1,997 research outputs found
Improved electrodes for skin contacts
Design is described of thick, flexible electrodes with appropriate metal surfaces which prevent unnecessary skin motion. Electrodes provide sufficient radial pressure directed toward body surface to depress skin a noticeable portion of its normal resilient thickness
On the possible role of massive neutrinos in cosmological structure formation
In addition to the problem of galaxy formation, one of the greatest open
questions of cosmology is represented by the existence of an asymmetry between
matter and antimatter in the baryonic component of the Universe. We believe
that a net lepton number for the three neutrino species can be used to
understand this asymmetry. This also implies an asymmetry in the
matter-antimatter component of the leptons. The existence of a nonnull lepton
number for the neutrinos can easily explain a cosmological abundance of
neutrinos consistent with the one needed to explain both the rotation curves of
galaxies and the flatness of the Universe. Some propedeutic results are
presented in order to attack this problem.Comment: RevTeX4, 25 pages, 5 figures, to appear in the "Proceedings of the
Xth Brazilian School of Cosmology and Gravitation", M. Novello, editor, AIP,
in pres
Detection and measurement of planetary systems with GAIA
We use detailed numerical simulations and the Andromedae,
planetary system as a template to evaluate the capability of the ESA
Cornerstone Mission GAIA in detecting and measuring multiple planets around
solar-type stars in the neighborhood of the Solar System. For the outer two
planets of the Andromedae, system, GAIA high-precision global
astrometric measurements would provide estimates of the full set of orbital
elements and masses accurate to better than 1--10%, and would be capable of
addressing the coplanarity issue by determining the true geometry of the system
with uncertainties of order of a few degrees. Finally, we discuss the
generalization to a variety of configurations of potential planetary systems in
the solar neighborhood for which GAIA could provide accurate measurements of
unique value for the science of extra-solar planets.Comment: 4 pages, 2 pictures, accepted for publication in A&A Letter
Evidence of a large scale positive rotation-metallicity correlation in the Galactic thick disk
This study is based on high quality astrometric and spectroscopic data from
the most recent releases by Gaia and APOGEE. We select thin and thick
disk red giants, in the Galactocentric (cylindrical) distance range ~kpc and within ~kpc, for which full chemo-kinematical information
is available. Radial chemical gradients, , and rotational velocity-metallicity correlations, , are re-derived firmly uncovering that the thick disk
velocity-metallicity correlation maintains its positiveness over the ~kpc
range explored. This observational result is important as it sets experimental
constraints on recent theoretical studies on the formation and evolution of the
Milky Way disk and on cosmological models of Galaxy formation.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Societ
A test of Gaia Data Release 1 parallaxes: implications for the local distance scale
We present a comparison of Gaia Data Release 1 (DR1) parallaxes with
photometric parallaxes for a sample of 212 Galactic Cepheids at a median
distance of 2~kpc, and explore their implications on the distance scale and the
local value of the Hubble constant H_0. The Cepheid distances are estimated
from a recent calibration of the near-infrared Period-Luminosity P-L relation.
The comparison is carried out in parallax space, where the DR1 parallax errors,
with a median value of half the median parallax, are expected to be
well-behaved. With the exception of one outlier, the DR1 parallaxes are in
remarkably good global agreement with the predictions, and the published errors
may be conservatively overestimated by about 20%. The parallaxes of 9 Cepheids
brighter than G = 6 may be systematically underestimated, trigonometric
parallaxes measured with the HST FGS for three of these objects confirm this
trend. If interpreted as an independent calibration of the Cepheid luminosities
and assumed to be otherwise free of systematic uncertainties, DR1 parallaxes
would imply a decrease of 0.3% in the current estimate of the local Hubble
constant, well within their statistical uncertainty, and corresponding to a
value 2.5 sigma (3.5 sigma if the errors are scaled) higher than the value
inferred from Planck CMB data used in conjunction with Lambda-CDM. We also test
for a zeropoint error in Gaia parallaxes and find none to a precision of ~20
muas. We caution however that with this early release, the complete systematic
properties of the measurements may not be fully understood at the statistical
level of the Cepheid sample mean, a level an order of magnitude below the
individual uncertainties. The early results from DR1 demonstrate again the
enormous impact that the full mission will likely have on fundamental questions
in astrophysics and cosmology.Comment: A&A, submitted, 6 pages, 3 figure
The Gaia Data Release 1 parallaxes and the distance scale of Galactic planetary nebulae
In this paper we gauge the potentiality of Gaia in the distance scale
calibration of planetary nebulae (PNe) by assessing the impact of DR1
parallaxes of central stars of Galactic PNe (CSPNe) against known physical
relations. For selected PNe targets with state-of-the-art data on angular sizes
and fluxes, we derive the distance-dependent parameters of the classical
distance scales, i.e., physical radii and ionized masses, from DR1 parallaxes;
we propagate the uncertainties in the estimated quantities and evaluate their
statistical properties in the presence of large relative parallax errors; we
populate the statistical distance scale diagrams with this sample and discuss
its significance in light of existing data and current calibrations.
We glean from DR1 parallaxes 8 CSPNe with S/N1. We show that this set of
potential calibrators doubles the number of extant trigonometric parallaxes
(from HST and ground-based), and increases by two orders of magnitude the
domain of physical parameters probed previously. We then use the combined
sample of suitable trigonometric parallaxes to fit the
physical-radius-to-surface-brightness relation. This distance scale
calibration, although preliminary, appears solid on statistical grounds, and
suggestive of new PNe physics.
With the tenfold improvement in PNe number statistics and astrometric
accuracy expected from future Gaia releases the new distance scale, already
very intriguing, will be definitively constrained.Comment: New Astronomy, in pres
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