816 research outputs found
The ACS Nearby Galaxy Survey Treasury. X. Quantifying the Star Cluster Formation Efficiency of Nearby Dwarf Galaxies
We study the relationship between the field star formation and cluster
formation properties in a large sample of nearby dwarf galaxies. We use optical
data from the Hubble Space Telescope and from ground-based telescopes to derive
the ages and masses of the young (t_age < 100Myr) cluster sample. Our data
provides the first constraints on two proposed relationships between the star
formation rate of galaxies and the properties of their cluster systems in the
low star formation rate regime. The data show broad agreement with these
relationships, but significant galaxy-to-galaxy scatter exists. In part, this
scatter can be accounted for by simulating the small number of clusters
detected from stochastically sampling the cluster mass function. However, this
stochasticity does not fully account for the observed scatter in our data
suggesting there may be true variations in the fraction of stars formed in
clusters in dwarf galaxies. Comparison of the cluster formation and the
brightest cluster in our sample galaxies also provide constraints on cluster
destruction models.Comment: 16 pages, 9 figures, Accepted to Ap
Infinite Volume and Continuum Limits of the Landau-Gauge Gluon Propagator
We extend a previous improved action study of the Landau gauge gluon
propagator, by using a variety of lattices with spacings from to
0.41 fm, to more fully explore finite volume and discretization effects. We
also extend a previously used technique for minimizing lattice artifacts, the
appropriate choice of momentum variable or ``kinematic correction'', by
considering it more generally as a ``tree-level correction''. We demonstrate
that by using tree-level correction, determined by the tree-level behavior of
the action being considered, it is possible to obtain scaling behavior over a
very wide range of momenta and lattice spacings. This makes it possible to
explore the infinite volume and continuum limits of the Landau-gauge gluon
propagator.Comment: 24 pages RevTex, 18 figures; Responses to referee comments, minor
change
Identification of proteins associated with ligand-activated estrogen receptor alpha in human breast cancer cell nuclei by tandem affinity purification and nanoLC-MS/MS.
Estrogen receptor a (ER-a) is a key mediator of estrogen actions in breast cancer (BC) cells. Understanding the effects of ligand-activated ER-a in target cells requires identification of the molecular partners acting in concert with this nuclear receptor to transduce the hormonal signal. We applied tandem affinity purification (TAP), glycerol gradient centrifugation and MS analysis to isolate and identify proteins interacting with ligand-activated ER-a in MCF-7 cell nuclei. This led to the identification of 264 ER-associated proteins, whose functions highlight the hinge role of ER-a in the coordination of multiple hormone-regulated nuclear processes in BC cells
Renormalization group flow with unstable particles
The renormalization group flow of an integrable two dimensional quantum field
theory which contains unstable particles is investigated. The analysis is
carried out for the Virasoro central charge and the conformal dimensions as a
function of the renormalization group flow parameter. This allows to identify
the corresponding conformal field theories together with their operator content
when the unstable particles vanish from the particle spectrum. The specific
model considered is the -homogeneous Sine-Gordon model.Comment: 5 pages Latex, 3 figure
Constructing Infinite Particle Spectra
We propose a general construction principle which allows to include an
infinite number of resonance states into a scattering matrix of hyperbolic
type. As a concrete realization of this mechanism we provide new S-matrices
generalizing a class of hyperbolic ones, which are related to a pair of simple
Lie algebras, to the elliptic case. For specific choices of the algebras we
propose elliptic generalizations of affine Toda field theories and the
homogeneous sine-Gordon models. For the generalization of the sinh-Gordon model
we compute explicitly renormalization group scaling functions by means of the
c-theorem and the thermodynamic Bethe ansatz. In particular we identify the
Virasoro central charges of the corresponding ultraviolet conformal field
theories.Comment: 7 pages Latex, 7 figures (typo in figure 3 corrected
A Chromosome-Length Reference Genome for the Endangered Pacific Pocket Mouse Reveals Recent Inbreeding in a Historically Large Population
High-quality reference genomes are fundamental tools for understanding population history, and can provide estimates of genetic and demographic parameters relevant to the conservation of biodiversity. The federally endangered Pacific pocket mouse (PPM), which persists in three small, isolated populations in southern California, is a promising model for studying how demographic history shapes genetic diversity, and how diversity in turn may influence extinction risk. To facilitate these studies in PPM, we combined PacBio HiFi long reads with Omni-C and Hi-C data to generate a de novo genome assembly, and annotated the genome using RNAseq. The assembly comprised 28 chromosome-length scaffolds (N50â=â72.6â
MB) and the complete mitochondrial genome, and included a long heterochromatic region on chromosome 18 not represented in the previously available short-read assembly. Heterozygosity was highly variable across the genome of the reference individual, with 18% of windows falling in runs of homozygosity (ROH) >1â
MB, and nearly 9% in tracts spanning >5â
MB. Yet outside of ROH, heterozygosity was relatively high (0.0027), and historical Ne estimates were large. These patterns of genetic variation suggest recent inbreeding in a formerly large population. Currently the most contiguous assembly for a heteromyid rodent, this reference genome provides insight into the past and recent demographic history of the population, and will be a critical tool for management and future studies of outbreeding depression, inbreeding depression, and genetic load
Asymptotic scaling of the gluon propagtor on the lattice
We pursue the study of the high energy behaviour of the gluon propagator on
the lattice in the Landau gauge in the flavorless case (n_f=0). It was shown in
a precedin g paper that the gluon propagator did not reach three-loop
asymptotic scaling at an energy scale as high as 5 GeV.
Our present high statistics analysis includes also a simulation at
( fm), which allows to reach GeV.
Special care has been devoted to the finite lattice-spacing artifacts as well
as to the finite volume effects, the latter being acute at where
the volume is bounded by technical limits. Our main conclusion is a strong
evidence that the gluon propagator has reached three-loop asymptotic scaling,
at ranging from 5.6 GeV to 9.5 GeV. We buttress up this conclusion on
several demanding criteria of asymptoticity, including scheme independence. Our
fit in the 5.6 GeV to 9.5 GeV window yields MeV, in good agreement with our previous result,
MeV, obtained from the three gluon
vertex, but it is significantly above the Schr\"odinger functional method
estimate : MeV. The latter difference is not understood.
Confirming our previous paper, we show that a fourth loop is necessary to fit
the whole () GeV energy window.Comment: latex-file, 19 pgs., 6 fig
When Will Adolescents Tell Someone About Dating Violence Victimization?
This study examined factors that influence help-seeking among a diverse sample of
adolescents who experienced dating violence. A sample of 57 high school students in
an urban community reported on the prevalence and characteristics of dating violence
in their relationships. Someone observing a dating violence incident and a survivorâs
attaching an emotional meaning to the event significantly influenced adolescents to talk
to someone. When dating violence occurred in isolation, survivors were more likely to
receive no support from others in the aftermath of the incident. Differences between
boysâ and girlsâ help-seeking and implications for dating violence intervention and prevention
programming are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90887/1/Black-Tolman-Callahan-Saunders- Weisz- 2008-When will adolescents tell someone about dating violence VAW.pd
Quantitative expression profiling of highly degraded RNA from formalin-fixed, paraffin-embedded breast tumor biopsies by oligonucleotide microarrays.
Microarray-based gene expression profiling is well suited for parallel quantitative analysis of large numbers of RNAs, but its application to cancer biopsies, particularly formalin-fixed, paraffin-embedded (FFPE) archived tissues, is limited by the poor quality of the RNA recovered. This represents a serious drawback, as FFPE tumor tissue banks are available with clinical and prognostic annotations, which could be exploited for molecular profiling studies, provided that reliable analytical technologies are found. We applied and evaluated here a microarray-based cDNA-mediated annealing, selection, extension and ligation (DASL) assay for analysis of 502 mRNAs in highly degraded total RNA extracted from cultured cells or FFPE breast cancer (MT) biopsies. The study included quantitative and qualitative comparison of data obtained by analysis of the same RNAs with genome-wide oligonucleotide microarrays vs DASL arrays and, by DASL, before and after extensive in vitro RNA fragmentation. The DASL-based expression profiling assay applied to RNA extracted from MCF-7 cells, before or after 24 h stimulation with a mitogenic dose of 17b-estradiol, consistently allowed to detect hormone-induced gene expression changes following extensive RNA degradation in vitro. Comparable results where obtained with tumor RNA extracted from FFPE MT biopsies (6 to 19 years old). The method proved itself sensitive, reproducible and accurate, when compared to results obtained by microarray analysis of RNA extracted from snap-frozen tissue of the same tumor
Star Formation Histories of the LEGUS Dwarf Galaxies (I): recent History of NGC1705, NGC4449 and Holmberg II
We use HST observations from the Legacy Extragalactic UV Survey to
reconstruct the recent star formation histories (SFHs) of three actively
star-forming dwarf galaxies, NGC4449, Holmberg II and NGC1705, from their UV
color-magnitude diagrams (CMDs). We apply a CMD fitting technique using two
independent sets of stellar isochrones, PARSEC-COLIBRI and MIST, to assess the
uncertainties related to stellar evolution modelling. Irrespective of the
adopted stellar models, all the three dwarfs are found to have had almost
constant star formation rates (SFRs) in the last 100-200 Myr, with modest
enhancements (a factor of 2) above the 100 Myr-averaged-SFR. Significant
differences among the three dwarfs are found in the overall SFR, the timing of
the most recent peak and the SFRarea. The Initial Mass Function (IMF) of
NGC1705 and Holmberg II is consistent with a Salpeter slope down to 5
M, whereas it is slightly flatter, s, in NGC4449. The SFHs
derived with the two different sets of stellar models are consistent with each
other, except for some quantitative details, attributable to their input
assumptions. They also share the drawback that all synthetic diagrams predict a
clear separation in color between upper main sequence and helium burning stars,
which is not apparent in the data. Since differential reddening, significant in
NGC4449, or unresolved binaries don't appear to be sufficient to fill the gap,
we suggest this calls for a revision of both sets of stellar evolutionary
tracks.Comment: 22 pages, 17 figures, accepted for publication on Ap
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