1,607 research outputs found
Purkinje image eyetracking: A market survey
The Purkinje image eyetracking system was analyzed to determine the marketability of the system. The eyetracking system is a synthesis of two separate instruments, the optometer that measures the refractive power of the eye and the dual Purkinje image eyetracker that measures the direction of the visual axis
Suggested approach for establishing a rehabilitation engineering information service for the state of California
An ever expanding body of rehabilitation engineering technology is developing in this country, but it rarely reaches the people for whom it is intended. The increasing concern of state and federal departments of rehabilitation for this technology lag was the stimulus for a series of problem-solving workshops held in California during 1977. As a result of the workshops, the recommendation emerged that the California Department of Rehabilitation take the lead in the development of a coordinated delivery system that would eventually serve the entire state and be a model for similar systems across the nation
Gravitational Wave Hotspots: Ranking Potential Locations of Single-Source Gravitational Wave Emission
The steadily improving sensitivity of pulsar timing arrays (PTAs) suggests
that gravitational waves (GWs) from supermassive black hole binary (SMBHB)
systems in the nearby universe will be de- tectable sometime during the next
decade. Currently, PTAs assume an equal probability of detection from every sky
position, but as evidence grows for a non-isotropic distribution of sources, is
there a most likely sky position for a detectable single source of GWs? In this
paper, a collection of galactic catalogs is used to calculate various metrics
related to the detectability of a single GW source resolv- able above a GW
background, assuming that every galaxy has the same probability of containing a
SMBHB. Our analyses of these data reveal small probabilities that one of these
sources is currently in the PTA band, but as sensitivity is improved regions of
consistent probability density are found in predictable locations, specifically
around local galaxy clusters.Comment: 9 pages, 9 figures, accepted for submission in Ap
Constraining multiple systems with GAIA
GAIA will provide observations of some multiple asteroid and dwarf systems.
These observations are a way to determine and improve the quantification of
dynamical parameters, such as the masses and the gravity fields, in these
multiple systems. Here we investigate this problem in the cases of Pluto's and
Eugenia's system. We simulate observations reproducing an approximate planning
of the GAIA observations for both systems, as well as the New Horizons
observations of Pluto. We have developed a numerical model reproducing the
specific behavior of multiple asteroid system around the Sun and fit it to the
simulated observations using least-square method, giving the uncertainties on
the fitted parameters. We found that GAIA will improve significantly the
precision of Pluto's and Charon's mass, as well as Petit Prince's orbital
elements and Eugenia's polar oblateness.Comment: 5 pages, accepted by Planetary and Space Science, Gaia GREAT-SSO-Pis
Uncertainties in determining parton distributions at large x
We critically examine uncertainties in parton distribution functions (PDFs)
at large x arising from nuclear effects in deuterium F2 structure function
data. Within a global PDF analysis, we assess the impact on the PDFs from
uncertainties in the deuteron wave function at short distances and nucleon
off-shell effects, the use of relativistic kinematics, as well as the use of
less a restrictive parametrization of the d/u ratio. We find that in particular
the d-quark and gluon PDFs vary significantly with the choice of nuclear model.
We highlight the impact of these uncertainties on the determination of the
neutron structure function, and on W boson production and parton luminosity at
the Tevatron and the LHC. Finally, we discuss prospects for new measurements
sensitive to the d-quark and gluon distributions but insensitive to nuclear
corrections.Comment: 37 pages, 13 figures. Final published versio
New parton distributions from large-x and low-Q^2 data
We report results of a new global next-to-leading order fit of parton
distribution functions in which cuts on W and Q are relaxed, thereby including
more data at high values of x. Effects of target mass corrections (TMCs),
higher twist contributions, and nuclear corrections for deuterium data are
significant in the large-x region. The leading twist parton distributions are
found to be stable to TMC model variations as long as higher twist
contributions are also included. The behavior of the d quark as x-->1 is
particularly sensitive to the deuterium corrections, and using realistic
nuclear smearing models the d-quark distribution at large x is found to be
softer than in previous fits performed with more restrictive cuts.Comment: 31 pages, 8 figures. Minor corrections. References added. To appear
in Phys.Rev.
Improving the mass determination of Galactic Cepheids
We have selected a sample of Galactic Cepheids for which accurate estimates
of radii, distances, and photometric parameters are available. The comparison
between their pulsation masses, based on new Period-Mass-Radius (PMR)
relations, and their evolutionary masses, based on both optical and NIR
Color-Magnitude (CM) diagrams, suggests that pulsation masses are on average of
the order of 10% smaller than the evolutionary masses. Current pulsation masses
show, at fixed radius, a strongly reduced dispersion when compared with values
published in literature.The increased precision in the pulsation masses is due
to the fact that our predicted PMR relations based on nonlinear, convective
Cepheid models present smaller standard deviations than PMR relations based on
linear models. At the same time, the empirical radii of our Cepheid sample are
typically accurate at the 5% level. Our evolutionary mass determinations are
based on stellar models constructed by neglecting the effect of mass-loss
during the He burning phase. Therefore, the difference between pulsation and
evolutionary masses could be intrinsic and does not necessarily imply a problem
with either evolutionary and/or nonlinear pulsation models. The marginal
evidence of a trend in the difference between evolutionary and pulsation masses
when moving from short to long-period Cepheids is also briefly discussed. The
main finding of our investigation is that the long-standing Cepheid mass
discrepancy seems now resolved at the 10% level either if account for canonical
or mild convective core overshooting evolutionary models.Comment: 14 pages, 4 postscript figures, accepted for publication on ApJ
Letter
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