3,383 research outputs found
Kinetic rate constants for the formation of trihalomethanes in chlorinated ammonia containing ground water
It is well established that trihalomethanes, in drinking water are byproducts of chlorine disinfection. A method to predict the distribution and concentration of trihalornethanes is important because of health risks associated with chronic exposure to these compounds. A literature review has provided information on the chemistry of water chlorination and a data base developed in the laboratory has provided data on trihalomethane formation under various conditions. These data were used to generate rate constants for the formation of trihalomethanes.
Trihalornethane formation kinetics appeared to be influenced primarily by the presence of ammonia. The influence of pH is not as profound as indicated in literature. The rate of formation is low at and before breakpoint, whereas it increases after breakpoint
The Fine Line Between Normal and Starburst Galaxies
Recent literature suggests that there are two modes through which galaxies
grow their stellar mass - a normal mode characterized by quasi-steady star
formation, and a highly efficient starburst mode possibly triggered by
stochastic events such as galaxy mergers. While these differences are
established for extreme cases, the population of galaxies in-between these two
regimes is poorly studied and it is not clear where the transition between
these two modes of star formation occurs. We utilize ALMA observations of the
CO J=3-2 line luminosity in a sample of 20 infrared luminous galaxies that lie
in the intermediate range between normal and starburst galaxies at z ~ 0.25-0.6
in the COSMOS field to examine the gas content and star formation efficiency of
these galaxies. We compare these quantities to the galaxies' deviation from the
well-studied "main sequence" correlation between star formation rate and
stellar mass (MS) and find that at log() < 0.6, a galaxy's
distance to the main sequence is mostly driven by increased gas content, and
not a more efficient star formation process.Comment: 21 pages, 10 figure
Compendium-Wide Analysis of Pseudomonas aeruginosa Core and Accessory Genes Reveals Transcriptional Patterns across Strains PAO1 and PA14.
Pseudomonas aeruginosa is an opportunistic pathogen that causes difficult-to-treat infections. Two well-studied divergent P. aeruginosa strain types, PAO1 and PA14, have significant genomic heterogeneity, including diverse accessory genes present in only some strains. Genome content comparisons find core genes that are conserved across both PAO1 and PA14 strains and accessory genes that are present in only a subset of PAO1 and PA14 strains. Here, we use recently assembled transcriptome compendia of publicly available P. aeruginosa RNA sequencing (RNA-seq) samples to create two smaller compendia consisting of only strain PAO1 or strain PA14 samples with each aligned to their cognate reference genome. We confirmed strain annotations and identified other samples for inclusion by assessing each sample\u27s median expression of PAO1-only or PA14-only accessory genes. We then compared the patterns of core gene expression in each strain. To do so, we developed a method by which we analyzed genes in terms of which genes showed similar expression patterns across strain types. We found that some core genes had consistent correlated expression patterns across both compendia, while others were less stable in an interstrain comparison. For each accessory gene, we also determined core genes with correlated expression patterns. We found that stable core genes had fewer coexpressed neighbors that were accessory genes. Overall, this approach for analyzing expression patterns across strain types can be extended to other groups of genes, like phage genes, or applied for analyzing patterns beyond groups of strains, such as samples with different traits, to reveal a deeper understanding of regulation
The Evolution of the Galaxy Stellar Mass Function at z= 4-8: A Steepening Low-mass-end Slope with Increasing Redshift
We present galaxy stellar mass functions (GSMFs) at 4-8 from a
rest-frame ultraviolet (UV) selected sample of 4500 galaxies, found via
photometric redshifts over an area of 280 arcmin in the CANDELS/GOODS
fields and the Hubble Ultra Deep Field. The deepest Spitzer/IRAC data
yet-to-date and the relatively large volume allow us to place a better
constraint at both the low- and high-mass ends of the GSMFs compared to
previous space-based studies from pre-CANDELS observations. Supplemented by a
stacking analysis, we find a linear correlation between the rest-frame UV
absolute magnitude at 1500 \AA\ () and logarithmic stellar mass
() that holds for galaxies with . We
use simulations to validate our method of measuring the slope of the - relation, finding that the bias is minimized with a hybrid
technique combining photometry of individual bright galaxies with stacked
photometry for faint galaxies. The resultant measured slopes do not
significantly evolve over 4-8, while the normalization of the trend
exhibits a weak evolution toward lower masses at higher redshift. We combine
the - distribution with observed rest-frame UV luminosity
functions at each redshift to derive the GSMFs, finding that the low-mass-end
slope becomes steeper with increasing redshift from
at to at
. The inferred stellar mass density, when integrated over
-, increases by a factor of
between and and is in good agreement with the time integral of the
cosmic star formation rate density.Comment: 27 pages, 17 figures, ApJ, in pres
ZFOURGE: Using Composite Spectral Energy Distributions to Characterize Galaxy Populations at 1<z<4
We investigate the properties of galaxies as they shut off star formation
over the 4 billion years surrounding peak cosmic star formation. To do this we
categorize galaxies from into groups based on the shape
of their spectral energy distributions (SEDs) and build composite SEDs with
resolution. These composite SEDs show a variety of spectral shapes
and also show trends in parameters such as color, mass, star formation rate,
and emission line equivalent width. Using emission line equivalent widths and
strength of the 4000\AA\ break, , we categorize the composite SEDs
into five classes: extreme emission line, star-forming, transitioning,
post-starburst, and quiescent galaxies. The transitioning population of
galaxies show modest H emission (\AA) compared to
more typical star-forming composite SEDs at
(\AA). Together with their smaller sizes (3 kpc vs. 4 kpc)
and higher S\'ersic indices (2.7 vs. 1.5), this indicates that morphological
changes initiate before the cessation of star formation. The transitional group
shows a strong increase of over one dex in number density from to
, similar to the growth in the quiescent population, while
post-starburst galaxies become rarer at . We calculate average
quenching timescales of 1.6 Gyr at and 0.9 Gyr at and
conclude that a fast quenching mechanism producing post-starbursts dominated
the quenching of galaxies at early times, while a slower process has become
more common since .Comment: Accepted for publication in The Astrophysical Journa
A Turnover in the Galaxy Main Sequence of Star Formation at for Redshifts
The relationship between galaxy star formation rates (SFR) and stellar masses
() is re-examined using a mass-selected sample of 62,000
star-forming galaxies at in the COSMOS 2-deg field. Using new
far-infrared photometry from -PACS and SPIRE and -MIPS 24
m, along with derived infrared luminosities from the NRK method based on
galaxies' locations in the restframe color-color diagram vs. , we are able to more accurately determine total SFRs for our complete
sample. At all redshifts, the relationship between median and
follows a power-law at low stellar masses, and flattens to nearly constant SFR
at high stellar masses. We describe a new parameterization that provides the
best fit to the main sequence and characterizes the low mass power-law slope,
turnover mass, and overall scaling. The turnover in the main sequence occurs at
a characteristic mass of about at all redshifts.
The low mass power-law slope ranges from 0.9-1.3 and the overall scaling rises
in SFR as a function of . A broken power-law fit below
and above the turnover mass gives relationships of below the turnover mass and above
the turnover mass. Galaxies more massive than have on average, a much lower specific star formation rate (sSFR) than
would be expected by simply extrapolating the traditional linear fit to the
main sequence found for less massive galaxies.Comment: 16 pages, 7 figures. Accepted for publication in Ap
Transmission of antibiotic resistance at the wildlife-livestock interface
Antibiotic-resistant microorganisms (ARMs) are widespread in natural environments, animals (wildlife and livestock), and humans, which has reduced our capacity to control life threatening infectious disease. Yet, little is known about their transmission pathways, especially at the wildlife-livestock interface. This study investigated the potential transmission of ARMs and antibiotic resistance genes (ARGs) between cattle and wildlife by comparing gut microbiota and ARG profiles of feral swine (Sus scrofa), coyotes (Canis latrans), cattle (Bos taurus), and environmental microbiota. Unexpectedly, wild animals harbored more abundant ARMs and ARGs compared to grazing cattle. Gut microbiota of cattle was significantly more similar to that of feral swine captured within the cattle grazing area where the home range of both species overlapped substantially. In addition, ARMs against medically important antibiotics were more prevalent in wildlife than grazing cattle, suggesting that wildlife could be a source of ARMs colonization in livestock
Universal corrections to the Fermi-liquid theory
We show that the singularities in the dynamical bosonic response functions of
a generic 2D Fermi liquid give rise to universal, non-analytic corrections to
the Fermi-liquid theory. These corrections yield a term in the specific
heat, terms in the effective mass and the uniform spin susceptibility
, and term in . The existence of these
terms has been the subject of recent controversy, which is resolved in this
paper. We present exact expressions for all non-analytic terms to second order
in a generic interaction and show that only U(0) and matter.Comment: references added, a typo correcte
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