29 research outputs found
A practical EMG-based human-computer interface for users with motor disabilities
In line with the mission of the Assistive Technology Act of 1998 (ATA), this study proposes an integrated assistive real-time system which affirms that technology is a valuable tool that can be used to improve the lives of people with disabilities . An assistive technology device is defined by the ATA as any item, piece of equipment, or product system, whether acquired commercially, modified, or customized, that is used to increase, maintain, or improve the functional capabilities of individuals with disabilities . The purpose of this study is to design and develop an alternate input device that can be used even by individuals with severe motor disabilities . This real-time system design utilizes electromyographic (EMG) biosignals from cranial muscles and electroencephalographic (EEG) biosignals from the cerebrum\u27s occipital lobe, which are transformed into controls for two-dimensional (2-D) cursor movement, the left-click (Enter) command, and an ON/OFF switch for the cursor-control functions . This HCI system classifies biosignals into mouse functions by applying amplitude thresholds and performing power spectral density (PSD) estimations on discrete windows of data. Spectral power summations are aggregated over several frequency bands between 8 and 500 Hz and then compared to produce the correct classification . The result is an affordable DSP-based system that, when combined with an on-screen keyboard, enables the user to fully operate a computer without using any extremities
On the future of astrostatistics: statistical foundations and statistical practice
This paper summarizes a presentation for a panel discussion on "The Future of
Astrostatistics" held at the Statistical Challenges in Modern Astronomy V
conference at Pennsylvania State University in June 2011. I argue that the
emerging needs of astrostatistics may both motivate and benefit from
fundamental developments in statistics. I highlight some recent work within
statistics on fundamental topics relevant to astrostatistical practice,
including the Bayesian/frequentist debate (and ideas for a synthesis),
multilevel models, and multiple testing. As an important direction for future
work in statistics, I emphasize that astronomers need a statistical framework
that explicitly supports unfolding chains of discovery, with acquisition,
cataloging, and modeling of data not seen as isolated tasks, but rather as
parts of an ongoing, integrated sequence of analyses, with information and
uncertainty propagating forward and backward through the chain. A prototypical
example is surveying of astronomical populations, where source detection,
demographic modeling, and the design of survey instruments and strategies all
interact.Comment: 8 pp, 2 figures. To appear in "Statistical Challenges in Modern
Astronomy V," (Lecture Notes in Statistics, Vol. 209), ed. Eric D. Feigelson
and G. Jogesh Babu; publication planned for Sep 2012; see
http://www.springer.com/statistics/book/978-1-4614-3519-
Decade time-scale modulation of low mass X-ray binaries
Regular observations by the All Sky Monitor aboard the Rossi X-ray Timing
Explorer satellite have yielded well-sampled light-curves with a time baseline
of over ten years. We find that up to eight of the sixteen brightest persistent
low mass X-ray binaries show significant, possible sinusoidal, variations with
periods of order ten years. We speculate on its possible origin and prevalence
in the population of low mass X-ray binaries and we find the presence of a
third object in the system, or long-period variability intrinsic to the donor
star, as being attractive origins for the X-ray flux modulation we detect. For
some of the objects in which we do not detect a signal, there is substantial
short-term variation which may hide modest modulation on long time-scales.
Decade time-scale modulations may thus be even more common.Comment: 8 pages, 4 figures, 2 tables. Accepted by MNRA
Multiwavelength Signatures of Magnetic Activity from Young Stellar Objects in the LkH\alpha101 Cluster
[abridged] We describe the results of our multi-wavelength observing campaign
on the young stellar objects in the LkH101 cluster. Our simultaneous
X-ray and multi-frequency radio observations are unique in providing
simultaneous constraints on short-timescale variability at both wavelengths as
well as constraints on the thermal or nonthermal nature of radio emission from
young stars. Focussing in on radio-emitting objects and the multi-wavelength
data obtained for them, we find that multi-frequency radio data indicate
nonthermal emission even in objects with infrared evidence for disks. We find
radio variability on timescales of decades, days and hours. About half of the
objects with X-ray and radio detections were variable at X-ray wavelengths,
despite lacking large-scale flares or large variations. Variability appears to
be a bigger factor affecting radio emission than X-ray emission. A star with
infrared evidence for a disk, [BW88]~3, was observed in the decay phase of a
radio flare. In this object and another ([BW88]~1), we find an inverse
correlation between radio flux and spectral index which contrasts with behavior
seen in the Sun and active stars. We interpret this behavior as the
repopulation of the hardest energy electrons due to particle acceleration. A
radio and X-ray source lacking an infrared counterpart, [BW88]~1, may be near
the substellar limit; its radio properties are similar to other cluster
members, but its much higher radio to X-ray luminosity ratio is reminiscent of
behavior in nearby very low mass stars/brown dwarfs. We find no correspondence
between signatures of particle acceleration and those of plasma heating, both
time-averaged and time-variable. The lack of correlated temporal variability in
multi-wavelength behavior, the breakdown of multi-wavelength correlations of...Comment: accepted for publication in Ap
Characterizing X-ray binary long-term variability
Long-term ("superorbital") periods or modulations have been detected in a
wide variety of both low and high-mass X-ray binaries at X-ray and optical
wavelengths. A variety of mechanisms have been proposed to account for the
variability properties, such as precessing and/or warped accretion discs,
amongst others. The All Sky Monitor on board the Rossi X-ray Timing Explorer
provides the most extensive (~15 years) and sensitive X-ray archive for
studying such behaviour. It is also clear that such variations can be
intermittent and/or a function of X-ray spectral state. Consequently, we use a
time-dependent Dynamic Power Spectrum method to examine how these modulations
vary with time in 25 X-ray binaries for which superorbital periodicities have
been previously reported. Our aim is to characterize these periodicities in a
completely systematic way. Some (such as Her X-1 and LMC X-4) are remarkably
stable, but others show a range of properties, from even longer variability
time-scales to quite chaotic behaviour.Comment: 17 pages, 26 figures, 4 tables, Accepted for publication in MNRAS on
4 November 201
On the multi-periodicities in the X-ray dipper XB 1916-053
Using the Rossi X-ray Timing Explorer and the Nordic Optical Telescope we
have obtained the highest ever quality X-ray/white-light high-speed photometry
of XB 1916-053. We refine the X-ray period (P_X) to 3000.6+/-0.2s via a
restricted cycle counting approach. Using our complete optical lightcurve, we
have extended the optical period (P_opt) ephemeris by another 4 years,
providing further evidence for its stability, although a slightly longer period
of 3027.555+/-0.002s now provides a marginally better fit. Moreover,
modulations at both P_X and P_opt are present in the optical data, with the
former dominating the nightly lightcurves (i.e. a few cycles of data). We have
also attempted to determine the ``beat'' period, as seen in the repeating
evolution of the X-ray dip structure, and the variation in primary dip phase.
We find that a quasi-period of 4.74+/-0.05d provides the best fit to the data,
even then requiring phase shifts between cycles, with the expected 3.90d
``beat'' of P_X and P_opt appearing to be less likely.
Finally, considering the nature of each of these temporal phenomena, we
outline possible models, which could explain all of the observed behaviour of
this enigmatic source, focusing on which of P_X or P_opt is the binary period.Comment: 22 pages, 17 figures (none require colour printing), accepted for
publication in MNRA
A Population of Gamma-Ray Millisecond Pulsars Seen with the Fermi Large Area Telescope
Gamma-Ray Pulsar Bonanza
Most of the pulsars we know about were detected through their radio emission; a few are known to pulse gamma rays but were first detected at other wavelengths (see the Perspective by
Halpern
). Using the Fermi Gamma-Ray Space Telescope,
Abdo
et al.
(p.
840
, published online 2 July; see the cover) report the detection of 16 previously unknown pulsars based on their gamma-ray emission alone. Thirteen of these coincide with previously unidentified gamma-ray sources, solving the 30-year-old mystery of their identities. Pulsars are fast-rotating neutron stars. With time they slow down and cease to radiate; however, if they are in a binary system, they can have their spin rates increased by mass transfer from their companion stars, starting a new life as millisecond pulsars. In another study,
Abdo
et al.
(p.
845
) report the detection of gamma-ray emission from the globular cluster 47 Tucanae, which is coming from an ensemble of millisecond pulsars in the cluster's core. The data imply that there are up to 60 millisecond pulsars in 47 Tucanae, twice as many as predicted by radio observations. In a further companion study,
Abdo
et al.
(p.
848
, published online 2 July) searched Fermi Large Area Telescope data for pulsations from all known millisecond pulsars outside of stellar clusters, finding gamma-ray pulsations for eight of them. Their properties resemble those of other gamma-ray pulsars, suggesting that they share the same basic emission mechanism. Indeed, both sets of pulsars favor emission models in which the gamma rays are produced in the outer magnetosphere of the neutron star
First Search for Gravitational Waves from Known Pulsars with Advanced LIGO
We present the result of searches for gravitational waves from 200 pulsars using data from the first observing run of the Advanced LIGO detectors. We find no significant evidence for a gravitational-wave signal from any of these pulsars, but we are able to set the most constraining upper limits yet on their gravitational-wave amplitudes and ellipticities. For eight of these pulsars, our upper limits give bounds that are improvements over the indirect spin-down limit values. For another 32, we are within a factor of 10 of the spin-down limit, and it is likely that some of these will be reachable in future runs of the advanced detector. Taken as a whole, these new results improve on previous limits by more than a factor of two