24,996 research outputs found
SPH simulations of star/planet formation triggered by cloud-cloud collisions
We present results of hydrodynamic simulations of star formation triggered by
cloud-cloud collisions. During the early stages of star formation, low-mass
objects form by gravitational instabilities in protostellar discs. A number of
these low-mass objects are in the sub-stellar mass range, including a few
objects of planetary mass. The disc instabilities that lead to the formation of
low-mass objects in our simulations are the product of disc-disc interactions
and/or interactions between the discs and their surrounding gas.Comment: 8 pages, 7 figures; accepted for publication in the proceedings of
IAU Symposium 249: Exoplanets: Detection, Formation and Dynamics, Y.-S. Sun,
S. Ferraz-Mello & J.-L. Zhou (eds.), Cambridge University Pres
Use of an audio-paced incremental swimming test in young national-level swimmers
Purpose:To evaluate the reliability and sensitivity to training of an audio-paced incremental swimming test.Methods:Eight young national-level male swimmers (age 15 ± 1 year) performed a 7 × 200-m incremental swimming test (velocities 1.19, 1.24, 1.28, 1.33, 1.39, and 1.45 m/s and maximal sprint pace) using an audio-pacing device. The same test was performed 4 times by each participant, 1 wk apart to assess reliability (WK1, WK2) and after 9 and 20 wk of training (WK9, WK20). Blood lactate concentration ([La−]) and heart rate (HR) were recorded after each stage. Outcome measures were the velocity (v) and HR at lactate markers of 2 mM, 4 mM, and Δ1 mM.Results:Velocities at the lactate markers proved to be more reliable than HR, with typical errors ranging from 0.66% to 2.30% and 1.28% to 4.50%, respectively (shifts in mean ranged –0.91% to 0.73% and –0.84% to 1.79%, respectively). Across WK1, WK9, and WK20 there were significant improvements in peak velocity (P < .001) and each of the velocities associated with the lactate markers (P < .05), whereas only HR at Δ1 mM improved (P < .05).Conclusions:This article demonstrates that an audio-paced incremental swimming test is reliable for use with junior swimmers and is sensitive to changes observed after training. The postswimming measurement of HR in the pool was comparatively less reliable.</jats:sec
Morphology and thermal conductivity of model organic aerogels
The intersection volume of two independent 2-level cut Gaussian random fields
is proposed to model the open-cell microstructure of organic aerogels. The
experimentally measured X-ray scattering intensity, surface area and solid
thermal conductivity of both polymeric and colloidal organic aerogels can be
accounted for by the model.Comment: 5 pages. RevTex with 4 encapsulated figures. Higher resolution
figures have been submitted for publication. To be published in Phys. Rev. E
(Rapid Comm.). email, [email protected]
Apparent multiple Delta m^2_32 in muon anti-neutrino and muon neutrino survival oscillations from non-standard interaction matter effect
Neutrinos propagating through matter may participate in forward coherent
neutral-current-like scattering arising from non-standard interactions as well
as from the Mikheyev-Smirnov-Wolfenstein matter potential . We show that
at fixed long baselines through matter of constant density, the non-standard
interaction potential can contribute an additional
term to the oscillation phase whose sign differs for \anumu versus \numu
propagation in matter. Its presence can cause different apparent
to be erroneously inferred on the basis of oscillations in vacuum, with values
lying above (for \anumu) or below (for \numu) the actual
for the case where is predominantly real-valued and of
sign opposite to . An NSI scenario invoking only
is shown to be capable of accounting for a disparity
recently reported between oscillation survival for \anumu and \numu fluxes
measured at by the MINOS experiment. Implications for mantle
traversal by atmospheric neutrinos are examined. The NSI matter potential with
non-maximal mixing could evade conventional atmospheric neutrino analyses which
do not distinguish \numu from \anumu on an event-by-event basis.Comment: 7 pages, 5 figures. Accepted for publication in Physical Review
On the evolution of the density pdf in strongly self-gravitating systems
The time evolution of the probability density function (PDF) of the mass
density is formulated and solved for systems in free-fall using a simple
appoximate function for the collapse of a sphere. We demonstrate that a
pressure-free collapse results in a power-law tail on the high-density side of
the PDF. The slope quickly asymptotes to the functional form
for the (volume-weighted) PDF and
for the corresponding mass-weighted
distribution. From the simple approximation of the PDF we derive analytic
descriptions for mass accretion, finding that dynamically quiet systems with
narrow density PDFs lead to retarded star formation and low star formation
rates. Conversely, strong turbulent motions that broaden the PDF accelerate the
collapse causing a bursting mode of star formation. Finally, we compare our
theoretical work with observations. The measured star formation rates are
consistent with our model during the early phases of the collapse. Comparison
of observed column density PDFs with those derived from our model suggests that
observed star-forming cores are roughly in free-fall.Comment: accepted for publication, 13 page
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Implantation of a leadless pacemaker in a pediatric patient with congenital heart disease.
Experimental program for real gas flow code validation at NASA Ames Research Center
The experimental program for validating real gas hypersonic flow codes at NASA Ames Rsearch Center is described. Ground-based test facilities used include ballistic ranges, shock tubes and shock tunnels, arc jet facilities and heated-air hypersonic wind tunnels. Also included are large-scale computer systems for kinetic theory simulations and benchmark code solutions. Flight tests consist of the Aeroassist Flight Experiment, the Space Shuttle, Project Fire 2, and planetary probes such as Galileo, Pioneer Venus, and PAET
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