4,105 research outputs found
Gender and Race Wage Gaps Attributable to Obesity
Currently, two out of three Americans are overweight or obese. In less than 20 years, roughly half of the population will be obese. Furthermore, obesity costs 48-66 billion per year. The societal costs of obesity are clear and staggering and the individual costs are equally chilling for most of those who are obese – particularly for Hispanic men and Caucasian and Hispanic women
Fischer-Tropsch-Type Production of Organic Materials in the Solar Nebula: Studies Using Graphite Catalysts and Measuring the Trapping of Noble Gases
The formation of abundant carbonaceous material in meteorites is a long standing problem and an important factor in the debate on the potential for the origin of life in other stellar systems. The Fischer-Tropsch-type (FTT) catalytic reduction of CO by hydrogen was once the preferred model for production of organic materials in the primitive solar nebula. We have demonstrated that many grain surfaces can catalyze both FTT and HB-type reactions, including amorphous iron and magnesium silicates, pure silica smokes as well as several minerals. Graphite is not a particularly good FTT catalyst, especially compared to iron powder or to amorphous iron silicate. However, like other silicates that we have studied, it gets better with exposure to CO. N2 and H2 over time: e.g., after formation of a macromolecular carbonaceous layer on the surfaces of the underlying gains. While amorphous iron silicates required only 1 or 2 experimental runs to achieve steady state reaction rates, graphite only achieved steady state after 6 or more experiments. We will present results showing the catalytic action of graphite grains increasing with increasing number of experiments and will also discuss the nature of the final "graphite" grains aster completion of our experiments
The Evolution of Early-type Field Galaxies Selected from a NICMOS Map of the Hubble Deep Field North
The redshift distribution of well-defined samples of distant early-type
galaxies offers a means to test the predictions of monolithic and hierarchical
galaxy formation scenarios. NICMOS maps of the entire Hubble Deep Field North
in the F110W and F160W filters, when combined with the available WFPC2 data,
allow us to calculate photometric redshifts and determine the morphological
appearance of galaxies at rest-frame optical wavelengths out to z ~ 2.5. Here
we report results for two subsamples of early-type galaxies, defined primarily
by their morphologies in the F160W band, which were selected from the NICMOS
data down to H160_{AB} < 24.0. The observed redshift distributions of our two
early-type samples do not match that predicted by a monolithic collapse model,
which shows an overabundance at z > 1.5. A hierarchical formation model better
matches the redshift distribution of the HDF-N early-types at z > 1.5, but
still does not adequately describe the observed early-types. The hierarchical
model predicts significantly bluer colors on average than the observed
early-type colors, and underpredicts the observed number of early-types at z <
1. [abridged]Comment: Accepted for publication in the Astronomical Journal; 54 pages, 21
figures. Figures 10 and 11 are included separately in JPEG forma
The Hubble Ultra Deep Field
This paper presents the Hubble Ultra Deep Field (HUDF), a one million second
exposure of an 11 square minute-of-arc region in the southern sky with the
Hubble Space Telescope. The exposure time was divided among four filters, F435W
(B435), F606W (V606), F775W (i775), and F850LP (z850), to give approximately
uniform limiting magnitudes mAB~29 for point sources. The image contains at
least 10,000 objects presented here as a catalog. Few if any galaxies at
redshifts greater than ~4 resemble present day spiral or elliptical galaxies.
Using the Lyman break dropout method, we find 504 B-dropouts, 204 V-dropouts,
and 54 i-dropouts. Using these samples that are at different redshifts but
derived from the same data, we find no evidence for a change in the
characteristic luminosity of galaxies but some evidence for a decrease in their
number densities between redshifts of 4 and 7. The ultraviolet luminosity
density of these samples is dominated by galaxies fainter than the
characteristic luminosity, and the HUDF reveals considerably more luminosity
than shallower surveys. The apparent ultraviolet luminosity density of galaxies
appears to decrease from redshifts of a few to redshifts greater than 6. The
highest redshift samples show that star formation was already vigorous at the
earliest epochs that galaxies have been observed, less than one billion years
after the Big Bang.Comment: 44 pages, 18 figures, to appear in the Astronomical Journal October
200
Morphologies and Spectral Energy Distributions of Extremely Red Galaxies in the GOODS-South Field
Using U'- through Ks-band imaging data in the GOODS-South field, we construct
a large, complete sample of 275 ``extremely red objects'' (EROs; K_s<22.0,
R-K_s>3.35; AB), all with deep HST/ACS imaging in B_435, V_606, i_775, and
z_850, and well-calibrated photometric redshifts. Quantitative concentration
and asymmetry measurements fail to separate EROs into distinct morphological
classes. We therefore visually classify the morphologies of all EROs into four
broad types: ``Early'' (elliptical-like), ``Late'' (disk galaxies),
``Irregular'' and ``Other'' (chain galaxies and low surface brightness
galaxies), and calculate their relative fractions and comoving space densities.
For a broad range of limiting magnitudes and color thresholds, the relative
number of early-type EROs is approximately constant at 33-44%, and the comoving
space densities of Early- and Late-type EROs are comparable. Mean rest-frame
spectral energy distributions (SEDs) at wavelengths between 0.1 and 1.2 um are
constructed for all EROs. The SEDs are extremely similar in their range of
shapes, independent of morphological type. The implication is that any
differences between the broad-band SEDs of Early-type EROs and the other types
are relatively subtle, and there is no robust way of photometrically
distinguishing between different morphological types with usual
optical/near-infrared photometry.Comment: Submitted to the ApJL. A version with full-resolution figures, all
GOODS data and all GOODS collaboration papers may be found at
http://www.stsci.edu/science/goods
Clumpy Galaxies in CANDELS. I. The Definition of UV Clumps and the Fraction of Clumpy Galaxies at 0.5<z<3
Although giant clumps of stars are crucial to galaxy formation and evolution,
the most basic demographics of clumps are still uncertain, mainly because the
definition of clumps has not been thoroughly discussed. In this paper, we study
the basic demographics of clumps in star-forming galaxies (SFGs) at 0.5<z<3,
using our proposed physical definition that UV-bright clumps are discrete
star-forming regions that individually contribute more than 8% of the
rest-frame UV light of their galaxies. Clumps defined this way are
significantly brighter than the HII regions of nearby large spiral galaxies,
either individually or blended, when physical spatial resolution and
cosmological dimming are considered. Under this definition, we measure the
fraction of SFGs that contain at least one off-center clump (Fclumpy) and the
contributions of clumps to the rest-frame UV light and star formation rate of
SFGs in the CANDELS/GOODS-S and UDS fields, where our mass-complete sample
consists of 3239 galaxies with axial ratio q>0.5. The redshift evolution of
Fclumpy changes with the stellar mass (M*) of the galaxies. Low-mass
(log(M*/Msun)<9.8) galaxies keep an almost constant Fclumpy of about 60% from
z~3.0 to z~0.5. Intermediate-mass and massive galaxies drop their Fclumpy from
55% at z~3.0 to 40% and 15%, respectively, at z~0.5. We find that (1) the trend
of disk stabilization predicted by violent disk instability matches the Fclumpy
trend of massive galaxies; (2) minor mergers are a viable explanation of the
Fclumpy trend of intermediate-mass galaxies at z<1.5, given a realistic
observability timescale; and (3) major mergers are unlikely responsible for the
Fclumpy trend in all masses at z<1.5. The clump contribution to the rest-frame
UV light of SFGs shows a broad peak around galaxies with log(M*/Msun)~10.5 at
all redshifts, possibly linked to the molecular gas fraction of the galaxies.
(Abridged)Comment: 22 pages, 15 figures. Appeared in ApJ (2015, 800, 39). A few typos
correcte
WFPC2 Observations of the Hubble Deep Field-South
The Hubble Deep Field-South observations targeted a high-galactic-latitude
field near QSO J2233-606. We present WFPC2 observations of the field in four
wide bandpasses centered at roughly 300, 450, 606, and 814 nm. Observations,
data reduction procedures, and noise properties of the final images are
discussed in detail. A catalog of sources is presented, and the number counts
and color distributions of the galaxies are compared to a new catalog of the
HDF-N that has been constructed in an identical manner. The two fields are
qualitatively similar, with the galaxy number counts for the two fields
agreeing to within 20%. The HDF-S has more candidate Lyman-break galaxies at z
> 2 than the HDF-N. The star-formation rate per unit volume computed from the
HDF-S, based on the UV luminosity of high-redshift candidates, is a factor of
1.9 higher than from the HDF-N at z ~ 2.7, and a factor of 1.3 higher at z ~ 4.Comment: 93 pages, 25 figures; contains very long table
Reconstruction of the diapsid ancestral genome permits chromosome evolution tracing in avian and non-avian dinosaurs
The file attached is the Published/publisher’s pdf version of the article.Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.NHM Repositor
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