2,220 research outputs found
Multi-Behavioral Endpoint Testing Of An 87-Chemical Compound Library In Freshwater Planarians
There is an increased recognition in the field of toxicology of the value of medium-to-high-throughput screening methods using in vitro and alternative animal models. We have previously introduced the asexual freshwater planarian Dugesia japonica as a new alternative animal model and proposed that it is particularly well-suited for the study of developmental neurotoxicology. In this paper, we discuss how we have expanded and automated our screening methodology to allow for fast screening of multiple behavioral endpoints, developmental toxicity, and mortality. Using an 87-compound library provided by the National Toxicology Program (NTP), consisting of known and suspected neurotoxicants, including drugs, flame retardants, industrial chemicals, polycyclic aromatic hydrocarbons (PAHs), pesticides and presumptive negative controls, we further evaluate the benefits and limitations of the system for medium-throughput screening, focusing on the technical aspects of the system. We show that, in the context of this library, planarians are the most sensitive to pesticides with 16/16 compounds causing toxicity and the least sensitive to PAHs, with only 5/17 causing toxicity. Furthermore, while none of the presumptive negative controls were bioactive in adult planarians, 2/5, acetaminophen and acetylsalicylic acid, were bioactive in regenerating worms. Notably, these compounds were previously reported as developmentally toxic in mammalian studies. Through parallel screening of adults and developing animals, planarians are thus a useful model to detect such developmental-specific effects, which was observed for 13 chemicals in this library. We use the data and experience gained from this screen to propose guidelines for best practices when using planarians for toxicology screens
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Hydrogeologic Characterization of the Saline Aquifers, East Texas Basin- Implications to Nuclear Waste Storage in East Texas salt Domes
Groundwaters in the deep aquifers (Nacatoch to Travis Peak) range in salinity from 20,000 to over 200,000 mg/L. Based on their isotopic compositions, they were originally recharged as continental meteoric waters. Recharge probably occurred predominantly during the Cretaceous time; therefore, the waters are very old. Because the basin has not been uplifted, there are no extensive recharge or discharge zones. The flanks of domes and radial faults associated with domes may function as localized discharge points. Both the water chemistry and the hydraulic pressures for the aquifers suggest that the basin can be subdivided into two major aquifer systems: (1) the upper Cretaceous aquifers (Woodbine and shallower) which are hydrostatic and (2) the deep lower Cretaceous and deeper formations (Glen Rose, Travis Peak, and older units), which are slightly overpressured. The source of sodium and chloride in the saline waters is considered to be from salt dome dissolution. Most of the dissolution occurred during the Cretaceous. Chlorine-36 analyses suggest that dome solution is not presently occurring. Salinity cross sections across individual domes do not indicate that ongoing solution is an important process. The major chemical reactions in the saline aquifers are dome dissolution, albitization, and dedolomitization. Albitization and dedolomitization are important only in the deeper formations. The high Na concentrations in the deeper aquifer system result in the alteration of plagioclase to albite and the release of Ca into solution. The increase in Ca concentrations causes a shift in the calcite/dolomite equilibrium. The increase in Mg results from dissolution of dolomite.Bureau of Economic Geolog
Little change in the sizes of the most massive galaxies since z = 1
Recent reports suggest that elliptical galaxies have increased their size
dramatically over the last ~8 Gyr. This result points to a major re-think of
the processes dominating the latetime evolution of galaxies. In this paper we
present the first estimates for the scale sizes of brightest cluster galaxies
(BCGs) in the redshift range 0.8 < z < 1.3 from an analysis of deep Hubble
Space Telescope imaging, comparing to a well matched local sample taken from
the Local Cluster Substructure Survey at z ~ 0.2. For a small sample of 5 high
redshift BCGs we measure half-light radii ranging from 14 - 53 kpc using de
Vaucuoleurs profile fits, with an average determined from stacking of 32.1 \pm
2.5 kpc compared to a value 43.2 \pm 1.0 kpc for the low redshift comparison
sample. This implies that the scale sizes of BCGs at z = 1 are ~ 30% smaller
than at z = 0.25. Analyses comparing either Sersic or Petrosian radii also
indicate little or no evolution between the two samples. The detection of only
modest evolution at most out to z = 1 argues against BCGs having undergone the
large increase in size reported for massive galaxies since z = 2 and in fact
the scale-size evolution of BCGs appears closer to that reported for radio
galaxies over a similar epoch. We conclude that this lack of size evolution,
particularly when coupled with recent results on the lack of BCG stellar mass
evolution, demonstrates that major merging is not an important process in the
late time evolution of these systems. The homogeneity and maturity of BCGs at z
= 1 continues to challenge galaxy evolution models.Comment: Accepted for publication in MNRA
Measurement of the intracluster light at z ~ 1
A significant fraction of the total photospheric light in nearby galaxy
clusters is thought to be contained within the diffuse intracluster light
(ICL), which extends 100s of kpc from cluster cores. The study of the ICL can
reveal details of the evolutionary histories and processes occurring within
galaxy clusters, however since it has a very low surface brightness it is often
difficult to detect. We present here the first measurements of the ICL as a
fraction of total cluster light at z \sim 1 using deep J-band (1.2 {\mu}m)
imaging from HAWK-I on the VLT. We investigate the ICL in 6 X-ray selected
galaxy clusters at 0.8< z <1.2 and find that the ICL below isophotes {\mu}(J) =
22 mag/arcsec2 constitutes 1-4% of the total cluster light within a radius
R500. This is broadly consistent with simulations of the ICL at a similar
redshift and when compared to nearby observations suggests that the fraction of
the total cluster light that is in the ICL has increased by a factor 2 - 4
since z\sim1. We also find the fraction of the total cluster light contained
within the Brightest Cluster Galaxy (BCG) to be 2.0-6.3% at these redshifts,
which in 5 out of 6 cases is larger than the fraction of the ICL component, in
contrast to results from nearby clusters. This suggests that the evolution in
cluster cores involves substantial stripping activity at late times, in
addition to the early build up of the BCG stellar mass through merging. The
presence of significant amounts of stellar light at large radii from these BCGs
may help towards solving the recent disagreement between the semi-analytic
model predictions of BCG mass growth (e.g. De Lucia & Blaziot, 2007) and the
observed large masses and scale sizes reported for BCGs at high redshift.Comment: 12 pages, 12 figures. Accepted for publication in MNRA
Growth Kinetics in a Phase Field Model with Continuous Symmetry
We discuss the static and kinetic properties of a Ginzburg-Landau spherically
symmetric model recently introduced (Phys. Rev. Lett. {\bf 75}, 2176,
(1995)) in order to generalize the so called Phase field model of Langer. The
Hamiltonian contains two invariant fields and bilinearly
coupled. The order parameter field evolves according to a non conserved
dynamics, whereas the diffusive field follows a conserved dynamics. In the
limit we obtain an exact solution, which displays an interesting
kinetic behavior characterized by three different growth regimes. In the early
regime the system displays normal scaling and the average domain size grows as
, in the intermediate regime one observes a finite wavevector
instability, which is related to the Mullins-Sekerka instability; finally, in
the late stage the structure function has a multiscaling behavior, while the
domain size grows as .Comment: 9 pages RevTeX, 9 figures included, files packed with uufiles to
appear on Phy. Rev.
Multi-lepton signals from the top-prime quark at the LHC
We analyze the collider signatures of models with a vector-like top-prime
quark and a massive color-octet boson. The top-prime quark mixes with the top
quark in the Standard Model, leading to richer final states than ones that are
investigated by experimental collaborations. We discuss the multi-lepton final
states, and show that they can provide increased sensitivity to models with a
top-prime quark and gluon-prime. Searches for new physics in high multiplicity
events are an important component of the LHC program and complementary to
analyses that have been performed.Comment: 7 pages, 4 figures, 2 table
Archiving multi-epoch data and the discovery of variables in the near infrared
We present a description of the design and usage of a new synoptic pipeline
and database model for time series photometry in the VISTA Data Flow System
(VDFS). All UKIRT-WFCAM data and most of the VISTA main survey data will be
processed and archived by the VDFS. Much of these data are multi-epoch, useful
for finding moving and variable objects. Our new database design allows the
users to easily find rare objects of these types amongst the huge volume of
data being produced by modern survey telescopes. Its effectiveness is
demonstrated through examples using Data Release 5 of the UKIDSS Deep
Extragalactic Survey (DXS) and the WFCAM standard star data. The synoptic
pipeline provides additional quality control and calibration to these data in
the process of generating accurate light-curves. We find that 0.6+-0.1% of
stars and 2.3+-0.6% of galaxies in the UKIDSS-DXS with K<15 mag are variable
with amplitudes \Delta K>0.015 magComment: 30 pages, 31 figures, MNRAS, in press Minor changes from previous
version due to refereeing and proof-readin
Environmental Dependence of the Structure of Brightest Cluster Galaxies
We measure the Petrosian structural properties of 33 brightest cluster
galaxies (BCGs) at redshifts z<0.1 in X-ray selected clusters with a wide range
of X-ray luminosities. We find that some BCGs show distinct signatures in their
Petrosian profiles, likely to be due to cD haloes. We also find that BCGs in
high X-ray luminosity clusters have shallower surface brightness profiles than
those in low X-ray luminosity clusters. This suggests that the BCGs in high
X-ray luminosity clusters have undergone up to twice as many equal-mass mergers
in their past as those in low X-ray luminosity clusters. This is qualitatively
consistent with the predictions of hierarchical structure formation.Comment: 11 pages, accepted for publication in MNRA
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