2,475 research outputs found
Accounting for Multiplicity in Calculating Eta Earth
Using the updated exoplanet population parameters of our previous study,
which includes the planetary radius updates from Gaia DR2 and an inferred
multiplicity distribution, we provide a revised calculation.
This is achieved by sampling planets from our derived population model and
determining which planets meet our criterion for habitability. To ensure robust
results, we provide probabilities calculated over a range of upper radius
limits. Our most optimistic criterion for habitability provides an
value of . We also
consider the effects of multiplicity and the number of habitable planets each
system may contain. Our calculation indicates that of GK dwarfs
have more than one planet within their habitable zone. This optimistic
habitability criterion also suggests that of solar-like stars
will harbor 5 or more habitable planets. These tightly packed highly habitable
system should be extremely rare, but still possible. Even with our most
pessimistic criterion we still expect that of solar-like stars
harbor more than one habitable planet.Comment: 7 pages, 1 figure; Accepted for publication in MNRA
Plastic deformation of metallic glasses: Size of shear transformation zones from molecular dynamics simulations
Plastic deformation in metallic glasses well below their glass transition temperatures Tg occurs spatially heterogeneously within highly localized regions, termed shear transformation zones (STZs). Yet, their size and the number of atoms involved in a local shear event, remains greatly unclear. With the help of classical molecular dynamics (MD) computer simulations on plastic deformation of the model glass CuTi during pure shearing, we address this issue by evaluating correlations in atomic-scale plastic displacements, viz. the displacement correlation function. From the correlation length, a universal diameter of about 15 Ã…, or, equivalently, approximately 120 atoms is derived for a variety of conditions, such as variable strains, strain rates, temperatures, and boundary conditions. Our findings are consistent with a recent model proposed by Johnson and Samwer [Phys. Rev. Lett. 95, 195501 (2005)]
Scaling K2. I. Revised Parameters for 222,088 K2 Stars and a K2 Planet Radius Valley at 1.9 R_⊕
Previous measurements of stellar properties for K2 stars in the Ecliptic Plane Input Catalog largely relied on photometry and proper motion measurements, with some added information from available spectra and parallaxes. Combining Gaia DR2 distances with spectroscopic measurements of effective temperatures, surface gravities, and metallicities from the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) DR5, we computed updated stellar radii and masses for 26,838 K2 stars. For 195,250 targets without a LAMOST spectrum, we derived stellar parameters using random forest regression on photometric colors trained on the LAMOST sample. In total, we measured spectral types, effective temperatures, surface gravities, metallicities, radii, and masses for 222,088 A, F, G, K, and M-type K2 stars. With these new stellar radii, we performed a simple reanalysis of 299 confirmed and 517 candidate K2 planet radii from Campaigns 1–13, elucidating a distinct planet radius valley around 1.9 R_⊕, a feature thus far only conclusively identified with Kepler planets, and tentatively identified with K2 planets. These updated stellar parameters are a crucial step in the process toward computing K2 planet occurrence rates
The Great Inequality and the Dynamical Disintegration of the Outer Solar System
Using an ensemble of N-body simulations, this paper considers the fate of the outer gas giants (Jupiter, Saturn, Uranus, and Neptune) after the Sun leaves the main sequence and completes its stellar evolution. Due to solar mass loss—which is expected to remove roughly half of the star's mass—the orbits of the giant planets expand. This adiabatic process maintains the orbital period ratios, but the mutual interactions between planets and the width of mean-motion resonances (MMR) increase, leading to the capture of Jupiter and Saturn into a stable 5:2 resonant configuration. The expanded orbits, coupled with the large-amplitude librations of the critical MMR angle, make the system more susceptible to perturbations from stellar flyby interactions. Accordingly, within about 30 Gyr, stellar encounters perturb the planets onto the chaotic subdomain of the 5:2 resonance, triggering a large-scale instability, which culminates in the ejections of all but one planet over the subsequent ~10 Gyr. After an additional ~50 Gyr, a close stellar encounter (with a perihelion distance less than ~200 au) liberates the final planet. Through this sequence of events, the characteristic timescale over which the solar system will be completely dissolved is roughly 100 Gyr. Our analysis thus indicates that the expected dynamical lifetime of the solar system is much longer than the current age of the universe, but is significantly shorter than previous estimates
Time-division SQUID multiplexers with reduced sensitivity to external magnetic fields
Time-division SQUID multiplexers are used in many applications that require
exquisite control of systematic error. One potential source of systematic error
is the pickup of external magnetic fields in the multiplexer. We present
measurements of the field sensitivity figure of merit, effective area, for both
the first stage and second stage SQUID amplifiers in three NIST SQUID
multiplexer designs. These designs include a new variety with improved
gradiometry that significantly reduces the effective area of both the first and
second stage SQUID amplifiers.Comment: 4 pages, 7 figures. Submitted for publication in the IEEE
Transactions on Applied Superconductivity, August 201
Nonbusiness Organizations: Federal Grants: The Single Audit Concept — With Multiple Problems
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