11,197 research outputs found
Vibration
Physiological and biomechanical responses of humans to vibrations during manned space flight and threshold data on tolerances to various vibrational modes and condition
Sound and noise
Sound and noise problems in space environment and human tolerance criteria at varying frequencies and intensitie
Evaporation of a Kerr black hole by emission of scalar and higher spin particles
We study the evolution of an evaporating rotating black hole, described by
the Kerr metric, which is emitting either solely massless scalar particles or a
mixture of massless scalar and nonzero spin particles. Allowing the hole to
radiate scalar particles increases the mass loss rate and decreases the angular
momentum loss rate relative to a black hole which is radiating nonzero spin
particles. The presence of scalar radiation can cause the evaporating hole to
asymptotically approach a state which is described by a nonzero value of . This is contrary to the conventional view of black hole
evaporation, wherein all black holes spin down more rapidly than they lose
mass. A hole emitting solely scalar radiation will approach a final asymptotic
state described by . A black hole that is emitting scalar
particles and a canonical set of nonzero spin particles (3 species of
neutrinos, a single photon species, and a single graviton species) will
asymptotically approach a nonzero value of only if there are at least 32
massless scalar fields. We also calculate the lifetime of a primordial black
hole that formed with a value of the rotation parameter , the minimum
initial mass of a primordial black hole that is seen today with a rotation
parameter , and the entropy of a black hole that is emitting scalar or
higher spin particles.Comment: 22 pages, 13 figures, RevTeX format; added clearer descriptions for
variables, added journal referenc
Optimal Moments for the Analysis of Peculiar Velocity Surveys
We present a new method for the analysis of peculiar velocity surveys which
removes contributions to velocities from small scale, nonlinear velocity modes
while retaining information about large scale motions. Our method utilizes
Karhunen--Lo\`eve methods of data compression to construct a set of moments out
of the velocities which are minimally sensitive to small scale power. The set
of moments are then used in a likelihood analysis. We develop criteria for the
selection of moments, as well as a statistic to quantify the overall
sensitivity of a set of moments to small scale power. Although we discuss our
method in the context of peculiar velocity surveys, it may also prove useful in
other situations where data filtering is required.Comment: 25 Pages, 3 figures. Submitted to Ap
Genetic ancestry of participants in the National Children's Study.
BackgroundThe National Children's Study (NCS) is a prospective epidemiological study in the USA tasked with identifying a nationally representative sample of 100,000 children, and following them from their gestation until they are 21 years of age. The objective of the study is to measure environmental and genetic influences on growth, development, and health. Determination of the ancestry of these NCS participants is important for assessing the diversity of study participants and for examining the effect of ancestry on various health outcomes.ResultsWe estimated the genetic ancestry of a convenience sample of 641 parents enrolled at the 7 original NCS Vanguard sites, by analyzing 30,000 markers on exome arrays, using the 1000 Genomes Project superpopulations as reference populations, and compared this with the measures of self-reported ethnicity and race. For 99% of the individuals, self-reported ethnicity and race agreed with the predicted superpopulation. NCS individuals self-reporting as Asian had genetic ancestry of either South Asian or East Asian groups, while those reporting as either Hispanic White or Hispanic Other had similar genetic ancestry. Of the 33 individuals who self-reported as Multiracial or Non-Hispanic Other, 33% matched the South Asian or East Asian groups, while these groups represented only 4.4% of the other reported categories.ConclusionsOur data suggest that self-reported ethnicity and race have some limitations in accurately capturing Hispanic and South Asian populations. Overall, however, our data indicate that despite the complexity of the US population, individuals know their ancestral origins, and that self-reported ethnicity and race is a reliable indicator of genetic ancestry
A decreased probability of habitable planet formation around low-mass stars
Smaller terrestrial planets (< 0.3 Earth masses) are less likely to retain
the substantial atmospheres and ongoing tectonic activity probably required to
support life. A key element in determining if sufficiently massive "sustainably
habitable" planets can form is the availability of solid planet-forming
material. We use dynamical simulations of terrestrial planet formation from
planetary embryos and simple scaling arguments to explore the implications of
correlations between terrestrial planet mass, disk mass, and the mass of the
parent star. We assume that the protoplanetary disk mass scales with stellar
mass as Mdisk ~ f Mstar^h, where f measures the relative disk mass, and 1/2 < h
< 2, so that disk mass decreases with decreasing stellar mass. We consider
systems without Jovian planets, based on current models and observations for M
stars. We assume the mass of a planet formed in some annulus of a disk with
given parameters is proportional to the disk mass in that annulus, and show
with a suite of simulations of late-stage accretion that the adopted
prescription is surprisingly accurate. Our results suggest that the fraction of
systems with sufficient disk mass to form > 0.3 Earth mass habitable planets
decreases for low-mass stars for every realistic combination of parameters.
This "habitable fraction" is small for stellar masses below a mass in the
interval 0.5 to 0.8 Solar masses, depending on disk parameters, an interval
that excludes most M stars. Radial mixing and therefore water delivery are
inefficient in lower-mass disks commonly found around low-mass stars, such that
terrestrial planets in the habitable zones of most low-mass stars are likely to
be small and dry.Comment: Accepted to ApJ. 11 pages, 6 figure
Polar waves and chaotic flows in thin rotating spherical shells
Convection in rotating spherical geometries is an important physical process
in planetary and stellar systems. Using continuation methods at low Prandtl
number, we find both strong equatorially asymmetric and symmetric polar
nonlinear rotating waves in a model of thermal convection in thin rotating
spherical shells with stress-free boundary conditions. For the symmetric waves
convection is confined to high latitude in both hemispheres but is only
restricted to one hemisphere close to the pole in the case of asymmetric waves.
This is in contrast to what is previously known from studies in the field.
These periodic flows, in which the pattern is rotating steadily in the
azimuthal direction, develop a strong axisymmetric component very close to
onset. Using stability analysis of periodic orbits the regions of stability are
determined and the topology of the stable/unstable oscillatory flows bifurcated
from the branches of rotating waves is described. By means of direct numerical
simulations of these oscillatory chaotic flows, we show that these
three-dimensional convective polar flows exhibit characteristics, such as force
balance or mean physical properties, which are similar to flows occuring in
planetary atmospheres. We show that these results may open a route to
understanding unexplained features of gas giant atmospheres, in particular for
the case of Jupiter. These include the observed equatorial asymmetry with a
pronounced decrease at the equator (the so-called dimple), and the coherent
vortices surrounding the poles recently observed by the Juno mission.Comment: Published in Physical Review Fluids (2019). Contains 2 tables and 8
figure
The onset of low Prandtl number thermal convection in thin spherical shells
This study considers the onset of stress-free Boussinesq thermal convection
in rotating spherical shells with aspect ratio ( and
being the inner and outer radius), Prandtl numbers , and Taylor numbers . We are
particularly interested in the form of the convective cell pattern that
develops, and in its time scales, since this may have observational
consequences. For a fixed and by decreasing from
0.1 to a transition between spiralling columnar (SC) and
equatorially-attached (EA) modes, and a transition between EA and equatorially
antisymmetric or symmetric polar (AP/SP) weakly multicellular modes are found.
The latter modes are preferred at very low . Surprisingly, for the unicellular polar modes become also preferred at
moderate because two new transition curves between EA and
AP/SP and between AP/SP and SC modes are born at a triple-point bifurcation.
The dependence on and of the transitions is studied to
estimate the type of modes, and their critical parameters, preferred at
different stellar regimes.Comment: Accepted for publication in Physical Review Fluids. Contains 17
pages, 8 figures and 3 tables. Added brief erratum correcting values used for
estimates of neutron star ocean viscosit
Acoustic emission monitoring of a soil slope: comparisons with continuous deformation measurements
Acoustic emission (AE) has become an established approach to monitor the stability of soil slopes. However, the challenge has been to develop strategies to interpret and quantify deformation behaviour from the measured AE. This paper presents the first comparison of continuous AE (measured using an active waveguide) and continuous subsurface deformation measurements. The active waveguide is installed in a borehole through a slope and comprises a metal waveguide rod or tube with a granular backfill surround. When the host slope deforms, the column of granular backfill also deforms, generating AE that can propagate along the waveguide. This paper presents results from a field trial at a reactivated soil slope in North Yorkshire, UK. The measurements confirm that AE rates generated are directly proportional to the velocity of slope movement (e.g. the AE rate versus velocity relationship determined for a series of slope movement events produced an R 2 value of 0·8) and demonstrate the performance of AE monitoring of active waveguides to provide continuous information on slope displacements and displacement rates with high temporal resolution
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