359 research outputs found
Cosmological Implications of Lyman-Break Galaxy Clustering
We review our analysis of the clustering properties of ``Lyman-break''
galaxies (LBGs) at redshift z~3, previously discussed in Wechsler et al (1998).
We examine the likelihood of spikes found by Steidel et al (1998) in the
redshift distribution of LBGs, within a suite of models for the evolution of
structure in the Universe. Using high-resolution dissipationless N-body
simulations, we analyze deep pencil-beam surveys from these models in the same
way that they are actually observed, identifying LBGs with the most massive
dark matter halos. We find that all the models (with SCDM as a marginal
exception) have a substantial probability of producing spikes similar to those
observed, because the massive halos are much more clumped than the underlying
matter -- i.e., they are biased. Therefore, the likelihood of such a spike is
not a good discriminator among these models. The LBG correlation functions are
less steep than galaxies today (gamma~1.4), but show similar or slightly longer
correlation lengths. We have extened this analysis and include a preliminary
comparison to the new data presented in Adelberger et al (1998). We also
discuss work in progress, in which we use semi-analytic models to identify
Lyman-break galaxies within dark-matter halos.Comment: 4 pages, 2 figures, Latex, uses aipproc.sty; to appear in the
proceedings of the 9th Annual October Maryland Astrophysics Conference,
"After the Dark Ages: When the Galaxies Were Young (the Universe at 2<z<5)
Clusters in Various Cosmological Models: Abundance and Evolution
The combination of measurements of the local abundance of rich clusters of
galaxies and its evolution to higher redshift offers the possibility of a
direct measurement of with little contribution from other
cosmological parameters. We investigate the significance of recent claims that
this evolution indicates that must be small. The most recent cluster
velocity dispersion function from a compilation including the ESO Northern
Abell Cluster Survey (ENACS) results in a significantly higher normalization
for models, corresponding to for , compared
to the Eke, Cole, & Frenk result of . Using the ENACS
data for a calibration results in strong evolution in the abundance of
clusters, and we find that the velocity dispersion function is consistent with
. The results are dependent upon the choice and analysis of
low-redshift and high-redshift data, so at present, the data is not good enough
to determine unambiguously.Comment: 4 pages Latex using sprocl.sty, 1 figure. To appear in Proceedings of
12th Potsdam Cosmology Workshop, "Large-Scale Structure: Tracks and Traces"
Sept. 15-19, 199
Plant essential oils synergize various pyrethroid insecticides and antagonize malathion in Aedes aegypti
Pyrethroid resistance is a significant threat to agricultural, urban and public health pest control activities. Because economic incentives for the production of novel active ingredients for the control of public health pests are lacking, this field is particularly affected by the potential failure of pyrethroid‐based insecticides brought about by increasing pyrethroid resistance. As a result, innovative approaches are desperately needed to overcome insecticide resistance, particularly in mosquitoes that transmit deadly and debilitating pathogens. Numerous studies have demonstrated the potential of plant essential oils to enhance the efficacy of pyrethroids. The toxicity of pyrethroids combined with plant oils is significantly greater than the baseline toxicity of either oils or pyrethroids applied alone, which suggests there are synergistic interactions between components of these mixtures. The present study examined the potential of eight plant essential oils applied in one of two concentrations (1% and 5%) to enhance the toxicity of various pyrethroids (permethrin, natural pyrethrins, deltamethrin and β‐cyfluthrin). The various plant essential oils enhanced the pyrethroids to differing degrees. The levels of enhancement provided by combinations of plant essential oils and pyrethroids in comparison with pyrethroids alone were calculated and synergistic outcomes characterized. Numerous plant essential oils significantly synergized a variety of pyrethroids; type I pyrethroids were synergized to a greater degree than type II pyrethroids. Eight plant essential oils significantly enhanced 24‐h mortality rates provided by permethrin and six plant essential oils enhanced 24‐h mortality rates obtained with natural pyrethrins. By contrast, only three plant essential plants significantly enhanced the toxicity of deltamethrin and β‐cyfluthrin. Of the plant essential oils that enhanced the toxicity of these pyrethroids, some produced varying levels of synergism and antagonism. Geranium, patchouli and Texas cedarwood oils produced the highest levels of synergism, displaying co‐toxicity factors of \u3e 100 in some combinations. To assess the levels of enhancement and synergism of other classes of insecticide, malathion was also applied in combination with the plant oils. Significant antagonism was provided by a majority of the plant essential oils applied in combination with this insecticide, which suggests that plant essential oils may act to inhibit the oxidative activation processes within exposed adult mosquitoes
CDM-Variant Cosmological Models - I: Simulations and Preliminary Comparisons
We present two matched sets of five simulations each, covering five presently
favored simple modifications to the standard cold dark matter (CDM) scenario.
One simulation suite, with a linear box size of 75 Mpc/h, is designed for high
resolution and good statistics on the group/poor cluster scale, and the other,
with a box size of 300 Mpc/h, is designed for good rich cluster statistics. All
runs had 57 million cold particles, and models with massive neutrinos had an
additional 113 million hot particles. We consider separately models with
massive neutrinos, tilt, curvature, and a nonzero cosmological constant in
addition to the standard CDM model. We find that our tilted
Omega+Omega_Lambda=1 (TLCDM) model produces too much small-scale power by a
factor of ~3, and our open Lambda=0 (OCDM) model also exceeds observed
small-scale power by a factor of 2. In addition, we take advantage of the large
dynamic range in detectable halo masses our simulations allow to check the
shape of the Press-Schechter approximation. We find good fits at cluster masses
for delta_c=1.27--1.35 for a Gaussian filter and delta_c=1.57--1.73 for a
tophat filter. However, Press-Schechter overpredicts the number density of
halos compared to the simulations in the high resolution suite by a weakly
cosmology-dependent factor of 1.5--2 at galaxy and group masses, which cannot
be fixed by adjusting delta_c within reasonable bounds. An appendix generalizes
the spherical collapse model to any isotropic cosmology.Comment: 18 pages Latex using Monthly Notices style, with 13 inlined EPS
figures. This version matches the one accepted by MNRAS. The appendix has
been removed and may now be found instead at
http://fozzie.gsfc.nasa.gov/thesis/appendixC.ps.g
Comparative Analysis of Pollution in Farmington Bay and the Great Salt Lake, Utah
Farmington Bay covers 94 mi2 (260 km2) in the SW comer of the Great Salt Lake, and is essentially a separate lake because it is enclosed by Antelope Island and a causeway leading to the island from the mainland. The bay has received wastes from the adjoining Salt Lake City metropolitan area for decades. Because of water quality concerns for Farmington 8ay, the Aquatic Ecology Laboratory class at Utah State University studied the bay and a nearby control site (Bridger Bay) in the Great Salt Lake during the fall of 2001. Field sampling and laboratory experiments, as well as other data sources, demonstrated the bay is severely eutrophic and is one of the most polluted water bodies in the state of Utah. A preliminary nutrient loading estimate for the bay indicates that total phosphorus coming into the system is a-times higher than necessary for the bay to be classed as eutrophic. Sewage treatment plants discharging directly to the bay contribute approximately 500/0 of the nutrients. Metrics of eutrophication (chlorophyll, Secchi depth and total phosphorus) all indicated that the bay was hypereutrophic and the combined Trophic State Index was 91, higher than any other lake or reservoir in the state. Oxygen was supersaturated in the surface waters of Farmington Bay during the day, but the bottom water was anoxic. During the night, nearly the entire water column became anoxic due to respiratory demand of the biota. The anoxic conditions allowed high concentrations \u27Of foul-smelling hydrogen sulfide to be produced. Brine shrimp were not abundant in Farmington Bay and the community was dominated by rotifers. In contrast, water quality in Bridger 8ay located on the main lake, was good and brine shrimp were abundant there. Our results, although restricted in scope, corroborate existing monitoring data from this bay. Water quality characteristics in Farmington Bay do not meet those mandated for the protection of aquatic life. Odor problems from the bay likely impact more people than are affected by any other polluted water body in the state. The impact of eutrophication and anoxia on the biota in Farmington Bay may also be substantial, although inadequate data exists to determine these impacts. There are substantial technical challenges to be overcome if water quality in the bay is to be improved to meet its designated use. However, before these technical issues can be solved, the responsible agencies will need to address the problem, and begin studies that may eventually lead to a solution to this serious water quality issue
Implications of Spikes in the Redshift Distribution of Galaxies
We address the high peaks found by Steidel et al (1997) in the redshift
distribution of ``Lyman-break'' objects (LBOs) at redshift z~3. The highest
spike represents a relative overdensity of 2.6 in the distribution of LBOs in
pixels of comoving size ~10Mpc/h. We examine the likelihood of such a spike in
the redshift distribution within a suite of models for the evolution of
structure in the Universe, including models with Omega=1 (SCDM and CHDM) and
with Omega=0.4-0.5 (LCDM and OCDM). Using high-resolution dissipationless
N-body simulations, we analyze deep pencil-beam surveys from these models in
the same way that they are actually observed, identifying LBOs with the most
massive dark matter halos. We find that all the models (with SCDM as a marginal
exception) have a substantial probability of producing spikes similar to those
observed, because the massive halos are much more clumped than the underlying
matter -- i.e., they are biased. Therefore, the likelihood of such a spike is
not a good discriminator among these models. We find in these models that the
mean biasing parameter b of LBOs with respect to dark matter varies within a
range b ~2-5 on a scale of ~10Mpc/h. We also compute the two-body correlation
functions of LBOs predicted in these models. The LBO correlation functions are
less steep than galaxies today (gamma ~1.4), but show similar or slightly
longer correlation lengths.Comment: 12 pages, 7 EPS inlined figures, 1 inlined table, LaTex + emulateapj,
multicol and graphics macro packages. Accepted for publication in the ApJ.
Revised version includes new appendix, table, updated references. A version
with higher quality inlined figures is available at
http://fozzie.gsfc.nasa.gov/wgpbd97/spikes.htm
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