2,566 research outputs found
Shoulder and thorax kinematics contribute to increased power output of competitive handcyclists
Current knowledge on recumbent handbike configuration and handcycling technique is limited. The purpose of this study was to evaluate and compare the upper limb kinematics and handbike configurations of recreational and competitive recumbent handcyclists, during sport specific intensities. Thirteen handcyclists were divided into two significantly different groups based on peak aerobic power output (POpeak) and race experience; competitive (n=7; 5 H3 and 2 H4 classes; POpeak: 247±20W) and recreational (n=6; 4 H3 and 2 H4 classes; POpeak: 198±21 W). Participants performed bouts of exercise at training (50% POpeak), competition (70% POpeak), and sprint intensity while three‐dimensional kinematic data (thorax, scapula, shoulder, elbow and wrist) were collected. Statistical parametric mapping was used to compare the kinematics of competitive and recreational handcyclists. Handbike configurations were determined from additional markers on the handbike. Competitive handcyclists flexed their thorax (~5°, P<0.05), extended their shoulder (~10°, P<0.01) and posteriorly tilted their scapular (~15°, P<0.05) more than recreational handcyclists. Differences in scapular motion occurred only at training intensity while differences in shoulder extension and thorax flexion occurred both at training and competition intensities. No differences were observed during sprinting. No significant differences in handbike configuration were identified. This study is the first to compare the upper limb kinematics of competitive recreational handcyclists at sport‐specific intensities. Competitive handcyclists employed significantly different propulsion strategies at training and competition intensities. Since no differences in handbike configuration were identified, these kinematic differences could be due to technical training adaptations potentially optimising muscle recruitment or force generation of the arm
Formation of Millisecond Pulsars from Accretion Induced Collapse and Constraints on Pulsar Gamma Ray Burst Models
We study accretion induced collapse of magnetized white dwarfs as an origin
of millisecond pulsars. We apply magnetized accretion disk models to the
pre-collapse accreting magnetic white dwarfs and calculate the white dwarf spin
evolution. If the pulsar magnetic field results solely from the flux-frozen
fossil white dwarf field, a typical millisecond pulsar is born with a field
strength . The uncertainty in the field strength is
mainly due to the uncertain physical parameters of the magnetized accretion
disk models. A simple correlation between the pulsar spin and the
magnetic field , , is
derived for a typical accretion rate \sim 5\times 10^{-8}M_{\sun}/yr. This
correlation remains valid for a wide pre-collapse physical conditions unless
the white dwarf spin and the binary orbit are synchronized prior to accretion
induced collapse. We critically examine the possibility of spin-orbit
synchronization in close binary systems. Using idealized homogeneous ellipsoid
models, we compute the electromagnetic and gravitational wave emission from the
millisecond pulsars and find that electromagnetic dipole emission remains
nearly constant while millisecond pulsars may spin up rather than spin down as
a result of gravitational wave emission. We also derive the physical conditions
under which electromagnetic emission from millisecond pulsars formed by
accretion induced collapse can be a source of cosmological gamma-ray bursts. We
find that relativistic beaming of gamma-ray emission and precession of
gamma-ray emitting jets are required unless the dipole magnetic field strengths
are G; such strong dipole fields are in excess of those allowed from
the accretion induced collapse formation process except in spin-orbit
synchronization.Comment: 36 pages, AASLATEX, 4 ps figures, Ap
Kepler Observations of V447 Lyr: An Eclipsing U Gem Cataclysmic Variable
We present the results of an analysis of data covering 1.5 years of the dwarf
nova V447 Lyr. We detect eclipses of the accretion disk by the mass donating
secondary star every 3.74 hrs which is the binary orbital period. V447 Lyr is
therefore the first dwarf nova in the Kepler field to show eclipses. We also
detect five long outbursts and six short outbursts showing V447 Lyr is a U Gem
type dwarf nova. We show that the orbital phase of the mid-eclipse occurs
earlier during outbursts compared to quiescence and that the width of the
eclipse is greater during outburst. This suggests that the bright spot is more
prominent during quiescence and that the disk is larger during outburst than
quiescence. This is consistent with an expansion of the outer disk radius due
to the presence of high viscosity material associated with the outburst,
followed by a contraction in quiescence due to the accretion of low angular
momentum material. We note that the long outbursts appear to be triggered by a
short outburst, which is also observed in the super-outbursts of SU UMa dwarf
novae as observed using Kepler.Comment: Accepted by MNRA
Superhumps in Cataclysmic Binaries. XXV. q_crit, epsilon(q), and Mass-Radius
We report on successes and failures in searching for positive superhumps in
cataclysmic variables, and show the superhumping fraction as a function of
orbital period. Basically, all short-period systems do, all long-period systems
don't, and a 50% success rate is found at P_orb=3.1+-0.2 hr. We can use this to
measure the critical mass ratio for the creation of superhumps. With a
mass-radius relation appropriate for cataclysmic variables, and an assumed mean
white-dwarf mass of 0.75 M_sol, we find a mass ratio q_crit=0.35+-0.02.
We also report superhump studies of several stars of independently known mass
ratio: OU Virginis, XZ Eridani, UU Aquarii, and KV UMa (= XTE J1118+480). The
latter two are of special interest, because they represent the most extreme
mass ratios for which accurate superhump measurements have been made. We use
these to improve the epsilon(q) calibration, by which we can infer the elusive
q from the easy-to-measure epsilon (the fractional period excess of P_superhump
over P_orb). This relation allows mass and radius estimates for the secondary
star in any CV showing superhumps. The consequent mass-radius law shows an
apparent discontinuity in radius near 0.2 M_sol, as predicted by the disrupted
magnetic braking model for the 2.1-2.7 hour period gap. This is effectively the
"empirical main sequence" for CV secondaries.Comment: PDF, 45 pages, 9 tables, 12 figures; accepted, in press, to appear
November 2005, PASP; more info at http://cba.phys.columbia.edu
Serendipitous Kepler observations of a background dwarf nova of SU UMa type
We have discovered a dwarf nova (DN) of type SU UMa in Kepler data which is
7.0 arcsec from the G-type exoplanet survey target KIC 4378554. The DN appears
as a background source in the pixel aperture of the foreground G star. We
extracted only the pixels where the DN is present and observed the source to
undergo five outbursts -- one a superoutburst -- over a timespan of 22 months.
The superoutburst was triggered by a normal outburst, a feature that has been
seen in all DNe superoutburst observed by Kepler. Superhumps during the super
outburst had a period of 1.842+/-0.004 h and we see a transition from
disc-dominated superhump signal to a mix of disc and accretion stream impact.
Predictions of the number of DNe present in Kepler data based on previously
published space densities vary from 0.3 to 258. An investigation of the
background pixels targets would lead to firmer constraints on the space density
of DN.Comment: Accepted for publication in MNRA
Transcriptomic Evidence That Longevity of Acquired Plastids in the Photosynthetic Slugs Elysia timida and Plakobranchus ocellatus Does Not Entail Lateral Transfer of Algal Nuclear Genes
Sacoglossan sea slugs are unique in the animal kingdom in that they sequester and maintain active plastids that they acquire from the siphonaceous algae upon which they feed, making the animals photosynthetic. Although most sacoglossan species digest their freshly ingested plastids within hours, four species from the family Plakobranchidae retain their stolen plastids (kleptoplasts) in a photosynthetically active state on timescales of weeks to months. The molecular basis of plastid maintenance within the cytosol of digestive gland cells in these photosynthetic metazoans is yet unknown but is widely thought to involve gene transfer from the algal food source to the slugs based upon previous investigations of single genes. Indeed, normal plastid development requires hundreds of nuclear-encoded proteins, with protein turnover in photosystem II in particular known to be rapid under various conditions. Moreover, only algal plastids, not the algal nuclei, are sequestered by the animals during feeding. If algal nuclear genes are transferred to the animal either during feeding or in the germ line, and if they are expressed, then they should be readily detectable with deep-sequencing methods. We have sequenced expressed mRNAs from actively photosynthesizing, starved individuals of two photosynthetic sea slug species, Plakobranchus ocellatus Van Hasselt, 1824 and Elysia timida Risso, 1818. We find that nuclear-encoded, algal-derived genes specific to photosynthetic function are expressed neither in P. ocellatus nor in E. timida. Despite their dramatic plastid longevity, these photosynthetic sacoglossan slugs do not express genes acquired from algal nuclei in order to maintain plastid function
Polarized QPOs from the INTEGRAL polar IGRJ14536-5522 (=Swift J1453.4-5524)
We report optical spectroscopy and high speed photometry and polarimetry of
the INTEGRAL source IGRJ14536-5522 (=Swift J1453.4-5524). The photometry,
polarimetry and spectroscopy are modulated on an orbital period of 3.1564(1)
hours. Orbital circularly polarized modulations are seen from 0 to -18 per
cent, unambiguously identifying IGRJ14536-5522 as a polar.
Some of the high speed photometric data show modulations that are consistent
with quasi-periodic oscillations (QPOs) on the order of 5-6 minutes.
Furthermore, for the first time, we detect the (5-6) minute QPOs in the
circular polarimetry. We discuss the possible origins of these QPOs. We also
include details of HIPPO, a new high-speed photo-polarimeter used for some of
our observations.Comment: Accepted for publication by MNRAS. The paper contains 7 figures and 1
tabl
Soft and non-soft structural transitions in disordered nematic networks
Properties of disordered nematic elastomers and gels are theoretically
investigated with emphasis on the roles of non-local elastic interactions and
crosslinking conditions. Networks originally crosslinked in the isotropic phase
lose their long-range orientational order by the action of quenched random
stresses, which we incorporate into the affine-deformation model of nematic
rubber elasticity. We present a detailed picture of mechanical quasi-Goldstone
modes, which accounts for an almost completely soft polydomain-monodomain (P-M)
transition under strain as well as a ``four-leaf clover'' pattern in
depolarized light scattering intensity. Dynamical relaxation of the domain
structure is studied using a simple model. The peak wavenumber of the structure
factor obeys a power-law-type slow kinetics and goes to zero in true mechanical
equilibrium. The effect of quenched disorder on director fluctuation in the
monodomain state is analyzed. The random frozen contribution to the fluctuation
amplitude dominates the thermal one, at long wavelengths and near the P-M
transition threshold. We also study networks obtained by crosslinking
polydomain nematic polymer melts. The memory of initial director configuration
acts as correlated and strong quenched disorder, which renders the P-M
transition non-soft. The spatial distribution of the elastic free energy is
strongly dehomogenized by external strain, in contrast to the case of
isotropically crosslinked networks.Comment: 19 pages, 15 EPS figure
Elevated levels of diesel range organic compounds in groundwater near Marcellus gas operations are derived from surface activities
Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of American 112 (2015): 13184-13189, doi: 10.1073/pnas.1511474112
.Hundreds of organic chemicals are utilized during natural gas extraction via high volume
hydraulic fracturing (HVHF). However, it is unclear if these chemicals, injected into deep
shale horizons, reach shallow groundwater aquifers and impact local water quality, either
from deep underground injection sites or from the surface or shallow subsurface. Here,
we report detectable levels of organic compounds in shallow groundwater samples from
private residential wells overlying the Marcellus Shale in northeastern Pennsylvania.
Analyses of purgeable and extractable organic compounds from 64 groundwater samples
revealed trace levels of volatile organic compounds, well below the Environmental
Protection Agency’s maximum contaminant levels, and low levels of both gasoline range
(GRO; 0-8 ppb) and diesel range organic compounds (DRO; 0-157 ppb). A compound-specific analysis revealed the presence of bis(2-ethylhexyl)phthalate, which is a disclosed
HVHF additive, that was notably absent in a representative geogenic water sample and
field blanks. Pairing these analyses with 1) inorganic chemical fingerprinting of deep
saline groundwater, 2) characteristic noble gas isotopes, and 3) spatial relationships
between active shale gas extraction wells and wells with disclosed environmental health
and safety (EHS) violations, we differentiate between a chemical signature associated
with naturally occurring saline groundwater and a one associated with alternative
anthropogenic routes from the surface (e.g., accidental spills or leaks). The data support a
transport mechanism of DRO to groundwater via accidental release of fracturing fluid
chemicals derived from the surface rather than subsurface flow of these fluids from the
underlying shale formation.The authors thank Duke University’s Pratt School of Engineering
and the National Science Foundation’s CBET Grant Number 1336702 and NSF EAGER
(EAR-1249255) for financial support.2016-04-1
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