12,082 research outputs found
Luminosity Density of Galaxies and Cosmic Star Formation Rate from Lambda-CDM Hydrodynamical Simulations
We compute the cosmic star formation rate (SFR) and the rest-frame comoving
luminosity density in various pass-bands as a function of redshift using
large-scale \Lambda-CDM hydrodynamical simulations with the aim of
understanding their behavior as a function of redshift. To calculate the
luminosity density of galaxies, we use an updated isochrone synthesis model
which takes metallicity variations into account. The computed SFR and the
UV-luminosity density have a steep rise from z=0 to 1, a moderate plateau
between z=1 - 3, and a gradual decrease beyond z=3. The raw calculated results
are significantly above the observed luminosity density, which can be explained
either by dust extinction or the possibly inappropriate input parameters of the
simulation. We model the dust extinction by introducing a parameter f; the
fraction of the total stellar luminosity (not galaxy population) that is
heavily obscured and thus only appears in the far-infrared to sub-millimeter
wavelength range. When we correct our input parameters, and apply dust
extinction with f=0.65, the resulting luminosity density fits various
observations reasonably well, including the present stellar mass density, the
local B-band galaxy luminosity density, and the FIR-to-submm extragalactic
background. Our result is consistent with the picture that \sim 2/3 of the
total stellar emission is heavily obscured by dust and observed only in the
FIR. The rest of the emission is only moderately obscured which can be observed
in the optical to near-IR wavelength range. We also argue that the steep
falloff of the SFR from z=1 to 0 is partly due to the shock-heating of the
universe at late times, which produces gas which is too hot to easily condense
into star-forming regions.Comment: 25 pages, 6 figures. Accepted version in ApJ. Substantially revised
from the previous version. More emphasis on the comparison with various
observations and the hidden star formation by dust extinctio
Operating experience with four 200 kW Mod-0A wind turbine generators
The windpowered generator, Mod-0A, and its advantages and disadvantages, particularly as it affects reliability, are discussed. The machine performance with regard to power availability and power output is discussed
New Zealand Agribusiness Success: An Approach to exploring the role of strategy, structure and conduct on firm performance
This paper presents a framework to explore agribusiness success in New Zealand. The framework provides the basis for historical analysis. It draws on existing theory based on the structure-conduct-performance paradigm but expanded to take account of firm strategy and the analysis of value chains.Agribusiness, structure, conduct, performance, history, Agribusiness,
The IRAS 1-Jy Survey of Ultraluminous Infrared Galaxies: I. The sample and Luminosity Function
A complete flux-limited sample of 118 ultraluminous infrared galaxies (ULIGs)
has been identified from the IRAS Faint Source Catalog (FSC). The selection
criteria were a 60 micron flux density greater than 1 Jy in a region of the sky
delta > -40 deg, |b| > 30 deg. All sources were subsequently reprocessed using
coadded IRAS maps in order to obtain the best available flux estimates in all
four IRAS wavelength bands. The maximum observed infrared luminosity is L_ir =
10^{12.90} L_{sun}, and the maximum redshift is z = 0.268. The luminosity
function for ULIGs over the decade luminosity range L_ir = 10^{12} - 10^{13}
L_{sun} can be approximated by a power law Phi (L) ~= L^{-2.35} Mpc^{-3}
mag^{-1}. In the local Universe z < 0.1, the space density of ULIGs appears to
be comparable to or slightly larger than that of optically selected QSOs at
comparable bolometric luminosities. A maximum likelihood test suggests strong
evolution for our sample; assuming density evolution proportional to
(1+z)^{alpha} we find alpha = 7.6+/-3.2. Examination of the two-point
correlation function shows a barely significant level of clustering, xi (r) =
1.6 +/- 1.2, on size scales r ~= 22 h^{-1} Mpc.Comment: 18 pages of text, 10 pages of figures 1 to 6, 6 pages of tables 1 to
3, ApJS accepte
PIN9 LENGTH OF STAY AND COSTS ASSOCIATED WITH SURGICAL SITE INFECTIONS IN COLON PROCEDURES IN A LARGE U.S. DATABASE
The Power Spectrum of the PSC Redshift Survey
We measure the redshift-space power spectrum P(k) for the recently completed
IRAS Point Source Catalogue (PSC) redshift survey, which contains 14500
galaxies over 84% of the sky with 60 micron flux >= 0.6 Jansky. Comparison with
simulations shows that our estimated errors on P(k) are realistic, and that
systematic errors due to the finite survey volume are small for wavenumbers k
>~ 0.03 h Mpc^-1. At large scales our power spectrum is intermediate between
those of the earlier QDOT and 1.2 Jansky surveys, but with considerably smaller
error bars; it falls slightly more steeply to smaller scales. We have fitted
families of CDM-like models using the Peacock-Dodds formula for non-linear
evolution; the results are somewhat sensitive to the assumed small-scale
velocity dispersion \sigma_V. Assuming a realistic \sigma_V \approx 300 km/s
yields a shape parameter \Gamma ~ 0.25 and normalisation b \sigma_8 ~ 0.75; if
\sigma_V is as high as 600 km/s then \Gamma = 0.5 is only marginally excluded.
There is little evidence for any `preferred scale' in the power spectrum or
non-Gaussian behaviour in the distribution of large-scale power.Comment: Latex, uses mn.sty, 14 pages including 11 Postscript figures.
Accepted by MNRA
Fracture resistance of human roots filled with mineral trioxide aggregate mixed with phosphate‐buffered saline, with and without calcium hydroxide pre‐medication
Moving Forward 21st Century Pathways to Strengthen the Ocean Science Workforce Through Graduate Education and Professional Development
The scope of emerging national and international ocean-related issues facing society demands that we develop broad perspectives on graduate education and training in the ocean sciences. A multifaceted ocean workforce and new kinds of intellectual partnerships are needed to address ocean science research priorities, strengthen our understanding of coupled human-natural ocean systems, engage and inform public policy and management decision making, and increase ocean literacy. Alumni from graduate programs in ocean sciences are following diverse career paths in academia, government, nongovernmental organizations, and industry, and thus can inform us about the diverse skills needed to succeed. The ocean science academic community should build on its current strengths (e.g., multidisciplinary and multi-institutional research and education, international partnerships), and capitalize on what some might view as limitations (e.g., remote, yet inviting, coastal campuses, diversity of ocean science programs), to become an incubator of innovation that will advance the field and strengthen graduate education and training. Partnerships within and among institutions with ocean-related programs, and with professional societies, employers, and others, can help us provide cutting-edge, relevant academic options, facilitate professional development, and proactively position graduates for career paths that reflect and address important societal needs
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