4,332 research outputs found
They are Small Worlds After All: Revised Properties of Kepler M Dwarf Stars and their Planets
We classified the reddest () stars observed by the NASA
mission into main sequence dwarf or evolved giant stars and determined the
properties of 4216 M dwarfs based on a comparison of available photometry with
that of nearby calibrator stars, as well as available proper motions and
spectra. We revised the properties of candidate transiting planets using the
stellar parameters, high-resolution imaging to identify companion stars, and,
in the case of binaries, fitting light curves to identify the likely planet
host. In 49 of 54 systems we validated the primary as the host star. We
inferred the intrinsic distribution of M dwarf planets using the method of
iterative Monte Carlo simulation. We compared several models of planet orbital
geometry and clustering and found that one where planets are exponentially
distributed and almost precisely coplanar best describes the distribution of
multi-planet systems. We determined that M dwarfs host an average of
planets with radii of 1-4 and orbital periods of
1.5-180 d. The radius distribution peaks at and is
essentially zero at , although we identify three giant planet
candidates other than the previously confirmed Kepler-45b. There is suggestive
but not significant evidence that the radius distribution varies with orbital
period. The distribution with logarithmic orbital period is flat except for a
decline for orbits less than a few days. Twelve candidate planets, including
two Jupiter-size objects, experience an irradiance below the threshold level
for a runaway greenhouse on an Earth-like planet and are thus in a "habitable
zone".Comment: MNRAS, in press. Tables 1, 3, and 4 are available in electronic form
in the "anc" director
Two Wide Planetary-mass Companions to Solar-type Stars in Upper Scorpius
At wide separations, planetary-mass and brown dwarf companions to solar-type stars occupy a curious region of
parameter space not obviously linked to binary star formation or solar system scale planet formation. These
companions provide insight into the extreme case of companion formation (either binary or planetary), and
due to their relative ease of observation when compared to close companions, they offer a useful template
for our expectations of more typical planets. We present the results from an adaptive optics imaging survey
for wide (~50–500 AU) companions to solar-type stars in Upper Scorpius. We report one new discovery of a
~14 M_J companion around GSC 06214−00210and confirm that the candidate planetary-mass companion 1RXS
J160929.1−210524 detected by Lafrenière et al. is in fact comoving with its primary star. In our survey, these
two detections correspond to ~4% of solar-type stars having companions in the 6–20 M_J mass and ~200–500 AU
separation range. This figure is higher than would be expected if brown dwarfs and planetary-mass companions
were drawn from an extrapolation of the binary mass function. Finally, we discuss implications for the formation
of these objects
The Glasgow outcome at discharge scale: an inpatient assessment of disability after brain injury
This study assesses the validity and reliability of the Glasgow Outcome at Discharge Scale (GODS), which is a tool that is designed to assess disability after brain injury in an inpatient setting. It is derived from the Glasgow Outcome Scale-Extended (GOS-E), which assesses disability in the community after brain injury. Inter-rater reliability on the GODS is high (quadratic-weighted kappa 0.982; 95% confidence interval [CI] 0.968, 0.996) as is concurrent validity with the Disability Rating Scale (DRS) (Spearman correlation −0.728; 95% CI −0.819, −0.601). The GODS is significantly associated with physical and fatigue subscales of the short form (SF)-36 in hospital. In terms of predictive validity the GODS is highly associated with the GOS-E after discharge (Spearman correlation 0.512; 95% CI 0.281, 0.687), with the DRS, and with physical, fatigue, and social subscales of the SF-36. The GODS is recommended as an assessment tool for disability after brain injury pre-discharge and can be used in conjunction with the GOS-E to monitor disability between hospital and the community
THE EFFECTS OF OXYGEN, CARBON DIOXIDE, AND PRESSURE ON GROWTH IN CHILOMONAS PARAMECIUM AND TETRAHYMENA GELEII FURGASON
1. The effects of O2, CO2, and pressure were studied in two very different species of protozoa, a flagellate, Chilomonas paramecium, grown in acetate-ammonium solution and a ciliate, Tetrahymena geleii, grown in 2 per cent proteose-peptone solution. 2. Chilomonas and Tetrahymena live and reproduce in solutions exposed to a wide range of O2 concentrations, but Chilomonas is killed at high O2 tensions in which Tetrahymena grows best. The optimum O2 concentration for Chilomonas is about 75 mm. pressure but it lives and reproduces in O2 tensions as low as 0.5 mm. while Tetrahymena fails to grow in concentrations below 10 mm. O2 pressure. 3. With a constant O2 tension of 50 mm. pressure, it was found that there is no significant variation in growth in Chilomonas between 50 mm. and 740 mm. total pressure. In Tetrahymena, however, under the same conditions, an optimum total pressure was found at about 500 mm. and growth is comparatively poor at 50 mm. total pressure. 4. Tetrahymena does not live very long in CO2 tensions over 122 mm., although Chilomonas grows as well at 400 mm. CO2 as in air at atmospheric pressure (0.2 mm. CO2). Tetrahymena grows best in an environment minus CO2, but the optimum for Chilomonas is 100 mm. CO2 at which pressure an average of 668,600 ± 30,000 organisms per ml. was produced (temperature, 25 ± 1° C.). 5. Chilomonads grown in high CO2 concentrations (e.g., 122 mm.) produce larger starch granules and more starch than those grown in ordinary air at atmospheric pressure. 6. In solutions exposed to 75 mm. O2 tension (optimum) and 122 mm. CO2 plus 540 mm. N2 pressure, chilomonads contain very little, if any, fat. This phenomenon seems to be due to the action of CO2 on the mechanisms concerned with fat production. 7. In Tetrahymena exposed to pure O2, there is very little fat compared to those grown in atmospheric air. This may be due to the greater oxidation of fat in the higher O2 concentrations. 8. Further evidence is presented in support of the contention that Chilomonas utilizes CO2 in the production of starch
On Tractable Exponential Sums
We consider the problem of evaluating certain exponential sums. These sums
take the form ,
where each x_i is summed over a ring Z_N, and f(x_1,...,x_n) is a multivariate
polynomial with integer coefficients. We show that the sum can be evaluated in
polynomial time in n and log N when f is a quadratic polynomial. This is true
even when the factorization of N is unknown. Previously, this was known for a
prime modulus N. On the other hand, for very specific families of polynomials
of degree \ge 3, we show the problem is #P-hard, even for any fixed prime or
prime power modulus. This leads to a complexity dichotomy theorem - a complete
classification of each problem to be either computable in polynomial time or
#P-hard - for a class of exponential sums. These sums arise in the
classifications of graph homomorphisms and some other counting CSP type
problems, and these results lead to complexity dichotomy theorems. For the
polynomial-time algorithm, Gauss sums form the basic building blocks. For the
hardness results, we prove group-theoretic necessary conditions for
tractability. These tests imply that the problem is #P-hard for even very
restricted families of simple cubic polynomials over fixed modulus N
Discovery of Seven Companions To Intermediate-Mass Stars With Extreme Mass Ratios in the Scorpius-Centaurus Association
We report the detection of seven low-mass companions to intermediate-mass stars (SpT B/A/F; M similar to 1.5-4.5M(circle dot)) in the Scorpius-Centaurus (Sco-Cen) Association using nonredundant aperture masking interferometry. Our newly detected objects have contrasts Delta L' approximate to 4-6, corresponding to masses as low as similar to 20 M-Jup and mass ratios of q approximate to 0.01-0.08, depending on the assumed age of the target stars. With projected separations rho approximate to 10-30 AU, our aperture masking detections sample an orbital region previously unprobed by conventional adaptive optics imaging of intermediate-mass Sco-Cen stars covering much larger orbital radii (similar to 30-3000 AU). At such orbital separations, these objects resemble higher-mass versions of the directly imaged planetary mass companions to the 10-30 Myr, intermediate-mass stars HR 8799, beta Pictoris, and HD 95086. These newly discovered companions span the brown dwarf desert, and their masses and orbital radii provide a new constraint on models of the Formation of low-mass stellar and substellar companions to intermediate-mass stars.NASA through the Sagan Fellowship ProgramNSF Astronomy and Astrophysics Postdoctoral Fellowship AST-1203023Clay FellowshipNASA through Hubble Fellowship 51257.01AURA, Inc., for NASA NAS 5-26555W. M. Keck FoundationAstronom
An ALMA Constraint on the GSC 6214-210 B Circum-Substellar Accretion Disk Mass
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations
of GSC 6214-210 A and B, a solar-mass member of the 5-10 Myr Upper Scorpius
association with a 15 2 Mjup companion orbiting at 330 AU
(2.2"). Previous photometry and spectroscopy spanning 0.3-5 m revealed
optical and thermal excess as well as strong H and Pa~ emission
originating from a circum-substellar accretion disk around GSC 6214-210 B,
making it the lowest mass companion with unambiguous evidence of a subdisk.
Despite ALMA's unprecedented sensitivity and angular resolution, neither
component was detected in our 880 m (341 GHz) continuum observations down
to a 3- limit of 0.22 mJy/beam. The corresponding constraints on the
dust mass and total mass are <0.15 Mearth and <0.05 Mjup, respectively, or
<0.003% and <0.3% of the mass of GSC 6214-210 B itself assuming a 100:1
gas-to-dust ratio and characteristic dust temperature of 10-20 K. If the host
star possesses a putative circum-stellar disk then at most it is a meager
0.0015% of the primary mass, implying that giant planet formation has certainly
ceased in this system. Considering these limits and its current accretion rate,
GSC 6214-210 B appears to be at the end stages of assembly and is not expected
to gain any appreciable mass over the next few Myr.Comment: Accepted to ApJ
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