153 research outputs found
On the origin of planets at very wide orbits from the re-capture of free floating planets
In recent years several planets have been discovered at wide orbits (>100 AU)
around their host stars. Theoretical studies encounter difficulties in
explaining their formation and origin. Here we propose a novel scenario for the
production of planetary systems at such orbits, through the dynamical recapture
of free floating planets (FFPs) in dispersing stellar clusters. This process is
a natural extension of the recently suggested scenario for the formation of
wide stellar binaries. We use N-body simulations of dispersing clusters with
10-1000 stars and comparable numbers of FFPs to study this process. We find
that planets are captured into wide orbits in the typical range ~100-10^6 AU,
and have a wide range of eccentricities (thermal distribution). Typically, 3-6
x (f_FFP/1) % of all stars capture a planetary companion with such properties
(where f_FFP is the number of FFP per star). The planetary capture efficiency
is comparable to that of capture-formed stellar-binaries, and shows a similar
dependence on the cluster size and structure. It is almost independent of the
specific planetary mass; planets as well as sub-stellar companions of any mass
can be captured. The capture efficiency decreases with increasing cluster size,
and for a given cluster size the it increases with the host/primary mass. More
than one planet can be captured around the same host and planets can be
captured into binary systems. Planets can also be captured into pre-existing
planetary and into orbits around black holes and massive white dwarfs, if these
formed early enough before the cluster dispersal. In particular, stellar black
holes have a high capture efficiency (>50 % and 5-10 x (f_FFP/1) % for capture
of stars and planetary companions, respectively) due to their large mass.
Finally, although rare, two FFPs or brown dwarfs can become bound and form a
FFP-binary system with no stellar host.Comment: ApJ, in press. Added two figure
Imaging Biomarkers in Acute Ischemic Stroke Trials: A Systematic Review
Imaging biomarkers are increasingly used to provide a better understanding of the pathophysiology of acute ischemic stroke. However, this approach of routinely using imaging biomarkers to inform treatment decisions has yet to be translated into successful randomized trials. The aim of this study was to systematically review the use of imaging biomarkers in randomized controlled trials in patients with acute ischemic stroke, exploring the purposes for which the imaging biomarkers were used.We performed a systematic review of imaging biomarkers used in randomized controlled trials of acute ischemic stroke, in which a therapeutic intervention was trialed within 48 hours of symptom onset. Data bases searched included MEDLINE, EMBASE, strokecenter.org, and the Virtual International Stroke Trials Archive (1995-2014).Eighty-four studies met the criteria, of which 49 used imaging to select patients; 31, for subgroup analysis; and 49, as an outcome measure. Imaging biomarkers were broadly used for 8 purposes. There was marked heterogeneity in the definitions and uses of imaging biomarkers and significant publication bias among post hoc analyses.Imaging biomarkers offer the opportunity to refine the trial cohort by minimizing participant variation, to decrease sample size, and to personalize treatment approaches for those who stand to benefit most. However, within imaging modalities, there has been little consistency between stroke trials. Greater effort to prospectively use consistent imaging biomarkers should help improve the development of novel treatment strategies in acute stroke and improve comparison between studies
The Hubble flow around the CenA / M83 galaxy complex
We present HST/ACS images and color-magnitude diagrams for 24 nearby galaxies
in and near the constellation of Centaurus with radial velocities V_LG < 550
km/s. Distances are determined based on the luminosities of stars at the tip of
the red giant branch that range from 3.0 Mpc to 6.5 Mpc. The galaxies are
concentrated in two spatially separated groups around Cen A (NGC 5128) and M 83
(NGC 5236). The Cen A group itself has a mean distance of 3.76 +/-0.05 Mpc, a
velocity dispersion of 136 km/s, a mean harmonic radius of 192 kpc, and an
estimated orbital/virial mass of (6.4 - 8.1) x 10^12 M_sun. This elliptical
dominated group is found to have a relatively high mass-to-light ratio: M/L_B =
125 M_sun/L_sun. For the M 83 group we derived a mean distance of 4.79 +/-0.10
Mpc, a velocity dispersion of 61 km/s, a mean harmonic radius of 89 kpc, and
estimated orbital/virial mass of (0.8 - 0.9) x 10^12 M_sun. This spiral
dominated group is found to have a relatively low M/L_B = 34 M_sun/L_sun. The
radius of the zero-velocity surface around Cen A lies at R_0 = 1.40 +/-0.11
Mpc, implying a total mass within R_0 of M_T = (6.0 +/-1.4) x 10^12 M_sun. This
value is in good agreement with the Cen A virial/orbital mass estimates and
provides confirmation of the relatively high M/L_B of this elliptical-dominated
group. The centroids of both the groups, as well as surrounding field galaxies,
have very small peculiar velocities, < 25 km/s, with respect to the local
Hubble flow with H_0 = 68 km/s/Mpc.Comment: 31 pages including 9 figures and 3 tables. Accepted for publication
in Astronomical Journal, 133, N0. 2 (February), 200
Distance and mass of the M104 (Sombrero) group
Distances and radial velocities of galaxies in the vicinity of the luminous
early-type galaxy M 104 (Sombrero) are used to derive its dark matter mass.
Two dwarf galaxies: UGCA 307 and KKSG 30 situated near M 104 were observed
with the Advanced Camera for Surveys on the Hubble Space Telescope. The
distances Mpc (UGCA 307) and Mpc
(KKSG 30) were determined using the tip of the red giant branch method. These
distances are consistent with the dwarf galaxies being satellites of Sombrero.
Using radial velocities and projected separations of UGCA 307, KKSG 30, and a
third galaxy with an accurate distance (KKSG 29), as well as 12 other assumed
companions with less accurate distances, the total mass of M 104 is estimated
to be . At the K-band luminosity of the
Sombrero galaxy of , its total mass-to-luminosity ratio
is , which is about three times higher
than that of luminous bulgeless galaxies.Comment: 6 pages, 5 figures, 3 tables, accepted to Astronomy & Astrophysic
KKH 22, the first dwarf spheroidal satellite of IC 342
We present observations with the Advanced Camera for Surveys on the Hubble
Space Telescope of the nearby dwarf spheroidal galaxy KKH 22 = LEDA 2807114 in
the vicinity of the massive spiral galaxy IC 342. We derived its distance of
3.12+-0.19 Mpc using the tip of red giant branch (TRGB) method. We also used
the 6 m BTA spectroscopy to measure a heliocentric radial velocity of the
globular cluster in KKH22 to be +30+-10 km/s. The dSph galaxy KKH 22 has the
V-band absolute magnitude of -12.19 mag and the central surface brightness
mu_v,0 = 24.1 mag/sq.arcsec. Both the velocity and the distance of KKH 22 are
consistent with the dSph galaxy being gravitationally bound to IC 342. Another
nearby dIr galaxy, KKH 34, with a low heliocentric velocity of +106 km/s has
the TRGB distance of 7.28+-0.36 Mpc residing in the background with respect to
the IC 342 group. KKH 34 has a surprisingly high negative peculiar velocity of
-236+-26 km/s.Comment: 7 pages, 6 figures, accepted in A&
ACS imaging of 25 galaxies in nearby groups and in the field
We present HST/ACS images and color-magnitude diagrams for 25 nearby galaxies
with radial velocities V_LG < 500 km/s. Distances are determined based on the
luminosities of stars at the tip of the red giant branch that range from 2 Mpc
to 12 Mpc. Two of the galaxies, NGC 4163 and IC 4662, are found to be the
nearest known representatives of blue compact dwarf (BCD) objects. Using
high-quality data on distances and radial velocities of 110 nearby field
galaxies, we derive their mean Hubble ratio to be 68 km/(s Mpc) with standard
deviation of 15 km/(s Mpc). Peculiar velocities of most of the galaxies, V_pec
= V_LG - 68 D, follow a Gaussian distribution with sigma_v = 63 km/s, but with
a tail towards high negative values. Our data displays the known correlation
between peculiar velocity and galaxy elevation above the Local Supercluster
plane. The small observed fraction of galaxies with high peculiar velocities,
V_pec < -500 km/s, may be understood as objects associated with nearby groups
(Coma I, Eridanus) outside the Local volume.Comment: 17 pages, 8 figures, accepted to A
Determinants of elevated healthcare utilization in patients with COPD
<p>Abstract</p> <p>Background</p> <p>Chronic obstructive pulmonary disease (COPD) imparts a substantial economic burden on western health systems. Our objective was to analyze the determinants of elevated healthcare utilization among patients with COPD in a single-payer health system.</p> <p>Methods</p> <p>Three-hundred eighty-nine adults with COPD were matched 1:3 to controls by age, gender and area of residency. Total healthcare cost 5 years prior recruitment and presence of comorbidities were obtained from a computerized database. Health related quality of life (HRQoL) indices were obtained using validated questionnaires among a subsample of 177 patients.</p> <p>Results</p> <p>Healthcare utilization was 3.4-fold higher among COPD patients compared with controls (p < 0.001). The "most-costly" upper 25% of COPD patients (n = 98) consumed 63% of all costs. Multivariate analysis revealed that independent determinants of being in the "most costly" group were (OR; 95% CI): age-adjusted Charlson Comorbidity Index (1.09; 1.01 - 1.2), history of: myocardial infarct (2.87; 1.5 - 5.5), congestive heart failure (3.52; 1.9 - 6.4), mild liver disease (3.83; 1.3 - 11.2) and diabetes (2.02; 1.1 - 3.6). Bivariate analysis revealed that cost increased as HRQoL declined and severity of airflow obstruction increased but these were not independent determinants in a multivariate analysis.</p> <p>Conclusion</p> <p>Comorbidity burden determines elevated utilization for COPD patients. Decision makers should prioritize scarce health care resources to a better care management of the "most costly" patients.</p
"Dark energy" in the Local Void
The unexpected discovery of the accelerated cosmic expansion in 1998 has
filled the Universe with the embarrassing presence of an unidentified "dark
energy", or cosmological constant, devoid of any physical meaning. While this
standard cosmology seems to work well at the global level, improved knowledge
of the kinematics and other properties of our extragalactic neighborhood
indicates the need for a better theory. We investigate whether the recently
suggested repulsive-gravity scenario can account for some of the features that
are unexplained by the standard model. Through simple dynamical considerations,
we find that the Local Void could host an amount of antimatter
() roughly equivalent to the mass of a typical
supercluster, thus restoring the matter-antimatter symmetry. The antigravity
field produced by this "dark repulsor" can explain the anomalous motion of the
Local Sheet away from the Local Void, as well as several other properties of
nearby galaxies that seem to require void evacuation and structure formation
much faster than expected from the standard model. At the global cosmological
level, gravitational repulsion from antimatter hidden in voids can provide more
than enough potential energy to drive both the cosmic expansion and its
acceleration, with no need for an initial "explosion" and dark energy.
Moreover, the discrete distribution of these dark repulsors, in contrast to the
uniformly permeating dark energy, can also explain dark flows and other
recently observed excessive inhomogeneities and anisotropies of the Universe.Comment: 6 pages, accepted as a Letter to the Editor by Astrophysics and Space
Scienc
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