2,931 research outputs found
Visualizing genetic constraints
Principal Components Analysis (PCA) is a common way to study the sources of
variation in a high-dimensional data set. Typically, the leading principal
components are used to understand the variation in the data or to reduce the
dimension of the data for subsequent analysis. The remaining principal
components are ignored since they explain little of the variation in the data.
However, evolutionary biologists gain important insights from these low
variation directions. Specifically, they are interested in directions of low
genetic variability that are biologically interpretable. These directions are
called genetic constraints and indicate directions in which a trait cannot
evolve through selection. Here, we propose studying the subspace spanned by low
variance principal components by determining vectors in this subspace that are
simplest. Our method and accompanying graphical displays enhance the
biologist's ability to visualize the subspace and identify interpretable
directions of low genetic variability that align with simple directions.Comment: Published in at http://dx.doi.org/10.1214/12-AOAS603 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Emergence of chaotic scattering in ultracold Er and Dy
We show that for ultracold magnetic lanthanide atoms chaotic scattering
emerges due to a combination of anisotropic interaction potentials and Zeeman
coupling under an external magnetic field. This scattering is studied in a
collaborative experimental and theoretical effort for both dysprosium and
erbium. We present extensive atom-loss measurements of their dense magnetic
Feshbach resonance spectra, analyze their statistical properties, and compare
to predictions from a random-matrix-theory inspired model. Furthermore,
theoretical coupled-channels simulations of the anisotropic molecular
Hamiltonian at zero magnetic field show that weakly-bound, near threshold
diatomic levels form overlapping, uncoupled chaotic series that when combined
are randomly distributed. The Zeeman interaction shifts and couples these
levels, leading to a Feshbach spectrum of zero-energy bound states with
nearest-neighbor spacings that changes from randomly to chaotically distributed
for increasing magnetic field. Finally, we show that the extreme temperature
sensitivity of a small, but sizeable fraction of the resonances in the Dy and
Er atom-loss spectra is due to resonant non-zero partial-wave collisions. Our
threshold analysis for these resonances indicates a large collision-energy
dependence of the three-body recombination rate
Low Fuel Convergence Path to Direct-Drive Fusion Ignition
A new class of inertial fusion capsules is presented that combines multishell targets with laser direct drive at low intensity (2.8×10¹⁴ W/cm²) to achieve robust ignition. The targets consist of three concentric, heavy, metal shells, enclosing a volume of tens of μg of liquid deuterium-tritium fuel. Ignition is designed to occur well “upstream” from stagnation, with minimal pusher deceleration to mitigate interface Rayleigh-Taylor growth. Laser intensities below thresholds for laser plasma instability and cross beam energy transfer facilitate high hydrodynamic efficiency (∼10%)
Critical temperature for kaon condensation in color-flavor locked quark matter
We study the behavior of Goldstone bosons in color-flavor-locked (CFL) quark
matter at nonzero temperature. Chiral symmetry breaking in this phase of cold
and dense matter gives rise to pseudo-Goldstone bosons, the lightest of these
being the charged and neutral kaons K^+ and K^0. At zero temperature,
Bose-Einstein condensation of the kaons occurs. Since all fermions are gapped,
this kaon condensed CFL phase can, for energies below the fermionic energy gap,
be described by an effective theory for the bosonic modes. We use this
effective theory to investigate the melting of the condensate: we determine the
temperature-dependent kaon masses self-consistently using the two-particle
irreducible effective action, and we compute the transition temperature for
Bose-Einstein condensation. Our results are important for studies of transport
properties of the kaon condensed CFL phase, such as bulk viscosity.Comment: 24 pages, 8 figures, v2: new section about effect of electric
neutrality on critical temperature added; references added; version to appear
in J.Phys.
Planet Hunters VII. Discovery of a New Low-Mass, Low-Density Planet (PH3 c) Orbiting Kepler-289 with Mass Measurements of Two Additional Planets (PH3 b and d)
We report the discovery of one newly confirmed planet ( days,
) and mass determinations of two previously
validated Kepler planets, Kepler-289 b ( days,
) and Kepler-289-c ( days,
), through their transit timing variations
(TTVs). We also exclude the possibility that these three planets reside in a
Laplace resonance. The outer planet has very deep (), high
signal-to-noise transits, which puts extremely tight constraints on its host
star's stellar properties via Kepler's Third Law. The star PH3 is a young
( Gyr as determined by isochrones and gyrochronology), Sun-like star
with , , and
K. The middle planet's large TTV amplitude (
hours) resulted either in non-detections or inaccurate detections in previous
searches. A strong chopping signal, a shorter period sinusoid in the TTVs,
allows us to break the mass-eccentricity degeneracy and uniquely determine the
masses of the inner, middle, and outer planets to be ,
, and , which we designate PH3 b, c, and
d, respectively. Furthermore, the middle planet, PH3 c, has a relatively low
density, g/cm for a planet of its mass, requiring a
substantial H/He atmosphere of by mass, and joins a
growing population of low-mass, low-density planets.Comment: 21 pages, 10 figures, 5 tables, accepted into Ap
Planet Hunters X: Searching for Nearby Neighbors of 75 Planet and Eclipsing Binary Candidates from the K2 Kepler Extended Mission
We present high-resolution observations of a sample of 75 K2 targets from
Campaigns 1-3 using speckle interferometry on the Southern Astrophysical
Research (SOAR) telescope and adaptive optics (AO) imaging at the Keck II
telescope. The median SOAR -band and Keck -band detection limits at 1"
were ~mag and ~mag, respectively. This
sample includes 37 stars likely to host planets, 32 targets likely to be
eclipsing binaries (EBs), and 6 other targets previously labeled as likely
planetary false positives. We find nine likely physically bound companion stars
within 3" of three candidate transiting exoplanet host stars and six likely
EBs. Six of the nine detected companions are new discoveries; one of the six,
EPIC 206061524, is associated with a planet candidate. Among the EB candidates,
companions were only found near the shortest period ones ( days), which is
in line with previous results showing high multiplicity near short-period
binary stars. This high-resolution data, including both the detected companions
and the limits on potential unseen companions, will be useful in future planet
vetting and stellar multiplicity rate studies for planets and binaries.Comment: Accepted in A
Bulk viscosity in kaon-condensed color-flavor locked quark matter
Color-flavor locked (CFL) quark matter at high densities is a color
superconductor, which spontaneously breaks baryon number and chiral symmetry.
Its low-energy thermodynamic and transport properties are therefore dominated
by the H (superfluid) boson, and the octet of pseudoscalar pseudo-Goldstone
bosons of which the neutral kaon is the lightest. We study the CFL-K^0 phase,
in which the stress induced by the strange quark mass causes the kaons to
condense, and there is an additional ultra-light "K^0" Goldstone boson arising
from the spontaneous breaking of isospin. We compute the bulk viscosity of
matter in the CFL-K^0 phase, which arises from the beta-equilibration processes
K^0H+H and K^0+HH. We find that the bulk viscosity varies as T^7, unlike
the CFL phase where it is exponentially Boltzmann-suppressed by the kaon's
energy gap. However, in the temperature range of relevance for r-mode damping
in compact stars, the bulk viscosity in the CFL-K^0 phase turns out to be even
smaller than in the uncondensed CFL phase, which already has a bulk viscosity
much smaller than all other known color-superconducting quark phases.Comment: 23 pages, 8 figures, v2: references added; minor rephrasings in the
conclusions; version to appear in J. Phys.
The Atacama Cosmology Telescope: The LABOCA/ACT Survey of Clusters at All Redshifts
We present a multi-wavelength analysis of eleven Sunyaev Zel'dovich effect
(SZE)-selected galaxy clusters (ten with new data) from the Atacama Cosmology
Telescope (ACT) southern survey. We have obtained new imaging from the Large
APEX Bolometer Camera (345GHz; LABOCA) on the Atacama Pathfinder EXperiment
(APEX) telescope, the Australia Telescope Compact Array (2.1GHz; ATCA), and the
Spectral and Photometric Imaging Receiver (250, 350, and ;
SPIRE) on the Herschel Space Observatory. Spatially-resolved 345GHz SZE
increments with integrated S/N > 5 are found in six clusters. We compute 2.1GHz
number counts as a function of cluster-centric radius and find significant
enhancements in the counts of bright sources at projected radii . By extrapolating in frequency, we predict that the combined
signals from 2.1GHz-selected radio sources and 345GHz-selected SMGs contaminate
the 148GHz SZE decrement signal by ~5% and the 345GHz SZE increment by ~18%.
After removing radio source and SMG emission from the SZE signals, we use ACT,
LABOCA, and (in some cases) new Herschel SPIRE imaging to place constraints on
the clusters' peculiar velocities. The sample's average peculiar velocity
relative to the cosmic microwave background is .Comment: 19 pages, 11 figures, Accepted for Publication in The Astrophysical
Journa
When who and how matter: explaining the success of referendums in Europe
This article aims to identify the institutional factors that make a referendum successful. This comparative analysis seeks to explain the success of top-down referendums organized in Europe between 2001 and 2013. It argues and tests for the main effect of three institutional factors (popularity of the initiator, size of parliamentary majority, and political cues during referendum campaigns) and controls for the type of referendum and voter turnout. The analysis uses data collected from referendums and electoral databases, public opinion surveys, and newspaper articles. Results show that referendums proposed by a large parliamentary majority or with clear messages from political parties during campaign are likely to be successful
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