4,620 research outputs found
Clusters of Extragalactic Ultra Compact HII Regions
We report on the detection of optically thick free-free radio sources in the
galaxies M33, NGC 253, and NGC 6946 using data in the literature. We interpret
these sources as being young, embedded star birth regions, which are likely to
be clusters of ultracompact HII regions. All 35 of the sources presented in
this article have positive radio spectral indices alpha>0 suggesting an
optically thick thermal bremsstrahlung emission arising in the HII region
surrounding hot stars. Energy requirements indicate a range of a several to
>500 O7V star equivalents powering each HII region. Assuming a Salpeter IMF,
this corresponds to integrated stellar masses of 0.1--60,000 Msun. For roughly
half of the sources in our sample, there is no obvious optical counterpart,
giving further support for their deeply embedded nature. Their luminosities and
radio spectral energy distributions are consistent with HII regions having
electron densities from 1500 cm^-3 to 15000 cm^-3 and radii of 1 - 7 pc. We
suggest that the less luminous of these sources are extragalactic ultracompact
HII region complexes, those of intermediate luminosity are similar to W49 in
the Galaxy, while the brightest will be counterparts to 30 Doradus. These
objects constitute the lower mass range of extragalactic ``ultradense HII
regions'' which we argue are the youngest stages of massive star cluster
formation yet observed. This sample is beginning to fill in the continuum of
objects between small associations of ultracompact HII regions and the massive
extragalactic clusters that may evolve into globular clusters.Comment: 37 pages, uses AASTeX; scheduled to appear in ApJ v. 559 October
2001. Full postscript version available from
http://www.astro.wisc.edu/~chip/Papers/Johnson_Kobulnicky_etal_ApJ559.ps.g
Rolling Tachyon in Brane World Cosmology from Superstring Field Theory
The pressureless tachyonic matter recently found in superstring field theory
has an over-abundance problem in cosmology. We argue that this problem is
naturally solved in the brane inflationary scenario if almost all of the
tachyon energy is drained (via its coupling to the inflaton and matter fields)
to heating the universe, while the rest of the tachyon energy goes to a network
of cosmic strings (lower-dimensional BPS D-branes) produced during the tachyon
rolling at the end of inflation.Comment: 4 pages, one figure. This version quantifies constraints on various
phenomenological models for tachyon deca
Transgenic Rescue of the LARGEmyd Mouse: A LARGE Therapeutic Window?
LARGE is a glycosyltransferase involved in glycosylation of α-dystroglycan (α-DG). Absence of this protein in the LARGEmyd mouse results in α-DG hypoglycosylation, and is associated with central nervous system abnormalities and progressive muscular dystrophy. Up-regulation of LARGE has previously been proposed as a therapy for the secondary dystroglycanopathies: overexpression in cells compensates for defects in multiple dystroglycanopathy genes. Counterintuitively, LARGE overexpression in an FKRP-deficient mouse exacerbates pathology, suggesting that modulation of α-DG glycosylation requires further investigation. Here we demonstrate that transgenic expression of human LARGE (LARGE-LV5) in the LARGEmyd mouse restores α-DG glycosylation (with marked hyperglycosylation in muscle) and that this corrects both the muscle pathology and brain architecture. By quantitative analyses of LARGE transcripts we also here show that levels of transgenic and endogenous LARGE in the brains of transgenic animals are comparable, but that the transgene is markedly overexpressed in heart and particularly skeletal muscle (20–100 fold over endogenous). Our data suggest LARGE overexpression may only be deleterious under a forced regenerative context, such as that resulting from a reduction in FKRP: in the absence of such a defect we show that systemic expression of LARGE can indeed act therapeutically, and that even dramatic LARGE overexpression is well-tolerated in heart and skeletal muscle. Moreover, correction of LARGEmyd brain pathology with only moderate, near-physiological LARGE expression suggests a generous therapeutic window
Spectral flow and boundary string field theory for angled D-branes
D-branes intersecting at an arbitrary fixed angle generically constitute a
configuration unstable toward recombination. The reconnection of the branes
nucleates at the intersection point and involves a generalization of the
process of brane decay of interest to non-perturbative string dynamics as well
as cosmology. After reviewing the string spectrum of systems of angled branes,
we show that worldsheet twist superfields may be used in the context of
Boundary Superstring Field Theory to describe the dynamics. Changing the angle
between the branes is seen from the worldsheet as spectral flow with boundary
insertions flowing from bosonic to fermionic operators. We calculate the
complete tachyon potential and the low energy effective action as a function of
angle and find an expression that interpolates between the brane-antibrane and
the Dirac-Born-Infeld actions. The potential captures the mechanism of D-brane
recombination and provides for interesting new physics for tachyon decay.Comment: 32 pages, 9 figures; v2 references added; v3 discussion clarifie
The Hubble PanCET program: Long-term chromospheric evolution and flaring activity of the M dwarf host GJ 3470
Neptune-size exoplanets seem particularly sensitive to atmospheric
evaporation, making it essential to characterize the stellar high-energy
radiation that drives this mechanism. This is particularly important with M
dwarfs, which emit a large and variable fraction of their luminosity in the UV
and can display strong flaring behavior. The warm Neptune GJ3470b, hosted by an
M2 dwarf, was found to harbor a giant hydrogen exosphere thanks to 3 transits
observed with the HST/STIS. Here we report on 3 additional transit observations
from the PanCET program, obtained with the HST/COS. These data confirm the
absorption signature from GJ3470b's exosphere in the stellar Ly-alpha line and
demonstrate its stability over time. No planetary signatures are detected in
other lines, setting a 3sigma limit on GJ3470b's FUV radius at 1.3x its Roche
lobe radius. We detect 3 flares from GJ3470. They show different spectral
energy distributions but peak consistently in the Si III line, which traces
intermediate-temperature layers in the transition region. These layers appear
to play a particular role in GJ3470's activity as emission lines that form at
lower or higher temperatures than Si III evolved differently over the long
term. Based on the measured emission lines, we derive synthetic XUV spectra for
the 6 observed quiescent phases, covering one year, as well as for the 3
flaring episodes. Our results suggest that most of GJ3470's quiescent
high-energy emission comes from the EUV domain, with flares amplifying the FUV
emission more strongly. The hydrogen photoionization lifetimes and mass loss
derived for GJ3470b show little variation over the epochs, in agreement with
the stability of the exosphere. Simulations informed by our XUV spectra are
required to understand the atmospheric structure and evolution of GJ3470b and
the role played by evaporation in the formation of the hot-Neptune desert.Comment: 21 pages, 18 figures, accepted in A&
The HST PanCET Program:Hints of Na I and Evidence of a Cloudy Atmosphere for the Inflated Hot Jupiter WASP-52b
We present an optical to near-infrared transmission spectrum of the inflated
hot Jupiter WASP-52b using three transit observations from the Space Telescope
Imaging Spectrograph (STIS) mounted on the Hubble Space Telescope, combined
with Spitzer/Infrared Array Camera (IRAC) photometry at 3.6 microns and 4.5
microns. Since WASP-52 is a moderately active (log(Lx/Lbol) = -4.7) star, we
correct the transit light curves for the effect of stellar activity using
ground-based photometric monitoring data from the All-Sky Automated Survey for
Supernovae (ASAS-SN) and Tennessee State University's Automatic Imaging
Telescope (AIT). We bin the data in 38 spectrophotometric light curves from
0.29 to 4.5 microns and measure the transit depths to a median precision of 90
ppm. We compare the transmission spectrum to a grid of forward atmospheric
models and find that our results are consistent with a cloudy spectrum and
evidence of sodium at 2.3-sigma confidence, but no observable evidence of
potassium absorption even in the narrowest spectroscopic channel. We find that
the optical transmission spectrum of WASP-52b is similar to that of the
well-studied inflated hot Jupiter HAT-P-1b, which has comparable surface
gravity, equilibrium temperature, mass, radius, and stellar irradiation levels.
At longer wavelengths, however, the best fitting models for WASP-52b and
HAT-P-1b predict quite dissimilar properties, which could be confirmed with
observations at wavelengths longer than ~1 micron. The identification of
planets with common atmospheric properties and similar system parameters will
be insightful for comparative atmospheric studies with the James Webb Space
Telescope.Comment: 35 pages, 16 figures, accepted for publication in A
Brane Inflation and Cosmic String Tension in Superstring Theory
In a simple reanalysis of the KKLMMT scenario, we argue that the slow roll
condition in the D3-anti-D3-brane inflationary scenario in superstring theory
requires no more than a moderate tuning. The cosmic string tension is very
sensitive to the conformal coupling: with less fine-tuning, the cosmic string
tension (as well as the ratio of tensor to scalar perturbation mode) increases
rapidly and can easily saturate the present observational bound. In a
multi-throat brane inflationary scenario, this feature substantially improves
the chance of detecting and measuring the properties of the cosmic strings as a
window to the superstring theory and our pre-inflationary universe.Comment: Combined bounds from WMAP and SDSS Lyman alpha experiments are added
for analysis, changes are added to the tabl
Amine functionalization of cholecyst-derived extracellular matrix with generation 1 PAMAM dendrimer
This document is the unedited author's version of a Submitted Work that was subsequently accepted for publication in Biomacromolecules, copyright © American Chemical Society after peer review. To access the final edited and published work, see http://pubs.acs.org/doi/pdf/10.1021/bm701055k.A method to functionalize cholecyst-derived extracellular matrix (CEM) with free amine groups was established in an attempt to improve its potential for tethering of bioactive molecules. CEM was incorporated with Generation-1 polyamidoamine (G1 PAMAM) dendrimer by using N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide and N-hydroxysuccinimide cross-linking system. The nature of incorporation of PAMAM dendrimer was evaluated using shrink temperature measurements, Fourier transform infrared (FTIR) assessment, ninhydrin assay, and swellability. The effects of PAMAM incorporation on mechanical and degradation properties of CEM were evaluated using a uniaxial mechanical test and collagenase degradation assay, respectively. Ninhydrin assay and FTIR assessment confirmed the presence of increasing free amine groups with increasing quantity of PAMAM in dendrimer-incorporated CEM (DENCEM) scaffolds. The amount of dendrimer used was found to be critical in controlling scaffold degradation, shrink temperature, and free amine content. Cell culture studies showed that fibroblasts seeded on DENCEM maintained their metabolic activity and ability to proliferate in vitro. In addition, fluorescence cell staining and scanning electron microscopy analysis of cell-seeded DENCEM showed preservation of normal fibroblast morphology and phenotype
Nitrogen transfer from forage legumes to nine neighbouring plants in a multi-species grassland
Legumes play a crucial role in nitrogen supply to grass-legume mixtures for ruminant fodder. To quantify N transfer from legumes to neighbouring plants in multi-species grasslands we established a grass-legume-herb mixture on a loamy-sandy site in Denmark. White clover (Trifolium repens L.), red clover (Trifolium pratense L.) and lucerne (Medicago sativa L.) were leaf-labelled with 15N enriched urea during one growing season. N transfer to grasses
(Lolium perenne L. and xfestulolium), white clover, red clover, lucerne, birdsfoot trefoil (Lotus corniculatus
L.), chicory (Cichorium intybus L.), plantain (Plantago
lanceolata L.), salad burnet (Sanguisorba minor L.)and caraway (Carum carvi L.) was assessed. Neighbouring plants contained greater amounts of N derived from white clover (4.8 gm-2) compared with red clover (2.2 gm-2) and lucerne (1.1 gm-2). Grasses having fibrous roots received greater amounts of N from legumes than dicotyledonous plants which generally have taproots. Slurry application mainly increased N transfer from legumes to grasses. During the growing season the three legumes transferred approximately 40 kg N ha-1 to neighbouring plants. Below-ground N transfer from legumes to neighbouring plants differed among nitrogen donors and nitrogen receivers and may depend on root characteristics and regrowth strategies of plant species in the multi-species grassland
Tamoxifen for prevention of breast cancer: extended long-term follow-up of the IBIS-I breast cancer prevention trial
© Cuzick et al. Open Access article distributed under the terms of CC BY.http://dx.doi.org/10.1016/S1470-2045(14)71171-
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