11,514 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
Superburst oscillations: ocean and crustal modes excited by Carbon-triggered Type I X-ray bursts
Accreting neutron stars (NS) can exhibit high frequency modulations in their
lightcurves during thermonuclear X-ray bursts, known as burst oscillations. The
frequencies can be offset from the spin frequency of the NS by several Hz, and
can drift by 1-3 Hz. One possible explanation is a mode in the bursting ocean,
the frequency of which would decrease (in the rotating frame) as the burst
cools, hence explaining the drifts. Most burst oscillations have been observed
during H/He triggered bursts, however there has been one observation of
oscillations during a superburst; hours' long Type I X-ray bursts caused by
unstable carbon burning deeper in the ocean. This paper calculates the
frequency evolution of an oceanic r-mode during a superburst. The rotating
frame frequency varies during the burst from 4-14 Hz, and is sensitive to the
background parameters, in particular the temperature of the ocean and ignition
depth. This calculation is compared to the superburst oscillations observed on
4U-1636-536. The predicted mode frequencies ( 10 Hz) would require a spin
frequency of 592 Hz to match observations; 6 Hz higher than the spin
inferred from an oceanic r-mode model for the H/He triggered burst
oscillations. This model also over-predicts the frequency drift during the
superburst by 90 %.Comment: Accepted for publication in MNRA
Active colloidal particles in emulsion droplets: A model system for the cytoplasm
In living cells, molecular motors create activity that enhances the diffusion
of particles throughout the cytoplasm, and not just ones attached to the
motors. We demonstrate initial steps toward creating artificial cells that
mimic this phenomenon. Our system consists of active, Pt-coated Janus particles
and passive tracers confined to emulsion droplets. We track the motion of both
the active particles and passive tracers in a hydrogen peroxide solution, which
serves as the fuel to drive the motion. We first show that correcting for bulk
translational and rotational motion of the droplets induced by bubble formation
is necessary to accurately track the particles. After drift correction, we find
that the active particles show enhanced diffusion in the interior of the
droplets and are not captured by the droplet interface. At the particle and
hydrogen peroxide concentrations we use, we observe little coupling between the
active and passive particles. We discuss the possible reasons for lack of
coupling and describe ways to improve the system to more effectively mimic
cytoplasmic activity
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
The (In)Stability of Planetary Systems
We present results of numerical simulations which examine the dynamical
stability of known planetary systems, a star with two or more planets. First we
vary the initial conditions of each system based on observational data. We then
determine regions of phase space which produce stable planetary configurations.
For each system we perform 1000 ~1 million year integrations. We examine
upsilon And, HD83443, GJ876, HD82943, 47UMa, HD168443, and the solar system
(SS). We find that the resonant systems, 2 planets in a first order mean motion
resonance, (HD82943 and GJ876) have very narrow zones of stability. The
interacting systems, not in first order resonance, but able to perturb each
other (upsilon And, 47UMa, and SS) have broad regions of stability. The
separated systems, 2 planets beyond 10:1 resonance, (we only examine HD83443
and HD168443) are fully stable. Furthermore we find that the best fits to the
interacting and resonant systems place them very close to unstable regions. The
boundary in phase space between stability and instability depends strongly on
the eccentricities, and (if applicable) the proximity of the system to perfect
resonance. In addition to million year integrations, we also examined stability
on ~100 million year timescales. For each system we ran ~10 long term
simulations, and find that the Keplerian fits to these systems all contain
configurations which may be regular on this timescale.Comment: 37 pages, 49 figures, 13 tables, 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 Dynamical Analysis of the 47 UMa Planetary System
The mass and period ratios of the two planets orbiting 47 UMa suggest a
possible kinship to the Jupiter-Saturn pair in our solar system. We explore the
current dynamical state of the 47 UMa system with numerical integrations, and
compare the results with analytic secular theory. We find that the planets in
the system are likely participating in a secular resonance in which the
difference in the longitudes of pericenter librates around zero. Alternately,
it is possible that the system is participating in the 7:3 mean motion
resonance. We show that stability considerations restrict the mutual
inclination between the two planets to 40 degrees or less, and that this result
is relatively insensitive to the total mass of the two planets. We present
hydrodynamical simulations which measure the torques exerted on the planets by
a hypothesized external protoplanetary disk. We show that planetary migration
in response to torques from the disk may have led to capture of the system into
a 7:3 mean-motion resonance, although it is unclear how the eccentricities of
the planets would have been damped after capture occured. We show that
Earth-mass planets can survive for long periods in some regions of the
habitable zone of the nominal co-planar system. A set of planetary accretion
calculations, however, shows that it is unlikely that large terrestrial planets
can form in the 47 UMa habitable zone.Comment: Accepted by the Astrophysical Journal (Original submission November
2001
Brutalism in Sound: Multi-Media Performance at Iklectik, London
A live presentation of the image-text-sound pieces Concrete Paris and The Gathering Grounds (Photolanguage (Nigel Green & Robin Wilson) with Iain Chambers
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