41,687 research outputs found
Bayesian Model Search for Nonstationary Periodic Time Series
We propose a novel Bayesian methodology for analyzing nonstationary time
series that exhibit oscillatory behaviour. We approximate the time series using
a piecewise oscillatory model with unknown periodicities, where our goal is to
estimate the change-points while simultaneously identifying the potentially
changing periodicities in the data. Our proposed methodology is based on a
trans-dimensional Markov chain Monte Carlo (MCMC) algorithm that simultaneously
updates the change-points and the periodicities relevant to any segment between
them. We show that the proposed methodology successfully identifies time
changing oscillatory behaviour in two applications which are relevant to
e-Health and sleep research, namely the occurrence of ultradian oscillations in
human skin temperature during the time of night rest, and the detection of
instances of sleep apnea in plethysmographic respiratory traces.Comment: Received 23 Oct 2018, Accepted 12 May 201
Near-critical fluctuations and cytoskeleton-assisted phase separation lead to subdiffusion in cell membranes
We address the relationship between membrane microheterogeneity and anomalous
subdiffusion in cell membranes by carrying out Monte Carlo simulations of
two-component lipid membranes. We find that near-critical fluctuations in the
membrane lead to transient subdiffusion, while membrane-cytoskeleton
interaction strongly affects phase separation, enhances subdiffusion, and
eventually leads to hop diffusion of lipids. Thus, we present a minimum
realistic model for membrane rafts showing the features of both microscopic
phase separation and subdiffusion.Comment: 21 pages, 5 figures; Supporting Material 5 pages, 1 figure, 1 tabl
The Rotation of M Dwarfs Observed by the Apache Point Galactic Evolution Experiment
We present the results of a spectroscopic analysis of rotational velocities
in 714 M dwarf stars observed by the SDSS III Apache Point Galactic Evolution
Experiment (APOGEE) survey. We use a template fitting technique to estimate
while simultaneously estimating , ,
and . We conservatively estimate that our detection limit is 8
km s. We compare our results to M dwarf rotation studies in the
literature based on both spectroscopic and photometric measurements. Like other
authors, we find an increase in the fraction of rapid rotators with decreasing
stellar temperature, exemplified by a sharp increase in rotation near the M
transition to fully convective stellar interiors, which is consistent with the
hypothesis that fully convective stars are unable to shed angular momentum as
efficiently as those with radiative cores. We compare a sample of targets
observed both by APOGEE and the MEarth transiting planet survey and find no
cases were the measured and rotation period are physically
inconsistent, requiring . We compare our spectroscopic results to
the fraction of rotators inferred from photometric surveys and find that while
the results are broadly consistent, the photometric surveys exhibit a smaller
fraction of rotators beyond the M transition by a factor of . We
discuss possible reasons for this discrepancy. Given our detection limit, our
results are consistent with a bi-modal distribution in rotation that is seen in
photometric surveys.Comment: 31 pages, 11 figures, 4 tables. Accepted for publication by A
Detection of Very Low-Frequency Quasi-Periodic Oscillations in the 2015 Outburst of V404 Cygni
In June 2015, the black hole X-ray binary (BHXRB) V404 Cygni went into
outburst for the first time since 1989. Here, we present a comprehensive search
for quasi-periodic oscillations (QPOs) of V404 Cygni during its recent
outburst, utilizing data from six instruments on board five different X-ray
missions: Swift/XRT, Fermi/GBM, Chandra/ACIS, INTEGRAL's IBIS/ISGRI and JEM-X,
and NuSTAR. We report the detection of a QPO at 18 mHz simultaneously with both
Fermi/GBM and Swift/XRT, another example of a rare but slowly growing new class
of mHz-QPOs in BHXRBs linked to sources with a high orbital inclination.
Additionally, we find a duo of QPOs in a Chandra/ACIS observation at 73 mHz and
1.03 Hz, as well as a QPO at 136 mHz in a single Swift/XRT observation that can
be interpreted as standard Type-C QPOs. Aside from the detected QPOs, there is
significant structure in the broadband power, with a strong feature observable
in the Chandra observations between 0.1 and 1 Hz. We discuss our results in the
context of current models for QPO formation.Comment: 17 pages, 9 figures, published in Ap
Exploiting correlogram structure for robust speech recognition with multiple speech sources
This paper addresses the problem of separating and recognising speech in a monaural acoustic mixture with the presence of competing speech sources. The proposed system treats sound source separation and speech recognition as
tightly coupled processes. In the first stage sound source separation is performed in the correlogram domain. For periodic sounds, the correlogram exhibits symmetric tree-like structures whose stems are located on the delay
that corresponds to multiple pitch periods. These pitch-related structures are exploited in the study to group spectral components at each time frame. Local
pitch estimates are then computed for each spectral group and are used to form simultaneous pitch tracks for temporal integration. These processes segregate a spectral representation of the acoustic mixture into several time-frequency regions such that the energy in each region is likely to have originated from a single periodic sound source. The identified time-frequency regions, together
with the spectral representation, are employed by a `speech fragment decoder' which employs `missing data' techniques with clean speech models to simultaneously search for the acoustic evidence that best matches model sequences. The paper presents evaluations based on artificially mixed simultaneous speech utterances. A coherence-measuring experiment is first reported which quantifies the consistency of the identified fragments with a single source. The system is then evaluated in a speech recognition task and compared to a conventional fragment generation approach. Results show that the proposed system produces more coherent fragments over different conditions,
which results in significantly better recognition accuracy
Resonant Orbits and the High Velocity Peaks Towards the Bulge
We extract the resonant orbits from an N-body bar that is a good
representation of the Milky Way, using the method recently introduced by Molloy
et al. (2015). By decomposing the bar into its constituent orbit families, we
show that they are intimately connected to the boxy-peanut shape of the
density. We highlight the imprint due solely to resonant orbits on the
kinematic landscape towards the Galactic centre. The resonant orbits are shown
to have distinct kinematic features and may be used to explain the cold
velocity peak seen in the APOGEE commissioning data (Nidever at al., 2012). We
show that high velocity peaks are a natural consequence of the motions of stars
in the 2:1 orbit family and that stars on other higher order resonances can
contribute to the peaks. The locations of the peaks vary with bar angle and,
with the tacit assumption that the observed peaks are due to the 2:1 family, we
find that the locations of the high velocity peaks correspond to bar angles in
the range 10 < theta_bar < 25 (deg). However, some important questions about
the nature of the peaks remain, such as their apparent absence in other surveys
of the Bulge and the deviations from symmetry between equivalent fields in the
north and south. We show that the absence of a peak in surveys at higher
latitudes is likely due to the combination of a less prominent peak and a lower
number density of bar supporting orbits at these latitudes.Comment: 7 Figures, 1 Table, Now includes figures & discussion of higher order
resonances, Minor revisions to text throughout, Conclusions unchange
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