6,156 research outputs found
Improving Patient Decision-Making in Health Care
Outlines regional variations within Minnesota in rates of patients with similar conditions receiving elective surgery, the concept of shared decision making, treatment choices for eight conditions, and steps for ensuring patients make informed decisions
Assessing the Effect of Stellar Companions from High-Resolution Imaging of Kepler Objects of Interest
We report on 176 close (<2") stellar companions detected with high-resolution
imaging near 170 hosts of Kepler Objects of Interest. These Kepler targets were
prioritized for imaging follow-up based on the presence of small planets, so
most of the KOIs in these systems (176 out of 204) have nominal radii <6 R_E .
Each KOI in our sample was observed in at least 2 filters with adaptive optics,
speckle imaging, lucky imaging, or HST. Multi-filter photometry provides color
information on the companions, allowing us to constrain their stellar
properties and assess the probability that the companions are physically bound.
We find that 60 -- 80% of companions within 1" are bound, and the bound
fraction is >90% for companions within 0.5"; the bound fraction decreases with
increasing angular separation. This picture is consistent with simulations of
the binary and background stellar populations in the Kepler field. We also
reassess the planet radii in these systems, converting the observed
differential magnitudes to a contamination in the Kepler bandpass and
calculating the planet radius correction factor, . Under the assumption that planets in bound binaries are equally
likely to orbit the primary or secondary, we find a mean radius correction
factor for planets in stellar multiples of . If stellar
multiplicity in the Kepler field is similar to the solar neighborhood, then
nearly half of all Kepler planets may have radii underestimated by an average
of 65%, unless vetted using high resolution imaging or spectroscopy.Comment: 23 pages, 12 figures. Accepted for publication in The Astronomical
Journa
Limits on Stellar Companions to Exoplanet Host Stars With Eccentric Planets
Though there are now many hundreds of confirmed exoplanets known, the
binarity of exoplanet host stars is not well understood. This is particularly
true of host stars which harbor a giant planet in a highly eccentric orbit
since these are more likely to have had a dramatic dynamical history which
transferred angular momentum to the planet. Here we present observations of
four exoplanet host stars which utilize the excellent resolving power of the
Differential Speckle Survey Instrument (DSSI) on the Gemini North telescope.
Two of the stars are giants and two are dwarfs. Each star is host to a giant
planet with an orbital eccentricity > 0.5 and whose radial velocity data
contain a trend in the residuals to the Keplerian orbit fit. These observations
rule out stellar companions 4-8 magnitudes fainter than the host star at
passbands of 692nm and 880nm. The resolution and field-of-view of the
instrument result in exclusion radii of 0.05-1.4 arcsecs which excludes stellar
companions within several AU of the host star in most cases. We further provide
new radial velocities for the HD 4203 system which confirm that the linear
trend previously observed in the residuals is due to an additional planet.
These results place dynamical constraints on the source of the planet's
eccentricities, constraints on additional planetary companions, and informs the
known distribution of multiplicity amongst exoplanet host stars.Comment: 10 pages, 7 figures, 2 tables, accepted to Ap
Twisted k-graph algebras associated to Bratteli diagrams
Given a system of coverings of k-graphs, we show that the cohomology of the
resulting (k+1)-graph is isomorphic to that of any one of the k-graphs in the
system. We then consider Bratteli diagrams of 2-graphs whose twisted
C*-algebras are matrix algebras over noncommutative tori. For such systems we
calculate the ordered K-theory and the gauge-invariant semifinite traces of the
resulting 3-graph C*-algebras. We deduce that every simple C*-algebra of this
form is Morita equivalent to the C*-algebra of a rank-2 Bratteli diagram in the
sense of Pask-Raeburn-R{\o}rdam-Sims.Comment: 28 pages, pictures prepared using tik
Amplification and Overexpression of Hsa-miR-30b, Hsa-miR-30d and KHDRBS3 at 8q24.22-q24.23 in Medulloblastoma
Medulloblastoma is the most common malignant brain tumour of childhood. The identification of critical genes involved in its pathogenesis will be central to advances in our understanding of its molecular basis, and the development of improved therapeutic approaches.We performed a SNP-array based genome-wide copy number analysis in medulloblastoma cell lines, to identify regions of genomic amplification and homozygous deletion, which may harbour critical disease genes. A series of novel and established medulloblastoma defects were detected (MYC amplification (n = 4), 17q21.31 high-level gain (n = 1); 9p21.1-p21.3 (n = 1) and 6q23.1 (n = 1) homozygous deletion). Most notably, a novel recurrent region of genomic amplification at 8q24.22-q24.23 was identified (n = 2), and selected for further investigation. Additional analysis by interphase fluorescence in situ hybridisation (iFISH), PCR-based mapping and SNP-array revealed this novel amplification at 8q24.22-q24.23 is independent of MYC amplification at 8q24.21, and is unique to medulloblastoma in over 800 cancer cell lines assessed from different tumour types, suggesting it contains key genes specifically involved in medulloblastoma development. Detailed mapping identified a 3Mb common minimal region of amplification harbouring 3 coding genes (ZFAT1, LOC286094, KHDRBS3) and two genes encoding micro-RNAs (hsa-miR-30b, hsa-miR-30d). Of these, only expression of hsa-miR-30b, hsa-miR-30d and KHDRBS3 correlated with copy number status, and all three of these transcripts also displayed evidence of elevated expression in sub-sets of primary medulloblastomas, measured relative to the normal cerebellum.These data implicate hsa-miR-30b, hsa-miR-30d and KHDRBS3 as putative oncogenic target(s) of a novel recurrent medulloblastoma amplicon at 8q24.22-q24.23. Our findings suggest critical roles for these genes in medulloblastoma development, and further support the contribution of micro-RNA species to medulloblastoma pathogenesis
Validation of Twelve Small Kepler Transiting Planets in the Habitable Zone
We present an investigation of twelve candidate transiting planets from
Kepler with orbital periods ranging from 34 to 207 days, selected from initial
indications that they are small and potentially in the habitable zone (HZ) of
their parent stars. Few of these objects are known. The expected Doppler
signals are too small to confirm them by demonstrating that their masses are in
the planetary regime. Here we verify their planetary nature by validating them
statistically using the BLENDER technique, which simulates large numbers of
false positives and compares the resulting light curves with the Kepler
photometry. This analysis was supplemented with new follow-up observations
(high-resolution optical and near-infrared spectroscopy, adaptive optics
imaging, and speckle interferometry), as well as an analysis of the flux
centroids. For eleven of them (KOI-0571.05, 1422.04, 1422.05, 2529.02, 3255.01,
3284.01, 4005.01, 4087.01, 4622.01, 4742.01, and 4745.01) we show that the
likelihood they are true planets is far greater than that of a false positive,
to a confidence level of 99.73% (3 sigma) or higher. For KOI-4427.01 the
confidence level is about 99.2% (2.6 sigma). With our accurate characterization
of the GKM host stars, the derived planetary radii range from 1.1 to 2.7
R_Earth. All twelve objects are confirmed to be in the HZ, and nine are small
enough to be rocky. Excluding three of them that have been previously validated
by others, our study doubles the number of known rocky planets in the HZ.
KOI-3284.01 (Kepler-438b) and KOI-4742.01 (Kepler-442b) are the planets most
similar to the Earth discovered to date when considering their size and
incident flux jointly.Comment: 27 pages in emulateapj format, including tables and figures. To
appear in The Astrophysical Journa
Critical behavior of 2 and 3 dimensional ferro- and antiferromagnetic spin ice systems in the framework of the Effective Field Renormalization Group technique
In this work we generalize and subsequently apply the Effective Field
Renormalization Group technique to the problem of ferro- and
antiferromagnetically coupled Ising spins with local anisotropy axes in
geometrically frustrated geometries (kagome and pyrochlore lattices). In this
framework, we calculate the various ground states of these systems and the
corresponding critical points. Excellent agreement is found with exact and
Monte Carlo results. The effects of frustration are discussed. As pointed out
by other authors, it turns out that the spin ice model can be exactly mapped to
the standard Ising model but with effective interactions of the opposite sign
to those in the original Hamiltonian. Therefore, the ferromagnetic spin ice is
frustrated, and does not order. Antiferromagnetic spin ice (in both 2 and 3
dimensions), is found to undergo a transition to a long range ordered state.
The thermal and magnetic critical exponents for this transition are calculated.
It is found that the thermal exponent is that of the Ising universality class,
whereas the magnetic critical exponent is different, as expected from the fact
that the Zeeman term has a different symmetry in these systems. In addition,
the recently introduced Generalized Constant Coupling method is also applied to
the calculation of the critical points and ground state configurations. Again,
a very good agreement is found with both exact, Monte Carlo, and
renormalization group calculations for the critical points. Incidentally, we
show that the generalized constant coupling approach can be regarded as the
lowest order limit of the EFRG technique, in which correlations outside a
frustrated unit are neglected, and scaling is substituted by strict equality of
the thermodynamic quantities.Comment: 28 pages, 9 figures, RevTeX 4 Some minor changes in the conclussions.
One reference adde
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