10,797 research outputs found
Toxicity of materials in fire situations: Laboratory data obtained at the University of San Francisco
Approximately 300 materials were evaluated using a specific set of test conditions. Materials tested included wood, fibers, fabrics and synthetic polymers. Data obtained using 10 different sets of test conditions are presented
PC1643+4631A,B: The Lyman-Alpha Forest at the Edge of Coherence
This is the first measurement and detection of coherence in the intergalactic
medium (IGM) at substantially high redshift (z~3.8) and on large physical
scales (~2.5 h^-1 Mpc). We perform the measurement by presenting new
observations from Keck LRIS of the high redshift quasar pair PC 1643+4631A, B
and their Ly-alpha absorber coincidences. This experiment extends multiple
sightline quasar absorber studies to higher redshift, higher opacity, larger
transverse separation, and into a regime where coherence across the IGM becomes
weak and difficult to detect. We fit 222 discrete Ly-alpha absorbers to
sightline A and 211 to sightline B. Relative to a Monte Carlo pairing test
(using symmetric, nearest neighbor matching) the data exhibit a 4sigma excess
of pairs at low velocity splitting (<150 km/s), thus detecting coherence on
transverse scales of ~2.5 h^-1 Mpc. We use spectra extracted from an SPH
simulation to analyze symmetric pair matching, transmission distributions as a
function of redshift and compute zero-lag cross-correlations to compare with
the quasar pair data. The simulations agree with the data with the same
strength (~4sigma) at similarly low velocity splitting above random chance
pairings. In cross-correlation tests, the simulations agree when the mean flux
(as a function of redshift) is assumed to follow the prescription given by
Kirkman et al. (2005). While the detection of flux correlation (measured
through coincident absorbers and cross-correlation amplitude) is only
marginally significant, the agreement between data and simulations is
encouraging for future work in which even better quality data will provide the
best insight into the overarching structure of the IGM and its understanding as
shown by SPH simulations.Comment: 15 pages, 11 figures; accepted for publication in Astronomical
Journa
Active Carbon and Oxygen Shell Burning Hydrodynamics
We have simulated 2.5 s of the late evolution of a star with full hydrodynamic behavior. We present the first simulations
of a multiple-shell burning epoch, including the concurrent evolution and
interaction of an oxygen and carbon burning shell. In addition, we have evolved
a 3D model of the oxygen burning shell to sufficiently long times (300 s) to
begin to assess the adequacy of the 2D approximation. We summarize striking new
results: (1) strong interactions occur between active carbon and oxygen burning
shells, (2) hydrodynamic wave motions in nonconvective regions, generated at
the convective-radiative boundaries, are energetically important in both 2D and
3D with important consequences for compositional mixing, and (3) a spectrum of
mixed p- and g-modes are unambiguously identified with corresponding adiabatic
waves in these computational domains. We find that 2D convective motions are
exaggerated relative to 3D because of vortex instability in 3D. We discuss the
implications for supernova progenitor evolution and symmetry breaking in core
collapse.Comment: 5 pages, 4 figures in emulateapj format. Accepted for publication in
ApJ Letters. High resolution figure version available at
http://spinach.as.arizona.ed
A Review of the Relationship of the ENC and DNC Hydrographic Vector Data Products
This document discusses the level of harmonization between the S-57 and DIGEST standards and the relationship between the ENC and DNC products. It is shown that the military and regulated commercial navigation have different needs, and that it is natural to have two different standards. However, in those areas where the needs overlap the standards should be equivalent. Commercial navigation requires "official" data whereas the military require a broad range of the "best available data". These needs are complementary. At the content level ENC data can be a pure subset of DNC data, however additional harmonization is required to achieve this
The Impact of Hydrodynamic Mixing on Supernova Progenitors
Recent multidimensional hydrodynamic simulations have demonstrated the
importance of hydrodynamic motions in the convective boundary and radiative
regions of stars to transport of energy, momentum, and composition. The impact
of these processes increases with stellar mass. Stellar models which
approximate this physics have been tested on several classes of observational
problems. In this paper we examine the implications of the improved treatment
on supernova progenitors. The improved models predict substantially different
interior structures. We present pre-supernova conditions and simple explosion
calculations from stellar models with and without the improved mixing treatment
at 23 solar masses. The results differ substantially.Comment: 12 pages, 2 figures, accepted for publication in the Astrophysical
Journal Letter
Near-Infrared MOSFIRE Spectra of Dusty Star-Forming Galaxies at 0.2<z<4
We present near-infrared and optical spectroscopic observations of a sample
of 450m and 850m-selected dusty star-forming galaxies (DSFGs)
identified in a 400 arcmin area in the COSMOS field. Thirty-one sources of
the 102 targets were spectroscopically confirmed at , identified
primarily in the near-infrared with Keck MOSFIRE and some in the optical with
Keck LRIS and DEIMOS. The low rate of confirmation is attributable both to high
rest-frame optical obscuration in our targets and limited sensitivity to
certain redshift ranges. The high-quality photometric redshifts available in
the COSMOS field allow us to test the robustness of photometric redshifts for
DSFGs. We find a subset (11/31%) of DSFGs with inaccurate () or non-existent photometric redshifts; these have very distinct
spectral energy distributions from the remaining DSFGs, suggesting a decoupling
of highly obscured and unobscured components. We present a composite rest-frame
4300--7300\AA\ spectrum for DSFGs, and find evidence of 20030 km s
gas outflows. Nebular line emission for a sub-sample of our detections indicate
that hard ionizing radiation fields are ubiquitous in high-z DSFGs, even more
so than typical mass or UV-selected high-z galaxies. We also confirm the
extreme level of dust obscuration in DSFGs, measuring very high Balmer
decrements, and very high ratios of IR to UV and IR to H luminosities.
This work demonstrates the need to broaden the use of wide bandwidth technology
in the millimeter to the spectroscopic confirmations of large samples of high-z
DSFGs, as the difficulty in confirming such sources at optical/near-infrared
wavelengths is exceedingly challenging given their obscuration.Comment: 14 pages, 13 figures, ApJ accepted. Composite DSFG Halpha spectrum
available at www.as.utexas.edu/~cmcasey/downloads.htm
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