised method for robustly detecting and localizing spikes in noisy neural recordings. The method does not require the construction of templates, or the supervised setting of thresholds. We present extensive Monte Carlo simulations, based on actual extracellular recordings, to show that this technique surpasses other commonly used methods in a wide variety of recording conditions. We further demonstrate that falsely detected spikes corresponding to our method resemble actual spikes more than the false positives of other techniques such as amplitude thresholding. Moreover, the simplicity of the method allows for nearly real-time execution
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